# Publications

## 2021

Arya, V. B.; Surendran, Sajani; Rajendran, KavirajanArya, V. B., S. Surendran, K. Rajendran, 2021: On the build-up of dust aerosols and possible indirect effect during Indian summer monsoon break spells using recent satellite observations of aerosols and cloud properties. Journal of Earth System Science, 130(1), 42. doi: 10.1007/s12040-020-01526-6. Association of higher (lower) rainfall with lower (higher) Aerosol Optical Depth (AOD) is consistent with the understanding that increased washout (build-up) and shorter (longer) life-time of aerosols occur in wetter (drier) conditions. Given the life-time of aerosols, it is imperative to examine how aerosols impact active/break (wetter/drier than normal) spells, prominent intraseasonal variability (ISV) of Indian summer monsoon (ISM), through their composite analysis using recent satellite observations of aerosols and cloud properties, circulation and rainfall. Dust aerosols can act as CCN and participate efficiently in cloud processes during active phase. During breaks, build-up of desert dust transported by prevalent circulation, is associated with lower cloud effective radius implying aerosols’ indirect effect where they can inhibit cloud growth in the presence of reduced moisture and decrease precipitation efficiency/rainfall. Correspondingly, correlation albeit small, between intraseasonal anomalies of AOD and rainfall is negative, when AOD leads rainfall by 3–5 days implying that indirect aerosols impact is effective during breaks, though it is not the dominant responsible factor. During breaks, lower shortwave flux at top of atmosphere hints at dust-induced semi-direct effect. As breaks are permanent features of ISM, incorporation of dust-induced feedbacks in models, is essential for improved ISV simulation and ISM prediction.
Bloxam, Kevin; Huang, YiBloxam, K., Y. Huang, 2021: Radiative Relaxation Time Scales Quantified from Sudden Stratospheric Warmings. Journal of Atmospheric Sciences, 78(1), 269-286. doi: 10.1175/JAS-D-20-0015.1. AbstractSudden stratospheric warmings (SSWs) are impressive events that occur in the winter hemisphere’s polar stratosphere and are capable of producing temperature anomalies upward of +50 K within a matter of days. While much work has been dedicated toward determining how SSWs occur and their ability to interact with the underlying troposphere, one underexplored aspect is the role of radiation, especially during the recovery phase of SSWs. Using a radiative transfer model and a heating rate analysis for distinct layers of the stratosphere averaged over the 60°–90°N polar region, this paper accounts for the radiative contribution to the removal of the anomalous temperatures associated with SSWs. In total 17 events are investigated over the 1979–2016 period. This paper reveals that in the absence of dynamical heating following major SSWs, longwave radiative cooling dominates and often results in a strong negative temperature anomaly. The polar winter stratospheric temperature change driven by the radiative cooling is characterized by an exponential decay of temperature with an increasing e-folding time of 5.7 ± 2.0 to 14.6 ± 4.4 days from the upper to middle stratosphere. The variability of the radiative relaxation rates among the SSWs was determined to be most impacted by the initial temperature of the stratosphere and the combined dynamic and solar heating rates following the onset of the events. We also found that trace-gas anomalies have little impact on the radiative heating rates and the temperature evolution during the SSWs in the mid- to upper stratosphere.
Campbell, James R.; Dolinar, Erica K.; Lolli, Simone; Fochesatto, Gilberto J.; Gu, Yu; Lewis, Jasper R.; Marquis, Jared W.; McHardy, Theodore M.; Ryglicki, David R.; Welton, Ellsworth J.Campbell, J. R., E. K. Dolinar, S. Lolli, G. J. Fochesatto, Y. Gu, J. R. Lewis, J. W. Marquis, T. M. McHardy, D. R. Ryglicki, E. J. Welton, 2021: Cirrus Cloud Top-of-the-Atmosphere Net Daytime Forcing in the Alaskan Subarctic from Ground-Based MPLNET Monitoring. J. Appl. Meteor. Climatol., (In Press). doi: 10.1175/JAMC-D-20-0077.1. AbstractCirrus cloud daytime top-of-the-atmosphere radiative forcing (TOA CRF) is estimated for a two-year NASA Micro-Pulse Lidar Network (532 nm; MPLNET) dataset collected at Fairbanks, Alaska. Two-year averaged daytime TOA CRF is estimated at between -1.08 and 0.78 W·m-2 (-0.49 to 1.10 W·m-2 in 2017, and -1.67 to 0.47 W·m-2 in 2018). This subarctic study completes a now trilogy of MPLNET ground-based cloud forcing investigations, following midlatitude and tropical studies by Campbell et al. (2016; C16) at Greenbelt, Maryland and Lolli et al. (2017) at Singapore. C16 hypothesize a global meridional daytime TOA CRF gradient that begins positive at the equator (2.20 – 2.59 W·m-2 over land and -0.46 – 0.42 W·m-2 over ocean at Singapore), becomes neutral in the midlatitudes (0.03 – 0.27 W·m-2 over land in Maryland) and turns negative moving poleward. This study does not completely confirm C16, as values are not found as exclusively negative. Evidence in historical reanalysis data suggests that daytime cirrus forcing in and around the subarctic likely once was exclusively negative. Increasing tropopause heights, inducing higher and colder cirrus, have likely increased regional forcing over the last forty years. We hypothesize that subarctic inter-annual cloud variability is likely a considerable influence on global cirrus cloud forcing sensitivity, given the irregularity of polar versus midlatitude synoptic weather intrusions. This study and hypothesis lays basis for an extrapolation of these MPLNET experiments to satellite-based lidar cirrus cloud datasets.
Cesana, Grégory V.; Del Genio, Anthony D.Cesana, G. V., A. D. Del Genio, 2021: Observational constraint on cloud feedbacks suggests moderate climate sensitivity. Nature Climate Change, 11(3), 213-218. doi: 10.1038/s41558-020-00970-y. Global climate models predict warming in response to increasing GHG concentrations, partly due to decreased tropical low-level cloud cover and reflectance. We use satellite observations that discriminate stratocumulus from shallow cumulus clouds to separately evaluate their sensitivity to warming and constrain the tropical contribution to low-cloud feedback. We find an observationally inferred low-level cloud feedback two times smaller than a previous estimate. Shallow cumulus clouds are insensitive to warming, whereas global climate models exhibit a large positive cloud feedback in shallow cumulus regions. In contrast, stratocumulus clouds show sensitivity to warming and the tropical inversion layer strength, controlled by the tropical Pacific sea surface temperature gradient. Models fail to reproduce the historical sea surface temperature gradient trends and therefore changes in inversion strength, generating an overestimate of the positive stratocumulus cloud feedback. Continued weak east Pacific warming would therefore produce a weaker low-cloud feedback and imply a more moderate climate sensitivity (3.47 ± 0.33 K) than many models predict.
Chen, Shiliu; McColl, Kaighin A.; Berg, Alexis; Huang, YuefeiChen, S., K. A. McColl, A. Berg, Y. Huang, 2021: Surface Flux Equilibrium Estimates of Evapotranspiration at Large Spatial Scales. J. Hydrometeor., 22(4), 765-779. doi: 10.1175/JHM-D-20-0204.1. AbstractA recent theory proposes that inland continental regions are in a state of surface flux equilibrium (SFE), in which tight coupling between the land and atmosphere allow estimation of the Bowen ratio at daily to monthly time scales solely from atmospheric measurements, without calibration, even when the land surface strongly constrains the surface energy budget. However, since the theory has only been evaluated at quasi-point spatial scales using eddy covariance measurements with limited global coverage, it is unclear if it is applicable to the larger spatial scales relevant to studies of global climate. In this study, SFE estimates of the Bowen ratio are combined with satellite observations of surface net radiation to obtain large-scale estimates of latent heat flux λE. When evaluated against multiyear mean annual λE obtained from catchment water balance estimates from 221 catchments across the United States, the resulting error statistics are comparable to those in the catchment water balance estimates themselves. The theory is then used to diagnostically estimate λE using historical simulations from 26 CMIP6 models. The resulting SFE estimates are typically at least as accurate as the CMIP6 model’s simulated λE, when compared with catchment water balance estimates. Globally, there is broad spatial and temporal agreement between CMIP6 model SFE estimates and the CMIP6 model’s simulated λE, although SFE likely overestimates λE in some arid regions. We conclude that SFE applies reasonably at large spatial scales relevant to climate studies, and is broadly reproduced in climate models.
Coelho, Caio A. S.; de Souza, Dayana C.; Kubota, Paulo Y.; Costa, Simone M. S.; Menezes, Layrson; Guimarães, Bruno S.; Figueroa, Silvio N.; Bonatti, José P.; Cavalcanti, Iracema F. A.; Sampaio, Gilvan; Klingaman, Nicholas P.; Baker, Jessica C. A.Coelho, C. A. S., D. C. de Souza, P. Y. Kubota, S. M. S. Costa, L. Menezes, B. S. Guimarães, S. N. Figueroa, J. Bonatti, . P., I. F. A. Cavalcanti, G. Sampaio, N. P. Klingaman, J. C. A. Baker, 2021: Evaluation of climate simulations produced with the Brazilian global atmospheric model version 1.2. Climate Dynamics, 56(3), 873-898. doi: 10.1007/s00382-020-05508-8. This paper presents an evaluation of climate simulations produced by the Brazilian Global Atmospheric Model version 1.2 (BAM-1.2) of the Center for Weather Forecast and Climate Studies (CPTEC). The model was run over the 1975–2017 period at two spatial resolutions, corresponding to ~ 180 and ~ 100 km, both with 42 vertical levels, following most of the Atmospheric Model Intercomparison Project (AMIP) protocol. In this protocol, observed sea surface temperatures (SSTs) are used as boundary conditions for the atmospheric model. Four ensemble members were run for each of the two resolutions. A series of diagnostics was computed for assessing the model’s ability to represent the top of the atmosphere (TOA) radiation, atmospheric temperature, circulation and precipitation climatological features. The representation of precipitation interannual variability, El Niño-Southern Oscillation (ENSO) precipitation teleconnections, the Madden and Julian Oscillation (MJO) and daily precipitation characteristics was also assessed. The model at both resolutions reproduced many observed temperature, atmospheric circulation and precipitation climatological features, despite several identified biases. The model atmosphere was found to be more transparent than the observations, leading to misrepresentation of cloud-radiation interactions. The net cloud radiative forcing, which produces a cooling effect on the global mean climate at the TOA, was well represented by the model. This was found to be due to the compensation between both weaker longwave cloud radiative forcing (LWCRF) and shortwave cloud radiative forcing (SWCRF) in the model compared to the observations. The model capability to represent inter-annual precipitation variability at both resolutions was found to be linked to the adequate representation of ENSO teleconnections. However, the model produced weaker than observed convective activity associated with the MJO. Light daily precipitation over the southeast of South America and other climatologically similar regions was diagnosed to be overestimated, and heavy daily precipitation underestimated by the model. Increasing spatial resolution helped to slightly reduce some of the diagnosed biases. The performed evaluation identified model aspects that need to be improved. These include the representation of polar continental surface and sea ice albedo, stratospheric ozone, low marine clouds, and daily precipitation features, which were found to be larger and last longer than the observed features.
Dong, Xiquan; Wu, Peng; Wang, Yuan; Xi, Baike; Huang, YiyiDong, X., P. Wu, Y. Wang, B. Xi, Y. Huang, 2021: New Observational Constraints on Warm Rain Processes and Their Climate Implications. Geophysical Research Letters, 48(6), e2020GL091836. doi: https://doi.org/10.1029/2020GL091836. Low stratiform clouds have profound impacts on the hydrological cycle and the Earth’s radiation budget. However, realistic simulation of low clouds in climate models presents a major challenge. Here we employ the newly retrieved cloud and drizzle microphysical properties to improve the autoconversion and accretion parameterizations in a microphysical scheme. We find that the new autoconversion (accretion) rate contributes 14% lower (greater) to total drizzle water content than the original scheme near the cloud top. Compared to satellite results, the simulated cloud liquid water path (LWP) and shortwave cloud radiative effect using the original scheme in a climate model agree well on global average but with large regional differences. Simulations using the updated scheme show a 7.3% decrease in the light rain frequency, and a 10% increase in LWP. The updated microphysics scheme alleviates the long-lasting problem in most climate models, that is “too frequent and too light precipitation.”
Feldman, D. R.; Su, W.; Minnis, P.Feldman, D. R., W. Su, P. Minnis, 2021: Subdiurnal to Interannual Frequency Analysis of Observed and Modeled Reflected Shortwave Radiation From Earth. Geophysical Research Letters, 48(4), e2020GL089221. doi: https://doi.org/10.1029/2020GL089221. Estimates of global top-of-atmosphere radiation on monthly, seasonal, annual, and longer time-scales require estimates of the diurnal variability in both insolation and surface and atmospheric reflection. We compare Earth Polychromatic Imaging Camera (EPIC) and National Institute of Standards and Technology Advanced Radiometer (NISTAR) observations from the Deep Space Climate Observatory (DSCOVR) satellite with Clouds and Earth’s Radiant Energy System (CERES) hourly synoptic fluxes, which are diurnally filled through geostationary observations, and find that their power spectral density functions substantially agree, showing strong relative power at subdiurnal, diurnal, seasonal, and annual time-scales, and power growing from diurnal to seasonal time-scales. Frequency analysis of fluxes from several coupled model intercomparison project 5 model (CMIP5) and CMIP6 models shows that they distribute too much power over periods greater than 1 day but less than one year, indicating that a closer look is needed into how models achieve longer-term stability in reflected shortwave radiation. Model developers can consider using these datasets for time-varying energetic constraints, since tuning parameter choices will impact modeled planetary shortwave radiation across timescales ranging from subdiurnal to decadal. diurnal cycle; Albedo; DSCOVR; shortwave radiative energy budget
Gasparini, Blaž; Rasch, Philip J.; Hartmann, Dennis L.; Wall, Casey J.; Dütsch, MarinaGasparini, B., P. J. Rasch, D. L. Hartmann, C. J. Wall, M. Dütsch, 2021: A Lagrangian Perspective on Tropical Anvil Cloud Lifecycle in Present and Future Climate. Journal of Geophysical Research: Atmospheres, 126(4), e2020JD033487. doi: https://doi.org/10.1029/2020JD033487. The evolution of tropical anvil clouds from their origin in deep convective cores to their slow decay determines the climatic effects of clouds in tropical convective regions. Despite the relevance of anvil clouds for climate and responses of clouds to global warming, processes dominating their evolution are not well understood. Currently available observational data reveal instantaneous snapshots of anvil cloud properties, but cannot provide a process-based perspective on anvil evolution. We therefore conduct simulations with the high resolution version of the exascale earth system model in which we track mesoscale convective systems over the tropical Western Pacific and compute trajectories that follow air parcels detrained from peaks of convective activity. With this approach we gain new insight into the anvil cloud evolution both in present day and future climate. Comparison with geostationary satellite data shows that the model is able to simulate maritime mesoscale convective systems reasonably well. Trajectory results indicate that anvil cloud lifetime is about 15 h with no significant change in a warmer climate. The anvil ice mixing ratio is larger in a warmer climate due to a larger source of ice by detrainment and larger depositional growth leading to a more negative net cloud radiative effect along detrained trajectories. However, the increases in sources are counteracted by increases in sinks of ice, particularly snow formation and sedimentation. Furthermore, we find that the mean anvil cloud feedback along trajectories is positive and consistent with results from more traditional cloud feedback calculation methods. cirrus clouds; cloud feedbacks; radiative effects; tropical convection; anvil clouds; convective life cycle
Gettelman, A.; Gagne, D. J.; Chen, C.-C.; Christensen, M. W.; Lebo, Z. J.; Morrison, H.; Gantos, G.Gettelman, A., D. J. Gagne, C. Chen, M. W. Christensen, Z. J. Lebo, H. Morrison, G. Gantos, 2021: Machine Learning the Warm Rain Process. Journal of Advances in Modeling Earth Systems, 13(2), e2020MS002268. doi: https://doi.org/10.1029/2020MS002268. Clouds are critical for weather and climate prediction. The multiple scales of cloud processes make simulation difficult. Often models and measurements are used to develop empirical relationships for large-scale models to be computationally efficient. Machine learning provides another potential tool to improve our empirical parameterizations of clouds. To explore these opportunities, we replace the warm rain formation process in a General Circulation Model (GCM) with a detailed treatment from a bin microphysical model that causes a 400% slowdown in the GCM. We analyze the changes in climate that result from the use of the bin microphysical calculation and find improvements in the rain onset and frequency of light rain compared to high resolution process models and observations. We also find a resulting change in the cloud feedback response of the model to warming, which will significantly impact the climate sensitivity. We then replace the bin microphysical model with several neural networks designed to emulate the autoconversion and accretion rates produced by the bin microphysical model. The neural networks are organized into two stages: the first stage identifies where tendencies will be nonzero (and the sign of the tendency), and the second stage predicts the magnitude of the autoconversion and accretion rates. We describe the risks of overfitting, extrapolation, and linearization by using perfect model experiments with and without the emulator. We can recover the solutions with the emulators in almost all respects, and get simulations that perform as the detailed model, but with the computational cost of the control simulation. clouds; microphysics; machine learning
Guigma, Kiswendsida H.; Guichard, Françoise; Todd, Martin; Peyrille, Philippe; Wang, YiGuigma, K. H., F. Guichard, M. Todd, P. Peyrille, Y. Wang, 2021: Atmospheric tropical modes are important drivers of Sahelian springtime heatwaves. Climate Dynamics, 56(5), 1967-1987. doi: 10.1007/s00382-020-05569-9. Heatwaves pose a serious threat to human health worldwide but remain poorly documented over Africa. This study uses mainly the ERA5 dataset to investigate their large-scale drivers over the Sahel region during boreal spring, with a focus on the role of tropical modes of variability including the Madden–Julian Oscillation (MJO) and the equatorial Rossby and Kelvin waves. Heatwaves were defined from daily minimum and maximum temperatures using a methodology that retains only intraseasonal scale events of large spatial extent. The results show that tropical modes have a large influence on the occurrence of Sahelian heatwaves, and, to a lesser extent, on their intensity. Depending on their convective phase, they can either increase or inhibit heatwave occurrence, with the MJO being the most important of the investigated drivers. A certain sensitivity to the geographic location and the diurnal cycle is observed, with nighttime heatwaves more impacted by the modes over the eastern Sahel and daytime heatwaves more affected over the western Sahel. The examination of the physical mechanisms shows that the modulation is made possible through the perturbation of regional circulation. Tropical modes thus exert a control on moisture and the subsequent longwave radiation, as well as on the advection of hot air. A detailed case study of a major event, which took place in April 2003, further supports these findings. Given the potential predictability offered by tropical modes at the intraseasonal scale, this study has key implications for heatwave risk management in the Sahel.
Henry, Matthew; Merlis, Timothy M.; Lutsko, Nicholas J.; Rose, Brian E. J.Henry, M., T. M. Merlis, N. J. Lutsko, B. E. J. Rose, 2021: Decomposing the Drivers of Polar Amplification with a Single-Column Model. J. Climate, 34(6), 2355-2365. doi: 10.1175/JCLI-D-20-0178.1. AbstractThe precise mechanisms driving Arctic amplification are still under debate. Previous attribution methods compute the vertically uniform temperature change required to balance the top-of-atmosphere energy imbalance caused by each forcing and feedback, with any departures from vertically uniform warming collected into the lapse-rate feedback. We propose an alternative attribution method using a single-column model that accounts for the forcing dependence of high-latitude lapse-rate changes. We examine this method in an idealized general circulation model (GCM), finding that, even though the column-integrated carbon dioxide (CO2) forcing and water vapor feedback are stronger in the tropics, they contribute to polar-amplified surface warming as they produce bottom-heavy warming in high latitudes. A separation of atmospheric temperature changes into local and remote contributors shows that, in the absence of polar surface forcing (e.g., sea ice retreat), changes in energy transport are primarily responsible for the polar-amplified pattern of warming. The addition of surface forcing substantially increases polar surface warming and reduces the contribution of atmospheric dry static energy transport to the warming. This physically based attribution method can be applied to comprehensive GCMs to provide a clearer view of the mechanisms behind Arctic amplification.
Hourdin, Frédéric; Williamson, Daniel; Rio, Catherine; Couvreux, Fleur; Roehrig, Romain; Villefranque, Najda; Musat, Ionela; Fairhead, Laurent; Diallo, F. Binta; Volodina, VictoriaHourdin, F., D. Williamson, C. Rio, F. Couvreux, R. Roehrig, N. Villefranque, I. Musat, L. Fairhead, F. B. Diallo, V. Volodina, 2021: Process-based climate model development harnessing machine learning: II. model calibration from single column to global. Journal of Advances in Modeling Earth Systems, (In Press). doi: https://doi.org/10.1029/2020MS002225. AbstractWe demonstrate a new approach for climate model tuning in a realistic situation. Our approach, the mathematical foundations and technical details of which are given in Part I, systematically uses a single-column configuration of a global atmospheric model on test cases for which reference large-eddy-simulations are available. The space of free parameters is sampled running the single-column model from which metrics are estimated in the full parameter space using emulators. The parameter space is then reduced by retaining only the values for which the emulated metrics match large eddy simulations within a given tolerance to error. The approach is applied to the 6A version of the LMDZ model which results from a long investment in the development of physics parameterizations and by-hand tuning. The boundary layer is revisited by increasing the vertical resolution and varying parameters that were kept fixed so far, which improves the representation of clouds at process scale. The approach allows us to automatically reach a tuning of this modified configuration as good as that of the 6A version. We show how this approach helps accelerate the introduction of new parameterizations. It allows us to maintain the physical foundations of the model and to ensure that the improvement of global metrics is obtained for a reasonable behavior at process level, reducing the risk of error compensations that may arise from over-fitting some climate metrics. That is, we get things right for the right reasons.
Huang, Han; Huang, Yi; Hu, YongyunHuang, H., Y. Huang, Y. Hu, 2021: Quantifying the energetic feedbacks in ENSO. Climate Dynamics, 56(1), 139-153. doi: 10.1007/s00382-020-05469-y. Energetic feedbacks play important roles during the El Niño-Southern Oscillation (ENSO). Here we conduct a thorough analysis of the radiative and non-radiative vertical fluxes and compare them to horizontal energy transport to provide a complete view of the energetics of ENSO. Our analyses affirm that cloud feedbacks are the most important radiative feedbacks, with cloud shortwave (SW) and longwave (LW) feedbacks dominating at the surface and in the atmosphere respectively. Oceanic energy transport dominates the oceanic heat content change in the developing phase and has significant effects on the sea surface temperature (SST) about 6 months earlier than vertical fluxes. Atmospheric horizontal energy transport is also important, acting to quickly remove the surplus of energy provided by the convergence of vertical energy fluxes in the atmosphere. The differential diabatic heating between the Central Pacific and the Warm Pool, induced by the latent heat release as well as LW radiation, strengthens the anomalous circulation and reinforces the Bjerknes positive feedback to strengthen the SST anomaly. This work reveals that the differential heating is more strongly correlated with the SST anomaly in the Central Pacific than the local SW negative feedback of clouds and supports the idea that the overall atmospheric effect is likely a positive feedback that acts to strengthen ENSO.
Huang, Yiyi; Ding, Qinghua; Dong, Xiquan; Xi, Baike; Baxter, IanHuang, Y., Q. Ding, X. Dong, B. Xi, I. Baxter, 2021: Summertime low clouds mediate the impact of the large-scale circulation on Arctic sea ice. Communications Earth & Environment, 2(1), 1-10. doi: 10.1038/s43247-021-00114-w. The rapid Arctic sea ice retreat in the early 21st century is believed to be driven by several dynamic and thermodynamic feedbacks, such as ice-albedo feedback and water vapor feedback. However, the role of clouds in these feedbacks remains unclear since the causality between clouds and these processes is complex. Here, we use NASA CERES satellite products and NCAR CESM model simulations to suggest that summertime low clouds have played an important role in driving sea ice melt by amplifying the adiabatic warming induced by a stronger anticyclonic circulation aloft. The upper-level high pressure regulates low clouds through stronger downward motion and increasing lower troposphere relative humidity. The increased low clouds favor more sea ice melt via emitting stronger longwave radiation. Then decreased surface albedo triggers a positive ice-albedo feedback, which further enhances sea ice melt. Considering the importance of summertime low clouds, accurate simulation of this process is a prerequisite for climate models to produce reliable future projections of Arctic sea ice.
Huang, Yiyi; Dong, Xiquan; Kay, Jennifer E.; Xi, Baike; McIlhattan, Elin A.Huang, Y., X. Dong, J. E. Kay, B. Xi, E. A. McIlhattan, 2021: The climate response to increased cloud liquid water over the Arctic in CESM1: a sensitivity study of Wegener–Bergeron–Findeisen process. Climate Dynamics. doi: 10.1007/s00382-021-05648-5. The surface radiative imbalance has large impacts on the long-term trends and year-to-year variability of Arctic sea ice. Clouds are believed to be a key factor in regulating this radiative imbalance, whose underlying processes and mechanisms, however, are not well understood. Compared with observations, the Community Earth System Model version 1 (CESM1) is known to underestimate Arctic cloud liquid water. Here, the following hypothesis is proposed and tested: this underestimation is caused by an overactive Wegener–Bergeron–Findeisen (WBF) process in model as too many supercooled liquid droplets are scavenged by ice crystals via deposition. In this study, the efficiency of the WBF process in CESM1 was reduced to investigate the Arctic climate response, and differentiate the responses induced by atmosphere–ocean–sea ice coupling and global warming. By weakening the WBF process, CESM1 simulated liquid cloud fractions increased, especially in winter and spring. The cloud response resulted in increased downwelling longwave flux and decreased shortwave flux at the surface. Arctic clouds and radiation in simulations with reduced WBF efficiency show a better agreement with satellite retrievals. In addition, both coupling and global warming amplify the cloud response to a less efficient WBF process, due to increased relative humidity and enhanced evaporation, respectively. As a response, the sea ice tends to melt over the North Atlantic Ocean, most likely caused by a positive feedback process between clouds, radiation and sea ice during non-summer months. These results improve our understanding of large-scale effects of the WBF process and the role of cloud liquid water in the Arctic climate system.
Itterly, Kyle; Taylor, Patrick; Roberts, J. BrentItterly, K., P. Taylor, J. B. Roberts, 2021: Satellite Perspectives of Sea Surface Temperature Diurnal Warming on Atmospheric Moistening and Radiative Heating During MJO. J. Climate, (In Press). doi: 10.1175/JCLI-D-20-0350.1.
Jian, Bida; Li, Jiming; Wang, Guoyin; Zhao, Yuxin; Li, Yarong; Wang, Jing; Zhang, Min; Huang, JianpingJian, B., J. Li, G. Wang, Y. Zhao, Y. Li, J. Wang, M. Zhang, J. Huang, 2021: Evaluation of the CMIP6 marine subtropical stratocumulus cloud albedo and its controlling factors. Atmospheric Chemistry and Physics Discussions, 1-29. doi: https://doi.org/10.5194/acp-2020-1245. Abstract. The cloud albedo at the subtropical marine subtropical stratocumulus regions has a key role in regulating the regional energy budget. Based on 12 years of monthly data from multiple satellite datasets, the long-term, monthly and seasonal cycle averaged cloud albedo at five stratocumulus regions were investigated to inter-compare the atmosphere-only simulations of Phase 5 and 6 of the Coupled Model Inter-comparison Project (AMIP5 and AMIP6). Statistical results showed that the long-term regressed cloud albedos were underestimated in most AMIP6 models compared with the satellite-driven cloud albedos, and the AMIP6 models produced a similar spread of AMIP5 at all regions. The monthly mean and seasonal cycle of cloud albedo of AMIP6 ensemble mean showed better correlation with the satellite-driven observation than that of AMIP5 ensemble mean, however, fail to reproduce the values and amplitude in some regions. By employing the Modern-Era Retrospective Analysis for Research and Applications Version 2 data, this study estimated the relative contributions of different aerosols and meteorological factors on the marine stratocumulus cloud albedo under different cloud liquid water path (LWP) conditions. The multiple regression models can explain ~60 % of the changes in the cloud albedo. Under the monthly mean LWP ≤ 60 g m−2, dust and black carbon dominantly contributed to the changes in the cloud albedo, while sulfate aerosol contributed the most under the condition of 60 g m−2
Joseph, Jofia; Girishkumar, M. S.; McPhaden, M. J.; Rao, E. Pattabhi RamaJoseph, J., M. S. Girishkumar, M. J. McPhaden, E. P. R. Rao, 2021: Diurnal variability of atmospheric cold pool events and associated air-sea interactions in the Bay of Bengal during the summer monsoon. Climate Dynamics, 56(3), 837-853. doi: 10.1007/s00382-020-05506-w. Atmospheric cold pools generated from convective downdrafts can significantly modulate air-sea interaction processes, though the variability in cold pool events is not yet documented in the Bay of Bengal (BoB). In this study, the seasonal and diurnal variability of cold pool events (defined as a drop in air temperature greater than 1 °C within 30 min) in the BoB is examined using moored buoy measurements with 10-min temporal resolution at 8°N, 12°N, and 15°N along 90°E. The analysis shows that cold pools are plentiful and frequent during summer (May–September) and fall (October–November) compared to winter (December-February) and spring (March–April). Results also indicate a significant diurnal variability at 15°N and 12°N (but not at 8°N) during summer, with more frequent and intense cold pool events in the afternoon. Cold pools lead to an intensification of turbulent heat exchange between the ocean and atmosphere, with increased latent heat loss (~ 80 Wm−2) through both an increase in wind speed and reduction in air specific humidity and increased sensible heat loss (~ 40 Wm−2) due primarily to air temperature drops. There is also a significant diurnal variability in these air-sea exchanges during the summer, with a twofold enhancement in latent and sensible heat fluxes associated with afternoon vs nighttime cold pools events. Finally, we establish the connection between the enhancement of afternoon cold pool events and southeastward propagating synoptic-scale rainfall activity on diurnal time scales from the western BoB.
Joseph, Jofia; Girishkumar, M. S.; Varikoden, Hamza; Thangaprakash, V. P.; Shivaprasad, S.; Rama Rao, E. PattabhiJoseph, J., M. S. Girishkumar, H. Varikoden, V. P. Thangaprakash, S. Shivaprasad, E. P. Rama Rao, 2021: Observed sub-daily variability of latent and sensible heat fluxes in the Bay of Bengal during the summer. Climate Dynamics, 56(3), 917-934. doi: 10.1007/s00382-020-05512-y. The sub-daily variability of latent (LHF) and sensible heat flux (SHF) in the Bay of Bengal (BoB) during the summer (May–September) is examined using moored buoys data at 8° N (2008 and 2011), 12° N (2010, 2011, 2012, 2013, 2014, and 2015), and 15° N (2009, 2013, 2014, and 2015) along 90° E. In the weak wind regime ( 6 ms−1) with a range of ~ 13 Wm−2 at 8° N and ~ 17 Wm−2 at 12° N and 15° N. In the strong wind regime, SHF shows heat gain by the ocean with a maximum (minimum) value during the daytime (night), while it shows heat loss from the ocean in the weak wind regime with maximum (minimum) value during the night (daytime). The diurnal range of SHF does not show significant meridional variation in the strong (~ 3.5 Wm−2) and weak (~ 2 Wm−2) wind regime. The difference in sub-daily evolution of air-temperature, air-specific humidity, and wind speed determines distinct evolutions of LHF and SHF in different wind regimes, which appears to be driven by atmospheric boundary layer processes and eastward propagating land-sea breeze signals over the BoB. Finally, we also establish the relationship between sub-daily evolutions of turbulent heat fluxes in the different wind regimes with synoptic conditions associated with the active and break phases of the Indian summer monsoon.
Kang, Litai; Marchand, Roger; Smith, WilliamKang, L., R. Marchand, W. Smith, 2021: Evaluation of MODIS and Himawari-8 Low Clouds Retrievals Over the Southern Ocean With In Situ Measurements From the SOCRATES Campaign. Earth and Space Science, 8(3), e2020EA001397. doi: https://doi.org/10.1029/2020EA001397. Aircraft observations collected during the Southern Ocean Cloud Radiation Aerosol Transport Experimental Study in January-February of 2018 are used to evaluate cloud properties from three satellite-imager datasets: (1) the Moderate Resolution Imaging Spectroradiometer level 2 (collection 6.1) cloud product, (2) the CERES-MODIS Edition 4 cloud product, and (3) the NASA SatCORPS Himawari-8 cloud product. Overall the satellite retrievals compare well with the in situ observations, with little bias and modest to good correlation coefficients when considering all aircraft profiles for which there are coincident MODIS observations. The Himawari-8 product does, however, show a statistically significant mean bias of about 1.2 μm for effective radius (re) and 2.6 for optical depth (τ) when applied to a larger set of profiles with coincident Himawari-8 observations. The low overall mean-bias in the re retrievals is due in part to compensating errors between cases that are non- or lightly precipitating, with cases that have heavier precipitation. re is slightly biased high (by about 0.5–1.0 μm) for non- and lightly precipitating cases and biased low by about 3–4 μm for heavily precipitating cases when precipitation exits near cloud top. The bias in non- and lightly precipitating conditions is due to (at least in part) having assumed a drop size distribution in the retrieval that is too broad. These biases in the re ultimately propagate into the retrieved liquid water path and number concentration. clouds; MODIS; remote sensing; southern ocean; himawari-8; SOCRATES
Kramer, Ryan J.; He, Haozhe; Soden, Brian J.; Oreopoulos, Lazaros; Myhre, Gunnar; Forster, Piers M.; Smith, Christopher J.Kramer, R. J., H. He, B. J. Soden, L. Oreopoulos, G. Myhre, P. M. Forster, C. J. Smith, 2021: Observational evidence of increasing global radiative forcing. Geophysical Research Letters, n/a(n/a), e2020GL091585. doi: https://doi.org/10.1029/2020GL091585. Changes in atmospheric composition, such as increasing greenhouse gases, cause an initial radiative imbalance to the climate system, quantified as the instantaneous radiative forcing. This fundamental metric has not been directly observed globally and previous estimates have come from models. In part, this is because current space-based instruments cannot distinguish the instantaneous radiative forcing from the climate’s radiative response. We apply radiative kernels to satellite observations to disentangle these components and find all-sky instantaneous radiative forcing has increased 0.53±0.11 W/m2 from 2003 through 2018, accounting for positive trends in the total planetary radiative imbalance. This increase has been due to a combination of rising concentrations of well-mixed greenhouse gases and recent reductions in aerosol emissions. These results highlight distinct fingerprints of anthropogenic activity in Earth’s changing energy budget, which we find observations can detect within 4 years. aerosols; greenhouse gases; radiative forcing; radiative kernels
Lang, Simon T. K.; Lock, Sarah-Jane; Leutbecher, Martin; Bechtold, Peter; Forbes, Richard M.Lang, S. T. K., S. Lock, M. Leutbecher, P. Bechtold, R. M. Forbes, 2021: Revision of the Stochastically Perturbed Parametrisations model uncertainty scheme in the Integrated Forecasting System. Quarterly Journal of the Royal Meteorological Society, 147(735), 1364-1381. doi: https://doi.org/10.1002/qj.3978. The Stochastically Perturbed Parametrisations scheme (SPP) represents model uncertainty in numerical weather prediction by introducing stochastic perturbations into the physical parametrisation schemes. The perturbations are constructed in such a way that the internal consistency of the physical parametrisation schemes is preserved. We developed a revised version of SPP for the Integrated Forecasting System of the European Centre for Medium-Range Weather Forecasts (ECMWF). The revised version introduces perturbations to additional quantities and modifies the probability distributions sampled by the scheme. Medium-range ensemble forecasts with the revised SPP are considerably more skilful than ensemble forecasts with the original implementation of SPP. The revised version of SPP is similar, in terms of forecast skill, to the Stochastically Perturbed Parametrisation Tendency scheme (SPPT), which is currently used to represent model uncertainty in the operational ECMWF ensemble forecasts. stochastic physics; ensemble forecasting; ensemble perturbation methods; SPP; SPPT
Liang, Shunlin; Cheng, Jie; Jia, Kun; Jiang, Bo; Liu, Qiang; Xiao, Zhiqiang; Yao, Yunjun; Yuan, Wenping; Zhang, Xiaotong; Zhao, Xiang; Zhou, JiLiang, S., J. Cheng, K. Jia, B. Jiang, Q. Liu, Z. Xiao, Y. Yao, W. Yuan, X. Zhang, X. Zhao, J. Zhou, 2021: The Global LAnd Surface Satellite (GLASS) product suite. Bull. Amer. Meteor. Soc., (In Press). doi: 10.1175/BAMS-D-18-0341.1.
Ma, Qianrong; You, Qinglong; Ma, Yujun; Cao, Yu; Zhang, Jie; Niu, Miaomiao; Zhang, YuqingMa, Q., Q. You, Y. Ma, Y. Cao, J. Zhang, M. Niu, Y. Zhang, 2021: Changes in cloud amount over the Tibetan Plateau and impacts of large-scale circulation. Atmospheric Research, 249, 105332. doi: 10.1016/j.atmosres.2020.105332. Using the Clouds and Earth's Radiant Energy System (CERES) Edition 4 dataset, characteristics and variations of cloud amounts over the Tibetan Plateau (Tibet) during 2001–2019 was analyzed. Our results reveal that the mid–high cloud cover (MHCC) constitutes the major proportion and shows similar seasonal variations and annual cycle to the total cloud cover (TCC). The high cloud cover (HCC) has the greatest seasonal variation, whereas the mid–low cloud cover (MLCC) has the least variation. TCC, MHCC, and HCC exhibit the largest values in summer. The summer TCC, MHCC and MLCC exhibited decreasing trends and MHCC is more significant. The summer HCC shows increasing trend. Clouds at different heights show different correlations with skin temperature, and decreased TCC likely influences recent warming over the Tibet. The increased skin temperature is mainly adjusted by the decreased cloud amount especially MHCC. Cloud amounts are highly responsible for the precipitation, and the summer precipitation over the Tibet is mainly influenced by HCC, followed by MHCC. The decreasing TCC is related to two Rossby wave trains over Eurasia, corresponding to the Eurasian teleconnection pattern and Silk Road pattern. They induce an anomalous anti-cyclone in north Tibet and restrain ascending motions. Meanwhile, the South Asia High weakens and further enhances the sinking movements. Precipitation; Cloud amounts; Rossby wave trains; South Asia High; Surface temperature
Mackie, Anna; Brindley, Helen E.; Palmer, Paul I.Mackie, A., H. E. Brindley, P. I. Palmer, 2021: Contrasting observed atmospheric responses to tropical SST warming patterns. Journal of Geophysical Research: Atmospheres, n/a(n/a), e2020JD033564. doi: https://doi.org/10.1029/2020JD033564. Equilibrium climate sensitivity (ECS) is a theoretical concept which describes the change in global mean surface temperature that results from a sustained doubling of atmospheric CO2. Current ECS estimates range from ∼1.8–5.6K, reflecting uncertainties in climate feedbacks. The sensitivity of the lower (1000-700 hPa) and upper (500-200 hPa) troposphere to changes in spatial patterns of tropical sea surface temperature (SST) have been proposed by recent model studies as key feedbacks controlling climate sensitivity. We examine empirical evidence for these proposed mechanisms using 14 years of satellite data. We examine the response of temperature and humidity profiles, clouds and top-of-the-atmosphere (TOA) radiation to relative warming in tropical ocean regions when there is either strong convection or subsidence. We find warmer SSTs in regions of strong subsidence are coincident with a decrease in lower tropospheric stability (-0.9±0.4 KK−1) and low cloud cover ( ∼-6 %K−1). This leads to a warming associated with the weakening in the shortwave cooling effect of clouds (4.2±1.9 Wm−2K−1), broadly consistent with model calculations. In contrast, warmer SSTs in regions of strong convection are coincident with an increase in upper tropospheric humidity (3.2±1.5 %K−1). In this scenario, the dominant effect is the enhancement of the warming longwave cloud radiative effect (3.8±3.0 Wm−2K−1 ) from an increase in high cloud cover ( ∼7 %K−1), though changes in the net (longwave and shortwave) effect are not statistically significant (p < 0.003). Our observational evidence supports the existence of mechanisms linking contrasting atmospheric responses to patterns in SST, mechanisms which have been linked to climate sensitivity. Climate sensitivity; Satellite observations; SST warming patterns; Tropical atmosphere
Marcianesi, F.; Aulicino, G.; Wadhams, P.Marcianesi, F., G. Aulicino, P. Wadhams, 2021: Arctic sea ice and snow cover albedo variability and trends during the last three decades. Polar Science, (In Press). doi: 10.1016/j.polar.2020.100617. The aim of the present study is to assess the full effect on the albedo of both sea ice extent decrease and snowline retreat in the Arctic during the last three decades. Averaged over the globe, the overall warming effect due to Arctic land and ocean albedo change corresponds to adding about 44% to the direct effect of human CO2 emissions during the same period. In fact, the area and thickness of Arctic sea ice have both been declining in this time frame. This has caused feedbacks affecting the whole global climate system. One such is albedo feedback of sea ice shrinking which was previously estimated (Pistone et al., 2014) to add about 25% to the direct warming effect of anthropogenic CO2 emissions. In this study, we demonstrate that the role of snowline retreat in albedo decrease is comparable to that of sea ice shrinking. To this aim, we estimate the radiative forcing (W/m2) due to snow and ice decrease during 34 years (1982–2015) from the analysis of changes of observed albedo based on the Clouds and the Earth's Radiant Energy System Energy Balanced And Filled (CERES EBAF) dataset, paired with sea ice and snow cover data from the US National Snow & Ice Data Center (NSIDC). Arctic; Albedo change; Global climate; Sea ice decrease; Snowline retreat
Ming, Yi; Loeb, Norman G.; Lin, Pu; Shen, Zhaoyi; Naik, Vaishali; Singer, Clare E.; Ward, Ryan X.; Paulot, Fabien; Zhang, Zhibo; Bellouin, Nicolas; Horowitz, Larry W.; Ginoux, Paul A.; Ramaswamy, V.Ming, Y., N. G. Loeb, P. Lin, Z. Shen, V. Naik, C. E. Singer, R. X. Ward, F. Paulot, Z. Zhang, N. Bellouin, L. W. Horowitz, P. A. Ginoux, V. Ramaswamy, 2021: Assessing the Influence of COVID-19 on the Shortwave Radiative Fluxes Over the East Asian Marginal Seas. Geophysical Research Letters, 48(3), e2020GL091699. doi: https://doi.org/10.1029/2020GL091699. The Coronavirus Disease 2019 (COVID-19) pandemic led to a widespread reduction in aerosol emissions. Using satellite observations and climate model simulations, we study the underlying mechanisms of the large decreases in solar clear-sky reflection (3.8 W m−2 or 7%) and aerosol optical depth (0.16 W m−2 or 32%) observed over the East Asian Marginal Seas in March 2020. By separating the impacts from meteorology and emissions in the model simulations, we find that about one-third of the clear-sky anomalies can be attributed to pandemic-related emission reductions, and the rest to weather variability and long-term emission trends. The model is skillful at reproducing the observed interannual variations in solar all-sky reflection, but no COVID-19 signal is discerned. The current observational and modeling capabilities will be critical for monitoring, understanding, and predicting the radiative forcing and climate impacts of the ongoing crisis.
Nga, Pham Thi Thanh; Ha, Pham Thanh; Hang, Vu ThanhNga, P. T. T., P. T. Ha, V. T. Hang, 2021: Satellite-Based Regionalization of Solar Irradiation in Vietnam by k-Means Clustering. J. Appl. Meteor. Climatol., 60(3), 391-402. doi: 10.1175/JAMC-D-20-0070.1. AbstractThis study presents the application of k-means clustering to satellite-based solar irradiation in different regions of Vietnam. The solar irradiation products derived from the Himawari-8 satellite, named AMATERASS by the solar radiation consortium under the Japan Science and Technology Agency (JST), are validated with observations recorded at five stations in the period from October 2017 to September 2018 before their use for clustering. High correlations among them enable the use of satellite-based daily global horizontal irradiation for spatial variability analysis and regionalization. With respect to the climate regime in Vietnam, the defined 6-cluster groups demonstrate better agreement with the conventionally classified seven climatic zones rather than the four climatic zones of the Köppen classification. The spatial distribution and seasonal variation in the regionalized solar irradiation reflect interchangeable influences of large-scale atmospheric circulation in terms of the East Asian winter monsoon and the South Asian summer monsoon as well as the effect of local topography. Higher daily averaged solar radiation and its weaker seasonal variation were found in two clusters in the southern region where the South Asian summer monsoon dominates in the rainy season. Pronounced seasonal variability in solar irradiation in four clusters in the northern region is associated with the influence of the East Asian monsoon, resulting in its clear reduction during the winter months.
Obregón, María Ángeles; Serrano, Antonio; Costa, Maria João; Silva, Ana MariaObregón, M. Á., A. Serrano, M. J. Costa, A. M. Silva, 2021: Global Spatial and Temporal Variation of the Combined Effect of Aerosol and Water Vapour on Solar Radiation. Remote Sensing, 13(4), 708. doi: 10.3390/rs13040708. This study aims to calculate the combined and individual effects of the optical thickness of aerosols (AOT) and precipitable water vapour (PWV) on the solar radiation reaching the Earth’s surface at a global scale and to analyse its spatial and temporal variation. For that purpose, a novel but validated methodology is applied to CERES SYN1deg products for the period 2000–2019. Spatial distributions of AOT and PWV effects, both individually and combined, show a close link with the spatial distributions of AOT and PWV. The spatially averaged combined effect results in a −13.9% reduction in irradiance, while the average AOT effect is −2.3%, and the PWV effect is −12.1%. The temporal analysis focuses on detecting trends in the anomalies. The results show overall positive trends for AOT and PWV. Consequently, significant negative overall trends are found for the effects. However, significant positive trends for the individual AOT and the combined AOT-PWV effects are found in specific regions, such as the eastern United States, Europe or Asia, indicating successful emission control policies in these areas. This study contributes to a better understanding of the individual and combined effects of aerosols and water vapour on solar radiation at a global scale. CERES; aerosol optical depth; precipitable water vapour; combined effects; global radiative effects
Painemal, David; Corral, Andrea F.; Sorooshian, Armin; Brunke, Michael A.; Chellappan, Seethala; Gorooh, Vesta Afzali; Ham, Seung-Hee; O'Neill, Larry; Smith, William L.; Tselioudis, George; Wang, Hailong; Zeng, Xubin; Zuidema, PaquitaPainemal, D., A. F. Corral, A. Sorooshian, M. A. Brunke, S. Chellappan, V. A. Gorooh, S. Ham, L. O'Neill, W. L. Smith, G. Tselioudis, H. Wang, X. Zeng, P. Zuidema, 2021: An Overview of Atmospheric Features Over the Western North Atlantic Ocean and North American East Coast—Part 2: Circulation, Boundary Layer, and Clouds. Journal of Geophysical Research: Atmospheres, 126(6), e2020JD033423. doi: https://doi.org/10.1029/2020JD033423. The Western North Atlantic Ocean (WNAO) is a complex land-ocean-atmosphere system that experiences a broad range of atmospheric phenomena, which in turn drive unique aerosol transport pathways, cloud morphologies, and boundary layer variability. This work, Part 2 of a 2-part paper series, provides an overview of the atmospheric circulation, boundary layer variability, three-dimensional cloud structure, and precipitation over the WNAO; the companion paper (Part 1) focused on chemical characterization of aerosols, gases, and wet deposition. Seasonal changes in atmospheric circulation and sea surface temperature explain a clear transition in cloud morphologies from small shallow cumulus clouds, convective clouds, and tropical storms in summer, to stratus/stratocumulus and multilayer cloud systems associated with winter storms. Synoptic variability in cloud fields is estimated using satellite-based weather states, and the role of postfrontal conditions (cold-air outbreaks) in the development of stratiform clouds is further analyzed. Precipitation is persistent over the ocean, with a regional peak over the Gulf Stream path, where offshore sea surface temperature gradients are large and surface fluxes reach a regional peak. Satellite data show a clear annual cycle in cloud droplet number concentration with maxima (minima) along the coast in winter (summer), suggesting a marked annual cycle in aerosol-cloud interactions. Compared with satellite cloud retrievals, four climate models qualitatively reproduce the annual cycle in cloud cover and liquid water path, but with large discrepancies across models, especially in the extratropics. The paper concludes with a summary of outstanding issues and recommendations for future work. air-sea interactions; atmospheric boundary layer; climate model evaluation; stratiform clouds; Western North Atlantic
Renner, Maik; Kleidon, Axel; Clark, Martyn; Nijssen, Bart; Heidkamp, Marvin; Best, Martin; Abramowitz, GabRenner, M., A. Kleidon, M. Clark, B. Nijssen, M. Heidkamp, M. Best, G. Abramowitz, 2021: How well can land-surface models represent the diurnal cycle of turbulent heat fluxes?. J. Hydrometeor., 22(1), 77-94. doi: 10.1175/JHM-D-20-0034.1. Abstract The diurnal cycle of solar radiation represents the strongest energetic forcing and dominates the exchange of heat and mass of the land surface with the atmosphere. This diurnal heat redistribution represents a core of land-atmosphere coupling that should be accurately represented in Land-Surface Models (LSM) which are critical parts of weather and climate models. We employ a diagnostic model evaluation approach using a signature-based metric which describes the diurnal variation of heat fluxes. The metric is obtained by decomposing the diurnal variation of surface heat fluxes into their direct response and the phase lag to incoming solar radiation. We employ the output of 13 different LSMs driven with meteorological forcing of 20 FLUXNET sites (PLUMBER dataset by Best et al., 2015). All LSMs show a poor representation of the evaporative fraction and thus the diurnal magnitude of the sensible and latent heat ux under cloud-free conditions. In addition, we find that the diurnal phase of both heat fluxes is poorly represented. The best performing model only reproduces 33% of the evaluated evaporative conditions across the sites. The poor performance of the diurnal cycle of turbulent heat exchange appears to be linked to how models solve for the surface energy balance and redistribute heat into the subsurface. We conclude that a systematic evaluation of diurnal signatures is likely to help to improve the simulated diurnal cycle, better represent land-atmosphere interactions and therefore improve simulations of the near-surface climate.
Ridout, James A.; Barton, Neil P.; Janiga, Matthew A.; Reynolds, Carolyn A.; May, Jackie C.; Rowley, Clark; Bishop, Craig H.Ridout, J. A., N. P. Barton, M. A. Janiga, C. A. Reynolds, J. C. May, C. Rowley, C. H. Bishop, 2021: Surface Radiative Flux Bias Reduction through Regionally Varying Cloud Fraction Parameter Nudging in a Global Coupled Forecast System. Journal of Advances in Modeling Earth Systems, (In Press). doi: 10.1029/2019MS002006. Key Points: A method is presented to nudge a cloud fraction parameter in a global coupled forecast system to reduce surface net shortwave flux biases. Results from a series of 45-day test forecasts are presented demonstrating the efficacy of the approach. Further tests are required to determine operational applicability using a suitable near real-time source of surface radiative flux data. cloud parameterization; coupled modelling; parameter adjustment; surface radiation budget
Shen, Lixing; Zhao, Chuanfeng; Yang, XingchuanShen, L., C. Zhao, X. Yang, 2021: Insight Into the Seasonal Variations of the Sea-Land Breeze in Los Angeles With Respect to the Effects of Solar Radiation and Climate Type. Journal of Geophysical Research: Atmospheres, 126(6), e2020JD033197. doi: https://doi.org/10.1029/2020JD033197. This study uses 20 years of observation data to analyze the long-term trend of the sea-land breeze (SLB) in the city of Los Angeles. The focus of the study is on the seasonal variation of the SLB and the main influencing factors both regionally and at a large scale. A new method which is suitable for automatic processing is introduced to analyze the SLB and determine the specific characteristics of the local SLB. The results show the sea wind speed has an obvious seasonal variation with peak value in summer and minimum value in winter. Note the sea wind speed is generally positively related to the in situ solar radiation. In contrast, the seasonal variation of the land wind speed is much weaker. Two main factors are responsible for this phenomenon. First, the response of the temperature difference between land and sea (TDLS) to the season is much more insensitive during nighttime than during daytime, and the TDLS is the direct driver of SLB. Second, the magnitude of the upper layer westerlies has an obvious seasonal variation under the local climate background, which is called the Mediterranean climate. During winter, the stronger upper westerlies enhance the land wind circulation, which further offsets the seasonal gap, and this even causes the fact that there is no corresponding relationship between the season and wind speed. In contrast, the seasonal variation of the westerlies has little effect on the sea wind speed, and the in situ solar radiation remains the determinant factor. solar radiation; Mediterranean climate; sea-land breeze; westerlies
Shi, Hongrong; Zhang, Jinqiang; Zhao, Bin; Xia, Xiangao; Hu, Bo; Chen, Hongbin; Wei, Jing; Liu, Mengqi; Bian, Yuxuan; Fu, Disong; Gu, Yu; Liou, Kuo-NanShi, H., J. Zhang, B. Zhao, X. Xia, B. Hu, H. Chen, J. Wei, M. Liu, Y. Bian, D. Fu, Y. Gu, K. Liou, 2021: Surface Brightening in Eastern and Central China Since the Implementation of the Clean Air Action in 2013: Causes and Implications. Geophysical Research Letters, 48(3), e2020GL091105. doi: https://doi.org/10.1029/2020GL091105. Surface brightening has been observed in China since 2005. However, it remains unclear whether the brightening has accelerated recently in response to the strictest ever air pollution control policies since 2013. By combining intensive surface and satellite observations, we find an unprecedented rapid increasing trend in surface solar radiation (SSR) of 0.70–1.16 W m−2 yr−1 over the eastern and central China for 2014–2019. Using a novel method to identify the relative contributions of aerosol and cloud radiative effects to the SSR trends, we find that the strongly declining aerosol radiative effect due to the strict air pollution controls is the main cause of the upward SSR trends; cloud variations should not be the main reason. Distinction exists in seasonal trends of SSR, with decreasing trends in winter and increasing trends in other seasons. Air pollution controls play an important role in regulating SSR, which has valuable implications for photovoltaic power generation. aerosol radiative effect; air pollutant control; eastern and central China; surface solar radiation brightening
Sledd, Anne; L'Ecuyer, TristanSledd, A., T. L'Ecuyer, 2021: Uncertainty in Forced and Natural Arctic Solar Absorption Variations in CMIP6 Models. J. Climate, 34(3), 931-948. doi: 10.1175/JCLI-D-20-0244.1.
Suselj, Kay; Teixeira, Joao; Kurowski, Marcin J.; Molod, AndreaSuselj, K., J. Teixeira, M. J. Kurowski, A. Molod, 2021: Improving the Representation of Subtropical Boundary Layer Clouds in the NASA GEOS Model with the Eddy-Diffusivity/Mass-Flux Parameterization. Mon. Wea. Rev., 149(3), 793-809. doi: 10.1175/MWR-D-20-0183.1. AbstractA systematic underestimation of subtropical planetary boundary layer (PBL) stratocumulus clouds by the GEOS model has been significantly improved by a new eddy-diffusivity/mass-flux (EDMF) parameterization. The EDMF parameterization represents the subgrid-scale transport in the dry and moist parts of the PBL in a unified manner and it combines an adjusted eddy-diffusivity PBL scheme from GEOS with a stochastic multiplume mass-flux model. The new EDMF version of the GEOS model is first compared against the CONTROL version in a single-column model (SCM) framework for two benchmark cases representing subtropical stratocumulus and shallow cumulus clouds, and validated against large-eddy simulations. Global simulations are performed and compared against observations and reanalysis data. The results show that the EDMF version of the GEOS model produces more realistic subtropical PBL clouds. The EDMF improvements first detected in the SCM framework translate into similar improvements of the global GEOS model.
Takahashi, Naoya; Hayasaka, Tadahiro; Qiu, Bo; Yamaguchi, RyoheiTakahashi, N., T. Hayasaka, B. Qiu, R. Yamaguchi, 2021: Observed response of marine boundary layer cloud to the interannual variations of summertime Oyashio extension SST front. Climate Dynamics. doi: 10.1007/s00382-021-05649-4. Active roles of both sea surface temperature (SST) and its frontal characteristics to the atmosphere in the mid-latitudes have been investigated around the western boundary current regions, and most studies have focused on winter season. The present study investigated the influence of the variation of the summertime Oyashio extension SST front (SSTF) in modulating low-level cloud properties (i.e., low-level cloud cover [LCC], cloud optical thickness [COT], and shortwave cloud radiative effect [SWCRE]) on inter-annual timescales, based on available satellite and Argo float datasets during 2003–2016. First, we examined the mechanism of summertime SSTF variability itself. The strength of the SSTF (SSSTF), defined as the maximum horizontal gradient of SST, has clear inter-annual variations. Frontogenesis equation analysis and regression analysis for subsurface temperature indicated that the inter-annual variations of the summertime SSSTF in the western North Pacific are closely related to the variations of not surface heat flux, but western boundary currents, particularly the Oyashio Extensions. The response of low-level cloud to intensified SSSTF is that negative SWCRE with positive COT anomaly in the northern flank of the SSTF can be induced by cold SST anomalies. The spatial scale of the low-level cloud response was larger than the SST frontal scale, and the spatial distribution of the response was mainly constrained by the pathways of Kuroshio and Oyashio Extensions. Multi-linear regression analysis revealed that the local SST anomaly played largest role in modulating the SWCRE and COT anomalies among the cloud controlling factors (e.g., estimated inversion strength, air-temperature advection) accounting for more than 50% of the variation. This study provides an observational evidence of the active role of local SST anomalies in summertime associated with the western boundary currents to the oceanic low-level cloud.
Talib, Joshua; Taylor, Christopher M.; Duan, Anmin; Turner, Andrew G.Talib, J., C. M. Taylor, A. Duan, A. G. Turner, 2021: Intraseasonal soil moisture-atmosphere feedbacks on the Tibetan Plateau circulation. J. Climate, (In Press). doi: 10.1175/JCLI-D-20-0377.1.
Tang, Wenjun; Qin, Jun; Yang, Kun; Zhu, Fuxin; Zhou, XuTang, W., J. Qin, K. Yang, F. Zhu, X. Zhou, 2021: Does ERA5 outperform satellite products in estimating atmospheric downward longwave radiation at the surface?. Atmospheric Research, 252, 105453. doi: 10.1016/j.atmosres.2021.105453. Atmospheric downward longwave radiation (DLR) is a key component of the surface energy budget in the Earth system. Satellite retrievals and atmospheric reanalysis estimates are the two typical approaches to obtaining a spatio-temporally continuous DLR product. In this study, we evaluated the DLR product from the latest ERA5 atmospheric reanalysis and the well-known Clouds and Earth's Radiant Energy System (CERES) satellite retrievals, against high-quality observations collected at 46 Baseline Surface Radiation Network (BSRN) stations over land surfaces and at 9 Global Tropical Moored Buoy Array (GTMBA) buoy stations. The accuracy of the ERA5 DLR product over land was found to be higher on average than that of CERES at hourly to monthly time scales. Conversely, ERA5 performed slightly worse than CERES-SYN when estimating DLR over the ocean surface. This is the first time that atmospheric reanalysis has performed better than satellite retrievals in estimating DLR over the land surface, demonstrating the potentially extensive application prospects for ERA5 as well as setting new challenges for quantitative remote sensing research. CERES; ERA5; Accuracy; Evaluation; Longwave radiation
Tang, Wenjun; Yang, Kun; Qin, Jun; Li, Jun; Ye, JiangangTang, W., K. Yang, J. Qin, J. Li, J. Ye, 2021: How Accurate Are Satellite-Derived Surface Solar Radiation Products over Tropical Oceans?. J. Atmos. Oceanic Technol., 38(2), 283-291. doi: 10.1175/JTECH-D-20-0099.1. AbstractSurface solar radiation (SSR) over the ocean is essential for studies of ocean–atmosphere interactions and marine ecology, and satellite remote sensing is a major way to obtain the SSR over ocean. A new high-resolution (10 km; 3 h) SSR product has recently been developed, mainly based on the newly released cloud product of the International Satellite Cloud Climatology Project H series (ISCCP-HXG), and is available for the period from July 1983 to December 2018. In this study, we compared this SSR product with in situ observations from 70 buoy sites in the Global Tropical Moored Buoy Array (GTMBA) and also compared it with another well-known satellite-derived SSR product from the Clouds and the Earth’s Radiant Energy System (CERES; edition 4.1), which has a spatial resolution of approximately 100 km. The results show that the ISCCP-HXG SSR product is generally more accurate than the CERES SSR product for both ocean and land surfaces. We also found that the accuracy of both satellite-derived SSR products (ISCCP-HXG and CRERS) was higher over ocean than over land and that the accuracy of ISCCP-HXG SSR improves greatly when the spatial resolution of the product is coarsened to ≥ 30 km.
Valdivieso, Maria; Peatman, Simon C.; Klingaman, Nicholas P.Valdivieso, M., S. C. Peatman, N. P. Klingaman, 2021: The influence of air-sea coupling on forecasts of the 2016 Indian summer monsoon and its intraseasonal variability. Quarterly Journal of the Royal Meteorological Society, (In Press). doi: 10.1002/qj.3914. Daily initialized coupled and uncoupled numerical weather prediction (NWP) forecasts from the global Met Office Unified Model (MetUM) are compared for the 2016 Indian summer monsoon. Three MetUM configurations are used: atmosphere-only (ATM), coupled to a mixed-layer ocean model (KPP), and coupled to a dynamical ocean model (NEMO). The analysis focuses on the impact of air-sea coupling, particularly in the Bay of Bengal (BoB), on NWP for monsoon rainfall. Seasonal-mean biases in all three configurations are highly consistent and driven by errors in atmospheric processes. Rainfall is initially overestimated over India, but underestimated over the BoB, the latter associated with too much shortwave radiation and too little cloud cover in MetUM. The excess shortwave radiation (>40 Wm -2 over the northwest BoB) is partially compensated by additional latent cooling, primarily due to overestimated surface wind speeds. In NEMO and KPP, coupling improves the timing of intraseasonal active and break phases over India, primarily the end of these phases, which are systematically too late in ATM. NEMO and KPP show a more realistic intraseasonal local phase relationship between sea surface temperature (SST) and rainfall throughout the BoB, but no configuration reproduces the observed significant lagged relationship between BoB SST and Indian rainfall. The lack of this relationship may be partly attributed to weak heat flux feedbacks to northern BoB SST, with the forecast shortwave feedback having systematically the wrong sign (positive) compared to satellite radiation, and thus contributing to SST warming at all lead times. Based on these MetUM forecasts, there is a limited impact of coupling on NWP for monsoon rainfall, both for the mean rainfall and intraseasonal variability. Further research to improve NWP for monsoon rainfall should focus on reducing MetUM atmospheric systematical biases. air–sea coupling; atmospheric convection; Bay of Bengal; Indian monsoon; intraseasonal variability; weather forecasting
Wang, Kai; Zhang, Yang; Yahya, KhairunnisaWang, K., Y. Zhang, K. Yahya, 2021: Decadal application of WRF/Chem over the continental U.S.: Simulation design, sensitivity simulations, and climatological model evaluation. Atmospheric Environment, 118331. doi: 10.1016/j.atmosenv.2021.118331. The WRF/Chem v3.7 is applied to 2001-2010 over the continental U.S. using the National Emission Inventory (NEI). This study will provide the baseline simulation for a future work to investigate the impacts of both climate and emission changes on the future regional air quality and human health. This paper focuses on the current year simulation design, comprehensive model evaluation, and sensitivity simulations that demonstrate the impacts of different reinitialization setup, cloud physical schemes, and emission inventories on the model predictions. Nine one-month sensitivity simulations by using different reinitialization setup and cloud microphysics and cumulus parameterizations are first conducted to provide the optimal model configurations. The model performance in predicting the regional meteorology and air quality on a decadal scale is further evaluated against available surface, satellite, and reanalysis data. The decadal WRF/Chem simulation by using NEI emissions (referred to as simulation NEI) performs well for major meteorological variables such as T2, RH2, WS10, and precipitation and shows good performance for major radiation variables such as SWDOWN, OLR, and SWCF. Large model biases still exist for cloud variables due to limitations of cloud dynamics/thermodynamics treatments and uncertainties associated with satellite retrievals. The simulation NEI also predicts O3 and PM2.5 well in terms of spatiotemporal distribution. Compared to a previous study using the Representative Concentration Pathway (RCP8.5) emissions, the simulation NEI performs better for most of variables, especially for precipitation and cloud radiative forcing due to better representation of cloud processes and also for O3 and PM2.5 in terms of spatiotemporal variations due to more accurate emission inventory. The evaluation results in this work are within the range or better than other previous studies using the WRF/Chem model and lay the foundation for more realistic projection of future climate and air quality in the future work. WRF/Chem; Climatological evaluation; Continental U.S.; Decadal simulation; NEI; RCP
Wei, Yu; Zhang, Xiaotong; Li, Wenhong; Hou, Ning; Zhang, Weiyu; Xu, Jiawen; Feng, Chunjie; Jia, Kun; Yao, Yunjun; Cheng, Jie; Jiang, Bo; Wang, Kaicun; Liang, ShunlinWei, Y., X. Zhang, W. Li, N. Hou, W. Zhang, J. Xu, C. Feng, K. Jia, Y. Yao, J. Cheng, B. Jiang, K. Wang, S. Liang, 2021: Trends and Variability of Atmospheric Downward Longwave Radiation Over China From 1958 to 2015. Earth and Space Science, 8(2), e2020EA001370. doi: https://doi.org/10.1029/2020EA001370. Surface downward longwave radiation (SDLR) is a major component of the energy budget. Although studies have reported the spatiotemporal variations of SDLR in China, the spatiotemporal coverage of the situ measurements used is always limited. In this study, the gradient boosting regression tree (GBRT) was developed to reconstruct SDLR based on air temperature (Ta), relative humidity (RH), and downward shortwave radiation (DSR). Ground measurements collected at the Baseline Surface Radiation Network (BSRN) and the Arid and Semi-arid Region Collaborative Observation Project (ASRCOP) were used to build and evaluate the GBRT model. The evaluation results showed that the daily SDLR estimates are correlated well with the SDLR in situ, with an overall root mean square errors (RMSE) of 16.5 Wm−2 and a correlation coefficient (R) value of 0.91 for the validation data set. Comparison with existing SDLR products showed that accuracy and trends of the SDLR estimates based on the GBRT method are reasonable. To obtain long-term SDLR data for spatiotemporal analysis over China, densely distributed reconstructed DSR and ground measured Ta and RH collected at 756 Chinese Meteorological Administration (CMA) stations were used as input to estimate the SDLR based on the GBRT method over China during 1958–2015. The long-term estimated SDLRs at the selected 563 stations showed that SDLR increased at an average rate of 1.3 Wm−2 per decade over China from 1958 to 2015. The trend of SDLR is positively correlated with the trend in Ta and water vapor pressure, whereas negatively correlated with the trend in DSR. downward longwave radiation; GBRT; CMA; MK trend test
Xu, Jianglei; Jiang, Bo; Liang, Shunlin; Li, Xiuxia; Wang, Yezhe; Peng, Jianghai; Chen, Hongkai; Liang, Hui; Li, ShaopengXu, J., B. Jiang, S. Liang, X. Li, Y. Wang, J. Peng, H. Chen, H. Liang, S. Li, 2021: Generating a High-Resolution Time-Series Ocean Surface Net Radiation Product by Downscaling J-OFURO3. IEEE Transactions on Geoscience and Remote Sensing, (In Press). doi: 10.1109/TGRS.2020.3021585. The ocean surface net radiation (Rn) characterizing ocean surface radiation budget is a key variable in ocean climate modeling and analysis. In this study, a downscaling scheme was developed to generate a high-resolution (0.05°) time-series (2002-2013) daily ocean surface Rn from the third-generation Japanese Ocean Flux Data Sets with Use of Remote-Sensing Observations (J-OFURO3) at 0.25° based on the Advanced Very-High-Resolution Radiometer (AVHRR) top-of-atmosphere (TOA) observations (AVH021C) and other ancillary information (Clearness Index and cloud mask). This downscaling scheme includes the statistical downscaling models and the residual correction post-processing. A series of angle-dependent downscaling statistical models were established between the daily ocean surface Rn in J-OFURO3 and the AVHRR TOA data, and then, the residual correction was conducted to the model estimates Rn_AVHRR_est to obtain the final downscaled data set Rn_AVHRR. Validation against the measurements from 57 moored buoy sites in six ocean observing networks shows the high accuracy of the downscaled estimates Rn_AVHRR_est with a R² of 0.88, RMSE of 23.44 W·m⁻², and bias of -0.14 W·m⁻² under all-sky condition. The results of the spatio-temporal analysis in Rn_AVHRR and intercomparison with Cloud and the Earth's Radiant Energy System (CERES) and the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim) products also indicated that the superior of the Rn_AVHRR with more detailed information especially in the hot spot regions, such as central tropical Pacific (warming pool), Atlantic and Equatorial Eastern Indian Ocean (EIO). Land surface; Remote sensing; Meteorology; Sea surface; net radiation; Advanced Very-High-Resolution Radiometer (AVHRR); downscaling; ocean surface; Ocean temperature; remote sensing.; Spatial resolution
You, Cheng; Tjernström, Michael; Devasthale, AbhayYou, C., M. Tjernström, A. Devasthale, 2021: Eulerian and Lagrangian views of warm and moist air intrusions into summer Arctic. Atmospheric Research, 256, 105586. doi: 10.1016/j.atmosres.2021.105586. In this study, warm and moist air intrusions (WaMAI) over the sea sectors of Kara, Laptev, East Siberian and Beaufort from 1979 to 2018 are identified in ERA5 reanalysis and their air-mass transformation is analysed using interpolation in ERA5 and satellite products along trajectories. The analysis shows that WaMAIs, driven by blocking high-pressure systems over the respective ocean sectors, induce surface warming (11–18 W m−2) and sea ice melt from positive anomalies of net longwave radiation (5–8 W m−2) and turbulent flux (8–13 W m−2) to the surface, although the anomaly of net shortwave radiation (−9 ~ +1 W m−2) is negative. From a Lagrangian perspective, the surface energy-budget anomaly decreases linearly, while total column cloud liquid water (TCLW) increases linearly with the downstream distance from the sea-ice edge. However, the cloud radiative effects of both longwave and shortwave radiation reach an equilibrium as TCLW increases in a much lower rate beyond 7 degrees north of the sea ice edge. The boundary-layer energy-budget pattern can be categorized into two classes: radiation-dominated and turbulence-dominated, comprised of 26% and 62% WaMAIs respectively. Statistically, turbulence-dominated cases occur with 3 times stronger large-scale subsidence, and also feature a larger anomaly in net shortwave radiation. In radiation-dominated WaMAIs, stratocumulus develops more strongly and hence exerts larger longwave and shortwave forcing to the surface. In both categories, a well-mixed boundary layer deepens by 500 m along the trajectories, from the continuous turbulent mixing. Arctic climate; Boundary-layer; Trajectories; Warm and moist air intrusion
Zhang, Chunyan; Wang, Donghai; Pang, Zihao; Zhang, Yu; Jiang, Xiaoling; Zeng, Zhilin; Wu, ZhenzhenZhang, C., D. Wang, Z. Pang, Y. Zhang, X. Jiang, Z. Zeng, Z. Wu, 2021: Large-scale dynamic, heat and moisture structures of monsoon-influenced precipitation in the East Asian monsoon rainy area. Quarterly Journal of the Royal Meteorological Society, 147(735), 1007-1030. doi: https://doi.org/10.1002/qj.3956. This study investigated large-scale dynamic structures along with heat and moisture budgets associated with monsoon-influenced precipitation over a typical rainy domain in the East Asian monsoon region. Large-scale dynamically and thermodynamically consistent forcing data based on multiple measurements were produced by a one-dimensional constrained variational analysis method. Using the forcing data, distinct characteristics of large-scale states were documented for cases of notable pre-monsoon rainfall before the South China Sea monsoon onset (SCSMO), extreme rainfall during SCSMO, and persistent strong rainfall after SCSMO. The pre-monsoon period mainly resulted from weak and discrete cloud regimes. The extreme-rain period was associated with a severe deep convective system moving from the west, and the persistent-rain period was related to moderate convective cells separated from the strong convective system over the northern South China Sea. Large-scale features including vertical velocity, wind convergence, and diabatic heating and drying were the strongest (weakest) during the extreme-rain (pre-monsoon) period. For the pre-monsoon and persistent-rain periods, the period-averaged profiles of vertical velocity and diabatic heating and drying showed a one-peak structure. However, during the extreme-rain period, a leap-forward mutation was seen in the vertical structure and magnitude of these large-scale states. The multiple peaks shown in the vertical profiles of vertical velocity and diabatic heating during the extreme-rain period may indicate various convective cloud systems co-existed. The diabatic heating profiles of extreme rainfall indicated that the first rainfall peak was related to the successive occurrence of stratiform anvils and convective clouds, while the second rainfall peak, which was most intense, was associated with shallow convective clouds, severe deep convective clouds, and detraining stratiform anvils. constrained variational analysis; heating profile; large-scale structures; monsoon-influenced precipitation; upward motion
Zhang, Taiping; Stackhouse, Paul W.; Cox, Stephen J.; Mikovitz, J. Colleen; Long, Charles N.Zhang, T., P. W. Stackhouse, S. J. Cox, J. C. Mikovitz, C. N. Long, 2021: Addendum to figs. 10 and 11 in “Clear-sky shortwave downward flux at the earth's surface: Ground-based data vs. satellite-based data” [J. Quant. Spec. and Rad. Tran. 224 (2019) 247-260]. Journal of Quantitative Spectroscopy and Radiative Transfer, 261, 107487. doi: 10.1016/j.jqsrt.2020.107487. While the CERES input aerosol optical depth and precipitable water data are continuously available, the same parameters derived from BSRN site measurements are available only intermittently. Cloudiness disrupts the aerosol optical depth (AOD) retrieval and precipitable water (w) observation sampling. Irregularly sampled records, such as these, can cause systematic biases if the averages of the continuous data are not sampled at the same times as the observed data, as shown by high biases in Fig. 10 in our original paper. This, however, does not suggest that the CERES input aerosol optical depth and precipitable water are systematically significantly higher than ground-based observations. In this addendum, we show that when the monthly means are computed from only those CERES hourly means that have a BSRN match, then the resulting monthly means differ from BSRN-derived parameters to a much lesser extent. To be precise, the biases in the original Fig. 10 decrease 82%, 69% and 52%, respectively; the magnitudes of slopes in the original Fig. 11 decrease by 69% and 65%, respectively. Imposing a cloud fraction less than or equal to 5% further reduces AOD and w mean values but not biases. Nevertheless, the flux bias reduces from -16.9 W m−2 to -4.2 W m−2 after imposing the cloud fraction restraint relative to the RADFlux clear-sky fluxes which appear to represent the driest and clearest conditions. CERES; Solar radiation; Satellite; GEWEX SRB; RadFlux
Zhou, Chen; Zelinka, Mark D.; Dessler, Andrew E.; Wang, MinghuaiZhou, C., M. D. Zelinka, A. E. Dessler, M. Wang, 2021: Greater committed warming after accounting for the pattern effect. Nature Climate Change, 11(2), 132-136. doi: 10.1038/s41558-020-00955-x. Our planet’s energy balance is sensitive to spatial inhomogeneities in sea surface temperature and sea ice changes, but this is typically ignored in climate projections. Here, we show the energy budget during recent decades can be closed by combining changes in effective radiative forcing, linear radiative damping and this pattern effect. The pattern effect is of comparable magnitude but opposite sign to Earth’s net energy imbalance in the 2000s, indicating its importance when predicting the future climate on the basis of observations. After the pattern effect is accounted for, the best-estimate value of committed global warming at present-day forcing rises from 1.31 K (0.99–2.33 K, 5th–95th percentile) to over 2 K, and committed warming in 2100 with constant long-lived forcing increases from 1.32 K (0.94–2.03 K) to over 1.5 K, although the magnitude is sensitive to sea surface temperature dataset. Further constraints on the pattern effect are needed to reduce climate projection uncertainty.
Zhou, Xiaoli; Atlas, Rachel; McCoy, Isabel L.; Bretherton, Christopher S.; Bardeen, Charles; Gettelman, Andrew; Lin, Pu; Ming, YiZhou, X., R. Atlas, I. L. McCoy, C. S. Bretherton, C. Bardeen, A. Gettelman, P. Lin, Y. Ming, 2021: Evaluation of cloud and precipitation simulations in CAM6 and AM4 using observations over the Southern Ocean. Earth and Space Science, (In Press). doi: https://doi.org/10.1029/2020EA001241. This study uses cloud and radiative properties collected from in-situ and remote sensing instruments during two coordinated campaigns over the Southern Ocean between Tasmania and Antarctica in January-February 2018 to evaluate the simulations of clouds and precipitation in nudged-meteorology simulations with the CAM6 and AM4 global climate models sampled at the times and locations of the observations. Fifteen SOCRATES research flights sampled cloud water content, cloud droplet number concentration, and particle size distributions in mixed-phase boundary-layer clouds at temperatures down to -25 C. The six-week CAPRICORN2 research cruise encountered all cloud regimes across the region. Data from vertically-pointing 94 GHz radars deployed was compared with radar-simulator output from both models. Satellite data was compared with simulated top-of-atmosphere (TOA) radiative fluxes. Both models simulate observed cloud properties fairly well within the variability of observations. Cloud base and top in both models are generally biased low. CAM6 overestimates cloud occurrence and optical thickness while cloud droplet number concentrations are biased low, leading to excessive TOA reflected shortwave radiation. In general, low clouds in CAM6 precipitate at the same frequency but are more homogeneous compared to observations. Deep clouds are better simulated but produce snow too frequently. AM4 underestimates cloud occurrence but overestimates cloud optical thickness even more than CAM6, causing excessive outgoing longwave radiation fluxes but comparable reflected shortwave radiation. AM4 cloud droplet number concentrations match observations better than CAM6. Precipitating low and deep clouds in AM4 have too little snow. Further investigation of these microphysical biases is needed for both models.

## 2020

Abera, Temesgen Alemayehu; Heiskanen, Janne; Pellikka, Petri K. E.; Maeda, Eduardo EijiAbera, T. A., J. Heiskanen, P. K. E. Pellikka, E. E. Maeda, 2020: Impact of rainfall extremes on energy exchange and surface temperature anomalies across biomes in the Horn of Africa. Agricultural and Forest Meteorology, 280, 107779. doi: 10.1016/j.agrformet.2019.107779. Precipitation extremes have a strong influence on the exchange of energy and water between the land surface and the atmosphere. Although the Horn of Africa has faced recurrent drought and flood events in recent decades, it is still unclear how these events impact energy exchange and surface temperature across different ecosystems. Here, we analyzed the impact of precipitation extremes on spectral albedo (total shortwave, visible, and near-infrared (NIR) broadband albedos), energy balance, and surface temperature in four natural vegetation types: forest, savanna, grassland, and shrubland. We used remotely sensed observations of surface biophysical properties and climate from 2001 to 2016. Our results showed that, in forests and savannas, precipitation extremes led to divergent spectral changes in visible and NIR albedos, which cancelled each other limiting shortwave albedo changes. An exception to this pattern was observed in shrublands and grasslands, where both visible and NIR albedo increased during drought events. Given that shrublands and grasslands occupy a large fraction of the Horn of Africa (52%), our results unveil the importance of these ecosystems in driving the magnitude of shortwave radiative forcing in the region. The average regional shortwave radiative forcing during drought events (−0.64 W m−2, SD 0.11) was around twice that of the extreme wet events (0.33 W m−2, SD 0.09). Such shortwave forcing, however, was too small to influence the surface–atmosphere coupling. In contrast, the surface feedback through turbulent flux changes was strong across vegetation types and had a significant (P  CERES; MODIS; Albedo; Energy exchange; Land surface temperature; Precipitation extremes
Ajoku, Osinachi; Norris, Joel R.; Miller, Arthur J.Ajoku, O., J. R. Norris, A. J. Miller, 2020: Observed monsoon precipitation suppression caused by anomalous interhemispheric aerosol transport. Climate Dynamics, 54(1), 1077-1091. doi: 10.1007/s00382-019-05046-y. This study uses observations and atmospheric reanalysis products in order to understand the impacts of smoke aerosols advected from the Southern Hemisphere on the dynamics of the West African monsoon. Seasonal biomass burning and resulting aerosol emissions have been well documented to affect regional weather patterns, especially low-level convection. Out of all monsoon months, precipitation shows the most variability over land during August, in which anomalous smoke aerosol values can increase (decrease) by 33% (29%) in the Northern Gulf of Guinea and precipitation can decrease (increase) by up to ~ 2.5 mm day−1 (~ 3 mm day−1) along the West African monsoon region accounting for a 17% (18%) change in precipitation. Smoke aerosols produced by biomass burning occurring near Central Africa are advected towards the Gulf of Guinea at elevations around the 850 hPa level. Satellite observations show an increase (decrease) in cloud fraction and optical depth below (above) the 300-hPa level in the Gulf of Guinea and along the West African coastline along with concurrent decreases (increases) in cloud droplet radius during dirty (clean) aerosol episodes. Additional observations of shortwave radiation quantify changes in cloud coverage and monsoon dynamics. On average, reductions in surface shortwave radiation of ~ 10–15 W m−2 occur over the Gulf of Guinea during increased aerosol transport, with aerosols accounting for ~ 33–50% of that reduction. Reductions in shortwave radiation are associated with decreased convective available potential energy (CAPE). This demonstrates that increased transport of aerosols perturbs surface radiation, convection in the lower troposphere and eventually cloud coverage, potentially leading to the observed monsoon precipitation suppression. In a broader social context, this region houses 200 million people and thus understanding these climate patterns may carry great importance.
Amos, Helen M.; Starke, Matthew J.; Rogerson, Tina M.; Robles, Marilé Colón; Andersen, Travis; Boger, Rebecca; Campbell, Brian A.; Low, Russanne D.; Nelson, Peder; Overoye, David; Taylor, Jessica E.; Weaver, Kristen L.; Ferrell, Trena M.; Kohl, Holli; Schwerin, Theresa G.Amos, H. M., M. J. Starke, T. M. Rogerson, M. Robles, . Colón, T. Andersen, R. Boger, B. A. Campbell, R. D. Low, P. Nelson, D. Overoye, J. E. Taylor, K. L. Weaver, T. M. Ferrell, H. Kohl, T. G. Schwerin, 2020: GLOBE Observer Data: 2016–2019. Earth and Space Science, 7(8), e2020EA001175. doi: 10.1029/2020EA001175. This technical report summarizes the GLOBE Observer data set from 1 April 2016 to 1 December 2019. GLOBE Observer is an ongoing NASA-sponsored international citizen science project that is part of the larger Global Learning and Observations to Benefit the Environment (GLOBE) Program, which has been in operation since 1995. GLOBE Observer has the greatest number of participants and geographic coverage of the citizen science projects in the Earth Science Division at NASA. Participants use the GLOBE Observer mobile app (launched in 2016) to collect atmospheric, hydrologic, and terrestrial observations. The app connects participants to satellite observations from Aqua, Terra, CALIPSO, GOES, Himawari, and Meteosat. Thirty-eight thousand participants have contributed 320,000 observations worldwide, including 1,000,000 georeferenced photographs. It would take an individual more than 13 years to replicate this effort. The GLOBE Observer app has substantially increased the spatial extent and sampling density of GLOBE measurements and more than doubled the number of measurements collected through the GLOBE Program. GLOBE Observer data are publicly available (at observer.globe.gov). cloud cover; citizen science; global data set; land cover; mosquitoes; tree height
Annamalai, H.Annamalai, H., 2020: ENSO Precipitation Anomalies along the Equatorial Pacific: Moist Static Energy Framework Diagnostics. J. Climate, 33(21), 9103-9127. doi: 10.1175/JCLI-D-19-0374.1.
Attada, Raju; Dasari, Hari Prasad; Kunchala, Ravi Kumar; Langodan, Sabique; Niranjan Kumar, Kondapalli; Knio, Omar; Hoteit, IbrahimAttada, R., H. P. Dasari, R. K. Kunchala, S. Langodan, K. Niranjan Kumar, O. Knio, I. Hoteit, 2020: Evaluating Cumulus Parameterization Schemes for the Simulation of Arabian Peninsula Winter Rainfall. J. Hydrometeor., 21(5), 1089-1114. doi: 10.1175/JHM-D-19-0114.1. This study investigates the sensitivity of winter seasonal rainfall over the Arabian Peninsula (AP) to different convective physical parameterization schemes using a high-resolution WRF Model. Three different parameterization schemes, Kain–Fritch (KF), Betts–Miller–Janjić (BMJ), and Grell–Freitas (GF), are used in winter simulations from 2001 to 2016. Results from seasonal simulations suggest that simulated AP winter rainfall with KF is in best agreement with observed rainfall in terms of spatial distribution and intensity. Higher spatial correlation coefficients and fewer biases with observations are also obtained with KF. In addition, the regional moisture transport, cloud distribution, and cloud microphysical responses are better simulated by KF. The AP low-level circulation, characterized by the Arabian anticyclone, is well captured by KF and BMJ, but its position is displaced in GF. KF is furthermore successful at simulating the moisture distribution in the lower atmosphere and atmospheric water plumes in the middle troposphere. The higher skill of rainfall simulation with the KF (and to some extent BMJ) is attributed to a better representation of the Arabian anticyclone and subtropical westerly jet, which guides the upper tropospheric synoptic transients and moisture. In addition, the vertical profile of diabatic heating from KF is in better agreement with the observations. Discrepancies in representing the diabatic heating profile by BMJ and GF show discrepancies in instability and in turn precipitation biases. Our results indicate that the selection of subgrid convective parameterization in a high-resolution atmospheric model over the AP is an important factor for accurate regional rainfall simulations.
Avtar, Ram; Komolafe, Akinola Adesuji; Kouser, Asma; Singh, Deepak; Yunus, Ali P.; Dou, Jie; Kumar, Pankaj; Gupta, Rajarshi Das; Johnson, Brian Alan; Thu Minh, Huynh Vuong; Aggarwal, Ashwani Kumar; Kurniawan, Tonni AgustionoAvtar, R., A. A. Komolafe, A. Kouser, D. Singh, A. P. Yunus, J. Dou, P. Kumar, R. D. Gupta, B. A. Johnson, H. V. Thu Minh, A. K. Aggarwal, T. A. Kurniawan, 2020: Assessing sustainable development prospects through remote sensing: A review. Remote Sensing Applications: Society and Environment, 20, 100402. doi: 10.1016/j.rsase.2020.100402. The Earth's ecosystems face severe environmental stress from unsustainable socioeconomic development linked to population growth, urbanization, and industrialization. Governments worldwide are interested in sustainability measures to address these issues. Remote sensing allows for the measurement, integration, and presentation of useful information for effective decision-making at various temporal and spatial scales. Scientists and decision-makers have endorsed extensive use of remote sensing to bridge gaps among disciplines and achieve sustainable development. This paper presents an extensive review of remote sensing technology used to support sustainable development efforts, with a focus on natural resource management and assessment of natural hazards. We further explore how remote sensing can be used in a cross-cutting, interdisciplinary manner to support decision-making aimed at addressing sustainable development challenges. Remote sensing technology has improved significantly in terms of sensor resolution, data acquisition time, and accessibility over the past several years. This technology has also been widely applied to address key issues and challenges in sustainability. Furthermore, an evaluation of the suitability and limitations of various satellite-derived indices proposed in the literature for assessing sustainable development goals showed that these older indices still perform reasonably well. Nevertheless, with advancements in sensor radiometry and resolution, they were less exploited and new indices are less explored. Decision support system; Indices; Natural hazards; Natural resource management; Sustainability
Baba, YuyaBaba, Y., 2020: Shallow convective closure in a spectral cumulus parameterization. Atmospheric Research, 233, 104707. doi: 10.1016/j.atmosres.2019.104707. A shallow convective closure (shallow closure) was introduced in a spectral cumulus parameterization (spectral scheme), and the validity was evaluated using an atmospheric general circulation model (AGCM) and Atmospheric Model Intercomparison Project (AMIP) experiments. The spectral scheme with shallow closure improved model simulated climatology and variability as compared with the spectral scheme only. The shallow closure enhanced shallow convection, leading to an improvements in dry bias in the tropics and cold bias in the extratropics. The simulated interannual variabilities were comparable regardless of the shallow closure; however, intraseasonal variability was greatly improved with the shallow closure. This is because detrainment from shallow convection during development of the Madden-Julian oscillation (MJO) contributes to supplying moisture in organized convection, and the spectral scheme with shallow closure was able to simulate this contribution well. Climatology; Atmospheric variability; Convection scheme; Convective closure; Shallow convection
Baba, Yuya; Giorgetta, Marco A.Baba, Y., M. A. Giorgetta, 2020: Tropical Variability Simulated in ICON-A With a Spectral Cumulus Parameterization. Journal of Advances in Modeling Earth Systems, 12(1), e2019MS001732. doi: 10.1029/2019MS001732. We implemented a spectral cumulus parameterization based on a cloud-resolving model (SC scheme) in the icosahedral nonhydrostatic atmospheric model (ICON-A). We compared the resulting simulated climatology and tropical variability with results from the standard version of ICON-A using a variant of the Tiedtke-Nordeng scheme (TK scheme) using observational and reanalysis data. The climatological errors of the SC scheme were similar to those of the TK scheme, but several biases, such as properties of meridional winds and precipitation pattern in the western Pacific, were much improved. For tropical variability, we found that the SC scheme improved the interannual response of the precipitation in the western Pacific and was able to simulate Madden-Julian oscillation (MJO) features much better than the TK scheme. We investigated the reason for the better simulation of the MJO using composite analysis and column process analysis for moisture. Our results suggest that the entrainment parameterization of the SC scheme is necessary to reproduce the MJO; however, spectral representation and improved convective closure are also found to contribute for better MJO simulation. These parameterizations improved moisture supply from low-level clouds and cloud mass flux which were needed to sustain the MJO. atmospheric general circulation model; convection scheme; tropical variability
Back, Seung-Yoon; Han, Ji-Young; Son, Seok-WooBack, S., J. Han, S. Son, 2020: Modeling Evidence of QBO-MJO Connection: A Case Study. Geophysical Research Letters, 47(20), e2020GL089480. doi: 10.1029/2020GL089480. The boreal winter Madden-Julian Oscillation (MJO) is modulated by the Quasi-Biennial Oscillation (QBO). The MJO becomes relatively strong during the easterly QBO (EQBO) winters but weak during the westerly QBO (WQBO) winters. To better understand their relationship, a set of WRF model experiments is conducted with varying lateral boundary conditions. The MJO event in December 2007, during EQBO winter, is chosen as a reference case. The control experiment qualitatively reproduces the observed MJO. When the lateral boundary conditions are switched with those of WQBO or strong WQBO winters, the MJO becomes weak over the Maritime Continent. All eight ensemble members exhibit enhanced outgoing longwave radiation and reduced precipitation from EQBO to WQBO, and to strong WQBO conditions, although the magnitude of changes is smaller than observations. This result, one of the first mesoscale modeling evidences of the QBO-MJO connection, suggests that the MJO is at least partly modulated by the QBO. tropics; Madden-Julian Oscillation; Quasi-Biennial Oscillation
Baek, Eun-Hyuk; Kim, Joo-Hong; Park, Sungsu; Kim, Baek-Min; Jeong, Jee-HoonBaek, E., J. Kim, S. Park, B. Kim, J. Jeong, 2020: Impact of poleward heat and moisture transports on Arctic clouds and climate simulation. Atmospheric Chemistry and Physics, 20(5), 2953-2966. doi: 10.5194/acp-20-2953-2020. Abstract. Many general circulation models (GCMs) have difficulty simulating Arctic clouds and climate, causing substantial inter-model spread. To address this issue, two Atmospheric Model Intercomparison Project (AMIP) simulations from the Community Atmosphere Model version 5 (CAM5) and Seoul National University (SNU) Atmosphere Model version 0 (SAM0) with a unified convection scheme (UNICON) are employed to identify an effective mechanism for improving Arctic cloud and climate simulations. Over the Arctic, SAM0 produced a larger cloud fraction and cloud liquid mass than CAM5, reducing the negative Arctic cloud biases in CAM5. The analysis of cloud water condensation rates indicates that this improvement is associated with an enhanced net condensation rate of water vapor into the liquid condensate of Arctic low-level clouds, which in turn is driven by enhanced poleward transports of heat and moisture by the mean meridional circulation and transient eddies. The reduced Arctic cloud biases lead to improved simulations of surface radiation fluxes and near-surface air temperature over the Arctic throughout the year. The association between the enhanced poleward transports of heat and moisture and increase in liquid clouds over the Arctic is also evident not only in both models, but also in the multi-model analysis. Our study demonstrates that enhanced poleward heat and moisture transport in a model can improve simulations of Arctic clouds and climate.
Bai, Heming; Wang, Minghuai; Zhang, Zhibo; Liu, YawenBai, H., M. Wang, Z. Zhang, Y. Liu, 2020: Synergetic Satellite Trend Analysis of Aerosol and Warm Cloud Properties ver Ocean and Its Implication for Aerosol-Cloud Interactions. Journal of Geophysical Research: Atmospheres, 125(6), e2019JD031598. doi: 10.1029/2019JD031598. Decadal-scale trends in aerosol and cloud properties provide important ways for understanding aerosol-cloud interactions. In this paper, by using MODIS products (2003–2017), we analyze synergetic trends in aerosol properties and warm cloud properties over global ocean. Cloud droplet number concentration (CDNC) and aerosol parameters (aerosol optical depth, angstrom exponent, and aerosol index) show consistent decreasing trend over East Coast of the United States (EUS), west coast of Europe (WEU), and east coast of China (EC), and no significant trend in liquid water path is found over these regions during the period 2003–2017. Over regions with significant long-term trends of aerosol loading and CDNC (e.g., EUS and WEU), the sensitivity of CDNC to aerosol loading based on the long-term trend is closer to those derived from ground and aircraft observations and larger than those derived from instantaneous satellite observations, providing an alternative way for quantifying aerosol-cloud interactions. A clear shift in the normalized probability density function of CDNC between the first 5 years (2003–2007) and the last 5 years (2013–2017) is found, with a decrease of around 50% in the occurrence frequency of high CDNC (>400 cm−3) over EUS and WEU. The relative variances of cloud droplet effective radius generally decrease with decreasing aerosol loading, providing large-scale evidence for the effects of anthropogenic aerosols on the dispersion of cloud droplet size distribution. The long-term satellite data sets provide great opportunities for quantifying aerosol-cloud interactions and further confronting these interactions in climate models in the future.
Barpanda, Pragallva; Shaw, Tiffany A.Barpanda, P., T. A. Shaw, 2020: Surface fluxes modulate the seasonality of zonal-mean storm tracks. J. Atmos. Sci., 77(2), 753–779. doi: 10.1175/JAS-D-19-0139.1. The observed zonal-mean extratropical storm tracks exhibit distinct hemispheric seasonality. Previously, the moist static energy (MSE) framework was used diagnostically to show that shortwave absorption (insolation) dominates seasonality but surface heat fluxes damp seasonality in the Southern Hemisphere (SH) and amplify it in the Northern Hemisphere (NH). Here we establish the causal role of surface fluxes (ocean energy storage), which affect surface heat fluxes, by varying the mixed layer depth (d) in zonally-symmetric 1) slab-ocean aquaplanet simulations with zero ocean energy transport and 2) Energy Balance Model (EBM) simulations. Using a scaling analysis we define a critical mixed layer depth (dc) and hypothesize 1) large mixed layer depths (d > dc) produce surface heat fluxes that are out of phase with shortwave absorption resulting in small storm track seasonality and 2) small mixed layer depths (d < dc) produce surface heat fluxes that are in phase with shortwave absorption resulting in large storm track seasonality. The aquaplanet simulations confirm the large mixed layer depth hypothesis and yield a useful idealization of the SH storm track. However, the small mixed layer depth hypothesis fails to account for the large contribution of the Ferrel cell and atmospheric storage. The small mixed layer limit does not yield a useful idealization of the NH storm track because the seasonality of the Ferrel cell contribution is opposite to the stationary eddy contribution in the NH. Varying the mixed layer depth in an EBM qualitatively supports the aquaplanet results.
Bauer, Susanne E.; Tsigaridis, Kostas; Faluvegi, Greg; Kelley, Maxwell; Lo, Ken K.; Miller, Ron L.; Nazarenko, Larissa; Schmidt, Gavin A.; Wu, JingboBauer, S. E., K. Tsigaridis, G. Faluvegi, M. Kelley, K. K. Lo, R. L. Miller, L. Nazarenko, G. A. Schmidt, J. Wu, 2020: Historical (1850-2014) aerosol evolution and role on climate forcing using the GISS ModelE2.1 contribution to CMIP6. Journal of Advances in Modeling Earth Systems, 12(8), e2019MS001978. doi: 10.1029/2019MS001978. The Earth’s climate is rapidly changing. Over the past centuries, aerosols, via their ability to absorb or scatter solar radiation and alter clouds, played an important role in counterbalancing some of the greenhouse gas (GHG) caused global warming. The multi-century anthropogenic aerosol cooling effect prevented present-day climate from reaching even higher surface air temperatures and subsequent more dramatic climate impacts. Trends in aerosol concentrations and optical depth show that in many polluted regions such as Europe and the United States of America, aerosol precursor emissions decreased back to levels of the 1950s. More recent polluting countries such as China may have reached a turning point in recent years as well, while India still follows an upward trend. Here we study aerosol trends in the CMIP6 simulations of the GISS ModelE2.1 climate model using a fully coupled atmosphere composition configuration, including interactive gas-phase chemistry, and either an aerosol microphysical (MATRIX) or a mass-based (OMA) aerosol module. Results show that whether global aerosol radiative forcing is already declining depends on the aerosol scheme used. Using the aerosol microphysical scheme, where the aerosol system reacts more strongly to the trend in sulfur dioxide (SO2) emissions, global peak direct aerosol forcing was reached in the 1980’s, whereas the mass-based scheme simulates peak direct aerosol forcing around 2010. aerosol microphysics; Aerosol Forcing; CMIP6 historical simulation; GISS model
Berry, Elizabeth; Mace, Gerald G.; Gettelman, AndrewBerry, E., G. G. Mace, A. Gettelman, 2020: Using A-Train Observations to Evaluate East Pacific Cloud Occurrence and Radiative Effects in the Community Atmosphere Model. J. Climate, 33(14), 6187-6203. doi: 10.1175/JCLI-D-19-0870.1.
Bock, L.; Lauer, A.; Schlund, M.; Barreiro, M.; Bellouin, N.; Jones, C.; Meehl, G. A.; Predoi, V.; Roberts, M. J.; Eyring, V.Bock, L., A. Lauer, M. Schlund, M. Barreiro, N. Bellouin, C. Jones, G. A. Meehl, V. Predoi, M. J. Roberts, V. Eyring, 2020: Quantifying Progress Across Different CMIP Phases With the ESMValTool. Journal of Geophysical Research: Atmospheres, 125(21), e2019JD032321. doi: 10.1029/2019JD032321. More than 40 model groups worldwide are participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6), providing a new and rich source of information to better understand past, present, and future climate change. Here, we use the Earth System Model Evaluation Tool (ESMValTool) to assess the performance of the CMIP6 ensemble compared to the previous generations CMIP3 and CMIP5. While CMIP5 models did not capture the observed pause in the increase in global mean surface temperature between 1998 and 2013, the historical CMIP6 simulations agree well with the observed recent temperature increase, but some models have difficulties in reproducing the observed global mean surface temperature record of the second half of the twentieth century. While systematic biases in annual mean surface temperature and precipitation remain in the CMIP6 multimodel mean, individual models and high-resolution versions of the models show significant reductions in many long-standing biases. Some improvements are also found in the vertical temperature, water vapor, and zonal wind speed distributions, and root-mean-square errors for selected fields are generally smaller with reduced intermodel spread and higher average skill in the correlation patterns relative to observations. An emerging property of the CMIP6 ensemble is a higher effective climate sensitivity with an increased range between 2.3 and 5.6 K. A possible reason for this increase in some models is improvements in cloud representation resulting in stronger shortwave cloud feedbacks than in their predecessor versions. climate model; evaluation; CMIP
Bony, S.; Semie, A.; Kramer, R. J.; Soden, B.; Tompkins, A. M.; Emanuel, K. A.Bony, S., A. Semie, R. J. Kramer, B. Soden, A. M. Tompkins, K. A. Emanuel, 2020: Observed Modulation of the Tropical Radiation Budget by Deep Convective Organization and Lower-Tropospheric Stability. AGU Advances, 1(3), e2019AV000155. doi: 10.1029/2019AV000155. This study analyzes the observed monthly deseasonalized and detrended variability of the tropical radiation budget and suggests that variations of the lower-tropospheric stability and of the spatial organization of deep convection both strongly contribute to this variability. Satellite observations show that on average over the tropical belt, when deep convection is more aggregated, the free troposphere is drier, the deep convective cloud coverage is less extensive, and the emission of heat to space is increased; an enhanced aggregation of deep convection is thus associated with a radiative cooling of the tropics. An increase of the tropical-mean lower-tropospheric stability is also coincident with a radiative cooling of the tropics, primarily because it is associated with more marine low clouds and an enhanced reflection of solar radiation, although the free-tropospheric drying also contributes to the cooling. The contributions of convective aggregation and lower-tropospheric stability to the modulation of the radiation budget are complementary, largely independent of each other, and equally strong. Together, they account for more than sixty percent of the variance of the tropical radiation budget. Satellite observations are thus consistent with the suggestion from modeling studies that the spatial organization of deep convection substantially influences the radiative balance of the Earth. This emphasizes the importance of understanding the factors that control convective organization and lower-tropospheric stability variations, and the need to monitor their changes as the climate warms. radiation budget; tropical variability; convective organization; tropospheric stability
Bony, Sandrine; Schulz, Hauke; Vial, Jessica; Stevens, BjornBony, S., H. Schulz, J. Vial, B. Stevens, 2020: Sugar, Gravel, Fish and Flowers: Dependence of Mesoscale Patterns of Trade-wind Clouds on Environmental Conditions. Geophysical Research Letters, 47(7), e2019GL085988. doi: 10.1029/2019GL085988. Trade-wind clouds exhibit a large diversity of spatial organizations at the mesoscale. Over the tropical western Atlantic, a recent study has visually identified four prominent mesoscale patterns of shallow convection, referred to as Flowers, Fish, Gravel and Sugar. We show that these four patterns can be identified objectively from satellite observations by analyzing the spatial distribution of infrared brightness temperatures. By applying this analysis to 19 years of data, we examine relationships between cloud patterns and large-scale environmental conditions. This investigation reveals that on daily and interannual timescales, the near-surface wind speed and the strength of the lower-tropospheric stability discriminate the occurrence of the different organization patterns. These results, combined with the tight relationship between cloud patterns, low-level cloud amount and cloud-radiative effects, suggest that the mesoscale organization of shallow clouds might change under global warming. The role of shallow convective organization in determining low-cloud feedback should thus be investigated. low-cloud feedback; mesoscale organization; shallow convection; tradewind clouds
Bosilovich, Michael G.; Robertson, Franklin R.; Stackhouse, Paul W.Bosilovich, M. G., F. R. Robertson, P. W. Stackhouse, 2020: El Niño–Related Tropical Land Surface Water and Energy Response in MERRA-2. J. Climate, 33(3), 1155-1176. doi: 10.1175/JCLI-D-19-0231.1. Although El Niño events each have distinct evolutionary character, they typically provide systematic large-scale forcing for warming and increased drought frequency across the tropical continents. We assess this response in the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), reanalysis and in a 10-member-model Atmospheric Model Intercomparison Project (AMIP) ensemble. The lagged response (3–4 months) of mean tropical land temperature to El Niño warming in the Pacific Ocean is well represented. MERRA-2 reproduces the patterns of precipitation in the tropical regions, and the AMIP ensemble reproduces some regional responses that are similar to those observed and some regions that are not simulating the response well. Model skill is dependent on event forcing strength and temporal proximity to the peak of the sea surface warming. A composite approach centered on maximum Niño-3.4 SSTs and lag relationships to energy fluxes and transports is used to identify mechanisms supporting tropical land warming. The composite necessarily moderates weather-scale variability of the individual events while retaining the systematic features across all events. We find that reduced continental upward motions lead to reduced cloudiness and more shortwave radiation at the surface, as well as reduced precipitation. The increased shortwave heating at the land surface, along with reduced soil moisture, leads to warmer surface temperature, more sensible heating, and warming of the lower troposphere. The composite provides a broad picture of the mechanisms governing the hydrologic response to El Niño forcing, but the regional and temporal responses can vary substantially for any given event. The 2015/16 El Niño, one of the strongest events, demonstrates some of the forced response noted in the composite, but with shifts in the evolution that depart from the composite, demonstrating the limitations of the composite and individuality of El Niño.
Brunner, Lukas; McSweeney, Carol; Ballinger, Andrew P.; Hegerl, Gabriele C.; Befort, Daniel J.; O’Reilly, Chris; Benassi, Marianna; Booth, Ben; Harris, Glen; Lowe, Jason; Coppola, Erika; Nogherotto, Rita; Knutti, Reto; Lenderink, Geert; de Vries, Hylke; Qasmi, Saïd; Ribes, Aurélien; Stocchi, Paolo; Undorf, SabineBrunner, L., C. McSweeney, A. P. Ballinger, G. C. Hegerl, D. J. Befort, C. O’Reilly, M. Benassi, B. Booth, G. Harris, J. Lowe, E. Coppola, R. Nogherotto, R. Knutti, G. Lenderink, H. de Vries, S. Qasmi, A. Ribes, P. Stocchi, S. Undorf, 2020: Comparing methods to constrain future European climate projections using a consistent framework. J. Climate, 33(20), 8671–8692. doi: 10.1175/JCLI-D-19-0953.1. Political decisions, adaptation planning, and impact assessments need reliable estimates of future climate change and related uncertainties. In order to provide these estimates, different approaches to constrain, filter, or weight climate model projections into probabilistic distributions have been proposed. However, an assessment of multiple such methods to, for example, expose cases of agreement or disagreement, is often hindered by a lack of coordination, with methods focusing on a variety of variables, time periods, regions, or model pools. Here, a consistent framework is developed to allow a quantitative comparison of eight different methods; focus is given to summer temperature and precipitation change in three spatial regimes in Europe in 2041-2060 relative to 1995-2014. The analysis draws on projections from several large ensembles, the CMIP5 multi-model ensemble, and perturbed physics ensembles, all using the high-emission scenario RCP8.5. The methods’ key features are summarized, assumptions are discussed and resulting constrained distributions are presented. Method agreement is found to be dependent on the investigated region but is generally higher for median changes than for the uncertainty ranges. This study, therefore, highlights the importance of providing clear context about how different methods affect the assessed uncertainty, particularly the upper and lower percentiles that are of interest to risk-averse stakeholders. The comparison also exposes cases where diverse lines of evidence lead to diverging constraints; additional work is needed to understand how the underlying differences between methods lead to such disagreements and to provide clear guidance to users.
Brutsaert, Wilfried; Cheng, Lei; Zhang, Lu; Brutsaert, Wilfried; Cheng, Lei; Zhang, LuBrutsaert, W., L. Cheng, L. Zhang, W. Brutsaert, L. Cheng, L. Zhang, 2020: Spatial Distribution of Global Landscape Evaporation in the Early Twenty-First Century by Means of a Generalized Complementary Approach. J. Hydrometeor., 21(2), 551–581. doi: 10.1175/JHM-D-19-0208.1. AbstractA generalized implementation of the complementary principle was applied to estimate global land surface evaporation and its spatial distribution. The single parameter in the method was cali...
Burgdorf, Martin J.; Müller, Thomas G.; Buehler, Stefan A.; Prange, Marc; Brath, ManfredBurgdorf, M. J., T. G. Müller, S. A. Buehler, M. Prange, M. Brath, 2020: Characterization of the High-Resolution Infrared Radiation Sounder Using Lunar Observations. Remote Sensing, 12(9), 1488. doi: 10.3390/rs12091488. The High-Resolution Infrared Radiation Sounder (HIRS) has been operational since 1975 on different satellites. In spite of this long utilization period, the available information about some of its basic properties is incomplete or contradictory. We have approached this problem by analyzing intrusions of the Moon in the deep space view of HIRS/2 through HIRS/4. With this method we found: (1) The diameters of the field of view of HIRS/2, HIRS/3, and HIRS/4 have the relative proportions of 1.4 ° to 1.3 ° to 0.7 ° with all channels; (2) the co-registration differs by up to 0.031 ° among the long-wave and by up to 0.015 ° among the shortwave spectral channels in the along-track direction; (3) the photometric calibration is consistent within 0.7% or less for channels 2–7 (1.2% for HIRS/2), similar values were found for channels 13–16; (4) the non-linearity of the short-wavelength channels is negligible; and (5) the contribution of reflected sunlight to the flux in the short-wavelength channels can be determined in good approximation, if the emissivity of the surface is known. calibration; surface; infrared sounder; moon
Butler, John C.Butler, J. C., 2020: CERES Gimbal Performance on Terra. Lubricants, 8(8), 79. doi: 10.3390/lubricants8080079. The Terra satellite has been operating in orbit for 20 years. The Terra satellite is also called the flagship earth-observing satellite. The two Clouds and the Earth’s Radiant Energy System CERES instruments on board continue to function nominally. Their expected mission lifetime was 7 years. Critical to their performance is the longevity of the scanning gimbals. This can be traced to the performance of the fluid-lubricated bearings. Two metrics are used to estimate their lifetime and health. Both lend themselves to readily available data and ease of interpretation. One is predicting the evaporative lubricant loss. This analysis indicates that the lubricant supply is adequate for the continual life of the gimbals. The second is trending the torque with time. Torque precursors are sampled quarterly. These data are converted to torque. Two types of torque behavior were examined. Contrasting torque data have supported the conclusion that the gimbals are operating nominally. This can be partially attributed to the design choices for the bearings and lubricant. The aim of this paper is to quantitatively describe the present health and expected life of the CERES gimbals on the Terra satellite. space vehicles; bearings; lubricant; torque
Cao, Yunfeng; Liang, Shunlin; Yu, MengCao, Y., S. Liang, M. Yu, 2020: Observed low-frequency linkage between Northern Hemisphere tropical expansion and polar vortex weakening from 1979 to 2012. Atmospheric Research, 243, 105034. doi: 10.1016/j.atmosres.2020.105034. In recent decades, the northern hemisphere (NH) atmospheric meridional circulation has experienced unprecedented changes. The NH tropical belt is significantly expanding toward high latitudes, and the Arctic polar vortex is continually weakening. Both phenomena have led to severe consequences on the Earth's surface, such as more frequent droughts in the subtropics and accelerated sea ice loss in the Arctic. However, the potential linkage between these phenomena and the underlying mechanisms have rarely been discussed. In this study, we report strong observational evidence that the NH tropical boundary and tropospheric polar vortex are synchronously changing, based on analysis of long-term satellite records from 1979 to 2012. Our investigation suggests that both the variance of the NH tropical boundary and tropospheric polar vortex from 1979 to 2012 are associated to the natural anomaly of NH mid-latitude sea surface temperature. The low-frequency sea surface temperature anomalies over the North Pacific (i.e., the Pacific Decadal Oscillation, PDO) and Atlantic (i.e., the Atlantic Multidecadal Oscillation, AMO) could explain 61% of the NH tropical boundary variance and 56% of the polar vortex variance from 1979 to 2012. Atlantic Multidecadal Oscillation; Low-frequency linkage; NH tropical expansion; Pacific Decadal Oscillation; Polar vortex weakening
Chen, Jiang; He, Tao; Jiang, Bo; Liang, ShunlinChen, J., T. He, B. Jiang, S. Liang, 2020: Estimation of all-sky all-wave daily net radiation at high latitudes from MODIS data. Remote Sensing of Environment, 245, 111842. doi: 10.1016/j.rse.2020.111842. Surface all-wave net radiation (Rn) plays an important role in various land surface processes, such as agricultural, ecological, hydrological, and biogeochemical processes. Recently, remote sensing of Rn at regional and global scales has attracted considerable attention and has achieved significant advances. However, there are many issues in estimating all-sky daily average Rn at high latitudes, such as posing greater uncertainty by surface and atmosphere satellite products at high latitudes, and unavailability of real-time and accurate cloud base height and temperature parameters. In this study, we developed the LRD (length ratio of daytime) classification model using the genetic algorithm-artificial neural network (GA-ANN) to estimate all-sky daily average Rn at high latitudes. With a very high temporal repeating frequency (~6 to 20 times per day) at high latitudes, data from the Moderate Resolution Imaging Spectroradiometer (MODIS) were used to test the proposed method. Rn measurements at 82 sites and top-of-atmosphere (TOA) data of MODIS from 2000 to 2017 were matched for model training and validation. Two models for estimating daily average Rn were developed: model I based on instantaneous daytime MODIS observation and model II based on instantaneous nighttime MODIS observation. Validation results of model I showed an R2 of 0.85, an RMSE of 23.66 W/m2, and a bias of 0.27 W/m2, whereas these values were 0.51, 15.04 W/m2, and −0.08 W/m2 for model II, respectively. Overall, the proposed machine learning algorithm with the LRD classification can accurately estimate the all-sky daily average Rn at high latitudes. Mapping of Rn over the high latitudes at 1 km spatial resolution showed a similar spatial distribution to Rn estimates from the Clouds and the Earth's Radiant Energy System (CERES) product. This method has the potential for operational monitoring of spatio-temporal change of Rn at high latitudes with a long-term coverage of MODIS observations. MODIS; Net radiation; High latitudes; High spatial resolution; Length ratio of daytime
Chen, Liang; Dirmeyer, Paul A.Chen, L., P. A. Dirmeyer, 2020: Reconciling the disagreement between observed and simulated temperature responses to deforestation. Nature Communications, 11(1), 1-10. doi: 10.1038/s41467-019-14017-0. Models show a cooler surface temperature response to deforestation than observations which has been attributed to uncertainties in the models. A comparison of satellite observations and model experiments shows that the disagreement is due to the role of atmospheric feedbacks, which are not well captured in the observational space-for-time approach.
Cherian, Ribu; Quaas, JohannesCherian, R., J. Quaas, 2020: Trends in AOD, Clouds, and Cloud Radiative Effects in Satellite Data and CMIP5 and CMIP6 Model Simulations Over Aerosol Source Regions. Geophysical Research Letters, 47(9), e2020GL087132. doi: 10.1029/2020GL087132. Several regions worldwide have seen significant trends in anthropogenic aerosol emissions during the period of detailed satellite observations since 2001. Over Europe (EUR) and North America (NAM) there were strong declines, over China increases then declines and over India, strong increases. Regional trends in model-simulated aerosol optical depth (AOD) and cloud radiative effects in both the Fifth and Sixth Coupled Model Intercomparison Projects (CMIP5 and CMIP6) are broadly consistent with the ones from satellite retrievals in most parts of EUR, NAM and India. CMIP6 models better match satellite-derived AOD trend in western NAM (increasing) and eastern China (decreasing), where CMIP5 models failed, pointing to improved anthropogenic aerosol emissions. Drop concentration trends in both observations and models qualitatively match AOD trends. The result for solar cloud radiative effect in models, however, is due to compensating errors: Models fail to reproduce observed liquid water path trends and show, in turn, opposite trends in cloud fraction. climate models; cloud radiative effects; aerosol optical depth; aerosol emission trend; aerosol source regions; CDNC
Cheruy, Frédérique; Ducharne, Agnés; Hourdin, Frédéric; Musat, Ionela; Vignon, Etienne; Gastineau, Guillaume; Bastrikov, Vladislav; Vuichard, Nicolas; Diallo, Binta; Dufresne, Jean-Louis; Ghattas, Josefine; Grandpeix, Jean-Yves; Idelkadi, Abderrahmane; Mellul, Lidia; Maignan, Fabienne; Menegoz, Martin; Ottlé, Catherine; Peylin, Philippe; Servonnat, Jérôme; Wang, Fuxing; Zhao, YanfengCheruy, F., A. Ducharne, F. Hourdin, I. Musat, E. Vignon, G. Gastineau, V. Bastrikov, N. Vuichard, B. Diallo, J. Dufresne, J. Ghattas, J. Grandpeix, A. Idelkadi, L. Mellul, F. Maignan, M. Menegoz, C. Ottlé, P. Peylin, J. Servonnat, F. Wang, Y. Zhao, 2020: Improved near surface continental climate in IPSL-CM6A-LR by combined evolutions of atmospheric and land surface physics. Journal of Advances in Modeling Earth Systems, 12(10), e2019MS002005. doi: 10.1029/2019MS002005. keypoints The representation of the land-atmosphere coupled system by the IPSL model is thoroughly evaluated. Improvements with respect to previous versions are documented in the context of the Coupled Model Intercomparison Project, CMIP. Advanced parameterization of land surface and atmospheric processes, tuning of the radiation and the turbulent mixing yielded many improvements. hydrology; climate modelling; atmosphere-land surface interactions; soil moisture; stable boundary layer; temperature bias
Cho, Heeje; Jun, Sang-Yoon; Ho, Chang-Hoi; McFarquhar, GregCho, H., S. Jun, C. Ho, G. McFarquhar, 2020: Simulations of Winter Arctic Clouds and Associated Radiation Fluxes Using Different Cloud Microphysics Schemes in the Polar WRF: Comparisons With CloudSat, CALIPSO, and CERES. Journal of Geophysical Research: Atmospheres, 125(2), e2019JD031413. doi: 10.1029/2019JD031413. Key Points Winter Arctic clouds simulated by the polar version of the Weather Research and Forecasting model are compared with satellite retrievals The cloud amount and cloud top height of model simulations agree well with those of satellite retrievals The downward longwave radiation at the surface shows realistic temporal variations, but is sensitive to the cloud microphysics scheme choice cloud microphysics; Polar WRF; satellite observation; surface radiation; winter Arctic cloud
Choi, Yong-Sang; Hwang, Jiwon; Ok, Jung; Park, Doo-Sun R.; Su, Hui; Jiang, Jonathan H.; Huang, Lei; Limpasuvan, TyChoi, Y., J. Hwang, J. Ok, D. R. Park, H. Su, J. H. Jiang, L. Huang, T. Limpasuvan, 2020: Effect of Arctic clouds on the ice-albedo feedback in midsummer. International Journal of Climatology, 40(10), 4707-4714. doi: 10.1002/joc.6469. The Arctic clouds should be an important factor that affects the summertime sea ice. By reflecting the incoming solar radiation before it reaches the surface, the Arctic clouds may prevent the surface from absorbing tremendous solar radiation due to the reduced sea ice. This cloud effect will lead to intervene the feedback relation between the solar radiation and the sea ice change. However, few studies have quantitatively investigated the Arctic cloud effect on the ice-albedo feedback. This study found that the Arctic clouds regulate the melting speed of sea ice in midsummer months (June to August) based on the data from multiple sources, that is, satellite, reanalysis, and climate models. During this period, the fraction of Arctic clouds with the net radiative cooling effect is almost invariable with sea ice reduction. However, despite of the steady cloud fraction in the midsummer months, the shortwave cloud radiative effect (total-sky minus clear-sky absorbed shortwave radiation) was found to significantly increase with the reduced sea ice concentration (0.64 W m−2%−1 in CERES, 0.73 W m−2%−1 in ERA5). This is because the clouds present more contrast of albedo with the sea ice-free ocean than the sea ice-covered ocean. Finally, our analyses show that the Arctic clouds are nearly halving the strength of the ice-albedo feedback in the midsummer months. These results imply that the sea ice reduction could have been much faster in the past decades in the absence of the cloud effect found here. Arctic clouds; Arctic Sea ice; cloud effect; ice-albedo feedback; midsummer
Christensen, Matthew W.; Jones, William K.; Stier, PhilipChristensen, M. W., W. K. Jones, P. Stier, 2020: Aerosols enhance cloud lifetime and brightness along the stratus-to-cumulus transition. Proceedings of the National Academy of Sciences, 117(30), 17591-17598. doi: 10.1073/pnas.1921231117. Anthropogenic aerosols are hypothesized to enhance planetary albedo and offset some of the warming due to the buildup of greenhouse gases in Earth’s atmosphere. Aerosols can enhance the coverage, reflectance, and lifetime of warm low-level clouds. However, the relationship between cloud lifetime and aerosol concentration has been challenging to measure from polar orbiting satellites. We estimate two timescales relating to the formation and persistence of low-level clouds over 1○×1○1○×1○1○×1○ spatial domains using multiple years of geostationary satellite observations provided by the Clouds and Earth’s Radiant Energy System (CERES) Synoptic (SYN) product. Lagrangian trajectories spanning several days along the classic stratus-to-cumulus transition zone are stratified by aerosol optical depth and meteorology. Clouds forming in relatively polluted trajectories tend to have lighter precipitation rates, longer average lifetime, and higher cloud albedo and cloud fraction compared with unpolluted trajectories. While liquid water path differences are found to be negligible, we find direct evidence of increased planetary albedo primarily through increased drop concentration (NdNdNd) and cloud fraction, with the caveat that the aerosol influence on cloud fraction is positive only for stable atmospheric conditions. While the increase in cloud fraction can be large typically in the beginning of trajectories, the Twomey effect accounts for the bulk (roughly 3/4) of the total aerosol indirect radiative forcing estimate. clouds; aerosols; radiative forcing
Colón Robles, Marilé; Amos, Helen M.; Dodson, J. Brant; Bouwman, Jeffrey; Rogerson, Tina; Bombosch, Annette; Farmer, Lauren; Burdick, Autumn; Taylor, Jessica; Chambers, Lin H.Colón Robles, M., H. M. Amos, J. B. Dodson, J. Bouwman, T. Rogerson, A. Bombosch, L. Farmer, A. Burdick, J. Taylor, L. H. Chambers, 2020: Clouds around the World: How a Simple Citizen Science Data Challenge Became a Worldwide Success. Bull. Amer. Meteor. Soc., 101(7), E1201-E1213. doi: 10.1175/BAMS-D-19-0295.1.
Danabasoglu, G.; Lamarque, J.-F.; Bacmeister, J.; Bailey, D. A.; DuVivier, A. K.; Edwards, J.; Emmons, L. K.; Fasullo, J.; Garcia, R.; Gettelman, A.; Hannay, C.; Holland, M. M.; Large, W. G.; Lauritzen, P. H.; Lawrence, D. M.; Lenaerts, J. T. M.; Lindsay, K.; Lipscomb, W. H.; Mills, M. J.; Neale, R.; Oleson, K. W.; Otto‐Bliesner, B.; Phillips, A. S.; Sacks, W.; Tilmes, S.; Kampenhout, L. van; Vertenstein, M.; Bertini, A.; Dennis, J.; Deser, C.; Fischer, C.; Fox‐Kemper, B.; Kay, J. E.; Kinnison, D.; Kushner, P. J.; Larson, V. E.; Long, M. C.; Mickelson, S.; Moore, J. K.; Nienhouse, E.; Polvani, L.; Rasch, P. J.; Strand, W. G.Danabasoglu, G., J. Lamarque, J. Bacmeister, D. A. Bailey, A. K. DuVivier, J. Edwards, L. K. Emmons, J. Fasullo, R. Garcia, A. Gettelman, C. Hannay, M. M. Holland, W. G. Large, P. H. Lauritzen, D. M. Lawrence, J. T. M. Lenaerts, K. Lindsay, W. H. Lipscomb, M. J. Mills, R. Neale, K. W. Oleson, B. Otto‐Bliesner, A. S. Phillips, W. Sacks, S. Tilmes, L. v. Kampenhout, M. Vertenstein, A. Bertini, J. Dennis, C. Deser, C. Fischer, B. Fox‐Kemper, J. E. Kay, D. Kinnison, P. J. Kushner, V. E. Larson, M. C. Long, S. Mickelson, J. K. Moore, E. Nienhouse, L. Polvani, P. J. Rasch, W. G. Strand, 2020: The Community Earth System Model Version 2 (CESM2). Journal of Advances in Modeling Earth Systems, 12(2), e2019MS001916. doi: 10.1029/2019MS001916. An overview of the Community Earth System Model Version 2 (CESM2) is provided, including a discussion of the challenges encountered during its development and how they were addressed. In addition, an evaluation of a pair of CESM2 long preindustrial control and historical ensemble simulations is presented. These simulations were performed using the nominal 1° horizontal resolution configuration of the coupled model with both the “low-top” (40 km, with limited chemistry) and “high-top” (130 km, with comprehensive chemistry) versions of the atmospheric component. CESM2 contains many substantial science and infrastructure improvements and new capabilities since its previous major release, CESM1, resulting in improved historical simulations in comparison to CESM1 and available observations. These include major reductions in low-latitude precipitation and shortwave cloud forcing biases; better representation of the Madden-Julian Oscillation; better El Niño-Southern Oscillation-related teleconnections; and a global land carbon accumulation trend that agrees well with observationally based estimates. Most tropospheric and surface features of the low- and high-top simulations are very similar to each other, so these improvements are present in both configurations. CESM2 has an equilibrium climate sensitivity of 5.1–5.3 °C, larger than in CESM1, primarily due to a combination of relatively small changes to cloud microphysics and boundary layer parameters. In contrast, CESM2's transient climate response of 1.9–2.0 °C is comparable to that of CESM1. The model outputs from these and many other simulations are available to the research community, and they represent CESM2's contributions to the Coupled Model Intercomparison Project Phase 6. Community Earth System Model (CESM); coupled model development and evaluation; global coupled Earth system modeling; preindustrial and historical simulations
Devasthale, Abhay; Sedlar, Joseph; Tjernström, Michael; Kokhanovsky, AlexanderDevasthale, A., J. Sedlar, M. Tjernström, A. Kokhanovsky, 2020: A Climatological Overview of Arctic Clouds. Physics and Chemistry of the Arctic Atmosphere, 331-360. The Arctic climate system is complex and clouds are one of its least understood components. Since cloud processes occur from micrometer to synoptic scales, their couplings with the other components of the Arctic climate system and their overall role in modulating the energy budget at different spatio-temporal scales is challenging to quantify. The in-situ measurements, as limited in space and time as they are, still reveal the complex nature of cloud microphysical and thermodynamical processes in the Arctic. However, the synoptic scale variability of cloud systems can only be obtained from the satellite observations. A considerable progress has been made in the last decade in understanding cloud processes in the Arctic due to the availability of valuable data from the multiple campaigns in the Central Arctic and due to the advances in the satellite remote sensing. This chapter provides an overview of this progress.First an overview of the lessons learned from the recent in-situ measurement campaigns in the Arctic is provided. In particular, the importance of supercooled liquid water clouds, their role in the radiation budget and their interaction with the vertical thermodynamical structure is discussed. In the second part of the chapter, a climatological overview of cloud properties using the state-of-the-art satellite based cloud climate datasets is provided. The agreements and disagreements in these datasets are highlighted. The third and the fourth parts of the chapter highlight two most important processes that are currently being researched, namely cloud response to the rapidly changing sea-ice extent and the role of moisture transport in to the Arctic in governing cloud variability. Both of these processes have implications for the cloud feedback in the Arctic. Arctic clouds; Arctic sea-ice; Climate data records; Cloud properties; Cloud variability; Moisture transport; Satellite remote sensing; Supercooled liquid clouds; Surface radiation budget; Thermodynamic structure
Diamond, Michael S.; Director, Hannah M.; Eastman, Ryan; Possner, Anna; Wood, RobertDiamond, M. S., H. M. Director, R. Eastman, A. Possner, R. Wood, 2020: Substantial Cloud Brightening From Shipping in Subtropical Low Clouds. AGU Advances, 1(1), e2019AV000111. doi: 10.1029/2019AV000111. The influence of aerosol particles on cloud reflectivity remains one of the largest sources of uncertainty in our understanding of anthropogenic climate change. Commercial shipping constitutes a large and concentrated aerosol perturbation in a meteorological regime where clouds have a disproportionally large effect on climate. Yet, to date, studies have been unable to detect climatologically relevant cloud radiative effects from shipping, despite models indicating that the cloud response should produce a sizable negative radiative forcing (perturbation to Earth's energy balance). We attribute a significant increase in cloud reflectivity to enhanced cloud droplet number concentrations within a major shipping corridor in the southeast Atlantic. Prevailing winds constrain emissions around the corridor, which cuts through a climatically important region of expansive low cloud cover. We use universal kriging, a classic geostatistical method, to estimate what cloud properties would have been in the absence of shipping. In the morning, cloud brightening is consistent with changes in microphysics alone, whereas in the afternoon, increases in cloud brightness from microphysical changes are offset by decreases in the total amount of cloud water. We calculate an effective radiative forcing within the southeast Atlantic shipping corridor of approximately −2 W/m2. Several years of data are required to identify a clear signal. Extrapolating our results globally, we calculate an effective radiative forcing due to aerosol-cloud interactions in low clouds of −1.0 W/m2 (95% confidence interval: −1.6 to −0.4 W/m2). The unique setup in the southeast Atlantic could be an ideal test for the representation of aerosol-cloud interactions in climate models. cloud; aerosol; radiative forcing; climate; shipping
Dolinar, Erica K.; Campbell, James R.; Lolli, Simone; Ozog, Scott C.; Yorks, John E.; Camacho, Christopher; Gu, Yu; Bucholtz, Anthony; McGill, Matthew J.Dolinar, E. K., J. R. Campbell, S. Lolli, S. C. Ozog, J. E. Yorks, C. Camacho, Y. Gu, A. Bucholtz, M. J. McGill, 2020: Sensitivities in Satellite Lidar-derived Estimates of Daytime Top-of-the-Atmosphere Optically-Thin Cirrus Cloud Radiative Forcing: A Case Study. Geophysical Research Letters, 47(17), e2020GL088871. doi: 10.1029/2020GL088871. An optically-thin cirrus cloud was profiled concurrently with nadir-pointing 1064 nm lidars on 11 August 2017 over eastern Texas, including NASA's airborne Cloud Physics Lidar (CPL) and space-borne Clouds and Aerosol Transport System (CATS) instruments. Despite resolving fewer (37% vs 94%) and denser (i.e., more emissive) clouds (average cloud optical depth of 0.10 vs 0.03, respectively), CATS data render a near-equal estimate of the top-of-atmosphere (TOA) net cloud radiative forcing (CRF) versus CPL. The sample-relative TOA net CRF solved from CPL is 1.39 W/m2, which becomes 1.32 W/m2 after normalizing by occurrence frequency. Since CATS overestimates extinction for this case, the sample-relative TOA net forcing is 3.0 W/m2 larger than CPL, with the absolute value reduced to within 0.3 W/m2 of CPL due its underestimation of cloud occurrence. We discuss the ramifications of thin cirrus cloud detectability from satellite and its impact on attempts at TOA CRF closure. cloud radiative forcing; cirrus cloud; radiative transfer model; cirrus cloud detection and retrieval; satellite lidar
Donohoe, Aaron; Armour, Kyle C.; Roe, Gerard H.; Battisti, David S.; Hahn, LilyDonohoe, A., K. C. Armour, G. H. Roe, D. S. Battisti, L. Hahn, 2020: The Partitioning of Meridional Heat Transport from the Last Glacial Maximum to CO2 Quadrupling in Coupled Climate Models. J. Climate, 33(10), 4141-4165. doi: 10.1175/JCLI-D-19-0797.1. Meridional heat transport (MHT) is analyzed in ensembles of coupled climate models simulating climate states ranging from the Last Glacial Maximum (LGM) to quadrupled CO2. MHT is partitioned here into atmospheric (AHT) and implied oceanic (OHT) heat transports. In turn, AHT is partitioned into dry and moist energy transport by the meridional overturning circulation (MOC), transient eddy energy transport (TE), and stationary eddy energy transport (SE) using only monthly averaged model output that is typically archived. In all climate models examined, the maximum total MHT (AHT + OHT) is nearly climate-state invariant, except for a modest (4%, 0.3 PW) enhancement of MHT in the Northern Hemisphere (NH) during the LGM. However, the partitioning of MHT depends markedly on the climate state, and the changes in partitioning differ considerably among different climate models. In response to CO2 quadrupling, poleward implied OHT decreases, while AHT increases by a nearly compensating amount. The increase in annual-mean AHT is a smooth function of latitude but is due to a spatially inhomogeneous blend of changes in SE and TE that vary by season. During the LGM, the increase in wintertime SE transport in the NH midlatitudes exceeds the decrease in TE resulting in enhanced total AHT. Total AHT changes in the Southern Hemisphere (SH) are not significant. These results suggest that the net top-of-atmosphere radiative constraints on total MHT are relatively invariant to climate forcing due to nearly compensating changes in absorbed solar radiation and outgoing longwave radiation. However, the partitioning of MHT depends on detailed regional and seasonal factors.
Donohoe, Aaron; Blanchard-Wrigglesworth, Ed; Schweiger, Axel; Rasch, Philip J.Donohoe, A., E. Blanchard-Wrigglesworth, A. Schweiger, P. J. Rasch, 2020: The Effect of Atmospheric Transmissivity on Model and Observational Estimates of the Sea Ice Albedo Feedback. J. Climate, 33(13), 5743-5765. doi: 10.1175/JCLI-D-19-0674.1.
Donohoe, Aaron; Dawson, Eliza; McMurdie, Lynn; Battisti, David S.; Rhines, AndyDonohoe, A., E. Dawson, L. McMurdie, D. S. Battisti, A. Rhines, 2020: Seasonal Asymmetries in the Lag between Insolation and Surface Temperature. J. Climate, 33(10), 3921-3945. doi: 10.1175/JCLI-D-19-0329.1. We analyze the temporal structure of the climatological seasonal cycle in surface air temperature across the globe. We find that, over large regions of Earth, the seasonal cycle of surface temperature departs from an annual harmonic: the duration of fall and spring differ by as much as 2 months. We characterize this asymmetry by the metric ASYM, defined as the phase lag of the seasonal maximum temperature relative to the summer solstice minus the phase lag of the seasonal minimum temperature relative to winter solstice. We present a global analysis of ASYM from weather station data and atmospheric reanalysis and find that ASYM is well represented in the reanalysis. ASYM generally features positive values over land and negative values over the ocean, indicating that spring has a longer duration over the land domain whereas fall has a longer duration over the ocean. However, ASYM also features more positive values over North America compared to Europe and negative values in the polar regions over ice sheets and sea ice. Understanding the root cause of the climatological ASYM will potentially further our understanding of controls on the seasonal cycle of temperature and its future/past changes. We explore several candidate mechanisms to explain the spatial structure of ASYM including 1) modification of the seasonal cycle of surface solar radiation by the seasonal evolution of cloud thickness, 2) differences in the seasonal cycle of the atmospheric boundary layer depth over ocean and over land, and 3) temperature advection by the seasonally evolving atmospheric circulation.
Duncan, Bryan N.; Ott, Lesley E.; Abshire, James B.; Brucker, Ludovic; Carroll, Mark L.; Carton, James; Comiso, Josefino C.; Dinnat, Emmanuel P.; Forbes, Bruce C.; Gonsamo, Alemu; Gregg, Watson W.; Hall, Dorothy K.; Ialongo, Iolanda; Jandt, Randi; Kahn, Ralph A.; Karpechko, Alexey; Kawa, Stephan R.; Kato, Seiji; Kumpula, Timo; Kyrölä, Erkki; Loboda, Tatiana V.; McDonald, Kyle C.; Montesano, Paul M.; Nassar, Ray; Neigh, Christopher S. R.; Parkinson, Claire L.; Poulter, Benjamin; Pulliainen, Jouni; Rautiainen, Kimmo; Rogers, Brendan M.; Rousseaux, Cecile S.; Soja, Amber J.; Steiner, Nicholas; Tamminen, Johanna; Taylor, Patrick C.; Tzortziou, Maria A.; Virta, Henrik; Wang, James S.; Watts, Jennifer D.; Winker, David M.; Wu, Dong L.Duncan, B. N., L. E. Ott, J. B. Abshire, L. Brucker, M. L. Carroll, J. Carton, J. C. Comiso, E. P. Dinnat, B. C. Forbes, A. Gonsamo, W. W. Gregg, D. K. Hall, I. Ialongo, R. Jandt, R. A. Kahn, A. Karpechko, S. R. Kawa, S. Kato, T. Kumpula, E. Kyrölä, T. V. Loboda, K. C. McDonald, P. M. Montesano, R. Nassar, C. S. R. Neigh, C. L. Parkinson, B. Poulter, J. Pulliainen, K. Rautiainen, B. M. Rogers, C. S. Rousseaux, A. J. Soja, N. Steiner, J. Tamminen, P. C. Taylor, M. A. Tzortziou, H. Virta, J. S. Wang, J. D. Watts, D. M. Winker, D. L. Wu, 2020: Space-Based Observations for Understanding Changes in the Arctic-Boreal Zone. Reviews of Geophysics, 58(1), e2019RG000652. doi: 10.1029/2019RG000652. Observations taken over the last few decades indicate that dramatic changes are occurring in the Arctic-Boreal Zone (ABZ), which are having significant impacts on ABZ inhabitants, infrastructure, flora and fauna, and economies. While suitable for detecting overall change, the current capability is inadequate for systematic monitoring and for improving process-based and large-scale understanding of the integrated components of the ABZ, which includes the cryosphere, biosphere, hydrosphere, and atmosphere. Such knowledge will lead to improvements in Earth system models, enabling more accurate prediction of future changes and development of informed adaptation and mitigation strategies. In this article, we review the strengths and limitations of current space-based observational capabilities for several important ABZ components and make recommendations for improving upon these current capabilities. We recommend an interdisciplinary and stepwise approach to develop a comprehensive ABZ Observing Network (ABZ-ON), beginning with an initial focus on observing networks designed to gain process-based understanding for individual ABZ components and systems that can then serve as the building blocks for a comprehensive ABZ-ON. Arctic; satellite; Arctic-Boreal Zone; Boreal; Observing Strategy
Dunne, J. P.; Horowitz, L. W.; Adcroft, A. J.; Ginoux, P.; Held, I. M.; John, J. G.; Krasting, J. P.; Malyshev, S.; Naik, V.; Paulot, F.; Shevliakova, E.; Stock, C. A.; Zadeh, N.; Balaji, V.; Blanton, C.; Dunne, K. A.; Dupuis, C.; Durachta, J.; Dussin, R.; Gauthier, P. P. G.; Griffies, S. M.; Guo, H.; Hallberg, R. W.; Harrison, M.; He, J.; Hurlin, W.; McHugh, C.; Menzel, R.; Milly, P. C. D.; Nikonov, S.; Paynter, D. J.; Ploshay, J.; Radhakrishnan, A.; Rand, K.; Reichl, B. G.; Robinson, T.; Schwarzkopf, D. M.; Sentman, L. T.; Underwood, S.; Vahlenkamp, H.; Winton, M.; Wittenberg, A. T.; Wyman, B.; Zeng, Y.; Zhao, M.Dunne, J. P., L. W. Horowitz, A. J. Adcroft, P. Ginoux, I. M. Held, J. G. John, J. P. Krasting, S. Malyshev, V. Naik, F. Paulot, E. Shevliakova, C. A. Stock, N. Zadeh, V. Balaji, C. Blanton, K. A. Dunne, C. Dupuis, J. Durachta, R. Dussin, P. P. G. Gauthier, S. M. Griffies, H. Guo, R. W. Hallberg, M. Harrison, J. He, W. Hurlin, C. McHugh, R. Menzel, P. C. D. Milly, S. Nikonov, D. J. Paynter, J. Ploshay, A. Radhakrishnan, K. Rand, B. G. Reichl, T. Robinson, D. M. Schwarzkopf, L. T. Sentman, S. Underwood, H. Vahlenkamp, M. Winton, A. T. Wittenberg, B. Wyman, Y. Zeng, M. Zhao, 2020: The GFDL Earth System Model version 4.1 (GFDL-ESM 4.1): Overall coupled model description and simulation characteristics. Journal of Advances in Modeling Earth Systems, 12(11), e2019MS002015. doi: 10.1029/2019MS002015. Key Points: A new coupled chemistry-carbon-climate Earth system model has been developed at the Geophysical Fluid Dynamics Laboratory. This model unifies component advances in chemistry, carbon, and ecosystem comprehensiveness within a single coupled climate framework. This model features much improved climate mean patterns and variability from previous chemistry and carbon coupled models. Earth System Model; Biogeochemistry; Climate Model
Fiedler, Stephanie; Crueger, Traute; D’Agostino, Roberta; Peters, Karsten; Becker, Tobias; Leutwyler, David; Paccini, Laura; Burdanowitz, Jörg; Buehler, Stefan A.; Cortes, Alejandro Uribe; Dauhut, Thibaut; Dommenget, Dietmar; Fraedrich, Klaus; Jungandreas, Leonore; Maher, Nicola; Naumann, Ann Kristin; Rugenstein, Maria; Sakradzija, Mirjana; Schmidt, Hauke; Sielmann, Frank; Stephan, Claudia; Timmreck, Claudia; Zhu, Xiuhua; Stevens, BjornFiedler, S., T. Crueger, R. D’Agostino, K. Peters, T. Becker, D. Leutwyler, L. Paccini, J. Burdanowitz, S. A. Buehler, A. U. Cortes, T. Dauhut, D. Dommenget, K. Fraedrich, L. Jungandreas, N. Maher, A. K. Naumann, M. Rugenstein, M. Sakradzija, H. Schmidt, F. Sielmann, C. Stephan, C. Timmreck, X. Zhu, B. Stevens, 2020: Simulated Tropical Precipitation Assessed Across Three Major Phases of the Coupled Model Intercomparison Project (CMIP). Mon. Wea. Rev., 148(9), 3653–368. doi: 10.1175/MWR-D-19-0404.1. The representation of tropical precipitation is evaluated across three generations of models participating in the Coupled Model Intercomparison Project (CMIP), phases 3, 5 and 6. Compared to state-of-the-art observations, improvements in tropical precipitation in the CMIP6 models are identified for some metrics, but we find no general improvement in tropical precipitation on different temporal and spatial scales. Our results indicate overall little changes across the CMIP phases for the summer monsoons, the double-ITCZ bias and the diurnal cycle of tropical precipitation. We find a reduced amount of drizzle events in CMIP6, but tropical precipitation occurs still too frequently. Continuous improvements across the CMIP phases are identified for the number of consecutive dry days, the representation of modes of variability, namely the Madden-Julian Oscillation and the El Niño Southern Oscillation, as well as the trends in dry months in the 20th century. The observed positive trend in extreme wet months is, however, not captured by any of the CMIP phases, which simulate negative trends for extremely wet months in the 20th century. The regional biases are larger than a climate-change signal one hopes to use the models to identify. Given the pace of climate change as compared to the pace of model improvements to simulate tropical precipitation, we question the past strategy of the development of the present class of global climate models as the mainstay of the scientific response to climate change. We suggest to explore alternative approaches such as high-resolution storm-resolving models that can offer better prospects to inform us about how tropical precipitation might change with anthropogenic warming.
Fiolleau, Thomas; Roca, Rémy; Cloché, Sophie; Bouniol, Dominique; Raberanto, PatrickFiolleau, T., R. Roca, S. Cloché, D. Bouniol, P. Raberanto, 2020: Homogenization of Geostationary Infrared Imager Channels for Cold Cloud Studies Using Megha-Tropiques/ScaRaB. IEEE Transactions on Geoscience and Remote Sensing, 58(9), 6609-6622. doi: 10.1109/TGRS.2020.2978171. Infrared (IR) observations from the fleet of multiagencies meteorological geostationary satellites have a great potential to support scientific and operational investigations at a quasi-global scale. In particular, such a data record, defined as the GEOring data set, is well suited to document the tropical convective systems life cycles by applying cloud tracking algorithms. Yet, this GEOring data set is far from being homogeneous, preventing the realization of its potential. A number of sources of inhomogeneities are identified ranging from spatiotemporal resolutions to spectral characteristics of the IR channels and calibration methodologies. While previous efforts have attempted to correct such issues, the adjustment of the cold part of the IR spectrum remains unfit for cold cloud studies. Here, a processing method is introduced to minimize the inhomogeneities against a reference observational data set from the Scanner for Radiation Budget (ScaRaB) instrument onboard the Megha-Tropiques satellite. The method relies on the collocations between the geostationary observations and the reference. The techniques exhibit significant sensitivity to the selection of the relevant pairs of observations requiring a dedicated filtering of the data. A second effort is then proposed to account for the limb-darkening effect and a method is developed to correct the brightness temperature (BT) dependence on the geostationary viewing zenith angle (VZA). Overall, results show a residual after the processing of 0 K between any of the geostationary data and the ScaRaB reference. The final calibrated and limb-adjusted IR observations are then homogeneous for cold BT lower than 240 K with a standard deviation lower than 1.5 K throughout the GEOring. calibration; clouds; infrared imaging; Satellites; atmospheric radiation; atmospheric techniques; Instruments; atmospheric measuring apparatus; convection; geostationary satellites; Temperature measurement; Spatial resolution; Satellite broadcasting; remote sensing; Clouds; atmospheric humidity; Calibration; Calibration and spectral corrections; cloud tracking algorithms; cold cloud studies; data record; final calibrated limb-adjusted IR observations; GEOring data set; geostationary data; geostationary infrared imager channels; geostationary observations; geostationary viewing zenith angle; homogenization; infrared (IR) image sensors; inhomogeneities; IR channels; IR spectrum; limb-darkening corrections; Megha-Tropiques satellite; meteorology; multiagencies meteorological geostationary satellites; operational investigations; quasiglobal scale; Radiation Budget instrument; reference observational data; ScaRaB reference; scientific investigations; tropical convective systems life cycles
Foster, M. J.; Di Girolamo, L.; Frey, R. A.; Heidinger, A. K.; Phillips, C.; Menzel, W.P.; Zhao, G.Foster, M. J., L. Di Girolamo, R. A. Frey, A. K. Heidinger, C. Phillips, W. Menzel, G. Zhao, 2020: Global Cloudiness [in “State of the Climate in 2019”].. Bull. Amer. Meteor. Soc, 101(8), S51-53. doi: 10.1175/2020BAMSStateoftheClimate.1..
Fountoukis, Christos; Harshvardhan, Harshvardhan; Gladich, Ivan; Ackermann, Luis; Ayoub, Mohammed A.Fountoukis, C., H. Harshvardhan, I. Gladich, L. Ackermann, M. A. Ayoub, 2020: Anatomy of a severe dust storm in the middle east: Impacts on aerosol optical properties and radiation budget. Aerosol and Air Quality Research, 20(1), 155-165. doi: 10.4209/aaqr.2019.04.0165.
Fowler, Laura D.; Barth, Mary C.; Alapaty, KiranFowler, L. D., M. C. Barth, K. Alapaty, 2020: Impact of scale-aware deep convection on the cloud liquid and ice water paths and precipitation using the Model for Prediction Across Scales (MPAS-v5.2). Geoscientific Model Development, 13(6), 2851-2877. doi: https://doi.org/10.5194/gmd-13-2851-2020. Abstract. The cloud liquid water path (LWP), ice water path (IWP), and precipitation simulated with uniform- and variable-resolution numerical experiments using the Model for Prediction Across Scales (MPAS) are compared against Clouds and the Earth's Radiant Energy System (CERES) and Tropical Rainfall Measuring Mission data. Our comparison between monthly-mean model diagnostics and satellite data focuses on the convective activity regions of the tropical Pacific Ocean, extending from the Tropical Eastern Pacific Basin where trade wind boundary layer clouds develop to the Western Pacific Warm Pool characterized by deep convective updrafts capped with extended upper-tropospheric ice clouds. Using the scale-aware Grell–Freitas (GF) and Multi-scale Kain–Fritsch (MSKF) convection schemes in conjunction with the Thompson cloud microphysics, uniform-resolution experiments produce large biases between simulated and satellite-retrieved LWP, IWP, and precipitation. Differences in the treatment of shallow convection lead the LWP to be strongly overestimated when using GF, while being in relatively good agreement when using MSKF compared to CERES data. Over areas of deep convection, uniform- and variable-resolution experiments overestimate the IWP with both MSKF and GF, leading to strong biases in the top-of-the-atmosphere longwave and shortwave radiation relative to satellite-retrieved data. Mesh refinement over the Western Pacific Warm Pool does not lead to significant improvement in the LWP, IWP, and precipitation due to increased grid-scale condensation and upward vertical motions. Results underscore the importance of evaluating clouds, their optical properties, and the top-of-the-atmosphere radiation budget in addition to precipitation when performing mesh refinement global simulations.
Francis, Diana; Chaboureau, Jean-Pierre; Nelli, Narendra; Cuesta, Juan; Alshamsi, Noor; Temimi, Marouane; Pauluis, Olivier; Xue, LulinFrancis, D., J. Chaboureau, N. Nelli, J. Cuesta, N. Alshamsi, M. Temimi, O. Pauluis, L. Xue, 2020: Summertime dust storms over the Arabian Peninsula and impacts on radiation, circulation, cloud development and rain. Atmospheric Research, 105364. doi: 10.1016/j.atmosres.2020.105364. This study investigates the underlying atmospheric dynamics associated with intense dust storms in summer 2018 over the Arabian Peninsula (AP); a major dust source at global scale. It reports, for the first time, on the formation of cyclone over the Empty Quarter Desert as important mechanism for intense dust storms over this source region. The dust direct and semi-direct radiative forcings are observed, for the first time over this source region, using high-resolution in-situ and CERES-SYN satellite observational data. The three-dimensional structure and evolution of the dust storms are inferred from state-of-the-art satellite products such as SEVIRI, AEROIASI and CALIPSO. The dynamics and thermodynamics of the boundary layer during this event are thoroughly analyzed using ERA5 reanalysis and ground based observations. We found that a large dust storm by Shamal winds led up, through radiative forcing, to cyclone development over the Empty Quarter Desert, subsequent dust emissions, development of convective clouds and rain. The cyclogenesis over this region initiated a second intense dust storm which developed and impacted the AP for 3 consecutive days. The uplifted dust by the cyclone reached 5 km in altitude and altered the radiative budget at the surface, inducing both significant warming during night and cooling during day. The dust load uplifted by the cyclone was estimated by the mesoscale model Meso-NH to be in the order of 20 Tg, and the associated aerosol optical depth was higher than 3. The model simulates reasonably the radiative impact of the dust in the shortwave but highly underestimated its impact in the LW. Our study stresses the importance of the dust radiative forcing in the longwave and that it should be accurately accounted for in models to properly represent the impact of dust on the Earth system especially near source areas. Missing the warming effect of dust aerosols would impact both the weather and air quality forecast, and the regional climate projections. SEVIRI; Dust aerosols; CALIPSO; Radiative forcing; Convective clouds; AEROIASI; Cyclogenesis; Meso-NH; Southwest Asia
Francis, Timmy; Jayakumar, A.; Mohandas, Saji; Sethunadh, Jisesh; Reddy, M. Venkatarami; Arulalan, T.; Rajagopal, E. N.Francis, T., A. Jayakumar, S. Mohandas, J. Sethunadh, M. V. Reddy, T. Arulalan, E. N. Rajagopal, 2020: Simulation of a mesoscale convective system over Northern India: Sensitivity to convection partitioning in a regional NWP model. Dynamics of Atmospheres and Oceans, 92, 101162. doi: 10.1016/j.dynatmoce.2020.101162. Simulations of a mesoscale convective system (MCS), which propagated across Northern India on 2nd May 2018 - leading to many fatalities when the gust front knocked down homes and tore apart building roofs - have been performed using the National Centre for Medium Range Weather Forecasting (NCMRWF) Unified Model – Regional (4 km horizontal grid spacing), to evaluate the model’s convective treatments. Though the model captures many of the qualitative and quantitative features, it slightly lags behind the observed MCS organisation and movement, produces lesser precipitation, and lacks the spatial separation between two adjacent organised convective systems in the satellite observations – leading to a faintly offset MCS track. Sensitivity simulations are then performed, for this non-equilibrium MCS case, with different partitioning between parametrized and explicit convection to assess the reliance of the convective treatments on the large-scale environment, as well as to test the notion of a breakdown of convective parametrization at the mesoscale model resolution. Fully parametrized (FP) convection produces even lesser rainfall and are dominated by orographic precipitations along the foot hills of Himalayas with no any trace of the MCS. Fully explicit (FE) convection realistically simulates most of the prominent convective cells and enhance precipitation along the MCS track that agree better with the observations, though the ‘two lobes’ of intense precipitation are not resolved; instead it produces a squall line of precipitation. The FE configuration generates the most vigorous convective updraft, along with a vertical shear that is tilted westward. The simulation with partially parametrized and partially explicit convection resembles the fashion in the FP and FE scenarios, with a transition over the duration of the run from parametrized to explicit precipitation. The results are in line with the notion from previous studies; that the majority of successful explicit simulations of mesoscale organisation are those associated with strong large-scale forcing for convection, wherein resolved vertical motions are sufficient to minimise delays in onset. Mesoscale convective systems; NWP; Thunderstorms; Unified model
Freitas, Saulo R.; Putman, William M.; Arnold, Nathan P.; Adams, David K.; Grell, Georg A.Freitas, S. R., W. M. Putman, N. P. Arnold, D. K. Adams, G. A. Grell, 2020: Cascading Toward a Kilometer-Scale GCM: Impacts of a Scale-Aware Convection Parameterization in the Goddard Earth Observing System GCM. Geophysical Research Letters, 47(17), e2020GL087682. doi: 10.1029/2020GL087682. The National Aeronautics and Space Administration (NASA) Goddard Earth Observing System global circulation model (GCM) is evaluated through a cascade of simulations with increasing horizontal resolution. This model employs a nonhydrostatic dynamical core and includes a scale-aware, deep convection parameterization (DPCP). The 40-day simulations at six resolutions (100 km to 3 km) with unvarying model formulation were produced. At the highest resolution, extreme experiments were carried out: one with no DPCP and one with its scale awareness eliminated. Simulated precipitation, radiative balance, and atmospheric thermodynamic and dynamical variables are well reproduced with respect to both observational and reanalysis data. As model resolution increases, the convective precipitation smoothly transitions from being mostly produced by the convection parameterization to the cloud microphysics parameterization. However, contrary to current thought, these extreme cases argue for maintaining, to some extent, the scale-aware DPCP even at 3-km scale, as the run relying solely on explicit grid-scale production of rainfall performs more poorly at this resolution. model evaluation; global circulation models; convection parameterization; convection-permitting GCM; GEOS GCM
Gettelman, A.; Bardeen, C. G.; McCluskey, C. S.; Järvinen, E.; Stith, J.; Bretherton, C.; McFarquhar, G.; Twohy, C.; D'Alessandro, J.; Wu, W.Gettelman, A., C. G. Bardeen, C. S. McCluskey, E. Järvinen, J. Stith, C. Bretherton, G. McFarquhar, C. Twohy, J. D'Alessandro, W. Wu, 2020: Simulating Observations of Southern Ocean Clouds and Implications for Climate. Journal of Geophysical Research: Atmospheres, 125(21), e2020JD032619. doi: 10.1029/2020JD032619. Southern Ocean (S. Ocean) clouds are important for climate prediction. Yet, previous global climate models failed to accurately represent cloud phase distributions in this observation-sparse region. In this study, data from the Southern Ocean Clouds, Radiation, Aerosol, Transport Experimental Study (SOCRATES) experiment is compared to constrained simulations from a global climate model (the Community Atmosphere Model, CAM). Nudged versions of CAM are found to reproduce many of the features of detailed in-situ observations, such as cloud location, cloud phase and boundary layer structure. The simulation in CAM6 has improved its representation of S. Ocean clouds with adjustments to the ice nucleation and cloud microphysics schemes that permit more supercooled liquid. Comparisons between modeled and observed hydrometeor size distributions suggest that the modeled hydrometeor size distributions represent the dual peaked shape and form of observed distributions, which is remarkable given the scale difference between model and observations. Comparison to satellite observations of cloud physics is difficult due to model assumptions that do not match retrieval assumptions. Some biases in the model's representation of S. Ocean clouds and aerosols remain, but the detailed cloud physical parameterization provides a basis for process level improvement and direct comparisons to observations. This is crucial because cloud feedbacks and climate sensitivity are sensitive to the representation of Southern Ocean clouds. clouds; observations; southern ocean; supercooled water
Gonçalves, Nathan Borges; Lopes, Aline Pontes; Dalagnol, Ricardo; Wu, Jin; Pinho, Davieliton Mesquita; Nelson, Bruce WalkerGonçalves, N. B., A. P. Lopes, R. Dalagnol, J. Wu, D. M. Pinho, B. W. Nelson, 2020: Both near-surface and satellite remote sensing confirm drought legacy effect on tropical forest leaf phenology after 2015/2016 ENSO drought. Remote Sensing of Environment, 237, 111489. doi: 10.1016/j.rse.2019.111489. Amazon forest leaf phenology patterns have often been inferred from the Moderate Resolution Imaging Spectroradiometer (MODIS) Enhanced Vegetation Index (EVI). But reliable MODIS detection of seasonal and interannual leaf phenology patterns has also been questioned and is generally not validated with field observation. Here we compare inter-annual patterns of local-scale upper canopy leaf phenology and demography derived from tower-mounted phenocams at two upland forest sites in the Central Amazon, to corresponding satellite vegetation indices retrieved from MODIS-MAIAC (Multi-Angle Implementation of Atmospheric Correction). We focus on forest response to an unprecedented drought caused by the El Niño of 2015-16. At both sites, multi-year phenocam data showed post-drought shifts in leaf demography. These were consistent with MODIS-MAIAC anomalies in two vegetation indices. Specifically, a precocious leaf flush at both sites during the first two post-drought months, Feb-Mar 2016, caused (1) an anomalous decrease in flushing trees in Jun–Jul of 2016 and (2) an increase of trees with early mature stage leaves (2-4 mo age) in Apr-May-Jun of 2016. At both sites, these two phenological anomalies showed up in MODIS-MAIAC as, respectively, (1) a strong negative anomaly in Gcc (Green chromatic coordinate), which prior work has shown to be sensitive to the abundance of leaves 0-1 mo old, and (2) a strong positive anomaly in EVI, which is sensitive to abundance of leaves 2-4 mo age. A shift to sub-optimal seasonal leaf age mix is expected to change the ecosystem-scale intrinsic photosynthetic capacity for ~18 month after the drought. El Niño; Amazon green-up; EVI seasonality; Leaf demography; MODIS-MAIAC; Phenocam
González-Bárcena, David; Fernández-Soler, Alejandro; Pérez-Grande, Isabel; Sanz-Andrés, ÁngelGonzález-Bárcena, D., A. Fernández-Soler, I. Pérez-Grande, Á. Sanz-Andrés, 2020: Real data-based thermal environment definition for the ascent phase of Polar-Summer Long Duration Balloon missions from Esrange (Sweden). Acta Astronautica, 170, 235-250. doi: 10.1016/j.actaastro.2020.01.024. Long Duration Balloon missions are key platforms for scientific research and space technology development. Thermal analyses of this kind of systems are crucial for the success of the mission. Even though the science is usually performed at float altitude, the ascent phase, usually non-operational, is where the extreme cold conditions occur, due to the convective effects caused by relative wind speed together with the low temperatures found in the tropopause, making this scenario a dimensioning case. In this paper, a thorough study of the thermal environmental conditions during the ascent is carried out, in particular winds, temperature, and radiative thermal loads have been obtained as a function of the altitude. The study is based on real data obtained from different sources, including atmospheric soundings, radar and satellite, and a meticulous statistical treatment. The study is focussed on one of the main stratospheric balloon launch sites in Europe, Esrange (Sweden), a center of the Swedish Space Corporation, and the analyses are performed for the summer period. However, the methodology can be extended to any other location and epoch. As an example, the convective effect of the horizontal winds on a plate has been studied, and the heat transfer during the ascent phase has been quantified. A subcooling of around 7 °C was found in this case, which make worth the dedicated analysis. Albedo; Ascent phase; Convection; Long duration balloon (LDB); Thermal environment; Winds
Gupta, Ashok Kumar; Rajeev, K.; Davis, Edwin V.; Mishra, Manoj Kumar; Nair, Anish Kumar M.Gupta, A. K., K. Rajeev, E. V. Davis, M. K. Mishra, A. K. M. Nair, 2020: Direct observations of the multi-year seasonal mean diurnal variations of TOA cloud radiative forcing over tropics using Megha-Tropiques-ScaRaB/3. Climate Dynamics, 55(11), 3289-3306. doi: 10.1007/s00382-020-05441-w. Diurnal variation of cloud radiative forcing (CRF) is a major factor that controls the global radiation balance. This study presents multi-year seasonal mean diurnal variations of longwave cloud radiative forcing (LWCRF) and daytime shortwave cloud radiative forcing (SWCRF) at the top of atmosphere over tropics, derived from the broadband radiation measurements made by ScaRaB/3 onboard the low-inclination Megha-Tropiques satellite. The largest LWCRF (60–80 Wm−2) occurs over the oceanic regions of the east equatorial Indian Ocean and the western Pacific during all seasons, as well as the South Pacific Convergence Zone, the northeast Bay of Bengal, Amazon region, central and southern Africa and north Indian landmass (monsoon trough) during the local summer. Diurnal variations of 15–25 Wm−2 in LWCRF (20–35% of the mean) are observed with peak values occurring at 18–21 local time (LT) over continents and 00–06 LT over oceans. The minimum LWCRF occurs at 09–12 LT throughout the tropics. Over convective regions, SWCRF maximizes at 12–15 LT (− 220 to − 300 Wm−2) and has a higher magnitude over continents due to early convection occurrence, indicating the importance of diurnal phase. Certain specific features including the CRF associated with the double inter-tropical convergence zone, day-night changes in net CRF, and the effect of El Ni$$\stackrel{\sim }{\mathrm{n}}$$n∼o on CRF are also presented. The net CRF and its zonal variations are strikingly similar during the normal and El Ni$$\stackrel{\sim }{\mathrm{n}}$$n∼o periods because the changes in LWCRF and SWCRF are mutually compensated.
Hahn, L. C.; Storelvmo, T.; Hofer, S.; Parfitt, R.; Ummenhofer, C. C.Hahn, L. C., T. Storelvmo, S. Hofer, R. Parfitt, C. C. Ummenhofer, 2020: Importance of Orography for Greenland Cloud and Melt Response to Atmospheric Blocking. J. Climate, 33(10), 4187-4206. doi: 10.1175/JCLI-D-19-0527.1. More frequent high pressure conditions associated with atmospheric blocking episodes over Greenland in recent decades have been suggested to enhance melt through large-scale subsidence and cloud dissipation, which allows more solar radiation to reach the ice sheet surface. Here we investigate mechanisms linking high pressure circulation anomalies to Greenland cloud changes and resulting cloud radiative effects, with a focus on the previously neglected role of topography. Using reanalysis and satellite data in addition to a regional climate model, we show that anticyclonic circulation anomalies over Greenland during recent extreme blocking summers produce cloud changes dependent on orographic lift and descent. The resulting increased cloud cover over northern Greenland promotes surface longwave warming, while reduced cloud cover in southern and marginal Greenland favors surface shortwave warming. Comparison with an idealized model simulation with flattened topography reveals that orographic effects were necessary to produce area-averaged decreasing cloud cover since the mid-1990s and the extreme melt observed in the summer of 2012. This demonstrates a key role for Greenland topography in mediating the cloud and melt response to large-scale circulation variability. These results suggest that future melt will depend on the pattern of circulation anomalies as well as the shape of the Greenland Ice Sheet.
Han, Ji-Young; Hong, Song-You; Kwon, Young CheolHan, J., S. Hong, Y. C. Kwon, 2020: The Performance of a Revised Simplified Arakawa–Schubert (SAS) Convection Scheme in the Medium-Range Forecasts of the Korean Integrated Model (KIM). Wea. Forecasting, 35(3), 1113-1128. doi: 10.1175/WAF-D-19-0219.1. The Korea Institute of Atmospheric Prediction Systems (KIAPS) has developed a new global numerical weather prediction model, named the Korean Integrated Model (KIM). This paper presents the cumulus parameterization scheme (CPS) used in KIM, which originates from the simplified Arakawa–Schubert (SAS) convection scheme in the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) and has undergone numerous modifications in an effort to improve the medium-range forecast skill for precipitation and large-scale fields. The modifications include the following: 1) the threshold of the trigger condition is updated to consider the dependency on the environmental relative humidity (RH) averaged over the subcloud layer in order to suppress the trigger of convection in dry low-level environments; 2) the entrainment rate is modified to increase the sensitivity to environmental humidity, so that enhanced entrainment under lower RH conditions leads to a greater decrease in the strength of the convection that develops in drier environments; 3) the autoconversion parameter from cloud condensate to convective precipitation is changed to have a temperature dependency above the freezing level; 4) the closure is modified to consider rapidly varying boundary layer forcing; 5) the effect of the convection-induced pressure gradient force in convective momentum transport is enhanced in the upper part of the convective updrafts; and 6) scale awareness that enables a mass-flux CPS to work seamlessly at various grid sizes across gray-zone resolutions is addressed. The evaluation of medium-range forecasts with the KIM CPS reveals higher forecast skill, especially over the tropics, in comparison with its original version.
Hayashi, Michiya; Jin, Fei-Fei; Stuecker, Malte F.Hayashi, M., F. Jin, M. F. Stuecker, 2020: Dynamics for El Niño-La Niña asymmetry constrain equatorial-Pacific warming pattern. Nature Communications, 11(1), 4230. doi: 10.1038/s41467-020-17983-y. The El Niño-Southern Oscillation (ENSO) results from the instability of and also modulates the strength of the tropical-Pacific cold tongue. While climate models reproduce observed ENSO amplitude relatively well, the majority still simulates its asymmetry between warm (El Niño) and cold (La Niña) phases very poorly. The causes of this major deficiency and consequences thereof are so far not well understood. Analysing both reanalyses and climate models, we here show that simulated ENSO asymmetry is largely proportional to subsurface nonlinear dynamical heating (NDH) along the equatorial Pacific thermocline. Most climate models suffer from too-weak NDH and too-weak linear dynamical ocean-atmosphere coupling. Nevertheless, a sizeable subset (about 1/3) having relatively realistic NDH shows that El Niño-likeness of the equatorial-Pacific warming pattern is linearly related to ENSO amplitude change in response to greenhouse warming. Therefore, better simulating the dynamics of ENSO asymmetry potentially reduces uncertainty in future projections.
Hinkelman, Laura M.; Marchand, RogerHinkelman, L. M., R. Marchand, 2020: Evaluation of CERES and CloudSat Surface Radiative Fluxes over Macquarie Island, the Southern Ocean. Earth and Space Science, 7(9), e2020EA001224. doi: 10.1029/2020EA001224. Many studies involving surface radiative fluxes rely on surface fluxes retrieved by the Clouds and the Earth's Radiant Energy System (CERES) project, or derived from spaceborne cloud radar and lidar observations (CloudSat-CALIPSO). In particular, most climate models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) were found to have too little shortwave radiation being reflected back to space and excessive shortwave radiation reaching the surface over the Southern Ocean – an error with significant consequences for predicting both regional and global climate. There have been few evaluations of CERES or CloudSat retrievals over the Southern Ocean. In this article, CERES and CloudSat retrieved surface shortwave (SW) and longwave (LW) downwelling fluxes are evaluated using surface observations collected over the Southern Ocean during the Macquarie Island Cloud and Radiation Experiment (MICRE). Overall, biases (CERES – surface observations) in the CERES- surface fluxes are found to be slightly larger over Macquarie Island than most other regions, approximately +10 Wm-2 for the SW and -10 Wm-2 for the LW in the annual mean, but with significant seasonal and diurnal variations. If the Macquarie observations are representative of the larger SO, these results imply that CMIP5 model errors in SW surface fluxes are (if anything) somewhat larger than previous evaluation studies suggest. The bias in LW surface flux shows a marked increase at night, which explains most of the total LW bias. The nighttime bias is due to poor representation of cloud base associated with low clouds. Southern Ocean; Macquarie Island; MICRE; Surface Radiative Fluxes
Hobeichi, Sanaa; Abramowitz, Gab; Contractor, Steefan; Evans, JasonHobeichi, S., G. Abramowitz, S. Contractor, J. Evans, 2020: Evaluating Precipitation Datasets Using Surface Water and Energy Budget Closure. J. Hydrometeor., 21(5), 989-1009. doi: 10.1175/JHM-D-19-0255.1. Evaluation of global gridded precipitation datasets typically entails using the in situ or satellite-based data used to derive them, so that out-of-sample testing is usually not possible. Here we detail a methodology that incorporates the physical balance constraints of the surface water and energy budgets to evaluate gridded precipitation estimates, providing the capacity for out-of-sample testing. Performance conclusions are determined by the ability of precipitation products to achieve closure of the linked budgets using adjustments that are within their prescribed uncertainty bounds. We evaluate and compare five global gridded precipitation datasets: IMERG, GPCP, GPCC, REGEN, and MERRA-2. At the spatial level, we show that precipitation is best estimated by GPCC over the high latitudes, by GPCP over the tropics, and by REGEN over North Africa and the Middle East. IMERG and REGEN appear best over Australia and South Asia. Furthermore, our results give insight into the adequacy of prescribed uncertainties of these products and shows that MERRA-2, while being less competent than the other four products in estimating precipitation, has the best representation of uncertainties in its precipitation estimates. The spatial extent of our results is not only limited to grid cells with in situ observations. Therefore, the approach enables a robust evaluation of precipitation estimates and goes some way to addressing the challenge of validation over observation scarce regions.
Hobeichi, Sanaa; Abramowitz, Gab; Evans, JasonHobeichi, S., G. Abramowitz, J. Evans, 2020: Conserving Land–Atmosphere Synthesis Suite (CLASS). J. Climate, 33(5), 1821-1844. doi: 10.1175/JCLI-D-19-0036.1. Accurate estimates of terrestrial water and energy cycle components are needed to better understand climate processes and improve models’ ability to simulate future change. Various observational estimates are available for the individual budget terms; however, these typically show inconsistencies when combined in a budget. In this work, a Conserving Land–Atmosphere Synthesis Suite (CLASS) of estimates of simultaneously balanced surface water and energy budget components is developed. Individual CLASS variable datasets, where possible, 1) combine a range of existing variable product estimates, and hence overcome the limitations of estimates from a single source; 2) are observationally constrained with in situ measurements; 3) have uncertainty estimates that are consistent with their agreement with in situ observations; and 4) are consistent with each other by being able to solve the water and energy budgets simultaneously. First, available datasets of a budget variable are merged by implementing a weighting method that accounts both for the ability of datasets to match in situ measurements and the error covariance between datasets. Then, the budget terms are adjusted by applying an objective variational data assimilation technique (DAT) that enforces the simultaneous closure of the surface water and energy budgets linked through the equivalence of evapotranspiration and latent heat. Comparing component estimates before and after applying the DAT against in situ measurements of energy fluxes and streamflow showed that modified estimates agree better with in situ observations across various metrics, but also revealed some inconsistencies between water budget terms in June over the higher latitudes. CLASS variable estimates are freely available via https://doi.org/10.25914/5c872258dc183.
Hogikyan, Allison; Cronin, Meghan F.; Zhang, Dongxiao; Kato, SeijiHogikyan, A., M. F. Cronin, D. Zhang, S. Kato, 2020: Uncertainty in Net Surface Heat Flux due to Differences in Commonly Used Albedo Products. J. Climate, 33(1), 303-315. doi: 10.1175/JCLI-D-18-0448.1. The ocean surface albedo is responsible for the distribution of solar (shortwave) radiant energy between the atmosphere and ocean and therefore is a key parameter in Earth’s surface energy budget. In situ ocean observations typically do not measure upward reflected solar radiation, which is necessary to compute net solar radiation into the ocean. Instead, the upward component is computed from the measured downward component using an albedo estimate. At two NOAA Ocean Climate Station buoy sites in the North Pacific, the International Satellite Cloud Climatology Project (ISCCP) monthly climatological albedo has been used, while for the NOAA Global Tropical Buoy Array a constant albedo is used. This constant albedo is also used in the Coupled Ocean–Atmosphere Response Experiment (COARE) bulk flux algorithm. This study considers the impacts of using the more recently available NASA Cloud and the Earth’s Radiant Energy System (CERES) albedo product for these ocean surface heat flux products. Differences between albedo estimates in global satellite products like these imply uncertainty in the net surface solar radiation heat flux estimates that locally exceed the target uncertainty of 1.0 W m−2 for the global mean, set by the Global Climate Observing System (GCOS) of the World Meteorological Organization (WMO). Albedo has large spatiotemporal variability on hourly, monthly, and interannual time scales. Biases in high-resolution SWnet (the difference between surface downwelling and upwelling shortwave radiation) can arise if the albedo diurnal cycle is unresolved. As a result, for periods when satellite albedo data are not available it is recommended that an hourly climatology be used when computing high-resolution net surface shortwave radiation.
Horowitz, Larry W.; Naik, Vaishali; Paulot, Fabien; Ginoux, Paul A.; Dunne, John P.; Mao, Jingqiu; Schnell, Jordan; Chen, Xi; He, Jian; John, Jasmin G.; Lin, Meiyun; Lin, Pu; Malyshev, Sergey; Paynter, David; Shevliakova, Elena; Zhao, MingHorowitz, L. W., V. Naik, F. Paulot, P. A. Ginoux, J. P. Dunne, J. Mao, J. Schnell, X. Chen, J. He, J. G. John, M. Lin, P. Lin, S. Malyshev, D. Paynter, E. Shevliakova, M. Zhao, 2020: The GFDL Global Atmospheric Chemistry-Climate Model AM4.1: Model Description and Simulation Characteristics. Journal of Advances in Modeling Earth Systems, 12(10), e2019MS002032. doi: 10.1029/2019MS002032. We describe the baseline model configuration and simulation characteristics of GFDL's Atmosphere Model version 4.1 (AM4.1), which builds on developments at GFDL over 2013–2018 for coupled carbon-chemistry-climate simulation as part of the sixth phase of the Coupled Model Intercomparison Project. In contrast with GFDL's AM4.0 development effort, which focused on physical and aerosol interactions and which is used as the atmospheric component of CM4.0, AM4.1 focuses on comprehensiveness of Earth system interactions. Key features of this model include doubled horizontal resolution of the atmosphere ( 200 km to 100 km) with revised dynamics and physics from GFDL's previous-generation AM3 atmospheric chemistry-climate model. AM4.1 features improved representation of atmospheric chemical composition, including aerosol and aerosol precursor emissions, key land-atmosphere interactions, comprehensive land-atmosphere-ocean cycling of dust and iron, and interactive ocean-atmosphere cycling of reactive nitrogen. AM4.1 provides vast improvements in fidelity over AM3, captures most of AM4.0's baseline simulations characteristics and notably improves on AM4.0 in the representation of aerosols over the Southern Ocean, India, and China—even with its interactive chemistry representation—and in its manifestation of sudden stratospheric warmings in the coldest months. Distributions of reactive nitrogen and sulfur species, carbon monoxide, and ozone are all substantially improved over AM3. Fidelity concerns include degradation of upper atmosphere equatorial winds and of aerosols in some regions. Aerosols; Ozone; Earth System Model; Atmospheric Chemistry; Chemistry-Climate Model
Hotta, Haruka; Suzuki, Kentaroh; Goto, Daisuke; Lebsock, MatthewHotta, H., K. Suzuki, D. Goto, M. Lebsock, 2020: Climate Impact of Cloud Water Inhomogeneity through Microphysical Processes in a Global Climate Model. J. Climate, 33(12), 5195-5212. doi: 10.1175/JCLI-D-19-0772.1. This study investigates how subgrid cloud water inhomogeneity within a grid spacing of a general circulation model (GCM) links to the global climate through precipitation processes. The effect of the cloud inhomogeneity on autoconversion rate is incorporated into the GCM as an enhancement factor using a prognostic cloud water probability density function (PDF), which is assumed to be a truncated skewed-triangle distribution based on the total water PDF originally implemented. The PDF assumption and the factor are evaluated against those obtained by global satellite observations and simulated by a global cloud-system-resolving model (GCRM). Results show that the factor implemented exerts latitudinal variations, with higher values at low latitudes, qualitatively consistent with satellite observations and the GCRM. The GCM thus validated for the subgrid cloud inhomogeneity is then used to investigate how the characteristics of the enhancement factor affect global climate through sensitivity experiments with and without the factor incorporated. The latitudinal variation of the factor is found to have a systematic impact that reduces the cloud water and the solar reflection at low latitudes in the manner that helps mitigate the too-reflective cloud bias common among GCMs over the tropical oceans. Due to the limitation of the factor arising from the PDF assumption, however, no significant impact is found in the warm rain formation process. Finally, it is shown that the functional form for the PDF in a GCM is crucial to properly characterize the observed cloud water inhomogeneity and its relationship with precipitation.
Hou, Ning; Zhang, Xiaotong; Zhang, Weiyu; Wei, Yu; Jia, Kun; Yao, Yunjun; Jiang, Bo; Cheng, JieHou, N., X. Zhang, W. Zhang, Y. Wei, K. Jia, Y. Yao, B. Jiang, J. Cheng, 2020: Estimation of Surface Downward Shortwave Radiation over China from Himawari-8 AHI Data Based on Random Forest. Remote Sensing, 12(1), 181. doi: 10.3390/rs12010181. Downward shortwave radiation (RS) drives many processes related to atmosphere–surface interactions and has great influence on the earth’s climate system. However, ground-measured RS is still insufficient to represent the land surface, so it is still critical to generate high accuracy and spatially continuous RS data. This study tries to apply the random forest (RF) method to estimate the RS from the Himawari-8 Advanced Himawari Imager (AHI) data from February to May 2016 with a two-km spatial resolution and a one-day temporal resolution. The ground-measured RS at 86 stations of the Climate Data Center of the Chinese Meteorological Administration (CDC/CMA) are collected to evaluate the estimated RS data from the RF method. The evaluation results indicate that the RF method is capable of estimating the RS well at both the daily and monthly time scales. For the daily time scale, the evaluation results based on validation data show an overall R value of 0.92, a root mean square error (RMSE) value of 35.38 (18.40%) Wm−2, and a mean bias error (MBE) value of 0.01 (0.01%) Wm−2. For the estimated monthly RS, the overall R was 0.99, the RMSE was 7.74 (4.09%) Wm−2, and the MBE was 0.03 (0.02%) Wm−2 at the selected stations. The comparison between the estimated RS data over China and the Clouds and Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) RS dataset was also conducted in this study. The comparison results indicate that the RS estimates from the RF method have comparable accuracy with the CERES-EBAF RS data over China but provide higher spatial and temporal resolution. downward shortwave radiation; Himawari-8 AHI; machine learning methods; multi-channel; Random Forest
Hourdin, Frédéric; Rio, Catherine; Grandpeix, Jean-Yves; Madeleine, Jean-Baptiste; Cheruy, Frédérique; Rochetin, Nicolas; Jam, Arnaud; Musat, Ionela; Idelkadi, Abderrahmane; Fairhead, Laurent; Foujols, Marie-Alice; Mellul, Lidia; Traore, Abdoul-Khadre; Dufresne, Jean-Louis; Boucher, Olivier; Lefebvre, Marie-Pierre; Millour, Ehouarn; Vignon, Etienne; Jouhaud, Jean; Diallo, F. Binta; Lott, François; Gastineau, Guillaume; Caubel, Arnaud; Meurdesoif, Yann; Ghattas, JosefineHourdin, F., C. Rio, J. Grandpeix, J. Madeleine, F. Cheruy, N. Rochetin, A. Jam, I. Musat, A. Idelkadi, L. Fairhead, M. Foujols, L. Mellul, A. Traore, J. Dufresne, O. Boucher, M. Lefebvre, E. Millour, E. Vignon, J. Jouhaud, F. B. Diallo, F. Lott, G. Gastineau, A. Caubel, Y. Meurdesoif, J. Ghattas, 2020: LMDZ6A: the atmospheric component of the IPSL climate model with improved and better tuned physics. Journal of Advances in Modeling Earth Systems, 12(7), e2019MS001892. doi: 10.1029/2019MS001892. This study presents the version of the LMDZ global atmospheric model used as the atmospheric component of the Institut Pierre Simon Laplace coupled model (IPSL-CM6A-LR) to contribute to the 6th phase of the international Coupled Model Intercomparison Project (CMIP6). This LMDZ6A version includes original convective parameterizations that define the LMDZ 'New Physics’: a mass flux parameterization of the organized structures of the convective boundary layer, the 'thermal plume model', and a parameterization of the cold pools created by reevaporation of convective rainfall. The vertical velocity associated with thermal plumes and gust fronts of cold pools are used to control the triggering and intensity of deep convection. Because of several shortcomings, the early version 5B of this ‘New Physics’ was worse than the previous 'Standard Physics' version 5A regarding several classical climate metrics. To overcome these deficiencies, version 6A includes new developments: a stochastic triggering of deep convection, a modification of the thermal plume model that allows the representation of stratocumulus and cumulus clouds in a unified framework, an improved parameterization of very stable boundary layers, and the modification of the gravity waves scheme targeting the quasi biennal oscillation in the stratosphere. These improvements to the physical content and a more well-defined tuning strategy led to major improvements in the LMDZ6A version model climatology. Beyond the presentation of this particular model version and documentation of its climatology, the present paper underlines possible methodological pathways toward model improvement that can be shared across modeling groups. Climate model development; tuning
Hourdin, Frédéric; Rio, Catherine; Jam, Arnaud; Traore, Abdoul-Khadre; Musat, IonelaHourdin, F., C. Rio, A. Jam, A. Traore, I. Musat, 2020: Convective Boundary Layer Control of the Sea Surface Temperature in the Tropics. Journal of Advances in Modeling Earth Systems, 12(6), e2019MS001988. doi: 10.1029/2019MS001988. Using successive versions of a global climate model, we show how convective transport to the free troposphere of the humidity evaporated at the surface or, reciprocally, entrainment of dry air from the free troposphere into the mixed layer, controls surface evaporative cooling and then sea surface temperature. This control is as important as the radiative effect of boundary layer clouds on radiation. Those aspects are shown to be improved when activating a mass flux representation of the organized structures of the convective boundary layer coupled to eddy diffusion, the so-called “thermal plume model,” leading to an increased near-surface drying compared to the use of turbulent diffusion alone. Controlling detrainment by air properties from just above the boundary layer allows the thermal plume model to be valid for both cumulus and stratocumulus regimes, improving the contrast in near-surface humidity between the trade winds region and East Tropical oceans. Using pairs of stand-alone atmospheric simulations forced by sea surface temperature and of coupled atmosphere-ocean simulations, we show how the improvement of the surface fluxes that arise from this improved physics projects into an improvement of the representation of sea surface temperature patterns in the coupled model, and in particular into a reduction of the East Tropical Ocean warm bias. The work presented here led to the bias reduction in sea surface temperature in the Institute Pierre Simon Laplace coupled model, IPSL-CM6A, developed recently for the 6th phase of the Coupled Model Intercomparison Project, CMIP6. convective boundary layer; SST warm biases; stratocumulus clouds
Hua, Shan; Liu, Yuzhi; Luo, Run; Shao, Tianbin; Zhu, QingzheHua, S., Y. Liu, R. Luo, T. Shao, Q. Zhu, 2020: Inconsistent aerosol indirect effects on water clouds and ice clouds over the Tibetan Plateau. International Journal of Climatology, 40(8), 3832-3848. doi: 10.1002/joc.6430. Recently, satellites have observed that dust events are occurring more frequently over the Tibetan Plateau (TP), which implies a new issue of aerosols influencing cloud properties and presents a new challenge in research on the role of the TP in climate change. In this study, combining satellite observations with Climate Model Intercomparison Project Phase 5 (CMIP5) model simulations, the inconsistent aerosol indirect effects on the properties of water clouds and ice clouds over the TP are compared and quantified. Analyses of satellite observations show that, compared with water clouds, ice clouds are observed more frequently and are more significantly correlated with aerosols over the TP. Correspondingly, the aerosol effect on the radiative forcing of ice clouds is more significant than that on the forcing of water clouds, in which the aerosol indirect effect is dominated by the effect on the shortwave radiative forcing of ice clouds. Both observations and CMIP5 model simulation results show that, due to the variation of aerosols, changes in the ice cloud radiative forcing cover most of the TP, while changes in the water cloud radiative forcing mainly appear over the southern edge of the TP. The CMIP5 simulation results suggest that the aerosol indirect effect on the total radiative forcing of water clouds over the TP is −0.34 (±0.03) W⋅m−2, while that on the forcing of ice clouds is −0.73 (±0.03) W⋅m−2. Overall, both the model simulations and satellite results show that the indirect effect of aerosols on ice clouds is more pronounced than that on water clouds. cloud; aerosol; indirect effect; Tibetan Plateau
Huang, Guan; Liu, Qiong; Wang, Yanyu; He, Qianshan; Chen, Yonghang; Jin, Lili; Liu, Tongqiang; He, Qing; Gao, Jiacheng; Zhao, Keming; Liu, PingpingHuang, G., Q. Liu, Y. Wang, Q. He, Y. Chen, L. Jin, T. Liu, Q. He, J. Gao, K. Zhao, P. Liu, 2020: The accuracy improvement of clear-sky surface shortwave radiation derived from CERES SSF dataset with a simulation analysis. Science of The Total Environment, 749, 141671. doi: 10.1016/j.scitotenv.2020.141671. Towards the Xiaotang region along the northern margin of the China's largest desert, a quantitative assessment of the precision of clear-sky satellite observations (the Single Scanner Footprint TOA/Surface Fluxes and Clouds downward surface shortwave radiation product of Clouds and the Earth's Radiant Energy System (CERES), DSSRCER) is conducted, the localized inversion mode of “absolutely clear-sky” downward surface shortwave radiation (DSSR) is established, and the “absolutely clear-sky” DSSR in Xiaotang during 2005–2018 is simulated by the Santa Barbara Discrete Atmospheric Radiative Transfer (SBDART) model. In general, under the “absolutely clear-sky” condition of Xiaotang region, there is a significant error in DSSRCER, and the simulated results of SBDART (DSSRSBD) with same input parameters as DSSRCER is better and more comparable. Single scattering albedo (SSA), asymmetry parameter (ASY) and aerosol optical depth (AOD) play crucial roles in deciding the accuracy of DSSR, and after parameter adjustment, the DSSRSBD is better than the initial, which is improved remarkably with all indexes of the fitting results greatly improved. The temporal variation of the DSSR during 2005–2018 indicates that the highest annual average value is found in 2008 (770.00 W·m−2), while the lowest appears in 2010 (600.97 W·m−2). Besides, the highest seasonal mean DSSR appears in summer, which between 860.6 and 935.07 W·m−2, while reaches the lowest in winter (403.79–587.53 W·m−2). Moreover, the monthly average DSSR changes as a curve with a single peak and is close to normal distribution, the highest appears in June (934.61 W·m−2), while the minimum with the value of 390.34 W·m−2 is found in December. All of the solar elevation angle, the characteristics of climate and aerosol particles in different seasons may contribute to the temporal variation. CERES; Correction; Downward surface shortwave radiation; LPSA; SBDART; Xiaotang
Hulswar, Shrivardhan; Menon, Harilal B.; Anilkumar, N.Hulswar, S., H. B. Menon, N. Anilkumar, 2020: Physical-chemical characteristics of composite aerosols in the Indian Ocean sector of the Southern Ocean and its associated effect on insolation: A climate perspective. Deep Sea Research Part II: Topical Studies in Oceanography, 104801. doi: 10.1016/j.dsr2.2020.104801. Aerosol optical depth (AOD), black carbon (BC) mass concentration, aerosol size, along with wind parameters, were derived during Southern Ocean expeditions (SOE) 7 and 8 carried out in austral summer of 2013 and 2015, with an aim to analyse the effect of aerosol on incoming solar radiation. The data were complemented with trace metals from aerosol samples of SOE-6 conducted in 2012. The AOD spectra north of 40oS followed Angstrom turbidity formulae while those in the south deviated from it. A statistically significant correlation (R2) of 0.79 (P « 0.0001) between the differences of AOD440 estimated from an Optical Properties of Aerosol and Cloud (OPAC) model and measured in situ and chlorophyll-a concentration revealed phytoplankton as a significant source of fine mode aerosols. Analysis of ten years of MODIS derived fine mode particle concentration indicated an increase as season advanced from winter to summer and a subsequent decrease towards the following winter, clearly showing a contribution from phytoplankton. BC mass concentration was found to be around 80 ng m−3. Prevalence of trace metals such as Cu, Cd and Zn and the anions SO4−4-2 and NO3−3-1 were observed in this part of the world ocean. An inverse relation was observed between Cu and phytoplankton derived SO4−4-2, indicating the detrimental effect of Cu on fine mode sulphate aerosols which are as significant as cloud condensation nuclei (CCN). The aerosol radiative forcing was found to be between 25 and –28 W m−2 to the north of the ITCZ while it was around 2–6 W m−2 in the south. The associated heating rate was from 0.05 to –0.09 and from 0.01 to –0.02 K day−1, respectively. The study revealed an increase in black carbon due to ship emissions. An increase in BC over the Southern Ocean atmosphere may have a far-reaching effect on the cloud formation and regional albedo.
Ji, Peng; Yuan, Xing; Li, DanJi, P., X. Yuan, D. Li, 2020: Atmospheric Radiative Processes Accelerate Ground Surface Warming over the Southeastern Tibetan Plateau during 1998–2013. J. Climate, 33(5), 1881-1895. doi: 10.1175/JCLI-D-19-0410.1. The Tibetan Plateau (TP), known as the world’s “Third Pole,” plays a vital role in regulating the regional and global climate and provides freshwater for about 1.5 billion people. Observations show an accelerated ground surface warming trend over the southeastern TP during the global warming slowdown period of 1998–2013, especially in the summer and winter seasons. The processes responsible for such acceleration are under debate as contributions from different radiative processes are still unknown. Here we estimate for the first time the contributions of each radiative component to the ground surface warming trend before and after 1998 by analyzing multisource datasets under an energy balance framework. Results show that declining cloud cover caused by the weakening of both the South Asian summer monsoon and local-scale atmospheric upward motion mainly led to the accelerated ground surface warming during the summers of 1998–2013, whereas the decreased surface albedo caused by the snow melting was the major warming factor in winter. Moreover, increased clear-sky longwave radiation induced by the warming middle and upper troposphere was the second largest factor, contributing to about 21%–48% of the ground surface warming trend in both the summer and winter seasons. Our results unravel the key processes driving the ground surface warming over the southeastern TP and have implications for the development of climate and Earth system models in simulating ground surface temperature change and other related complex cryosphere–hydrosphere–atmosphere interactions over high-altitude land areas.
Jian, Bida; Li, Jiming; Zhao, Yuxin; He, Yongli; Wang, Jing; Huang, JianpingJian, B., J. Li, Y. Zhao, Y. He, J. Wang, J. Huang, 2020: Evaluation of the CMIP6 planetary albedo climatology using satellite observations. Climate Dynamics, 54(11), 5145-5161. doi: 10.1007/s00382-020-05277-4. The Earth’s planetary albedo (PA) has an essential impact on the global radiation budget. Based on 14 years of monthly data from the Clouds and the Earth’s Radiant Energy System energy balanced and filled (CERES-EBAF) Ed4.1 dataset and atmosphere-only simulations of the Coupled Model Intercomparison Project Phase6 (CMIP6/AMIP), this study investigates the ability of CMIP6/AMIP model in reproducing the observed inter-month changes, annual cycle and trend of PA at near-global and regional scales. Statistical results indicate that some persistent biases in the previous models continue to exist in the CMIP6 models; however, some progresses have been made. In CMIP6/AMIP, large negative correlations for PA between the model ensemble mean and observation are addressed over the subtropical stratocumulus regions. In addition, the simulation of PA in drylands and tropical oceans remains a challenge in CMIP6 models. Over the most regions, PA biases are governed by cloud albedo forcing biases. These results demonstrate the importance of improving cloud process simulations for accurately representing the PA in models. For the annual cycles, the model ensemble mean captures the difference in amplitude between the two peak values of PA (June and December), as well as the phase of the seasonal cycle, despite PA is systematically overestimated. The differences between different terrestrial climatic regions are also examined. Results indicate that the relative biases of PA are greatest in semi-arid (2.2%) and semi-humid (2.8%) regions, whereas the minimum relative bias occurs in arid regions (0.3%) due to compensating errors.
Jin, Qinjian; Pryor, S. C.Jin, Q., S. C. Pryor, 2020: Long-term trends of high aerosol pollution events and their climatic impacts in North America using multiple satellite retrievals and MERRA-2. Journal of Geophysical Research: Atmospheres, 125(4), e2019JD031137. doi: 10.1029/2019JD031137. Mean magnitudes and temporal trends in Aerosol Optical Depth (AOD) from satellite observations and an aerosol reanalysis exhibit a negative-positive east-northwest dipole across the contiguous US with large magnitude negative trends over the eastern US while small magnitude positive trends over the northwestern states. Based on analyses of MERRA-2, the AOD reduction over the eastern US appears to be largely attributable to reductions in aerosol-sulfate, while there have been marked increases in aerosol-organic and elemental carbon over almost all of the contiguous US and particularly the northwestern states. Long-term trends of high aerosol pollution events (HAPE; days with AOD over the long-term local 90th daily AOD percentile) during 2000-2017 also indicate that over the eastern US, both the frequency and spatial scale of summer HAPEs exhibit significant negative trends, while those of moderate aerosol events (days with AOD between the local 30th and 70th AOD percentiles) exhibit weak upward trends. Opposing trends, of smaller magnitude, are derived in the north-western US and southwestern Canada. Net and shortwave solar radiation show positive trends at the surface and top of atmosphere under clear-sky conditions over the eastern US consistent with the reduction in AOD. However, skin temperatures do not indicate significant trends during all days or HAPEs, indicating that the aerosol-induced radiation trends are not sufficient to manifest trends in surface temperature. Precipitation during HAPEs appears to have increased during 2000-2017 over the eastern and central US, indicating that the reduction in aerosol may already be enhancing the precipitation through aerosol-cloud interactions. CERES; aerosol-precipitation interaction; extreme aerosol trend; MERRA2; North America; satellite retrieval
Johnson, Richard H.; Ciesielski, Paul E.Johnson, R. H., P. E. Ciesielski, 2020: Potential Vorticity Generation by West African Squall Lines. Mon. Wea. Rev., 148(4), 1691-1715. doi: 10.1175/MWR-D-19-0342.1. The West African summer monsoon features multiple, complex interactions between African easterly waves (AEWs), moist convection, variable land surface properties, dust aerosols, and the diurnal cycle. One aspect of these interactions, the coupling between convection and AEWs, is explored using observations obtained during the 2006 African Monsoon Multidisciplinary Analyses (AMMA) field campaign. During AMMA, a research weather radar operated at Niamey, Niger, where it surveilled 28 squall-line systems characterized by leading convective lines and trailing stratiform regions. Nieto Ferreira et al. found that the squall lines were linked with the passage of AEWs and classified them into two tracks, northerly and southerly, based on the position of the African easterly jet (AEJ). Using AMMA sounding data, we create a composite of northerly squall lines that tracked on the cyclonic shear side of the AEJ. Latent heating within the trailing stratiform regions produced a midtropospheric positive potential vorticity (PV) anomaly centered at the melting level, as commonly observed in such systems. However, a unique aspect of these PV anomalies is that they combined with a 400–500-hPa positive PV anomaly extending southward from the Sahara. The latter feature is a consequence of the deep convective boundary layer over the hot Saharan Desert. Results provide evidence of a coupling and merging of two PV sources—one associated with the Saharan heat low and another with latent heating—that ends up creating a prominent midtropospheric positive PV maximum to the rear of West African squall lines.
Jose, Subin; Nair, Vijayakumar S.; Babu, S. SureshJose, S., V. S. Nair, S. S. Babu, 2020: Anthropogenic emissions from South Asia reverses the aerosol indirect effect over the northern Indian Ocean. Scientific Reports, 10(1), 18360. doi: 10.1038/s41598-020-74897-x. Atmospheric aerosols play an important role in the formation of warm clouds by acting as efficient cloud condensation nuclei (CCN) and their interactions are believed to cool the Earth-Atmosphere system (‘first indirect effect or Twomey effect’) in a highly uncertain manner compared to the other forcing agents. Here we demonstrate using long-term (2003–2016) satellite observations (NASA’s A-train satellite constellations) over the northern Indian Ocean, that enhanced aerosol loading (due to anthropogenic emissions) can reverse the first indirect effect significantly. In contrast to Twomey effect, a statistically significant increase in cloud effective radius (CER, µm) is observed with respect to an increase in aerosol loading for clouds having low liquid water path (LWP
Jouan, Caroline; Milbrandt, Jason A.; Vaillancourt, Paul A.; Chosson, Frédérick; Morrison, HughJouan, C., J. A. Milbrandt, P. A. Vaillancourt, F. Chosson, H. Morrison, 2020: Adaptation of the Predicted Particles Properties (P3) microphysics scheme for large-scale numerical weather prediction. Wea. Forecasting, 35(6), 2541-2565. doi: 10.1175/WAF-D-20-0111.1.
Kang, Hyoji; Choi, Yong-Sang; Hwang, Jiwon; Kim, Hye-SilKang, H., Y. Choi, J. Hwang, H. Kim, 2020: On the cloud radiative effect for tropical high clouds overlying low clouds. Geoscience Letters, 7(1), 7. doi: 10.1186/s40562-020-00156-6. Since high and low clouds ubiquitously overlie the Tropical Western Pacific (TWP) region, the cloud radiative effect (CRE) cannot be influenced by either high or low clouds, but by combinations of the clouds. This study investigates the CRE of multi-layered clouds in TWP via a radiative transfer model, Streamer. We assumed that multi-layered clouds are composed of full coverage of high clouds overlying low clouds with fractional coverage. The simulation results show that low clouds readily change CREs from positive to negative in the case of optically thin high clouds, even if the fraction of low clouds takes 10% of that of high clouds. Also, various combinations of physical properties of multi-layered high and low clouds allow more CRE variability (− 253.76 to 93.10 W m−2) than single-layered clouds do (− 101.62 to 96.95 W m−2). Even in the same conditions (total column cloud optical thickness = 15 and high cloud top pressure = 200 hPa), the multi-layer clouds have various CREs from − 180.55 to 45.64 W m−2, while the single-layer high clouds − 2.00 W m−2. These findings are also comparable with satellite observations from CERES and CALIPSO. The present study suggests that considerable uncertainty of radiative effects of high clouds over TWP can attribute to low clouds below high clouds.
Kato, Seiji; Rose, Fred G.Kato, S., F. G. Rose, 2020: Global and Regional Entropy Production by Radiation Estimated from Satellite Observations. J. Climate, 33(8), 2985-3000. doi: 10.1175/JCLI-D-19-0596.1. Vertical profiles of shortwave and longwave irradiances computed with satellite-derived cloud properties and temperature and humidity profiles from reanalysis are used to estimate entropy production. Entropy production by shortwave radiation is computed by the absorbed irradiance within layers in the atmosphere and by the surface divided by their temperatures. Similarly, entropy production by longwave radiation is computed by emitted irradiance to space from layers in the atmosphere and surface divided by their temperatures. Global annual mean entropy production by shortwave absorption and longwave emission to space are, respectively, 0.852 and 0.928 W m−2 K−1. With a steady-state assumption, entropy production by irreversible processes within the Earth system is estimated to be 0.076 W m−2 K−1 and by nonradiative irreversible processes to be 0.049 W m−2 K−1. Both global annual mean entropy productions by shortwave absorption and longwave emission to space increase with increasing shortwave absorption (i.e., with decreasing the planetary albedo). The increase of entropy production by shortwave absorption is, however, larger than the increase of entropy production by longwave emission to space. The result implies that global annual mean entropy production by irreversible processes decreases with increasing shortwave absorption. Input and output temperatures derived by dividing the absorbed shortwave irradiance and emitted longwave irradiance to space by respective entropy production are, respectively, 282 and 259 K, which give the Carnot efficiency of the Earth system of 8.5%.
Kelley, Maxwell; Schmidt, Gavin A.; Nazarenko, Larissa S.; Bauer, Susanne E.; Ruedy, Reto; Russell, Gary L.; Ackerman, Andrew S.; Aleinov, Igor; Bauer, Michael; Bleck, Rainer; Canuto, Vittorio; Cesana, Grégory; Cheng, Ye; Clune, Thomas L.; Cook, Ben I.; Cruz, Carlos A.; Genio, Anthony D. Del; Elsaesser, Gregory S.; Faluvegi, Greg; Kiang, Nancy Y.; Kim, Daehyun; Lacis, Andrew A.; Leboissetier, Anthony; LeGrande, Allegra N.; Lo, Ken K.; Marshall, John; Matthews, Elaine E.; McDermid, Sonali; Mezuman, Keren; Miller, Ron L.; Murray, Lee T.; Oinas, Valdar; Orbe, Clara; García‐Pando, Carlos Pérez; Perlwitz, Jan P.; Puma, Michael J.; Rind, David; Romanou, Anastasia; Shindell, Drew T.; Sun, Shan; Tausnev, Nick; Tsigaridis, Kostas; Tselioudis, George; Weng, Ensheng; Wu, Jingbo; Yao, Mao-SungKelley, M., G. A. Schmidt, L. S. Nazarenko, S. E. Bauer, R. Ruedy, G. L. Russell, A. S. Ackerman, I. Aleinov, M. Bauer, R. Bleck, V. Canuto, G. Cesana, Y. Cheng, T. L. Clune, B. I. Cook, C. A. Cruz, A. D. D. Genio, G. S. Elsaesser, G. Faluvegi, N. Y. Kiang, D. Kim, A. A. Lacis, A. Leboissetier, A. N. LeGrande, K. K. Lo, J. Marshall, E. E. Matthews, S. McDermid, K. Mezuman, R. L. Miller, L. T. Murray, V. Oinas, C. Orbe, C. P. García‐Pando, J. P. Perlwitz, M. J. Puma, D. Rind, A. Romanou, D. T. Shindell, S. Sun, N. Tausnev, K. Tsigaridis, G. Tselioudis, E. Weng, J. Wu, M. Yao, 2020: GISS-E2.1: Configurations and Climatology. Journal of Advances in Modeling Earth Systems, 12(8), e2019MS002025. doi: 10.1029/2019MS002025. This paper describes the GISS-E2.1 contribution to the Coupled Model Intercomparison Project, Phase 6 (CMIP6). This model version differs from the predecessor model (GISS-E2) chiefly due to parameterization improvements to the atmospheric and ocean model components, while keeping atmospheric resolution the same. Model skill when compared to modern era climatologies is significantly higher than in previous versions. Additionally, updates in forcings have a material impact on the results. In particular, there have been specific improvements in representations of modes of variability (such as the Madden-Julian Oscillation and other modes in the Pacific) and significant improvements in the simulation of the climate of the Southern Oceans, including sea ice. The effective climate sensitivity to 2 × CO2 is slightly higher than previously at 2.7–3.1°C (depending on version) and is a result of lower CO2 radiative forcing and stronger positive feedbacks. climate change; CMIP6; General Circulation Model; NASA GISS
Kotsuki, Shunji; Sato, Yousuke; Miyoshi, TakemasaKotsuki, S., Y. Sato, T. Miyoshi, 2020: Data Assimilation for Climate Research: Model Parameter Estimation of Large-Scale Condensation Scheme. Journal of Geophysical Research: Atmospheres, 125(1), e2019JD031304. doi: 10.1029/2019JD031304. This study proposes using data assimilation (DA) for climate research as a tool for optimizing model parameters objectively. Mitigating radiation bias is very important for climate change assessments with general circulation models. With the Nonhydrostatic ICosahedral Atmospheric Model (NICAM), this study estimated an autoconversion parameter in a large-scale condensation scheme. We investigated two approaches to reducing radiation bias: examining useful satellite observations for parameter estimation and exploring the advantages of estimating spatially varying parameters. The parameter estimation accelerated autoconversion speed when we used liquid water path, outgoing longwave radiation, or outgoing shortwave radiation (OSR). Accelerated autoconversion reduced clouds and mitigated overestimated OSR bias of the NICAM. An ensemble-based DA with horizontal localization can estimate spatially varying parameters. When liquid water path was used, the local parameter estimation resulted in better cloud representations and improved OSR bias in regions where shallow clouds are dominant. radiation; data assimilation; global climate model; large-scale condensation; liquid water path; parameter estimation
Kratz, David P.; Gupta, Shashi K.; Wilber, Anne C.; Sothcott, Victor E.Kratz, D. P., S. K. Gupta, A. C. Wilber, V. E. Sothcott, 2020: Validation of the CERES Edition-4A Surface-Only Flux Algorithms. J. Appl. Meteor. Climatol., 59(2), 281-295. doi: 10.1175/JAMC-D-19-0068.1. Surface radiative fluxes have been derived with the objective of supplementing top-of-atmosphere (TOA) radiative fluxes being measured under NASA’s Clouds and the Earth’s Radiant Energy System (CERES) project. This has been accomplished by using combinations of CERES TOA measurements, parameterized radiative transfer algorithms, and high-quality meteorological datasets available from reanalysis projects. Current CERES footprint-level products include surface fluxes derived from two shortwave (SW) and three longwave (LW) algorithms designated as SW models A and B and LW models A, B, and C. The SW and LW models A work for clear conditions only; the other models work for both clear and cloudy conditions. The current CERES Edition-4A computed surface fluxes from all models are validated against ground-based flux measurements from high-quality surface networks like the Baseline Surface Radiation Network and NOAA’s Surface Radiation Budget Network (SURFRAD). Validation results as systematic and random errors are provided for all models, separately for five different surface types and combined for all surface types as tables and scatterplots. Validation of surface fluxes is now a part of CERES processing and is used to continually improve the above algorithms. Since both models B work for clear and cloudy conditions alike and meet the accuracy requirement, their results are considered to be the most reliable and most likely to be retained for future work. Both models A have limited use given that they work for clear skies only. Models B will continue to undergo further improvement as more validation results become available.
Kuma, P.; McDonald, A. J.; Morgenstern, O.; Alexander, S. P.; Cassano, J. J.; Garrett, S.; Halla, J.; Hartery, S.; Harvey, M. J.; Parsons, S.; Plank, G.; Varma, V.; Williams, J.Kuma, P., A. J. McDonald, O. Morgenstern, S. P. Alexander, J. J. Cassano, S. Garrett, J. Halla, S. Hartery, M. J. Harvey, S. Parsons, G. Plank, V. Varma, J. Williams, 2020: Evaluation of Southern Ocean cloud in the HadGEM3 general circulation model and MERRA-2 reanalysis using ship-based observations. Atmospheric Chemistry and Physics, 20(11), 6607–6630. doi: 10.5194/acp-20-6607-2020.
Largeron, Yann; Guichard, Françoise; Roehrig, Romain; Couvreux, Fleur; Barbier, JessicaLargeron, Y., F. Guichard, R. Roehrig, F. Couvreux, J. Barbier, 2020: The April 2010 North African heatwave: when the water vapor greenhouse effect drives nighttime temperatures. Climate Dynamics, 54(9), 3879-3905. doi: 10.1007/s00382-020-05204-7. North Africa experienced a severe heatwave in April 2010 with daily maximum temperatures ($$T_{max}$$Tmax) frequently exceeding $$40\,^{\circ }\mathrm{C}$$40∘Cand daily minimum temperatures ($$T_{min}$$Tmin) over $$27\,^{\circ }\mathrm{C}$$27∘Cfor more than five consecutive days in extended Saharan and Sahelian areas. Observations show that areas and periods affected by the heatwave correspond to strong positive anomalies of surface incoming longwave fluxes ($$LW_{in}$$LWin) and negative anomalies of incoming shortwave fluxes ($$SW_{in}$$SWin). The latter are explained by clouds in the Sahara, and by both clouds and dust loadings in the Sahel. However, the strong positive anomalies of $$LW_{in}$$LWinare hardly related to cloud or aerosol radiative effects. An analysis based on climate-model simulations (CNRM-AM) complemented by a specially-designed conceptual soil-atmospheric surface layer model (SARAWI) shows that this positive anomaly of $$LW_{in}$$LWinis mainly due to a water vapor greenhouse effect. SARAWI, which represents the two processes driving temperatures, namely turbulence and longwave radiative transfer between the soil and the atmospheric surface layer, points to the crucial impact of synoptic low-level advection of water vapor on $$T_{min}$$Tmin. By increasing the atmospheric infrared emissivity, the advected water vapor dramatically increases the nocturnal radiative warming of the soil surface, then in turn reducing the nocturnal cooling of the atmospheric surface layer, which remains warm throughout the night. Over Western Sahel, this advection is related to an early northward incursion of the monsoon flow. Over Sahara, the anomalously high precipitable water is due to a tropical plume event. Both observations and simulations support this major influence of the low-level water vapor radiative effect on $$T_{min}$$Tminduring this spring heatwave.
Lehmann, Peter; Bickel, Samuel; Wei, Zhongwang; Or, DaniLehmann, P., S. Bickel, Z. Wei, D. Or, 2020: Physical Constraints for Improved Soil Hydraulic Parameter Estimation by Pedotransfer Functions. Water Resources Research, 56(4), e2019WR025963. doi: 10.1029/2019WR025963. Global land surface models use spatially distributed soil information for the parameterization of soil hydraulic properties (SHP). Parameters of measured SHP are correlated with easy-to-measure soil properties to construct general pedotransfer functions (PTFs) used to predict SHP from spatial soil information. Global PTFs are based on a limited number of samples yielding highly variable and poorly constrained SHP. The study implements a physical constraint, soil-specific capillary length, to reduce unphysical combinations of SHP. The procedure fits concurrently soil water retention and capillary length using the same parameters. Results suggest that meeting the capillary length constraint has minor effects on the goodness of fit to soil water retention data. Constrained SHP were applied to represent 4 years of lysimeter fluxes yielding evapotranspiration values in close agreement with measurements relative to slight overestimation by unconstrained SHP. The procedure was applied for testing constraint SHP at a regional scale in New Zealand using the surface evaporation capacitance model and Noah-MP for detailed simulations of land surface processes. The use of constrained SHP in both models yields higher surface runoff in agreement with observations (unconstrained SHP severely underestimated runoff generation). The concept of constrained SHP could be extended to include other physical constraints to improve PTFs, for example, by consideration of vegetation cover and soil structure effects on infiltration. characteristic length; pedotransfer function; soil hydraulic properties; soil water characteristics
León, José Andrés PérezLeón, J., . Andrés Pérez, 2020: Progress towards assimilating cloud radar and lidar observations. ECMWF. Successful weather forecasts start from accurate estimates of the current state of the Earth system. Such estimates are obtained by combining model information with Earth system observations in a process called data assimilation. Recent work at ECMWF has demonstrated for the first time that assimilating cloud observations from satellite radar and lidar instruments into a global, operational forecasting system using a 4D-Var data assimilation system is feasible and improves weather forecasts.
Letu, Husi; Shi, Jiancheng; Li, Ming; Wang, Tianxing; Shang, Huazhe; Lei, Yonghui; Ji, Dabin; Wen, Jianguang; Yang, Kun; Chen, LiangfuLetu, H., J. Shi, M. Li, T. Wang, H. Shang, Y. Lei, D. Ji, J. Wen, K. Yang, L. Chen, 2020: A review of the estimation of downward surface shortwave radiation based on satellite data: Methods, progress and problems. Science China Earth Sciences, 63(6), 774-789. doi: 10.1007/s11430-019-9589-0. The estimation of downward surface shortwave radiation (DSSR) is important for the Earth’s energy budget and climate change studies. This review was organised from the perspectives of satellite sensors, algorithms and future trends, retrospects and summaries of the satellite-based retrieval methods of DSSR that have been developed over the past 10 years. The shortwave radiation reaching the Earth’s surface is affected by both atmospheric and land surface parameters. In recent years, studies have given detailed considerations to the factors which affect DSSR. It is important to improve the retrieval accuracy of cloud microphysical parameters and aerosols and to reduce the uncertainties caused by complex topographies and high-albedo surfaces (such as snow-covered areas) on DSSR estimation. This review classified DSSR retrieval methods into four categories: empirical, parameterisation, look-up table and machine-learning methods, and evaluated their advantages, disadvantages and accuracy. Further efforts are needed to improve the calculation accuracy of atmospheric parameters such as cloud, haze, water vapor and other land surface parameters such as albedo of complex terrain and bright surface, organically combine machine learning and other methods, use the new-generation geostationary satellite and polar orbit satellite data to produce high-resolution DSSR products, and promote the application of radiation products in hydrological and climate models.
Li, Jiandong; You, Qinglong; He, BianLi, J., Q. You, B. He, 2020: Distinctive spring shortwave cloud radiative effect and its inter-annual variation over southeastern China. Atmospheric Science Letters, 21(6), e970. doi: 10.1002/asl.970. The shortwave cloud radiative effect (SWCRE) plays a critical role in the earth's radiation balance, and its global mean magnitude is much larger than the warming effect induced by greenhouse gases. This study investigates the SWCRE at the top of the atmosphere and its inter-annual variation over southeastern China (SEC) using satellite retrievals and ERA-Interim reanalysis data. The results show that in this region the largest SWCRE with the maximum intensity up to −120 W·m−2 occurs in spring and is also the strongest between 60°S and 60°N. The domain-averaged intensity of SWCRE is much larger than the longwave cloud radiative effect (LWCRE), suggesting the dominant cooling role of SWCRE in the regional atmosphere–surface system. The spring SWCRE over SEC shows a weak increasing trend and its anomalies in most years exceed those of LWCRE during 2000–2017. This means that SWCRE also plays a dominant role in the inter-annual variation of regional cloud radiative effects. Over SEC, low- to mid-level ascending motion and water vapor convergence during spring favor the generation and maintenance of cloud water, leading to strong SWCRE. Statistical analysis shows that the spatial pattern and intensity of the spring SWCRE are well correlated with the low- to mid-level ascending motion and water vapor convergence. The temporal correlation coefficient between domain-averaged spring SWCRE and 850–500-hPa vertical velocity is .76 during 2000–2017. The long-term variation in spring SWCRE over SEC can be inferred to some extent from regional ascending motion and associated large-scale circulations. southeastern China; ascending motion; inter-annual variation; shortwave cloud radiative effect; spring
Li, Lijuan; Dong, Li; Xie, Jinbo; Tang, Yanli; Xie, Feng; Guo, Zhun; Liu, Hongbo; Feng, Tao; Wang, Lu; Pu, Ye; Sun, Wenqi; Xia, Kun; Liu, Li; Xie, Zhenghui; Wang, Yan; Wang, Longhuan; Shi, Xiangjun; Jia, Binghao; Liu, Juanjuan; Wang, BinLi, L., L. Dong, J. Xie, Y. Tang, F. Xie, Z. Guo, H. Liu, T. Feng, L. Wang, Y. Pu, W. Sun, K. Xia, L. Liu, Z. Xie, Y. Wang, L. Wang, X. Shi, B. Jia, J. Liu, B. Wang, 2020: The GAMIL3: Model Description and Evaluation. Journal of Geophysical Research: Atmospheres, 125(15), e2020JD032574. doi: 10.1029/2020JD032574. The Grid-point Atmospheric Model of the IAP LASG version 3 (GAMIL3) has been developed by upgrading the horizontal resolution, methods of parallel computation, boundary layer scheme, aerosol parameterization, convective parameterization, stratocumulus cloud fraction scheme, land component, and coupler, as well as tuning some moist physical parameters with large uncertainties. Its performance is evaluated, and the results show significant improvements compared with the previous version, GAMIL2. The simulated performance of mean states is notably enhanced, including the energy budget terms at the top of the atmosphere (TOA) and surface, shortwave/longwave cloud radiative forcing (SWCF/LWCF), precipitation, zonal wind, low-level temperature, 500-hPa geopotential height, and snow cover fraction in the Northern Hemisphere. The characteristics of internal variability are captured well, such as the frequency band and active areas of quasi-biweekly (QBW) oscillation, spectral power of convectively coupled equatorial waves (CCEWs), Madden-Julian Oscillation (MJO) eastward propagation, and heat flux response to El Niño-Southern Oscillation (ENSO), and these variabilities are generally strengthened in GAMIL3. In addition, the anthropogenic aerosol climate effects are weakened when using the forcings recommended by CMIP6.
Li, Xiaoyuan; Mauzerall, Denise L.; Bergin, Mike H.Li, X., D. L. Mauzerall, M. H. Bergin, 2020: Global reduction of solar power generation efficiency due to aerosols and panel soiling. Nature Sustainability, 3(9), 720-727. doi: 10.1038/s41893-020-0553-2. Air pollution and dust prevail over many regions that have rapid growth of solar photovoltaic (PV) electricity generation, potentially reducing PV generation. Here we combine solar PV performance modelling with long-term satellite-observation-constrained surface irradiance, aerosol deposition and precipitation rates to provide a global picture of the impact of particulate matter (PM) on PV generation. We consider attenuation caused by both atmospheric PM and PM deposition on panels (soiling) in calculating the overall effect of PM on PV generation, and include precipitation removal of soiling and the benefits of panel cleaning. Our results reveal that, with no cleaning and precipitation-only removal, PV generation in heavily polluted and desert regions is reduced by more than 50% by PM, with soiling accounting for more than two-thirds of the total reduction. Our findings highlight the benefit of cleaning panels in heavily polluted regions with low precipitation and the potential to increase PV generation through air-quality improvements.
Li, Xin; Liang, Hongyu; Cheng, WeimingLi, X., H. Liang, W. Cheng, 2020: Spatio-Temporal Variation in AOD and Correlation Analysis with PAR and NPP in China from 2001 to 2017. Remote Sensing, 12(6), 976. doi: 10.3390/rs12060976. Atmospheric aerosols can elicit variations in how much solar radiation reaches the ground surface due to scattering and absorption, which may affect plant photosynthesis and carbon uptake in terrestrial ecosystems. In this study, the spatio-temporal variations in aerosol optical depth (AOD) are compared with that in photosynthetically active radiation (PAR) and net primary productivity (NPP) during 2001–2017 in China using multiple remote sensing data. The correlations between them are analyzed at different scales. Overall, the AOD exhibited a northeast-to-southwest decreasing pattern in space. A national increasing trend of 0.004 year−1 and a declining trend of −0.007 year−1 of AOD are observed during 2001–2008 and 2009–2017. The direct PAR (PARdir) and diffuse PAR (PARdif) present consistent and opposite tendency with AOD during two periods, respectively. The total PAR (PARtotal) shows a similar variation pattern with PARdir. In terms of annual variation, the peaks of AOD coincide with the peaks of PARdif and the troughs of PARdir, indicating that aerosols have a significant positive impact on PARdir and a negative impact on PARdif. Furthermore, the PARdir has a stronger negative association with AOD than the positive correlation between PARdif and AOD at national and regional scales, indicating that PARdir is more sensitive to aerosol changes. The NPP has higher values in the east than in the west and exhibits a significant increasing trend of 0.035 gCm−2day−1 after 2008. The NPP has a negative correlation (−0.4–0) with AOD and PARdif and a positive correlation (0–0.4) with PARdir in most areas of China. The area covered by forests has the highest NPP-PAR correlation, indicating that NPP in forests is more sensitive to the PAR than is the NPP in grasslands and croplands. This study is beneficial for interpreting the aerosol-induced PAR impact on plant growth and for predicting plant production on haze days. AOD; PAR; correlation; NPP; spatio-temporal variation
Li, Zhujun; Xu, Kuan-ManLi, Z., K. Xu, 2020: Arctic Clouds Simulated by a Multiscale Modeling Framework and Comparisons With Observations and Conventional GCMs. Journal of Geophysical Research: Atmospheres, 125(1), e2019JD030522. doi: 10.1029/2019JD030522. Clouds are an important component of the Arctic climate system through their regulation of the surface energy budget; however, Arctic clouds are poorly simulated in global climate models (GCMs). In this study, we evaluate the Arctic clouds simulated by a multiscale modeling framework (MMF). The results are compared against a merged CloudSat-CALIPSO radar-lidar cloud product and contrasted with an atmospheric reanalysis and conventional GCMs. The comparisons focus on the annual cycle of cloud covers, vertical structures of cloud fraction, and condensate mixing ratio, as well as the relationships between low-cloud cover and atmospheric static stability. The MMF is found to represent Arctic boundary layer clouds slightly more realistically than the reanalysis and GCMs in both the annual cycle and vertical distribution except that middle- and high-cloud covers are underestimated and the amplitude of annual cycle of total cloud cover is larger. The relationship between low-cloud cover and near-surface atmospheric stability produced by MMF is remarkably similar to the satellite observation during autumn, winter, and early spring, as low-cloud cover decreases with colder surface and stronger stability. Such relationships over the annual cycle are not reproduced by other modeling approaches. Lastly, MMF yields a positive correlation between low-cloud cover and atmospheric stability over the Arctic ocean from May to August, opposite to the satellite observation, implying stronger control of horizontal advection on low-cloud formation. This modeled relationship is contributed by cloud fraction near the surface, which is known to be underestimated due to radar's surface clutter.
Lin, Yanluan; Huang, Xiaomeng; Liang, Yishuang; Qin, Yi; Xu, Shiming; Huang, Wenyu; Xu, Fanghua; Liu, Li; Wang, Yong; Peng, Yiran; Wang, Lanning; Xue, Wei; Fu, Haohuan; Zhang, Guang Jun; Wang, Bin; Li, Ruizhe; Zhang, Cheng; Lu, Hui; Yang, Kun; Luo, Yong; Bai, Yuqi; Song, Zhenya; Wang, Minqi; Zhao, Wenjie; Zhang, Feng; Xu, Jingheng; Zhao, Xi; Lu, Chunsong; Chen, Yizhao; Luo, Yiqi; Hu, Yong; Tang, Qiang; Chen, Dexun; Yang, Guangwen; Gong, PengLin, Y., X. Huang, Y. Liang, Y. Qin, S. Xu, W. Huang, F. Xu, L. Liu, Y. Wang, Y. Peng, L. Wang, W. Xue, H. Fu, G. J. Zhang, B. Wang, R. Li, C. Zhang, H. Lu, K. Yang, Y. Luo, Y. Bai, Z. Song, M. Wang, W. Zhao, F. Zhang, J. Xu, X. Zhao, C. Lu, Y. Chen, Y. Luo, Y. Hu, Q. Tang, D. Chen, G. Yang, P. Gong, 2020: Community Integrated Earth System Model (CIESM): Description and Evaluation. Journal of Advances in Modeling Earth Systems, 12(8), e2019MS002036. doi: 10.1029/2019MS002036. A team effort to develop a Community Integrated Earth System Model (CIESM) was initiated in China in 2012. The model was based on NCAR Community Earth System Model (Version 1.2.1) with several novel developments and modifications aimed to overcome some persistent systematic biases, such as the double Intertropical Convergence Zone problem and underestimated marine boundary layer clouds. Aerosols' direct and indirect effects are prescribed using the MACv2-SP approach and data sets. The spin-up of a 500-year preindustrial simulation and three historical simulations are described and evaluated. Prominent improvements include alleviated double Intertropical Convergence Zone problem, increased marine boundary layer clouds, and better El Niño Southern Oscillation amplitude and periods. One deficiency of the model is the significantly underestimated Arctic and Antarctic sea ice in warm seasons. The historical warming is about 0.55 °C greater than observations toward 2014. CIESM has an equilibrium climate sensitivity of 5.67 K, mainly resulted from increased positive shortwave cloud feedback. Our efforts on porting and redesigning CIESM for the heterogeneous Sunway TaihuLight supercomputer are also introduced, including some ongoing developments toward a future version of the model. preindustrial and historical simulations; Community Integrated Earth System Model; coupled model evaluation
Liu, Xin; Kang, Yanming; Liu, Qiong; Guo, Zijia; Chen, Yonghang; Huang, Dizhi; Chen, Chunmei; Zhang, HuaLiu, X., Y. Kang, Q. Liu, Z. Guo, Y. Chen, D. Huang, C. Chen, H. Zhang, 2020: Evaluation of net shortwave radiation over China with a regional climate model. Climate Research, 80(2), 147-163. doi: 10.3354/cr01598. The regional climate model RegCM version 4.6, developed by the European Centre for Medium-Range Weather Forecasts Reanalysis, was used to simulate the radiation budget over China. Clouds and the Earth’s Radiant Energy System (CERES) satellite data were utilized to evaluate the simulation results based on 4 radiative components: net shortwave (NSW) radiation at the surface of the earth and top of the atmosphere (TOA) under all-sky and clear-sky conditions. The performance of the model for low-value areas of NSW was superior to that for high-value areas. NSW at the surface and TOA under all-sky conditions was significantly underestimated; the spatial distribution of the bias was negative in the north and positive in the south, bounded by 25°N for the annual and seasonal averaged difference maps. Compared with the all-sky condition, the simulation effect under clear-sky conditions was significantly better, which indicates that the cloud fraction is the key factor affecting the accuracy of the simulation. In particular, the bias of the TOA NSW under the clear-sky condition was China; Net shortwave radiation; RegCM4.6; Regional climate mode
Loeb, Norman G.; Doelling, David R.Loeb, N. G., D. R. Doelling, 2020: CERES Energy Balanced and Filled (EBAF) from Afternoon-Only Satellite Orbits. Remote Sensing, 12(8), 1280. doi: 10.3390/rs12081280. The Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) data product uses a diurnal correction methodology to produce a shortwave (SW) top-of-atmosphere (TOA) radiative flux time series that accounts for diurnal cycle changes between CERES observation times while ensuring that the stability of the EBAF record is tied as closely as possible to CERES instrument calibration stability. The current EBAF Ed4.1 data product combines observations from Terra and Aqua after July 2002. However, the Terra satellite will start to drift in Mean Local Time (MLT) in early 2021, and Aqua’s MLT will start to drift in 2022. To ensure the EBAF record remains temporally stable, we explore the feasibility of using only CERES instruments from afternoon satellite orbits with a tight 1330 MLT after July 2002. We test this approach by directly comparing SW TOA fluxes generated after applying diurnal corrections to Aqua-only and to Terra + Aqua for 07/2002–06/2019. We find that global climatological mean SW TOA fluxes for these two cases are within 0.01 Wm−2 and the trend of the difference is < is 0.03 Wm−2 per decade. climate; radiation budget; diurnal
Loeb, Norman G.; Wang, Hailan; Allan, Richard P.; Andrews, Timothy; Armour, Kyle; Cole, Jason N. S.; Dufresne, Jean-Louis; Forster, Piers; Gettelman, Andrew; Guo, Huan; Mauritsen, Thorsten; Ming, Yi; Paynter, David; Proistosescu, Cristian; Stuecker, Malte F.; Willén, Ulrika; Wyser, KlausLoeb, N. G., H. Wang, R. P. Allan, T. Andrews, K. Armour, J. N. S. Cole, J. Dufresne, P. Forster, A. Gettelman, H. Guo, T. Mauritsen, Y. Ming, D. Paynter, C. Proistosescu, M. F. Stuecker, U. Willén, K. Wyser, 2020: New Generation of Climate Models Track Recent Unprecedented Changes in Earth's Radiation Budget Observed by CERES. Geophysical Research Letters, 47(5), e2019GL086705. doi: 10.1029/2019GL086705. We compare top-of-atmosphere (TOA) radiative fluxes observed by the Clouds and the Earth's Radiant Energy System (CERES) and simulated by seven general circulation models forced with observed sea-surface temperature (SST) and sea-ice boundary conditions. In response to increased SSTs along the equator and over the eastern Pacific (EP) following the so-called global warming “hiatus” of the early 21st century, simulated TOA flux changes are remarkably similar to CERES. Both show outgoing shortwave and longwave TOA flux changes that largely cancel over the west and central tropical Pacific, and large reductions in shortwave flux for EP low-cloud regions. A model's ability to represent changes in the relationship between global mean net TOA flux and surface temperature depends upon how well it represents shortwave flux changes in low-cloud regions, with most showing too little sensitivity to EP SST changes, suggesting a “pattern effect” that may be too weak compared to observations.
Ma, Libin; Yang, ShuangyanMa, L., S. Yang, 2020: Impacts of the stochastic multicloud parameterization on the simulation of Western North Pacific summer rainfall. Atmospheric Research, 244, 105067. doi: 10.1016/j.atmosres.2020.105067. This study investigated the sensitivity of the western North Pacific (WNP) summer precipitation to the convection schemes and discussed the associated dynamical processes. Two convection schemes were compared: one is the default mass-flux convection scheme used in the state-of-the-art ECHAM6.3 atmosphere model and the other incorporates the Stochastic Multicloud Model (SMCM) into ECHAM6.3. Incorporation of the SMCM reduces the bias of cloud cover and shortwave and longwave radiation by regulating the shortwave and longwave cloud radiative forcing over the WNP. Compared to the default model, the modified model with the SMCM alleviates the dry bias in the WNP, which is associated with enhanced ascending motion. The moist static energy balance revealed that improved simulation of precipitation in the modified model is contributed by enhanced horizontal advection of moist enthalpy and increased net energy in the atmosphere, which is attributed to increased total cloud cover, over the WNP. Additionally, intensified latent energy advection over the WNP dominates enhanced horizontal advection of moist enthalpy in the modified model. On the other hand, the moisture budget analysis of the WNP demonstrated that strengthened convergence of moisture flux in the modified model plays the most influential role in reducing precipitation bias. Further analysis unraveled that enhanced zonal-mean moisture transported by the stationary eddy zonal flow convergence in the WNP dominates intensified zonal moisture convergence, thus increased horizontal convergence of moist flux in the modified model. ECHAM6.3 atmosphere model; Moist static energy balance; Moisture budget analysis; The Stochastic Multicloud Model; The western North Pacific precipitation
Ma, Qianrong; Zhang, Jie; Gu, Yu; Ma, Yujun; Cao, YuMa, Q., J. Zhang, Y. Gu, Y. Ma, Y. Cao, 2020: Seasonal and Regional Variability of Long-Wave Effective Radiation in China and Associated Modulating Factors. Advances in Meteorology, 2020, 1689431. doi: 10.1155/2020/1689431. Variations in all-sky and clear-sky long-wave effective radiation (LER) in China during the period 2001–2016 were determined using monthly radiative datasets from the Clouds and the Earth’s Radiant Energy System (CERES). Annual and seasonal spatial distributions are found to be quite similar and show a decreasing trend from northwest to southeast, although highest values are found in spring. Mean LER under clear-sky conditions is approximately 20–30 Wm−2 higher than that under all-sky conditions. There is a consistent downward trend in annual and seasonal variations of LER under different weather conditions in China especially after 2007. In northwest China, the eastern Tibetan Plateau, and southeast and northeast China, LER is significantly reduced in two weather conditions and this is more pronounced in spring. However, decreases in clear-sky LER are more obvious. Empirical orthogonal function (EOF) results for LER differences between all-sky conditions and clear-sky conditions were used to analyze regional characteristics and modulating factors. The first mode shows that the LER differences of two weather conditions over China become larger and significant after 2007. The second mode reflects the spatial characteristics, and four climate regions are divided according to the second pattern. According to the definition of LER, regression analysis shows that downward long-wave radiation has a greater influence on LER. When considering cloud effects and other modulating factors, LER has higher correlation with relative humidity in climate regions 3 and 4. However, there are higher negative correlations with middle and high clouds in regions 1 and 2, which are modulated by cloud characteristics. When these factors influence LER together, their correlation is significant in all regions (correlation coefficients are on average higher than 0.7). In summary, changes of LER can well reflect the change of climate system.
Mantsis, Damianos F.; Sherwood, Steven; Dixit, Vishal; Morrison, Hugh; Thompson, GregMantsis, D. F., S. Sherwood, V. Dixit, H. Morrison, G. Thompson, 2020: Mid-level clouds over the Sahara in a convection-permitting regional model. Climate Dynamics, 54(7), 3425-3439. doi: 10.1007/s00382-020-05188-4. The simulation of Saharan mid tropospheric clouds is investigated with the weather research and forecasting (WRF) regional atmospheric model at convection permitting (4 km) horizontal grid-spacing. We identify two potential problems in such simulations: one that affects cloud cover, and another that affects the mean and geographic patterns of both cloud and precipitation. Our simulations show that using a vertical grid typical of GCMs (38 levels) inhibits the formation of Saharan mid-level clouds. In particular, it underestimates the supercooled water content that often resides at the top of these clouds, in favour of ice which falls out of the cloud quickly. When the vertical resolution becomes high enough to allow layers of supercooled water and ice to exist separately, the simulation of the Saharan mid-level clouds improves significantly. Additional improvement is achieved by using realistic high resolution surface albedo, which also shows that low albedo areas favour the formation of mid-level clouds much more than high albedo ones. The simulation of precipitation on the northern edge of the Sahel is also improved with the use of realistic surface albedo. Overall, despite the disagreement of the simulated and the observed clouds, our results show that using increased resolution and realistic surface albedo seems to fully reproduce their observed radiative effect.
Marchand, Roger T; Hinkelman, Laura M.Marchand, R. T., L. M. Hinkelman, 2020: Evaluation of CERES and CloudSat Surface Radiative Fluxes over the Southern Ocean. Earth and Space Science Open Archive, 32. doi: 10.1002/essoar.10502814.1. Many studies involving surface radiative fluxes rely on surface fluxes retrieved by the Clouds and the Earth&rsquo;s Radiant Energy System (CERES) project, or derived from spaceborne cloud radar and lidar observations (CloudSat-CALIPSO). In particular, most climate models that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) were found to have too little shortwave radiation being reflected back to space and excessive shortwave radiation reaching the surface over the Southern Ocean &ndash; an error with significant consequences for predicting both regional and global climate. There have been few evaluations of CERES or CloudSat retrievals over the Southern Ocean. In this article, CERES and CloudSat retrieved surface shortwave (SW) and longwave (LW) downwelling fluxes are evaluated using surface observations collected over the Southern Ocean during the Macquarie Island Cloud and Radiation Experiment (MICRE). Overall, biases (CERES &ndash; surface observations) in the CERES- surface fluxes are found to be slightly larger over Macquarie Island than most other regions, approximately +10 Wm for the SW and -10 Wm for the LW in the annual mean, but with significant seasonal and diurnal variations. If the Macquarie observations are representative of the larger SO, these results imply that CMIP5 model errors in SW surface fluxes are (if anything) somewhat larger than previous evaluation studies suggest. The bias in LW surface flux shows a marked increase at night, which explains most of the total LW bias. The nighttime bias is due to poor representation of cloud base associated with low clouds.
McCoy, Daniel T.; Field, Paul; Bodas-Salcedo, Alejandro; Elsaesser, Gregory S.; Zelinka, Mark D.McCoy, D. T., P. Field, A. Bodas-Salcedo, G. S. Elsaesser, M. D. Zelinka, 2020: A regime-oriented approach to observationally constraining extratropical shortwave cloud feedbacks. J. Climate, 33(23), 9967–9983. doi: 10.1175/JCLI-D-19-0987.1.
McGraw, Zachary; Storelvmo, Trude; David, Robert O.; Sagoo, NavjitMcGraw, Z., T. Storelvmo, R. O. David, N. Sagoo, 2020: Global Radiative Impacts of Mineral Dust Perturbations Through Stratiform Clouds. Journal of Geophysical Research: Atmospheres, 125(23), e2019JD031807. doi: https://doi.org/10.1029/2019JD031807. Airborne mineral dust influences cloud occurrence and optical properties, which may provide a pathway for recent and future changes in dust concentration to alter the temperature at Earth's surface. However, despite prior suggestions that dust-cloud interactions are an important control on the Earth's radiation balance, we find global mean cloud radiative effects to be insensitive to widespread dust changes. Here we simulate uniformly applied shifts in dust amount in a present-day atmosphere using a version of the CAM5 atmosphere model (within CESM v1.2.2) modified to incorporate laboratory-based ice nucleation parameterizations in stratiform clouds. Increasing and decreasing dustiness from current levels to paleoclimate extremes caused effective radiative forcings through clouds of +0.02 ± 0.01 and −0.05 ± 0.02 W/m2, respectively, with ranges of −0.26 to +0.13 W/m2 and −0.21 to +0.39 W/m2 from sensitivity tests. Our simulations suggest that these forcings are limited by several factors. Longwave and shortwave impacts largely cancel, particularly in mixed-phase clouds, while in warm and cirrus clouds opposite responses between regions further reduce each global forcing. Additionally, changes in dustiness cause opposite forcings through aerosol indirect effects in mixed-phase clouds as in cirrus, while in warm clouds indirect effects are weak at nearly all locations. Nevertheless, regional forcings and global impacts on longwave and shortwave radiation were found to be nonnegligible, suggesting that cloud-mediated dust effects have significance in simulations of present and future climate. cirrus clouds; mineral dust; aerosol indirect effects; mixed-phase clouds; climate modeling; ice nucleation
Minnis, Patrick; Sun-Mack, Szedung; Chen, Yan; Chang, Fu-Lung; Yost, Christopher R.; Smith, William L.; Heck, Patrick W.; Arduini, Robert F.; Bedka, Sarah T.; Yi, Yuhong; Hong, Gang; Jin, Zhonghai; Painemal, David; Palikonda, Rabindra; Scarino, Benjamin R.; Spangenberg, Douglas A.; Smith, Rita A.; Trepte, Qing Z.; Yang, Ping; Xie, YuMinnis, P., S. Sun-Mack, Y. Chen, F. Chang, C. R. Yost, W. L. Smith, P. W. Heck, R. F. Arduini, S. T. Bedka, Y. Yi, G. Hong, Z. Jin, D. Painemal, R. Palikonda, B. R. Scarino, D. A. Spangenberg, R. A. Smith, Q. Z. Trepte, P. Yang, Y. Xie, 2020: CERES MODIS Cloud Product Retrievals for Edition 4–Part I: Algorithm Changes. IEEE Transactions on Geoscience and Remote Sensing, 1-37. doi: 10.1109/TGRS.2020.3008866. The Edition 2 (Ed2) cloud property retrieval algorithm system was upgraded and applied to the MODerate-resolution Imaging Spectroradiometer (MODIS) data for the Clouds and the Earth's Radiant Energy System (CERES) Edition 4 (Ed4) products. New calibrations for solar channels and the use of the 1.24-μm channel for cloud optical depth (COD) over snow improve the daytime consistency between Terra and Aqua MODIS retrievals. Use of additional spectral channels and revised logic enhanced the cloud-top phase retrieval accuracy. A new ice crystal reflectance model and a CO₂-channel algorithm retrieved higher ice clouds, while a new regional lapse rate technique produced more accurate water cloud heights than in Ed2. Ice cloud base heights are more accurate due to a new cloud thickness parameterization. Overall, CODs increased, especially over the polar (PO) regions. The mean particle sizes increased slightly for water clouds, but more so for ice clouds in the PO areas. New experimental parameters introduced in Ed4 are limited in utility, but will be revised for the next CERES edition. As part of the Ed4 retrieval evaluation, the average properties are compared with those from other algorithms and the differences between individual reference data and matched Ed4 retrievals are explored. Part II of this article provides a comprehensive, objective evaluation of selected parameters. More accurate interpretation of the CERES radiation measurements has resulted from the use of the Ed4 cloud properties. cloud; Meteorology; MODIS; Optical imaging; Integrated optics; Clouds; Ice; Climate; Cloud computing; cloud height; cloud optical depth (COD); cloud phase; validation.; cloud particle size; cloud remote sensing MODerate-resolution Imaging Spectroradiometer (MODIS); clouds and the Earth's radiant energy system (CERES)
Muench, Steffen; Lohmann, UlrikeMuench, S., U. Lohmann, 2020: Developing a Cloud Scheme with Prognostic Cloud Fraction and Two Moment Microphysics for ECHAM-HAM. Journal of Advances in Modeling Earth Systems, 12(8), e2019MS001824. doi: 10.1029/2019MS001824. We present a new cloud scheme for the ECHAM-HAM global climate model (GCM) that includes prognostic cloud fraction, and allows for sub- and supersaturation with respect to ice separately in the cloud-free and cloudy air. Stratiform clouds form by convective detrainment, turbulent vertical diffusion, and large-scale ascent. For each process, the corresponding cloud fraction is calculated and the individual updraft velocities are used to determine cloud droplet/ice crystal number concentrations. Further, convective condensate is always detrained as supercooled cloud droplets at mixed-phase temperatures (between 235 and 273 K), and convectively detrained ice crystal number concentrations are calculated based on the updraft velocity. Finally, the new scheme explicitly calculates condensation/evaporation and deposition/sublimation rates for phase-change calculations. The new cloud scheme simulates a reasonable present-day climate, reduces the previously overestimated cirrus cloud fraction, and in general improves the simulation of ice clouds. The model simulates the observed in-cloud supersaturation for cirrus clouds, and it allows for a better representation of the tropical to extra-tropical ratio of the longwave cloud radiative effect. Further, the ice water path, the ice crystal number concentrations, and the supercooled liquid fractions in mixed-phase clouds agree better with observations in the new model than in the reference model. Ice crystal formation is dominated by the liquid-origin processes of convective detrainment and homogeneous freezing of cloud droplets. The simulated ice clouds strongly depend on model tuning choices, in particular, the enhancement of the aggregation rate of ice crystals. Cloud microphysics; Cloud cover; Clouds; Ice clouds; Climate model
Myers, Timothy A.; Mechoso, Carlos R.Myers, T. A., C. R. Mechoso, 2020: Relative Contributions of Atmospheric, Oceanic, and Coupled Processes to North Pacific and North Atlantic Variability. Geophysical Research Letters, 47(5), e2019GL086321. doi: 10.1029/2019GL086321. Patterns of sea surface temperature (SST) variability over the northern oceans arise from a combination of atmospheric, oceanic, and coupled processes. Here we use a novel methodology and a suite of observations to quantify the processes contributing to the dominant patterns of interannual SST variability over these regions. We decompose the upper ocean heat content tendency associated with such dominant patterns into contributions from different heat fluxes: (a) atmospherically driven, (b) surface feedbacks, and (c) oceanic. We find that in the subtropics, cloud radiative flux, turbulent heat flux, and residual oceanic processes each contributes substantially to North Pacific SST variability, whereas turbulent heat flux primarily induces North Atlantic SST variability. Cloud radiative fluxes therefore provide a major source of interannual SST variability in the North Pacific but not in the North Atlantic. In midlatitudes, SST fluctuations over the northern oceans are driven by the combination of turbulent and oceanic heat fluxes.
Niyogi, Dev; Jamshidi, Sajad; Smith, David; Kellner, OliviaNiyogi, D., S. Jamshidi, D. Smith, O. Kellner, 2020: Evapotranspiration Climatology of Indiana Using In Situ and Remotely Sensed Products. J. Appl. Meteor. Climatol., 59(12), 2093-2111. doi: 10.1175/JAMC-D-20-0024.1. AbstractAn intercomparison of multiresolution evapotranspiration (ET) datasets with reference to ground-based measurements for the development of regional reference (ETref) and actual (ETa) evapotranspiration maps over Indiana is presented. A representative ETref equation for the state is identified by evaluating 10 years of in situ measurements (2009–19). A statewide ETref climatology is developed using the ETref equation and high-resolution surface meteorological data from the gridded surface meteorological dataset (gridMET). For ETa analyses, MODIS, Simplified Surface Energy Balance Operational dataset (SSEBop), Global Land Evaporation Amsterdam Model (GLEAM) (versions 3.3a and 3.3b), and NLDAS (Noah and VIC) datasets are evaluated using AmeriFlux data. Thirty years of rainfall data from Climate Hazards Group Infrared Precipitation with Station Data Rainfall (CHIRPS) are used with the ET datasets to develop effective precipitation fields. Results show that the standardized Penman–Monteith equation performs as the best ETref equation with median symmetric accuracy (MSA) of 0.37, Taylor’s skill score (TSC) of 0.89, and r2 = 0.83. The analysis shows that the gridMET dataset overestimates wind speed and requires adjustment before a series of statewide ETref climatology maps are generated (1990–2020). For ETa, the MODIS and GLEAM (3.3b) datasets outperform the rest, with MSA = 0.5, TSC = 0.8, and r2 = 0.8. The state ETa dataset is generated using all MODIS data from 2003 and blending the MODIS data with GLEAM (3.3b) to cover data unavailability. Using the top-performing datasets, annual ETref for Indiana is computed as 1110 mm, ETa as 708 mm, and precipitation as 1091 mm. A marginal increasing climatological trend is found for Indiana’s ETref (0.013 mm yr−1) while ETa is found to be relatively stable. The state’s water availability, defined as rainfall minus ETa, has remained positive and stable at 0.99 mm day−1 (annual magnitude of +3820 mm).
Obregón, Maria A.; Costa, Maria João; Silva, Ana Maria; Serrano, AntonioObregón, M. A., M. J. Costa, A. M. Silva, A. Serrano, 2020: Spatial and Temporal Variation of Aerosol and Water Vapour Effects on Solar Radiation in the Mediterranean Basin during the Last Two Decades. Remote Sensing, 12(8), 1316. doi: 10.3390/rs12081316. This study aims to calculate and analyse the spatial and temporal variation of aerosol optical thickness (AOT) and precipitable water vapour (PWV) and their effects on solar radiation at the surface in the Mediterranean basin, one of the maritime areas with the largest aerosol loads in the world. For the achievement of this objective, a novel and validated methodology was applied. Satellite data, specifically CERES (Clouds and the Earth’s Radiant Energy System) SYN1deg products during the period 2000–2018, were used. Results show that the spatial distribution of AOT and PWV are closely linked to the spatial distributions of its effects on solar radiation. These effects are negative, indicating a reduction of solar radiation reaching the surface due to aerosol and water vapour effects. This reduction ranges between 2% and 8% for AOT, 11.5% and 15% for PWV and 14% and 20% for the combined effect. The analysis of the temporal distribution has focused on the detection of trends from their anomalies. This study has contributed to a better understanding of AOT and PWV effects on solar radiation over the Mediterranean basin, one of the most climatically sensitive regions of the planet, and highlighted the importance of water vapour. CERES; radiative effects; aerosol optical depth; Mediterranean basin; precipitable water vapour
Ollila, AnteroOllila, A., 2020: The Pause End and Major Temperature Impacts during Super El Niños are Due to Shortwave Radiation Anomalies. Physical Science International Journal, 1-20. doi: 10.9734/psij/2020/v24i230174. climate change; El Niño; ENSO; hiatus; Pause; shortwave changes
Oreopoulos, Lazaros; Cho, Nayeong; Lee, DongminOreopoulos, L., N. Cho, D. Lee, 2020: A Global Survey of Apparent Aerosol-Cloud Interaction Signals. Journal of Geophysical Research: Atmospheres, 125(1), e2019JD031287. doi: 10.1029/2019JD031287. We update and expand analysis of the apparent responses to aerosol variations of the planet's cloud regimes seen by the Moderate Resolution Imaging Spectroradiometer (MODIS). We distinguish between morning aerosol loadings and afternoon clouds and consider local scales explicitly. Aerosol loading is represented by gridded aerosol optical depth (AOD) from either MODIS or a reanalysis data set, while cloud information comes exclusively from MODIS. The afternoon cloud affected quantities (CAQs) examined in conjunction with morning AOD include precipitation and cloud radiative effect, in addition to cloud properties. One analysis thrust focuses on calculating global means distinguished by morning cloud regime, of afternoon CAQs, for distinct percentiles of grid cell seasonal morning AOD distributions. When the dependence of these global means on AOD is examined, we find persistent increases in cloud radiative fluxes with AOD as predicted by classic aerosol-cloud interaction paradigms, and also deviations from expected cloud responses, especially for precipitation. The other analysis thrust involves calculations at 1° scales of logarithmic CAQ sensitivities to AOD perturbations, approximated by linear regression slopes for distinct morning cloud regime groups. While the calculations are fundamentally local, we concentrate on the prevailing sensitivity signs in statistics of the slopes at global scales. Results from this second analysis approach indicate CAQ directions of change with AOD that are largely consistent with the first approach. When using a rather simple methodology where meteorological variables are treated as if they were CAQs, no conclusive results on the potential influence of meteorology on our findings are inferred. clouds; aerosol; MODIS; indirect effects; MERRA; satellite
Painemal, David; Chang, Fu-Lung; Ferrare, Richard; Burton, Sharon; Li, Zhujun; Smith Jr., William L.; Minnis, Patrick; Feng, Yan; Clayton, MarianPainemal, D., F. Chang, R. Ferrare, S. Burton, Z. Li, W. L. Smith Jr., P. Minnis, Y. Feng, M. Clayton, 2020: Reducing uncertainties in satellite estimates of aerosol–cloud interactions over the subtropical ocean by integrating vertically resolved aerosol observations. Atmospheric Chemistry and Physics, 20(12), 7167-7177. doi: https://doi.org/10.5194/acp-20-7167-2020. Abstract. Satellite quantification of aerosol effects on clouds relies on aerosol optical depth (AOD) as a proxy for aerosol concentration or cloud condensation nuclei (CCN). However, the lack of error characterization of satellite-based results hampers their use for the evaluation and improvement of global climate models. We show that the use of AOD for assessing aerosol–cloud interactions (ACIs) is inadequate over vast oceanic areas in the subtropics. Instead, we postulate that a more physical approach that consists of matching vertically resolved aerosol data from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite at the cloud-layer height with Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua cloud retrievals reduces uncertainties in satellite-based ACI estimates. Combined aerosol extinction coefficients (σ) below cloud top (σBC) from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and cloud droplet number concentrations (Nd) from MODIS Aqua yield high correlations across a broad range of σBC values, with σBC quartile correlations ≥0.78. In contrast, CALIOP-based AOD yields correlations with MODIS Nd of 0.54–0.62 for the two lower AOD quartiles. Moreover, σBC explains 41 % of the spatial variance in MODIS Nd, whereas AOD only explains 17 %, primarily caused by the lack of spatial covariability in the eastern Pacific. Compared with σBC, near-surface σ weakly correlates in space with MODIS Nd, accounting for a 16 % variance. It is concluded that the linear regression calculated from ln(Nd)–ln(σBC) (the standard method for quantifying ACIs) is more physically meaningful than that derived from the Nd–AOD pair.
Palchetti, L.; Brindley, H.; Bantges, R.; Buehler, S. A.; Camy-Peyret, C.; Carli, B.; Cortesi, U.; Bianco, S. Del; Natale, G. Di; Dinelli, B. M.; Feldman, D.; Huang, X. L.; C.-Labonnote, L.; Libois, Q.; Maestri, T.; Mlynczak, M. G.; Murray, J. E.; Oetjen, H.; Ridolfi, M.; Riese, M.; Russell, J.; Saunders, R.; Serio, C.Palchetti, L., H. Brindley, R. Bantges, S. A. Buehler, C. Camy-Peyret, B. Carli, U. Cortesi, S. D. Bianco, G. D. Natale, B. M. Dinelli, D. Feldman, X. L. Huang, L. C.-Labonnote, Q. Libois, T. Maestri, M. G. Mlynczak, J. E. Murray, H. Oetjen, M. Ridolfi, M. Riese, J. Russell, R. Saunders, C. Serio, 2020: FORUM: Unique Far-Infrared Satellite Observations to Better Understand How Earth Radiates Energy to Space. Bull. Amer. Meteor. Soc., 101(12), E2030-E2046. doi: 10.1175/BAMS-D-19-0322.1. AbstractThe outgoing longwave radiation (OLR) emitted to space is a fundamental component of the Earth’s energy budget. There are numerous, entangled physical processes that contribute to OLR and that are responsible for driving, and responding to, climate change. Spectrally resolved observations can disentangle these processes, but technical limitations have precluded accurate space-based spectral measurements covering the far infrared (FIR) from 100 to 667 cm−1 (wavelengths between 15 and 100 µm). The Earth’s FIR spectrum is thus essentially unmeasured even though at least half of the OLR arises from this spectral range. The region is strongly influenced by upper-tropospheric–lower-stratospheric water vapor, temperature lapse rate, ice cloud distribution, and microphysics, all critical parameters in the climate system that are highly variable and still poorly observed and understood. To cover this uncharted territory in Earth observations, the Far-Infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission has recently been selected as ESA’s ninth Earth Explorer mission for launch in 2026. The primary goal of FORUM is to measure, with high absolute accuracy, the FIR component of the spectrally resolved OLR for the first time with high spectral resolution and radiometric accuracy. The mission will provide a benchmark dataset of global observations which will significantly enhance our understanding of key forcing and feedback processes of the Earth’s atmosphere to enable more stringent evaluation of climate models. This paper describes the motivation for the mission, highlighting the scientific advances that are expected from the new measurements.
Pan, Fang; Kato, Seiji; Rose, Fred G.; Radkevich, Alexander; Liu, Xu; Huang, XiangleiPan, F., S. Kato, F. G. Rose, A. Radkevich, X. Liu, X. Huang, 2020: An Algorithm to Derive Temperature and Humidity Profile Changes Using Spatially and Temporally Averaged Spectral Radiance Differences. J. Atmos. Oceanic Technol., 37(7), 1173-1187. doi: 10.1175/JTECH-D-19-0143.1.
Pan, Zengxin; Mao, Feiyue; Lu, Xin; Gong, Wei; Shen, Huanfeng; Mao, QingzhouPan, Z., F. Mao, X. Lu, W. Gong, H. Shen, Q. Mao, 2020: Enhancement of vertical cloud-induced radiative heating in East Asian monsoon circulation derived from CloudSat-CALIPSO observations. International Journal of Remote Sensing, 41(2), 595-614. doi: 10.1080/01431161.2019.1646935. Improving the understanding of cloud–radiation–monsoon interactions is difficult due to the limited knowledge regarding the impacts of vertical cloud radiative forcing on monsoon circulation. Here, we focus on the annual cycle of the vertical structure of cloud-induced radiative heating (CRH) to evaluate further their impacts on the East Asian monsoon circulation (100°–140° E, 20°–45° N) derived from satellite observations and reanalysis datasets. Entire troposphere and lower stratosphere are heated by vertical CRH, with the peak reaching 1 K day−1 at the mid-level troposphere (4–10 km) during summer. Although radiative warming occurs below 3 km from the prevailing stratocumulus, widespread weak radiative cooling (approximately −0.2 K day−1) occurs at a wide vertical range above 3 km during winter. Consequently, the wind vector variations resulting from vertical CRH highly coincide with the monsoon circulation, leading to the increase in wind speeds by 1.8 and 0.5 m s−1 during summer and winter, respectively, while a weakly negative influence (about 0.3 m s−1) occurs at the low-level troposphere below 3 km during winter. Although high clouds, stratiform clouds, and stratocumulus dominate these wind vector variations, deep convective clouds generate the strongest updraft (up to 7 m s−1) amongst all cloud categories despite their low occurrence frequency. Results highlight the important enhancement of vertical CRH to East Asian monsoon circulation by perturbing the vertical structure of heating rate.
Pandey, Satyendra Kumar; Vinoj, V.; Panwar, AnnuPandey, S. K., V. Vinoj, A. Panwar, 2020: The short-term variability of aerosols and their impact on cloud properties and radiative effect over the Indo-Gangetic Plain. Atmospheric Pollution Research, 11(3), 630-638. doi: 10.1016/j.apr.2019.12.017. Anthropogenic activities have been shown to have a significant effect on weather and hence climate. However, discerning them from various observations over a certain region including India has been a challenge due to the large role played by natural variability. We show that anthropogenic signals in terms of sub-weekly scale are quite significant (of the order of 20%) in aerosol loading over the Indo-Gangetic Plains. These, in turn, clouds become thinner and less reflective with weekly variations of aerosol, which indicate the possible effect of aerosol on clouds. In terms of changes to Short Wave (SW) and Long Wave (LW) radiation fluxes, we find that change in aerosol direct effect is larger during cloudy sky conditions than clear sky conditions showing that aerosol induced changes to dynamics and hence clouds are dominant factors. This is also manifested in changes to cloud macro physical properties such as cloud optical depth (COD), cloud top temperature (CTT), cloud top pressure (CTP) and liquid water path (LWP). The changes in clear-sky and all-sky top of the atmosphere aerosol direct radiative effect (DRE) and cloud radiative effect (CRE) using CERES derived fluxes were found to be ~7–10% different during weekends with respect to weekly means. Similarly, the change in longwave cloud radiative effect is double that of the shortwave CRE. Aerosol direct effect; Anthropogenic aerosols; Cloud radiative effect; Indo-Gangetic plain
Papavasileiou, Georgios; Voigt, Aiko; Knippertz, PeterPapavasileiou, G., A. Voigt, P. Knippertz, 2020: The role of observed cloud-radiative anomalies for the dynamics of the North Atlantic Oscillation on synoptic time-scales. Quarterly Journal of the Royal Meteorological Society, 146(729), 1822-1841. doi: 10.1002/qj.3768. Clouds shape weather and climate by regulating the latent and radiative heating in the atmosphere. Recent work has demonstrated the importance of cloud-radiative effects (CRE) for the mean circulation of the extratropical atmosphere and its response to global warming. In contrast, little research has been done regarding the impact of CRE on internal variability. Here, we study how clouds and the North Atlantic Oscillation (NAO) couple on synoptic time-scales during Northern Hemisphere winter via CRE within the atmosphere (ACRE). A regression analysis based on 5-day mean data from CloudSat/CALIPSO, CERES and GERB satellite observations and ERA-Interim short-term forecast data reveals a robust dipole of high-level and low-level cloud-incidence anomalies during a positive NAO, with increased high-level cloud incidence along the storm track (near 45°N) and the subpolar Atlantic, and decreased high-level cloud incidence poleward and equatorward of this track. Opposite changes occur for low-level cloud incidence. The cloud anomalies lead to an anomalous column-mean heating from ACRE over the region of the Iceland low, and to a cooling over the region of the Azores high. To quantify the impact of the ACRE anomalies on the NAO, and to thereby test the hypothesis of a cloud-radiative feedback on the NAO persistence, we apply the surface pressure tendency equation for ERA-Interim short-term forecast data. The NAO-generated ACRE anomalies amplify the NAO-related surface pressure anomalies over the Azores high but have no area-averaged impact on the Iceland low. In contrast, diabatic processes as a whole, including latent heating and clear-sky radiation, strongly amplify the NAO-related surface pressure anomalies over both the Azores high and the Iceland low, and their impact is much more spatially coherent. This suggests that, while atmospheric cloud-radiative effects lead to an increase in NAO persistence on synoptic time-scales, their impact is relatively minor and much smaller than other diabatic processes. latent heating; atmospheric cloud-radiative effects (ACRE); cloud–circulation coupling; diabatic processes; North Atlantic Oscillation (NAO)
Pasut, Chiara; Tang, Fiona H. M.; Maggi, FedericoPasut, C., F. H. M. Tang, F. Maggi, 2020: A Mechanistic Analysis of Wetland Biogeochemistry in Response to Temperature, Vegetation, and Nutrient Input Changes. Journal of Geophysical Research: Biogeosciences, 125(4), e2019JG005437. doi: 10.1029/2019JG005437. Wetlands represent the most significant natural greenhouse gas (GHG) source and their annual emissions tightly depend on climatic and anthropogenic factors. Biogeochemical processes occurring in wetlands are still poorly described by mechanistic models and hence their dynamic response to environmental changes are weakly predicted. We investigated wetland GHG emissions, relevant electron acceptors and donors concentrations, and microbial composition resulting from changes in temperature, CH4 plant uptake efficiency, and SO deposition using a mechanistic biogeochemical model (here called BAMS3) that integrates the carbon (C), nitrogen (N), and sulfur (S) cycles. Parameters constraining the coupled C-N-S cycles were retrieved from controlled experiments and were validated against independent field data of CH4 emissions, and CH4(aq) and SO concentration profiles in a wetland in southern Michigan, USA (Shannon & White, 1994, http://hdl.handle.net/102.100.100/236252?index=1). We found that +1.75 °C increase in temperature leads to 22% and 30% increment in CH4 and N2O emissions, respectively. A decrease in the CH4 plant uptake efficiency causes the prevalent CH4 emission pathway to become diffusion mediated and resulted in 50% increase in the daily average CH4 emissions. Finally, a decreasing SO deposition rate can increase CH4 emissions up to 5%. We conclude that the increasing GHG emissions from wetlands is a result of both environmental and anthropogenic causes rather than global warming alone. An increase in model complexity does not necessary improve the estimation of GHG emissions but it aids interpretation of intermediate processes to a greater detail. modeling; nutrients; wetland
Pathak, Harshavardhana Sunil; Satheesh, Sreedharan Krishnakumari; Moorthy, Krishnaswamy Krishna; Nanjundiah, Ravi ShankarPathak, H. S., S. K. Satheesh, K. K. Moorthy, R. S. Nanjundiah, 2020: Assessment of Regional Aerosol Radiative Effects under SWAAMI Campaign – PART 2: Clear-sky Direct Shortwave Radiative Forcing using Multi-year Assimilated Data. Atmospheric Chemistry and Physics Discussions, 1-31. doi: https://doi.org/10.5194/acp-2020-454. Abstract. Clear-sky, direct shortwave Aerosol Radiative Forcing (ARF) has been estimated over the Indian region, for the first time employing multi-year (2009–2013) gridded, assimilated aerosol products. The aerosol datasets have been constructed following statistical assimilation of concurrent data from a dense network of ground-based observatories, and multi-satellite products, as described in Part-1 of this two-part paper. The ARF, thus estimated, are assessed for their superiority or otherwise over other ARF estimates based on satellite-retrieved aerosol products, over the Indian region, by comparing the radiative fluxes (upward) at Top of Atmosphere (TOA) estimated using assimilated products with spatio-temporally matched radiative flux values provided by CERES (Clouds and Earth's Radiant Energy System) Single Scan Footprint (SSF) product. This clearly demonstrated improved accuracy of the forcing estimates using the assimilated vis-a-vis satellite-based aerosol datasets; at regional, sub-regional and seasonal scales. The regional distribution of diurnally averaged ARF estimates has revealed (a) significant differences from similar estimates made using currently available satellite data, not only in terms of magnitude but also sign of TOA forcing; (b) largest magnitudes of surface cooling and atmospheric warming over IGP and arid regions from north-western India; and (c) negative TOA forcing over most parts of the Indian region, except for three sub-regions – the Indo-Gangetic plains (IGP), north-western India and eastern parts of peninsular India where the TOA forcing changes to positive during pre-monsoon season. Aerosol induced atmospheric warming rates, estimated using the assimilated data, demonstrate substantial spatial heterogeneities (~ 0.2 to 2.0 K day−1) over the study domain with the IGP demonstrating relatively stronger atmospheric heating rates (~ 0.6 to 2.0 K day−1). There exists a strong seasonality as well; with atmospheric warming being highest during pre-monsoon and lowest during winter seasons. It is to be noted that the present ARF estimates demonstrate substantially smaller uncertainties than their satellite counterparts, which is a natural consequence of reduced uncertainties in assimilated vis-a-vis satellite aerosol properties. The results demonstrate the potential application of the assimilated datasets and ARF estimates for improving accuracies of climate impact assessments at regional and sub-regional scales.
Pendergrass, A. G.Pendergrass, A. G., 2020: The Global-Mean Precipitation Response to CO2-Induced Warming in CMIP6 Models. Geophysical Research Letters, 47(17), e2020GL089964. doi: 10.1029/2020GL089964. We examine the response of globally averaged precipitation to global warming—the hydrologic sensitivity (HS)—in the Coupled Model Intercomparison Project phase 6 (CMIP6) multi-model ensemble. Multi-model mean HS is 2.5% K−1 (ranging from 2.1–3.1% K−1 across models), a modest decrease compared to CMIP5 (where it was 2.6% K−1). This new set of simulations is used as an out-of-sample test for observational constraints on HS proposed based on CMIP5. The constraint based on clear-sky shortwave absorption sensitivity to water vapor has weakened, and it is argued that a proposed constraint based on surface low cloud longwave radiative effects does not apply to HS. Finally, while a previously proposed mechanism connecting HS and climate sensitivity via low clouds is present in the CMIP6 ensemble, it is not an important factor for variations in HS. This explains why HS is uncorrelated with climate sensitivity across the CMIP5 and CMIP6 ensembles. climate change; climate models; precipitation; CMIP; climate sensitivity; emergent constraints
Perdigão, João; Canhoto, Paulo; Salgado, Rui; Costa, Maria JoãoPerdigão, J., P. Canhoto, R. Salgado, M. J. Costa, 2020: Assessment of Direct Normal Irradiance Forecasts Based on IFS/ECMWF Data and Observations in the South of Portugal. Forecasting, 2(2), 130-150. doi: 10.3390/forecast2020007. Direct Normal Irradiance (DNI) predictions obtained from the Integrated Forecasting System of the European Centre for Medium-Range Weather Forecast (IFS/ECMWF) were compared against ground-based observational data for one location at the south of Portugal (Évora). Hourly and daily DNI values were analyzed for different temporal forecast horizons (1 to 3 days ahead) and results show that the IFS/ECMWF slightly overestimates DNI for the period of analysis (1 August 2018 until 31 July 2019) with a fairly good agreement between model and observations. Hourly basis evaluation shows relatively high errors, independently of the forecast day. Root mean square error increases as the forecast time increases with a relative error of ~45% between the first and the last forecast. Similar patterns are observed in the daily analysis with comparable magnitude errors. The correlation coefficients between forecast and observed data are above 0.7 for both hourly and daily data. A methodology based on a new DNI attenuation Index (DAI) was developed to estimate cloud fraction from hourly values integrated over a day and, with that, to correlate the accuracy of the forecast with sky conditions. This correlation with DAI reveals that in IFS/ECMWF model, the atmosphere as being more transparent than reality since cloud cover is underestimated in the majority of the months of the year, taking the ground-based measurements as a reference. The use of the DAI estimator confirms that the errors in IFS/ECMWF are larger under cloudy skies than under clear sky. The development and application of a post-processing methodology improves the DNI predictions from the IFS/ECMWF outputs, with a decrease of error of the order of ~30%, when compared with raw data. evaluation; bias correction; Direct Normal Irradiance (DNI); DNI attenuation Index (DAI); forecast; IFS/ECMWF
Qin, Boxiong; Cao, Biao; Li, Hua; Bian, Zunjian; Hu, Tian; Du, Yongming; Yang, Yingpin; Xiao, Qing; Liu, QinhuoQin, B., B. Cao, H. Li, Z. Bian, T. Hu, Y. Du, Y. Yang, Q. Xiao, Q. Liu, 2020: Evaluation of Six High-Spatial Resolution Clear-Sky Surface Upward Longwave Radiation Estimation Methods with MODIS. Remote Sensing, 12(11), 1834. doi: 10.3390/rs12111834. Surface upward longwave radiation (SULR) is a critical component in the calculation of the Earth’s surface radiation budget. Multiple clear-sky SULR estimation methods have been developed for high-spatial resolution satellite observations. Here, we comprehensively evaluated six SULR estimation methods, including the temperature-emissivity physical methods with the input of the MYD11/MYD21 (TE-MYD11/TE-MYD21), the hybrid methods with top-of-atmosphere (TOA) linear/nonlinear/artificial neural network regressions (TOA-LIN/TOA-NLIN/TOA-ANN), and the hybrid method with bottom-of-atmosphere (BOA) linear regression (BOA-LIN). The recently released MYD21 product and the BOA-LIN—a newly developed method that considers the spatial heterogeneity of the atmosphere—is used initially to estimate SULR. In addition, the four hybrid methods were compared with simulated datasets. All the six methods were evaluated using the Moderate Resolution Imaging Spectroradiometer (MODIS) products and the Surface Radiation Budget Network (SURFRAD) in situ measurements. Simulation analysis shows that the BOA-LIN is the best one among four hybrid methods with accurate atmospheric profiles as input. Comparison of all the six methods shows that the TE-MYD21 performed the best, with a root mean square error (RMSE) and mean bias error (MBE) of 14.0 and −0.2 W/m2, respectively. The RMSE of BOA-LIN, TOA-NLIN, TOA-LIN, TOA-ANN, and TE-MYD11 are equal to 15.2, 16.1, 17.2, 21.2, and 18.5 W/m2, respectively. TE-MYD21 has a much better accuracy than the TE-MYD11 over barren surfaces (NDVI < 0.3) and a similar accuracy over non-barren surfaces (NDVI ≥ 0.3). BOA-LIN is more stable over varying water vapor conditions, compared to other hybrid methods. We conclude that this study provides a valuable reference for choosing the suitable estimation method in the SULR product generation. MODIS; SURFRAD; temperature-emissivity method; hybrid method; method evaluation; surface upward longwave radiation
Rampal, Neelesh; Davies, RogerRampal, N., R. Davies, 2020: On the Factors That Determine Boundary Layer Albedo. Journal of Geophysical Research: Atmospheres, 125(15), e2019JD032244. doi: 10.1029/2019JD032244. This study investigates the factors that control marine boundary layer cloud albedo measured by the Multiangle Imaging SpectroRadiometer (MISR) over domains of (200 km)2. We use three key metrics to investigate domain albedo: cloud fraction, cloud heterogeneity, and cloud morphology. Cloud heterogeneity is quantified at the domain level with a unified heterogeneity index. Cloud morphology is determined from a cloud classification algorithm using an Artificial Neural Network (ANN) to classify each domain into one of four categories: (i) closed-cell Mesoscale Cellular Convection (MCC); (ii) open-cell MCC; (iii) disorganized MCC; and (iv) No MCC. These different types of MCC are usefully defined as low clouds of different morphologies. Classifications from the ANN are also combined with the satellite observations of MISR to develop relationships between cloud morphology, domain albedo, cloud fraction, and cloud heterogeneity. Cloud morphology is found to play an essential role in modulating these relationships. The cloud fraction-albedo relationships are found to be directly a function of cloud morphology. Relationships between domain albedo and cloud heterogeneity are also found to be a function of MCC type. Our results indicate that the albedo has a strong dependence on cloud morphology and cloud heterogeneity. Understanding both the physical properties and the meteorological controls on MCC has important implications for understanding low cloud behavior and improving their representation in General Circulation Models. albedo; MISR; mesoscale cellular convection; boundary layer cloud; heterogeneity
Rehbein, Amanda; Rugna, Martín; Hobouchian, M. Paula; Moral, Anna del; Goodman, Steven J.; Lindsey, Daniel T.; Thomas, JanelRehbein, A., M. Rugna, M. P. Hobouchian, A. d. Moral, S. J. Goodman, D. T. Lindsey, J. Thomas, 2020: A Workshop on the Next-Generation Environmental Satellite Constellations. Bull. Amer. Meteor. Soc., 101(6), E763-E770. doi: 10.1175/BAMS-D-19-0349.1.
Ren, Tong; Yang, Ping; Schumacher, Courtney; Huang, Xianglei; Lin, WuyinRen, T., P. Yang, C. Schumacher, X. Huang, W. Lin, 2020: Impact of Cloud Longwave Scattering on Radiative Fluxes Associated With the Madden-Julian Oscillation in the Indian Ocean and Maritime Continent. Journal of Geophysical Research: Atmospheres, 125(13), e2020JD032591. doi: 10.1029/2020JD032591. Previous studies suggested that cloud longwave radiation contributes to the development and maintenance of the Madden-Julian Oscillation (MJO) and model-based convection is highly sensitive to the radiation scheme. However, currently used radiation schemes do not take cloud longwave scattering into account, resulting in an overestimation of the outgoing longwave radiation (OLR) and an underestimation of the downward longwave flux at the surface. We use combined active and passive satellite cloud property retrievals to quantify the one-layer cloud OLR and heating rate (HR) biases introduced by neglecting cloud longwave scattering in the Indian Ocean and Maritime Continent in the context of MJO, with a focus on its phases 3, 5, and 6. The results show that the satellite-detected one-layer cloud area consists primarily of ice clouds, particularly during the boreal winter in the 4-year study period. An increased ice cloud area fraction of one-layer cloud groups is present up to 5 days before the onset of MJO events. If longwave scattering is neglected, the composite mean OLR overestimation over the one-layer ice cloud area from 5 days before to 4 days after the MJO passage is approximately 3.5 to 5.0 W m−2. Neglecting longwave scattering also leads to a HR underestimation at cloud base and an overestimation at cloud top, making the base-to-top heating gradient less sharp at the cloud-resolving scale.
Righi, Mattia; Andela, Bouwe; Eyring, Veronika; Lauer, Axel; Predoi, Valeriu; Schlund, Manuel; Vegas-Regidor, Javier; Bock, Lisa; Brötz, Björn; Mora, Lee de; Diblen, Faruk; Dreyer, Laura; Drost, Niels; Earnshaw, Paul; Hassler, Birgit; Koldunov, Nikolay; Little, Bill; Loosveldt Tomas, Saskia; Zimmermann, KlausRighi, M., B. Andela, V. Eyring, A. Lauer, V. Predoi, M. Schlund, J. Vegas-Regidor, L. Bock, B. Brötz, L. d. Mora, F. Diblen, L. Dreyer, N. Drost, P. Earnshaw, B. Hassler, N. Koldunov, B. Little, S. Loosveldt Tomas, K. Zimmermann, 2020: Earth System Model Evaluation Tool (ESMValTool) v2.0 – technical overview. Geoscientific Model Development, 13(3), 1179-1199. doi: 10.5194/gmd-13-1179-2020. Abstract. This paper describes the second major release of the Earth System Model Evaluation Tool (ESMValTool), a community diagnostic and performance metrics tool for the evaluation of Earth system models (ESMs) participating in the Coupled Model Intercomparison Project (CMIP). Compared to version 1.0, released in 2016, ESMValTool version 2.0 (v2.0) features a brand new design, with an improved interface and a revised preprocessor. It also features a significantly enhanced diagnostic part that is described in three companion papers. The new version of ESMValTool has been specifically developed to target the increased data volume of CMIP Phase 6 (CMIP6) and the related challenges posed by the analysis and the evaluation of output from multiple high-resolution or complex ESMs. The new version takes advantage of state-of-the-art computational libraries and methods to deploy an efficient and user-friendly data processing. Common operations on the input data (such as regridding or computation of multi-model statistics) are centralized in a highly optimized preprocessor, which allows applying a series of preprocessing functions before diagnostics scripts are applied for in-depth scientific analysis of the model output. Performance tests conducted on a set of standard diagnostics show that the new version is faster than its predecessor by about a factor of 3. The performance can be further improved, up to a factor of more than 30, when the newly introduced task-based parallelization options are used, which enable the efficient exploitation of much larger computing infrastructures. ESMValTool v2.0 also includes a revised and simplified installation procedure, the setting of user-configurable options based on modern language formats, and high code quality standards following the best practices for software development.
Righi, Mattia; Hendricks, Johannes; Lohmann, Ulrike; Beer, Christof Gerhard; Hahn, Valerian; Heinold, Bernd; Heller, Romy; Krämer, Martina; Ponater, Michael; Rolf, Christian; Tegen, Ina; Voigt, ChristianeRighi, M., J. Hendricks, U. Lohmann, C. G. Beer, V. Hahn, B. Heinold, R. Heller, M. Krämer, M. Ponater, C. Rolf, I. Tegen, C. Voigt, 2020: Coupling aerosols to (cirrus) clouds in the global EMAC-MADE3 aerosol–climate model. Geoscientific Model Development, 13(3), 1635-1661. doi: 10.5194/gmd-13-1635-2020. Abstract. A new cloud microphysical scheme including a detailed parameterization for aerosol-driven ice formation in cirrus clouds is implemented in the global ECHAM/MESSy Atmospheric Chemistry (EMAC) chemistry–climate model and coupled to the third generation of the Modal Aerosol Dynamics model for Europe adapted for global applications (MADE3) aerosol submodel. The new scheme is able to consistently simulate three regimes of stratiform clouds – liquid, mixed-, and ice-phase (cirrus) clouds – considering the activation of aerosol particles to form cloud droplets and the nucleation of ice crystals. In the cirrus regime, it allows for the competition between homogeneous and heterogeneous freezing for the available supersaturated water vapor, taking into account different types of ice-nucleating particles, whose specific ice-nucleating properties can be flexibly varied in the model setup. The new model configuration is tuned to find the optimal set of parameters that minimizes the model deviations with respect to observations. A detailed evaluation is also performed comparing the model results for standard cloud and radiation variables with a comprehensive set of observations from satellite retrievals and in situ measurements. The performance of EMAC-MADE3 in this new coupled configuration is in line with similar global coupled models and with other global aerosol models featuring ice cloud parameterizations. Some remaining discrepancies, namely a high positive bias in liquid water path in the Northern Hemisphere and overestimated (underestimated) cloud droplet number concentrations over the tropical oceans (in the extratropical regions), which are both a common problem in these kinds of models, need to be taken into account in future applications of the model. To further demonstrate the readiness of the new model system for application studies, an estimate of the anthropogenic aerosol effective radiative forcing (ERF) is provided, showing that EMAC-MADE3 simulates a relatively strong aerosol-induced cooling but within the range reported in the Intergovernmental Panel on Climate Change (IPCC) assessments.
Rind, D.; Orbe, C.; Jonas, J.; Nazarenko, L.; Zhou, T.; Kelley, M.; Lacis, A.; Shindell, D.; Faluvegi, G.; Romanou, A.; Russell, G.; Tausnev, N.; Bauer, M.; Schmidt, G.Rind, D., C. Orbe, J. Jonas, L. Nazarenko, T. Zhou, M. Kelley, A. Lacis, D. Shindell, G. Faluvegi, A. Romanou, G. Russell, N. Tausnev, M. Bauer, G. Schmidt, 2020: GISS Model E2.2: A Climate Model Optimized for the Middle Atmosphere—Model Structure, Climatology, Variability, and Climate Sensitivity. Journal of Geophysical Research: Atmospheres, 125(10), e2019JD032204. doi: 10.1029/2019JD032204. We introduce a new climate model (GISS E2.2) that has been specially optimized for the middle atmosphere and whose output is being contributed to the CMIP6 archive. The top of the model is at a geopotential altitude of 89 km, and parameterizations of moist convection and various forms of gravity wave drag based on tropospheric processes are chosen specifically for this optimization. We first evaluate the model in its configuration as a coupled atmosphere-chemistry model with respect to its simulation of the mean state of the middle atmosphere, from the mesosphere down through the upper troposphere/lower stratosphere. Then we assess its use as a coupled atmosphere-ocean climate model by exploring its mean ocean climatology. To evaluate its variability, we report on its simulation of the primary modes in the troposphere, stratosphere, and ocean. Two climate change simulations are presented, the responses to instantaneous increases of 2xCO2 and 4xCO2, run with two different ocean models. Sensitivity studies are performed to illustrate the effect of parameterizations on the model results. We compare these results to the lower vertical resolution/top GISS Model E2.1, whose output has also been submitted to CMIP6. The different choices made for these models are explored. It is shown that important improvements in the circulation above and below the tropopause can be obtained when attention is paid to representation of middle atmosphere processes in climate model development. climate model; model development; middle atmosphere
Rivoire, Louis; Birner, Thomas; Knaff, John A.; Tourville, NatalieRivoire, L., T. Birner, J. A. Knaff, N. Tourville, 2020: Quantifying the Radiative Impact of Clouds on Tropopause Layer Cooling in Tropical Cyclones. J. Climate, 33(15), 6361-6376. doi: 10.1175/JCLI-D-19-0813.1.
Robson, Jon; Aksenov, Yevgeny; Bracegirdle, Thomas J.; Dimdore‐Miles, Oscar; Griffiths, Paul T.; Grosvenor, Daniel P.; Hodson, Daniel L. R.; Keeble, James; MacIntosh, Claire; Megann, Alex; Osprey, Scott; Povey, Adam C.; Schröder, David; Yang, Mingxi; Archibald, Alexander T.; Carslaw, Ken S.; Gray, Lesley; Jones, Colin; Kerridge, Brian; Knappett, Diane; Kuhlbrodt, Till; Russo, Maria; Sellar, Alistair; Siddans, Richard; Sinha, Bablu; Sutton, Rowan; Walton, Jeremy; Wilcox, Laura J.Robson, J., Y. Aksenov, T. J. Bracegirdle, O. Dimdore‐Miles, P. T. Griffiths, D. P. Grosvenor, D. L. R. Hodson, J. Keeble, C. MacIntosh, A. Megann, S. Osprey, A. C. Povey, D. Schröder, M. Yang, A. T. Archibald, K. S. Carslaw, L. Gray, C. Jones, B. Kerridge, D. Knappett, T. Kuhlbrodt, M. Russo, A. Sellar, R. Siddans, B. Sinha, R. Sutton, J. Walton, L. J. Wilcox, 2020: The Evaluation of the North Atlantic Climate System in UKESM1 Historical Simulations for CMIP6. Journal of Advances in Modeling Earth Systems, 12(9), e2020MS002126. doi: 10.1029/2020MS002126. Earth system models enable a broad range of climate interactions that physical climate models are unable to simulate. However, the extent to which adding Earth system components changes or improves the simulation of the physical climate is not well understood. Here we present a broad multivariate evaluation of the North Atlantic climate system in historical simulations of the UK Earth System Model (UKESM1) performed for CMIP6. In particular, we focus on the mean state and the decadal time scale evolution of important variables that span the North Atlantic climate system. In general, UKESM1 performs well and realistically simulates many aspects of the North Atlantic climate system. Like the physical version of the model, we find that changes in external forcing, and particularly aerosol forcing, are an important driver of multidecadal change in UKESM1, especially for Atlantic Multidecadal Variability and the Atlantic Meridional Overturning Circulation. However, many of the shortcomings identified are similar to common biases found in physical climate models, including the physical climate model that underpins UKESM1. For example, the summer jet is too weak and too far poleward; decadal variability in the winter jet is underestimated; intraseasonal stratospheric polar vortex variability is poorly represented; and Arctic sea ice is too thick. Forced shortwave changes may be also too strong in UKESM1, which, given the important role of historical aerosol forcing in shaping the evolution of the North Atlantic in UKESM1, motivates further investigation. Therefore, physical model development, alongside Earth system development, remains crucial in order to improve climate simulations. model evaluation; CMIP6; Earth system model; North Atlantic
Roehrig, Romain; Beau, Isabelle; Saint‐Martin, David; Alias, Antoinette; Decharme, Bertrand; Guérémy, Jean-Francois; Voldoire, Aurore; Younous, Abdel-Lathif Ahmat; Bazile, Eric; Belamari, Sophie; Blein, Sébastien; Bouniol, Dominique; Bouteloup, Yves; Cattiaux, Julien; Chauvin, Fabrice; Chevallier, Matthieu; Colin, Jeanne; Douville, Hervé; Marquet, Pascal; Michou, Martine; Nabat, Pierre; Oudar, Thomas; Peyrillé, Philippe; Piriou, Jean-Marcel; Melia, David Salas y; Séférian, Roland; Sénési, StéphaneRoehrig, R., I. Beau, D. Saint‐Martin, A. Alias, B. Decharme, J. Guérémy, A. Voldoire, A. A. Younous, E. Bazile, S. Belamari, S. Blein, D. Bouniol, Y. Bouteloup, J. Cattiaux, F. Chauvin, M. Chevallier, J. Colin, H. Douville, P. Marquet, M. Michou, P. Nabat, T. Oudar, P. Peyrillé, J. Piriou, D. S. y. Melia, R. Séférian, S. Sénési, 2020: The CNRM global atmosphere model ARPEGE-Climat 6.3: description and evaluation. Journal of Advances in Modeling Earth Systems, 12(7), e2020MS002075. doi: 10.1029/2020MS002075. keypoints The version 6.3 of the ARPEGE-Climat atmospheric model includes an increased vertical resolution and a major update of the moist physics Improvements include radiation, cloud and precipitation climatology, daily rainfall distribution and water discharge at major river outlets Weaknesses still include biases in low clouds and some dynamical fields, while the West African monsoon is a new model deficiency
Saidou Chaibou, Abdoul Aziz; Ma, Xiaoyan; Sha, TongSaidou Chaibou, A. A., X. Ma, T. Sha, 2020: Dust radiative forcing and its impact on surface energy budget over West Africa. Scientific Reports, 10(1), 12236. doi: 10.1038/s41598-020-69223-4. Dust is the dominant aerosol type over West Africa (WA), and therefore accurate simulation of dust impact is critical for better prediction of weather and climate change. The dust radiative forcing (DRF) is estimated using two sets of experiments in this study: one without and the other with dust aerosol and its feedbacks with the Weather Research and Forecasting with Chemistry model (WRF-Chem). Results show that DRF presents a net warming effect at the top-of-atmosphere (TOA) and in the atmosphere (ATM), and cooling at the surface (SFC). The net DRF over WA is estimated to be 9 W/m2 at the TOA, 23 W/m2 in the ATM, and − 13 W/m2 at the SFC. Furthermore, dust-induced a reduction of sensible heat up to 24 W/m2 and SFC temperature up to 2 °C cooling over WA, an increase of latent heat up to 12 W/m2 over Sahara, a decrease up to 24 W/m2 over the vegetated surfaces and an increase in the surface energy balance up to 12 W/m2 over WA. The presence of dust significantly influences the surface energy budget over WA, suggesting that dust effects should be considered in more climate studies to improve the accuracy of climate predictions.
Salazar, Germán; Gueymard, Christian; Galdino, Janis Bezerra; de Castro Vilela, Olga; Fraidenraich, NaumSalazar, G., C. Gueymard, J. B. Galdino, O. de Castro Vilela, N. Fraidenraich, 2020: Solar irradiance time series derived from high-quality measurements, satellite-based models, and reanalyses at a near-equatorial site in Brazil. Renewable and Sustainable Energy Reviews, 117, 109478. doi: 10.1016/j.rser.2019.109478. This study analyzes five years of 1-min solar global horizontal irradiance (GHI) and direct normal irradiance (DNI) observations obtained at Petrolina (northeast Brazil). Quality-assured hourly and daily averages are obtained after applying filters and methodologies based on a Baseline Solar Radiation Network (BSRN) quality-control procedure. To calculate correct hourly averages, a minimum fraction of 20% of valid GHI or DNI minutely data is needed, as well as at least 60% of valid days to calculate correct daily-mean monthly values. An asymmetric diurnal pattern is found in GHI and DNI during all months, attributed to consistently higher cloudiness in the morning. The quality-assured hourly and monthly-mean GHI and DNI time series are compared to estimates from 11 solar databases regularly used in solar resource assessment studies: CAMS, CERES, ERA5, INPE, MERRA-2, Meteonorm, NASA-POWER, NSRDB, SARAH, SWERA-BR, and SWERA-US. For hourly GHI values, a range of RMS differences is found between the best (CAMS, 17.3%) and the worst (MERRA-2, 38.9%) results. The latter database is also affected by a larger bias (18.7%) than CAMS (4%). Larger RMS differences are found with hourly DNI, in a range extending from 37% (CAMS) to 63.4% (ERA5). Biases are all above 12%, except for CERES (−1%). For long-term mean-monthly GHI results, low biases of less than 1% are obtained with CAMS, CERES and NASA-POWER, whereas MERRA-2 overestimates (13%). Larger biases are found for mean-monthly DNI, spanning between CAMS (3%) and Meteonorm (−18.4%). Overall, CAMS appears the most consistent solar database for long-term irradiance time series at Petrolina. The significant differences found here between modeled databases are larger than expected, and underline the importance of regional validation studies like this one to decrease the incidence of uncertainties in solar resource assessments on the design and performance of solar energy projects. Data gaps; Data quality control; Solar irradiance; Solar resource assessment; Validation
Sayago, Silvina; Ovando, Gustavo; Almorox, Javier; Bocco, MónicaSayago, S., G. Ovando, J. Almorox, M. Bocco, 2020: Daily solar radiation from NASA-POWER product: assessing its accuracy considering atmospheric transparency. International Journal of Remote Sensing, 41(3), 897-910. doi: 10.1080/01431161.2019.1650986. Satellite remote sensing in estimating solar energy budget components at the top of the atmosphere (TOA) level and at the terrestrial level plays a very important role in various types of applications. Solar radiation data are especially problematic because of a quite generalized lack of sufficient data in quantity and quality. Satellite images allow solving the problem of continuity or lack of solar radiation data. The objective of this work was to fit daily solar radiation from NASA-POWER (National Aeronautics and Space Administration – Prediction Of Worldwide Energy Resources), considering different intervals of atmospheric transparency index. The accuracy was assessed from the analysis of voluminous data-sets registered by meteorological ground stations, 31 in number, located in whole Spain, during the period from 2000 to 2017. Clearness index (KT) was calculated to define nine classes of cloud cover conditions. The study reveals that the degree of correlation between the satellite data and observatory data depends upon atmospheric conditions and the correlation accuracy improves for higher values of KT. The coefficients of determination (R2), considering all KT values, were between 0.85 and 0.96; particularly for clear days R2 = 0.96 and root-mean-square error equal to 1.78 MJ m−2 d−1 were obtained. Geographically, the better statistic values were located in the central region of the country. NASA-POWER shows potential to estimate solar radiation and that it is an important information resource for different applications.
Scarino, Benjamin R.; Bedka, Kristopher; Bhatt, Rajendra; Khlopenkov, Konstantin; Doelling, David R.; Smith Jr., William L.Scarino, B. R., K. Bedka, R. Bhatt, K. Khlopenkov, D. R. Doelling, W. L. Smith Jr., 2020: A kernel-driven BRDF model to inform satellite-derived visible anvil cloud detection. Atmospheric Measurement Techniques, 13(10), 5491-5511. doi: https://doi.org/10.5194/amt-13-5491-2020. Abstract. Satellites routinely observe deep convective clouds across the world. The cirrus outflow from deep convection, commonly referred to as anvil cloud, has a ubiquitous appearance in visible and infrared (IR) wavelength imagery. Anvil clouds appear as broad areas of highly reflective and cold pixels relative to the darker and warmer clear sky background, often with embedded textured and colder pixels that indicate updrafts and gravity waves. These characteristics would suggest that creating automated anvil cloud detection products useful for weather forecasting and research should be straightforward, yet in practice such product development can be challenging. Some anvil detection methods have used reflectance or temperature thresholding, but anvil reflectance varies significantly throughout a day as a function of combined solar illumination and satellite viewing geometry, and anvil cloud top temperature varies as a function of convective equilibrium level and tropopause height. This paper highlights a technique for facilitating anvil cloud detection based on visible observations that relies on comparative analysis with expected cloud reflectance for a given set of angles, thereby addressing limitations of previous methods. A 1-year database of anvil-identified pixels, as determined from IR observations, from several geostationary satellites was used to construct a bidirectional reflectance distribution function (BRDF) model to quantify typical anvil reflectance across almost all expected viewing, solar, and azimuth angle configurations, in addition to the reflectance uncertainty for each angular bin. Application of the BRDF model for cloud optical depth retrieval in deep convection is described as well.
Scarino, Benjamin; Doelling, David R.; Bhatt, Rajendra; Gopalan, Arun; Haney, ConorScarino, B., D. R. Doelling, R. Bhatt, A. Gopalan, C. Haney, 2020: Evaluating the Magnitude of VIIRS Out-of-Band Response for Varying Earth Spectra. Remote Sensing, 12(19), 3267. doi: 10.3390/rs12193267. Prior evaluations of Visible Infrared Imaging Radiometer Suite (VIIRS) out-of-band (OOB) contribution to total signal revealed specification exceedance for multiple key solar reflective and infrared bands that are of interest to the passive remote-sensing community. These assessments are based on laboratory measurements, and although highly useful, do not necessarily translate to OOB contribution with consideration of true Earth-reflected or Earth-emitted spectra, especially given the significant spectral variation of Earth targets. That is, although the OOB contribution of VIIRS is well known, it is not a uniform quantity applicable across all scene types. As such, this article quantifies OOB contribution for multiple relative spectral response characterization versions across the S-NPP, NOAA-20, and JPSS-2 VIIRS sensors as a function of varied SCIAMACHY- and IASI-measured hyperspectral Earth-reflected and Earth-emitted scenes. For instance, this paper reveals measured radiance variations of nearly 2% for the S-NPP VIIRS M5 (~0.67 μm) band, and up to 5.7% for certain VIIRS M9 (~1.38 μm) and M13 (~4.06 μm) bands that are owed solely to the truncation of OOB response for a set of spectrally distinct Earth scenes. If unmitigated, e.g., by only considering the published extended bandpass, such variations may directly translate to scene-dependent scaling discrepancies or subtle errors in vegetative index determinations. Therefore, knowledge of OOB effects is especially important for inter-calibration or environmental retrieval efforts that rely on specific or multiple categories of Earth scene spectra, and also to researchers whose products rely on the impacted channels. Additionally, instrument teams may find this evaluation method useful for pre-launch characterization of OOB contribution with specific Earth targets in mind rather than relying on general models. VIIRS; S-NPP; hyperspectral; in-band; JPSS-2; NOAA-20; out-of-band; spectral response
Schifano, Luca; Smeesters, Lien; Berghmans, Francis; Dewitte, StevenSchifano, L., L. Smeesters, F. Berghmans, S. Dewitte, 2020: Optical System Design of a Wide Field-of-View Camera for the Characterization of Earth’s Reflected Solar Radiation. Remote Sensing, 12(16), 2556. doi: 10.3390/rs12162556. We report on the conceptual design of a new wide field-of-view shortwave camera, for measuring Earth’s reflected solar radiation. The camera comprises a commercial-off-the-shelf CMOS sensor, and a custom-designed wide field-of-view lens system with an opening angle of 140°. The estimated effective nadir resolution is 2.2 km. The simulated stand-alone random error of the broadband albedo is 3%. The camera is suited for integration within 1U of a CubeSat. earth radiation budget; radiative transfer; aspherical optical design; earth energy imbalance; reflected solar radiation; refractive imaging system; space instrumentation; wide field-of-view
Schwarz, M.; Folini, D.; Yang, S.; Allan, R. P.; Wild, M.Schwarz, M., D. Folini, S. Yang, R. P. Allan, M. Wild, 2020: Changes in atmospheric shortwave absorption as important driver of dimming and brightening. Nature Geoscience, 13(2), 110-115. doi: 10.1038/s41561-019-0528-y. Changes in the atmospheric absorption of shortwave radiation, probably through cloud and aerosol effects, is the main reason for the dimming and brightening over China and Europe in past decades, according to co-located surface and space observations.
Scott, Ryan C.; Myers, Timothy A.; Norris, Joel R.; Zelinka, Mark D.; Klein, Stephen A.; Sun, Moguo; Doelling, David R.Scott, R. C., T. A. Myers, J. R. Norris, M. D. Zelinka, S. A. Klein, M. Sun, D. R. Doelling, 2020: Observed Sensitivity of Low-Cloud Radiative Effects to Meteorological Perturbations over the Global Oceans. J. Climate, 33(18), 7717-7734. doi: 10.1175/JCLI-D-19-1028.1.
Semmler, Tido; Danilov, Sergey; Gierz, Paul; Goessling, Helge F.; Hegewald, Jan; Hinrichs, Claudia; Koldunov, Nikolay; Khosravi, Narges; Mu, Longjiang; Rackow, Thomas; Sein, Dmitry V.; Sidorenko, Dmitry; Wang, Qiang; Jung, ThomasSemmler, T., S. Danilov, P. Gierz, H. F. Goessling, J. Hegewald, C. Hinrichs, N. Koldunov, N. Khosravi, L. Mu, T. Rackow, D. V. Sein, D. Sidorenko, Q. Wang, T. Jung, 2020: Simulations for CMIP6 With the AWI Climate Model AWI-CM-1-1. Journal of Advances in Modeling Earth Systems, 12(9), e2019MS002009. doi: 10.1029/2019MS002009. The Alfred Wegener Institute Climate Model (AWI-CM) participates for the first time in the Coupled Model Intercomparison Project (CMIP), CMIP6. The sea ice-ocean component, FESOM, runs on an unstructured mesh with horizontal resolutions ranging from 8 to 80 km. FESOM is coupled to the Max Planck Institute atmospheric model ECHAM 6.3 at a horizontal resolution of about 100 km. Using objective performance indices, it is shown that AWI-CM performs better than the average of CMIP5 models. AWI-CM shows an equilibrium climate sensitivity of 3.2°C, which is similar to the CMIP5 average, and a transient climate response of 2.1°C which is slightly higher than the CMIP5 average. The negative trend of Arctic sea-ice extent in September over the past 30 years is 20–30% weaker in our simulations compared to observations. With the strongest emission scenario, the AMOC decreases by 25% until the end of the century which is less than the CMIP5 average of 40%. Patterns and even magnitude of simulated temperature and precipitation changes at the end of this century compared to present-day climate under the strong emission scenario SSP585 are similar to the multi-model CMIP5 mean. The simulations show a 11°C warming north of the Barents Sea and around 2°C to 3°C over most parts of the ocean as well as a wetting of the Arctic, subpolar, tropical, and Southern Ocean. Furthermore, in the northern middle latitudes in boreal summer and autumn as well as in the southern middle latitudes, a more zonal atmospheric flow is projected throughout the year. climate change; global climate model; AWI climate model; Coupled Model Intercomparison Project; unstructured mesh
Seo, Minji; Kim, Hyun-Cheol; Lee, Kyeong-Sang; Seong, Noh-Hun; Lee, Eunkyung; Kim, Jinsoo; Han, Kyung-SooSeo, M., H. Kim, K. Lee, N. Seong, E. Lee, J. Kim, K. Han, 2020: Characteristics of the Reanalysis and Satellite-Based Surface Net Radiation Data in the Arctic. Journal of Sensors. In this study, we compared four net radiation products: the fifth generation of European Centre for Medium-Range Weather Forecasts atmospheric reanalysis of the global climate (ERA5), National Centers for Environmental Prediction (NCEP), Clouds and the Earth’s Radiant Energy System Energy Balanced and Filled (EBAF), and Global Energy and Water Exchanges (GEWEX), based on ground observation data and intercomparison data. ERA5 showed the highest accuracy, followed by EBAF, GEWEX, and NCEP. When analyzing the validation grid, ERA5 showed the most similar data distribution to ground observation data. Different characteristics were observed between the reanalysis data and satellite data. In the case of satellite-based data, the net radiation value tended to increase at high latitudes. Compared with the reanalysis data, Greenland and the central Arctic appeared to be overestimated. All data were highly correlated, with a difference of 6–21 W/m2 among the products examined in this study. Error was attributed mainly to difficulties in predicting long-term climate change and having to combine net radiation data from several sources. This study highlights criteria that may be helpful in selecting data for future climate research models of this region.
Shell, Karen M.; de Szoeke, Simon P.; Makiyama, Michael; Feng, ZheShell, K. M., S. P. de Szoeke, M. Makiyama, Z. Feng, 2020: Vertical Structure of Radiative Heating Rates of the MJO during DYNAMO. J. Climate, 33(12), 5317-5335. doi: 10.1175/JCLI-D-19-0519.1. The vertical structure of radiative heating rates over the region of the tropical Indian Ocean associated with the MJO during the DYNAMO/ARM MJO Investigation Experiment is presented. The mean and variability of heating rates during active, suppressed, and disturbed phases are determined from the Pacific Northwest National Laboratory Combined Remote Sensing Retrieval (CombRet) from Gan Island, Maldives (0.69°S, 73.15°E). TOA and surface fluxes from the CombRet product are compared with collocated 3-hourly CERES SYN1deg Ed4A satellite retrievals. The fluxes are correlated in time with correlation coefficients around 0.9, yet CombRet time-mean OLR is 15 W m−2 larger. Previous work has suggested that CombRet undersamples high clouds, due to signal attenuation by low-level clouds and reduced instrument sensitivity with altitude. However, mean OLR differs between CombRet and CERES for all values of OLR, not just the lowest values corresponding to widespread high clouds. The discrepancy peaks for midrange OLR, suggestive of precipitating, towering cumulus convective clouds, rather than stratiform cirrus clouds. Low biases in the cloud-top height of thick clouds substantially contribute to the overestimate of OLR by CombRet. CombRet data are used to generate composite shortwave and longwave atmospheric heating rate profiles as a function of the local OLR. Although there is considerable variability in CombRet not directly related to OLR, the time–height structure of mean heating rate composites generated using OLR as the interpolant is broadly representative of tropical convective variability on intraseasonal time scales.
Sherwood, S.; Webb, M. J.; Annan, J. D.; Armour, K. C.; Forster, P. M.; Hargreaves, J. C.; Hegerl, G.; Klein, S. A.; Marvel, K. D.; Rohling, E. J.; Watanabe, M.; Andrews, T.; Braconnot, P.; Bretherton, C. S.; Foster, G. L.; Hausfather, Z.; Heydt, A. S. von der; Knutti, R.; Mauritsen, T.; Norris, J. R.; Proistosescu, C.; Rugenstein, M.; Schmidt, G. A.; Tokarska, K. B.; Zelinka, M. D.Sherwood, S., M. J. Webb, J. D. Annan, K. C. Armour, P. M. Forster, J. C. Hargreaves, G. Hegerl, S. A. Klein, K. D. Marvel, E. J. Rohling, M. Watanabe, T. Andrews, P. Braconnot, C. S. Bretherton, G. L. Foster, Z. Hausfather, A. S. v. d. Heydt, R. Knutti, T. Mauritsen, J. R. Norris, C. Proistosescu, M. Rugenstein, G. A. Schmidt, K. B. Tokarska, M. D. Zelinka, 2020: An assessment of Earth's climate sensitivity using multiple lines of evidence. Reviews of Geophysics, 58(4), e2019RG000678. doi: 10.1029/2019RG000678. We assess evidence relevant to Earth's equilibrium climate sensitivity per doubling of atmospheric CO2, characterized by an effective sensitivity S. This evidence includes feedback process understanding, the historical climate record, and the paleoclimate record. An S value lower than 2 K is difficult to reconcile with any of the three lines of evidence. The amount of cooling during the Last Glacial Maximum provides strong evidence against values of S greater than 4.5 K. Other lines of evidence in combination also show that this is relatively unlikely. We use a Bayesian approach to produce a probability density (PDF) for S given all the evidence, including tests of robustness to difficult-to-quantify uncertainties and different priors. The 66% range is 2.6-3.9 K for our Baseline calculation, and remains within 2.3-4.5 K under the robustness tests; corresponding 5-95% ranges are 2.3-4.7 K, bounded by 2.0-5.7 K (although such high-confidence ranges should be regarded more cautiously). This indicates a stronger constraint on S than reported in past assessments, by lifting the low end of the range. This narrowing occurs because the three lines of evidence agree and are judged to be largely independent, and because of greater confidence in understanding feedback processes and in combining evidence. We identify promising avenues for further narrowing the range in S, in particular using comprehensive models and process understanding to address limitations in the traditional forcing-feedback paradigm for interpreting past changes. Bayesian methods; global warming; climate sensitivity; Climate
Shi, Tenglong; Pu, Wei; Zhou, Yue; Cui, Jiecan; Zhang, Daizhou; Wang, XinShi, T., W. Pu, Y. Zhou, J. Cui, D. Zhang, X. Wang, 2020: Albedo of Black Carbon-Contaminated Snow Across Northwestern China and the Validation With Model Simulation. Journal of Geophysical Research: Atmospheres, 125(9), e2019JD032065. doi: 10.1029/2019JD032065. Light-absorbing particles in snow can significantly reduce the snow albedo. Quantification of the influence of black carbon (BC), one of the most important light-absorbing particles, on snow albedo is essential for understanding the budgets of solar radiation on snow-covered areas. We measured BC concentration in snow at 28 sites and snow albedo at 18 sites in a vast region across northwestern China in January 2018. The BC concentration was in a wide range of 40–1,850 ng g−1. The presence of the BC reduced the snow albedo by 0.01–0.20 at the visible wavelength band (400–750 nm). The reduction differed from sites to sites with large values close to industrial areas that are characterized by high pollutants emission. Albedos simulated with a Snow, Ice, and Aerosol Radiation model based on the measured BC agreed well with the measured albedos, with the deviation within ±0.03 and the average underestimation of
Shukla, Ravi P.; Huang, BohuaShukla, R. P., B. Huang, 2020: Cumulative Influence of Summer Subsurface Soil Temperature on North America Surface Temperature in the CFSv2. Journal of Geophysical Research: Atmospheres, 125(6), e2019JD031899. doi: 10.1029/2019JD031899. Analyzing a long simulation and a set of seasonal reforecasts of the Climate Forecast System version 2 (CFSv2), this study demonstrates a large model cold bias in the deep soil layer (100–200 cm) over most of North America continent during summer due to weaker seasonal change in summer. The summer subsurface temperature (SUBT) cold bias influences the land surface temperature (LST) during the summer and subsequent seasons in different ways over different geographical regions in North America: West of the Rocky Mountains, the SUBT's effect on LST is largely overruled by the stronger upstream marine influence from the Pacific. Over the central Great Plains, however, it is a major cause for severe cold LST bias during summer in the model simulation and reforecasts. As a result, model underestimates sensible heat flux into the atmosphere but overestimates latent heat flux. The latter may contribute to an excessive summer rainfall in the region. Over the northeast region, the SUBT cold bias persists to August and September, which causes an additional surface cooling in the fall and helps to bring LST to the freezing point early. This sets up the stage for a prolonged snow-albedo feedback. In particular, the model long simulation that passes through previous summer and fall demonstrates longer persistence of snow cover over the northeast region than reforecasts initialized in late winter and spring do. A cold bias of the water temperature in the North Atlantic seems also to play a role to prolong cold bias in the northeast region. deep soil layer (100–200 cm); NCEP CFSv2; North America continent; simulation and seasonal reforecasts; snow-albedo feedback; subsurface soil temperature
Sorooshian, Armin; Corral, Andrea F.; Braun, Rachel A.; Cairns, Brian; Crosbie, Ewan; Ferrare, Richard; Hair, Johnathan; Kleb, Mary M.; Mardi, Ali Hossein; Maring, Hal; McComiskey, Allison; Moore, Richard; Painemal, David; Scarino, Amy Jo; Schlosser, Joseph; Shingler, Taylor; Shook, Michael; Wang, Hailong; Zeng, Xubin; Ziemba, Luke; Zuidema, PaquitaSorooshian, A., A. F. Corral, R. A. Braun, B. Cairns, E. Crosbie, R. Ferrare, J. Hair, M. M. Kleb, A. H. Mardi, H. Maring, A. McComiskey, R. Moore, D. Painemal, A. J. Scarino, J. Schlosser, T. Shingler, M. Shook, H. Wang, X. Zeng, L. Ziemba, P. Zuidema, 2020: Atmospheric Research Over the Western North Atlantic Ocean Region and North American East Coast: A Review of Past Work and Challenges Ahead. Journal of Geophysical Research: Atmospheres, 125(6), e2019JD031626. doi: 10.1029/2019JD031626. Decades of atmospheric research have focused on the Western North Atlantic Ocean (WNAO) region because of its unique location that offers accessibility for airborne and ship measurements, gradients in important atmospheric parameters, and a range of meteorological regimes leading to diverse conditions that are poorly understood. This work reviews these scientific investigations for the WNAO region, including the East Coast of North America and the island of Bermuda. Over 50 field campaigns and long-term monitoring programs, in addition to 715 peer-reviewed publications between 1946 and 2019 have provided a firm foundation of knowledge for these areas. Of particular importance in this region has been extensive work at the island of Bermuda that is host to important time series records of oceanic and atmospheric variables. Our review categorizes WNAO atmospheric research into eight major categories, with some studies fitting into multiple categories (relative %): Aerosols (25%), Gases (24%), Development/Validation of Techniques, Models, and Retrievals (18%), Meteorology and Transport (9%), Air-Sea Interactions (8%), Clouds/Storms (8%), Atmospheric Deposition (7%), and Aerosol-Cloud Interactions (2%). Recommendations for future research are provided in the categories highlighted above. ACTIVATE; Aerosol; Atlantic Ocean; Cloud; Deposition; Gas
Steffen, John; Bourassa, MarkSteffen, J., M. Bourassa, 2020: Upper-Ocean Response to Precipitation Forcing in an Ocean Model Hindcast of Hurricane Gonzalo. J. Phys. Oceanogr., 50(11), 3219-3234. doi: 10.1175/JPO-D-19-0277.1.
Subba, Tamanna; Gogoi, Mukunda M.; Pathak, Binita; Bhuyan, Pradip K.; Babu, S. SureshSubba, T., M. M. Gogoi, B. Pathak, P. K. Bhuyan, S. S. Babu, 2020: Recent trend in the global distribution of aerosol direct radiative forcing from satellite measurements. Atmospheric Science Letters, 21(11), e975. doi: 10.1002/asl.975. Global distribution of aerosol direct radiative forcing (DRF) is estimated using Clouds and Earth's Radiant Energy System (CERES) synoptic (SYN) 1° datasets. During 2001–2017, a statistically significant change of global DRFs is revealed with a general decreasing trend (i.e., a reduced cooling effect) at the top of the atmosphere (DRFTOA 0.017 W⋅m−2⋅year−1) and at the surface (DRFSFC 0.033 W⋅m−2⋅year−1) with rapid change over the land compared to the global ocean. South Asia and Africa/Middle East regions depict significant increasing trend of atmospheric warming by 0.025 and 0.002 W·m−2⋅year−1 whereas, the rest of the regions show a decline. These regional variations significantly modulate the global mean DRF (−5.36 ± 0.04 W·m−2 at the TOA and − 9.64 ± 0.07 W·m−2 at the surface during the study period). The observed DRF trends are coincident with the change in the underlying aerosol properties, for example, aerosol optical depth, Ångström exponent and partly due to the increasing columnar burden of SO2 over some of the regions. This indicates that increasing industrialization and urbanization have caused prominent change in the DRF during recent decades. trend; angstrom exponent; aerosol optical depth; global aerosol radiative forcing
Suseno, Dwi Prabowo Yuga; Yamada, Tomohito J.Suseno, D. P. Y., T. J. Yamada, 2020: Simulating Flash Floods Using Geostationary Satellite-Based Rainfall Estimation Coupled with a Land Surface Model. Hydrology, 7(1), 9. doi: 10.3390/hydrology7010009. Clarifying hydrologic behavior, especially behavior related to extreme events such as flash floods, is vital for flood mitigation and management. However, discharge and rainfall measurement data are scarce, which is a major obstacle to flood mitigation. This study: (i) simulated flash floods on a regional scale using three types of rainfall forcing implemented in a land surface model; and (ii) evaluated and compared simulated flash floods with the observed discharge. The three types of rainfall forcing were those observed by the Automated Meteorological Data Acquisition System (AMeDAS) (Simulation I), the observed rainfall from the Ministry of Land, Infrastructure and Transportation (MLIT) (Simulation II), and the estimated rainfall from the Multi-purpose Transport Satellite (MTSAT), which was downscaled by AMeDAS rainfall (Simulation III). MLIT rainfall observations have a denser station network over the Ishikari River basin (spacing of approximately 10 km) compared with AMeDAS (spacing of approximately 20 km), so they are expected to capture the rainfall spatial distribution more accurately. A land surface model, the Minimal Advance Treatments of Surface Interaction and Runoff (MATSIRO), was implemented for the flash flood simulation. The river flow simulations were run over the Ishikari river basin at a 1-km grid resolution and a 1-h temporal resolution during August 2010. The statistical performance of the river flow simulations during a flash flood event on 23 and 24 August 2010 demonstrated that Simulation I was reasonable compared with Simulation III. The findings also suggest that the advantages of the MTSAT-based estimated rainfall (i.e., good spatial distribution) can be coupled with the benefit of direct AMeDAS observations (i.e., representation of the true rainfall). MTSAT; flash flood; heavy rainfall; LSM
Takahashi, Naoya; Hayasaka, TadahiroTakahashi, N., T. Hayasaka, 2020: Air–Sea Interactions among Oceanic Low-Level Cloud, Sea Surface Temperature, and Atmospheric Circulation on an Intraseasonal Time Scale in the Summertime North Pacific Based on Satellite Data Analysis. J. Climate, 33(21), 9195-9212. doi: 10.1175/JCLI-D-19-0670.1.
Terai, C. R.; Pritchard, M. S.; Blossey, P.; Bretherton, C. S.Terai, C. R., M. S. Pritchard, P. Blossey, C. S. Bretherton, 2020: The impact of resolving sub-kilometer processes on aerosol-cloud interactions of low-levels clouds in global model simulations. Journal of Advances in Modeling Earth Systems, 12(11), e2020MS002274. doi: 10.1029/2020MS002274. Sub-kilometer processes are critical to the physics of aerosol-cloud interaction but have been dependent on parameterizations in global model simulations. We thus report the strength of aerosol-cloud interaction in the Ultra-Parameterized Community Atmosphere Model (UPCAM), a multiscale climate model that uses coarse exterior resolution to embed explicit cloud resolving models with enough resolution (250-m horizontal, 20-m vertical) to quasi-resolve sub-kilometer eddies. To investigate the impact on aerosol-cloud interactions, UPCAM’s simulations are compared to a coarser multi-scale model with 4 km horizontal resolution. UPCAM produces cloud droplet number concentrations (Nd) and cloud liquid water path (LWP) values that are higher than the coarser model but equally plausible compared to observations. Our analysis focuses on the Northern Hemisphere (20° - 50°N) oceans, where historical aerosol increases have been largest. We find similarities in the overall radiative forcing from aerosol-cloud interactions in the two models, but this belies fundamental underlying differences. The radiative forcing from increases in LWP is weaker in UPCAM, whereas the forcing from increases in Nd is larger. Surprisingly, the weaker LWP increase is not due to a weaker increase in LWP in raining clouds, but a combination of weaker increase in LWP in non-raining clouds and a smaller fraction of raining clouds in UPCAM. The implication is that as global modeling moves towards finer than storm-resolving grids, nuanced model validation of ACI statistics conditioned on the existence of precipitation and good observational constraints on the baseline probability of precipitation will become key for tighter constraints and better conceptual understanding. clouds; climate change; GCM; aerosol-cloud interaction; multi-scale model
Thomas, Christopher M.; Dong, Bo; Haines, KeithThomas, C. M., B. Dong, K. Haines, 2020: Inverse modelling of global and regional energy and water cycle fluxes using Earth observation data. J. Climate, 33(5), 1707–1723. doi: 10.1175/JCLI-D-19-0343.1. The NASA Energy and Water Cycle Study (NEWS) climatology is a self–consistent coupled annual and seasonal cycle solution for radiative, turbulent and water fluxes over the Earth’s surface using Earth observation data covering 2000–2009. Here we seek to improve the NEWS solution, particularly over the ocean basins, by considering spatial covariances in the observation errors (some evidence for which is found by comparing five turbulent flux products over the oceans) and by introducing additional horizontal transports from ocean reanalyses as weak constraints. By explicitly representing large error covariances between surface heat flux components over the major ocean basins we retain the flux contrasts present in the original data and infer additional heat losses over the North Atlantic, more consistent with a strong Atlantic overturning. This change does not alter the global flux balance but if only the errors in evaporation and precipitation are correlated then those fluxes experience larger adjustments (e.g. the surface latent heat flux increases to 85±2 Wm−2). Replacing SeaFlux v1 with J-OFURO v3 ocean fluxes also leads to a considerable increase in the global latent heat loss as well as a larger North Atlantic heat loss. Furthermore, including a weak constraint on the horizontal transports of heat and freshwater from high-resolution ocean reanalyses improves the net fluxes over the North Atlantic, Caribbean and Arctic Oceans, without any impact on the global flux balances. These results suggest that better characterised flux uncertainties can greatly improve the quality of the optimised flux solution.
Thorsen, Tyler J.; Ferrare, Richard A.; Kato, Seiji; Winker, David M.Thorsen, T. J., R. A. Ferrare, S. Kato, D. M. Winker, 2020: Aerosol Direct Radiative Effect Sensitivity Analysis. J. Climate, 33(14), 6119-6139. doi: 10.1175/JCLI-D-19-0669.1.
Thorsen, Tyler J.; Winker, David M.; Ferrare, Richard A.Thorsen, T. J., D. M. Winker, R. A. Ferrare, 2020: Uncertainty in Observational Estimates of the Aerosol Direct Radiative Effect and Forcing. J. Climate, 34(1), 195-214. doi: 10.1175/JCLI-D-19-1009.1. AbstractA lower bound on the uncertainty in observational estimates of the aerosol direct radiative effect (DRE; the direct interaction with solar radiation by all aerosols) and the aerosol direct radiative forcing [DRF; the radiative effect of just anthropogenic aerosols (RFari)] is quantified by making the optimistic assumption that global aerosol observations can be made with the accuracy found in the Aerosol Robotic Network (AERONET) sun photometer retrievals. The global-mean all-sky aerosol DRE uncertainty was found to be 1.1 W m−2 (one standard deviation). The global-mean all-sky aerosol DRF (RFari) uncertainty was determined to be 0.31 W m−2. The total uncertainty in both quantities is dominated by contributions from the aerosol single scattering albedo uncertainty. These uncertainty estimates were compared to a literature survey of mostly satellite-based aerosol DRE/DRF values. Comparisons to previous studies reveal that most have significantly underestimated the aerosol DRE uncertainty. Past estimates of the aerosol DRF uncertainty are smaller (on average) than our optimistic observational estimates, including the aerosol DRF uncertainty given in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5). This disconnect between our observation-based uncertainty and that found in past aerosol DRF studies that rely, at least in part, on modeling is discussed. Also quantified is a potential reduction in the current observational uncertainty possible with a future generation of satellite observations that would leverage aerosol typing and more refined vertical information.
Tian, Jingjing; Dong, Xiquan; Xi, Baike; Feng, ZheTian, J., X. Dong, B. Xi, Z. Feng, 2020: Characteristics of Ice Cloud–Precipitation of Warm Season Mesoscale Convective Systems over the Great Plains. J. Hydrometeor., 21(2), 317-334. doi: 10.1175/JHM-D-19-0176.1. In this study, the mesoscale convective systems (MCSs) are tracked using high-resolution radar and satellite observations over the U.S. Great Plains during April–August from 2010 to 2012. The spatiotemporal variability of MCS precipitation is then characterized using the Stage IV product. We found that the spatial variability and nocturnal peaks of MCS precipitation are primarily driven by the MCS occurrence rather than the precipitation intensity. The tracked MCSs are further classified into convective core (CC), stratiform rain (SR), and anvil clouds regions. The spatial variability and diurnal cycle of precipitation in the SR regions of MCSs are not as significant as those of MCS precipitation. In the SR regions, the high-resolution, long-term ice cloud microphysical properties [ice water content (IWC) and ice water paths (IWPs)] are provided. The IWCs generally decrease with height. Spatially, the IWC, IWP, and precipitation are all higher over the southern Great Plains than over the northern Great Plains. Seasonally, those ice and precipitation properties are all higher in summer than in spring. Comparing the peak timings of MCS precipitation and IWPs from the diurnal cycles and their composite evolutions, it is found that when using the peak timing of IWPSR as a reference, the heaviest precipitation in the MCS convective core occurs earlier, while the strongest SR precipitation occurs later. The shift of peak timings could be explained by the stratiform precipitation formation process. The IWP and precipitation relationships are different at MCS genesis, mature, and decay stages. The relationships and the transition processes from ice particles to precipitation also depend on the low-level humidity.
Unglaub, Claudia; Block, Karoline (ORCID:0000000244582327); Mülmenstädt, Johannes (ORCID:0000000311056678); Sourdeval, Odran (ORCID:0000000228225303); Quaas, Johannes (ORCID:000000017057194X)Unglaub, C., K. Block, J. Mülmenstädt, O. Sourdeval, J. Quaas, 2020: A new classification of satellite-derived liquid water cloud regimes at cloud scale. Atmospheric Chemistry and Physics (Online), 20(4). doi: 10.5194/acp-20-2407-2020. The U.S. Department of Energy's Office of Scientific and Technical Information
Vargas Zeppetello, Lucas R.; Battisti, David S.; Baker, Marcia B.Vargas Zeppetello, L. R., D. S. Battisti, M. B. Baker, 2020: A New Look at the Variance of Summertime Temperatures over Land. J. Climate, 33(13), 5465-5477. doi: 10.1175/JCLI-D-19-0887.1. The increasing frequency of very high summertime temperatures has motivated growing interest in the processes determining the probability distribution of surface temperature over land. Here, we show that on monthly time scales, temperature anomalies can be modeled as linear responses to fluctuations in shortwave radiation and precipitation. Our model contains only three adjustable parameters, and, surprisingly, these can be taken as constant across the globe, notwithstanding large spatial variability in topography, vegetation, and hydrological processes. Using observations of shortwave radiation and precipitation from 2000 to 2017, the model accurately reproduces the observed pattern of temperature variance throughout the Northern Hemisphere midlatitudes. In addition, the variance in latent heat flux estimated by the model agrees well with the few long-term records that are available in the central United States. As an application of the model, we investigate the changes in the variance of monthly averaged surface temperature that might be expected due to anthropogenic climate change. We find that a climatic warming of 4°C causes a 10% increase in temperature variance in parts of North America.
Vielberg, Kristin; Kusche, JürgenVielberg, K., J. Kusche, 2020: Extended forward and inverse modeling of radiation pressure accelerations for LEO satellites. Journal of Geodesy, 94(4), 43. doi: 10.1007/s00190-020-01368-6. For low Earth orbit (LEO) satellites, activities such as precise orbit determination, gravity field retrieval, and thermospheric density estimation from accelerometry require modeled accelerations due to radiation pressure. To overcome inconsistencies and better understand the propagation of modeling errors into estimates, we here suggest to extend the standard analytical LEO radiation pressure model with emphasis on removing systematic errors in time-dependent radiation data products for the Sun and the Earth. Our extended unified model of Earth radiation pressure accelerations is based on hourly CERES SYN1deg data of the Earth’s outgoing radiation combined with angular distribution models. We apply this approach to the GRACE (Gravity Recovery and Climate Experiment) data. Validations with 1 year of calibrated accelerometer measurements suggest that the proposed model extension reduces RMS fits between 5 and 27%, depending on how measurements were calibrated. In contrast, we find little changes when implementing, e.g., thermal reradiation or anisotropic reflection at the satellite’s surface. The refined model can be adopted to any satellite, but insufficient knowledge of geometry and in particular surface properties remains a limitation. In an inverse approach, we therefore parametrize various combinations of possible systematic errors to investigate estimability and understand correlations of remaining inconsistencies. Using GRACE-A accelerometry data, we solve for corrections of material coefficients and CERES fluxes separately over ocean and land. These results are encouraging and suggest that certain physical radiation pressure model parameters could indeed be determined from satellite accelerometry data.
Wall, Casey J.; Norris, Joel R.; Gasparini, Blaž; Smith, William L.; Thieman, Mandana M.; Sourdeval, OdranWall, C. J., J. R. Norris, B. Gasparini, W. L. Smith, M. M. Thieman, O. Sourdeval, 2020: Observational Evidence that Radiative Heating Modifies the Life Cycle of Tropical Anvil Clouds. J. Climate, 33(20), 8621–8640. doi: 10.1175/JCLI-D-20-0204.1.
Wan, Hui; Woodward, Carol S.; Zhang, Shixuan; Vogl, Christopher J.; Stinis, Panos; Gardner, David J.; Rasch, Philip J.; Zeng, Xubin; Larson, Vincent E.; Singh, BalwinderWan, H., C. S. Woodward, S. Zhang, C. J. Vogl, P. Stinis, D. J. Gardner, P. J. Rasch, X. Zeng, V. E. Larson, B. Singh, 2020: Improving time-step convergence in an atmosphere model with simplified physics: the impacts of closure assumption and process coupling. Journal of Advances in Modeling Earth Systems, (In Press). doi: 10.1029/2019MS001982. Convergence testing is a common practice in the development of dynamical cores of atmospheric models but is not as often exercised for the parameterization of sub-grid physics. An earlier study revealed that the stratiform cloud parameterizations in several predecessors of the Energy Exascale Earth System Model (E3SM) showed strong time-step sensitivity and slower-than-expected convergence when the model's time step was systematically refined. In this work, a simplified atmosphere model is configured that consists of the spectral-element dynamical core of the E3SM atmosphere model coupled with a large-scale condensation parameterization based on commonly used assumptions. This simplified model also resembles E3SM and its predecessors in the numerical implementation of process coupling and shows poor time-step convergence in short ensemble tests. We present a formal error analysis to reveal the expected time-step convergence rate and the conditions for obtaining such convergence. Numerical experiments are conducted to investigate the root causes of convergence problems. We show that revisions in the process coupling and closure assumption help to improve convergence in short simulations using the simplified model; the same revisions applied to a full atmosphere model lead to significant changes in the simulated long-term climate. This work demonstrates that causes of convergence issues in atmospheric simulations can be understood by combining analyses from physical and mathematical perspectives. Addressing convergence issues can help to obtain a discrete model that is more consistent with the intended representation of the physical phenomena. Parameterization; Atmospheric model; Convergence; Time stepping
Wang, Dongdong; Liang, Shunlin; Zhang, Yi; Gao, Xueyuan; Brown, Meredith G. L.; Jia, AolinWang, D., S. Liang, Y. Zhang, X. Gao, M. G. L. Brown, A. Jia, 2020: A New Set of MODIS Land Products (MCD18): Downward Shortwave Radiation and Photosynthetically Active Radiation. Remote Sensing, 12(1), 168. doi: 10.3390/rs12010168. Surface downward shortwave radiation (DSR) and photosynthetically active radiation (PAR), its visible component, are key parameters needed for many land process models and terrestrial applications. Most existing DSR and PAR products were developed for climate studies and therefore have coarse spatial resolutions, which cannot satisfy the requirements of many applications. This paper introduces a new global high-resolution product of DSR (MCD18A1) and PAR (MCD18A2) over land surfaces using the MODIS data. The current version is Collection 6.0 at the spatial resolution of 5 km and two temporal resolutions (instantaneous and three-hour). A look-up table (LUT) based retrieval approach was chosen as the main operational algorithm so as to generate the products from the MODIS top-of-atmosphere (TOA) reflectance and other ancillary data sets. The new MCD18 products are archived and distributed via NASA’s Land Processes Distributed Active Archive Center (LP DAAC). The products have been validated based on one year of ground radiation measurements at 33 Baseline Surface Radiation Network (BSRN) and 25 AmeriFlux stations. The instantaneous DSR has a bias of −15.4 W/m2 and root mean square error (RMSE) of 101.0 W/m2, while the instantaneous PAR has a bias of −0.6 W/m2 and RMSE of 45.7 W/m2. RMSE of daily DSR is 32.3 W/m2, and that of the daily PAR is 13.1 W/m2. The accuracy of the new MODIS daily DSR data is higher than the GLASS product and lower than the CERES product, while the latter incorporates additional geostationary data with better capturing DSR diurnal variability. MCD18 products are currently under reprocessing and the new version (Collection 6.1) will provide improved spatial resolution (1 km) and accuracy. MODIS; validation; downward shortwave radiation; photosynthetically active radiation; satellite product; solar radiation
Wang, Minqi; Peng, Yiran; Liu, Yangang; Liu, Yu; Xie, Xiaoning; Guo, ZengyuanWang, M., Y. Peng, Y. Liu, Y. Liu, X. Xie, Z. Guo, 2020: Understanding cloud droplet spectral dispersion effect using empirical and semi-analytical parameterizations in NCAR CAM5.3. Earth and Space Science, 7(8), e2020EA001276. doi: 10.1029/2020EA001276. Five parameterizations of cloud droplet spectral shape are implemented in a global climate model to investigate the dispersion effect and aerosol indirect effect (AIE). We design a series of experiments by modifying the microphysical cloud scheme of NCAR CAM5.3 (Community Atmospheric Model Version 5.3). We employ four empirical (Martin94, RLiu03, PengL03, Liu08) and one semi-analytical (LiuLi15) expressions for cloud droplet spectral shape parameters. Analysis focuses on the instantaneous differences in the simulated cloud microphysical properties and the comparison between model output and satellite data. The results show that RLiu03, PengL03 and LiuLi15 produce wider droplet spectrum and faster autoconversion rate, but Liu08 has a narrower droplet spectrum and slower autoconversion rate than the default parameterization (Martin94) in CAM5.3. Global dispersion effects caused by the five parameterizations modify the aerosol indirect effect by -10% (counteract) to 13% (strengthen). The simulated AIEs and dispersion effects exhibit noticeably spatial inhomogeneity. In the sensitive regions of AIE (Southeast Asia, North Pacific and west coast of South America), we decompose the response of shortwave cloud forcing to the change in droplet number for analysis. The varying dispersion effects can be explained by different responses of cloud properties in different spectral parameterizations.
Wang, Tianxing; Shi, Jiancheng; Ma, Ya; Letu, Husi; Li, XingcaiWang, T., J. Shi, Y. Ma, H. Letu, X. Li, 2020: All-sky longwave downward radiation from satellite measurements: General parameterizations based on LST, column water vapor and cloud top temperature. ISPRS Journal of Photogrammetry and Remote Sensing, 161, 52-60. doi: 10.1016/j.isprsjprs.2020.01.011. Remotely sensed surface longwave downward radiation (LWDR) plays an essential role in studying the surface energy budget and greenhouse effect. Most existing satellite-based methods or products depend on variables that are not readily available from space such as, liquid water path, air temperature, vapor pressure and/or cloud-base temperature etc., which seriously restrict the wide applications of satellite data. In this paper, new nonlinear parameterizations and a machine learning-based model for deriving all-sky LWDR are proposed based only on land surface temperature (LST), column water vapor and cloud-top temperature (CTT), that are relatively readily available day and night for most satellite missions. It is the first time to incorporate the CTT in the parameterizations for estimating LWDR under the cloudy-sky conditions. The results reveal that the new models work well and can derive all-sky global LWDR with reasonable accuracies (RMSE  CERES; Land surface temperature; Cloud-top temperature; Cloudy-sky; Column water vapor; Surface longwave downward radiation
Weaver, Clark J.; Wu, Dong L.; Bhartia, Pawan K.; Labow, Gordon J.; Haffner, David P.Weaver, C. J., D. L. Wu, P. K. Bhartia, G. J. Labow, D. P. Haffner, 2020: A Long-Term Cloud Albedo Data Record Since 1980 from UV Satellite Sensors. Remote Sensing, 12(12), 1982. doi: 10.3390/rs12121982. Black-sky cloud albedo (BCA) is derived from satellite UV 340 nm observations from NOAA and NASA satellites to infer long-term (1980–2018) shortwave cloud albedo variations induced by volcano eruptions, the El Niño–Southern Oscillation, and decadal warming. While the UV cloud albedo has shown no long-term trend since 1980, there are statistically significant reductions over the North Atlantic and over the marine stratocumulus decks off the coast of California; increases in cloud albedo can be seen over Southeast Asia and over cloud decks off the coast of South America. The derived BCA assumes a C-1 water cloud model with varying cloud optical depths and a Cox–Munk surface BRDF over the ocean, using radiances calibrated over the East Antarctic Plateau and Greenland ice sheets during summer. ENSO; diurnal cycle; cloud feedback; cloud albedo; OMPS; SBUV; volcanoes
Whitburn, Simon; Clarisse, Lieven; Bauduin, Sophie; George, Maya; Hurtmans, Daniel; Safieddine, Sarah; Coheur, Pierre François; Clerbaux, CathyWhitburn, S., L. Clarisse, S. Bauduin, M. George, D. Hurtmans, S. Safieddine, P. F. Coheur, C. Clerbaux, 2020: Spectrally Resolved Fluxes from IASI Data: Retrieval Algorithm for Clear-Sky Measurements. J. Climate, 33(16), 6971-6988. doi: 10.1175/JCLI-D-19-0523.1.
Wild, MartinWild, M., 2020: The global energy balance as represented in CMIP6 climate models. Climate Dynamics, 55(3), 553-577. doi: 10.1007/s00382-020-05282-7. A plausible simulation of the global energy balance is a first-order requirement for a credible climate model. Here I investigate the representation of the global energy balance in 40 state-of-the-art global climate models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6). In the CMIP6 multi-model mean, the magnitudes of the energy balance components are often in better agreement with recent reference estimates compared to earlier model generations on a global mean basis. However, the inter-model spread in the representation of many of the components remains substantial, often on the order of 10–20 Wm−2 globally, except for aspects of the shortwave clear-sky budgets, which are now more consistently simulated by the CMIP6 models. The substantial inter-model spread in the simulated global mean latent heat fluxes in the CMIP6 models, exceeding 20% (18 Wm−2), further implies also large discrepancies in their representation of the global water balance. From a historic perspective of model development over the past decades, the largest adjustments in the magnitudes of the simulated present-day global mean energy balance components occurred in the shortwave atmospheric clear-sky absorption and the surface downward longwave radiation. Both components were gradually adjusted upwards over several model generations, on the order of 10 Wm−2, to reach 73 and 344 Wm−2, respectively in the CMIP6 multi-model means. Thereby, CMIP6 has become the first model generation that largely remediates long-standing model deficiencies related to an overestimation in surface downward shortwave and compensational underestimation in downward longwave radiation in its multi-model mean.
Williams, K. D.; Hewitt, A. J.; Bodas‐Salcedo, A.Williams, K. D., A. J. Hewitt, A. Bodas‐Salcedo, 2020: Use of Short-Range Forecasts to Evaluate Fast Physics Processes Relevant for Climate Sensitivity. Journal of Advances in Modeling Earth Systems, 12(4), e2019MS001986. doi: 10.1029/2019MS001986. The configuration of the Met Office Unified Model being submitted to CMIP6 has a high climate sensitivity. Previous studies have suggested that the impact of model changes on initial tendencies in numerical weather prediction (NWP) should be used to guide their suitability for inclusion in climate models. In this study we assess, using NWP experiments, the atmospheric model changes which lead to the increased climate sensitivity in the CMIP6 configuration, namely, the replacement of the aerosol scheme with GLOMAP-mode and the introduction of a scheme for representing the turbulent production of liquid water within mixed-phase cloud. Overall, the changes included in this latest configuration were found to improve the initial tendencies of the model state variables over the first 6 hr of the forecast, this timescale being before significant dynamical feedbacks are likely to occur. The reduced model drift through the forecast appears to be the result of increased cloud liquid water, leading to enhanced radiative cooling from cloud top and contributing to a stronger shortwave cloud radiative effect. These changes improve the 5-day forecast in traditional metrics used for numerical weather prediction. This study was conducted after the model was frozen and the climate sensitivity of the model determined; hence, it provides an independent test of the model changes contributing to the higher climate sensitivity. The results, along with the large body process-orientated evaluation conducted during the model development process, provide reassurance that these changes are improving the physical processes simulated by the model.
Wolf, Kevin; Ehrlich, André; Mech, Mario; Hogan, Robin J.; Wendisch, ManfredWolf, K., A. Ehrlich, M. Mech, R. J. Hogan, M. Wendisch, 2020: Evaluation of ECMWF Radiation Scheme Using Aircraft Observations of Spectral Irradiance above Clouds. J. Atmos. Sci., 77(8), 2665-2685. doi: 10.1175/JAS-D-19-0333.1.
Wong, T.; Stackhouse, P. W.; Kratz, D. P.; Sawaengphokhai, Parnchai; Wilber, A. C.; Gupta, S. K.; Loeb, N. GWong, T., P. W. Stackhouse, D. P. Kratz, P. Sawaengphokhai, A. C. Wilber, S. K. Gupta, N. G. Loeb, 2020: Earth Radiation Budget at Top-Of-Atmosphere [in “State of the Climate in 2019”].. Bull. Amer. Meteor. Soc, 101(8), S68-69. doi: 10.1175/BAMS-D-20-0104.1.
Wright, J. S.; Sun, X.; Konopka, P.; Krüger, K.; Legras, B.; Molod, A. M.; Tegtmeier, S.; Zhang, G. J.; Zhao, X.Wright, J. S., X. Sun, P. Konopka, K. Krüger, B. Legras, A. M. Molod, S. Tegtmeier, G. J. Zhang, X. Zhao, 2020: Differences in tropical high clouds among reanalyses: origins and radiative impacts. Atmospheric Chemistry and Physics, 20(14), 8989–9030. doi: 10.5194/acp-20-8989-2020.
Wu, Dong L.; Lee, Jae Nyung; Kim, Kyu-Myong; Lim, Young-KwonWu, D. L., J. N. Lee, K. Kim, Y. Lim, 2020: Interannual Variations of TOA Albedo over the Arctic, Antarctic and Tibetan Plateau in 2000–2019. Remote Sensing, 12(9), 1460. doi: 10.3390/rs12091460. Recent changes in Earth’s climate system have significantly affected the radiation budget and its year-to-year variations at top of the atmosphere (TOA). Observing high-latitude TOA fluxes is still challenging from space, because spatial inhomogeneity of surface/atmospheric radiative processes and spectral variability can reflect sunlight very differently. In this study we analyze the 20-year TOA flux and albedo data from CERES and MISR over the Arctic, the Antarctic, and Tibetan Plateau (TP), and found overall great consistency in the TOA albedo trend and interannual variations. The observations reveal a lagged correlation between the Arctic and subarctic albedo fluctuations. The observed year-to-year variations are further used to evaluate the reanalysis data, which exhibit substantial shortcomings in representing the polar TOA flux variability. The observed Arctic flux variations are highly correlated with cloud fraction (CF), except in the regions where CF > 90% or where the surface is covered by ice. An empirical orthogonal function (EOF) analysis shows that the first five EOFs can account for ~50% of the Arctic TOA variance, whereas the correlation with climate indices suggests that Sea Ice Extent (SIE), North Atlantic Oscillation (NAO) and 55°N–65°N cloudiness are the most influential processes in driving the TOA flux variabilities. albedo; shortwave radiation; 4-year oscillation; interannual variations; lagged correlation; top of the atmosphere
Wunderling, Nico; Willeit, Matteo; Donges, Jonathan F.; Winkelmann, RicardaWunderling, N., M. Willeit, J. F. Donges, R. Winkelmann, 2020: Global warming due to loss of large ice masses and Arctic summer sea ice. Nature Communications, 11(1), 5177. doi: 10.1038/s41467-020-18934-3. Several large-scale cryosphere elements such as the Arctic summer sea ice, the mountain glaciers, the Greenland and West Antarctic Ice Sheet have changed substantially during the last century due to anthropogenic global warming. However, the impacts of their possible future disintegration on global mean temperature (GMT) and climate feedbacks have not yet been comprehensively evaluated. Here, we quantify this response using an Earth system model of intermediate complexity. Overall, we find a median additional global warming of 0.43 °C (interquartile range: 0.39−0.46 °C) at a CO2 concentration of 400 ppm. Most of this response (55%) is caused by albedo changes, but lapse rate together with water vapour (30%) and cloud feedbacks (15%) also contribute significantly. While a decay of the ice sheets would occur on centennial to millennial time scales, the Arctic might become ice-free during summer within the 21st century. Our findings imply an additional increase of the GMT on intermediate to long time scales.
Xu, Xiaoqi; Lu, Chunsong; Liu, Yangang; Gao, Wenhua; Wang, Yuan; Cheng, Yueming; Luo, Shi; Weverberg, Kwinten VanXu, X., C. Lu, Y. Liu, W. Gao, Y. Wang, Y. Cheng, S. Luo, K. V. Weverberg, 2020: Effects of Cloud Liquid-Phase Microphysical Processes in Mixed-Phase Cumuli Over the Tibetan Plateau. Journal of Geophysical Research: Atmospheres, 125(19), e2020JD033371. doi: 10.1029/2020JD033371. Numerical simulations often overpredict precipitation over the Tibetan Plateau (TP). To examine the factors causing precipitation overprediction, different parameterizations of liquid-phase microphysical processes (accretion, autoconversion, and entrainment mixing) are implemented into the Morrison microphysics scheme to simulate a TP precipitation event in summer with the Weather Research and Forecasting (WRF) model. The general spatial distribution and temporal trend of precipitation are captured by all simulations, but the precipitation rate is overpredicted. The results from sensitivity experiments suggest that compared to other examined liquid-phase processes, the accretion process is more important in precipitation simulation over the TP region. Further investigation with the Heidke skill scores reveals that accretion parameterization that takes into account the raindrop size produces the most accurate results in terms of the total surface precipitation. This parameterization suppresses spurious accretion and does not produce liquid-phase precipitation until cloud droplets are big enough. It is also confirmed that increasing the model resolution can reduce precipitation overprediction. Results from the case study are confirmed by the use of a 1-month simulation. Tibetan Plateau; cloud microphysics; precipitation; warm rain processes
Yang, DazhiYang, D., 2020: Quantifying the spatial scale mismatch between satellite-derived solar irradiance and in situ measurements: A case study using CERES synoptic surface shortwave flux and the Oklahoma Mesonet. Journal of Renewable and Sustainable Energy, 12(5), 056104. doi: 10.1063/5.0025771.
Yang, Feng; Cheng, JieYang, F., J. Cheng, 2020: A framework for estimating cloudy sky surface downward longwave radiation from the derived active and passive cloud property parameters. Remote Sensing of Environment, 248, 111972. doi: 10.1016/j.rse.2020.111972. The cloud-base temperature (CBT) is one of the parameters that dominates the cloudy sky surface downward longwave radiation (SDLR). However, CBT is rarely available at regional and global scales, and its application in estimating cloud sky SDLR is limited. In this study, a framework to globally estimate cloud sky SDLR during both daytime and nighttime is proposed. This framework is composed of three parts. First, a global cloudy property database was constructed by combing the extracted cloud vertical structure (CVS) parameters from the active CloudSat data and cloud properties from passive MODIS data. Second, the empirical methods for estimating cloud thickness (CT) under ISCCP cloud classification system and MODIS cloud classification system were developed. Additionally, the coefficients of CERES CT estimate models were refitted using the constructed cloud property database. With the estimated CT and reanalysis data, calculating the CBT is straightforward. The accuracy of the estimated CT for ISCCP cloud type is compared with the existing studies that were conducted at local scales. Our CT estimate accuracy is comparable to that of the existing studies. According to the validation results at ARM NSA and SGP stations, the CT estimated by the developed CT model for MODIS cloud type is better than that estimated by the original CERES CT model. Finally, the cloudy sky SDLR values were derived by feeding the estimated CBT and other parameters to the single-layer cloud model (SLCM). When validated by the ground measured SDLR collected from the SURFRAD network, the bias and RMSE are 5.42 W∙m−2 and 30.3 W∙m−2, respectively. This accuracy is comparable to the evaluation results of the mainstream SDLR products (Gui et al. 2010), the new evaluation results of SLCMs (Yu et al. 2018), and the accuracy of a new cloudy sky SDLR estimate method (Wang et al. 2018). All the derived CBTs improve the SDLR estimate accuracy more than the SLCM that directly uses cloud-top temperature (CTT). We will collect more ground measurements and continue to validate the developed framework in the future. Remote sensing; Cloud-top temperature; Cloud thickness; Cloud-base temperature; Single-layer cloud model; Surface downward longwave radiation
Yang, Qiguang; Liu, Xu; Wu, WanYang, Q., X. Liu, W. Wu, 2020: A Hyperspectral Bidirectional Reflectance Model for Land Surface. Sensors, 20(16), 4456. doi: 10.3390/s20164456. A hyperspectral bidirectional reflectance (HSBR) model for land surface has been developed in this work. The HSBR model includes a very diverse land surface bidirectional reflectance distribution function (BRDF) database with ~40,000 spectra. The BRDF database is saved as Ross-Li parameters, which can generate hyperspectral reflectance spectra at different sensor and solar observation geometries. The HSBR model also provides an improved method for generating hyperspectral surface reflectance using multiband satellite measurements. It is shown that the land surface reflective spectrum can be easily simulated using BRDF parameters or reflectance at few preselected wavelengths. The HSBR model is validated using the U.S. Geological Survey (USGS) vegetation database and the AVIRIS reflectance product. The simulated reflective spectra fit the measurements very well with standard deviations normally smaller than 0.01 in the unit of reflectivity. The HSBR model could be used to significantly improve the quality of the reflectance products of satellite and airborne sensors. It also plays important role for intercalibration among space-based instruments and other land surface related applications. remote sensing; BRDF; hyperspectral bidirectional reflectance model; land surface; Ross-Li model
Yang, Quan; Zhang, Feng; Zhang, Hua; Wang, Zhili; Iwabuchi, Hironobu; Li, JiangnanYang, Q., F. Zhang, H. Zhang, Z. Wang, H. Iwabuchi, J. Li, 2020: Impact of δ-Four-Stream Radiative Transfer Scheme on global climate model simulation. Journal of Quantitative Spectroscopy and Radiative Transfer, 243, 106800. doi: 10.1016/j.jqsrt.2019.106800. The impact of radiative transfer scheme on global climate model (GCM) simulation is presented in this paper by comparing the difference between δ-two-stream adding method (δ-2DDA) and adding algorithm of the δ-four-stream discrete ordinates method (δ-4DDA) radiation schemes in the Atmospheric General Circulation Model of the Beijing Climate Center (BCC_AGCM). Only consider the effects of the calculation method itself, the δ-4DDA reduces the negative shortwave cloud radiative effect (CRE) in the areas with a significant fraction of low cloud, while enhances the negative shortwave CRE in the areas with the large fraction of high cloud. For the longwave CRE, the δ-4DDA enhances the longwave CRE drastically in the regions with a significant fraction of the high cloud. The feedback of clouds results in more interesting results. The δ-4DDA produces more accurate shortwave CRE in the region over the land and ocean in the middle and high latitude areas. The longwave CRE simulated by δ-4DDA is better than that affected by δ-2DDA over the ground in Africa, South America, and Atlantic. The change of radiation scheme affects the simulation of other meteorological variables. The simulation of global humidity by δ-4DDA is improved obviously. The δ-4DDA simulates more accurate temperature in continents of the northern hemisphere and precipitation in North America, Africa, northern Indian Ocean and western Pacific. Although the improvement of every physical process is required to develop the models, implementing δ-4DDA scheme into GCM and evaluating the effect of it are necessary and meaningful. Global climate model; Radiative transfer scheme; δ-4DDA
Yarahmadi, Mehran; Mahan, J. Robert; McFall, Kevin; Ashraf, Anum BarkiYarahmadi, M., J. R. Mahan, K. McFall, A. B. Ashraf, 2020: Numerical Focusing of a Wide-Field-Angle Earth Radiation Budget Imager Using an Artificial Neural Network. Remote Sensing, 12(1), 176. doi: 10.3390/rs12010176. Narrow field-of-view scanning thermistor bolometer radiometers have traditionally been used to monitor the earth’s radiant energy budget from low earth orbit (LEO). Such instruments use a combination of cross-path scanning and along-path spacecraft motion to obtain a patchwork of punctual observations which are ultimately assembled into a mosaic. Monitoring has also been achieved using non-scanning instruments operating in a push-broom mode in LOE and imagers operating in geostationary orbit. The current contribution considers a fourth possibility, that of an imager operating in LEO. The system under consideration consists of a Ritchey-Chrétien telescope illuminating a plane two-dimensional microbolometer array. At large field angles, the focal length of the candidate instrument is field-angle dependent, resulting in a blurred image in the readout plane. Presented is a full-field focusing algorithm based on an artificial neural network (ANN). Absorbed power distributions on the microbolometer array produced by discretized scenes are obtained using a high-fidelity Monte Carlo ray-trace (MCRT) model of the imager. The resulting readout array/scene pairs are then used to train an ANN. We demonstrate that a properly trained ANN can be used to convert the readout power distribution into an accurate image of the corresponding discretized scene. This opens the possibility of using an ANN based on a high-fidelity imager model for numerical focusing of an actual imager. artificial neural networks; earth radiation budget monitoring; image deblurring; numerical focusing
Yin, Jun; Molini, Annalisa; Porporato, AmilcareYin, J., A. Molini, A. Porporato, 2020: Impacts of solar intermittency on future photovoltaic reliability. Nature Communications, 11(1), 4781. doi: 10.1038/s41467-020-18602-6. As photovoltaic power is expanding rapidly worldwide, it is imperative to assess its promise under future climate scenarios. While a great deal of research has been devoted to trends in mean solar radiation, less attention has been paid to its intermittent character, a key challenge when compounded with uncertainties related to climate variability. Using both satellite data and climate model outputs, we characterize solar radiation intermittency to assess future photovoltaic reliability. We find that the relation between the future power supply and long-term mean solar radiation trends is spatially heterogeneous, showing power reliability is more sensitive to the fluctuations of mean solar radiation in hot arid regions. Our results highlight how reliability analysis must account simultaneously for the mean and intermittency of solar inputs when assessing the impacts of climate change on photovoltaics.
Yost, Christopher R.; Minnis, Patrick; Sun-Mack, Sunny; Chen, Yan; Smith, William L.Yost, C. R., P. Minnis, S. Sun-Mack, Y. Chen, W. L. Smith, 2020: CERES MODIS Cloud Product Retrievals for Edition 4–Part II: Comparisons to CloudSat and CALIPSO. IEEE Transactions on Geoscience and Remote Sensing, 1-30. doi: 10.1109/TGRS.2020.3015155. Assessments of the Clouds and the Earth's Radiant Energy System Edition 4 (Ed4) cloud retrievals are critical for climate studies. Ed4 cloud parameters are evaluated using instruments in the A-Train Constellation. Cloud-Aerosol LiDAR with Orthogonal Polarization (CALIOP) and Cloud Profiling Radar (CPR) retrievals are compared with Ed4 retrievals from the Aqua Moderate-Resolution Imaging Spectroradiometer (MODIS) as a function of the CALIOP horizontal averaging (HA) scale. Regardless of the HA scale, MODIS daytime (nighttime) water cloud fraction (CF) is greater (less) than that from CALIOP. MODIS ice CF is less than CALIOP overall, with the largest differences in polar regions. Ed4 and CALIOP retrieve the same cloud phase in 70%-98% of simultaneous observations depending on the time of day, surface conditions, HA scales, and type of cloud vertical structure. Mean cloud top height (CTH) differences for single-layer water clouds over snow-/ice-free surfaces are less than 100 m. Base altitude positive biases of 170-460 m may be impacted by CPR detection limitations. Average MODIS ice CTHs are underestimated by 70 m for some deep convective clouds and up to 2.2 km for thin cirrus. Ice cloud base altitudes are typically underestimated (overestimated) during daytime (nighttime). MODIS and CALIOP cirrus optical depths over oceans are within 46% and 5% for daytime and nighttime observations, respectively. Ice water path differences depend on the CALIOP retrieval version and warrant further investigation. Except for daytime cirrus optical depth, Ed4 cloud property retrievals are at least as accurate as other long-term operational cloud property retrieval systems. cloud; Clouds and the Earth's Radiant Energy System (CERES); cloud remote sensing; Climate; cloud height; cloud optical depth (COD); cloud phase; Cloud-Aerosol LiDAR and Infrared Pathfinder Satellite Observation (CALIPSO); MODerate-resolution Imaging Spectroradiometer (MODIS); validation.
You, Cheng; Tjernström, Michael; Devasthale, AbhayYou, C., M. Tjernström, A. Devasthale, 2020: Warm-Air Advection Over Melting Sea-Ice: A Lagrangian Case Study. Boundary-Layer Meteorology. doi: 10.1007/s10546-020-00590-1. Observations from the 2014 Arctic Clouds in Summer Experiment indicate that, in summer, warm-air advection over melting sea-ice results in a strong surface melting feedback forced by a very strong surface-based temperature inversion and fog formation exerting additional heat flux on the surface. Here, we analyze this case further using a combination of reanalysis dataset and satellite products in a Lagrangian framework, thereby extending the view spatially from the local icebreaker observations into a Langrangian perspective. The results confirm that warm-air advection induces a positive net surface-energy-budget anomaly, exerting positive longwave radiation and turbulent heat flux on the surface. Additionally, as warm and moist air penetrates farther into the Arctic, cloud-top cooling and surface mixing eventually erode the surface inversion downstream. The initial surface inversion splits into two elevated inversions while the air columns below the elevated inversions transform into well-mixed layers.
You, Qinglong; Chen, Deliang; Wu, Fangying; Pepin, Nick; Cai, Ziyi; Ahrens, Bodo; Jiang, Zhihong; Wu, Zhiwei; Kang, Shichang; AghaKouchak, AmirYou, Q., D. Chen, F. Wu, N. Pepin, Z. Cai, B. Ahrens, Z. Jiang, Z. Wu, S. Kang, A. AghaKouchak, 2020: Elevation dependent warming over the Tibetan Plateau: Patterns, mechanisms and perspectives. Earth-Science Reviews, 210, 103349. doi: 10.1016/j.earscirev.2020.103349. The Tibetan Plateau (TP) is also known as the “Third Pole”. Elevation dependent warming (EDW), the phenomenon that warming rate changes systematically with elevation, is of high significance for realistically estimating warming rates and their impacts over the TP. This review summarizes studies of characteristics and mechanisms behind EDW over the TP based on multiple observed datasets and model simulations. Spatial expression of EDW and explanatory mechanisms are still largely unknown because of the lack of suitable data over the TP. The focus is on the roles played by known mechanisms such as snow/ice-albedo feedback, cloud feedback, atmospheric water vapor feedback, aerosol feedback, and changes in land use, ozone and vegetation. At present, there is limited consensus on the main mechanisms controlling EDW. Finally, new perspectives and unresolved issues are outlined, including quantification of EDW in climate model simulations, explanation of the long-term EDW reconstructed from proxies, interaction between the Asian summer monsoon and EDW, importance of EDW for future environmental changes and water resources, and current gaps in understanding EDW over extremely high elevations. Further progress requires a more comprehensive ground observation network, greater use of remote sensing data, and high-resolution climate modeling with better representation of both atmospheric and cryospheric processes. Tibetan Plateau; Elevation dependent warming; Patterns and trends; Physical mechanisms
Young, Cindy L.; Lukashin, Constantine; Taylor, Patrick C.; Swanson, Rand; Kirk, William S.; Cooney, Michael; Swartz, William H.; Goldberg, Arnold; Stone, Thomas; Jackson, Trevor; Doelling, David R.; Shaw, Joseph A.; Buleri, ChristineYoung, C. L., C. Lukashin, P. C. Taylor, R. Swanson, W. S. Kirk, M. Cooney, W. H. Swartz, A. Goldberg, T. Stone, T. Jackson, D. R. Doelling, J. A. Shaw, C. Buleri, 2020: Trutinor: A Conceptual Study for a Next-Generation Earth Radiant Energy Instrument. Remote Sensing, 12(20), 3281. doi: 10.3390/rs12203281. Uninterrupted and overlapping satellite instrument measurements of Earth’s radiation budget from space are required to sufficiently monitor the planet’s changing climate, detect trends in key climate variables, constrain climate models, and quantify climate feedbacks. The Clouds and Earth’s Radiant Energy System (CERES) instruments are currently making these vital measurements for the scientific community and society, but with modern technologies, there are more efficient and cost-effective alternatives to the CERES implementation. We present a compact radiometer concept, Trutinor (meaning “balance” in Latin), with two broadband channels, shortwave (0.2–3 μm) and longwave (5–50 μm), capable of continuing the CERES record by flying in formation with an existing imager on another satellite platform. The instrument uses a three-mirror off-axis anastigmat telescope as the front optics to image these broadband radiances onto a microbolometer array coated with gold black, providing the required performance across the full spectral range. Each pixel of the sensor has a field of view of 0.6°, which was chosen so the shortwave band can be efficiently calibrated using the Moon as an on-orbit light source with the same angular extent, thereby reducing mass and improving measurement accuracy, towards the goal of a gap-tolerant observing system. The longwave band will utilize compact blackbodies with phase-change cells for an absolute calibration reference, establishing a clear path for SI-traceability. Trutinor’s instrument breadboard has been designed and is currently being built and tested. earth radiation budget; CERES; climate change; carbon nanotubes; ARCSTONE; lunar calibration; microbolometer array; phase change cells; RAVAN; small satellite constellation
Yu, Lisan; Stackhouse, P. W.; Wilber, A. C.; Weller, R.Yu, L., P. W. Stackhouse, A. C. Wilber, R. Weller, 2020: Global ocean heat, freshwater, and momentum fluxes.[in "State of the Climate in 2019"]. Bull. Amer. Meteor. Soc, 101(8), S149-152. doi: 10.1175/BAMS-D-20-0105.1.
Zhang, Baichao; Guo, Zhun; Zhang, Lixia; Zhou, Tianjun; Hayasaya, TadahiroZhang, B., Z. Guo, L. Zhang, T. Zhou, T. Hayasaya, 2020: Cloud Characteristics and Radiation Forcing in the Global Land Monsoon Region From Multisource Satellite Data Sets. Earth and Space Science, 7(3), e2019EA001027. doi: 10.1029/2019EA001027. The global land monsoon region has the highest land cloud amount in the world affecting two thirds of the world's population. Understanding the characteristics of cloud-radiation relies heavily on satellite data set, while few studies have addressed the advantages and weaknesses of current existing satellite data sets in estimating the cloud-radiation characteristics over global land monsoon regions. Multisource satellite data sets are used in this study to show the cloud characteristics in different monsoon regions. We find that all satellite data sets consistently show a peak of cloud fraction, cloud top height and cloud radiation forcing during summer over the global land monsoon regions. A regional difference in cloud characteristics is observed from multisource data sets. The seasonal cycle of cloud amount in the North American monsoon region is relatively smaller than that of the other monsoon regions. High-level clouds dominate the North African monsoon, while Low-level clouds dominate the Asian monsoon. The cloud properties and their radiative forcings revealed by four cloud-parameter data sets with multispectral imagers, that is, International Satellite Cloud Climatology Project (ISCCP)-D2, ISCCP-H, Moderate Resolution Imaging Spectroradiometer (MODIS)-MYD, and MODIS-MOD, are similar to one another, except stronger short-wave cloud radiative forcing in ISCCP-FD. Multidata comparison confirmed the climate and seasonal cycles of cloud characteristics in this study, demonstrating a better representation of cloud vertical structure in CloudSat over global land monsoon region. cloud; satellite data; global monsoon; multidata comparison
Zhang, He; Zhang, Minghua; Jin, Jiangbo; Fei, Kece; Ji, Duoying; Wu, Chenglai; Zhu, Jiawen; He, Juanxiong; Chai, Zhaoyang; Xie, Jinbo; Dong, Xiao; Zhang, Dongling; Bi, Xunqiang; Cao, Hang; Chen, Huansheng; Chen, Kangjun; Chen, Xueshun; Gao, Xin; Hao, Huiqun; Jiang, Jinrong; Kong, Xianghui; Li, Shigang; Li, Yangchun; Lin, Pengfei; Lin, Zhaohui; Liu, Hailong; Liu, Xiaohong; Shi, Ying; Song, Mirong; Wang, Huijun; Wang, Tianyi; Wang, Xiaocong; Wang, Zifa; Wei, Ying; Wu, Baodong; Xie, Zhenghui; Xu, Yongfu; Yu, Yongqiang; Yuan, Liang; Zeng, Qingcun; Zeng, Xiaodong; Zhao, Shuwen; Zhou, Guangqing; Zhu, JiangZhang, H., M. Zhang, J. Jin, K. Fei, D. Ji, C. Wu, J. Zhu, J. He, Z. Chai, J. Xie, X. Dong, D. Zhang, X. Bi, H. Cao, H. Chen, K. Chen, X. Chen, X. Gao, H. Hao, J. Jiang, X. Kong, S. Li, Y. Li, P. Lin, Z. Lin, H. Liu, X. Liu, Y. Shi, M. Song, H. Wang, T. Wang, X. Wang, Z. Wang, Y. Wei, B. Wu, Z. Xie, Y. Xu, Y. Yu, L. Yuan, Q. Zeng, X. Zeng, S. Zhao, G. Zhou, J. Zhu, 2020: CAS-ESM 2: Description and Climate Simulation Performance of the Chinese Academy of Sciences (CAS) Earth System Model (ESM) Version 2. Journal of Advances in Modeling Earth Systems, 12(12), e2020MS002210. doi: 10.1029/2020MS002210. The second version of Chinese Academy of Sciences Earth System Model (CAS-ESM 2) is described with emphasis on the development process, strength and weakness, and climate sensitivities in simulations of the Coupled Model Intercomparison Project (CMIP6) DECK experiments. CAS-ESM 2 was built as a numerical model to simulate both the physical climate system as well as atmospheric chemistry and carbon cycle. It is a newcomer in the international modeling community to provide sufficiently independent solutions of climate simulations from those of other models. Performances of the model in simulating the basic states of the radiation budget of the atmosphere and ocean, precipitation, circulations, variabilities, and the 20th Century warming are presented. Model biases and their possible causes are discussed. Strength includes horizontal heat transport in the atmosphere and oceans, vertical profile of the Atlantic Meridional Overturning Circulation; weakness includes the double Inter-Tropical Convergence Zone (ITCZ) and stronger amplitude of the El Niño-Southern Oscillation (ENSO) that are also common in many other models. The simulated the 20th Century warming shares a similar discrepancy with observations as in several other models—less warming in the 1920s and stronger cooling in the 1960s than in observation—at the time when there was a steep increase of anthropogenic aerosols. As a result, the 20th Century warming is about 60% of the observed warming despite that the model simulated a similar slope of warming trend after 1980 to observation. The model has an equilibrium climate sensitivity of 3.4 K with a positive cloud feedback from the shortwave radiation. climate sensitivity; Earth System Model; CAS-ESM; DECK experiments; Model calibration
Zhang, Taiping; Stackhouse, Paul W.; Cox, Stephen J.; Mikovitz, J. ColleenZhang, T., P. W. Stackhouse, S. J. Cox, J. C. Mikovitz, 2020: The uncertainty of the BSRN monthly mean Global 1 and Global 2 fluxes due to missing hourly means with and without quality-control and an examination through validation of the NASA GEWEX SRB datasets. Journal of Quantitative Spectroscopy and Radiative Transfer, 255, 107272. doi: 10.1016/j.jqsrt.2020.107272. The Baseline Surface Radiation Network (BSRN) is a project of the Data and Assessments Panel from the Global Energy and Water Exchanges (GEWEX) under the umbrella of the World Climate Research Programme (WCRP). Currently in the archive there are data from 67 sites located in all seven continents spanning from 1992 to the present. The original BSRN records are at 1-, 2-, 3- or 5-minute intervals, and sophisticated quality-control procedures have been developed to eliminate erroneous records before hourly, daily and monthly means are computed. The resulting gaps from quality-control, however, give rise to uncertainties in computed temporal averages on various scales. There are two types of total shortwave downward fluxes: The Global 1 which is the sum of direct horizontal and diffuse irradiances, observed using the pyrheliometer and radiometer, respectively, and is recommended by the BSRN committee for its higher precision, and the Global 2 which is observed using the pyranometer. It has been found that, compared to Global 2, Global 1 is more susceptible to errors, thus resulting in more gaps in the original records. Here we examine the effect of quality-control on the monthly mean Global 1 and Global 2 and attempt to quantify the resulting uncertainties through analysis of the quality-control procedure and averaging algorithm and comparison with the NASA GEWEX Surface Radiation Budget (SRB) dataset. The SRB project is now making progress toward its Release 4.0 Integrated Products (Rel. 4.0-IP or V4.0-IP) with changes in both algorithm and inputs on the basis of its Release 3.0 (Rel. 3.0 or V3.0) products. The preliminary results from Rel. 4.0-IP span 34 years continuously from July 1983 to June 2017 on a 1° by 1° quasi-equal-area grid system in the form of 3-hourly, daily and monthly means. It is found that Global 2 generally has fewer missing records and is less affected by the quality-check procedure; on average, the monthly mean Global 1 and Global 2 differ by less than 1 W m−2; the GEWEX SRB preliminary GSW(V4.0-IP) monthly mean shortwave downward fluxes agree the best with the BSRN Global 1 monthly means computed from observational records that are nearly complete and that survive the quality-check nearly completely. BSRN; GEWEX SRB; Global 1; Global 2; Uncertainty
Zhang, Xingxing; Lu, Ning; Jiang, Hou; Yao, LingZhang, X., N. Lu, H. Jiang, L. Yao, 2020: Evaluation of Reanalysis Surface Incident Solar Radiation Data in China. Scientific Reports, 10(1), 1-20. doi: 10.1038/s41598-020-60460-1. Surface incident solar radiation (Rs) of reanalysis products is widely used in ecological conservation, agricultural production, civil engineering and various solar energy applications. It is of great importance to have a good knowledge of the uncertainty of reanalysis Rs products. In this study, we evaluated the Rs estimates from two representative global reanalysis (ERA-Interim and MERRA-2) using quality- controlled surface measurements from China Meteorological Administration (CMA) and Multi-layer Simulation and Data Assimilation Center of the Tibetan Plateau (DAM) from 2000 to 2009. Error causes are further analyzed in combination radiation products from the Earth’s Radiant Energy System (CERES) EBAF through time series estimation, hotspot selection and Geodetector methods. Both the ERA-Interim and MERRA-2 products overestimate the Rs in China, and the MERRA-2 overestimation is more pronounced. The errors of the ERA-Interim are greater in spring and winter, while that of the MERRA-2 are almost the same in all seasons. As more quality-controlled measurements were used for validation, the conclusions seem more reliable, thereby providing scientific reference for rational use of these datasets. It was also found that the main causes of errors are the cloud coverage in the southeast coastal area, aerosol optical depth (AOD) and water vapor content in the Sichuan Basin, and cloud coverage and AOD in the northeast and middle east of China.

## 2019

Ackerman, S. A.; Platnick, S.; Bhartia, P. K.; Duncan, B.; L’Ecuyer, T.; Heidinger, A.; Skofronick-Jackson, G.; Loeb, N.; Schmit, T.; Smith, N.Ackerman, S. A., S. Platnick, P. K. Bhartia, B. Duncan, T. L’Ecuyer, A. Heidinger, G. Skofronick-Jackson, N. Loeb, T. Schmit, N. Smith, 2019: Satellites see the World’s Atmosphere. Meteorological Monographs, 59, 4.1–4.53. doi: 10.1175/AMSMONOGRAPHS-D-18-0009.1. Satellite meteorology is a relatively new branch of the atmospheric sciences. The field emerged in the late 1950’s during the Cold War and built on the advances in rocketry after World War II. In less than seventy years, satellite observations have transformed the way scientists observe and study Earth. This paper discusses some of the key advances in our understanding of the energy and water cycles, weather forecasting and atmospheric composition enabled by satellite observations. While progress truly has been an international achievement, in accord with a monograph observing the centennial of the American Meteorological Society, as well as limited space, the emphasis of this chapter is on the U.S. satellite effort.
Albrecht, Bruce; Ghate, Virendra; Mohrmann, Johannes; Wood, Robert; Zuidema, Paquita; Bretherton, Christopher; Schwartz, Christian; Eloranta, Edwin; Glienke, Susanne; Donaher, Shaunna; Sarkar, Mampi; McGibbon, Jeremy; Nugent, Alison D.; Shaw, Raymond A.; Fugal, Jacob; Minnis, Patrick; Paliknoda, Robindra; Lussier, Louis; Jensen, Jorgen; Vivekanandan, J.; Ellis, Scott; Tsai, Peisang; Rilling, Robert; Haggerty, Julie; Campos, Teresa; Stell, Meghan; Reeves, Michael; Beaton, Stuart; Allison, John; Stossmeister, Gregory; Hall, Samuel; Schmidt, SebastianAlbrecht, B., V. Ghate, J. Mohrmann, R. Wood, P. Zuidema, C. Bretherton, C. Schwartz, E. Eloranta, S. Glienke, S. Donaher, M. Sarkar, J. McGibbon, A. D. Nugent, R. A. Shaw, J. Fugal, P. Minnis, R. Paliknoda, L. Lussier, J. Jensen, J. Vivekanandan, S. Ellis, P. Tsai, R. Rilling, J. Haggerty, T. Campos, M. Stell, M. Reeves, S. Beaton, J. Allison, G. Stossmeister, S. Hall, S. Schmidt, 2019: Cloud System Evolution in the Trades—CSET Following the Evolution of Boundary Layer Cloud Systems with the NSF/NCAR GV. Bull. Amer. Meteor. Soc., 100(1), 93–12. doi: 10.1175/BAMS-D-17-0180.1. The evolution of the boundary layer aerosol, cloud, precipitation, and thermodynamic structures along trajectories within the north-Pacific trade-winds was investigated using the NSF NCAR Gulfstream V.
Anderson, Martha; Diak, George; Gao, Feng; Knipper, Kyle; Hain, Christopher; Eichelmann, Elke; Hemes, Kyle S.; Baldocchi, Dennis; Kustas, William; Yang, YunAnderson, M., G. Diak, F. Gao, K. Knipper, C. Hain, E. Eichelmann, K. S. Hemes, D. Baldocchi, W. Kustas, Y. Yang, 2019: Impact of Insolation Data Source on Remote Sensing Retrievals of Evapotranspiration over the California Delta. Remote Sensing, 11(3), 216. doi: 10.3390/rs11030216. The energy delivered to the land surface via insolation is a primary driver of evapotranspiration (ET)—the exchange of water vapor between the land and atmosphere. Spatially distributed ET products are in great demand in the water resource management community for real-time operations and sustainable water use planning. The accuracy and deliverability of these products are determined in part by the characteristics and quality of the insolation data sources used as input to the ET models. This paper investigates the practical utility of three different insolation datasets within the context of a satellite-based remote sensing framework for mapping ET at high spatiotemporal resolution, in an application over the Sacramento–San Joaquin Delta region in California. The datasets tested included one reanalysis product: The Climate System Forecast Reanalysis (CFSR) at 0.25° spatial resolution, and two remote sensing insolation products generated with geostationary satellite imagery: a product for the continental United States at 0.2°, developed by the University of Wisconsin Space Sciences and Engineering Center (SSEC) and a coarser resolution (1°) global Clouds and the Earth’s Radiant Energy System (CERES) product. The three insolation data sources were compared to pyranometer data collected at flux towers within the Delta region to establish relative accuracy. The satellite products significantly outperformed CFSR, with root-mean square errors (RMSE) of 2.7, 1.5, and 1.4 MJ·m−2·d−1 for CFSR, CERES, and SSEC, respectively, at daily timesteps. The satellite-based products provided more accurate estimates of cloud occurrence and radiation transmission, while the reanalysis tended to underestimate solar radiation under cloudy-sky conditions. However, this difference in insolation performance did not translate into comparable improvement in the ET retrieval accuracy, where the RMSE in daily ET was 0.98 and 0.94 mm d−1 using the CFSR and SSEC insolation data sources, respectively, for all the flux sites combined. The lack of a notable impact on the aggregate ET performance may be due in part to the predominantly clear-sky conditions prevalent in central California, under which the reanalysis and satellite-based insolation data sources have comparable accuracy. While satellite-based insolation data could improve ET retrieval in more humid regions with greater cloud-cover frequency, over the California Delta and climatologically similar regions in the western U.S., the CFSR data may suffice for real-time ET modeling efforts. data fusion; evapotranspiration; California Delta; insolation; surface energy balance; water resource management
Armour, Kyle C.; Siler, Nicholas; Donohoe, Aaron; Roe, Gerard H.Armour, K. C., N. Siler, A. Donohoe, G. H. Roe, 2019: Meridional Atmospheric Heat Transport Constrained by Energetics and Mediated by Large-Scale Diffusion. J. Climate, 32(12), 3655–3680. doi: 10.1175/JCLI-D-18-0563.1. Meridional atmospheric heat transport (AHT) has been investigated through three broad perspectives: a dynamic perspective, linking AHT to the poleward flux of moist static energy (MSE) by atmospheric motions; an energetic perspective, linking AHT to energy input to the atmosphere by top-of-atmosphere radiation and surface heat fluxes; and a diffusive perspective, representing AHT in terms down-gradient energy transport. It is shown here that the three perspectives provide complementary diagnostics of meridional AHT and its changes under greenhouse-gas forcing. When combined, the energetic and diffusive perspectives offer prognostic insights: anomalous AHT is constrained to satisfy the net energetic demands of radiative forcing, radiative feedbacks, and ocean heat uptake; in turn, the meridional pattern of warming must adjust to produce those AHT changes, and does so approximately according to diffusion of anomalous MSE. The relationship between temperature and MSE exerts strong constraints on the warming pattern, favoring polar amplification. These conclusions are supported by use of a diffusive moist energy balance model (EBM) that accurately predicts zonal-mean warming and AHT changes within comprehensive general circulation models (GCMs). A dry diffusive EBM predicts similar AHT changes in order to satisfy the same energetic constraints, but does so through tropically-amplified warming – at odds with the GCMs’ polar-amplified warming pattern. The results suggest that polar-amplified warming is a near-inevitable consequence of a moist, diffusive atmosphere’s response to greenhouse-gas forcing. In this view, atmospheric circulations must act to satisfy net AHT as constrained by energetics.
Bae, S. Y.; Park, R.-S.Bae, S. Y., R. Park, 2019: Consistency between the cloud and radiation processes in a numerical forecasting model. Meteorology and Atmospheric Physics, 131(5), 1429-1436. doi: 10.1007/s00703-018-0647-9. In this study, the radiation process in the Korean Integrated Model (KIM) is modified to calculate the cloud radiative forcing keeping a physical consistency with the microphysics, convection, and cloudiness schemes in an aspect of hydrometeor. A formula to calculate effective radii of cloud water in radiation scheme of the KIM is modified to be consistent with that in the microphysics scheme and the radiative effect of a subgrid-scale hydrometeor is considered along with convective parameterization and cloudiness schemes. The impacts of these modifications on radiation and precipitation are diagnosed via an observation comparison, and a detailed analysis of these impacts is conducted. Especially, the contrasting feedback of the subgrid-scale hydrometeor on precipitation over the land and the ocean is separately discussed.
Beucler, Tom; Abbott, Tristan H.; Cronin, Timothy W.; Pritchard, Michael S.Beucler, T., T. H. Abbott, T. W. Cronin, M. S. Pritchard, 2019: Comparing Convective Self-Aggregation in Idealized Models to Observed Moist Static Energy Variability Near the Equator. Geophysical Research Letters, 46(17-18), 10589-10598. doi: 10.1029/2019GL084130. Idealized convection-permitting simulations of radiative-convective equilibrium have become a popular tool for understanding the physical processes leading to horizontal variability of tropical water vapor and rainfall. However, the applicability of idealized simulations to nature is still unclear given that important processes are typically neglected, such as lateral water vapor advection by extratropical intrusions, or interactive ocean coupling. Here, we exploit spectral analysis to compactly summarize the multiscale processes supporting convective aggregation. By applying this framework to high-resolution reanalysis data and satellite observations in addition to idealized simulations, we compare convective-aggregation processes across horizontal scales and data sets. The results affirm the validity of the radiative-convective equilibrium simulations as an analogy to the real world. Column moist static energy tendencies share similar signs and scale selectivity in convection-permitting models and observations: Radiation increases variance at wavelengths above 1,000 km, while advection damps variance across wavelengths, and surface fluxes mostly reduce variance between 1,000 and 10,000 km. radiation; convection; water vapor; cloud physics; aggregation; spectral analysis
Blunden, Jessica; Arndt, Derek S.Blunden, J., D. S. Arndt, 2019: State of the Climate in 2018. Bull. Amer. Meteor. Soc., 100(9), Si-S306. doi: 10.1175/2019BAMSStateoftheClimate.1. Editor’s note: For easy download the posted pdf of the State of the Climate for 2019 is a low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.
Bodas‐Salcedo, A.; Mulcahy, J. P.; Andrews, T.; Williams, K. D.; Ringer, M. A.; Field, P. R.; Elsaesser, G. S.Bodas‐Salcedo, A., J. P. Mulcahy, T. Andrews, K. D. Williams, M. A. Ringer, P. R. Field, G. S. Elsaesser, 2019: Strong Dependence of Atmospheric Feedbacks on Mixed-Phase Microphysics and Aerosol-Cloud Interactions in HadGEM3. Journal of Advances in Modeling Earth Systems, 11(6), 1735-1758. doi: 10.1029/2019MS001688. We analyze the atmospheric processes that explain the large changes in radiative feedbacks between the two latest climate configurations of the Hadley Centre Global Environmental model. We use a large set of atmosphere-only climate change simulations (amip and amip-p4K) to separate the contributions to the differences in feedback parameter from all the atmospheric model developments between the two latest model configurations. We show that the differences are mostly driven by changes in the shortwave cloud radiative feedback in the midlatitudes, mainly over the Southern Ocean. Two new schemes explain most of the differences: the introduction of a new aerosol scheme and the development of a new mixed-phase cloud scheme. Both schemes reduce the strength of the preexisting shortwave negative cloud feedback in the midlatitudes. The new aerosol scheme dampens a strong aerosol-cloud interaction, and it also suppresses a negative clear-sky shortwave feedback. The mixed-phase scheme increases the amount of cloud liquid water path (LWP) in the present day and reduces the increase in LWP with warming. Both changes contribute to reducing the negative radiative feedback of the increase of LWP in the warmer climate. The mixed-phase scheme also enhances a strong, preexisting, positive cloud fraction feedback. We assess the realism of the changes by comparing present-day simulations against observations and discuss avenues that could help constrain the relevant processes. cloud feedbacks; HadGEM3
Bright, Jamie M.; Gueymard, Christian A.Bright, J. M., C. A. Gueymard, 2019: Climate-specific and global validation of MODIS Aqua and Terra aerosol optical depth at 452 AERONET stations. Solar Energy, 183, 594-605. doi: 10.1016/j.solener.2019.03.043. Aerosol optical depth (AOD) is a highly influential variable in solar resource assessment and clear-sky radiation modelling. Hence, the accuracy of solar energy estimates ultimately depends on the accuracy of the measured or assumed AOD. Gridded satellite information is often used for solar modelling due to its geographical coverage, and so a global validation of commonly utilised AOD products is imperative. Here, all Level-3 Moderate Resolution Imaging Spectroradiometer (MODIS) daily observations of AOD (at 470, 550 and 660 nm, noted AOD470, AOD550 and AOD660, respectively) from the Aqua and Terra satellites (of 1° × 1° spatial resolution) from 2000 to 02/2018 are compared and validated against all of NASA’s ground sensing Aerosol Robotic NETwork (AERONET) V3 Level 2 AOD daily averages from sites that reported at least one year of observations during 2000–2018 (452 sites representing at least 653,000 observations per variable). Furthermore, sub-categorisation by Köppen-Geiger climate regions enables a novel climate-specific validation to ascertain any distinct climatic influence. The results demonstrate significant climatological influences that impact the derived AOD product at all three wavelengths. It is found that blending the two Aqua and Terra products results in a higher accuracy of daily estimates of all AOD products. Each AOD product is validated similarly and separately. AOD550, which is most commonly used in solar resource assessment, is found worst in the equatorial climate (absolute root mean square error (RMSE) of 0.194) and best in the temperate climate (RMSE of 0.126). Globally, the combined Aqua + Terra AOD550 experiences an absolute RMSE of 0.106 and a mean absolute error of 0.109. The most common MODIS AOD retrievals are between 0.01 and 0.25, suggesting that the MODIS daily AOD products may introduce a significant source of uncertainty in modelled irradiance estimates, and that other sources of input data should be used instead whenever their applications demand high accuracy. MODIS; AERONET; Aerosol optical depth; Global validation; Irradiance modelling
Bright, Ryan M.; O'Halloran, Thomas L.Bright, R. M., T. L. O'Halloran, 2019: Developing a monthly radiative kernel for surface albedo change from satellite climatologies of Earth's shortwave radiation budget: CACK v1.0. Geoscientific Model Development, 12(9), 3975-3990. doi: https://doi.org/10.5194/gmd-12-3975-2019. Abstract. Due to the potential for land-use–land-cover change (LULCC) to alter surface albedo, there is need within the LULCC science community for simple and transparent tools for predicting radiative forcings (ΔF) from surface albedo changes (Δαs). To that end, the radiative kernel technique – developed by the climate modeling community to diagnose internal feedbacks within general circulation models (GCMs) – has been adopted by the LULCC science community as a tool to perform offline ΔF calculations for Δαs. However, the codes and data behind the GCM kernels are not readily transparent, and the climatologies of the atmospheric state variables used to derive them vary widely both in time period and duration. Observation-based kernels offer an attractive alternative to GCM-based kernels and could be updated annually at relatively low costs. Here, we present a radiative kernel for surface albedo change founded on a novel, simplified parameterization of shortwave radiative transfer driven with inputs from the Clouds and the Earth's Radiant Energy System (CERES) Energy Balance and Filled (EBAF) products. When constructed on a 16-year climatology (2001–2016), we find that the CERES-based albedo change kernel – or CACK – agrees remarkably well with the mean kernel of four GCMs (rRMSE = 14 %). When the novel parameterization underlying CACK is applied to emulate two of the GCM kernels using their own boundary fluxes as input, we find even greater agreement (mean rRMSE = 7.4 %), suggesting that this simple and transparent parameterization represents a credible candidate for a satellite-based alternative to GCM kernels. We document and compute the various sources of uncertainty underlying CACK and include them as part of a more extensive dataset (CACK v1.0) while providing examples showcasing its application.
Caldwell, Peter M.; Mametjanov, Azamat; Tang, Qi; Roekel, Luke P. Van; Golaz, Jean-Christophe; Lin, Wuyin; Bader, David C.; Keen, Noel D.; Feng, Yan; Jacob, Robert; Maltrud, Mathew E.; Roberts, Andrew F.; Taylor, Mark A.; Veneziani, Milena; Wang, Hailong; Wolfe, Jonathan D.; Balaguru, Karthik; Cameron‐Smith, Philip; Dong, Lu; Klein, Stephen A.; Leung, L. Ruby; Li, Hong-Yi; Li, Qing; Liu, Xiaohong; Neale, Richard B.; Pinheiro, Marielle; Qian, Yun; Ullrich, Paul A.; Xie, Shaocheng; Yang, Yang; Zhang, Yuying; Zhang, Kai; Zhou, TianCaldwell, P. M., A. Mametjanov, Q. Tang, L. P. V. Roekel, J. Golaz, W. Lin, D. C. Bader, N. D. Keen, Y. Feng, R. Jacob, M. E. Maltrud, A. F. Roberts, M. A. Taylor, M. Veneziani, H. Wang, J. D. Wolfe, K. Balaguru, P. Cameron‐Smith, L. Dong, S. A. Klein, L. R. Leung, H. Li, Q. Li, X. Liu, R. B. Neale, M. Pinheiro, Y. Qian, P. A. Ullrich, S. Xie, Y. Yang, Y. Zhang, K. Zhang, T. Zhou, 2019: The DOE E3SM Coupled Model Version 1: Description and Results at High Resolution. Journal of Advances in Modeling Earth Systems, 11(12), 4095-4146. doi: 10.1029/2019MS001870. This study provides an overview of the coupled high-resolution Version 1 of the Energy Exascale Earth System Model (E3SMv1) and documents the characteristics of a 50-year-long high-resolution control simulation with time-invariant 1950 forcings following the HighResMIP protocol. In terms of global root-mean-squared error metrics, this high-resolution simulation is generally superior to results from the low-resolution configuration of E3SMv1 (due to resolution, tuning changes, and possibly initialization procedure) and compares favorably to models in the CMIP5 ensemble. Ocean and sea ice simulation is particularly improved, due to better resolution of bathymetry, the ability to capture more variability and extremes in winds and currents, and the ability to resolve mesoscale ocean eddies. The largest improvement in this regard is an ice-free Labrador Sea, which is a major problem at low resolution. Interestingly, several features found to improve with resolution in previous studies are insensitive to resolution or even degrade in E3SMv1. Most notable in this regard are warm bias and associated stratocumulus deficiency in eastern subtropical oceans and lack of improvement in El Niño. Another major finding of this study is that resolution increase had negligible impact on climate sensitivity (measured by net feedback determined through uniform +4K prescribed sea surface temperature increase) and aerosol sensitivity. Cloud response to resolution increase consisted of very minor decrease at all levels. Large-scale patterns of precipitation bias were also relatively unaffected by grid spacing.
Carlson, Barbara; Lacis, Andrew; Colose, Christopher; Marshak, Alexander; Su, Wenying; Lorentz, StevenCarlson, B., A. Lacis, C. Colose, A. Marshak, W. Su, S. Lorentz, 2019: Spectral Signature of the Biosphere: NISTAR Finds It in Our Solar System From the Lagrangian L-1 Point. Geophysical Research Letters, 46(17-18), 10679-10686. doi: 10.1029/2019GL083736. NISTAR, aboard the DSCOVR spacecraft, is one of the National Aeronautics and Space Administration's energy budget instruments designed to measure the seasonal changes in Earth's total outgoing radiation from a unique vantage point at the Lagrangian L-1 point a million miles from Earth. Global radiation energy balance measurements are important constraints for climate models, but are difficult measurements to quantify. CERES data offer the best current observational constraints, but need extensive modeling to get global energy. NISTAR observes the entire dayside hemisphere of the Earth as a single pixel, splitting the shortwave radiation into broadband visible and near-infrared components (analogous to the narrowband spectral ratios used to define vegetation indices). This spectral partitioning at the 0.7-μm vegetation red edge offers unique constraints on climate model spectral treatment of cloud and surface albedos. Moreover, NISTAR's unique viewing geometry amounts to observing the Earth as an exoplanet, which opens a new perspective on exoplanet observations. diurnal cycle; satellite data; global energy budget; remote sensing; climate model validation; exoplanet studies
Cesana, G.; Waliser, D. E.; Henderson, D.; L’Ecuyer, T. S.; Jiang, X.; Li, J-L. F.Cesana, G., D. E. Waliser, D. Henderson, T. S. L’Ecuyer, X. Jiang, J. F. Li, 2019: The Vertical Structure Of Radiative Heating Rates: A Multimodel Evaluation Using A-Train Satellite Observations. J. Climate, 32, 1573–1590. doi: 10.1175/JCLI-D-17-0136.1. We assess the vertical distribution of radiative heating rates (RHR) in climate models using a model experiment and A-train satellite observations, for the first time. As RHR relies on the representation of cloud amount and properties, we first compare the modeled vertical distribution of clouds directly against lidar-radar combined cloud observations (i.e., without simulator). On a near-global scale (50°S/N), two systematic differences arise: an excess of high-level clouds around 200hPa in the tropics, and a general lack of middle- and low-level clouds compared to the observations. Then, using RHR profiles calculated with constraints from A-train and reanalysis data, along with their associated maximum uncertainty estimates, we show that the excess clouds and ice water content in the upper troposphere results in excess infrared heating in the vicinity and below the clouds as well as a lack of solar heating below the clouds. In the lower troposphere, the smaller cloud amount and the underestimation of cloud-top height is coincident with a shift of the infrared cooling to lower levels, substantially reducing the greenhouse effect, that is slightly compensated for by an erroneous excess absorption of solar radiation. Clear sky RHR differences between the observations and the models mitigate cloudy RHR biases in the low levels while they enhance them in the high levels. Finally, our results indicate that a better agreement between observed and modeled cloud profiles could substantially improve the RHR profiles. However, more work is needed to precisely quantify modeled cloud errors and their subsequent effect on RHR.
Cesana, Grégory; Genio, Anthony D. Del; Ackerman, Andrew S.; Kelley, Maxwell; Elsaesser, Gregory; Fridlind, Ann M.; Cheng, Ye; Yao, Mao-SungCesana, G., A. D. D. Genio, A. S. Ackerman, M. Kelley, G. Elsaesser, A. M. Fridlind, Y. Cheng, M. Yao, 2019: Evaluating models' response of tropical low clouds to SST forcings using CALIPSO observations. Atmospheric Chemistry and Physics, 19(5), 2813-2832. doi: 10.5194/acp-19-2813-2019. Abstract. Recent studies have shown that, in response to a surface warming, the marine tropical low-cloud cover (LCC) as observed by passive-sensor satellites substantially decreases, therefore generating a smaller negative value of the top-of-the-atmosphere (TOA) cloud radiative effect (CRE). Here we study the LCC and CRE interannual changes in response to sea surface temperature (SST) forcings in the GISS model E2 climate model, a developmental version of the GISS model E3 climate model, and in 12 other climate models, as a function of their ability to represent the vertical structure of the cloud response to SST change against 10 years of CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) observations. The more realistic models (those that satisfy the observational constraint) capture the observed interannual LCC change quite well (ΔLCC/ΔSST=-3.49±1.01 % K−1 vs. ΔLCC/ΔSSTobs=-3.59±0.28 % K−1) while the others largely underestimate it (ΔLCC/ΔSST=-1.32±1.28 % K−1). Consequently, the more realistic models simulate more positive shortwave (SW) feedback (ΔCRE/ΔSST=2.60±1.13 W m−2 K−1) than the less realistic models (ΔCRE/ΔSST=0.87±2.63
Chang, Kai-Wei; L'Ecuyer, Tristan S.Chang, K., T. S. L'Ecuyer, 2019: Role of Latent Heating Vertical Distribution in the Formation of the Tropical Cold Trap. Journal of Geophysical Research: Atmospheres, 124(14), 7836-7851. doi: 10.1029/2018JD030194. This study examines the role of latent heating (LH) vertical distribution in tropical tropopause layer (TTL) cooling and upper-tropospheric warming associated with equatorial wave responses using LH from the Tropical Rainfall Measurement Mission and temperature from radio occultation observations. We distinguish the effects of convective and stratiform LH in tropical convection on temperature in the upper troposphere and lower stratosphere. Cross-spectral analysis of time series of temperature and LH shows that stratiform LH exhibits higher coherence with temperature throughout most of the upper troposphere and lower stratosphere, especially in the equatorial Rossby wave response. Coherence between total LH and temperature tends to increase with the altitude of heating. Highest coherences occur almost exclusively at time scales of the Madden-Julian Oscillation, suggesting the importance of mesoscale convective activity in TTL cooling and subsequent dehydration processes. These results demonstrate that TTL and upper-tropospheric temperature perturbations depend on the vertical distribution of LH and that stratiform LH release has strong relationship with the formation of the horseshoe-shaped cold trap over the Maritime Continent and West Pacific. Madden-Julian Oscillation; equatorial waves; latent heating; stratosphere-troposphere coupling; tropical tropopause layer
Chen, Gengxin; Han, Weiqing; Li, Yuanlong; Yao, Jinglong; Wang, DongxiaoChen, G., W. Han, Y. Li, J. Yao, D. Wang, 2019: Intraseasonal Variability of the Equatorial Undercurrent in the Indian Ocean. J. Phys. Oceanogr., 49(1), 85-101. doi: 10.1175/JPO-D-18-0151.1. By analyzing in situ observations and conducting a series of ocean general circulation model experiments, this study investigates the physical processes controlling intraseasonal variability (ISV) of the Equatorial Undercurrent (EUC) of the Indian Ocean. ISV of the EUC leads to time-varying water exchanges between the western and eastern equatorial Indian Ocean. For the 2001–14 period, standard deviations of the EUC transport variability are 1.92 and 1.77 Sv (1 Sv ≡ 106 m3 s−1) in the eastern and western basins, respectively. The ISV of the EUC is predominantly caused by the wind forcing effect of atmospheric intraseasonal oscillations (ISOs) but through dramatically different ocean dynamical processes in the eastern and western basins. The stronger ISV in the eastern basin is dominated by the reflected Rossby waves associated with intraseasonal equatorial zonal wind forcing. It takes 20–30 days to set up an intraseasonal EUC anomaly through the Kelvin and Rossby waves associated with the first and second baroclinic modes. In the western basin, the peak intraseasonal EUC anomaly is generated by the zonal pressure gradient force, which is set up by radiating equatorial Kelvin and Rossby waves induced by the equatorial wind stress. Directly forced and reflected Rossby waves from the eastern basin propagate westward, contributing to intraseasonal zonal current near the surface but having weak impact on the peak ISV of the EUC.
Chen, Jinghua; Wu, Xiaoqing; Yin, Yan; Lu, Chunsong; Xiao, Hui; Huang, Qian; Deng, LipingChen, J., X. Wu, Y. Yin, C. Lu, H. Xiao, Q. Huang, L. Deng, 2019: Thermal Effects of the Surface Heat Flux on Cloud Systems over the Tibetan Plateau in Boreal Summer. J. Climate, 32(15), 4699-4714. doi: 10.1175/JCLI-D-18-0604.1. The influence of surface heat fluxes on the generation and development of cloud and precipitation and its relative importance to the large-scale circulation patterns are investigated via cloud-resolving model (CRM) simulations over the Tibetan Plateau (TP) during boreal summer. Over the lowland (e.g., along the middle and lower reaches of the Yangtze River), the dynamical and thermal properties of the atmosphere take more responsibility than the surface heat fluxes for the triggering of heavy rainfall events. However, the surface thermal driving force is a necessary criterion for the triggering of heavy rainfall in the eastern and western TP (ETP and WTP). Strong surface heat fluxes can trigger shallow convections in the TP. Furthermore, moisture that is mainly transported from the southern tropical ocean has a greater influence on the heavy rainfall events of the WTP than those of the ETP. Cloud microphysical processes are substantially less active and heavy rainfall cannot be produced when surface heat fluxes are weakened by half in magnitude over the TP. In addition, surface heating effects are largely responsible for the high occurrence frequency of convection during the afternoon, and the cloud tops of convective systems show a positive relationship with the intensity of surface heat fluxes.
Chen, Yi-Hsuan; Huang, Xianglei; Chen, Xiuhong; Flanner, MarkChen, Y., X. Huang, X. Chen, M. Flanner, 2019: The Effects of Surface Longwave Spectral Emissivity on Atmospheric Circulation and Convection over the Sahara and Sahel. J. Climate, 32(15), 4873-4890. doi: 10.1175/JCLI-D-18-0615.1. This study quantifies the impact of the inclusion of realistic surface spectral emissivity in the Sahara and Sahel on the simulated local climate and beyond. The surface emissivity in these regions can be as low as 0.6–0.7 over the infrared window band while close to unity in other spectral bands, but such spectral dependence has been ignored in current climate models. Realistic surface spectral emissivities over the Sahara and Sahel are incorporated into the Community Earth System Model (CESM) version 1.1.1, while treatments of surface emissivity for the rest of the globe remain unchanged. Both the modified and standard CESM are then forced with prescribed climatological SSTs and fixed present-day forcings for 35-yr simulations. The outputs from the last 30 years are analyzed. Compared to the standard CESM, the modified CESM has warmer surface air temperature, as well as a warmer and wetter planetary boundary layer over the Sahara and Sahel. The modified CESM thus favors more convection in these regions and has more convective rainfall, especially in the Sahara. The moisture convergence induced by such inclusion of surface spectral emissivity also contributes to the differences in simulated precipitation in the Sahel and the region south to it. Compared to observations, inclusion of surface spectral emissivity reduces surface temperature biases in the Sahara and precipitation biases in the Gulf of Guinea but exacerbates the wet biases in the Sahara. Such realistic representation of surface spectral emissivity can help unmask other factors contributing to regional biases in the original CESM.
Chen, Yilun; Chong, Kezhen; Fu, YunfeiChen, Y., K. Chong, Y. Fu, 2019: Impacts of distribution patterns of cloud optical depth on the calculation of radiative forcing. Atmospheric Research, 218, 70-77. doi: 10.1016/j.atmosres.2018.11.007. The gridding process applied to satellite-retrieved cloud properties results in the loss of certain information. In this study, we analyzed the error associated with using gridded cloud optical depth (τ) in calculating radiative forcing from the perspective of the distribution pattern of τ. Utilizing the simulated results from SBDART (Santa Babara DISORT Atmospheric Radiative Transfer), we calculated this error in ideal probability distribution functions (PDFs) of τ while keeping the average τ constant, and then used the τ retrieved from MODIS (Moderate Resolution Imaging Spectroradiometer) pixel-level observations to simulate real case studies. The results from both the ideal experiments and real case studies indicate that there is a large dependence of the error caused by gridding process on the PDF of τ. The greatest relative error occurs in the cases when τ fits a two-point or uniform distribution, reaching 10–20%, while this error is below 5% when τ follows a binomial distribution. From the analysis of MODIS pixel-level data from June 2016, we found that the PDFs of τ within one grid point (1° × 1°) could not be simply described by a normal distribution. Although using the logarithmic mean of τ controls the error effectively, the error can still be up to 4%. Our study suggests that using gridded data (especially the arithmetic mean) to calculate radiative forcing may result in uncertainty to a certain extent, which depends strongly on the distribution pattern of cloud properties within the grid point. The PDF of cloud properties should be comprehensively considered in the gridding process in the future. MODIS; Cloud optical depth; Distribution pattern; Grid; Radiative forcing
Choi, In-Jin; Park, Rae-Seol; Lee, JoonsukChoi, I., R. Park, J. Lee, 2019: Impacts of a newly-developed aerosol climatology on numerical weather prediction using a global atmospheric forecasting model. Atmospheric Environment, 197, 77-91. doi: 10.1016/j.atmosenv.2018.10.019. New four-dimensional aerosol climatology for global weather forecasting model is developed to take aerosol direct effect into account and its impacts on numerical weather prediction are investigated. The proposed aerosol climatology provides the global distribution of monthly-varying species-wise aerosol optical depths with more realistic aerosol vertical profiles. Including aerosol climatology enhances vertical stratification by surface cooling and atmospheric heating through the lower atmosphere by affecting radiation budget. Weakened vertical mixing and reduced surface fluxes related to aerosol loading result in decreased cloud fraction, particularly in the lower atmosphere. Evaluation of medium-range forecasts using the proposed aerosol climatology shows the overall improvement statistically for large-scale variable with reducing their biases, and the alleviation of systematic biases of overestimated light precipitation over the northern hemisphere. Aerosol climatology; Forecast skill; Global NWP; MACC; MOZART
Cronin, Meghan F.; Gentemann, Chelle L.; Edson, James; Ueki, Iwao; Bourassa, Mark; Brown, Shannon; Clayson, Carol Anne; Fairall, Chris W.; Farrar, J. Thomas; Gille, Sarah T.; Gulev, Sergey; Josey, Simon A.; Kato, Seiji; Katsumata, Masaki; Kent, Elizabeth; Krug, Marjolaine; Minnett, Peter J.; Parfitt, Rhys; Pinker, Rachel T.; Stackhouse, Paul W.; Swart, Sebastiaan; Tomita, Hiroyuki; Vandemark, Douglas; Weller, A. Robert; Yoneyama, Kunio; Yu, Lisan; Zhang, DongxiaoCronin, M. F., C. L. Gentemann, J. Edson, I. Ueki, M. Bourassa, S. Brown, C. A. Clayson, C. W. Fairall, J. T. Farrar, S. T. Gille, S. Gulev, S. A. Josey, S. Kato, M. Katsumata, E. Kent, M. Krug, P. J. Minnett, R. Parfitt, R. T. Pinker, P. W. Stackhouse, S. Swart, H. Tomita, D. Vandemark, A. R. Weller, K. Yoneyama, L. Yu, D. Zhang, 2019: Air-Sea Fluxes With a Focus on Heat and Momentum. Frontiers in Marine Science, 6, 430. doi: 10.3389/fmars.2019.00430. Turbulent and radiative exchanges of heat between the ocean and atmosphere (hereafter heat fluxes), ocean surface wind stress, and state variables used to estimate them, are Essential Ocean Variables (EOVs) and Essential Climate Variables (ECVs) influencing weather and climate. This paper describes an observational strategy for producing 3-hourly, 25-km (and an aspirational goal of hourly at 10-km) heat flux and wind stress fields over the global, ice-free ocean with breakthrough 1-day random uncertainty of 15 W m–2 and a bias of less than 5 W m–2. At present this accuracy target is met only for OceanSITES reference station moorings and research vessels (RVs) that follow best practices. To meet these targets globally, in the next decade, satellite-based observations must be optimized for boundary layer measurements of air temperature, humidity, sea surface temperature, and ocean wind stress. In order to tune and validate these satellite measurements, a complementary global in situ flux array, built around an expanded OceanSITES network of time series reference station moorings, is also needed. The array would include 500–1000 measurement platforms, including autonomous surface vehicles, moored and drifting buoys, RVs, the existing OceanSITES network of 22 flux sites, and new OceanSITES expanded in 19 key regions. This array would be globally distributed, with 1–3 measurement platforms in each nominal 10° by 10° box. These improved moisture and temperature profiles and surface data, if assimilated into Numerical Weather Prediction (NWP) models, would lead to better representation of cloud formation processes, improving state variables and surface radiative and turbulent fluxes from these models. The in situ flux array provides globally distributed measurements and metrics for satellite algorithm development, product validation, and for improving satellite-based, NWP and blended flux products. In addition, some of these flux platforms will also measure direct turbulent fluxes, which can be used to improve algorithms for computation of air-sea exchange of heat and momentum in flux products and models. With these improved air-sea fluxes, the ocean’s influence on the atmosphere will be better quantified and lead to improved long-term weather forecasts, seasonal-interannual-decadal climate predictions, and regional climate projections.
Cui, Wenjun; Dong, Xiquan; Xi, Baike; Fan, Jiwen; Tian, Jingjing; Wang, Jingyu; McHardy, Theodore M.Cui, W., X. Dong, B. Xi, J. Fan, J. Tian, J. Wang, T. M. McHardy, 2019: Understanding Ice Cloud-Precipitation Properties of Three Modes of Mesoscale Convective Systems During PECAN. Journal of Geophysical Research: Atmospheres, 124(7), 4121-4140. doi: 10.1029/2019JD030330. This study analyzes the precipitation and ice cloud microphysical features of three common modes of linear mesoscale convective systems during the Plains Elevated Convection at Night (PECAN) campaign. Three cases, one for each linear mesoscale convective system archetype (trailing stratiform, leading stratiform, and parallel stratiform precipitation), are selected. We focus primarily on analyzing ice cloud microphysical properties and precipitation rates (PRs) over the classified convective core (CC) and stratiform rain (SR) regions, as well as the two stratiform regions that developed behind (SR1) and ahead (SR2) of the convective line relative to the storm motion. In the three selected cases, the ice water path (IWP) and PR have strong correlations in the CC, but not in the SR. In terms of the temporal evolution of the mean IWPs and PRs, both CC and SR IWPs, as well as CC PRs, reach peaks quickly but take a longer time to dissipate than the increase period. For all the three cases, both SR1 and SR2 IWPs are 20–70% of their corresponding CC values in both the leading stratiform and parallel stratiform cases and up to 95% for the trailing stratiform case, while all of their PRs are only 7–25% of their CC values. These values suggest not only that the SR PRs may depend on IWPs but also that the microphysical properties of ice particles such as habit and size distribution may play an important role. Utilizing cloud-resolving simulations of these systems may provide better understanding of the physical meanings behind the results in the future.
Danso, Derrick Kwadwo; Anquetin, Sandrine; Diedhiou, Arona; Lavaysse, Christophe; Kobea, Arsène; Touré, N'Datchoh EvelyneDanso, D. K., S. Anquetin, A. Diedhiou, C. Lavaysse, A. Kobea, N. E. Touré, 2019: Spatio-temporal variability of cloud cover types in West Africa with satellite-based and reanalysis data. Quarterly Journal of the Royal Meteorological Society, 145(725), 3715-3731. doi: 10.1002/qj.3651. This study aims to understand and document the occurrence and variability of cloud cover types in West Africa (WA). Investigations are carried out with a 10-year hourly record of two cloud data products: CERES passive satellite observations and ERA5 reanalysis. The seasonal evolutions of high (HCC), middle (MCC), low (LCC) and total (TCC) cloud cover are examined. Both products agree on the seasonal and spatial occurrence of cloud cover, although CERES presents lower values of cloud fraction than ERA5 which is partly attributed to the inability of the satellite sensor to detect optically thin clouds in the atmosphere. Southern WA is found to be cloudier than other parts of the region in all seasons with mean TCC fractions of 70 and 80% for CERES and ERA5 respectively during the monsoon season. In all seasons, the presence of LCC over large areas of the Sahel/Sahara region is noted in the CERES product. This could be due to a possible misinterpretation of Saharan dust as low clouds which may have thus, caused it to overestimate the occurrences and fractions of LCC over this region. Northern WA is associated with higher frequencies of no cloud occurrence events, unlike the south where cloudless skies are rarely observed. Furthermore, in southern WA, overcast conditions of LCC are observed for a significant number of times (up to 20% of the time during the rainy season in CERES and 40% in ERA5). The climatology of cloud cover presented in this study could be useful for the planning of solar energy projects. CERES; West Africa; cloud cover; variability; ERA5; occurrence frequency
Dewitte, Steven; Clerbaux, Nicolas; Cornelis, JanDewitte, S., N. Clerbaux, J. Cornelis, 2019: Decadal Changes of the Reflected Solar Radiation and the Earth Energy Imbalance. Remote Sensing, 11(6), 663. doi: 10.3390/rs11060663. Decadal changes of the Reflected Solar Radiation (RSR) as measured by CERES from 2000 to 2018 are analysed. For both polar regions, changes of the clear-sky RSR correlate well with changes of the Sea Ice Extent. In the Arctic, sea ice is clearly melting, and as a result the earth is becoming darker under clear-sky conditions. However, the correlation between the global all-sky RSR and the polar clear-sky RSR changes is low. Moreover, the RSR and the Outgoing Longwave Radiation (OLR) changes are negatively correlated, so they partly cancel each other. The increase of the OLR is higher then the decrease of the RSR. Also the incoming solar radiation is decreasing. As a result, over the 2000–2018 period the Earth Energy Imbalance (EEI) appears to have a downward trend of −0.16 ± 0.11 W/m2dec. The EEI trend agrees with a trend of the Ocean Heat Content Time Derivative of −0.26 ± 0.06 (1 σ ) W/m2dec. Earth Radiation Budget; Earth Energy Imbalance; Reflected Solar Radiation
Dolinar, Erica K.; Dong, Xiquan; Xi, Baike; Jiang, Jonathan H.; Loeb, Norman G.; Campbell, James R.; Su, HuiDolinar, E. K., X. Dong, B. Xi, J. H. Jiang, N. G. Loeb, J. R. Campbell, H. Su, 2019: A global record of single-layered ice cloud properties and associated radiative heating rate profiles from an A-Train perspective. Climate Dynamics, 1-20. doi: 10.1007/s00382-019-04682-8. A record of global single-layered ice cloud properties has been generated using the CloudSat and CALIPSO Ice Cloud Property Product (2C-ICE) during the period 2007–2010. These ice cloud properties are used as inputs for the NASA Langley modified Fu–Liou radiative transfer model to calculate cloud radiative heating rate profiles and are compared with the NASA CERES observed top-of-atmosphere fluxes. The radiative heating rate profiles calculated in the CloudSat/CALIPSO 2B-FLXHR-LIDAR and CCCM_CC products are also examined to assess consistency and uncertainty of their properties using independent methods. Based on the methods and definitions used herein, single-layered ice clouds have a global occurrence frequency of ~ 18%, with most of them occurring in the tropics above 12 km. Zonal mean cloud radiative heating rate profiles from the three datasets are similar in their patterns of SW warming and LW cooling with small differences in magnitude; nevertheless, all three datasets show that the strongest net heating (> + 1.0 K day−1) occurs in the tropics (latitude < 30°) near the cloud-base while cooling occurs at higher latitudes (> ~ 50°). Differences in radiative heating rates are also assessed based on composites of the 2C-ICE ice water path (IWP) and total column water vapor (TCWV) mixing ratio to facilitate model evaluation and guide ice cloud parameterization improvement. Positive net cloud radiative heating rates are maximized in the upper troposphere for large IWPs and large TCWV, with an uncertainty of 10–25% in the magnitude and vertical structure of this heating. Satellite remote sensing; Radiative heating rate profiles; Single-layered ice cloud properties
Douglas, Alyson; L'Ecuyer, TristanDouglas, A., T. L'Ecuyer, 2019: Quantifying variations in shortwave aerosol–cloud–radiation interactions using local meteorology and cloud state constraints. Atmospheric Chemistry and Physics, 19(9), 6251-6268. doi: 10.5194/acp-19-6251-2019. Abstract. While many studies have tried to quantify the sign and the magnitude of the warm marine cloud response to aerosol loading, both remain uncertain, owing to the multitude of factors that modulate microphysical and thermodynamic processes within the cloud. Constraining aerosol–cloud interactions using the local meteorology and cloud liquid water may offer a way to account for covarying influences, potentially increasing our confidence in observational estimates of warm cloud indirect effects. A total of 4 years of collocated satellite observations from the NASA A-Train constellation, combined with reanalysis from MERRA-2, are used to partition marine warm clouds into regimes based on stability, the free atmospheric relative humidity, and liquid water path. Organizing the sizable number of satellite observations into regimes is shown to minimize the covariance between the environment or liquid water path and the indirect effect. Controlling for local meteorology and cloud state mitigates artificial signals and reveals substantial variance in both the sign and magnitude of the cloud radiative response, including regions where clouds become systematically darker with increased aerosol concentration in dry, unstable environments. A darkening effect is evident even under the most stringent of constraints. These results suggest it is not meaningful to report a single global sensitivity of cloud radiative effect to aerosol. To the contrary, we find the sensitivity can range from −0.46 to 0.11 Wm−2 ln(AI)−1 regionally.
Duda, David P.; Bedka, Sarah T.; Minnis, Patrick; Spangenberg, Douglas; Khlopenkov, Konstantin; Chee, Thad; Smith Jr., William L.Duda, D. P., S. T. Bedka, P. Minnis, D. Spangenberg, K. Khlopenkov, T. Chee, W. L. Smith Jr., 2019: Northern Hemisphere contrail properties derived from Terra and Aqua MODIS data for 2006 and 2012. Atmospheric Chemistry and Physics, 19(8), 5313-5330. doi: 10.5194/acp-19-5313-2019. Abstract. Linear contrail coverage, optical property, and radiative forcing data over the Northern Hemisphere (NH) are derived from a year (2012) of Terra and Aqua Moderate-resolution Imaging Spectroradiometer (MODIS) imagery and compared with previously published 2006 results (Duda et al., 2013; Bedka et al., 2013; Spangenberg et al., 2013) using a consistent retrieval methodology. Differences in the observed Terra-minus-Aqua screened contrail coverage and patterns in the 2012 annual-mean air traffic estimated with respect to satellite overpass time suggest that most contrails detected by the contrail detection algorithm (CDA) form approximately 2 h before overpass time. The 2012 screened NH contrail coverage (Mask B) shows a relative 3 % increase compared to 2006 data for Terra and increases by almost 7 % for Aqua, although the differences are not expected to be statistically significant. A new post-processing algorithm added to the contrail mask processing estimated that the total contrail cirrus coverage visible in the MODIS imagery may be 3 to 4 times larger than the linear contrail coverage detected by the CDA. This estimate is similar in magnitude to the spreading factor estimated by Minnis et al. (2013). Contrail property retrievals of the 2012 data indicate that both contrail optical depth and contrail effective diameter decreased approximately 10 % between 2006 and 2012. The decreases may be attributed to better background cloudiness characterization, changes in the waypoint screening, or changes in contrail temperature. The total mean contrail radiative forcings (TCRFs) for all 2012 Terra observations were −6.3, 14.3, and 8.0 mW m−2 for the shortwave (SWCRF), longwave (LWCRF), and net forcings, respectively. These values are approximately 20 % less than the corresponding 2006 Terra estimates. The decline in TCRF results from the decrease in normalized CRF, partially offset by the 3 % increase in overall contrail coverage in 2012. The TCRFs for 2012 Aqua are similar, −6.4, 15.5, and 9.0 mW m−2 for shortwave, longwave, and net radiative forcing. The strong correlation between the relative changes in both total SWCRF and LWCRF between 2006 and 2012 and the corresponding relative changes in screened contrail coverage over each air traffic region suggests that regional changes in TCRF from year to year are dominated by year-to-year changes in contrail coverage over each area.
El Masri, Bassil; Rahman, Abdullah F.; Dragoni, DaniloEl Masri, B., A. F. Rahman, D. Dragoni, 2019: Evaluating a new algorithm for satellite-based evapotranspiration for North American ecosystems: Model development and validation. Agricultural and Forest Meteorology, 268, 234-248. doi: 10.1016/j.agrformet.2019.01.025. We introduce a different operational approach to estimate 8-day average daily evapotranspiration (ET) using both routinely available data and the Penman-Monteith (P-M) equation for canopy transpiration and evaporation of intercepted water and Priestley and Taylor for soil evaporation. Our algorithm considered the environmental constraints on canopy resistance and ET by (1) including vapor pressure deficit (VPD), incoming solar radiation, soil moisture, and temperature constraints on stomatal conductance; (2) using leaf area index (LAI) to scale from the leaf to canopy conductance; and (3) calculating canopy resistance as a function of environmental variables such as net radiation and VPD. Remote sensing data from the Moderate Resolution Spectroradiometer (MODIS) and satellite soil moisture data were used to derive the ET model. The algorithm was calibrated and evaluated using measured ET data from 20 AmeriFlux Eddy covariance flux sites for the period of 2003–2012. We found good agreements between our 8-day ET estimates and observations with mean absolute error (MAE) ranges from 0.17 mm/day to 0.94 mm/day compared with MAE ranging from 0.28 mm/day to 1.50 mm/day for MODIS ET. Compared to MODIS ET, our proposed algorithm has higher correlations and higher Willmott’s index of agreement with observations for the majority of the Ameriflux sites. The strong relationship between the model estimated ET and the flux tower observations implies that our model has the potential to be applied to different ecosystems and at different temporal scales. Remote sensing; MODIS; Evapotranspiration; Eddy covariance flux; Penman-Monteith
Feng, Fei; Wang, KaicunFeng, F., K. Wang, 2019: Does the modern-era retrospective analysis for research and applications-2 aerosol reanalysis introduce an improvement in the simulation of surface solar radiation over China?. International Journal of Climatology, 39(3), 1305-1318. doi: 10.1002/joc.5881. Surface incident solar radiation (Rs) is a key parameter of energy and water cycles of the Earth. Reanalyses represent important sources of information on Rs. However, reanalyses Rs may have important bias due to their imperfect parameterizations and input errors of cloud and aerosol. NASA's Global Modelling and Assimilation Office has recently released Version 2 of the Modern-Era Retrospective Analysis for Research and Applications (MERRA2), which incorporates a reanalysis of atmospheric optical depth for the first time. In this study, we evaluate Rs from MERRA2 and its predecessor (MERRA) in China from 1980 to 2014. We first compare three possible reference data sources: (a) observed Rs at 122 stations, (b) satellite retrievals of Rs and (c) Rs values derived from sunshine durations measured at 2,400 weather stations. We find sunshine duration derived Rs is a reliable reference and use it to evaluate MERRA and MERRA2. Our results show that both MERRA and MERRA2 have a high mean bias of 38.63 and 43.86 W/m2 over China due to their underestimation of cloud fraction, which is greater in southern China. MERRA2 displays improved capability in reproducing monthly and annual variability, and national mean trend of Rs. MERRA overestimates the trend of Rs by 3.23 W/m2 in eastern China. MERRA2 reduced this trend bias over the North China Plain likely due to its aerosol assimilation. However, MERRA2 show a negative bias in trend of Rs (?3.44 W/m2) in the south China likely due to its overestimation of atmospheric aerosols loading and aerosol-cloud interaction. The results provide guidance for future development of reanalysis and its scientific applications for ecological and hydrological models. cloud; aerosol; surface incident solar radiation; MERRA2
Feng, Huihui; Zou, BinFeng, H., B. Zou, 2019: Satellite-based estimation of the aerosol forcing contribution to the global land surface temperature in the recent decade. Remote Sensing of Environment, 232, 111299. doi: 10.1016/j.rse.2019.111299. The aerosol forcing is an essential factor of global climate change, which can be estimated by various models. However, the model results ranging from −2.8 to 2.2 K remain controversial because of unavoidable uncertainty, leaving a great gap for global change prediction. This study aims to evaluate the forcing on the land surface temperature (Ts) using satellite-based observations. Based on the Blackbody radiation and surface radiation budget, first, a semi-physical framework is developed to estimate the Ts. Subsequently, the aerosol forcing is calculated by measuring the Ts difference between the changing aerosol scenario and baseline scenario with a fixed aerosol amount. Results show that the framework simulates Ts with acceptable accuracy (R = 0.62 and RMSE = 1.48 K), which supports the estimation of aerosol forcing. Generally, the change in the aerosol contributes 0.005 ± 0.237 K to the global Ts, which presents significant temporal and spatial variabilities. Temporally, the forcing shows a decreasing trend of −0.0006 K/year (R2 = 0.29, p = 0.031). Spatially, the forcing tends to warm the surface in regions with arid climate, low-cloud fraction, and moderate vapor or in sparsely vegetated and cool regions because of the potential interactions with climatic and environmental factors. The result of this study helps to reduce the uncertainty and validate the model results, which further supports the research on global climatic and environmental change. Satellite; Aerosol forcing; Land surface temperature; Radiation budget; Global change
Fueglistaler, S.Fueglistaler, S., 2019: Observational Evidence for Two Modes of Coupling Between Sea Surface Temperatures, Tropospheric Temperature Profile, and Shortwave Cloud Radiative Effect in the Tropics. Geophysical Research Letters, 46(16), 9890-9898. doi: 10.1029/2019GL083990. Tropical average shortwave cloud radiative effect (SWCRE) anomalies observed by CERES/EBAF v4 are explained by observed average sea surface temperature ( ) and the difference between the warmest 30% where deep convection occurs and ). Observed tropospheric temperatures show variations in boundary layer capping strength over time consistent with the evolution of SST#. The CERES/EBAF v4 data confirm that associated cloud fraction changes over the colder waters dominate SWCRE. This observational evidence for the “pattern effect” noted in General Circulation Model simulations suggests that SST# captures much of this effect. The observed sensitivities (dSWCRE/d W·m−2·K−1, dSWCRE/dSST#≈−4.8W·m−2·K−1) largely reflect El Niño–Southern Oscillation. As El Niño develops, increases and SST# decreases (both increasing SWCRE). Only after the El Niño peak, SST# increases and SWCRE decreases. SST# is also relevant for the tropical temperature trend profile controversy and the discrepancy between observed and modeled equatorial Pacific SST trends. Causality and implications for future climates are discussed. ENSO; cloud albedo; tropical convection; climate sensitivity; sea surface temperatures
Furtado, Kalli; Field, Paul; Luo, Yali; Zhou, Tianjun; Hill, AdrianFurtado, K., P. Field, Y. Luo, T. Zhou, A. Hill, 2019: The effects of cloud-aerosol-interaction complexity on simulations of presummer rainfall over southern China. Atmospheric Chemistry and Physics Discussions, 1-19. doi: https://doi.org/10.5194/acp-2019-596. Abstract. Convection-permitting simulations are used to understand the effects of cloud-aerosol interactions on a case of heavy rainfall over south China. The simulations are evaluated using radar observations from the South China Monsoon Rainfall Experiment and remotely sensed estimates of precipitation, clouds and radiation. We focus on the effects of complexity in cloud-aerosol interactions, especially processing and transport of dissolved material inside clouds. In particular, simulations with aerosol concentrations held constant are compared with a fully coupled cloud-aerosol-interacting system to isolate the effects of processing on a line of organised-deep convection. It is shown that in-cloud processing of aerosols can change the vertical structure of squall lines thereby inducing changes in the statistics of surface rainfall. These effects are shown to be consistent with a modulation by aerosol of the timescale of the converting cloud-droplets to rain.
Ge, Jinming; Wang, Zhenquan; Liu, Yuanyong; Su, Jing; Wang, Chen; Dong, ZixiangGe, J., Z. Wang, Y. Liu, J. Su, C. Wang, Z. Dong, 2019: Linkages between mid-latitude cirrus cloud properties and large-scale meteorology at the SACOL site. Climate Dynamics, 53(7), 5035-5046. doi: 10.1007/s00382-019-04843-9. The linkages between midlatitude cirrus properties and large-scale meteorology are investigated in this study by using 2-year observations from a ground Ka-band Zenith Radar (KAZR) and the Earth’s Radiant Energy System (CERES) SYN1deg satellite product over the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). Four atmospheric parameters (i.e. upward motion, relative humidity, stability and temperature at upper atmosphere) are used to examine the cirrus dependence on these factors. It is found that cirrus properties significantly depend on the changes of the four parameters and are most linearly correlated with upper atmosphere temperature. Cirrus infrared (IR) emissivity and ice water path (IWP) are sensitive to the strength of upward motions (ω), while cirrus thickness and albedo are more sensitive to relative humidity. An Empirical Orthogonal Function (EOF) is used to combine the four meteorological factors into a single variable and isolate the irrelevant synoptic noise to cirrus development and dissipation from the structure strongly associated with cirrus variations. The first leading principle component (PC1) is much better correlated with cirrus properties than any one of the four parameters. We further apply the EOF analysis to all 37 vertical levels of the four parameters. It is found that a negative area of the main structure between 6 and 10 km above ground level (AGL) is well collocated with the cirrus distribution from the KAZR observations on a diurnal time scale, indicating a robust relationship between cirrus and the combined meteorological fields.
Gettelman, A.; Mills, M. J.; Kinnison, D. E.; Garcia, R. R.; Smith, A. K.; Marsh, D. R.; Tilmes, S.; Vitt, F.; Bardeen, C. G.; McInerny, J.; Liu, H.-L.; Solomon, S. C.; Polvani, L. M.; Emmons, L. K.; Lamarque, J.-F.; Richter, J. H.; Glanville, A. S.; Bacmeister, J. T.; Phillips, A. S.; Neale, R. B.; Simpson, I. R.; DuVivier, A. K.; Hodzic, A.; Randel, W. J.Gettelman, A., M. J. Mills, D. E. Kinnison, R. R. Garcia, A. K. Smith, D. R. Marsh, S. Tilmes, F. Vitt, C. G. Bardeen, J. McInerny, H. Liu, S. C. Solomon, L. M. Polvani, L. K. Emmons, J. Lamarque, J. H. Richter, A. S. Glanville, J. T. Bacmeister, A. S. Phillips, R. B. Neale, I. R. Simpson, A. K. DuVivier, A. Hodzic, W. J. Randel, 2019: The Whole Atmosphere Community Climate Model Version 6 (WACCM6). Journal of Geophysical Research: Atmospheres, 124(23), 12380-12403. doi: 10.1029/2019JD030943. The Whole Atmosphere Community Climate Model version 6 (WACCM6) is a major update of the whole atmosphere modeling capability in the Community Earth System Model (CESM), featuring enhanced physical, chemical and aerosol parameterizations. This work describes WACCM6 and some of the important features of the model. WACCM6 can reproduce many modes of variability and trends in the middle atmosphere, including the quasi-biennial oscillation, stratospheric sudden warmings, and the evolution of Southern Hemisphere springtime ozone depletion over the twentieth century. WACCM6 can also reproduce the climate and temperature trends of the 20th century throughout the atmospheric column. The representation of the climate has improved in WACCM6, relative to WACCM4. In addition, there are improvements in high-latitude climate variability at the surface and sea ice extent in WACCM6 over the lower top version of the model (CAM6) that comes from the extended vertical domain and expanded aerosol chemistry in WACCM6, highlighting the importance of the stratosphere and tropospheric chemistry for high-latitude climate variability.
Golaz, Jean-Christophe; Caldwell, Peter M.; Roekel, Luke P. Van; Petersen, Mark R.; Tang, Qi; Wolfe, Jonathan D.; Abeshu, Guta; Anantharaj, Valentine; Asay‐Davis, Xylar S.; Bader, David C.; Baldwin, Sterling A.; Bisht, Gautam; Bogenschutz, Peter A.; Branstetter, Marcia; Brunke, Michael A.; Brus, Steven R.; Burrows, Susannah M.; Cameron‐Smith, Philip J.; Donahue, Aaron S.; Deakin, Michael; Easter, Richard C.; Evans, Katherine J.; Feng, Yan; Flanner, Mark; Foucar, James G.; Fyke, Jeremy G.; Griffin, Brian M.; Hannay, Cécile; Harrop, Bryce E.; Hoffman, Mattthew J.; Hunke, Elizabeth C.; Jacob, Robert L.; Jacobsen, Douglas W.; Jeffery, Nicole; Jones, Philip W.; Keen, Noel D.; Klein, Stephen A.; Larson, Vincent E.; Leung, L. Ruby; Li, Hong-Yi; Lin, Wuyin; Lipscomb, William H.; Ma, Po-Lun; Mahajan, Salil; Maltrud, Mathew E.; Mametjanov, Azamat; McClean, Julie L.; McCoy, Renata B.; Neale, Richard B.; Price, Stephen F.; Qian, Yun; Rasch, Philip J.; Eyre, J. E. Jack Reeves; Riley, William J.; Ringler, Todd D.; Roberts, Andrew F.; Roesler, Erika L.; Salinger, Andrew G.; Shaheen, Zeshawn; Shi, Xiaoying; Singh, Balwinder; Tang, Jinyun; Taylor, Mark A.; Thornton, Peter E.; Turner, Adrian K.; Veneziani, Milena; Wan, Hui; Wang, Hailong; Wang, Shanlin; Williams, Dean N.; Wolfram, Phillip J.; Worley, Patrick H.; Xie, Shaocheng; Yang, Yang; Yoon, Jin-Ho; Zelinka, Mark D.; Zender, Charles S.; Zeng, Xubin; Zhang, Chengzhu; Zhang, Kai; Zhang, Yuying; Zheng, Xue; Zhou, Tian; Zhu, QingGolaz, J., P. M. Caldwell, L. P. V. Roekel, M. R. Petersen, Q. Tang, J. D. Wolfe, G. Abeshu, V. Anantharaj, X. S. Asay‐Davis, D. C. Bader, S. A. Baldwin, G. Bisht, P. A. Bogenschutz, M. Branstetter, M. A. Brunke, S. R. Brus, S. M. Burrows, P. J. Cameron‐Smith, A. S. Donahue, M. Deakin, R. C. Easter, K. J. Evans, Y. Feng, M. Flanner, J. G. Foucar, J. G. Fyke, B. M. Griffin, C. Hannay, B. E. Harrop, M. J. Hoffman, E. C. Hunke, R. L. Jacob, D. W. Jacobsen, N. Jeffery, P. W. Jones, N. D. Keen, S. A. Klein, V. E. Larson, L. R. Leung, H. Li, W. Lin, W. H. Lipscomb, P. Ma, S. Mahajan, M. E. Maltrud, A. Mametjanov, J. L. McClean, R. B. McCoy, R. B. Neale, S. F. Price, Y. Qian, P. J. Rasch, J. E. J. R. Eyre, W. J. Riley, T. D. Ringler, A. F. Roberts, E. L. Roesler, A. G. Salinger, Z. Shaheen, X. Shi, B. Singh, J. Tang, M. A. Taylor, P. E. Thornton, A. K. Turner, M. Veneziani, H. Wan, H. Wang, S. Wang, D. N. Williams, P. J. Wolfram, P. H. Worley, S. Xie, Y. Yang, J. Yoon, M. D. Zelinka, C. S. Zender, X. Zeng, C. Zhang, K. Zhang, Y. Zhang, X. Zheng, T. Zhou, Q. Zhu, 2019: The DOE E3SM Coupled Model Version 1: Overview and Evaluation at Standard Resolution. Journal of Advances in Modeling Earth Systems, 11(7), 2089-2129. doi: 10.1029/2018MS001603. This work documents the first version of the U.S. Department of Energy (DOE) new Energy Exascale Earth System Model (E3SMv1). We focus on the standard resolution of the fully coupled physical model designed to address DOE mission-relevant water cycle questions. Its components include atmosphere and land (110-km grid spacing), ocean and sea ice (60 km in the midlatitudes and 30 km at the equator and poles), and river transport (55 km) models. This base configuration will also serve as a foundation for additional configurations exploring higher horizontal resolution as well as augmented capabilities in the form of biogeochemistry and cryosphere configurations. The performance of E3SMv1 is evaluated by means of a standard set of Coupled Model Intercomparison Project Phase 6 (CMIP6) Diagnosis, Evaluation, and Characterization of Klima simulations consisting of a long preindustrial control, historical simulations (ensembles of fully coupled and prescribed SSTs) as well as idealized CO2 forcing simulations. The model performs well overall with biases typical of other CMIP-class models, although the simulated Atlantic Meridional Overturning Circulation is weaker than many CMIP-class models. While the E3SMv1 historical ensemble captures the bulk of the observed warming between preindustrial (1850) and present day, the trajectory of the warming diverges from observations in the second half of the twentieth century with a period of delayed warming followed by an excessive warming trend. Using a two-layer energy balance model, we attribute this divergence to the model's strong aerosol-related effective radiative forcing (ERFari+aci = −1.65 W/m2) and high equilibrium climate sensitivity (ECS = 5.3 K).
Gristey, Jake J.; Chiu, J. Christine; Gurney, Robert J.; Shine, Keith P.; Havemann, Stephan; Thelen, Jean-Claude; Hill, Peter G.Gristey, J. J., J. C. Chiu, R. J. Gurney, K. P. Shine, S. Havemann, J. Thelen, P. G. Hill, 2019: Shortwave Spectral Radiative Signatures and Their Physical Controls. J. Climate, 32(15), 4805-4828. doi: 10.1175/JCLI-D-18-0815.1. The spectrum of reflected solar radiation emerging at the top of the atmosphere is rich with Earth system information. To identify spectral signatures in the reflected solar radiation and directly relate them to the underlying physical properties controlling their structure, over 90 000 solar reflectance spectra are computed over West Africa in 2010 using a fast radiation code employing the spectral characteristics of the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). Cluster analysis applied to the computed spectra reveals spectral signatures related to distinct surface properties, and cloud regimes distinguished by their spectral shortwave cloud radiative effect (SWCRE). The cloud regimes exhibit a diverse variety of mean broadband SWCREs, and offer an alternative approach to define cloud type for SWCRE applications that does not require any prior assumptions. The direct link between spectral signatures and distinct physical properties extracted from clustering remains robust between spatial scales of 1, 20, and 240 km, and presents an excellent opportunity to understand the underlying properties controlling real spectral reflectance observations. Observed SCIAMACHY spectra are assigned to the calculated spectral clusters, showing that cloud regimes are most frequent during the active West African monsoon season of June–October in 2010, and all cloud regimes have a higher frequency of occurrence during the active monsoon season of 2003 compared with the inactive monsoon season of 2004. Overall, the distinct underlying physical properties controlling spectral signatures show great promise for monitoring evolution of the Earth system directly from solar spectral reflectance observations.
Guo, Zhun; Wang, Minghuai; Larson, Vincent E.; Zhou, TianjunGuo, Z., M. Wang, V. E. Larson, T. Zhou, 2019: A Cloud Top Radiative Cooling Model Coupled With CLUBB in the Community Atmosphere Model: Description and Simulation of Low Clouds. Journal of Advances in Modeling Earth Systems, 11(4), 979-997. doi: 10.1029/2018MS001505. In this study, a higher-order closure scheme known as Cloud Layers Unified By Binormals (CLUBB) is coupled with a cloud top radiative cooling scheme (RAD). The cloud top radiative cooling scheme treats the buoyancy flux generated near the top of the boundary layer which helps the CLUBB scheme to better represent the radiation-turbulence interaction on the condition of coarse vertical resolution. CLUBB with RAD is found to improve subtropical low-cloud simulations, and the improvement is particularly evident for nocturnal stratocumulus. The improvements are caused by the stronger and more symmetric vertical turbulent mixing in the boundary layer, as CLUBB with RAD increases the variance of vertical velocity and vertical turbulent transports and reduces the skewness of vertical velocity by enhancing the radiative cooling effects and buoyancy fluxes at the cloud layer. The pumping effect related to the stronger vertical turbulent transports further cools and dries the lower boundary layer, which increases the local surface heating fluxes and further improves the low-cloud simulations. buoyancy flux; low cloud; cloud top radiative cooling; higher-order closure scheme
Hahn, Gregory G.; Adoram-Kershner, Lauren Andrea; Cantin, Heather P.; Shafer, Michael W.Hahn, G. G., L. A. Adoram-Kershner, H. P. Cantin, M. W. Shafer, 2019: Assessing Solar Power for Globally Migrating Marine and Submarine Systems. IEEE Journal of Oceanic Engineering, 44(3), 693-706. doi: 10.1109/JOE.2018.2835178. Remote marine sensing systems, such as autonomous underwater vehicles or telemetry tags, can be limited in data collection and deployment duration due to the finite energy of the onboard battery. With these technologies migrating vast distances over long-term deployments, maintaining high data resolution is difficult and often yields nonideal data sets. Furthermore, electronics systems used in telemetry tags are often potted in epoxy, which makes replacing or recharging the battery impractical. The implementation of solar energy harvesting on these technologies could increase the fidelity of collected data and/or tag longevity. This paper presents an assessment model that estimates the energy output of a stationary or migrating solar cell above or below the ocean's surface. The theory and assumptions behind the model are explained, including a review of established concepts for the purpose of consolidation and variable consistency. The model is then compared to benchmark data for verification. Finally, a preliminary analysis is conducted on the previously collected time, depth, and global location data from a northern elephant seal deployment to demonstrate the resulting model outputs and how they can be used for analysis in future works. oceanographic equipment; oceanographic techniques; solar energy; Sea surface; Ocean temperature; solar power; assessing solar power; assessment model; autonomous underwater vehicles; benchmark data; collected time; data collection; deployment duration; electronics systems; energy harvesting; energy output; global location data; globally migrating marine; high data resolution; long-term deployments; Marine technology; migrating solar cell; model outputs; nonideal data sets; northern elephant seal deployment; onboard battery; Photovoltaic cells; predictive models; radiotelemetry; remote marine sensing systems; remotely operated vehicles; Solar energy; solar energy harvesting; stationary cell; submarine systems; Sun; tag longevity; telemetry; Telemetry; telemetry tags; underwater equipment; underwater vehicles; Underwater vehicles; wireless sensor networks
Hang, Yun; L’Ecuyer, Tristan S.; Henderson, David S.; Matus, Alexander V.; Wang, ZhienHang, Y., T. S. L’Ecuyer, D. S. Henderson, A. V. Matus, Z. Wang, 2019: Reassessing the Effect of Cloud Type on Earth’s Energy Balance in the Age of Active Spaceborne Observations. Part II: Atmospheric Heating. J. Climate, 32(19), 6219-6236. doi: 10.1175/JCLI-D-18-0754.1. The role of clouds in modulating vertically integrated atmospheric heating is investigated using CloudSat’s multisensor radiative flux dataset. On the global mean, clouds are found to induce a net atmospheric heating of 0.07 ± 0.08 K day−1 that derives largely from 0.06 ± 0.07 K day−1 of enhanced shortwave absorption and a small, 0.01 ± 0.04 K day−1 reduction of longwave cooling. However, this small global average longwave effect results from the near cancellation of much larger regional warming by multilayered cloud systems in the tropics and cooling from stratocumulus clouds in subtropical oceans. Clouds are observed to warm the tropical atmosphere by 0.23 K day−1 and cool the polar atmosphere by −0.13 K day−1 enhancing required zonal heat redistribution by the meridional overturning circulation. Zonal asymmetries in the occurrence of multilayered clouds that are more frequent in the Northern Hemisphere and stratocumulus that occur more frequently over the southern oceans also leads to 3 times as much cloud heating in the Northern Hemisphere (0.1 K day−1) than the Southern Hemisphere (0.04 K day−1). These findings suggest that clouds very likely make the strongest contribution to the annual mean atmospheric energy imbalance between the hemispheres (2.0 ± 3.5 PW).
Hayatbini, Negin; Hsu, Kuo-lin; Sorooshian, Soroosh; Zhang, Yunji; Zhang, FuqingHayatbini, N., K. Hsu, S. Sorooshian, Y. Zhang, F. Zhang, 2019: Effective Cloud Detection and Segmentation Using a Gradient-Based Algorithm for Satellite Imagery: Application to Improve PERSIANN-CCS. J. Hydrometeor., 20(5), 901-913. doi: 10.1175/JHM-D-18-0197.1. The effective identification of clouds and monitoring of their evolution are important toward more accurate quantitative precipitation estimation and forecast. In this study, a new gradient-based cloud-image segmentation algorithm is developed using image processing techniques. This method integrates morphological image gradient magnitudes to separate cloud systems and patches boundaries. A varying scale kernel is implemented to reduce the sensitivity of image segmentation to noise and to capture objects with various finenesses of the edges in remote sensing images. The proposed method is flexible and extendable from single to multispectral imagery. Case studies were carried out to validate the algorithm by applying the proposed segmentation algorithm to synthetic radiances for channels of the Geostationary Operational Environmental Satellite (GOES-16) simulated by a high-resolution weather prediction model. The proposed method compares favorably with the existing cloud-patch-based segmentation technique implemented in the Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks–Cloud Classification System (PERSIANN-CCS) rainfall retrieval algorithm. Evaluation of event-based images indicates that the proposed algorithm has potentials comparing to the conventional segmentation technique used in PERSIANN-CCS to improve rain detection and estimation skills with an accuracy rate of up to 98% in identifying cloud regions.
He, Min; Hu, Yongxiang; Chen, Nan; Wang, Donghai; Huang, Jianping; Stamnes, KnutHe, M., Y. Hu, N. Chen, D. Wang, J. Huang, K. Stamnes, 2019: High cloud coverage over melted areas dominates the impact of clouds on the albedo feedback in the Arctic. Scientific Reports, 9(1), 1-11. doi: 10.1038/s41598-019-44155-w. Warming in the Arctic is larger than the global average. A primary reason for this Arctic Amplification is the albedo feedback. The contrasting albedo of sea ice and dark melted surface areas is the key component of albedo feedback. Cloud coverage over the changing surface and the response of the clouds to the changing surface conditions will modify the change in planetary albedo when sea ice melts. Space-based lidar measurements provide a unique opportunity for cloud measurements in the Arctic. The response of clouds to the changing sea ice concentration was directly observed. Based on CALIPSO satellite observations of cloud properties, this study found that cloud coverage in ice-free regions in the Arctic linearly increased with the area of ice-free water during the melt seasons in the past 10 years, while sea ice coverage varies significantly year-to-year. The observations suggest that when sea-ice retreats, cloud fraction of the ice-free region remains fixed at nearly 81%. The high cloud coverage over melted areas significantly reduces the albedo feedback. These results indicate that space-based lidar cloud and surface observations of the Arctic can help constrain and improve climate models.
Hecht, Matthew; Veneziani, Milena; Weijer, Wilbert; Kravitz, Ben; Burrows, Susannah; Comeau, Darin; Hunke, Elizabeth; Jeffery, Nicole; Urrego‐Blanco, Jorge; Wang, Hailong; Wang, Shanlin; Zhang, Jiaxu; Bailey, David; Mills, Catrin; Rasch, Philip; Urban, NathanHecht, M., M. Veneziani, W. Weijer, B. Kravitz, S. Burrows, D. Comeau, E. Hunke, N. Jeffery, J. Urrego‐Blanco, H. Wang, S. Wang, J. Zhang, D. Bailey, C. Mills, P. Rasch, N. Urban, 2019: E3SMv0-HiLAT: A Modified Climate System Model Targeted for the Study of High-Latitude Processes. Journal of Advances in Modeling Earth Systems, 11(8), 2814-2843. doi: 10.1029/2018MS001524. We document the configuration, tuning, and evaluation of a modified version of the Community Earth System Model version 1 (Hurrell et al., 2013, https://doi.org/10.1175/BAMS-D-12), introduced here as E3SMv0-HiLAT, intended for study of high-latitude processes. E3SMv0-HiLAT incorporates changes to the atmospheric model affecting aerosol transport to high northern latitudes and to reduce shortwave cloud bias over the Southern Ocean. An updated sea ice model includes biogeochemistry that is coupled to an extended version of the ocean model's biogechemistry. This enables cloud nucleation to depend on the changing marine emissions of aerosol precursors, which may be expected in scenarios with strongly changing sea ice extent, oceanic stratification and associated nutrient availability, and atmospheric state. An evaluation of the basic preindustrial state of E3SMv0-HiLAT is presented in order to ensure that its climate is adequate to support future experimentation. Additional capability is not achieved without some cost, relative to the extraordinarily well-tuned model from which it was derived. In particular, a reduction of bias in cloud forcing achieved over the Southern Hemisphere also allows for greater Southern Ocean sea ice extent, a tendency that has been partially but not fully alleviated through experimentation and tuning. The most interesting change in the behavior of the model may be its response to greenhouse gas forcing: While the climate sensitivity is found to be essentially unchanged from that of Community Earth System Model version 1, the adjusted radiative forcing has increased from within one standard deviation above that of Coupled Model Intercomparison Project Phase 5 models to nearly two standard deviations. clouds; CESM; Earth System Model; high latitudes
Held, I. M.; Guo, H.; Adcroft, A.; Dunne, J. P.; Horowitz, L. W.; Krasting, J.; Shevliakova, E.; Winton, M.; Zhao, M.; Bushuk, M.; Wittenberg, A. T.; Wyman, B.; Xiang, B.; Zhang, R.; Anderson, W.; Balaji, V.; Donner, L.; Dunne, K.; Durachta, J.; Gauthier, P. P. G.; Ginoux, P.; Golaz, J.-C.; Griffies, S. M.; Hallberg, R.; Harris, L.; Harrison, M.; Hurlin, W.; John, J.; Lin, P.; Lin, S.-J.; Malyshev, S.; Menzel, R.; Milly, P. C. D.; Ming, Y.; Naik, V.; Paynter, D.; Paulot, F.; Rammaswamy, V.; Reichl, B.; Robinson, T.; Rosati, A.; Seman, C.; Silvers, L. G.; Underwood, S.; Zadeh, N.Held, I. M., H. Guo, A. Adcroft, J. P. Dunne, L. W. Horowitz, J. Krasting, E. Shevliakova, M. Winton, M. Zhao, M. Bushuk, A. T. Wittenberg, B. Wyman, B. Xiang, R. Zhang, W. Anderson, V. Balaji, L. Donner, K. Dunne, J. Durachta, P. P. G. Gauthier, P. Ginoux, J. Golaz, S. M. Griffies, R. Hallberg, L. Harris, M. Harrison, W. Hurlin, J. John, P. Lin, S. Lin, S. Malyshev, R. Menzel, P. C. D. Milly, Y. Ming, V. Naik, D. Paynter, F. Paulot, V. Rammaswamy, B. Reichl, T. Robinson, A. Rosati, C. Seman, L. G. Silvers, S. Underwood, N. Zadeh, 2019: Structure and Performance of GFDL's CM4.0 Climate Model. Journal of Advances in Modeling Earth Systems, 11(11), 3691-3727. doi: 10.1029/2019MS001829. We describe the Geophysical Fluid Dynamics Laboratory's CM4.0 physical climate model, with emphasis on those aspects that may be of particular importance to users of this model and its simulations. The model is built with the AM4.0/LM4.0 atmosphere/land model and OM4.0 ocean model. Topics include the rationale for key choices made in the model formulation, the stability as well as drift of the preindustrial control simulation, and comparison of key aspects of the historical simulations with observations from recent decades. Notable achievements include the relatively small biases in seasonal spatial patterns of top-of-atmosphere fluxes, surface temperature, and precipitation; reduced double Intertropical Convergence Zone bias; dramatically improved representation of ocean boundary currents; a high-quality simulation of climatological Arctic sea ice extent and its recent decline; and excellent simulation of the El Niño-Southern Oscillation spectrum and structure. Areas of concern include inadequate deep convection in the Nordic Seas; an inaccurate Antarctic sea ice simulation; precipitation and wind composites still affected by the equatorial cold tongue bias; muted variability in the Atlantic Meridional Overturning Circulation; strong 100 year quasiperiodicity in Southern Ocean ventilation; and a lack of historical warming before 1990 and too rapid warming thereafter due to high climate sensitivity and strong aerosol forcing, in contrast to the observational record. Overall, CM4.0 scores very well in its fidelity against observations compared to the Coupled Model Intercomparison Project Phase 5 generation in terms of both mean state and modes of variability and should prove a valuable new addition for analysis across a broad array of applications. climate; model; CMIP6; CM4; coupled; GFDL
Hinkelman, Laura M.Hinkelman, L. M., 2019: The global radiative energy budget in MERRA Version 1 and Version 2: Evaluation with respect to CERES EBAF data. J. Climate, 32(6), 1973–1994. doi: 10.1175/JCLI-D-18-0445.1. The representation of the long-term radiative energy budgets in NASA’s MERRA and MERRA-2 reanalyses has been evaluated, emphasizing changes associated with the reanalysis system update. Data from the CERES EBAF Edition 2.8 satellite product over 2001-2015 were used as a reference. For both MERRA and MERRA-2, the climatological global means of most TOA radiative flux terms agree to within ∼3 Wm-2 of EBAF. However, MERRA-2’s all-sky reflected shortwave flux is ∼7 Wm-2 higher than either MERRA or EBAF’s, resulting in a net TOA flux imbalance of -4 Wm-2. At the surface, all-sky downward longwave fluxes are problematic for both reanalyses while high clear-sky downward shortwave fluxes indicate that their atmospheres are too transmissive. Although MERRA-2’s individual all-sky flux terms agree better with EBAF, its net flux agreement is worse (-8.3 Wm-2 vs -3.3 Wm-2 for MERRA) because MERRA benefits from cancellation of errors. Analysis by region and surface type gives mixed outcomes. The results consistently indicate that clouds are over-represented over the tropical oceans in both reanalyses, particularly MERRA-2, and somewhat under-represented in marine stratocumulus areas. MERRA-2 also exhibits signs of excess cloudiness in the Southern Ocean. Notable discrepancies occur in the polar regions, where the effects of snow and ice cover are important. In most cases, MERRA-2 better represents variability and trends in the global mean radiative fluxes over the period of analysis. Overall, the performance of MERRA-2 relative to MERRA is mixed; there is still room for improvement in the radiative fluxes in this family of reanalysis products.
Hogikyan, Allison; Cronin, Meghan F.; Zhang, Dongxiao; Kato, SeijiHogikyan, A., M. F. Cronin, D. Zhang, S. Kato, 2019: Uncertainty in Net Surface Heat Flux due to Differences in Commonly Used Albedo Products. J. Climate, 33(1), 303-315. doi: 10.1175/JCLI-D-18-0448.1. The ocean surface albedo is responsible for the distribution of solar (shortwave) radiant energy between the atmosphere and ocean and therefore is a key parameter in Earth’s surface energy budget. In situ ocean observations typically do not measure upward reflected solar radiation, which is necessary to compute net solar radiation into the ocean. Instead, the upward component is computed from the measured downward component using an albedo estimate. At two NOAA Ocean Climate Station buoy sites in the North Pacific, the International Satellite Cloud Climatology Project (ISCCP) monthly climatological albedo has been used, while for the NOAA Global Tropical Buoy Array a constant albedo is used. This constant albedo is also used in the Coupled Ocean–Atmosphere Response Experiment (COARE) bulk flux algorithm. This study considers the impacts of using the more recently available NASA Cloud and the Earth’s Radiant Energy System (CERES) albedo product for these ocean surface heat flux products. Differences between albedo estimates in global satellite products like these imply uncertainty in the net surface solar radiation heat flux estimates that locally exceed the target uncertainty of 1.0 W m−2 for the global mean, set by the Global Climate Observing System (GCOS) of the World Meteorological Organization (WMO). Albedo has large spatiotemporal variability on hourly, monthly, and interannual time scales. Biases in high-resolution SWnet (the difference between surface downwelling and upwelling shortwave radiation) can arise if the albedo diurnal cycle is unresolved. As a result, for periods when satellite albedo data are not available it is recommended that an hourly climatology be used when computing high-resolution net surface shortwave radiation.
Hourdin, Frédéric; Jam, Arnaud; Rio, Catherine; Couvreux, Fleur; Sandu, Irina; Lefebvre, Marie-Pierre; Brient, Florent; Idelkadi, AbderrahmaneHourdin, F., A. Jam, C. Rio, F. Couvreux, I. Sandu, M. Lefebvre, F. Brient, A. Idelkadi, 2019: Unified Parameterization of Convective Boundary Layer Transport and Clouds With the Thermal Plume Model. Journal of Advances in Modeling Earth Systems, 11(9), 2910-2933. doi: 10.1029/2019MS001666. The representation of stratocumulus clouds, and of the stratocumulus to cumulus transitions which are ubiquitous features of marine boundary layer clouds, remains a challenge for climate models. We show how a mass flux representation of boundary layer convective structures combined with an eddy diffusivity scheme, the “thermal plume model,” first developed to represent cumulus clouds, can also adequately simulate stratocumulus and the stratocumulus to cumulus transition in a climate model. To achieve this, the detrainment formulation, in which detrainment increases for increasing negative buoyancy, has to be slightly modified: the buoyancy of a thermal plume parcel of air is computed by comparing the virtual potential temperature θv,th of the parcel with that of the surrounding environment θv,env at a given distance above instead of at the same level. This is consistent with the picture of detrained air parcels that experience some overshoot and reach a final destination at a level lower than the one at which they effectively leave the cloud or organized convective plume. The impacts of this modification are documented both for selected cases of stratocumulus, in comparison with large-eddy simulations, and in full 3-D climate simulations, in comparison with satellite observations of cloud cover. The modified scheme provides a uniform treatment of the dry convective boundary layer, of cumulus clouds, of stratocumulus, and of the transition from stratocumulus to cumulus. It is included in the most recent version of the LMDZ atmospheric general circulation model. global climate model; stratocumulus; convective boundary layer; mass flux scheme
Huang, Guanghui; Li, Zhanqing; Li, Xin; Liang, Shunlin; Yang, Kun; Wang, Dongdong; Zhang, YiHuang, G., Z. Li, X. Li, S. Liang, K. Yang, D. Wang, Y. Zhang, 2019: Estimating surface solar irradiance from satellites: Past, present, and future perspectives. Remote Sensing of Environment, 233, 111371. doi: 10.1016/j.rse.2019.111371. Surface Solar Irradiance (SSI) is a key parameter dictating surface-atmosphere interactions, driving radiative, hydrological, and land surface processes, and can thus impinge greatly upon weather and climate. It is thereby a prerequisite of many studies and applications. Estimating SSI from satellites began in the 1960s, and is currently the principal way to map SSI spatiotemporal distributions from regional to global scales. Starting from an overview of historical studies carried out in the past several decades, this paper reviews the progresses made in methodology, validation, and products over these years. First, the requirements of SSI in various studies or applications are presented along with the theoretical background of SSI satellite estimation. Methods to estimate SSI from satellites are then summarized as well as their advantages and limitations. Validations of satellite-based SSI on two typical spatial scales are discussed followed by a brief description of existing products and their accuracies. Finally, the challenges faced by current SSI satellite estimation are analyzed, and possible improvements to implement in the future are suggested. This review not only updates the review paper by Pinker et al. (1995) on satellite methods to derive SSI but also offers a more comprehensive summary of the related studies and applications. Remote sensing; Satellites; Radiation budget; Review; Surface solar irradiance
Huang, Yi; Chou, Gina; Xie, Yan; Soulard, NicholasHuang, Y., G. Chou, Y. Xie, N. Soulard, 2019: Radiative Control of the Interannual Variability of Arctic Sea Ice. Geophysical Research Letters, 46(16), 9899-9908. doi: 10.1029/2019GL084204. On top of a declining trend driven by global warming, the Arctic sea ice extent (SIE) exhibits considerable interannual variations. In this study, we analyze the interannual anomalies of September SIE in relation to the surface radiation anomalies. We find that the accumulation of radiation energy in the early months (June, July, and August) very well explains the September SIE variability (R2 = 0.81). In Particular, strong correlations are found between September SIE and June radiation anomalies, which in the shortwave is due to cloud and surface albedo changes and in the longwave due to atmospheric warming. The results show that monitoring the radiation anomalies affords a potential means to improve the prediction of the late summer sea ice. radiative forcing; cloud; sea ice; Arctic; interannual variability; NAO
Huang, Yiyi; Dong, Xiquan; Bailey, David A.; Holland, Marika M.; Xi, Baike; DuVivier, Alice K.; Kay, Jennifer E.; Landrum, Laura L.; Deng, YiHuang, Y., X. Dong, D. A. Bailey, M. M. Holland, B. Xi, A. K. DuVivier, J. E. Kay, L. L. Landrum, Y. Deng, 2019: Thicker Clouds and Accelerated Arctic Sea Ice Decline: The Atmosphere-Sea Ice Interactions in Spring. Geophysical Research Letters, 46(12), 6980-6989. doi: 10.1029/2019GL082791. Observations show that increased Arctic cloud cover in the spring is linked with sea ice decline. As the atmosphere and sea ice can influence each other, which one plays the leading role in spring remains unclear. Here we demonstrate, through observational data diagnosis and numerical modeling, that there is active coupling between the atmosphere and sea ice in early spring. Sea ice melting and thus the presence of more open water lead to stronger evaporation and promote cloud formation that increases downward longwave flux, leading to even more ice melt. Spring clouds are a driving force in the disappearance of sea ice and displacing the mechanism of atmosphere-sea ice coupling from April to June. These results suggest the need to accurately model interactions of Arctic clouds and radiation in Earth System Models in order to improve projections of the future of the Arctic. Arctic sea ice retreat; atmosphere-sea ice coupling; atmospheric physical processes; cloud and radiation impact
Huang, Yiyi; Dong, Xiquan; Xi, Baike; Deng, YiHuang, Y., X. Dong, B. Xi, Y. Deng, 2019: A survey of the atmospheric physical processes key to the onset of Arctic sea ice melt in spring. Climate Dynamics, 52(7), 4907-4922. doi: 10.1007/s00382-018-4422-x. September sea ice concentration (SIC) is found to be most sensitive to the early melt onset over the East Siberian Sea and Laptev Sea (73°–84°N, 90°–155°) in the Arctic, a region defined here as the area of focus (AOF). The areal initial melt date for a given year is marked when sea ice melting extends beyond 10% of the AOF size. With this definition, four early melting years (1990, 2012, 2003, 1991) and four late melting years (1996, 1984, 1983, 1982) were selected. The impacts and feedbacks of atmospheric physical and dynamical variables on the Arctic SIC variations were investigated for the selected early and late melting years based on the NASA MERRA-2 reanalysis. The sea ice melting tends to happen in a shorter period of time with larger magnitude in late melting years, while the melting lasts longer and tends to be more temporally smooth in early melting years. The first major melting event in each year has been further investigated and compared. In the early melting years, the positive Arctic Oscillation (AO) phase is dominant during springtime, which is accompanied by intensified atmospheric transient eddy activities in the Arctic and enhanced moisture flux convergence in the AOF and consequently enhanced northward transport of moist and warm air. As a result, positive anomalies of air temperature, precipitable water vapor (PWV) and/or cloud fraction and cloud water path were found over the AOF, increasing downward longwave radiative flux at the surface. The associated warming effect further contributes to the initial melt of sea ice. In contrast, the late melt onset is usually linked to the negative AO phase in spring accompanied with negative anomalies of PWV and downward longwave flux at the surface. The increased downward shortwave radiation during middle to late June plays a more important role in triggering the melting, aided further by the stronger than normal cloud warming effects. Arctic sea ice melt onset; Arctic September sea ice minimum retreat; Atmospheric physical processes; Cloud and radiation impact; Moisture and heat transport
Hwang, Jiwon; Choi, Yong-Sang; Yoo, Changhyun; Wang, Yuan; Su, Hui; Jiang, Jonathan H.Hwang, J., Y. Choi, C. Yoo, Y. Wang, H. Su, J. H. Jiang, 2019: Interpretation of the Top-of-Atmosphere Energy Flux for Future Arctic Warming. Scientific Reports, 9(1), 1-10. doi: 10.1038/s41598-019-49218-6. With the trend of amplified warming in the Arctic, we examine the observed and modeled top-of-atmosphere (TOA) radiative responses to surface air-temperature changes over the Arctic by using TOA energy fluxes from NASA’s CERES observations and those from twelve climate models in CMIP5. Considerable inter-model spreads in the radiative responses suggest that future Arctic warming may be determined by the compensation between the radiative imbalance and poleward energy transport (mainly via transient eddy activities). The poleward energy transport tends to prevent excessive Arctic warming: the transient eddy activities are weakened because of the reduced meridional temperature gradient under polar amplification. However, the models that predict rapid Arctic warming do not realistically simulate the compensation effect. This role of energy compensation in future Arctic warming is found only when the inter-model differences in cloud radiative effects are considered. Thus, the dynamical response can act as a buffer to prevent excessive Arctic warming against the radiative response of 0.11 W m−2 K−1 as measured from satellites, which helps the Arctic climate system retain an Arctic climate sensitivity of 4.61 K. Therefore, if quantitative analyses of the observations identify contribution of atmospheric dynamics and cloud effects to radiative imbalance, the satellite-measured radiative response will be a crucial indicator of future Arctic warming.
Jakob, C.; Singh, M. S.; Jungandreas, L.Jakob, C., M. S. Singh, L. Jungandreas, 2019: Radiative Convective Equilibrium and Organized Convection: An Observational Perspective. Journal of Geophysical Research: Atmospheres, 124(10), 5418-5430. doi: 10.1029/2018JD030092. Radiative convective equilibrium (RCE) describes a balance between the cooling of the atmosphere by radiation and the heating through latent heat release and surface heat fluxes. While RCE is known to provide an energetic constraint on the atmosphere at the global scale, little is known about the proximity of the atmosphere to RCE at smaller spatial and temporal scales, despite the common use of RCE in idealized modeling studies. Here we provide the first observational evaluation of the scales at which the atmosphere is near RCE. We further use observations of cloud characteristics to investigate the role played by organized convection in the RCE state. While the tropical atmosphere as a whole is near RCE on daily time scales and longer, this is not the case for any given location. Rather, areas in excess of 5,000 × 5,000 km2 must be considered to ensure the atmosphere remains near RCE at least 80% of the time, even for monthly averaged conditions. We confirm that RCE is established through the interplay of regions of active deep convection with high precipitation and weak radiative cooling and regions of subsiding motions leading to shallow cloud states that allow strong radiative cooling with no precipitation. The asymmetry in the maximum amount of radiative cooling and latent heating leads to the well-known ratio of small areas of precipitation and large regions of subsidence observed in the tropics. Finally, we show that organized deep convection does not occur when regions smaller than 1,000 × 1,000 km2 are near RCE. radiation; convection; tropics; climate
Jia, Hailing; Ma, Xiaoyan; Quaas, Johannes; Yin, Yan; Qiu, TomJia, H., X. Ma, J. Quaas, Y. Yin, T. Qiu, 2019: Is positive correlation between cloud droplet effective radius and aerosol optical depth over land due to retrieval artifacts or real physical processes?. Atmospheric Chemistry and Physics, 19(13), 8879-8896. doi: https://doi.org/10.5194/acp-19-8879-2019. Abstract. The Moderate Resolution Imaging Spectroradiometer (MODIS) C6 L3, Clouds and the Earth's Radiant Energy System (CERES) Edition-4 L3 products, and the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis data are employed to systematically study aerosol–cloud correlations over three anthropogenic aerosol regions and their adjacent oceans, as well as explore the effect of retrieval artifacts and underlying physical mechanisms. This study is confined to warm phase and single-layer clouds without precipitation during the summertime (June, July, and August). Our analysis suggests that cloud effective radius (CER) is positively correlated with aerosol optical depth (AOD) over land (positive slopes), but negatively correlated with aerosol index (AI) over oceans (negative slopes) even with small ranges of liquid water path (quasi-constant). The changes in albedo at the top of the atmosphere (TOA) corresponding to aerosol-induced changes in CER also lend credence to the authenticity of this opposite aerosol–cloud correlation between land and ocean. It is noted that potential artifacts, such as the retrieval biases of both cloud (partially cloudy and 3-D-shaped clouds) and aerosol, can result in a serious overestimation of the slope of CER–AOD/AI. Our results show that collision–coalescence seems not to be the dominant cause for positive slope over land, but the increased CER caused by increased aerosol might further increase CER by initializing collision–coalescence, generating a positive feedback. By stratifying data according to the lower tropospheric stability and relative humidity near cloud top, it is found that the positive correlations more likely occur in the case of drier cloud top and stronger turbulence in clouds, while negative correlations occur in the case of moister cloud top and weaker turbulence in clouds, which implies entrainment mixing might be a possible physical interpretation for such a positive CER–AOD slope.
Jiang, Bo; Liang, Shunlin; Jia, Aolin; Xu, Jianglei; Zhang, Xiaotong; Xiao, Zhiqiang; Zhao, Xiang; Jia, Kun; Yao, YunjunJiang, B., S. Liang, A. Jia, J. Xu, X. Zhang, Z. Xiao, X. Zhao, K. Jia, Y. Yao, 2019: Validation of the Surface Daytime Net Radiation Product From Version 4.0 GLASS Product Suite. IEEE Geoscience and Remote Sensing Letters, 16(4), 509-513. doi: 10.1109/LGRS.2018.2877625. The daytime surface net radiation (Rn) product from version 4.0 Global LAnd Surface Satellite (GLASS) product suite was recently generated from Moderate Resolution Imaging Spectroradiometer data. It is the daytime average product of Rn derived from 2000 to 2015 at a spatial resolution of 0.05°. This letter describes the results of validation of this new Rn product using ground measurements collected from 142 sites distributed worldwide. The overall accuracy of the GLASS daytime Rn product was satisfactory, with an R2 of 0.80, root-mean-square error of 51.35 Wm-2, and mean bias error of 0.11 Wm-2. Its accuracy and quality were highly consistent for different land cover classes and elevation zones. atmospheric techniques; atmospheric radiation; Satellites; Land surface; Atmospheric modeling; mean square error methods; spatial resolution; Clouds; net radiation; remote sensing; Spatial resolution; Ice; 4.0 Global LAnd Surface Satellite product suite; daytime average product; daytime surface net radiation; Glass; GLASS daytime R; Global LAnd Surface Satellite (GLASS); Moderate Resolution Imaging Spectroradiometer data; product; Rn; Rn product; Surface daytime net radiation product; version 4.0 GLASS product
Jing, Xianwen; Suzuki, Kentaroh; Michibata, TakuroJing, X., K. Suzuki, T. Michibata, 2019: The Key Role of Warm Rain Parameterization in Determining the Aerosol Indirect Effect in a Global Climate Model. J. Climate, 32(14), 4409-4430. doi: 10.1175/JCLI-D-18-0789.1. Global climate models (GCMs) have been found to share the common too-frequent bias in the warm rain formation process. In this study, five different autoconversion schemes are incorporated into a single GCM, to systematically evaluate the warm rain formation processes in comparison with satellite observations and investigate their effects on aerosol indirect effect (AIE). It is found that some schemes generate warm rain less efficiently under polluted conditions in the manner closer to satellite observations, while the others generate warm rain too frequently. Large differences in AIE are found among these schemes. It is remarkable that the schemes with more observation-like warm rain formation processes exhibit larger AIEs that far exceed the uncertainty range reported in IPCC AR5, to an extent that can cancel much of the warming trend in the past century, whereas schemes with too-frequent rain formations yield AIEs that are well bounded by the reported range. The power-law dependence of autoconversion rate on cloud droplet number concentration (β) is found to affect substantially the susceptibility of rain formation to aerosols: the more negative β is, the more difficult for rain to be triggered in polluted clouds, leading to larger AIE through substantial contributions from the wet scavenging feedback. The appropriate use of droplet size threshold can mitigate the effect of a less negative β. The role of the warm rain formation process on AIE in this particular model has broad implications for others that share the too-frequent rain-formation bias.
Joos, HannaJoos, H., 2019: Warm Conveyor Belts and Their Role for Cloud Radiative Forcing in the Extratropical Storm Tracks. J. Climate, 32(16), 5325-5343. doi: 10.1175/JCLI-D-18-0802.1. The link between cloud radiative forcing (CRF) and warm conveyor belts (WCBs), which are strongly ascending airstreams in extratropical cyclones, is investigated based on ERA-Interim reanalysis from 1979 to 2011. Clouds associated with WCBs can be liquid, mixed phase, or ice clouds. They interact with the longwave and shortwave radiation in different ways and thus strongly influence Earth’s radiative budget in the extratropical storm tracks in a complex way. In this study, WCBs are identified with a Lagrangian method, where WCBs are represented by trajectories that rise at least 600 hPa in 48 h in the vicinity of an extratropical cyclone, and CRF is traced along all WCB trajectories during the considered 30-yr period. The results show that due to the poleward ascent of WCBs, they exhibit negative net cloud forcing (NetCRF) in the southern part of the associated cloud band, whereas in their northern part, NetCRF gets positive due to the lack of sunlight in the winter months. This nonuniform CRF along WCBs from low to high latitudes increases the meridional NetCRF gradient. Furthermore, in their outflow regions in the North Atlantic, where WCBs are mainly associated with ice clouds, WCBs contribute up to 10 W m−2 to the global climatological NetCRF maximum in winter. The results highlight the importance of WCBs in modulating the radiative budget in the extratropics. Furthermore, the results emphasize the need for a correct representation of WCBs in climate models to correctly simulate the cloud–circulation coupling.
Kant, Sunny; Panda, Jagabandhu; Gautam, RiteshKant, S., J. Panda, R. Gautam, 2019: A seasonal analysis of aerosol-cloud-radiation interaction over Indian region during 2000–2017. Atmospheric Environment, 201, 212-222. doi: 10.1016/j.atmosenv.2018.12.044. The present study uses 18 years (March 2000–May 2017) of satellite–derived relevant parameters to examine the impact of aerosols on cloud properties, radiative fluxes and ACI (aerosol-cloud interaction) over Indian region. The study includes consideration of shortwave cloud radiative forcing (SWCRF), longwave cloud radiative forcing (LWCRF) and net cloud radiative forcing (NetCRF) from CERES (Clouds and Earth's Radiant Energy System). Also, aerosol optical depth (AOD) and cloud properties such as ice/liquid CER (Cloud Effective Radius), CF (Cloud Fraction), COD (Cloud Optical Depth), CTP (Cloud Top Pressure) and ice/liquid CWP (Cloud Water Path; i.e., ICWP and LCWP) are also considered. Moderate to high aerosol loading and the significant increasing trend of AOD is observed over several parts of Indian region depending upon the seasons. CF is found to be moderate to higher during monsoon months with increasing trend over several parts of the country. Optically thicker high-level clouds have low SWCRF value; whereas, middle-level and low-level clouds have low to moderate SWCRF value. In the majority of cases, Twomey effect is observed whereas in some scenarios Anti-Twomey effect is seen. Aerosol; Cloud; Cloud properties; Cloud radiative forcing
Kelleher, Mitchell K.; Grise, Kevin M.Kelleher, M. K., K. M. Grise, 2019: Examining Southern Ocean cloud controlling factors on daily timescales and their connections to midlatitude weather systems. J. Climate, 32(16), 5145–5160. doi: 10.1175/JCLI-D-18-0840.1. Clouds and their associated radiative effects are a large source of uncertainty in global climate models. One region with particularly large model biases in shortwave cloud radiative effects (CRE) is the Southern Ocean. Previous research has shown that many dynamical “cloud controlling factors” influence shortwave CRE on monthly timescales, and that two important cloud controlling factors over the Southern Ocean are mid-tropospheric vertical velocity and estimated inversion strength (EIS). Model errors may thus arise from biases in representing cloud controlling factors (atmospheric dynamics), representing how clouds respond to those cloud controlling factors (cloud parametrizations), or some combination thereof.This study extends previous work by examining cloud controlling factors over the Southern Ocean on daily timescales in both observations and global climate models. This allows the cloud controlling factors to be examined in the context of transient weather systems. Composites of EIS and mid-tropospheric vertical velocity are constructed around extratropical cyclones and anticyclones to examine how the different dynamical cloud controlling factors influence shortwave CRE around midlatitude weather systems and to assess how models compare to observations. On average, models tend to produce a realistic cyclone and anticyclone, when compared to observations, in terms of the dynamical cloud controlling factors. The difference between observations and models instead lies in how the models’ shortwave CRE respond to the dynamics. In particular, the models’ shortwave CRE are too sensitive to perturbations in mid-tropospheric vertical velocity and, thus, they tend to produce clouds that excessively brighten in the frontal region of the cyclone and excessively dim in the center of the anticyclone.
Khazaei, Bahram; Khatami, Sina; Alemohammad, Seyed Hamed; Rashidi, Lida; Wu, Changshan; Madani, Kaveh; Kalantari, Zahra; Destouni, Georgia; Aghakouchak, AmirKhazaei, B., S. Khatami, S. H. Alemohammad, L. Rashidi, C. Wu, K. Madani, Z. Kalantari, G. Destouni, A. Aghakouchak, 2019: Climatic or regionally induced by humans? Tracing hydro-climatic and land-use changes to better understand the Lake Urmia tragedy. Journal of Hydrology, 569, 203-217. doi: 10.1016/j.jhydrol.2018.12.004. Lake Urmia—a shallow endemic hypersaline lake in northwest Iran—has undergone a dramatic decline in its water level (WL), by about 8 m, since 1995. The primary cause of the WL decline in Lake Urmia has been debated in the scientific literature, regarding whether it has been predominantly driven by atmospheric climate change or by human activities in the watershed landscape. Using available climate, hydrological, and vegetation data for the period 1981–2015, this study analyzes and aims to explain the lake desiccation based on other observed hydro-climatic and vegetation changes in the Lake Urmia watershed and classical exploratory statistical methods. The analysis accounts for the relationships between atmospheric climate change (precipitation P, temperature T), and hydrological (soil moisture SM, and WL) and vegetation cover (VC; including agricultural crops and other vegetation) changes in the landscape. Results show that P, T, and SM changes cannot explain the sharp decline in lake WL since 2000. Instead, the agricultural increase of VC in the watershed correlates well with the lake WL change, indicating this human-driven VC and associated irrigation expansion as the dominant human driver of the Lake Urmia desiccation. Specifically, the greater transpiration from the expanded and increasingly irrigated agricultural crops implies increased total evapotranspiration and associated consumptive use of water (inherently related to the irrigation and water diversion and storage developments in the watershed). Thereby the runoff from the watershed into the lake has decreased, and the remaining smaller inflow to the lake has been insufficient for keeping up the previous lake WL, causing the observed WL drop to current conditions. Climate change; Vegetation; Anthropogenic change; Lake Urmia; Land-use change; Water resources management
Kim, Bu-Yo; Lee, Kyu-TaeKim, B., K. Lee, 2019: Using the Himawari-8 AHI Multi-Channel to Improve the Calculation Accuracy of Outgoing Longwave Radiation at the Top of the Atmosphere. Remote Sensing, 11(5), 589. doi: 10.3390/rs11050589. In this study, Himawari-8 Advanced Himawari Imager (AHI) longwave channel data that is sensitive to clouds and absorption gas were used to improve the accuracy of the algorithm used to calculate outgoing longwave radiation (OLR) at the top of the atmosphere. A radiative transfer model with a variety of atmospheric conditions was run using Garand vertical profile data as input data. The results of the simulation showed that changes in AHI channels 8, 12, 15, and 16, which were used to calculate OLR, were sensitive to changes in cloud characteristics (cloud optical thickness and cloud height) and absorption gases (water vapor, O3, CO2, aerosol optical thickness) in the atmosphere. When compared to long-term analysis OLR data from 2017, as recorded by the Cloud and Earth’s Radiant Energy System (CERES), the OLR calculated in this study had an annual mean bias of 2.28 Wm−2 and a root mean square error (RMSE) of 11.03 Wm−2. The new calculation method mitigated the problem of overestimations in OLR in mostly cloudy and overcast regions and underestimated OLR in cloud-free desert regions. It is also an improvement over the result from the existing OLR calculation algorithm, which uses window and water vapor channels. algorithm improvement; Cloud and Earth’s Radiant Energy System (CERES); Himawari-8 Advanced Himawari Imager (AHI); multi-channel; outgoing longwave radiation at the top of the atmosphere (TOA OLR); radiative transfer model
Kim, Jiwon; Kim, Kwangjin; Cho, Jaeil; Kang, Yong Q.; Yoon, Hong-Joo; Lee, Yang-WonKim, J., K. Kim, J. Cho, Y. Q. Kang, H. Yoon, Y. Lee, 2019: Satellite-Based Prediction of Arctic Sea Ice Concentration Using a Deep Neural Network with Multi-Model Ensemble. Remote Sensing, 11(1), 19. doi: 10.3390/rs11010019. Warming of the Arctic leads to a decrease in sea ice, and the decrease of sea ice, in turn, results in warming of the Arctic again. Several microwave sensors have provided continuously updated sea ice data for over 30 years. Many studies have been conducted to investigate the relationships between the satellite-derived sea ice concentration (SIC) of the Arctic and climatic factors associated with the accelerated warming. However, linear equations using the general circulation model (GCM) data, with low spatial resolution, cannot sufficiently cope with the problem of complexity or non-linearity. Time-series techniques are effective for one-step-ahead forecasting, but are not appropriate for future prediction for about ten or twenty years because of increasing uncertainty when forecasting multiple steps ahead. This paper describes a new approach to near-future prediction of Arctic SIC by employing a deep learning method with multi-model ensemble. We used the regional climate model (RCM) data provided in higher resolution, instead of GCM. The RCM ensemble was produced by Bayesian model averaging (BMA) to minimize the uncertainty which can arise from a single RCM. The accuracies of RCM variables were much improved by the BMA2 method, which took into consideration temporal and spatial variations to minimize the uncertainty of individual RCMs. A deep neural network (DNN) method was used to deal with the non-linear relationships between SIC and climate variables, and to provide a near-future prediction for the forthcoming 10 to 20 years. We adjusted the DNN model for optimized SIC prediction by adopting best-fitted layer structure, loss function, optimizer algorithm, and activation function. The accuracy was much improved when the DNN model was combined with BMA2 ensemble, showing the correlation coefficient of 0.888. This study provides a viable option for monitoring Arctic sea ice change of the near future. regional climate model; Bayesian model averaging; deep neural network; sea ice concentration
Kim, So-Young; Bae, Soo Ya; Park, Rae-Seol; Hong, Song-YouKim, S., S. Y. Bae, R. Park, S. Hong, 2019: Effects of Partial Cloudiness in a Cloud Microphysics Scheme on Simulated Precipitation Processes During a Boreal Summer. Journal of Geophysical Research: Atmospheres, 124(6), 3476-3491. doi: 10.1029/2018JD029519. The effect of partial cloudiness is included in a cloud microphysics scheme, and its impact on precipitation processes is examined through global-model simulations for a boreal summer. An excessive precipitation rate in the simulations is reduced by considering the partial cloudiness effect in microphysical processes, especially in the tropical western Pacific region where convective activity is strong. The reduction of the precipitation rate in this region is mainly due to a decrease in convective precipitation, as the partial cloudiness effect in cloud microphysical processes modulates the convective activity by interacting with radiative processes. Cloud radiative forcings are weaker in the simulations including the partial cloudiness effect, as more cloud water and ice are converted to rain and snow mainly due to enhanced accretion rates. This leads to a decrease in cloud radiative forcing for both shortwave and longwave fluxes, which is overestimated overall over the ocean in the simulations. Temperature is lowered overall as increased longwave radiative cooling overcompensates increased shortwave radiative heating. This reduces the convective available potential energy and results in a decrease in convective precipitation. The weakened instability and upward motion over the tropical western Pacific region due to the partial cloudiness effect not only affect the local precipitation processes in this region but also suppress the downward motion over the tropical eastern Pacific regions by modulating the large-scale zonal circulation over the tropical Pacific ocean.
Kniffka, Anke; Knippertz, Peter; Fink, Andreas H.Kniffka, A., P. Knippertz, A. H. Fink, 2019: The role of low-level clouds in the West African monsoon system. Atmospheric Chemistry and Physics, 19(3), 1623-1647. doi: 10.5194/acp-19-1623-2019. Abstract. Realistically simulating the West African monsoon system still poses a substantial challenge to state-of-the-art weather and climate models. One particular issue is the representation of the extensive and persistent low-level clouds over southern West Africa (SWA) during boreal summer. These clouds are important in regulating the amount of solar radiation reaching the surface, but their role in the local energy balance and the overall monsoon system has never been assessed. Based on sensitivity experiments using the ICON model for July 2006, we show for the first time that rainfall over SWA depends logarithmically on the optical thickness of low clouds, as these control the diurnal evolution of the planetary boundary layer, vertical stability and finally convection. In our experiments, the increased precipitation over SWA has a small direct effect on the downstream Sahel, as higher temperatures due to increased surface radiation are accompanied by decreases in low-level moisture due to changes in advection, leading to almost unchanged equivalent potential temperatures in the Sahel. A systematic comparison of simulations with and without convective parameterization reveals agreement in the direction of the precipitation signal but larger sensitivity for explicit convection. For parameterized convection the main rainband is too far south and the diurnal cycle shows signs of unrealistic vertical mixing, leading to a positive feedback on low clouds. The results demonstrate that relatively minor errors, variations or trends in low-level cloudiness over SWA can have substantial impacts on precipitation. Similarly, they suggest that the dimming likely associated with an increase in anthropogenic emissions in the future would lead to a decrease in summer rainfall in the densely populated Guinea coastal area. Future work should investigate longer-term effects of the misrepresentation of low clouds in climate models, e.g. moderated through effects on rainfall, soil moisture and evaporation.
Kubar, Terence L.; Jiang, Jonathan H.Kubar, T. L., J. H. Jiang, 2019: Net Cloud Thinning, Low-Level Cloud Diminishment, and Hadley Circulation Weakening of Precipitating Clouds with Tropical West Pacific SST Using MISR and Other Satellite and Reanalysis Data. Remote Sensing, 11(10), 1250. doi: 10.3390/rs11101250. Daily gridded Multi-Angle Imaging Spectroradiometer (MISR) satellite data are used in conjunction with CERES, TRMM, and ERA-Interim reanalysis data to investigate horizontal and vertical high cloud structure, top-of-atmosphere (TOA) net cloud forcing and albedo, and dynamics relationships against local SST and precipitation as a function of the mean Tropical West Pacific (TWP; 120°E to 155°W; 30°S–30°N) SST. As the TWP warms, the SST mode (~29.5 °C) is constant, but the area of the mode grows, indicating increased kurtosis of SSTs and decreased SST gradients overall. This is associated with weaker low-level convergence and mid-tropospheric ascent (ω500) over the highest SSTs as the TWP warms, but also a broader area of weak ascent away from the deepest convection, albeit stronger when compared to when the mean TWP is cooler. These associated dynamics changes are collocated with less anvil and thick cloud cover over the highest SSTs and similar thin cold cloud fraction when the TWP is warmer, but broadly more anvil and cirrus clouds over lower local SSTs (SST < 27 °C). For all TWP SST quintiles, anvil cloud fraction, defined as clouds with tops > 9 km and TOA albedos between 0.3–0.6, is closely associated with rain rate, making it an excellent proxy for precipitation; but for a given heavier rain rate, cirrus clouds are more abundant with increasing domain-mean TWP SST. Clouds locally over SSTs between 29–30 °C have a much less negative net cloud forcing, up to 25 W m−2 greater, when the TWP is warm versus cool. When the local rain rate increases, while the net cloud fraction with tops < 9 km decreases, mid-level clouds (4 km < Ztop < 9 km) modestly increase. In contrast, combined low-level and mid-level clouds decrease as the domain-wide SST increases (−10% deg−1). More cirrus clouds for heavily precipitating systems exert a stronger positive TOA effect when the TWP is warmer, and anvil clouds over a higher TWP SST are less reflective and have a weaker cooling effect. For all precipitating systems, total high cloud cover increases modestly with higher TWP SST quintiles, and anvil + cirrus clouds are more expansive, suggesting more detrainment when TWP SSTs are higher. Total-domain anvil cloud fraction scales mostly with domain-mean ω500, but cirrus clouds mostly increase with domain-mean SST, invoking an explanation other than circulation. The overall thinning and greater top-heaviness of clouds over the TWP with warming are possible TWP positive feedbacks not previously identified. cloud fraction; cloud radiative forcing; cloud feedbacks; tropical convection; remote sensing; precipitation
Kumar, Amit; Singh, Virendra; Mukherjee, Sunil; Singh, RandhirKumar, A., V. Singh, S. Mukherjee, R. Singh, 2019: Quality assessment of Outgoing Longwave Radiation (OLR) derived from INSAT-3D Imager: Impact of GSICS correction. Mausam, 70(2), 309-320. The INSAT-3D Outgoing longwave radiation (OLR), a fast-delivery level-2 product at pixel resolution, is being generated operationally from every half hourly acquisition of Imager Payload of INSAT-3D. In addition to this, binned daily and monthly OLR products are also generated. The OLR is estimated from the radiance observations in the infrared windows (TIR1: 10.3-11.3 mu m, TIR2: 11.5-12.5 mu m) and water vapor (WV: 6.5-7.1 mu m) channels of INSAT-3D Imager. In the present study, OLR estimated using the INSAT-3D Imager radiance observation is validated with the CERES (Cloud and Earth's Radiant Energy System; on board NPP satellite) from February, 2014 to December, 2017. For the uniform scenes, OLR estimated using INSAT-3D Imager radiance is of good quality with mean CC 0.93, bias -5.03 Wm(-2) & RMSD 10.39 Wm(-)(2) and it could be used in the various applications studies. validation; assimilation; ceres; Validation; diurnal-variation; erbe; insat-3d; olr
Lee, Wei-Liang; Li, Jui-Lin Frank; Xu, Kuan-Man; Suhas, Ettamal; Jiang, Jonathan H.; Wang, Yi-Hui; Stephens, Graeme; Fetzer, Eric; Yu, Jia-YuhLee, W., J. F. Li, K. Xu, E. Suhas, J. H. Jiang, Y. Wang, G. Stephens, E. Fetzer, J. Yu, 2019: Relating Precipitating Ice Radiative Effects to Surface Energy Balance and Temperature Biases Over the Tibetan Plateau in Winter. Journal of Geophysical Research: Atmospheres, 124(23), 12455-12467. doi: 10.1029/2018JD030204. Key Points Surface temperature bias is primarily determined by biases of surface radiative fluxes Underestimated ice water path in models is related to radiation deficiency and cold bias over the Tibetan Plateau in winter Precipitating ice radiative effects are responsible for some reduction of biases in surface radiative fluxes and temperature CMIP5; Tibetan Plateau; snow radiative effect
Lee, Wei-Liang; Liou, Kuo-Nan; Wang, Chia-chi; Gu, Yu; Hsu, Huang-Hsiung; Li, Jui-Lin F.Lee, W., K. Liou, C. Wang, Y. Gu, H. Hsu, J. F. Li, 2019: Impact of 3-D Radiation-Topography Interactions on Surface Temperature and Energy Budget Over the Tibetan Plateau in Winter. Journal of Geophysical Research: Atmospheres, 24(3), 1537-1549. doi: 10.1029/2018JD029592. We incorporate a parameterization to quantify the effect of three-dimensional (3-D) radiation-topography interactions on the solar flux absorbed by the surfaces, including multiple reflections between surfaces and differences in sunward/shaded slopes, in the Community Climate System Model version 4 (CCSM4). A sensitivity experiment is carried out using CCSM4 with the prescribed sea surface temperature for year 2000 to investigate its impact on energy budget and surface temperature over the Tibetan Plateau (TP). The results show that the topographic effect reduces the upward surface shortwave flux and, at the same time, enhance snowmelt rate over the central and southern parts of TP. Comparing to observations and the ensemble of Coupled Model Intercomparison Project Phase 5 (CMIP5), we found that CMIP5 models have a strong cold bias of 3.9 K over TP, partially induced by the strong reflection of shortwave fluxes. We show that the inclusion of topographic effect reduces the substantial biases of upward shortwave fluxes and surface air temperatures over TP by 13% in the CCSM4 model. CMIP5; Tibetan Plateau; 3-D radiative transfer; topographic effect
Lehmann, Peter; Berli, Markus; Koonce, Jeremy E.; Or, DaniLehmann, P., M. Berli, J. E. Koonce, D. Or, 2019: Surface Evaporation in Arid Regions: Insights From Lysimeter Decadal Record and Global Application of a Surface Evaporation Capacitor (SEC) Model. Geophysical Research Letters, 46(16), 9648-9657. doi: 10.1029/2019GL083932. Surface evaporation in arid regions determines the fraction of rainfall that remains to support vegetation and recharge. The surface evaporation capacitor approach was used to estimate rainfall partitioning to surface evaporation and leakage into deeper layers. The surface evaporation capacitor estimates a soil-specific surface evaporation depth and critical storage capacitance that defines rainfall events that exceed local capacitance and result in leakage into deeper layers protected from surface evaporation. A decade-long record of hydrologic observations in deep and barren lysimeters near Las Vegas revealed the dominance of a few large rainfall events in generating leakage and increasing interannual soil water storage. The surface evaporation capacitor was used to estimate mean annual surface evaporation and leakage protected from surface evaporation in all arid regions globally. About 13% of arid region rainfall contributes to soil water storage (in the absence of vegetation), similar to 11% found in the lysimeter study. water balance; evaporation; aridity; redistribution
Lemburg, Alexander; Bader, Jürgen; Claussen, MartinLemburg, A., J. Bader, M. Claussen, 2019: Sahel rainfall – Tropical Easterly Jet relationship on synoptic to intraseasonal time scales. Mon. Wea. Rev., 147, 1733–1752. doi: 10.1175/MWR-D-18-0254.1. The Tropical Easterly Jet (TEJ) is a characteristic upper-level feature of the West African Monsoon (WAM) circulation. Moreover, the TEJ over West Africa is significantly correlated with summer Sahel rainfall on interannual and decadal time scales. In contrast, the relationship between Sahel rainfall and the regional TEJ on synoptic to intraseasonal time scales is unclear. Therefore, this relationship is investigated by means of multiple statistical analyses using temporally highly resolved measurement and reanalysis data. It is shown that average correlations between convective activity and regional TEJ intensity remain below 0.3 for all synoptic to intraseasonal time scales. Especially on the synoptic time scale, the TEJ significantly lags anomalies in convective activity by one or two days which indicates that convection anomalies are more likely to drive changes in the regional TEJ than vice versa. To further shed light on the role of the TEJ for rainfall over West Africa, a previously proposed effect of TEJ-induced upper-level divergence on the development of mesoscale convective systems (MCS) is examined more closely. An analysis of nearly 300 Sahelian MCSs shows that their initiation is generally not associated with significant TEJ anomalies or jet-induced upper-level divergence. Furthermore, no statistically significant evidence is found that preexisting TEJ-related upper-level divergence anomalies affect intensity, size and lifetime of MCSs. A limiting factor of this study is the focus on TEJinduced upper-level divergence. Therefore, a possible effect of the TEJ on Sahel rainfall via other mechanisms cannot be ruled out and should be subject to future studies.
Li, Jiandong; Wang, Wei-Chyung; Mao, Jiangyu; Wang, Ziqian; Zeng, Gang; Chen, GuoxingLi, J., W. Wang, J. Mao, Z. Wang, G. Zeng, G. Chen, 2019: Persistent Spring Shortwave Cloud Radiative Effect and the Associated Circulations over Southeastern China. J. Climate, 32(11), 3069-3087. doi: 10.1175/JCLI-D-18-0385.1. Clouds strongly modulate regional radiation balance and their evolution is profoundly influenced by circulations. This study uses 2001–16 satellite and reanalysis data together with regional model simulations to investigate the spring shortwave cloud radiative effect (SWCRE) and the associated circulations over southeastern China (SEC). Strong SWCRE, up to −110 W m−2, persists throughout springtime in this region and its spring mean is the largest among the same latitudes of the Northern Hemisphere. SWCRE exhibits pronounced subseasonal variation and is closely associated with persistent regional ascending motion and moisture convergence, which favor large amounts of cloud liquid water and resultant strong SWCRE. Around pentad 12 (late February), SWCRE abruptly increases and afterward remains stable between 22° and 32°N. The thermal and dynamic effects of Tibetan Plateau and westerly jet provide appropriate settings for the maintenance of ascending motion, while water vapor, as cloud water supply, stably comes from the southern flank of the Tibetan Plateau and South China Sea. During pentads 25–36 (early May to late June), SWCRE is further enhanced by the increased water vapor transport caused by the march of East Asian monsoon systems, particularly after the onset of the South China Sea monsoon. After pentad 36, these circulations quickly weaken and the SWCRE decreases accordingly. Individual years with spring strong and weak rainfall are chosen to highlight the importance of the strength of the ascending motion. The simulation broadly reproduced the observed results, although biases exist. Finally, the model biases in SWCRE–circulation associations are discussed.
Li, Jui-Lin Frank; Richardson, Mark; Lee, Wei-Liang; Fetzer, Eric; Stephens, Graeme; Jiang, Jonathan; Hong, Yulan; Wang, Yi-Hui; Yu, Jia-Yuh; Liu, YinghuiLi, J. F., M. Richardson, W. Lee, E. Fetzer, G. Stephens, J. Jiang, Y. Hong, Y. Wang, J. Yu, Y. Liu, 2019: Potential faster Arctic sea ice retreat triggered by snowflakes' greenhouse effect. The Cryosphere, 13(3), 969-980. doi: https://doi.org/10.5194/tc-13-969-2019. Abstract. Recent Arctic sea ice retreat has been quicker than in most general circulation model (GCM) simulations. Internal variability may have amplified the observed retreat in recent years, but reliable attribution and projection requires accurate representation of relevant physics. Most current GCMs do not fully represent falling ice radiative effects (FIREs), and here we show that the small set of Coupled Model Intercomparison Project Phase 5 (CMIP5) models that include FIREs tend to show faster observed retreat. We investigate this using controlled simulations with the CESM1-CAM5 model. Under 1pctCO2 simulations, including FIREs results in the first occurrence of an “ice-free” Arctic (monthly mean extent <1×106 km2) at 550 ppm CO2, compared with 680 ppm otherwise. Over 60–90∘ N oceans, snowflakes reduce downward surface shortwave radiation and increase downward surface longwave radiation, improving agreement with the satellite-based CERES EBAF-Surface dataset. We propose that snowflakes' equivalent greenhouse effect reduces the mean sea ice thickness, resulting in a thinner pack whose retreat is more easily triggered by global warming. This is supported by the CESM1-CAM5 surface fluxes and a reduced initial thickness in perennial sea ice regions by approximately 0.3 m when FIREs are included. This explanation does not apply across the CMIP5 ensemble in which inter-model variation in the simulation of other processes likely dominates. Regardless, we show that FIRE can substantially change Arctic sea ice projections and propose that better including falling ice radiative effects in models is a high priority.
Li, R. L.; Storelvmo, T.; Fedorov, A. V.; Choi, Y.-S.Li, R. L., T. Storelvmo, A. V. Fedorov, Y. Choi, 2019: A Positive Iris Feedback: Insights from Climate Simulations with Temperature-Sensitive Cloud–Rain Conversion. J. Climate, 32(16), 5305-5324. doi: 10.1175/JCLI-D-18-0845.1. Estimates for equilibrium climate sensitivity from current climate models continue to exhibit a large spread, from 2.1 to 4.7 K per carbon dioxide doubling. Recent studies have found that the treatment of precipitation efficiency in deep convective clouds—specifically the conversion rate from cloud condensate to rain Cp—may contribute to the large intermodel spread. It is common for convective parameterization in climate models to carry a constant Cp, although its values are model and resolution dependent. In this study, we investigate how introducing a potential iris feedback, the cloud–climate feedback introduced by parameterizing Cp to increase with surface temperature, affects future climate simulations within a slab ocean configuration of the Community Earth System Model. Progressively stronger dependencies of Cp on temperature unexpectedly increase the equilibrium climate sensitivity monotonically from 3.8 to up to 4.6 K. This positive iris feedback puzzle, in which a reduction in cirrus clouds increases surface temperature, is attributed to changes in the opacity of convectively detrained cirrus. Cirrus clouds reduced largely in ice content and marginally in horizontal coverage, and thus the positive shortwave cloud radiative feedback dominates. The sign of the iris feedback is robust across different cloud macrophysics schemes, which control horizontal cloud cover associated with detrained ice. These results suggest a potentially strong but highly uncertain connection among convective precipitation, detrained anvil cirrus, and the high cloud feedback in a climate forced by increased atmospheric carbon dioxide concentrations.
Liu, Yuzhi; Hua, Shan; Jia, Rui; Huang, JianpingLiu, Y., S. Hua, R. Jia, J. Huang, 2019: Effect of Aerosols on the Ice Cloud Properties Over the Tibetan Plateau. Journal of Geophysical Research: Atmospheres, 124(16), 9594-9608. doi: 10.1029/2019JD030463. With the highlight of environmental problems over the Tibetan Plateau (TP), aerosol pollution and the influence of this pollution on cloud properties are becoming a new area of research. Based on the aerosol index and cloud property parameters derived from satellite observations, in this study, the inconsistent effects of aerosols on ice cloud properties between daytime and nighttime over the TP are investigated. The results indicate that ice clouds are mainly distributed over the TP margin area, especially over the north slope, during both daytime and nighttime. The occurrence frequency of ice cloud is higher during the daytime than during the nighttime over the margin areas of the TP. Similarly, aerosols are mainly concentrated over the northern margin of the TP. A potential relationship may exist between the aerosol index and ice cloud properties. When the aerosol index increases from 0.05 to 0.17, the ice cloud droplet radius (ICDR) during the daytime decreases from 32.1 to 27.9 μm, while the ICDR during the nighttime remains almost constant (approximately 25 μm); furthermore, the ice water path (IWP) during the daytime decreases slightly due to the saturation effect, while the nocturnal IWP increases significantly. The changes in ice cloud optical depth (ICOD) during daytime and nighttime show significant and completely opposite trends. The removal of the influence of meteorological factors showed that aerosols have a more dominant influence than meteorological conditions on ice cloud properties (except for the nocturnal ICDR and IWP during the daytime). Tibetan Plateau; aerosol; ice cloud; cloud droplet radius; cloud optical property
Liu, Yuzhi; Tang, Yuhan; Hua, Shan; Luo, Run; Zhu, QingzheLiu, Y., Y. Tang, S. Hua, R. Luo, Q. Zhu, 2019: Features of the Cloud Base Height and Determining the Threshold of Relative Humidity over Southeast China. Remote Sensing, 11(24), 2900. doi: 10.3390/rs11242900. Clouds play a critical role in adjusting the global radiation budget and hydrological cycle; however, obtaining accurate information on the cloud base height (CBH) is still challenging. In this study, based on Lidar and aircraft soundings, we investigated the features of the CBH and determined the thresholds of the environmental relative humidity (RH) corresponding to the observed CBHs over Southeast China from October 2017 to September 2018. During the observational period, the CBHs detected by Lidar/aircraft were commonly higher in cold months and lower in warm months; in the latter, 75.91% of the CBHs were below 2000 m. Overall, the RHs at the cloud base were mainly distributed between 70 and 90% for the clouds lower than 1000 m, in which the most concentrated RH was approximately 80%. In addition, for the clouds with a cloud base higher than 1000 m, the RH thresholds decreased dramatically with increasing CBH, where the RH thresholds at cloud bases higher than 2000 m could be lower than 60%. On average, the RH thresholds for determining the CBHs were the highest (72.39%) and lowest (63.56%) in the summer and winter, respectively, over Southeast China. Therefore, to determine the CBH, a specific threshold of RH is needed. Although the time period covered by the collected CBH data from Lidar/aircraft is short, the above analyses can provide some verification and evidence for using the RH threshold to determine the CBH. cloud base height; ground-based observations; relative humidity profile; threshold
Liu, Yuzhi; Zhu, Qingzhe; Huang, Jianping; Hua, Shan; Jia, RuiLiu, Y., Q. Zhu, J. Huang, S. Hua, R. Jia, 2019: Impact of dust-polluted convective clouds over the Tibetan Plateau on downstream precipitation. Atmospheric Environment, 209, 67-77. doi: 10.1016/j.atmosenv.2019.04.001. Based on satellite observations and reanalysis datasets, this study focuses on the effect of aerosols on clouds over the Tibetan Plateau (TP) and the impact of dust-polluted convective clouds on precipitation over downstream regions. A heavy dust event is detected by Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) over the northern slope of the TP on 16 July and 17 July 2016. The high aerosol optical depth (AOD) values are mainly distributed over the northern slope of the TP. Simultaneously, the CloudSat satellite observes deep convective clouds over the northern slope area of the TP, in which convective clouds and dust mix at the same height. With the AOD increasing from 16 July to its peak on 17 July, the ice particle size decreases to a minimum, and convective clouds develop at higher heights because of the prolonged cloud life. Accordingly, a larger ice water path (IWP) is induced by the development of convective clouds that move eastwardly from 16 to 17 July. In the following days, under favorable meteorological conditions, some of the developed convective clouds continuously move eastward and merge with the convective cloud clusters along the motion path, which induces significant precipitation over the Yangtze River basin on 17 July. Furthermore, driven by the northward wind, some developed convective cloud clusters move northward and induce strong precipitation over North China on 19 July. The indirect effect of dust aerosols over the TP could enhance the plateau's cloud development and potentially contribute to downstream precipitation, which is a meaningful factor for weather forecasting. Precipitation; Aerosols; Tibetan plateau; Convective clouds
Loeb, Norman G.; Wang, Hailan; Rose, Fred G.; Kato, Seiji; Smith, William L.; Sun-Mack, SunnyLoeb, N. G., H. Wang, F. G. Rose, S. Kato, W. L. Smith, S. Sun-Mack, 2019: Decomposing Shortwave Top-of-Atmosphere and Surface Radiative Flux Variations in Terms of Surface and Atmospheric Contributions. J. Climate, 32(16), 5003–501. doi: 10.1175/JCLI-D-18-0826.1. A diagnostic tool for determining surface and atmospheric contributions to interannual variations in top-of-atmosphere (TOA) reflected shortwave (SW) and net downward SW surface radiative fluxes is introduced. The method requires only upward and downward radiative fluxes at the TOA and surface as input and therefore can readily be applied to both satellite-derived and model-generated radiative fluxes. Observations from the Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) Ed4.0 product show that 81% of the monthly variability in global mean reflected SW TOA flux anomalies is associated with atmospheric variations (mainly clouds), 6% is from surface variations, and 13% is from atmosphere-surface covariability. Over the Arctic Ocean, most of the variability in both reflected SW TOA flux and net downward SW surface flux anomalies is explained by variations in sea-ice and cloud fraction alone (r2=0.94). Compared to CERES, variability in two reanalyses—ECMWF Interim Reanalysis (ERA-Interim) and NASA’s Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2)—show large differences in the regional distribution of variance for both the atmospheric and surface contributions to anomalies in net downward SW surface flux. For MERRA-2 the atmospheric contribution is 17% too large compared to CERES while ERA-Interim underestimates the variance by 15%. The difference is mainly due to how cloud variations are represented in the reanalyses. The overall surface contribution in both ERA-Interim and MERRA- 2 is smaller than CERES EBAF by 15% for ERA-Interim and 58% for MERRA-2, highlighting limitations of the reanalyses in representing surface albedo variations and their influence on SW radiative fluxes.
L’Ecuyer, Tristan S.; Hang, Yun; Matus, Alexander V.; Wang, ZhienL’Ecuyer, T. S., Y. Hang, A. V. Matus, Z. Wang, 2019: Reassessing the Effect of Cloud Type on Earth’s Energy Balance in the Age of Active Spaceborne Observations. Part I: Top of Atmosphere and Surface. J. Climate, 32(19), 6197-6217. doi: 10.1175/JCLI-D-18-0753.1. This study revisits the classical problem of quantifying the radiative effects of unique cloud types in the era of spaceborne active observations. The radiative effects of nine cloud types, distinguished based on their vertical structure defined by CloudSat and CALIPSO observations, are assessed at both the top of the atmosphere and the surface. The contributions from single- and multilayered clouds are explicitly diagnosed. The global, annual mean net cloud radiative effect at the top of the atmosphere is found to be −17.1 ± 4.2 W m−2 owing to −44.2 ± 2 W m−2 of shortwave cooling and 27.1 ± 3.7 W m−2 of longwave heating. Leveraging explicit cloud base and vertical structure information, we further estimate the annual mean net cloud radiative effect at the surface to be −24.8 ± 8.7 W m−2 (−51.1 ± 7.8 W m−2 in the shortwave and 26.3 ± 3.8 W m−2 in the longwave). Multilayered clouds are found to exert the strongest influence on the top-of-atmosphere energy balance. However, a strong asymmetry in net cloud radiative cooling between the hemispheres (8.6 W m−2) is dominated by enhanced cooling from stratocumulus over the southern oceans. It is found that there is no corresponding asymmetry at the surface owing to enhanced longwave emission by southern ocean clouds in winter, which offsets a substantial fraction of their impact on solar absorption in summer. Thus the asymmetry in cloud radiative effects is entirely realized as an atmosphere heating imbalance between the hemispheres.
Maher, Nicola; Milinski, Sebastian; Suarez‐Gutierrez, Laura; Botzet, Michael; Dobrynin, Mikhail; Kornblueh, Luis; Kröger, Jürgen; Takano, Yohei; Ghosh, Rohit; Hedemann, Christopher; Li, Chao; Li, Hongmei; Manzini, Elisa; Notz, Dirk; Putrasahan, Dian; Boysen, Lena; Claussen, Martin; Ilyina, Tatiana; Olonscheck, Dirk; Raddatz, Thomas; Stevens, Bjorn; Marotzke, JochemMaher, N., S. Milinski, L. Suarez‐Gutierrez, M. Botzet, M. Dobrynin, L. Kornblueh, J. Kröger, Y. Takano, R. Ghosh, C. Hedemann, C. Li, H. Li, E. Manzini, D. Notz, D. Putrasahan, L. Boysen, M. Claussen, T. Ilyina, D. Olonscheck, T. Raddatz, B. Stevens, J. Marotzke, 2019: The Max Planck Institute Grand Ensemble: Enabling the Exploration of Climate System Variability. Journal of Advances in Modeling Earth Systems, 11(7), 2050-2069. doi: 10.1029/2019MS001639. The Max Planck Institute Grand Ensemble (MPI-GE) is the largest ensemble of a single comprehensive climate model currently available, with 100 members for the historical simulations (1850–2005) and four forcing scenarios. It is currently the only large ensemble available that includes scenario representative concentration pathway (RCP) 2.6 and a 1% CO2 scenario. These advantages make MPI-GE a powerful tool. We present an overview of MPI-GE, its components, and detail the experiments completed. We demonstrate how to separate the forced response from internal variability in a large ensemble. This separation allows the quantification of both the forced signal under climate change and the internal variability to unprecedented precision. We then demonstrate multiple ways to evaluate MPI-GE and put observations in the context of a large ensemble, including a novel approach for comparing model internal variability with estimated observed variability. Finally, we present four novel analyses, which can only be completed using a large ensemble. First, we address whether temperature and precipitation have a pathway dependence using the forcing scenarios. Second, the forced signal of the highly noisy atmospheric circulation is computed, and different drivers are identified to be important for the North Pacific and North Atlantic regions. Third, we use the ensemble dimension to investigate the time dependency of Atlantic Meridional Overturning Circulation variability changes under global warming. Last, sea level pressure is used as an example to demonstrate how MPI-GE can be utilized to estimate the ensemble size needed for a given scientific problem and provide insights for future ensemble projects. internal variability; forced response; large ensemble; MPI-GE
Maldonado, Walter; Valeriano, Taynara Tuany Borges; de Souza Rolim, GlaucoMaldonado, W., T. T. B. Valeriano, G. de Souza Rolim, 2019: EVAPO: A smartphone application to estimate potential evapotranspiration using cloud gridded meteorological data from NASA-POWER system. Computers and Electronics in Agriculture, 156, 187-192. doi: 10.1016/j.compag.2018.10.032. In this study a new android app for smartphones to estimate potential evapotranspuration (PET) in real time, using gridded data from NASA-POWER, to any location in the world, would result in a more efficient irrigation and increase irrigation water conservation. The smartphone app called EVAPO uses meteorological data to calculate PET using the Penman–Monteith (FAO56) method. To evaluate performance of the proposed method, we compared PET estimated by the EVAPO with that estimated from climatic data from conventional surface meteorological stations. The accuracy, tendency and precision of the models were determined using the Willmott et al. (1985) concordance index (d), systematic root mean square error (RMSEs) and determination index (R2), respectively. The results obtained were satisfactory for all studied locations whit mean values of 0.67, 0.95 (mm) and 0.72 for d, RMSEs and R2, respectively. The app can be accessed in the Play Store (free): https://play.google.com/store/apps/details?id=br.com.maldonado.instantet0. Big data; Internet of things; Irrigation; Rational use of water
Maloney, Christopher; Bardeen, Charles; Toon, Owen Brian; Jensen, Eric; Woods, Sarah; Thornberry, Troy; Pfister, Leonhard; Diskin, Glenn; Bui, Thao PaulMaloney, C., C. Bardeen, O. B. Toon, E. Jensen, S. Woods, T. Thornberry, L. Pfister, G. Diskin, T. P. Bui, 2019: An Evaluation of the Representation of Tropical Tropopause Cirrus in the CESM/CARMA Model Using Satellite and Aircraft Observations. Journal of Geophysical Research: Atmospheres, 124(15), 8659-8687. doi: 10.1029/2018JD029720. Observations from the third campaign of the National Aeronautics and Space Administration Airborne Tropical Tropopause Experiment (ATTREX 3) field mission and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations satellite mission are used to evaluate simulations of tropical tropopause layer (TTL) cirrus clouds in the Community Earth System Model's (CESM) Community Atmosphere Model, CAM5. In this study, CAM5 is coupled with a sectional ice cloud model, the Community Aerosol and Radiation Model for Atmospheres (CARMA). We find that both model variants underrepresent cloud frequency along the ATTREX 3 flight path and both poorly represent relative humidity in the TTL. Furthermore, simulated in-cloud ice size distributions contained erroneous amounts of ice crystals throughout the distribution. In response, we present a modified ice cloud fraction scheme that boosts the cloud fraction within the TTL. Due to coarse vertical model resolution in the TTL, we also prescribe a 2-K decrease in cold point tropopause temperatures to better align with observed temperatures. Our modifications improve both CAM5 and CAM5/CARMA's in-cloud ice size and mass distributions. However, only CAM5/CARMA has a significant improvement in cloud frequency and relative humidity. An investigation of cloud extinction in the ATTREX 3 region found that each model variant struggles to reproduce observed extinctions. As a first-order approximation, we introduce randomly generated temperature perturbations to simulate the effect of gravity waves into the CAM5/CARMA simulation. These gravity waves significantly increase the incidence of low extinction ( cirrus; CARMA; ice clouds; CESM; tropical tropopause layer; ATTREX
Mauritsen, Thorsten; Bader, Jürgen; Becker, Tobias; Behrens, Jörg; Bittner, Matthias; Brokopf, Renate; Brovkin, Victor; Claussen, Martin; Crueger, Traute; Esch, Monika; Fast, Irina; Fiedler, Stephanie; Fläschner, Dagmar; Gayler, Veronika; Giorgetta, Marco; Goll, Daniel S.; Haak, Helmuth; Hagemann, Stefan; Hedemann, Christopher; Hohenegger, Cathy; Ilyina, Tatiana; Jahns, Thomas; Jimenéz‐de‐la‐Cuesta, Diego; Jungclaus, Johann; Kleinen, Thomas; Kloster, Silvia; Kracher, Daniela; Kinne, Stefan; Kleberg, Deike; Lasslop, Gitta; Kornblueh, Luis; Marotzke, Jochem; Matei, Daniela; Meraner, Katharina; Mikolajewicz, Uwe; Modali, Kameswarrao; Möbis, Benjamin; Müller, Wolfgang A.; Nabel, Julia E. M. S.; Nam, Christine C. W.; Notz, Dirk; Nyawira, Sarah-Sylvia; Paulsen, Hanna; Peters, Karsten; Pincus, Robert; Pohlmann, Holger; Pongratz, Julia; Popp, Max; Raddatz, Thomas Jürgen; Rast, Sebastian; Redler, Rene; Reick, Christian H.; Rohrschneider, Tim; Schemann, Vera; Schmidt, Hauke; Schnur, Reiner; Schulzweida, Uwe; Six, Katharina D.; Stein, Lukas; Stemmler, Irene; Stevens, Bjorn; Storch, Jin-Song von; Tian, Fangxing; Voigt, Aiko; Vrese, Philipp; Wieners, Karl-Hermann; Wilkenskjeld, Stiig; Winkler, Alexander; Roeckner, ErichMauritsen, T., J. Bader, T. Becker, J. Behrens, M. Bittner, R. Brokopf, V. Brovkin, M. Claussen, T. Crueger, M. Esch, I. Fast, S. Fiedler, D. Fläschner, V. Gayler, M. Giorgetta, D. S. Goll, H. Haak, S. Hagemann, C. Hedemann, C. Hohenegger, T. Ilyina, T. Jahns, D. Jimenéz‐de‐la‐Cuesta, J. Jungclaus, T. Kleinen, S. Kloster, D. Kracher, S. Kinne, D. Kleberg, G. Lasslop, L. Kornblueh, J. Marotzke, D. Matei, K. Meraner, U. Mikolajewicz, K. Modali, B. Möbis, W. A. Müller, J. E. M. S. Nabel, C. C. W. Nam, D. Notz, S. Nyawira, H. Paulsen, K. Peters, R. Pincus, H. Pohlmann, J. Pongratz, M. Popp, T. J. Raddatz, S. Rast, R. Redler, C. H. Reick, T. Rohrschneider, V. Schemann, H. Schmidt, R. Schnur, U. Schulzweida, K. D. Six, L. Stein, I. Stemmler, B. Stevens, J. v. Storch, F. Tian, A. Voigt, P. Vrese, K. Wieners, S. Wilkenskjeld, A. Winkler, E. Roeckner, 2019: Developments in the MPI-M Earth System Model version 1.2 (MPI-ESM1.2) and Its Response to Increasing CO2. Journal of Advances in Modeling Earth Systems, 11(4), 998-1038. doi: 10.1029/2018MS001400. A new release of the Max Planck Institute for Meteorology Earth System Model version 1.2 (MPI-ESM1.2) is presented. The development focused on correcting errors in and improving the physical processes representation, as well as improving the computational performance, versatility, and overall user friendliness. In addition to new radiation and aerosol parameterizations of the atmosphere, several relatively large, but partly compensating, coding errors in the model's cloud, convection, and turbulence parameterizations were corrected. The representation of land processes was refined by introducing a multilayer soil hydrology scheme, extending the land biogeochemistry to include the nitrogen cycle, replacing the soil and litter decomposition model and improving the representation of wildfires. The ocean biogeochemistry now represents cyanobacteria prognostically in order to capture the response of nitrogen fixation to changing climate conditions and further includes improved detritus settling and numerous other refinements. As something new, in addition to limiting drift and minimizing certain biases, the instrumental record warming was explicitly taken into account during the tuning process. To this end, a very high climate sensitivity of around 7 K caused by low-level clouds in the tropics as found in an intermediate model version was addressed, as it was not deemed possible to match observed warming otherwise. As a result, the model has a climate sensitivity to a doubling of CO2 over preindustrial conditions of 2.77 K, maintaining the previously identified highly nonlinear global mean response to increasing CO2 forcing, which nonetheless can be represented by a simple two-layer model. model development; climate sensitivity; coupled climate model
Mayer, Michael; Tietsche, Steffen; Haimberger, Leopold; Tsubouchi, Takamasa; Mayer, Johannes; Zuo, HaoMayer, M., S. Tietsche, L. Haimberger, T. Tsubouchi, J. Mayer, H. Zuo, 2019: An Improved Estimate of the Coupled Arctic Energy Budget. J. Climate, 32(22), 7915-7934. doi: 10.1175/JCLI-D-19-0233.1. This study combines state-of-the-art reanalyses such as the fifth-generation European Re-Analysis (ERA5) and the Ocean Reanalysis System 5 (ORAS5) with novel observational products to present an updated estimate of the coupled atmosphere–ocean–sea ice Arctic energy budget, including flux and storage terms covering 2001–17. Observational products provide independent estimates of crucial budget terms, including oceanic heat transport from unique mooring-derived data, radiative fluxes from satellites, and sea ice volume from merged satellite data. Results show that the time averages of independent estimates of radiative, atmospheric, and oceanic energy fluxes into the Arctic Ocean domain are remarkably consistent in the sense that their sum closely matches the observed rate of regional long-term oceanic heat accumulation of ~1 W m−2. Atmospheric and oceanic heat transports are found to be stronger compared to earlier assessments (~100 and ~16 W m−2, respectively). Data inconsistencies are larger when considering the mean annual cycle of the coupled energy budget, with RMS values of the monthly budget residual between 7 and 15 W m−2, depending on the employed datasets. This nevertheless represents an average reduction of ~72% of the residual compared to earlier work and demonstrates the progress made in data quality and diagnostic techniques. Finally, the budget residual is eliminated using a variational approach to provide a best estimate of the mean annual cycle. The largest remaining sources of uncertainty are ocean heat content and latent heat associated with sea ice melt and freeze, which both suffer from the lack of observational constraints. More ocean in situ observations and reliable sea ice thickness observations and their routinely assimilation into reanalyses are needed to further reduce uncertainty.
McTaggart‐Cowan, R.; Vaillancourt, P. A.; Zadra, A.; Chamberland, S.; Charron, M.; Corvec, S.; Milbrandt, J. A.; Paquin‐Ricard, D.; Patoine, A.; Roch, M.; Separovic, L.; Yang, J.McTaggart‐Cowan, R., P. A. Vaillancourt, A. Zadra, S. Chamberland, M. Charron, S. Corvec, J. A. Milbrandt, D. Paquin‐Ricard, A. Patoine, M. Roch, L. Separovic, J. Yang, 2019: Modernization of Atmospheric Physics Parameterization in Canadian NWP. Journal of Advances in Modeling Earth Systems, 11(11), 3593-3635. doi: 10.1029/2019MS001781. Atmospheric physics is represented in numerical models by parameterizations that use resolved-scale information to estimate the effects of physical processes on the atmospheric state. Over time, our understanding of these processes improves, new techniques are introduced to represent physics in a numerical model, and increased resolution changes the relative importance of different parameterizations within the system. As a result, the physical parameterization packages of numerical weather prediction (NWP) models undergo regular updates as older schemes are replaced with newer ones that offer an improved, and often more complex, depiction of relevant physical processes. Such changes are typically combined with a rebalancing of the physics suite because of strong interactions between parameterization schemes and the presence of compensating errors in the system. In this study, a major update to the package of physical parameterizations used in Canadian operational NWP is introduced. The primary goals of this effort were to improve the global energy budget and to facilitate an increase in the vertical resolution of operational configurations. Both of these objectives were achieved, along with a significant improvement in guidance quality for global and regional prediction systems. atmospheric physics; forecast evaluation; numerical weather prediction; physical parameterization; physical processes
Meyssignac, Benoit; Boyer, Tim; Zhao, Zhongxiang; Hakuba, Maria Z.; Landerer, Felix W.; Stammer, Detlef; Köhl, Armin; Kato, Seiji; L’Ecuyer, Tristan; Ablain, Michael; Abraham, John Patrick; Blazquez, Alejandro; Cazenave, Anny; Church, John A.; Cowley, Rebecca; Cheng, Lijing; Domingues, Catia M.; Giglio, Donata; Gouretski, Viktor; Ishii, Masayoshi; Johnson, Gregory C.; Killick, Rachel E.; Legler, David; Llovel, William; Lyman, John; Palmer, Matthew Dudley; Piotrowicz, Steve; Purkey, Sarah G.; Roemmich, Dean; Roca, Rémy; Savita, Abhishek; Schuckmann, Karina von; Speich, Sabrina; Stephens, Graeme; Wang, Gongjie; Wijffels, Susan Elisabeth; Zilberman, NathalieMeyssignac, B., T. Boyer, Z. Zhao, M. Z. Hakuba, F. W. Landerer, D. Stammer, A. Köhl, S. Kato, T. L’Ecuyer, M. Ablain, J. P. Abraham, A. Blazquez, A. Cazenave, J. A. Church, R. Cowley, L. Cheng, C. M. Domingues, D. Giglio, V. Gouretski, M. Ishii, G. C. Johnson, R. E. Killick, D. Legler, W. Llovel, J. Lyman, M. D. Palmer, S. Piotrowicz, S. G. Purkey, D. Roemmich, R. Roca, A. Savita, K. v. Schuckmann, S. Speich, G. Stephens, G. Wang, S. E. Wijffels, N. Zilberman, 2019: Measuring Global Ocean Heat Content to Estimate the Earth Energy Imbalance. Frontiers in Marine Science, 6, 432. doi: 10.3389/fmars.2019.00432. The energy radiated by the Earth towards space does not compensate the incoming radiation from the Sun leading to a small positive energy imbalance at the top of the atmosphere (0.4-1.Wm-2). This imbalance is coined Earth’s Energy Imbalance (EEI). It is mostly caused by anthropogenic greenhouse gases emissions and is driving the current warming of the planet. Precise monitoring of EEI is critical to assess the current status of climate change and the future evolution of climate. But the monitoring of EEI is challenging as EEI is two order of magnitude smaller than the radiation fluxes in and out of the Earth. Over 93% of the excess energy that is gained by the Earth in response to the positive EEI accumulates into the ocean in the form of heat. This accumulation of heat can be tracked with the ocean observing system such that today, the monitoring of Ocean Heat Content (OHC) and its long-term change provide the most efficient approach to estimate EEI. In this community paper we review the current four state-of-the-art methods to estimate global OHC changes and evaluate their relevance to derive EEI estimate on different time scales. These four methods make use of : 1) direct observations of in situ temperature; 2) satellite-based measurements of the ocean surface net heat fluxes; 3) satellite-based estimates of the thermal expansion of the ocean and 4) ocean reanalyses that assimilate observations from both satellite and in situ instruments. For each method we review the potential and the uncertainty of the method to estimate global OHC changes. We also analyze gaps in the current capability of each method and identify ways of progress for the future to fulfill the requirements of EEI monitoring. Achieving the observation of EEI with sufficient accuracy will depend on merging the remote sensing techniques with in situ measurements of key variables as an integral part of the Ocean Observing System. CERES; altimetry; Earth Energy Imbalance; ARGO; GRACE (Gravity recovery and climate experiment); internal tide tomography; ocean heat content (OHC); Ocean mass; Ocean surface fluxes; Sea level
Michibata, Takuro; Suzuki, Kentaroh; Sekiguchi, Miho; Takemura, ToshihikoMichibata, T., K. Suzuki, M. Sekiguchi, T. Takemura, 2019: Prognostic Precipitation in the MIROC6-SPRINTARS GCM: Description and Evaluation Against Satellite Observations. Journal of Advances in Modeling Earth Systems, 11(3), 839-860. doi: 10.1029/2018MS001596. A comprehensive two-moment microphysics scheme is incorporated into the MIROC6-SPRINTARS general circulation model (GCM). The new scheme includes prognostic precipitation for both rain and snow and considers their radiative effects. To evaluate the impacts of applying different treatments of precipitation and the associated radiative effect, we perform climate simulations employing both the traditional diagnostic and new prognostic precipitation schemes, the latter also being tested with and without incorporating the radiative effect of snow. The prognostic precipitation, which maintains precipitation in the atmosphere across multiple time steps, models the ratio of accretion to autoconversion as being approximately an order of magnitude higher than that for the diagnostic scheme. Such changes in microphysical process rates tend to reduce the cloud water susceptibility as the autoconversion process is the only pathway through which aerosols can influence rain formation. The resultant anthropogenic aerosol effect is reduced by approximately 21% in the prognostic precipitation scheme. Modifications to the microphysical process rates also change the vertical distribution of hydrometeors in the manner that increases the fractional occurrence of single-layered warm clouds by 38%. The new scheme mitigates the excess of supercooled liquid water produced by the previous scheme and increases the total mass of ice hydrometeors. Both characteristics are consistent with CloudSat/CALIPSO retrievals. The radiative effect of snow is significant at both longwave and shortwave (6.4 and 5.1 W/m2 in absolute values, respectively) and can alter the precipitation fields via energetic controls on precipitation. These results suggest that the prognostic precipitation scheme, with its radiative effects incorporated, makes an indispensable contribution to improving the reliability of climate modeling. climate; GCM; microphysics; aerosol-cloud-precipitation interactions; prognostic precipitation
Middlemas, Eleanor A.; Clement, Amy C.; Medeiros, Brian; Kirtman, BenMiddlemas, E. A., A. C. Clement, B. Medeiros, B. Kirtman, 2019: Cloud radiative feedbacks and El Niño Southern Oscillation. J. Climate, 32(15), 4661-4680. doi: 10.1175/JCLI-D-18-0842.1. Cloud radiative feedbacks are disabled via “cloud-locking” in the Community Earth System Model, version 1.2, (CESM1.2) to result in a shift in El Niño Southern Oscillation (ENSO) periodicity from 2-7 years to decadal timescales. We hypothesize that cloud radiative feedbacks may impact the periodicity in three ways: by (1) modulating heat flux locally into the equatorial Pacific subsurface through negative shortwave cloud feedback on sea surface temperature anomalies (SSTA), (2) damping the persistence of subtropical Southeast Pacific SSTA such that the South Pacific Meridional Mode impacts the duration of ENSO events, or (3) controlling the meridional width of off-equatorial westerly winds, which impact the periodicity of ENSO by initiating longer Rossby waves. The result of cloud-locking in CESM1.2 contrasts that of another study which found that cloud-locking in a different global climate model led to decreased ENSO magnitude across all timescales due to a lack of positive longwave feedback on the anomalous Walker circulation. CESM1.2 contains this positive longwave feedback on the anomalous Walker circulation, but either its influence on the surface is decoupled from ocean dynamics or the feedback is only active on interannual timescales. The role of cloud radiative feedbacks in ENSO in other global climate models are additionally considered. In particular, it is shown that one cannot predict the role of cloud radiative feedbacks in ENSO through a multimodel diagnostic analysis. Instead, they must be directly altered.
Mohino, Elsa; Rodríguez-Fonseca, Belén; Mechoso, C. Roberto; Losada, Teresa; Polo, IreneMohino, E., B. Rodríguez-Fonseca, C. R. Mechoso, T. Losada, I. Polo, 2019: Relationships Among Inter-model Spread and Biases in Tropical Atlantic Sea Surface Temperatures. J. Climate, 32(12), 3615–3635. doi: 10.1175/JCLI-D-18-0846.1. State-of-the-art general circulation models show important systematic errors in their simulation of sea surface temperatures (SST), especially in the Tropical Atlantic. In this work the spread in the simulation of climatological SST in the Tropical Atlantic by 24 CMIP5 models is examined, and its relationship with the mean systematic biases in the region is explored. The modes of inter-model variability are estimated by applying Principal Component (PC) analysis to the SSTs in the region 70°W-20°E, 20°S-20°N. The inter-model variability is approximately explained by the first three modes. The first mode is related to warmer SSTs in the basin, shows worldwide connections with same-signed loads over most of the tropics and is connected with lower low cloud cover over the eastern parts of the subtropical oceans. The second mode is restricted to the Atlantic, where it shows negative and positive loads to the north and south of the equator, respectively, and is connected to a too weak Atlantic Meridional Overturning Circulation (AMOC). The third mode is related to the double Intertropical Convergence Zone bias in the Pacific and to an interhemispheric asymmetry in the net radiation at the top of the atmosphere. The structure of second mode is closer to the mean bias than that of the others in the Tropical Atlantic, suggesting that model difficulties with the AMOC contribute to the regional biases.
Mohrmann, Johannes; Bretherton, Christopher S.; McCoy, Isabel L.; McGibbon, Jeremy; Wood, Robert; Ghate, Virendra; Albrecht, Bruce; Sarkar, Mampi; Zuidema, Paquita; Palikonda, RabindraMohrmann, J., C. S. Bretherton, I. L. McCoy, J. McGibbon, R. Wood, V. Ghate, B. Albrecht, M. Sarkar, P. Zuidema, R. Palikonda, 2019: Lagrangian Evolution of the Northeast Pacific Marine Boundary Layer Structure and Cloud during CSET. Mon. Wea. Rev., 147(12), 4681-4700. doi: 10.1175/MWR-D-19-0053.1. Flight data from the Cloud System Evolution over the Trades (CSET) campaign over the Pacific stratocumulus-to-cumulus transition are organized into 18 Lagrangian cases suitable for study and future modeling, made possible by the use of a track-and-resample flight strategy. Analysis of these cases shows that 2-day Lagrangian coherence of long-lived species (CO and O3) is high (r = 0.93 and 0.73, respectively), but that of subcloud aerosol, MBL depth, and cloud properties is limited. Although they span a wide range in meteorological conditions, most sampled air masses show a clear transition when considering 2-day changes in cloudiness (−31% averaged over all cases), MBL depth (+560 m), estimated inversion strength (EIS; −2.2 K), and decoupling, agreeing with previous satellite studies and theory. Changes in precipitation and droplet number were less consistent. The aircraft-based analysis is augmented by geostationary satellite retrievals and reanalysis data along Lagrangian trajectories between aircraft sampling times, documenting the evolution of cloud fraction, cloud droplet number concentration, EIS, and MBL depth. An expanded trajectory set spanning the summer of 2015 is used to show that the CSET-sampled air masses were representative of the season, with respect to EIS and cloud fraction. Two Lagrangian case studies attractive for future modeling are presented with aircraft and satellite data. The first features a clear Sc–Cu transition involving MBL deepening and decoupling with decreasing cloud fraction, and the second undergoes a much slower cloud evolution despite a greater initial depth and decoupling state. Potential causes for the differences in evolution are explored, including free-tropospheric humidity, subsidence, surface fluxes, and microphysics.
Naegele, A. C.; Randall, D. A.Naegele, A. C., D. A. Randall, 2019: Geographical and Seasonal Variability of Cloud-Radiative Feedbacks on Precipitation. Journal of Geophysical Research: Atmospheres, 124(2), 684-699. doi: 10.1029/2018JD029186. We have used observations to study the temporal covariability of precipitation and atmospheric radiative cooling (ARC, defined as positive when the atmosphere is radiatively cooled) on seasonal and longer time scales. Clouds act to decrease the globally averaged ARC, but their radiative effect on the ARC varies with latitude. Clouds decrease the ARC in the tropics, mainly by reducing the outgoing longwave radiation, but they increase the ARC in higher latitudes, primarily by increasing the downwelling longwave radiation at the surface. The temporal correlation of the zonally averaged precipitation rate and the zonally averaged ARC is about -0.7 in the tropics and +0.5 in higher latitudes, and it changes sign almost discontinuously toward the poles at approximately 30° N and 30° S. This suggests that changes in the ARC feed back negatively on precipitating tropical systems, and positively on precipitating systems at higher latitudes. cloud feedback; convective aggregation; cloud radiative effects; hydrologic cycle; precipitation
Naud, Catherine M.; Booth, James F.; Jeyaratnam, Jeyavinoth; Donner, Leo J.; Seman, Charles J.; Zhao, Ming; Guo, Huan; Ming, YiNaud, C. M., J. F. Booth, J. Jeyaratnam, L. J. Donner, C. J. Seman, M. Zhao, H. Guo, Y. Ming, 2019: Extratropical Cyclone Clouds in the GFDL Climate Model: Diagnosing Biases and the Associated Causes. J. Climate, 32(20), 6685-6701. doi: 10.1175/JCLI-D-19-0421.1. The clouds in Southern Hemisphere extratropical cyclones generated by the GFDL climate model are analyzed against MODIS, CloudSat, and CALIPSO cloud and precipitation observations. Two model versions are used: one is a developmental version of “AM4,” a model GFDL that will utilize for CMIP6, and the other is the same model with a different parameterization of moist convection. Both model versions predict a realistic top-of-atmosphere cloud cover in the southern oceans, within 5% of the observations. However, an examination of cloud cover transects in extratropical cyclones reveals a tendency in the models to overestimate high-level clouds (by differing amounts) and underestimate cloud cover at low levels (again by differing amounts), especially in the post–cold frontal (PCF) region, when compared with observations. In focusing only on the models, it is seen that their differences in high and midlevel clouds are consistent with their differences in convective activity and relative humidity (RH), but the same is not true for the PCF region. In this region, RH is higher in the model with less cloud fraction. These seemingly contradictory cloud and RH differences can be explained by differences in the cloud-parameterization tuning parameters that ensure radiative balance. In the PCF region, the model cloud differences are smaller than either of the model biases with respect to observations, suggesting that other physics changes are needed to address the bias. The process-oriented analysis used to assess these model differences will soon be automated and shared.
Or, D.; Lehmann, P.Or, D., P. Lehmann, 2019: Surface Evaporative Capacitance: How Soil Type and Rainfall Characteristics Affect Global-Scale Surface Evaporation. Water Resources Research, 55(1), 519-539. doi: 10.1029/2018WR024050. The separation of evapotranspiration (ET) into its surface evaporation (E) and transpiration (T) components remains a challenge despite its importance for linking water and carbon cycles, for water management, and for attribution of hydrologic isotope fractionation. Regional and global estimates of surface evaporation often rely on estimates of ET (e.g., Penman-Monteith) where E is deduced as a residual or as a fraction of potential evaporation. We propose a novel and direct method for estimating E from soil properties considering regional rainfall characteristics and accounting for internal drainage dynamics. A soil-dependent evaporative characteristic length defines an active surface evaporative capacitor depth below which soil water is sheltered from capillary pull to the evaporating surface. A site-specific evaporative capacitor is periodically recharged by rainfall and discharges at rates determined by interplay between internal drainage and surface evaporation. The surface evaporative capacitor concept was tested using field measurements and subsequently applied to generate a global map of climatic surface evaporation. Latitudinal comparisons with estimates from other global models (e.g., Penman-Monteith method modified by Leuning et al., 2008, https://doi.org/10.1029/2007WR006562 [PML]; Moderate Resolution Imaging Spectroradiometer [MODIS]; and Global Land-surface Evaporation: the Amsterdam Methodology [GLEAM]) show good agreement but also point to potential shortcomings of present estimates of surface evaporation. Interestingly, the ratio of surface evaporation (E) to potential evapotranspiration (ET0) is relatively constant across climates, biomes, and soil types with E/ET0 < 0.15 for 60% of all terrestrial surfaces, in agreement with recent studies. evapotranspiration; evaporation; global data; soil physics
Pagán, Brianna R.; Maes, Wouter H.; Gentine, Pierre; Martens, Brecht; Miralles, Diego G.Pagán, B. R., W. H. Maes, P. Gentine, B. Martens, D. G. Miralles, 2019: Exploring the Potential of Satellite Solar-Induced Fluorescence to Constrain Global Transpiration Estimates. Remote Sensing, 11(4), 413. doi: 10.3390/rs11040413. The opening and closing of plant stomata regulates the global water, carbon and energy cycles. Biophysical feedbacks on climate are highly dependent on transpiration, which is mediated by vegetation phenology and plant responses to stress conditions. Here, we explore the potential of satellite observations of solar-induced chlorophyll fluorescence (SIF)—normalized by photosynthetically-active radiation (PAR)—to diagnose the ratio of transpiration to potential evaporation (‘transpiration efficiency’, τ). This potential is validated at 25 eddy-covariance sites from seven biomes worldwide. The skill of the state-of-the-art land surface models (LSMs) from the eartH2Observe project to estimate τ is also contrasted against eddy-covariance data. Despite its relatively coarse (0.5°) resolution, SIF/PAR estimates, based on data from the Global Ozone Monitoring Experiment 2 (GOME-2) and the Clouds and Earth’s Radiant Energy System (CERES), correlate to the in situ τ significantly (average inter-site correlation of 0.59), with higher correlations during growing seasons (0.64) compared to decaying periods (0.53). In addition, the skill to diagnose the variability of in situ τ demonstrated by all LSMs is on average lower, indicating the potential of SIF data to constrain the formulations of transpiration in global models via, e.g., data assimilation. Overall, SIF/PAR estimates successfully capture the effect of phenological changes and environmental stress on natural ecosystem transpiration, adequately reflecting the timing of this variability without complex parameterizations. eddy-covariance; GOME-2; solar-induced chlorophyll fluorescence; transpiration; transpiration efficiency
Park, Sungsu; Oh, Eunsil; Kim, Siyun; Shin, JihoonPark, S., E. Oh, S. Kim, J. Shin, 2019: Impact of Interactive Vertical Overlap of Cumulus and Stratus on Global Aerosol, Precipitation, and Radiation Processes in the Seoul National University Atmosphere Model Version 0 With a Unified Convection Scheme (SAM0-UNICON). Journal of Advances in Modeling Earth Systems, 11(12), 4016-4043. doi: 10.1029/2019MS001643. The previously proposed parameterization for the integrated vertical overlap of cumulus and stratus is generalized to handle both conventional exponential-random stratus overlap and nonconventional (i.e., other than exponential-random) cumulus overlap in a simultaneous way. With the parameterization of the decorrelation length scale of stratus as a function of vertical wind shear, our parameterization simulates various interactive feedback between vertical cloud overlap and other physical processes. This interactive vertical overlap parameterization of cumulus and stratus was implemented into all relevant physics parameterizations (i.e., convection, stratus microphysics, radiation, aerosol wet deposition, and aerosol activation at the base of stratus) of the Seoul National University Atmosphere Model version 0 with a Unified Convection Scheme (SAM0-UNICON) in a fully consistent way. It is shown that the overall performance of the interactive cloud overlap parameterization to simulate the observed mean climate is similar to that of the original overlap parameterization. Given that an intensive tuning has not yet been performed with the new overlap parameterization, this result is quite encouraging. cloud; parameterization; overlap
Park, Sungsu; Shin, Jihoon; Kim, Siyun; Oh, Eunsil; Kim, YoonjaePark, S., J. Shin, S. Kim, E. Oh, Y. Kim, 2019: Global Climate Simulated by the Seoul National University Atmosphere Model Version 0 with a Unified Convection Scheme (SAM0-UNICON). J. Climate, 32(10), 2917-2949. doi: 10.1175/JCLI-D-18-0796.1. As a contribution to phase 6 of the Coupled Model Intercomparison Project (CMIP6), the global climate simulated by an atmospheric general circulation model (GCM), the Seoul National University Atmosphere Model version 0 with a Unified Convection Scheme (SAM0-UNICON), is compared with observation and climates simulated by the Community Atmosphere Model version 5 (CAM5) and Community Earth System Model version 1 (CESM1), on which SAM0-UNICON is based. Both SAM0-UNICON and CESM1 successfully reproduce observed global warming after 1970. The global mean climate simulated by SAM0-UNICON is roughly similar to that of CAM5/CESM1. However, SAM0-UNICON improves the simulations of the double intertropical convergence zone, shortwave cloud forcing, near-surface air temperature, aerosol optical depth, sea ice fraction, and sea surface temperature (SST), but is slightly poorer for the simulation of tropical relative humidity, Pacific surface wind stress, and ocean rainfall. Two important biases in the simulated mean climate in both models are a set of horseshoe-shaped biases of SST, sea level pressure, precipitation, and cloud radiative forcings in the central equatorial Pacific and a higher sea ice fraction in the Arctic periphery and Southern Hemispheric circumpolar regions. Both SAM0-UNICON and CESM1 simulate the observed El Niño–Southern Oscillation (ENSO) reasonably well. However, compared with CAM5/CESM1, SAM0-UNICON performs better in simulating the Madden–Julian oscillation (MJO), diurnal cycle of precipitation, and tropical cyclones. The aerosol indirect effect (AIE) simulated by SAM0-UNICON is similar to that from CAM5 but the magnitudes of the individual shortwave and longwave AIEs are substantially reduced.
Patel, Piyushkumar N.; Gautam, Ritesh; Michibata, Takuro; Gadhavi, HarishPatel, P. N., R. Gautam, T. Michibata, H. Gadhavi, 2019: Strengthened Indian Summer Monsoon Precipitation Susceptibility Linked to Dust-Induced Ice Cloud Modification. Geophysical Research Letters, 46(14), 8431-8441. doi: 10.1029/2018GL081634. A growing body of research has underscored the radiative impact of mineral dust in influencing Indian summer monsoon rainfall variability. However, the various aerosol-cloud-precipitation interaction mechanisms remain poorly understood. Here we analyze multisatellite observations to examine dust-induced modification in ice clouds and precipitation susceptibility. We show contrasting dust-induced changes in ice cloud regimes wherein despite a 25% reduction in ice particle radius in thin ice clouds, we find 40% increase in ice particle radius and ice water path in thick ice clouds resulting in the cloud deepening and subsequently strengthened precipitation susceptibility, under strong updraft regimes. The observed dust-ice cloud-precipitation interactions are supported by a strong correlation between the interannual monsoon rainfall variability and dust frequency. This microphysical-dynamical coupling appears to provide negative feedback to aerosol-cloud interactions, which acts to buffer enhanced aerosol wet scavenging. Our results underscore the importance of incorporating meteorological regime-dependent dust-ice cloud-precipitation interactions in climate simulations. satellite remote sensing; aerosol-cloud-precipitation interactions; cloud invigoration; dust-ice cloud interactions; dynamical feedback; Indian Monsoon
Peterson, Colten A.; Chen, Xiuhong; Yue, Qing; Huang, XiangleiPeterson, C. A., X. Chen, Q. Yue, X. Huang, 2019: The Spectral Dimension of Arctic Outgoing Longwave Radiation and Greenhouse Efficiency Trends From 2003 to 2016. Journal of Geophysical Research: Atmospheres, 124(15), 8467-8480. doi: 10.1029/2019JD030428. Fourteen years of spectral fluxes derived from collocated Atmospheric Infrared Sounder (AIRS) and Clouds and the Earth's Radiant Energy System (CERES) observations are used in conjunction with AIRS retrievals to examine the trends of zonal mean spectral outgoing longwave radiation (OLR) and greenhouse efficiency (GHE) in the Arctic. AIRS retrieved profiles are fed into a radiative transfer model to generate synthetic clear-sky spectral OLR. Trends are derived from the simulated clear-sky spectral OLR and GHE and then compared with their counterparts derived from collocated observations. Spectral trends in different seasons are distinctively different. March and September exhibit positive trends in spectral OLR over the far-IR dirty window and mid-IR window region for most of the Arctic. In contrast, spectral OLR trends in July are negative over the far-IR dirty window and can be positive or negative in the mid-IR window depending on the latitude. Sensitivity studies reveal that surface temperature contributes much more than atmospheric temperature and humidity to the spectral OLR and GHE trends, while the contributions from the latter two are also discernible over many spectral regions (e.g., trends in the far-IR dirty window in March). The largest increase of spectral GHE is seen north of 80°N in March across the water vapor v2 band and far-IR. When the secular fractional change of spectral OLR is less than that of surface spectral emission, an increase of spectral GHE can be expected. Spectral trend analyses reveal more information than broadband trend analyses alone. outgoing longwave radiation; Arctic climate; greenhouse efficiency; spectral flux
Pistone, Kristina; Eisenman, Ian; Ramanathan, VeerabhadranPistone, K., I. Eisenman, V. Ramanathan, 2019: Radiative Heating of an Ice-Free Arctic Ocean. Geophysical Research Letters, 46, 7474-7480. doi: 10.1029/2019GL082914. During recent decades, there has been dramatic Arctic sea ice retreat. This has reduced the top-of-atmosphere albedo, adding more solar energy to the climate system. There is substantial uncertainty regarding how much ice retreat and associated solar heating will occur in the future. This is relevant to future climate projections, including the timescale for reaching global warming stabilization targets. Here we use satellite observations to estimate the amount of solar energy that would be added in the worst-case scenario of a complete disappearance of Arctic sea ice throughout the sunlit part of the year. Assuming constant cloudiness, we calculate a global radiative heating of 0.71 W/m2 relative to the 1979 baseline state. This is equivalent to the effect of one trillion tons of CO2 emissions. These results suggest that the additional heating due to complete Arctic sea ice loss would hasten global warming by an estimated 25 years.
Popp, Max; Bony, SandrinePopp, M., S. Bony, 2019: Stronger zonal convective clustering associated with a wider tropical rain belt. Nature Communications, 10(1), 1-12. doi: 10.1038/s41467-019-12167-9. How the spatial patterns of deep convection affect the large-scale dynamics of the atmosphere remains an open question. Here, it is shown that if convection along the equator is clustered, the tropical rain belt widens and exhibits a double peak structure.
Posselt, Derek J.; Wu, Longtao; Mueller, Kevin; Huang, Lei; Irion, Fredrick W.; Brown, Shannon; Su, Hui; Santek, David; Velden, Christopher S.Posselt, D. J., L. Wu, K. Mueller, L. Huang, F. W. Irion, S. Brown, H. Su, D. Santek, C. S. Velden, 2019: Quantitative Assessment of State-Dependent Atmospheric Motion Vector Uncertainties. J. Appl. Meteor. Climatol., 58(11), 2479-2495. doi: 10.1175/JAMC-D-19-0166.1. This study examines the error characteristics of atmospheric motion vectors (AMVs) obtained by tracking the movement of water vapor features. A high-resolution numerical simulation of a dynamic weather event is used as a baseline, and AMVs tracked from retrieved water vapor fields are compared with the “true” winds produced by the model. The sensitivity of AMV uncertainty to time interval, AMV tracking window size, water vapor content, horizontal gradient, and wind structure is examined. AMVs are derived from the model water vapor field at a specific height and also from water vapor fields vertically blurred using smoothing functions consistent with high-spectral-resolution infrared (IR) and high-frequency microwave (MW) water vapor sounders. Uncertainties in water vapor AMVs are state dependent and are largest for regions with small water vapor content and small water vapor spatial gradient and in places where the flow runs parallel to contours of constant water vapor content. Smoothing of water vapor consistent with IR and MW retrievals does not increase AMV uncertainty; however, the yield of AMVs from IR sounders is much lower than from MW sounders because of the inability of IR sounders to retrieve water vapor below clouds. The yield and error are similar for AMVs in the lower and upper troposphere, even though the water vapor content in the upper troposphere is much smaller. The results have implications for the design of new observing systems, as well as the specification of errors when AMVs are ingested in data assimilation systems.
Qiu, Yun; Han, Weiqing; Lin, Xinyu; West, B. Jason; Li, Yuanlong; Xing, Wen; Zhang, Xiaolin; Arulananthan, K.; Guo, XiaogangQiu, Y., W. Han, X. Lin, B. J. West, Y. Li, W. Xing, X. Zhang, K. Arulananthan, X. Guo, 2019: Upper-Ocean Response to the Super Tropical Cyclone Phailin (2013) over the Freshwater Region of the Bay of Bengal. J. Phys. Oceanogr., 49(5), 1201-1228. doi: 10.1175/JPO-D-18-0228.1. This study investigates the impact of salinity stratification on the upper-ocean response to a category 5 tropical cyclone, Phailin, that crossed the northern Bay of Bengal (BOB) from 8 to 13 October 2013. A drastic increase of up to 5.0 psu in sea surface salinity (SSS) was observed after Phailin’s passage, whereas a weak drop of below 0.5°C was observed in sea surface temperature (SST). Rightward biases were apparent in surface current and SSS but not evident in SST. Phailin-induced SST variations can be divided into the warming and cooling stages, corresponding to the existence of the thick barrier layer (BL) and temperature inversion before and erosion after Phailin’s passage, respectively. During the warming stage, SST increased due to strong entrainment of warmer water from the BL, which overcame the cooling induced by surface heat fluxes and horizontal advection. During the cooling stage, the entrainment and upwelling dominated the SST decrease. The preexistence of the BL, which reduced entrainment cooling by ~1.09°C day−1, significantly weakened the overall Phailin-induced SST cooling. The Hybrid Coordinate Ocean Model (HYCOM) experiments confirm the crucial roles of entrainment and upwelling in the Phailin-induced dramatic SSS increase and weak SST decrease. Analyses of upper-ocean stratification associated with 16 super TCs that occurred in the BOB during 1980–2015 show that intensifications of 13 TCs were associated with a thick isothermal layer, and 5 out of the 13 were associated with a thick BL. The calculation of TC intensity with and without considering subsurface temperature demonstrates the importance of large upper-ocean heat storage in TC growth.
Raghuraman, Shiv Priyam; Paynter, David; Ramaswamy, V.Raghuraman, S. P., D. Paynter, V. Ramaswamy, 2019: Quantifying the Drivers of the Clear Sky Greenhouse Effect, 2000–2016. Journal of Geophysical Research: Atmospheres, 124(21), 11354-11371. doi: 10.1029/2019JD031017. The clear sky greenhouse effect (G) is defined as the trapping of infrared radiation by the atmosphere in the absence of clouds. The magnitude and variability of G is an important element in the understanding of Earth's energy balance; yet the quantification of the governing factors of G is poor. The global mean G averaged over 2000 to 2016 is 130–133 W m−2 across data sets. We use satellite observations from Clouds and the Earth's Radiant Energy System Energy Balance and Filled (CERES EBAF) to calculate the monthly anomalies in the clear sky greenhouse effect (ΔG). We quantify the contributions to ΔG due to changes in surface temperature, atmospheric temperature, and water vapor by performing partial radiation perturbation experiments using ERA-Interim and Geophysical Fluid Dynamics Laboratory's Atmospheric Model 4.0 climatological data. Water vapor in the middle troposphere and upper troposphere is found to contribute equally to the global mean and tropical mean ΔG. Holding relative humidity (RH) fixed in the radiative transfer calculations captures the temporal variability of global mean ΔG while variations in RH control the regional ΔG signal. The variations in RH are found to help generate the clear sky super greenhouse effect (SGE). Thirty-six percent of Earth's area exhibits SGE, and this disproportionately contributes to 70% of the globally averaged magnitude of ΔG. In the global mean, G's sensitivity to surface temperature is 3.1–4.0 W m−2 K−1, and the clear sky longwave feedback parameter is 1.5–2.0 W m−2 K−1. Observations from CERES EBAF lie at the more sensitive ends of these ranges and the spread arises from its cloud removal treatment, suggesting that it is difficult to constrain clear sky feedbacks. relative humidity; water vapor; greenhouse effect; climate feedback; middle troposphere; super greenhouse effect
Rasch, P. J.; Xie, S.; Ma, P.-L.; Lin, W.; Wang, H.; Tang, Q.; Burrows, S. M.; Caldwell, P.; Zhang, K.; Easter, R. C.; Cameron‐Smith, P.; Singh, B.; Wan, H.; Golaz, J.-C.; Harrop, B. E.; Roesler, E.; Bacmeister, J.; Larson, V. E.; Evans, K. J.; Qian, Y.; Taylor, M.; Leung, L. R.; Zhang, Y.; Brent, L.; Branstetter, M.; Hannay, C.; Mahajan, S.; Mametjanov, A.; Neale, R.; Richter, J. H.; Yoon, J.-H.; Zender, C. S.; Bader, D.; Flanner, M.; Foucar, J. G.; Jacob, R.; Keen, N.; Klein, S. A.; Liu, X.; Salinger, A. G.; Shrivastava, M.; Yang, Y.Rasch, P. J., S. Xie, P. Ma, W. Lin, H. Wang, Q. Tang, S. M. Burrows, P. Caldwell, K. Zhang, R. C. Easter, P. Cameron‐Smith, B. Singh, H. Wan, J. Golaz, B. E. Harrop, E. Roesler, J. Bacmeister, V. E. Larson, K. J. Evans, Y. Qian, M. Taylor, L. R. Leung, Y. Zhang, L. Brent, M. Branstetter, C. Hannay, S. Mahajan, A. Mametjanov, R. Neale, J. H. Richter, J. Yoon, C. S. Zender, D. Bader, M. Flanner, J. G. Foucar, R. Jacob, N. Keen, S. A. Klein, X. Liu, A. G. Salinger, M. Shrivastava, Y. Yang, 2019: An Overview of the Atmospheric Component of the Energy Exascale Earth System Model. Journal of Advances in Modeling Earth Systems, 11(8), 2377-2411. doi: 10.1029/2019MS001629. The Energy Exascale Earth System Model Atmosphere Model version 1, the atmospheric component of the Department of Energy's Energy Exascale Earth System Model is described. The model began as a fork of the well-known Community Atmosphere Model, but it has evolved in new ways, and coding, performance, resolution, physical processes (primarily cloud and aerosols formulations), testing and development procedures now differ significantly. Vertical resolution was increased (from 30 to 72 layers), and the model top extended to 60 km ( 0.1 hPa). A simple ozone photochemistry predicts stratospheric ozone, and the model now supports increased and more realistic variability in the upper troposphere and stratosphere. An optional improved treatment of light-absorbing particle deposition to snowpack and ice is available, and stronger connections with Earth system biogeochemistry can be used for some science problems. Satellite and ground-based cloud and aerosol simulators were implemented to facilitate evaluation of clouds, aerosols, and aerosol-cloud interactions. Higher horizontal and vertical resolution, increased complexity, and more predicted and transported variables have increased the model computational cost and changed the simulations considerably. These changes required development of alternate strategies for tuning and evaluation as it was not feasible to “brute force” tune the high-resolution configurations, so short-term hindcasts, perturbed parameter ensemble simulations, and regionally refined simulations provided guidance on tuning and parameterization sensitivity to higher resolution. A brief overview of the model and model climate is provided. Model fidelity has generally improved compared to its predecessors and the CMIP5 generation of climate models. climate; climate change; climate modeling; atmospheric model; Earth system; general circulation modeling
Rizvi, Shahnilla Haider; Alam, Khan; Iqbal, Muhammad JawedRizvi, S. H., K. Alam, M. J. Iqbal, 2019: Spatio -temporal variations in urban heat island and its interaction with heat wave. Journal of Atmospheric and Solar-Terrestrial Physics, 185, 50-57. doi: 10.1016/j.jastp.2019.02.001. Most of the urban localities are facing the effects of Urban Heat Island (UHI) and extreme heat wave (HW) events. It is expected that these HW events are likely to be intensified by the effect of UHI in the future. As these events project to increase in both severity and frequency therefore, it is crucial to assess the intensity of UHI and examine the relationship between HW and UHI. In this study, observations for different coastal areas are used to quantify the impacts of UHI during the HW events. The spatial and temporal variability patterns of UHI in the metropolitan city of Karachi were also investigated using hourly temperature observations for a period of 10 years in two phases (a) from 1998 to 2002 (b) from 2012 to 2016. During the first phase (1998–2001), the maximum Urban Heat Island Intensity (UHII) for night time in summer was 1.9 °C, while during the second phase (2012–2016), it increased by 0.6 °C. Despite the fact that both phases have shown similar pattern for seasonal UHII, urban-rural temperature difference was found to be significant in summer especially in the night time. Temporal distribution of UHII for winter shows that average intensity of UHI during daytime varies between 0.1 °C and 3.2 °C, considering the overall time duration. The results indicate that UHII increased significantly during the HW period which caused more than 800 deaths in Karachi between 17th June and 24th June 2015. Heat index; Heat stroke; Heat wave; Urban heat island intensity
Rodríguez, José Antonio SobrinoRodríguez, J., . Antonio Sobrino, 2019: Fifth recent advances in quantitative remote sensing. The Fifth International Symposium on Recent Advances in Quantitative Remote Sensing was held in Torrent, Spain from 18 to 22 September 2018. It was sponsored and organized by the Global Change Unit (GCU) from the Image Processing Laboratory (IPL), University of Valencia (UVEG), Spain. This Symposium addressed the scientific advances in quantitative remote sensing in connection with real applications. Its main goal was to assess the state of the art of both theory and applications in the analysis of remote sensing data, as well as to provide a forum for researcher in this subject area to exchange views and report their latest results. In this book 89 of the 262 contributions presented in both plenary and poster sessions are arranged according to the scientific topics selected. The papers are ranked in the same order as the final programme. Science / Mechanics / Thermodynamics
Rowell, David P.Rowell, D. P., 2019: An Observational Constraint on CMIP5 Projections of the East African Long Rains and Southern Indian Ocean Warming. Geophysical Research Letters, 46(11), 6050-6058. doi: 10.1029/2019GL082847. Two outlying projections of the East African Long Rains suggest the seasonal rainfall may double by the late 21st century. Previous work has linked these extremes—found in the IPSL-CM5A model—to an exceptional March to May warming of the southern Indian Ocean. The current study shows a strong feedback between sea surface temperature (SST) increases and reduced low-level cloud cover (with similar behavior in other southern subtropical oceans). An observational constraint is developed by demonstrating a correlation across 28 models between the strength of present-day interannual SST-cloud sensitivity and future SST response. Verification of the present-day sensitivity finds that IPSL-CM5A's feedbacks are very likely overestimated. It is therefore suggested its projections should be discounted for the March to May southern Indian Ocean and East African Long Rains. This narrows the CMIP5 plausible range of Long Rains totals by a third. CMIP5; climate change; Indian Ocean; cloud feedbacks; East Africa; emergent constraint
Ruan, Ruomei; Chen, Xianyao; Zhao, Jinping; Perrie, William; Mottram, Ruth; Zhang, Minghong; Diao, Yina; Du, Ling; Wu, LixinRuan, R., X. Chen, J. Zhao, W. Perrie, R. Mottram, M. Zhang, Y. Diao, L. Du, L. Wu, 2019: Decelerated Greenland Ice Sheet Melt Driven by Positive Summer North Atlantic Oscillation. Journal of Geophysical Research: Atmospheres, 124(14), 7633-7646. doi: 10.1029/2019JD030689. The abrupt deceleration of accelerated Greenland Ice Sheet (GrIS) melting since 2013, after a period of acceleration previously noted, is studied here. It is shown that the deceleration of GrIS melting since 2013 is due to the reduction in short-wave solar radiation in the presence of increasing total cloud cover, which is driven by a more persistent positive summer North Atlantic Oscillation on the decadal time scale. By presenting the coherence with the temperature variability at the weather stations in Greenland, which have century-long records, we deduce that the acceleration of GrIS melting during the early 2000s and the subsequent deceleration since 2013 will reoccur frequently on decadal time scales, with the amplitude nearly half of the multidecadal warming trend of the GrIS melt. It can reduce the mass loss from the GrIS on short to medium time scales but is unlikely to halt mass loss related to climate change in the future. This finding highlights the importance of internal climate variability on the mass budget of the GrIS and therefore on predictions of future global sea level change and may help to assist planning for associated social and economic consequences. Greenland Ice Sheet; mass balance; summer North Atlantic Oscillation; time scale
Saito, Masanori; Yang, Ping; Hu, Yongxiang; Liu, Xu; Loeb, Norman; Smith, William L.; Minnis, PatrickSaito, M., P. Yang, Y. Hu, X. Liu, N. Loeb, W. L. Smith, P. Minnis, 2019: An Efficient Method for Microphysical Property Retrievals in Vertically Inhomogeneous Marine Water Clouds Using MODIS-CloudSat Measurements. Journal of Geophysical Research: Atmospheres, 124(4), 2174-2193. doi: 10.1029/2018JD029659. An efficient method is developed to infer cloud optical thickness (COT) and cloud droplet effective radius (CDER) of marine water clouds from Moderate Resolution Imaging Spectroradiometer (MODIS) and CloudSat measurements, incorporating droplet size vertical inhomogeneity. Empirical orthogonal function (EOF) analysis is employed to reduce the degrees of freedom of the droplet size profile. The first two EOFs can explain 94% of the variability in the droplet size profile. Compared to the existing bispectral CDER retrieval from MODIS assuming plane parallel vertically homogeneous clouds, the new retrieval produces smaller CDER values in clouds in which the adiabatic growth process is dominant and larger CDER values in clouds in which the collision-coalescence process is dominant. To evaluate the performance of the retrieval algorithm, we compare retrieved COT and CDER in this study with their MODIS and CloudSat counterparts on a pixel-by-pixel basis. CDER retrieval based on the vertically homogeneous assumption may be underestimated by 30% due to droplet size vertical inhomogeneity when COT is large and the collision-coalescence process is dominant in the cloud. Retrieved CDER in conjunction with the two scores for EOFs can reconstruct the vertical profile of CDER, which is useful for cloud microphysical process studies. Furthermore, potential expansion of this algorithm to MODIS pixels without CloudSat collocations is discussed. remote sensing; droplet size; EOF; marine water clouds
Saito, Masanori; Yang, Ping; Loeb, Norman G.; Kato, SeijiSaito, M., P. Yang, N. G. Loeb, S. Kato, 2019: A Novel Parameterization of Snow Albedo Based on a Two-Layer Snow Model with a Mixture of Grain Habits. J. Atmos. Sci., 76(5), 1419-1436. doi: 10.1175/JAS-D-18-0308.1. Snow albedo plays a critical role in the surface energy budget in snow-covered regions and is subject to large uncertainty due to variable physical and optical characteristics of snow. We develop an optically and microphysically consistent snow grain habit mixture (SGHM) model, aiming at an improved representation of bulk snow properties in conjunction with considering the particle size distribution, particle shape, and internally mixed black carbon (BC). Spectral snow albedos computed with two snow layers with the SGHM model implemented in an adding–doubling radiative transfer model agree with observations. Top-snow-layer optical properties essentially determine spectral snow albedo when the top-layer snow water equivalent (SWE) is large. When the top-layer SWE is less than 1 mm, the second-snow-layer optical properties have nonnegligible impacts on the albedo of the snow surface. Snow albedo enhancement with increasing solar zenith angle (SZA) largely depends on snow particle effective radius and also internally mixed BC. Based on the SGHM model and various sensitivity studies, single- and two-layer snow albedos are parameterized for six spectral bands used in NASA Langley Research Center’s modified Fu–Liou broadband radiative transfer model. Parameterized albedo is expressed as a function of snow particle effective radii of the two layers, SWE in the top layer, internally mixed BC mass fraction in both layers, and SZA. Both single-layer and two-layer parameterizations provide band-mean snow albedo consistent with rigorous calculations, achieving correlation coefficients close to 0.99 for all bands.
Schmeisser, Lauren; Bond, Nicholas A.; Siedlecki, Samantha A.; Ackerman, Thomas P.Schmeisser, L., N. A. Bond, S. A. Siedlecki, T. P. Ackerman, 2019: The Role of Clouds and Surface Heat Fluxes in the Maintenance of the 2013–2016 Northeast Pacific Marine Heatwave. Journal of Geophysical Research: Atmospheres, 124(20), 10772-10783. doi: 10.1029/2019JD030780. Starting in late 2013, the Northeast (NE) Pacific Ocean experienced anomalously warm sea surface temperatures (SSTs) that persisted for over 2 years. This marine heatwave, known as “the Blob,” produced many devastating ecological impacts with socioeconomic implications for coastal communities. The warm waters observed during the NE Pacific 2013/2016 marine heatwave altered the surface energy balance and disrupted ocean–atmosphere interactions in the region. In principle, ocean–atmosphere interactions following the formation of the marine heatwave could have perpetuated warm SSTs through a positive SST-cloud feedback. The actual situation was more complicated. While reanalysis data show a decrease in boundary layer cloud fraction and an increase in downward shortwave radiative flux at the surface coincident with warm SSTs, this was accompanied by an increase in longwave radiative fluxes at the surface, as well as an increase in sensible and latent heat fluxes out of the ocean mixed layer. The result is a small negative net heat flux anomaly (compared to the anomalies of the individual terms contributing to the net heat flux). This provides new information about the midlatitude ocean–atmosphere system while it was in a perturbed state. More specifically, a mixed layer heat budget reveals that anomalies in both the atmospheric and oceanic processes offset each other such that the anomalously warm SSTs persisted for multiple years. The results show how the atmosphere–ocean system in the NE Pacific is able to maintain itself in an anomalous state for an extended period of time. cloud feedback; marine heatwave; atmosphere–ocean interactions; extreme event; midlatitude; surface heat fluxes
Schuddeboom, Alex; Varma, Vidya; McDonald, Adrian J.; Morgenstern, Olaf; Harvey, Mike; Parsons, Simon; Field, Paul; Furtado, KalliSchuddeboom, A., V. Varma, A. J. McDonald, O. Morgenstern, M. Harvey, S. Parsons, P. Field, K. Furtado, 2019: Cluster-based Evaluation of Model Compensating Errors: A Case Study of Cloud Radiative Effect in the Southern Ocean. Geophysical Research Letters, 46(6), 3446-3453. doi: 10.1029/2018GL081686. Model evaluation is difficult and generally relies on analysis which can mask compensating errors. This paper defines new metrics, using clusters generated from a machine learning algorithm, to estimate mean and compensating errors in different model runs. As a test case, we investigate the Southern Ocean shortwave radiative bias using clusters derived by applying self-organizing maps to satellite data. In particular, the effects of changing cloud phase parameterizations in the MetOffice Unified Model are examined. Differences in cluster properties show that the regional radiative biases are substantially different than the global bias, with two distinct regions identified within the Southern Ocean, each with a different signed bias. Changing cloud phase parameterizations can reduce errors at higher latitudes, but increase errors at lower latitudes of the Southern Ocean. Ranking the parameterizations often shows a contrast in mean and compensating errors, notably in all cases large compensating errors remain. Southern Ocean; Cloud simulation; Compensating errors; Model Evaluation
Schwarz, M.; Folini, D.; Yang, S.; Wild, M.Schwarz, M., D. Folini, S. Yang, M. Wild, 2019: The Annual Cycle of Fractional Atmospheric Shortwave Absorption in Observations and Models: Spatial Structure, Magnitude, and Timing. J. Climate, 32(20), 6729-6748. doi: 10.1175/JCLI-D-19-0212.1. We use the best currently available in situ and satellite-derived surface and top-of-the-atmosphere (TOA) shortwave radiation observations to explore climatological annual cycles of fractional (i.e., normalized by incoming radiation at the TOA) atmospheric shortwave absorption a˜a˜a˜ on a global scale. The analysis reveals that a˜a˜a˜ is a rather regional feature where the reported nonexisting a˜a˜a˜ in Europe is an exception rather than the rule. In several regions, large and distinctively different a˜a˜a˜ are apparent. The magnitudes of a˜a˜a˜ reach values up to 10% in some regions, which is substantial given that the long-term global mean atmospheric shortwave absorption is roughly 23%. Water vapor and aerosols are identified as major drivers for a˜a˜a˜ while clouds seem to play only a minor role for a˜a˜a˜. Regions with large annual cycles in aerosol emissions from biomass burning also show the largest a˜a˜a˜. As biomass burning is generally related to human activities, a˜a˜a˜ is likely also anthropogenically intensified or forced in the respective regions. We also test if climate models are able to simulate the observed pattern of a˜a˜a˜. In regions where a˜a˜a˜ is driven by the annual cycle of natural aerosols or water vapor, the models perform well. In regions with large a˜a˜a˜ induced by biomass-burning aerosols, the models’ performance is very limited.
Sellar, Alistair A.; Jones, Colin G.; Mulcahy, Jane P.; Tang, Yongming; Yool, Andrew; Wiltshire, Andy; O'Connor, Fiona M.; Stringer, Marc; Hill, Richard; Palmieri, Julien; Woodward, Stephanie; Mora, Lee de; Kuhlbrodt, Till; Rumbold, Steven T.; Kelley, Douglas I.; Ellis, Rich; Johnson, Colin E.; Walton, Jeremy; Abraham, Nathan Luke; Andrews, Martin B.; Andrews, Timothy; Archibald, Alex T.; Berthou, Ségolène; Burke, Eleanor; Blockley, Ed; Carslaw, Ken; Dalvi, Mohit; Edwards, John; Folberth, Gerd A.; Gedney, Nicola; Griffiths, Paul T.; Harper, Anna B.; Hendry, Maggie A.; Hewitt, Alan J.; Johnson, Ben; Jones, Andy; Jones, Chris D.; Keeble, James; Liddicoat, Spencer; Morgenstern, Olaf; Parker, Robert J.; Predoi, Valeriu; Robertson, Eddy; Siahaan, Antony; Smith, Robin S.; Swaminathan, Ranjini; Woodhouse, Matthew T.; Zeng, Guang; Zerroukat, MohamedSellar, A. A., C. G. Jones, J. P. Mulcahy, Y. Tang, A. Yool, A. Wiltshire, F. M. O'Connor, M. Stringer, R. Hill, J. Palmieri, S. Woodward, L. d. Mora, T. Kuhlbrodt, S. T. Rumbold, D. I. Kelley, R. Ellis, C. E. Johnson, J. Walton, N. L. Abraham, M. B. Andrews, T. Andrews, A. T. Archibald, S. Berthou, E. Burke, E. Blockley, K. Carslaw, M. Dalvi, J. Edwards, G. A. Folberth, N. Gedney, P. T. Griffiths, A. B. Harper, M. A. Hendry, A. J. Hewitt, B. Johnson, A. Jones, C. D. Jones, J. Keeble, S. Liddicoat, O. Morgenstern, R. J. Parker, V. Predoi, E. Robertson, A. Siahaan, R. S. Smith, R. Swaminathan, M. T. Woodhouse, G. Zeng, M. Zerroukat, 2019: UKESM1: Description and Evaluation of the U.K. Earth System Model. Journal of Advances in Modeling Earth Systems, 11(12), 4513-4558. doi: 10.1029/2019MS001739. We document the development of the first version of the U.K. Earth System Model UKESM1. The model represents a major advance on its predecessor HadGEM2-ES, with enhancements to all component models and new feedback mechanisms. These include a new core physical model with a well-resolved stratosphere; terrestrial biogeochemistry with coupled carbon and nitrogen cycles and enhanced land management; tropospheric-stratospheric chemistry allowing the holistic simulation of radiative forcing from ozone, methane, and nitrous oxide; two-moment, five-species, modal aerosol; and ocean biogeochemistry with two-way coupling to the carbon cycle and atmospheric aerosols. The complexity of coupling between the ocean, land, and atmosphere physical climate and biogeochemical cycles in UKESM1 is unprecedented for an Earth system model. We describe in detail the process by which the coupled model was developed and tuned to achieve acceptable performance in key physical and Earth system quantities and discuss the challenges involved in mitigating biases in a model with complex connections between its components. Overall, the model performs well, with a stable pre-industrial state and good agreement with observations in the latter period of its historical simulations. However, global mean surface temperature exhibits stronger-than-observed cooling from 1950 to 1970, followed by rapid warming from 1980 to 2014. Metrics from idealized simulations show a high climate sensitivity relative to previous generations of models: Equilibrium climate sensitivity is 5.4 K, transient climate response ranges from 2.68 to 2.85 K, and transient climate response to cumulative emissions is 2.49 to 2.66 K TtC−1.
Seviour, W. J. M.; Codron, F.; Doddridge, E. W.; Ferreira, D.; Gnanadesikan, A.; Kelley, M.; Kostov, Y.; Marshall, J.; Polvani, L. M.; Thomas, J. L.; Waugh, D. W.Seviour, W. J. M., F. Codron, E. W. Doddridge, D. Ferreira, A. Gnanadesikan, M. Kelley, Y. Kostov, J. Marshall, L. M. Polvani, J. L. Thomas, D. W. Waugh, 2019: The Southern Ocean sea surface temperature response to ozone depletion: A multi-model comparison. J. Climate, 32(16), 5107–5121. doi: 10.1175/JCLI-D-19-0109.1. The effect of the Antarctic ozone hole extends downwards from the stratosphere, with clear signatures in surface weather patterns including a positive trend in the Southern Annular Mode (SAM). Several recent studies have used coupled climate models to investigate the impact of these changes on Southern Ocean sea surface temperature (SST), notably motivated by the observed cooling from the late 1970s. Here we examine the robustness of these model results through comparison of both previously published and new simulations. We focus on the calculation of ‘climate response functions’ (CRFs), transient responses to an instantaneous step-change in ozone concentrations. The CRF for most models consists of a rapid cooling of SST, followed by a slower warming trend. However, inter-model comparison reveals large uncertainties, such that even the sign of the impact of ozone depletion on historical SST, when reconstructed from the CRF, remains unconstrained. Comparison of these CRFs with SST responses to a hypothetical step-change in the SAM, inferred through lagged linear regression, shows broadly similar results. Causes of uncertainty are explored by examining relationships between model climatologies and their CRFs. The inter-model spread in CRFs can be reproduced by varying a single subgrid-scale mixing parameter within a single model. Antarctic sea-ice CRFs are also calculated: these do not generally exhibit the two-time-scale behavior of SST, suggesting a complex relationship between the two. Finally, by constraining model climatology-response relationships with observational values, we conclude that ozone depletion in unlikely to have been the primary driver of the observed SST cooling trend.
Shukla, Ravi P.; Huang, Bohua; Dirmeyer, Paul A.; Kinter, James L.Shukla, R. P., B. Huang, P. A. Dirmeyer, J. L. Kinter, 2019: The Influence of Summer Deep Soil Temperature on Early Winter Snow Conditions in Eurasia in the NCEP CFSv2 Simulation. Journal of Geophysical Research: Atmospheres, 124(16), 9062-9077. doi: 10.1029/2019JD030279. The National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2) has a large cold bias in the model's deep soil temperature during summer. This study explores the potential triggering effect of that bias on excessive Eurasian snow cover in early winter. Snow cover appears erroneously early in the fall, especially in western Eurasia, in long simulations with CFSv2. The seasonal transition may be too early because the model land surface temperature (LST) reaches its freezing point earlier than observed, so that new snow cannot melt. This process initiates snow-albedo feedback too early. The early cooling of LST is partially influenced by a seasonal resurfacing of the cold bias in the deep soil layer. From winter to early spring, a cold bias prevails in LST and upper soil temperature as snow cover remains. During this season, the temperature in the deep soil is generally warmer than in the upper soil and has relatively little bias. From spring to summer, the cold bias in the upper soil becomes smaller as it warms up in response to solar heating. On the other hand, the deep soil temperature has a noticeably smaller seasonal change than observed, resulting in a severe cold bias during summer. As the solar radiation declines quickly in early fall, the cold deep soil temperature causes additional cooling in the upper soil layer and helps to bring LST to the freezing point early in the western Eurasia, which leads to enhanced bias in the snow properties. deep soil temperature; Eurasia; NCEP CFSv2; seasonal transition; snow-albedo feedback; subsurface soil temperature
Sicard, MichaëlSicard, M., 2019: Validation of AERONET-Estimated Upward Broadband Solar Fluxes at the Top-Of-The-Atmosphere with CERES Measurements. Remote Sensing, 11(18), 2168. doi: 10.3390/rs11182168. The AERONET (Aerosol Robotic Network) global network provides estimations of broadband solar radiative fluxes at the surface and at the TOA (Top-Of-the-Atmosphere). This paper reports on the validation of AERONET flux estimations at the TOA with the CERES (Clouds and the Earth’s Radiant Energy System) instrument. The validation was made at eight AERONET sites worldwide with at least seven years of Level 2.0 and Version 3 data and representatives of mineral dust, biomass burning, background continental, and urban-industrial aerosol regimes. To co-locate in time and space the AERONET and CERES fluxes, several criteria based on time and distance differences and cloud coverage were defined. When the strictest criterion was applied to all sites, the linear relationship between the observed and estimated fluxes (y = 1.04x – 3.67 Wm−2) was very close to the 1:1 ideal line. The correlation coefficient was 0.96 and nearly all points were contained in the ±15% region around the 1:1 line. The average flux difference was –2.52 Wm−2 (–0.84% in relative terms). AERONET overestimations were observed at two sites and were correlated with large aerosol optical depth (AOD) (>0.2) Underestimations were observed at one desert site and were correlated with large surface albedos (>0.2). CERES; AERONET; flux comparison; Top-Of-the-Atmosphere (TOA) upward solar fluxes
Silber, Israel; Fridlind, Ann M.; Verlinde, Johannes; Ackerman, Andrew S.; Chen, Yao-Sheng; Bromwich, David H.; Wang, Sheng-Hung; Cadeddu, Maria; Eloranta, Edwin W.Silber, I., A. M. Fridlind, J. Verlinde, A. S. Ackerman, Y. Chen, D. H. Bromwich, S. Wang, M. Cadeddu, E. W. Eloranta, 2019: Persistent Supercooled Drizzle at Temperatures Below −25 °C Observed at McMurdo Station, Antarctica. Journal of Geophysical Research: Atmospheres, 124(20), 10878-10895. doi: 10.1029/2019JD030882. The rarity of reports in the literature of brief and spatially limited observations of drizzle at temperatures below −20 °C suggest that riming and other temperature-dependent cloud microphysical processes such as heterogeneous ice nucleation and ice crystal depositional growth prevent drizzle persistence in cold environments. In this study, we report on a persistent drizzle event observed by ground-based remote sensing measurements at McMurdo Station, Antarctica. The temperatures in the drizzle-producing cloud were below −25 °C and the drizzle persisted for a period exceeding 7.5 hr. Using ground-based, satellite, and reanalysis data, we conclude that drizzle was likely present in parts of a widespread cloud field, which stretched more than 1,000 km along the Ross Ice Shelf coast. Parameter space sensitivity tests using two-moment bulk microphysics in large eddy simulations constrained by the observations suggest that activated ice freezing nuclei and accumulation-mode aerosol number concentrations aloft during this persistent drizzle period were likely on the order of 0.2 L−1 and 20 cm−3, respectively. In such constrained simulations, the drizzle moisture flux through cloud base exceeds that of ice. The simulations also indicate that drizzle can lead to the formation of multiple peaks in cloud water content profiles. This study suggests that persistent drizzle at these low temperatures may be common at the low aerosol concentrations typical of the Antarctic and Southern Ocean atmospheres. Antarctica; mixed-phase clouds; LES; McMurdo Station; Persistent drizzle; Supercooled drizzle
Sindhu, Kapil Dev; Sahany, SandeepSindhu, K. D., S. Sahany, 2019: Long-term cloud fraction biases in CMIP5 GCMs over India during monsoon season. Theoretical and Applied Climatology, 137(3-4), 2559–2571. doi: 10.1007/s00704-018-02760-1. Using 24 years of cloud fraction (CF) data from the International Satellite Cloud Climatology Project (ISCCP) observations and their corresponding simulators in general circulation models (GCMs) from the Coupled Model Intercomparison Project phase 5 (CMIP5), we have analyzed cloud biases and their role on radiation over the Indian region (65–100° E and 5–40° N) for the monsoon season of June to September. The present study reports the spatial patterns of CFs and their biases in GCMs compared to observations. It is found that the simulated CFs are highly underestimated up to ~ 40%. Mean of total CF from ISCCP observations is 75% with at least 10% difference with simulated CFs. For high-topped clouds, this difference is about 3–4%. Except for high-topped clouds, other cloud types are not simulated realistically by CMIP5 models used in this study. Further, we investigated the individual cloud types classified based on cloud optical depth and cloud top pressure. We found that, in general, individual cloud types are poorly simulated by models, although some (Max Planck Institute Earth System Model, Low Resolution and Hadley Centre Global Environmental Model, version 2, Earth System) models convincingly simulate high-topped thin clouds. To assess the impact of cloud biases on the simulated radiative forcings, we studied shortwave and longwave cloud radiative forcings from CERES (Clouds and the Earth’s Radiant Energy System) observations and CMIP5 GCMs. It is noticed that the spatial patterns of biases in radiative forcings are similar to the patterns of biases in CFs for high-topped clouds, specifically over the oceanic regions. We find that the biases in cloud radiative forcings could potentially be caused due to the inefficacy of CMIP5 models in simulating high-topped anvil clouds (high-topped cirrus/stratocirrus clouds). The present study confirms that the uncertainty in simulating cloud fractions over the Indian region is still a prominent issue to be addressed in general circulation models.
Sivan, C.; Manoj, M. G.Sivan, C., M. G. Manoj, 2019: Aerosol and cloud radiative forcing over various hot spot regions in India. Advances in Space Research, 64(8), 1577-1591. doi: 10.1016/j.asr.2019.07.028. Twelve years of NASA CERES (Clouds and Earth’s Radiant Energy System) data have been used to examine the spatio-temporal variability of aerosol– and cloud– induced shortwave radiative forcing over selected hot spot regions in India. Four regions (northern semiarid – R1; monsoon trough – R2; densely populated urban – R3; and southern peninsula – R4) are selected with different surface characteristics and notable difference in meteorological and geographical features. The analysis shows that three out of the four regions (viz. R1, R2, and R3) experience high aerosol loading and forcing in the monsoon season followed by moderate forcing in pre-monsoon season. While all the seasons except the post-monsoon period show a positive linear relation between cloud optical depth and aerosol optical depth for all the regions, the post-monsoon season shows a negative relation. However, the relation between aerosol forcing and cloud forcing shows adequate non-linearity owing to the numerous factors that control cloud radiative effect. The estimated aerosol induced heating rate shows exponential decrease with height, but with high variability during each season. Irrespective of any region, the maximum heating rate is observed in the pre-monsoon season (2.86 ± 0.78, 2.49 ± 0.78, 1.89 ± 0.57, and 0.88 ± 0.28 K/day for R1, R2, R3, and R4, respectively). Plausible reasons for the variation in the above parameters are discussed. The results suggest that increased anthropogenic activities affect the thermodynamics and hence the dynamics through retention and exchange of heat, and it could affect the precipitation pattern adversely. Aerosol optical depth; CERES data; Heating rate; Cloud; Radiative forcing
Sledd, Anne; L’Ecuyer, TristanSledd, A., T. L’Ecuyer, 2019: How Much Do Clouds Mask the Impacts of Arctic Sea Ice and Snow Cover Variations? Different Perspectives from Observations and Reanalyses. Atmosphere, 10(1), 12. doi: 10.3390/atmos10010012. Decreasing sea ice and snow cover are reducing the surface albedo and changing the Arctic surface energy balance. How these surface albedo changes influence the planetary albedo is a more complex question, though, that depends critically on the modulating effects of the intervening atmosphere. To answer this question, we partition the observed top of atmosphere (TOA) albedo into contributions from the surface and atmosphere, the latter being heavily dependent on clouds. While the surface albedo predictably declines with lower sea ice and snow cover, the TOA albedo decreases approximately half as much. This weaker response can be directly attributed to the fact that the atmosphere contributes more than 70% of the TOA albedo in the annual mean and is less dependent on surface cover. The surface accounts for a maximum of 30% of the TOA albedo in spring and less than 10% by the end of summer. Reanalyses (ASR versions 1 and 2, ERA-Interim, MERRA-2, and NCEP R2) represent the annual means of surface albedo fairly well, but biases are found in magnitudes of the TOA albedo and its contributions, likely due to their representations of clouds. Reanalyses show a wide range of TOA albedo sensitivity to changing sea ice concentration, 0.04–0.18 in September, compared to 0.11 in observations. sea ice; reanalyses; arctic clouds; ice-albedo feedback
Smalley, Mark; Suselj, Kay; Lebsock, Matthew; Teixeira, JoaoSmalley, M., K. Suselj, M. Lebsock, J. Teixeira, 2019: A novel framework for evaluating and improving parameterized subtropical marine boundary layer cloudiness. Mon. Wea. Rev., 147(9), 3241–3260. doi: 10.1175/MWR-D-18-0394.1. A Single Column Model (SCM) is used to simulate a variety of environmental conditions between Los Angeles and Hawaii in order to identify physical elements of parameterizations that are required to reproduce the observed behavior of marine boundary layer (MBL) cloudiness. The SCM is composed of the JPL Eddy-Diffusivity/Mass-Flux mixing formulation and the RRTM-G radiation model. Model forcings are provided by the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA2). Simulated low cloud cover (LCC), rain rate, albedo, and liquid water path are compared to co-located pixel-level observations from A-Train satellites. This framework ensures that the JPL EDMF is able to simulate a continuum of real-world conditions.First, the JPL EDMF is shown to reproduce the observed mean LCC as a function of lower tropospheric stability. Joint probability distributions of lower-tropospheric cloud fraction, height, and LTS show that the JPL EDMF improves upon its MERRA2 input but struggles to match the frequency of observed intermediate-range LCC.We then illustrate the physical roles of plume lateral entrainment and eddy-diffusivity mixing length in producing a realistic behavior of LCC as a function of LTS. In low-LTS conditions, LCC is mostly sensitive to the ability of convection to mix moist air out of the MBL. In high-LTS conditions, LCC is also sensitive to the turbulent mixing of free-tropospheric air into the MBL. In the intermediate LTS regime typical of stratocumulus-cumulus transition there is proportional sensitivity to both mixing mechanisms, emphasizing the utility of a combined Eddy-Diffusivity/Mass-Flux approach for representing mixing processes.
Smith, Samantha A.; Field, Paul R.; Vosper, Simon B.; Derbyshire, Steve H.Smith, S. A., P. R. Field, S. B. Vosper, S. H. Derbyshire, 2019: Verification of a seeder–feeder orographic precipitation enhancement scheme accounting for low-level blocking. Quarterly Journal of the Royal Meteorological Society, 145(724), 2909-2932. doi: 10.1002/qj.3584. A subgrid parametrization scheme representing the enhancement of precipitation due to subgrid orography via the seeder–feeder (SF) effect has been modified to account for flow blocking in small Froude number situations. The scheme was validated in a set of limited-area model simulations with a 1.5 km grid spacing, in which the orography was degraded by varying amounts. For simulations in which the largest orographic scales are still fairly well represented, the SF scheme was able to reduce the precipitation deficit by 30 to 70%. For simulations where the hills were completely subgrid, the SF scheme was still able to reduce the precipitation deficit by 10 to 30%. As well as increasing the integrated precipitation in global simulations with various grid spacings, some of the precipitation production was shifted from the convection scheme, with its very simple microphysical representation, to the microphysics scheme. In a long-duration climate simulation, the SF scheme enhancements of orographic precipitation perturb the large-scale hydrological cycle, as evidenced by the far-field changes in both microphysical and convective precipitation. Changes over major mountain ranges were similar to those described for the case-studies, so long as the upstream precipitation impinging on the mountains was not reduced by these changes in the global hydrological cycle. Increased atmospheric drying reduces column-integrated resolved cloud water mixing ratios over mountains, reducing a positive bias in the amount of optically thick cloud with low- to mid-level tops compared to ISCCP satellite observations. The associated reductions in cloud albedo slightly reduced the RMS error in the top-of-atmosphere outgoing short-wave radiative fluxes over mountains compared to CERES satellite observations. parametrization; climate simulation; low-level flow blocking; orographic precipitation enhancement; precipitation forecasting; seeder–feeder mechanism
Soldatenko, Sergei; Colman, RobertSoldatenko, S., R. Colman, 2019: Climate variability from annual to multi-decadal timescales in a two-layer stochastic energy balance model: analytic solutions and implications for general circulation models. Tellus A: Dynamic Meteorology and Oceanography, 71(1), 1-15. doi: 10.1080/16000870.2018.1554421. A low-order stochastically forced two-layer global energy balance model (EBM) admitting an analytical solution is developed for studying natural inter-annual, decadal and multi-decadal climate variability, and ultimately to better understand forced climate change. The EBM comprises upper and lower oceanic layers with a diffusive coupling, a radiative damping term including feedbacks and stochastic atmospheric forcing. The EBM is used to analyse the influence of radiative forcing, feedbacks and climate system inertia on the global mean surface temperature variance (climate variability) and to understand why Coupled Model Intercomparison Project, Phase 5 (CMIP5) models exhibit such a wide range in the level of variability in globally averaged surface air temperature. We examine the influence of the model parameters on the climate variability on different timescales. To this end, we derive the Fokker–Planck equation for the EBM and then obtain the analytical expression that quantifies the sensitivity coefficients for all model parameters. For all timescales, the most influential factors are as follows: (1) the magnitude of the stochastic forcing, (2) the feedback mechanisms, (3) the upper layer depth, (4) the diffusion parameter and (5) the lower ocean depth. Results from the EBM imply that the range of stochastic forcing in the CMIP5 climate models is around twice as important as the strength of radiative feedback or upper layer depth in causing the model-to-model spread in the magnitude of globally averaged climate model variability. climate variability; sensitivity analysis; climate sensitivity; radiative feedbacks
Sorooshian, Armin; Anderson, Bruce; Bauer, Susanne E.; Braun, Rachel A.; Cairns, Brian; Crosbie, Ewan; Dadashazar, Hossein; Diskin, Glenn; Ferrare, Richard; Flagan, Richard C.; Hair, Johnathan; Hostetler, Chris; Jonsson, Haflidi H.; Kleb, Mary M.; Liu, Hongyu; MacDonald, Alexander B.; McComiskey, Allison; Moore, Richard; Painemal, David; Russell, Lynn M.; Seinfeld, John H.; Shook, Michael; Smith, William L.; Thornhill, Kenneth; Tselioudis, George; Wang, Hailong; Zeng, Xubin; Zhang, Bo; Ziemba, Luke; Zuidema, PaquitaSorooshian, A., B. Anderson, S. E. Bauer, R. A. Braun, B. Cairns, E. Crosbie, H. Dadashazar, G. Diskin, R. Ferrare, R. C. Flagan, J. Hair, C. Hostetler, H. H. Jonsson, M. M. Kleb, H. Liu, A. B. MacDonald, A. McComiskey, R. Moore, D. Painemal, L. M. Russell, J. H. Seinfeld, M. Shook, W. L. Smith, K. Thornhill, G. Tselioudis, H. Wang, X. Zeng, B. Zhang, L. Ziemba, P. Zuidema, 2019: Aerosol–Cloud–Meteorology Interaction Airborne Field Investigations: Using Lessons Learned from the U.S. West Coast in the Design of ACTIVATE off the U.S. East Coast. Bull. Amer. Meteor. Soc., 100(8), 1511-1528. doi: 10.1175/BAMS-D-18-0100.1. We report on a multiyear set of airborne field campaigns (2005–16) off the California coast to examine aerosols, clouds, and meteorology, and how lessons learned tie into the upcoming NASA Earth Venture Suborbital (EVS-3) campaign: Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE; 2019–23). The largest uncertainty in estimating global anthropogenic radiative forcing is associated with the interactions of aerosol particles with clouds, which stems from the variability of cloud systems and the multiple feedbacks that affect and hamper efforts to ascribe changes in cloud properties to aerosol perturbations. While past campaigns have been limited in flight hours and the ability to fly in and around clouds, efforts sponsored by the Office of Naval Research have resulted in 113 single aircraft flights (>500 flight hours) in a fixed region with warm marine boundary layer clouds. All flights used nearly the same payload of instruments on a Twin Otter to fly below, in, and above clouds, producing an unprecedented dataset. We provide here i) an overview of statistics of aerosol, cloud, and meteorological conditions encountered in those campaigns and ii) quantification of model-relevant metrics associated with aerosol–cloud interactions leveraging the high data volume and statistics. Based on lessons learned from those flights, we describe the pragmatic innovation in sampling strategy (dual-aircraft approach with combined in situ and remote sensing) that will be used in ACTIVATE to generate a dataset that can advance scientific understanding and improve physical parameterizations for Earth system and weather forecasting models, and for assessing next-generation remote sensing retrieval algorithms.
Stackhouse, P. W.; Wong, T.; Kratz, D. P.; Sawaengphokhai, Parnchai; Wilber, A. C.; Gupta, S. K.; Loeb, N. GStackhouse, P. W., T. Wong, D. P. Kratz, P. Sawaengphokhai, A. C. Wilber, S. K. Gupta, N. G. Loeb, 2019: Earth Radiation Budget at Top-Of-Atmosphere [in “State of the Climate in 2018”].. Bull. Amer. Meteor. Soc, 100(9), S46-48. doi: 10.1175/2019BAMSStateoftheClimate.1.
Stephens, Benjamin A.; Jackson, Charles S.; Wagman, Benjamin M.Stephens, B. A., C. S. Jackson, B. M. Wagman, 2019: Effect of Tropical Nonconvective Condensation on Uncertainty in Modeled Projections of Rainfall. J. Climate, 32(19), 6571-6588. doi: 10.1175/JCLI-D-18-0833.1. We find that part of the uncertainty in the amplitude and pattern of the modeled precipitation response to CO2 forcing traces to tropical condensation not directly involved with parameterized convection. The fraction of tropical rainfall associated with large-scale condensation can vary from a few percent to well over half depending on model details and parameter settings. In turn, because of the coupling between condensation and tropical circulation, the different ways model assumptions affect the large-scale rainfall fraction also affect the patterns of the response within individual models. In two single-model ensembles based on the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM), versions 3.1 and 5.3, we find strong correlations between the fraction of tropical large-scale rain and both climatological rainfall and circulation and the response to CO2 forcing. While the effects of an increasing tropical large-scale rain fraction are opposite in some ways in the two ensembles—for example, the Hadley circulation weakens with the large-scale rainfall fraction in the CAM3.1 ensemble while strengthening in the CAM5.3 ensemble—we can nonetheless understand these different effects in terms of the relationship between latent heating and circulation, and we propose explanations for each ensemble. We compare these results with data from phase 5 of the Coupled Model Intercomparison Project (CMIP5), for which some of the same patterns hold. Given the importance of this partitioning, there is a need for constraining this source of uncertainty using observations. However, since a “large-scale rainfall fraction” is a modeling construct, it is not clear how observations may be used to test various modeling assumptions determining this fraction.
Stephens, Graeme L.; Christensen, Matthew; Andrews, Timothy; Haywood, James; Malavelle, Florent F.; Suzuki, Kentaroh; Jing, Xianwen; Lebsock, Mathew; Li, Jui-Lin F.; Takahashi, Hanii; Sy, OusmaneStephens, G. L., M. Christensen, T. Andrews, J. Haywood, F. F. Malavelle, K. Suzuki, X. Jing, M. Lebsock, J. F. Li, H. Takahashi, O. Sy, 2019: Cloud physics from space. Quarterly Journal of the Royal Meteorological Society, 145(724), 2854-2875. doi: 10.1002/qj.3589. A review of the progression of cloud physics from a subdiscipline of meteorology into the global science it is today is described. The discussion briefly touches on the important post-war contributions of three key individuals who were instrumental in developing cloud physics into a global science. These contributions came on the heels of the post-war weather modification efforts that influenced much of the early development of cloud physics. The review is centred on the properties of warm clouds primarily to limit the scope of the article and the connection between the early contributions to cloud physics and the current vexing problem of aerosol effects on cloud albedo is underlined. Progress toward estimating cloud properties from space and insights on warm cloud processes are described. Measurements of selected cloud properties, such as cloud liquid water path are now mature enough that multi-decadal time series of these properties exist and this climatology is used to compare to analogous low-cloud properties taken from global climate models. The too-wet (and thus too bright) and the too-dreary biases of models are called out underscoring the challenges we still face in representing warm clouds in Earth system models. We also provide strategies for using observations to constrain the indirect radiative forcing of the climate system. clouds; climate; atmosphere; microphysics; observations; remote sensing
Su, Chun-Yian; Wu, Chien-Ming; Chen, Wei-Ting; Chen, Jen-HerSu, C., C. Wu, W. Chen, J. Chen, 2019: Object-based precipitation system bias in grey zone simulation: the 2016 South China Sea summer monsoon onset. Climate Dynamics, 53(1), 617-630. doi: 10.1007/s00382-018-04607-x. This study aims to evaluate the precipitation bias in the grey zone simulation (~ 15 km) using the Central Weather Bureau Global Forecast System (CWBGFS). We develop a new evaluation method using the object-based precipitation system (OPS) to examine the bias associated with the degree of convection organization. The 2016 South China Sea (SCS) Summer Monsoon onset is selected to evaluate the model’s performance due to its sharp transition of large-scale circulation, which contributes to the complexity of precipitation pattern. The results based on OPS show that the observed precipitation tends to aggregate toward the central part of SCS during the post-onset period, while the precipitation in the model distributes more sparsely over the ocean. The observed precipitation intensity increases with the size of OPS especially for the extremes; however, the model underrepresents the relationship between the precipitation spectrum and the size of OPS. Moreover, the model simulates earlier diurnal peak time of precipitation over land in the organized systems than observation. The results also suggest that the convection scheme is insensitive to column moisture during the pre-onset period which seems to be one of the key factors to the excessive precipitation in the model. Using high horizontal resolution, however, does not improve the simulation of precipitation much in the model. The current study suggests that the precipitation bias related to aggregation of the convective systems should be regarded as an essential objective of model evaluation and improvement.
Sujith, K.; Saha, Subodh Kumar; Rai, Archana; Pokhrel, Samir; Chaudhari, Hemantkumar S.; Hazra, Anupam; Murtugudde, Raghu; Goswami, B.n.Sujith, K., S. K. Saha, A. Rai, S. Pokhrel, H. S. Chaudhari, A. Hazra, R. Murtugudde, B. Goswami, 2019: Effects of a Multilayer Snow Scheme on the Global Teleconnections of the Indian Summer Monsoon. Quarterly Journal of the Royal Meteorological Society, 145(720), 1102-1117. doi: 10.1002/qj.3480. Eurasian snow is one of the slowly varying boundary forcings, that is known to have significant influences on the mean and variability of the Indian summer monsoon rainfall (ISMR). A multilayer complex snow scheme, incorporated into the state-of-the-art coupled Climate Forecast System version 2 (CFSv2) showed significant improvements in the simulation of mean ISMR, snow, northern hemisphere surface and tropospheric temperature. Here we show that a realistic simulation of high latitude snow decreases the north-south temperature gradient, which in turn decreases the meridional transport of energy from the equator to the pole, consequently affecting the tropical sea surface temperature (SST) and air-sea interactions. The global teleconnections of the ISMR with SST and 2m temperature over land are also improved considerably in association with improved simulation of the oceanic natural modes of variability. Our findings provide new insights for the relationship between the winter Eurasian snow and the following ISMR, namely that the same relationship may be understood through a framework of meridional atmospheric energy transport and its effects on the tropical air-sea interactions. The improvements in the global teleconnection in the modified version of CFSv2 may have implications in the ISMR predictability and prediction skill. air-sea interactions; Eurasian Snow; Monsoon; teleconnections
Sun, Jian; Zhang, Kai; Wan, Hui; Ma, Po-Lun; Tang, Qi; Zhang, ShixuanSun, J., K. Zhang, H. Wan, P. Ma, Q. Tang, S. Zhang, 2019: Impact of Nudging Strategy on the Climate Representativeness and Hindcast Skill of Constrained EAMv1 Simulations. Journal of Advances in Modeling Earth Systems, 11(12), 3911-3933. doi: 10.1029/2019MS001831. Nudging is a simulation technique widely used in sensitivity studies and in the evaluation of atmosphere models. Care is needed in the experimental setup in order to achieve the desired constraint on the simulated atmospheric processes without introducing undue intervention. In this study, sensitivity experiments are conducted with the Energy Exascale Earth System Model (E3SM) Atmosphere Model Version 1 (EAMv1) to identify setups that can give results representative of the model's long-term climate and meanwhile reasonably capture characteristics of the observed meteorological conditions to facilitate the comparison of model results with measurements. We show that when the prescribed meteorological conditions are temporally interpolated to the model time to constrain EAM's horizontal winds at each time step, a nudged simulation can reproduce the characteristic evolution of the observed weather events (especially in middle and high latitudes) as well as the model's long-term climatology, although nudging also leads to nonnegligible regional changes in wind-driven aerosol emissions, low-level clouds in the stratocumulus regime, and cloud and precipitation near the maritime continent. Compared to its predecessor model used in an earlier study, EAMv1 is less sensitive to temperature nudging, although significant impacts on the cloud radiative effects still exist. EAMv1 remains very sensitive to humidity nudging. Constraining humidity substantially improves the correlation between the simulated and observed tropical precipitation but also leads to large changes in the long-term statistics of the simulated precipitation, clouds, and aerosol lifecycle. E3SM; EAMv1; hindcast; nudging
Tan, J.; Frouin, R.Tan, J., R. Frouin, 2019: Seasonal and Interannual Variability of Satellite-Derived Photosynthetically Available Radiation Over the Tropical Oceans. Journal of Geophysical Research: Oceans, 124(5), 3073-3088. doi: 10.1029/2019JC014942. The seasonal and interannual variability of photosynthetically available radiation (PAR) over the tropical oceans is examined using satellite imagery acquired from 1997 to 2017. Spatial and temporal biases between monthly PAR estimates from different instruments are determined and corrected, resulting in a consistent time series over the 20-year record. Uncertainty is evaluated in comparisons with in situ measurements at various sites. Empirical orthogonal function (EOF) analysis is performed with both seasonal and nonseasonal PAR signals, and linear trends are quantified. Seasonal cycles dominate PAR variability, with the first three seasonal EOF modes explaining 84.7% of the total variance. The seasonal patterns are related to solar position and monsoon. Canonical El Niño–Southern Oscillation (ENSO) and Modoki ENSO are related to the two leading nonseasonal EOF modes, with a correlation coefficient of 0.84 between the first mode and the multivariate ENSO index and of 0.48 between the second mode and the El Niño Modoki index. Trend analysis reveals that PAR tends to decrease by 0.2%/year in the central Pacific north of the equator and to increase by 0.2%/year in the central Pacific around 5°S. The tendency is also for PAR to increase west of Central and South America. These changes are consistent with patterns of cloud change evidenced in the satellite cloud record and predicted by global climate models. The long-term satellite PAR data set, together with information of nutrient availability and temperature, enables further studies to elucidate the causes of phytoplankton variability in the tropical oceans.
Tang, Wenjun; Yang, Kun; Qin, Jun; Li, Xin; Niu, XiaoleiTang, W., K. Yang, J. Qin, X. Li, X. Niu, 2019: A 16-year dataset (2000–2015) of high-resolution (3 h, 10 km) global surface solar radiation. Earth System Science Data, 11(4), 1905-1915. doi: https://doi.org/10.5194/essd-11-1905-2019. Abstract. The recent release of the International Satellite Cloud Climatology Project (ISCCP) HXG cloud products and new ERA5 reanalysis data enabled us to produce a global surface solar radiation (SSR) dataset: a 16-year (2000–2015) high-resolution (3 h, 10 km) global SSR dataset using an improved physical parameterization scheme. The main inputs were cloud optical depth from ISCCP-HXG cloud products; the water vapor, surface pressure and ozone from ERA5 reanalysis data; and albedo and aerosol from Moderate Resolution Imaging Spectroradiometer (MODIS) products. The estimated SSR data were evaluated against surface observations measured at 42 stations of the Baseline Surface Radiation Network (BSRN) and 90 radiation stations of the China Meteorological Administration (CMA). Validation against the BSRN data indicated that the mean bias error (MBE), root mean square error (RMSE) and correlation coefficient (R) for the instantaneous SSR estimates at 10 km scale were −11.5 W m−2, 113.5 W m−2 and 0.92, respectively. When the estimated instantaneous SSR data were upscaled to 90 km, its error was clearly reduced, with RMSE decreasing to 93.4 W m−2 and R increasing to 0.95. For daily SSR estimates at 90 km scale, the MBE, RMSE and R at the BSRN were −5.8 W m−2, 33.1 W m−2 and 0.95, respectively. These error metrics at the CMA radiation stations were 2.1 W m−2, 26.9 W m−2 and 0.95, respectively. Comparisons with other global satellite radiation products indicated that our SSR estimates were generally better than those of the ISCCP flux dataset (ISCCP-FD), the global energy and water cycle experiment surface radiation budget (GEWEX-SRB), and the Earth's Radiant Energy System (CERES). Our SSR dataset will contribute to the land-surface process simulations and the photovoltaic applications in the future. The dataset is available at https://doi.org/10.11888/Meteoro.tpdc.270112 (Tang, 2019).
Taylor, Patrick C.; Boeke, Robyn C.; Li, Ying; Thompson, David W. J.Taylor, P. C., R. C. Boeke, Y. Li, D. W. J. Thompson, 2019: Arctic cloud annual cycle biases in climate models. Atmospheric Chemistry and Physics, 19(13), 8759-8782. doi: 10.5194/acp-19-8759-2019. Abstract. Arctic clouds exhibit a robust annual cycle with maximum cloudiness in fall and minimum cloudiness in winter. These variations affect energy flows in the Arctic with a large influence on the surface radiative fluxes. Contemporary climate models struggle to reproduce the observed Arctic cloud amount annual cycle and significantly disagree with each other. The goal of this analysis is to quantify the cloud-influencing factors that contribute to winter–summer cloud amount differences, as these seasons are primarily responsible for the model discrepancies with observations. We find that differences in the total cloud amount annual cycle are primarily caused by differences in low, rather than high, clouds; the largest differences occur between the surface and 950 hPa. Grouping models based on their seasonal cycles of cloud amount and stratifying cloud amount by cloud-influencing factors, we find that model groups disagree most under strong lower tropospheric stability, weak to moderate mid-tropospheric subsidence, and cold lower tropospheric air temperatures. Intergroup differences in low cloud amount are found to be a function of lower tropospheric thermodynamic characteristics. Further, we find that models with a larger low cloud amount in winter have a larger ice condensate fraction, whereas models with a larger low cloud amount in summer have a smaller ice condensate fraction. Stratifying model output by the specifics of the cloud microphysical scheme reveals that models treating cloud ice and liquid condensate as separate prognostic variables simulate a larger ice condensate fraction than those that treat total cloud condensate as a prognostic variable and use a temperature-dependent phase partitioning. Thus, the cloud microphysical parameterization is the primary cause of inter-model differences in the Arctic cloud annual cycle, providing further evidence of the important role that cloud ice microphysical processes play in the evolution and modeling of the Arctic climate system.
Thomas, Manu Anna; Devasthale, Abhay; Koenigk, Torben; Wyser, Klaus; Roberts, Malcolm; Roberts, Christopher; Lohmann, KatjaThomas, M. A., A. Devasthale, T. Koenigk, K. Wyser, M. Roberts, C. Roberts, K. Lohmann, 2019: A statistical and process-oriented evaluation of cloud radiative effects in high-resolution global models. Geoscientific Model Development, 12(4), 1679-1702. doi: 10.5194/gmd-12-1679-2019. Abstract. This study evaluates the impact of atmospheric horizontal resolution on the representation of cloud radiative effects (CREs) in an ensemble of global climate model simulations following the protocols of the High Resolution Model Intercomparison Project (HighResMIP). We compare results from four European modelling centres, each of which provides data from “standard”- and “high”-resolution model configurations. Simulated radiative fluxes are compared with observation-based estimates derived from the Clouds and Earth's Radiant Energy System (CERES) dataset. Model CRE biases are evaluated using both conventional statistics (e.g. time and spatial averages) and after conditioning on the phase of two modes of internal climate variability, namely the El Niño–Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO). Simulated top-of-atmosphere (TOA) and surface CREs show large biases over the polar regions, particularly over regions where seasonal sea-ice variability is strongest. Increasing atmospheric resolution does not significantly improve these biases. The spatial structure of the cloud radiative response to ENSO and NAO variability is simulated reasonably well by all model configurations considered in this study. However, it is difficult to identify a systematic impact of atmospheric resolution on the associated CRE errors. Mean absolute CRE errors conditioned on the ENSO phase are relatively large (5–10 W m−2) and show differences between models. We suggest this is a consequence of differences in the parameterization of SW radiative transfer and the treatment of cloud optical properties rather than a result of differences in resolution. In contrast, mean absolute CRE errors conditioned on the NAO phase are generally smaller (0–2 W m−2) and more similar across models. Although the regional details of CRE biases show some sensitivity to atmospheric resolution within a particular model, it is difficult to identify patterns that hold across all models. This apparent insensitivity to increased atmospheric horizontal resolution indicates that physical parameterizations play a dominant role in determining the behaviour of cloud–radiation feedbacks. However, we note that these results are obtained from atmosphere-only simulations and the impact of changes in atmospheric resolution may be different in the presence of coupled climate feedbacks.
Tian, Jingjing; Dong, Xiquan; Xi, Baike; Williams, Christopher R.; Wu, PengTian, J., X. Dong, B. Xi, C. R. Williams, P. Wu, 2019: Estimation of liquid water path below the melting layer in stratiform precipitation systems using radar measurements during MC3E. Atmospheric Measurement Techniques, 12(7), 3743-3759. doi: 10.5194/amt-12-3743-2019. Abstract. In this study, the liquid water path (LWP) below the melting layer in stratiform precipitation systems is retrieved, which is a combination of rain liquid water path (RLWP) and cloud liquid water path (CLWP). The retrieval algorithm uses measurements from the vertically pointing radars (VPRs) at 35 and 3 GHz operated by the US Department of Energy Atmospheric Radiation Measurement (ARM) and National Oceanic and Atmospheric Administration (NOAA) during the field campaign Midlatitude Continental Convective Clouds Experiment (MC3E). The measured radar reflectivity and mean Doppler velocity from both VPRs and spectrum width from the 35 GHz radar are utilized. With the aid of the cloud base detected by a ceilometer, the LWP in the liquid layer is retrieved under two different situations: (I) no cloud exists below the melting base, and (II) cloud exists below the melting base. In (I), LWP is primarily contributed from raindrops only, i.e., RLWP, which is estimated by analyzing the Doppler velocity differences between two VPRs. In (II), cloud particles and raindrops coexist below the melting base. The CLWP is estimated using a modified attenuation-based algorithm. Two stratiform precipitation cases (20 and 11 May 2011) during MC3E are illustrated for two situations, respectively. With a total of 13 h of samples during MC3E, statistical results show that the occurrence of cloud particles below the melting base is low (9 %); however, the mean CLWP value can be up to 0.56 kg m−2, which is much larger than the RLWP (0.10 kg m−2). When only raindrops exist below the melting base, the average RLWP value is larger (0.32 kg m−2) than the with-cloud situation. The overall mean LWP below the melting base is 0.34 kg m−2 for stratiform systems during MC3E.
Tornow, F.; Domenech, C.; Fischer, J.Tornow, F., C. Domenech, J. Fischer, 2019: On the Use of Geophysical Parameters for the Top-of-Atmosphere Shortwave Clear-Sky Radiance-to-Flux Conversion in EarthCARE. J. Atmos. Oceanic Technol., 36(4), 717-732. doi: 10.1175/JTECH-D-18-0087.1. We have investigated whether differences across Clouds and the Earth’s Radiant Energy System (CERES) top-of-atmosphere (TOA) clear-sky angular distribution models, estimated separately over regional (1° × 1° longitude–latitude) and temporal (monthly) bins above land, can be explained by geophysical parameters from Max Planck Institute Aerosol Climatology, version 1 (MAC-v1), ECMWF twentieth-century reanalysis (ERA-20C), and a MODIS bidirectional reflectance distribution function (BRDF)/albedo/nadir BRDF-adjusted reflectance (NBAR) Climate Modeling Grid (CMG) gap-filled products (MCD43GF) climatology. Our research aimed to dissolve binning and to isolate inherent properties or indicators of such properties, which govern the TOA radiance-to-flux conversion in the absence of clouds. We collocated over seven million clear-sky footprints from CERES Single Scanner Footprint (SSF), edition 4, data with above geophysical auxiliary data. Looking at data per surface type and per scattering direction—as perceived by the broadband radiometer (BBR) on board Earth Clouds, Aerosol and Radiation Explorer (EarthCARE)—we identified optimal subsets of geophysical parameters using two different methods: random forest regression followed by a permutation test and multiple linear regression combined with the genetic algorithm. Using optimal subsets, we then trained artificial neural networks (ANNs). Flux error standard deviations on unseen test data were on average 2.7–4.0 W m−2, well below the 10 W m−2 flux accuracy threshold defined for the mission, with the exception of footprints containing fresh snow. Dynamic surface types (i.e., fresh snow and sea ice) required simpler ANN input sets to guarantee mission-worthy flux estimates, especially over footprints consisting of several surface types.
Trenberth, Kevin E.; Zhang, YongxinTrenberth, K. E., Y. Zhang, 2019: Observed inter-hemispheric meridional heat transports and the role of the Indonesian Throughflow in the Pacific Ocean. J. Climate, 32(24), 8523–8536. doi: 10.1175/JCLI-D-19-0465.1. The net surface energy flux is computed as a residual of the energy budget using top-of-atmosphere radiation combined with the divergence of the column-integrated atmospheric energy transports, and then used with the vertically-integrated ocean heat content tendencies to compute the ocean meridional heat transports (MHTs). The mean annual cycles, and 12-month running mean MHTs as a function of latitude are presented for 2000-2016. Effects of the Indonesian Throughflow (ITF), associated with a net volume flow around Australia accompanied by a heat transport are fully included. Because the ITF-related flow necessitates a return current northward in the Tasman Sea that relaxes during El Niño, the reduced ITF during El Niño may contribute to warming in the south Tasman Sea by allowing the East Australian current to push farther south even as it gains volume from the tropical waters not flowing through the ITF. Although evident in 2015-16, when a major marine heat wave occurred, these effects can be overwhelmed by changes in the atmospheric circulation. Large interannual MHT variability in the Pacific is four times that of the Atlantic. Strong relationships reveal influences from the southern subtropics on ENSO for this period. At the equator, northward ocean MHT arises mainly in the Atlantic (0.75 PW), offset by the Pacific (-0.33 PW) and Indian Oceans (-0.20 PW) while the atmosphere transports energy southward (-0.35 PW). The net equatorial MHT southward (-0.18 PW) is enhanced by -0.1 PW that contributes to the greater warming of the southern (vs northern) oceans.
Trenberth, Kevin E.; Zhang, Yongxin; Fasullo, John T.; Cheng, LijingTrenberth, K. E., Y. Zhang, J. T. Fasullo, L. Cheng, 2019: Observation-based estimate of global and basin ocean meridional heat transport time series. J. Climate, 32(14), 4567–4583. doi: 10.1175/JCLI-D-18-0872.1. Ocean meridional heat transports (MHTs) are deduced as a residual using energy budgets to produce latitude vs time series for the globe, Indo-Pacific and Atlantic. The top-of-atmosphere (TOA) radiation is combined with the vertically-integrated atmospheric energy divergence from atmospheric reanalyses to produce the net surface energy fluxes everywhere. The latter is then combined with estimates of the vertically-integrated ocean heat content (OHC) tendency to produce estimates of the ocean heat divergence. Because seasonal sea-ice and land runoff effects are not fully considered, the mean annual cycle is incomplete, but those effects are small for interannual variability. However, there is a mismatch between 12-month inferred surface flux and the corresponding OHC changes globally, requiring adjustments to account for the Earth’s global energy imbalance. Estimates are greatly improved by building in the constraint that MHT must go to zero at the northern and southern extents of the ocean basin at all times, enabling biases between the TOA and OHC data to be reconciled. Zonal mean global, Indo-Pacific and Atlantic basin ocean MHTs are computed and presented as 12-month running means and for the mean annual cycle for 2000 to 2016. For the Indo-Pacific, the tropical and subtropical MHTs feature a strong relationship with El Niño-Southern Oscillation (ENSO), and in the Atlantic, MHT interannual variability is significantly affected by and likely influences the North Atlantic Oscillation (NAO). However, Atlantic and Pacific changes are linked, suggesting that the Northern Annular Mode (versus NAO) is predominant. There is also evidence of decadal variability or trends.
Vargas Zeppetello, Lucas R.; Battisti, David S.; Baker, Marcia B.Vargas Zeppetello, L. R., D. S. Battisti, M. B. Baker, 2019: The Origin of Soil Moisture Evaporation “Regimes”. J. Climate, 32(20), 6939-6960. doi: 10.1175/JCLI-D-19-0209.1. Evaporation plays an extremely important role in determining summertime surface temperature variability over land. Observations show the relationship between evaporation and soil moisture generally conforms to the Budyko “two regime” framework; namely, that evaporation is limited by available soil moisture in dry climates and by radiation in wet climates. This framework has led climate models to different parameterizations of the relationship between evaporation and soil moisture in wet and dry regions. We have developed the Simple Land–Atmosphere Model (SLAM) as a tool for studying land–atmosphere interaction in general, and summertime temperature variability in particular. We use the SLAM to show that a negative feedback between evaporation and surface temperature gives rise to the two apparent evaporation “regimes” and provide analytic solutions for evaporative cooling anomalies that demonstrate the nonlinear impact of soil moisture perturbations. Stemming from the temperature dependence of vapor pressure deficit, the feedback we identify has important implications for how transitions between wet and dry land surfaces may impact temperature variability as the climate warms. We also elucidate the impacts of surface moisture and insolation perturbations on latent and sensible heat fluxes and on surface temperature variability.
Voldoire, A.; Saint‐Martin, D.; Sénési, S.; Decharme, B.; Alias, A.; Chevallier, M.; Colin, J.; Guérémy, J.-F.; Michou, M.; Moine, M.-P.; Nabat, P.; Roehrig, R.; Mélia, D. Salas y; Séférian, R.; Valcke, S.; Beau, I.; Belamari, S.; Berthet, S.; Cassou, C.; Cattiaux, J.; Deshayes, J.; Douville, H.; Ethé, C.; Franchistéguy, L.; Geoffroy, O.; Lévy, C.; Madec, G.; Meurdesoif, Y.; Msadek, R.; Ribes, A.; Sanchez‐Gomez, E.; Terray, L.; Waldman, R.Voldoire, A., D. Saint‐Martin, S. Sénési, B. Decharme, A. Alias, M. Chevallier, J. Colin, J. Guérémy, M. Michou, M. Moine, P. Nabat, R. Roehrig, D. S. y. Mélia, R. Séférian, S. Valcke, I. Beau, S. Belamari, S. Berthet, C. Cassou, J. Cattiaux, J. Deshayes, H. Douville, C. Ethé, L. Franchistéguy, O. Geoffroy, C. Lévy, G. Madec, Y. Meurdesoif, R. Msadek, A. Ribes, E. Sanchez‐Gomez, L. Terray, R. Waldman, 2019: Evaluation of CMIP6 DECK Experiments With CNRM-CM6-1. Journal of Advances in Modeling Earth Systems, 11(7), 2177-2213. doi: 10.1029/2019MS001683. This paper describes the main characteristics of CNRM-CM6-1, the fully coupled atmosphere-ocean general circulation model of sixth generation jointly developed by Centre National de Recherches Météorologiques (CNRM) and Cerfacs for the sixth phase of the Coupled Model Intercomparison Project 6 (CMIP6). The paper provides a description of each component of CNRM-CM6-1, including the coupling method and the new online output software. We emphasize where model's components have been updated with respect to the former model version, CNRM-CM5.1. In particular, we highlight major improvements in the representation of atmospheric and land processes. A particular attention has also been devoted to mass and energy conservation in the simulated climate system to limit long-term drifts. The climate simulated by CNRM-CM6-1 is then evaluated using CMIP6 historical and Diagnostic, Evaluation and Characterization of Klima (DECK) experiments in comparison with CMIP5 CNRM-CM5.1 equivalent experiments. Overall, the mean surface biases are of similar magnitude but with different spatial patterns. Deep ocean biases are generally reduced, whereas sea ice is too thin in the Arctic. Although the simulated climate variability remains roughly consistent with CNRM-CM5.1, its sensitivity to rising CO2 has increased: the equilibrium climate sensitivity is 4.9 K, which is now close to the upper bound of the range estimated from CMIP5 models. climate model; CMIP6 DECK; CNRM-CM6-1
Wall, Casey J.; Hartmann, Dennis L.; Norris, Joel R.Wall, C. J., D. L. Hartmann, J. R. Norris, 2019: Is the Net Cloud Radiative Effect Constrained to be Uniform Over the Tropical Warm Pools?. Geophysical Research Letters, 46(21), 12495-12503. doi: 10.1029/2019GL083642. Global radiative-convective equilibrium simulations are used to investigate the hypothesis that mutual interactions among cloud albedo, sea surface temperature gradients, and atmospheric circulation constrain the net cloud radiative effect (CRE) to be similar in convective and nonconvective regions over the tropical warm pools. We perform an experiment in which convective clouds interact naturally with the ocean and atmosphere by forming over the warmest water and shading it and an experiment in which this interaction is removed by randomizing cloud shading of the ocean. Removing the cloud shading interaction enhances sea surface temperature gradients, lateral atmospheric heat transport, and large-scale convective aggregation and produces convective clouds with much more negative net CRE. These findings support the hypothesis that feedbacks between sea surface temperature and convection are critical to obtaining similar net CRE in convective and nonconvective regions over the tropical warm pools. Tropical Convection; Cloud Radiative Effects; Ocean-Atmosphere Interactions
Walther, Sophia; Duveiller, Gregory; Jung, Martin; Guanter, Luis; Cescatti, Alessandro; Camps‐Valls, GustauWalther, S., G. Duveiller, M. Jung, L. Guanter, A. Cescatti, G. Camps‐Valls, 2019: Satellite Observations of the Contrasting Response of Trees and Grasses to Variations in Water Availability. Geophysical Research Letters, 46(3), 1429-1440. doi: 10.1029/2018GL080535. Interannual variations in ecosystem primary productivity are dominated by water availability. Until recently, characterizing the photosynthetic response of different ecosystems to soil moisture anomalies was hampered by observational limitations. Here, we use a number of satellite-based proxies for productivity, including spectral indices, sun-induced chlorophyll fluorescence, and data-driven estimates of gross primary production, to reevaluate the relationship between terrestrial photosynthesis and water. In contrast to nonwoody vegetation, we find a resilience of forested ecosystems to reduced soil moisture. Sun-induced chlorophyll fluorescence and data-driven gross primary production indicate an increase in photosynthesis as a result of the accompanying higher amounts of light and temperature despite lowered light-use-efficiency. Conversely, remote sensing indicators of greenness reach their detection limit and largely remain stable. Our study thus highlights the differential responses of ecosystems along a tree cover gradient and illustrates the importance of differentiating photosynthesis indicators from those of greenness for the monitoring and understanding of ecosystems. SIF; GPP; satellite; forest; photosynthesis; water effects
Wang, Jianjie; Liu, Chao; Yao, Bin; Min, Min; Letu, Husi; Yin, Yan; Yung, Yuk L.Wang, J., C. Liu, B. Yao, M. Min, H. Letu, Y. Yin, Y. L. Yung, 2019: A multilayer cloud detection algorithm for the Suomi-NPP Visible Infrared Imager Radiometer Suite (VIIRS). Remote Sensing of Environment, 227, 1-11. doi: 10.1016/j.rse.2019.02.024. A new multilayer (ML) cloud detection algorithm based on three shortwave infrared (SWIR) and two longwave infrared (LWIR) channels is developed and applied to the Visible Infrared Imager Radiometer Suite (VIIRS) onboard the Suomi-NPP satellite. The algorithm identifies ML clouds, i.e., ice clouds overlying water clouds, based on satellite multispectral observations in the 1.38, 1.6, 2.25, 8.5, and 11 μm channels. We perform synthetic radiative transfer simulations to understand the sensitivities of the aforementioned channels on ML and single-layer (SL) clouds. Active CALIOP observations are used to evaluate the algorithm. Compared with the collocated CALIOP results, the algorithm can determine SL and ML clouds correctly with success rates of approximately 80% and 60%, respectively, and has similar performance to that of the current MODIS operational ML cloud detection algorithm. The misclassification of ML clouds as SL clouds is primarily caused by thin ice clouds that are practically undetectable using LWIR tests. Furthermore, the algorithm is extended to analyze data from radiometers onboard the geostationary Himawari-8 and FengYun-4A satellites, and results similar to those of VIIRS are obtained. VIIRS; Radiometer; Longwave infrared; Multilayer clouds; Shortwave infrared
Wang, Qian; Zhang, Su-Ping; Xie, Shang-Ping; Norris, Joel R.; Sun, Jian-Xiang; Jiang, Yu-XiWang, Q., S. Zhang, S. Xie, J. R. Norris, J. Sun, Y. Jiang, 2019: Observed Variations of the Atmospheric Boundary Layer and Stratocumulus over a Warm Eddy in the Kuroshio Extension. Mon. Wea. Rev., 147(5), 1581-1591. doi: 10.1175/MWR-D-18-0381.1. A research vessel sailing across a warm eddy in the Kuroshio Extension on 13 April 2016 captured an abrupt development of stratocumulus under synoptic high pressure. Shipboard observations and results from regional atmospheric model simulations indicate that increased surface heat flux over the ocean eddy lowered surface pressure and thereby accelerated southeasterly winds. The southeasterly winds transported moisture toward the low pressure and enhanced the air–sea interface heat flux, which in turn deepened the low pressure and promoted low-level convergence and rising motion over the warm eddy. The lifting condensation level lowered and the top of the marine atmospheric boundary layer (MABL) rose, thereby aiding the development of the stratocumulus. Further experiments showed that 6°C sea surface temperature anomalies associated with the 400-km-diameter warm eddy accounted for 80% of the total ascending motion and 95% of total cloud water mixing ratio in the marine atmospheric boundary layer during the development of stratocumulus. The synthesis of in situ soundings and modeling contributes to understanding of the mechanism by which the MABL and marine stratocumulus respond to ocean eddies.
Wang, Tao; Wu, Dong L.; Gong, Jie; Tsai, VictoriaWang, T., D. L. Wu, J. Gong, V. Tsai, 2019: Tropopause Laminar Cirrus and Its Role in the Lower Stratosphere Total Water Budget. Journal of Geophysical Research: Atmospheres, 124(13), 7034-7052. doi: 10.1029/2018JD029845. Laminar cirrus are thin, extensive, isolated layers of ice clouds frequently observed in the tropical tropopause layer. Widespread laminar cirrus significantly affects tropical tropopause layer total water and thermal budget. In this study, we extract laminar cirrus from the Cloud-Aerosol Lidar with Orthogonal Polarization Level 1 attenuated total backscatter images for January 2009, in order to characterize statistical properties of laminar cirrus cloud length, base, thickness, optical depth, and layer partial ice water path. These characteristics are used to develop an algorithm identifying laminar cirrus automatically from the Cloud-Aerosol Lidar with Orthogonal Polarization Level 2 layer product for 2008–2017. The nearly 10-year records reveal that tropopause laminar cirrus occurrence (30–40% of total cirrus) is strongly anticorrelated with the tropopause temperatures in that colder tropopause in frequent (super)saturation during boreal winter favors in situ formation of clouds. Interannually, anomalously warmer troposphere temperature (ΔT), easterly shear of the quasi-biennial oscillation, and stronger upwelling branch of the Brewer-Dobson circulation enhance laminar cirrus formation via cooling of the tropopause. The tropopause laminar cirrus carries 0.05 mg/m3 ( 0.5 ppmv) of ice water content during boreal winter and tropopause; TTL; ice water content (IWC); laminar cirrus; total water budget; water vapor (H2O)
Wang, Wenshan; Zender, Charles S.; van As, Dirk; Miller, Nathaniel B.Wang, W., C. S. Zender, D. van As, N. B. Miller, 2019: Spatial distribution of melt-season cloud radiative effects over Greenland: Evaluating satellite observations, reanalyses, and model simulations against in situ measurements. Journal of Geophysical Research: Atmospheres, 124(1), 57-71. doi: 10.1029/2018JD028919. Arctic clouds can profoundly influence surface radiation and thus surface melt. Over Greenland, these cloud radiative effects (CRE) vary greatly with the diverse topography. To investigate the ability of assorted platforms to reproduce heterogeneous CRE, we evaluate CRE spatial distributions from a satellite product, reanalyses, and a global climate model against estimates from 21 automatic weather stations (AWS). Net CRE estimated from AWS generally decreases with elevation, forming a “warm center” distribution. CRE areal averages from the five large-scale data sets we analyze are all around 10 W m−2. MERRA-2, ERA-Interim, and CERES CRE estimates agree with AWS and reproduce the “warm center” distribution. However, the NCAR Arctic System Reanalysis (ASR) and the CESM Large ENSemble community project (LENS) show strong warming in the south and northwest, forming a “warm L-shape” distribution. Discrepancies are mainly caused by longwave CRE in the accumulation zone. MERRA-2, ERA-Interim, and CERES successfully reproduce cloud fraction and its dominant positive influence on longwave CRE in this region. On the other hand, longwave CRE from ASR and LENS correlates strongly with ice water path instead of with cloud fraction or liquid water path. Moreover, ASR overestimates cloud fraction and LENS underestimates liquid water path substantially, both with limited spatial variability. MERRA-2 best captures the observed inter-station changes, captures most of the observed cloud-radiation physics, and largely reproduces both albedo and cloud properties. The “warm center” CRE spatial distribution indicates that clouds enhance surface melt in the higher accumulation zone and reduce surface melt in the lower ablation zone. Greenland; Cloud; Radiation; Automatic weather stations
Wang, Yipu; Li, Rui; Min, Qilong; Zhang, Leiming; Yu, Guirui; Bergeron, YvesWang, Y., R. Li, Q. Min, L. Zhang, G. Yu, Y. Bergeron, 2019: Estimation of Vegetation Latent Heat Flux over Three Forest Sites in ChinaFLUX using Satellite Microwave Vegetation Water Content Index. Remote Sensing, 11(11), 1359. doi: 10.3390/rs11111359. Latent heat flux (LE) and the corresponding water vapor lost from the Earth’s surface to the atmosphere, which is called Evapotranspiration (ET), is one of the key processes in the water cycle and energy balance of the global climate system. Satellite remote sensing is the only feasible technique to estimate LE over a large-scale region. While most of the previous satellite LE methods are based on the optical vegetation index (VI), here we propose a microwave-VI (EDVI) based LE algorithm which can work for both day and night time, and under clear or non-raining conditions. This algorithm is totally driven by multiple-sensor satellite products of vegetation water content index, solar radiation, and cloud properties, with some aid from a reanalysis dataset. The satellite inputs and the performance of this algorithm are validated with in situ measurements at three ChinaFLUX forest sites. Our results show that the selected satellite observations can indeed serve as the inputs for the purpose of estimating ET. The instantaneous estimations of LE (LEcal) from this algorithm show strong positive temporal correlations with the in situ measured LE (LEobs) with the correlation coefficients (R) of 0.56–0.88 in the study years. The mean bias is kept within 16.0% (23.0 W/m2) across the three sites. At the monthly scale, the correlations between the retrieval and the in situ measurements are further improved to an R of 0.84–0.95 and the bias is less than 14.3%. The validation results also indicate that EDVI-based LE method can produce stable LEcal under different cloudy skies with good accuracy. Being independent of any in situ measurements as inputs, this algorithm shows great potential for estimating ET under both clear and cloudy skies on a global scale for climate study. satellite remote sensing; cloudy sky; ChinaFLUX; clouds and earth’s radiation energy system (CERES); evapotranspiration (ET); Microwave emissivity difference vegetation index (EDVI)
Wehrli, Kathrin; Guillod, Benoit P.; Hauser, Mathias; Leclair, Matthieu; Seneviratne, Sonia I.Wehrli, K., B. P. Guillod, M. Hauser, M. Leclair, S. I. Seneviratne, 2019: Identifying Key Driving Processes of Major Recent Heat Waves. Journal of Geophysical Research: Atmospheres, 124(22), 11746-11765. doi: 10.1029/2019JD030635. Heat waves lead to major impacts on human health, food production, and ecosystems. To assess their predictability and how they are projected to change under global warming, it is crucial to improve our understanding of the underlying processes affecting their occurrence and intensity under present-day climate conditions. Beside greenhouse gas forcing, processes in the different components of the climate system—in particular the land surface, atmospheric circulation, and the oceans—may play a key role in changing the odds for a particular event. This study aims to identify the role of the individual drivers for five heat waves (and, in some cases, of concurrent droughts) in the recent decade. Simulations are performed with the Community Earth System Model using nudging of horizontal atmospheric circulation and prescription of soil moisture. The fully constrained model accurately reproduces how anomalous an event was. Factorial experiments, which force the model toward observations for one or several key components at a time, allow us to identify how much of the observed temperature anomaly of each event can be attributed to each driver. Considering all analyzed events, atmospheric circulation and soil moisture play similarly important roles, each contributing between 20% and 70% to the events' anomalies. This highlights that the role of thermodynamics can be just as important as that of the dynamics for temperature extremes, a possibly underestimated feature. In addition, recent climate change amplified the events and contributed between 10% and 40% of the events' anomalies. extreme events; atmospheric nudging; global climate models; heat waves; soil moisture prescription