Liang, Lusheng; Su, Wenying; Sejas, Sergio; Eitzen, Zachary A.; Loeb, Norman G.Liang, L., W. Su, S. Sejas, Z. A. Eitzen, N. G. Loeb, 2023: Next-generation radiance unfiltering process for the Clouds and Earth’s Radiant Energy System instrument. EGUsphere, 1-25. doi: 10.5194/egusphere-2023-1670. Abstract. The filtered radiances measured by the Clouds and the Earth’s Radiant Energy System (CERES) instruments are converted to shortwave (SW), longwave (LW), and window unfiltered radiances based on regressions developed from theoretical radiative transfer simulations to relate filtered and unfiltered radiances. This paper describes an update to the existing Edition 4 CERES unfiltering algorithm (Loeb et al., 2001), incorporating the most recent developments in radiative transfer modeling, ancillary input datasets, and increased computational and storage capabilities during the past 20 years. Simulations are performed with MODTRAN 5.4. Over land and snow, the surface Bidirectional Reflectance Distribution Function (BRDF) is characterized by a kernel-based representation in the simulations, instead of the Lambertian surface used in the Edition 4 unfiltering process. Radiance unfiltering is explicitly separated into 4 seasonally dependent land surface groups based on the spectral radiation similarities of different surface types (defined by International Geosphere-Biosphere Programme); over snow, it is separated into fresh snow, permanent snow, and sea ice. It contrasts to the Edition 4 unfiltering process that one set of regressions for land and snow, respectively. The instantaneous unfiltering errors are estimated with independent test cases generated from radiative transfer simulations in which the ‘true’ unfiltered radiances from radiative transfer simulations are compared with the unfiltered radiances calculated from the regressions. Overall, the relative errors are mostly within ±0.5 % for SW, within ±0.2 % for daytime LW, and within ±0.1 % for nighttime LW for both CERES Terra Flight Model 1 (FM1) and Aqua FM3 instruments. The unfiltered radiances are converted to fluxes and compared to CERES Edition 4 fluxes. The global mean instantaneous fluxes for Aqua FM3 are reduced by less than 0.42 Wm-2 for SW and increased by less than 0.47 Wm-2 for daytime LW; for Terra FM1, they are reduced by less than 0.31 Wm-2 for SW and increased by less than 0.29 Wm-2 for daytime LW, though regional differences can be as large as 2.0 Wm-2. Nighttime LW flux differences are nearly negligible for both instruments.
Reed, K. A.; Stansfield, A. M.; Hsu, W.-C.; Kooperman, G. J.; Akinsanola, A. A.; Hannah, W. M.; Pendergrass, A. G.; Medeiros, B.Reed, K. A., A. M. Stansfield, W. Hsu, G. J. Kooperman, A. A. Akinsanola, W. M. Hannah, A. G. Pendergrass, B. Medeiros, 2023: Evaluating the Simulation of CONUS Precipitation by Storm Type in E3SM. Geophysical Research Letters, 50(12), e2022GL102409. doi: 10.1029/2022GL102409. Conventional low-resolution (LR) climate models, including the Energy Exascale Earth System Model (E3SMv1), have well-known biases in simulating the frequency, intensity, and timing of precipitation. Approaches to next-generation E3SM, whether the high-resolution (HR) or multiscale modeling framework (MMF) configuration, improve the simulation of the intensity and frequency of precipitation, but regional and seasonal deficiencies still exist. Here we apply a methodology to assess the contribution of tropical cyclones (TCs), extratropical cyclones (ETCs), and mesoscale convective systems (MCSs) to simulated precipitation in E3SMv1-HR and E3SMv1-MMF relative to E3SMv1-LR. Across the United States, E3SMv1-MMF provides the best simulation in terms of precipitation accumulation, frequency and intensity from MCSs and TCs compared to E3SMv1-LR and E3SMv1-HR. All E3SMv1 configurations overestimate precipitation amounts from and the frequency of ETCs over CONUS, with conventional E3SMv1-LR providing the best simulation compared to observations despite limitations in precipitation intensity within these events. Earth system model; precipitation; energy exascale earth system model; high resolution; extremes; multiscale modeling framework
Taylor, Patrick C.; Itterly, Kyle F.; Corbett, Joe; Bucholtz, Anthony; Sejas, Sergio; Su, Wenying; Doelling, Dave; Kato, SeijiTaylor, P. C., K. F. Itterly, J. Corbett, A. Bucholtz, S. Sejas, W. Su, D. Doelling, S. Kato, 2022: A Comparison of Top-Of-Atmosphere Radiative Fluxes From CERES and ARISE. Journal of Geophysical Research: Atmospheres, 127(24), e2022JD037573. doi: 10.1029/2022JD037573. Uncertainty in Arctic top-of-atmosphere (TOA) radiative flux observations stems from the low sun angles and the heterogeneous scenes. Advancing our understanding of the Arctic climate system requires improved TOA radiative fluxes. We compare Cloud and Earth's Radiant Energy System (CERES) TOA radiative fluxes with Arctic Radiation-IceBridge Sea and Ice Experiment (ARISE) airborne measurements using two approaches: grid box averages and instantaneously matched footprints. Both approaches indicate excellent agreement in the longwave and good agreement in the shortwave (SW), within 2σ uncertainty considering all error sources (CERES and airborne radiometer calibration, inversion, and sampling). While the SW differences are within 2σ uncertainty, both approaches show a ∼−10 W m−2 average CERES-aircraft flux difference. Investigating the source of this negative difference, we find a substantial sensitivity of the flux differences to the sea ice concentration data set. Switching from imager-based to passive microwave-based sea ice data in the CERES inversion process reduces the differences in the grid box average fluxes and in the sea ice partly cloudy scene anisotropy in the matched footprints. In the long-term, more accurate sea ice concentration data are needed to reduce CERES TOA SW flux uncertainties. Switching from imager to passive microwave sea ice data, in the short-term, could improve CERES TOA SW fluxes in polar regions, additional testing is required. Our analysis indicates that calibration and sampling uncertainty limit the ability to place strong constraints ( CERES; sea ice; remote sensing; ARISE; polar energy budget; TOA radiative fluxes
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
Gristey, Jake J.; Su, Wenying; Loeb, Norman G.; Vonder Haar, Thomas H.; Tornow, Florian; Schmidt, K. Sebastian; Hakuba, Maria Z.; Pilewskie, Peter; Russell, Jacqueline E.Gristey, J. J., W. Su, N. G. Loeb, T. H. Vonder Haar, F. Tornow, K. S. Schmidt, M. Z. Hakuba, P. Pilewskie, J. E. Russell, 2021: Shortwave Radiance to Irradiance Conversion for Earth Radiation Budget Satellite Observations: A Review. Remote Sensing, 13(13), 2640. doi: 10.3390/rs13132640. Observing the Earth radiation budget (ERB) from satellites is crucial for monitoring and understanding Earth’s climate. One of the major challenges for ERB observations, particularly for reflected shortwave radiation, is the conversion of the measured radiance to the more energetically relevant quantity of radiative flux, or irradiance. This conversion depends on the solar-viewing geometry and the scene composition associated with each instantaneous observation. We first outline the theoretical basis for algorithms to convert shortwave radiance to irradiance, most commonly known as empirical angular distribution models (ADMs). We then review the progression from early ERB satellite observations that applied relatively simple ADMs, to current ERB satellite observations that apply highly sophisticated ADMs. A notable development is the dramatic increase in the number of scene types, made possible by both the extended observational record and the enhanced scene information now available from collocated imager information. Compared with their predecessors, current shortwave ADMs result in a more consistent average albedo as a function of viewing zenith angle and lead to more accurate instantaneous and mean regional irradiance estimates. One implication of the increased complexity is that the algorithms may not be directly applicable to observations with insufficient accompanying imager information, or for existing or new satellite instruments where detailed scene information is not available. Recent advances that complement and build on the base of current approaches, including machine learning applications and semi-physical calculations, are highlighted. angular distribution model; shortwave radiation; irradiance; radiance
Loeb, Norman G.; Su, Wenying; Bellouin, Nicolas; Ming, YiLoeb, N. G., W. Su, N. Bellouin, Y. Ming, 2021: Changes in Clear-Sky Shortwave Aerosol Direct Radiative Effects Since 2002. Journal of Geophysical Research: Atmospheres, 126(5), e2020JD034090. doi: https://doi.org/10.1029/2020JD034090. A new method for determining clear-sky shortwave aerosol direct radiative effects (ADRE) from the Clouds and the Earth's Radiant Energy System is used to examine changes in ADRE since 2002 alongside changes in aerosol optical depth (AOD) from the Moderate Resolution Spectroradiometer. At global scales, neither ADRE nor AOD show a significant trend. Over the northern hemisphere (NH), ADRE increases by 0.18 ± 0.17 Wm−2 per decade (less reflection to space) but shows no significant change over the southern hemisphere. The increase in the NH is primarily due to emission reductions in China, the United States, and Europe. The COVID-19 shutdown shows no noticeable impact on either global ADRE or AOD, but there is a substantial influence over northeastern China in March 2020. In contrast, February 2020 anomalies in ADRE and AOD are within natural variability even though the impact of the shutdown on industry was more pronounced in February than March. The reason is because February 2020 was exceptionally hot and humid over China, which compensated for reduced emissions. After accounting for meteorology and normalizing by incident solar flux, February ADRE anomalies increase substantially, exceeding the climatological mean ADRE by 23%. February and March 2020 correspond to the only period in which adjusted anomalies exceed the 95% confidence interval for 2 consecutive months. Distinct water-land differences over northeastern China are observed in ADRE but not in AOD. This is likely due to the influence of surface albedo on ADRE in the presence of absorbing aerosols.
Su, Wenying; Liang, Lusheng; Myhre, Gunnar; Thorsen, Tyler J.; Loeb, Norman G.; Schuster, Gregory L.; Ginoux, Paul; Paulot, Fabien; Neubauer, David; Checa-Garcia, Ramiro; Matsui, Hitoshi; Tsigaridis, Kostas; Skeie, Ragnhild B.; Takemura, Toshihiko; Bauer, Susanne E.; Schulz, MichaelSu, W., L. Liang, G. Myhre, T. J. Thorsen, N. G. Loeb, G. L. Schuster, P. Ginoux, F. Paulot, D. Neubauer, R. Checa-Garcia, H. Matsui, K. Tsigaridis, R. B. Skeie, T. Takemura, S. E. Bauer, M. Schulz, 2021: Understanding Top-of-Atmosphere Flux Bias in the AeroCom Phase III Models: A Clear-Sky Perspective. Journal of Advances in Modeling Earth Systems, 13(9), e2021MS002584. doi: 10.1029/2021MS002584. Biases in aerosol optical depths (AOD) and land surface albedos in the AeroCom models are manifested in the top-of-atmosphere (TOA) clear-sky reflected shortwave (SW) fluxes. Biases in the SW fluxes from AeroCom models are quantitatively related to biases in AOD and land surface albedo by using their radiative kernels. Over ocean, AOD contributes about 25% to the S–N mean SW flux bias for the multi-model mean (MMM) result. Over land, AOD and land surface albedo contribute about 40% and 30%, respectively, to the S–N mean SW flux bias for the MMM result. Furthermore, the spatial patterns of the SW flux biases derived from the radiative kernels are very similar to those between models and CERES observation, with the correlation coefficient of 0.6 over ocean and 0.76 over land for MMM using data of 2010. Satellite data used in this evaluation are derived independently from each other, consistencies in their bias patterns when compared with model simulations suggest that these patterns are robust. This highlights the importance of evaluating related variables in a synergistic manner to provide an unambiguous assessment of the models, as results from single parameter assessments are often confounded by measurement uncertainty. Model biases in land surface albedos can and must be corrected to accurately calculate TOA flux. We also compare the AOD trend from three models with the observation-based counterpart. These models reproduce all notable trends in AOD except the decreasing trend over eastern China and the adjacent oceanic regions due to limitations in the emission data set. aerosols; radiative flux; surface albedo
Loeb, Norman G.; Rose, Fred G.; Kato, Seiji; Rutan, David A.; Su, Wenying; Wang, Hailan; Doelling, David R.; Smith, William L.; Gettelman, AndrewLoeb, N. G., F. G. Rose, S. Kato, D. A. Rutan, W. Su, H. Wang, D. R. Doelling, W. L. Smith, A. Gettelman, 2020: Toward a Consistent Definition between Satellite and Model Clear-Sky Radiative Fluxes. J. Climate, 33(1), 61-75. doi: 10.1175/JCLI-D-19-0381.1. A new method of determining clear-sky radiative fluxes from satellite observations for climate model evaluation is presented. The method consists of applying adjustment factors to existing satellite clear-sky broadband radiative fluxes that make the observed and simulated clear-sky flux definitions more consistent. The adjustment factors are determined from the difference between observation-based radiative transfer model calculations of monthly mean clear-sky fluxes obtained by ignoring clouds in the atmospheric column and by weighting hourly mean clear-sky fluxes with imager-based clear-area fractions. The global mean longwave (LW) adjustment factor is −2.2 W m−2 at the top of the atmosphere and 2.7 W m−2 at the surface. The LW adjustment factors are pronounced at high latitudes during winter and in regions with high upper-tropospheric humidity and cirrus cloud cover, such as over the west tropical Pacific, and the South Pacific and intertropical convergence zones. In the shortwave (SW), global mean adjustment is 0.5 W m−2 at TOA and −1.9 W m−2 at the surface. It is most pronounced over sea ice off of Antarctica and over heavy aerosol regions, such as eastern China. However, interannual variations in the regional SW and LW adjustment factors are small compared to those in cloud radiative effect. After applying the LW adjustment factors, differences in zonal mean cloud radiative effect between observations and climate models decrease markedly between 60°S and 60°N and poleward of 65°N. The largest regional improvements occur over the west tropical Pacific and Indian Oceans. In contrast, the impact of the SW adjustment factors is much smaller.
Shankar, Mohan; Su, Wenying; Manalo-Smith, Natividad; Loeb, Norman G.Shankar, M., W. Su, N. Manalo-Smith, N. G. Loeb, 2020: Generation of a Seamless Earth Radiation Budget Climate Data Record: A New Methodology for Placing Overlapping Satellite Instruments on the Same Radiometric Scale. Remote Sensing, 12(17), 2787. doi: 10.3390/rs12172787. The Clouds and the Earth’s Radiant Energy System (CERES) instruments have enabled the generation of a multi-decadal Earth radiation budget (ERB) climate data record (CDR) at the top of the Earth’s atmosphere, within the atmosphere, and at the Earth’s surface. Six CERES instruments have been launched over the course of twenty years, starting in 1999. To seamlessly continue the data record into the future, there is a need to radiometrically scale observations from newly launched instruments to observations from the existing data record. In this work, we describe a methodology to place the CERES Flight Model (FM) 5 instrument on the Suomi National Polar-orbiting Partnership (SNPP) spacecraft on the same radiometric scale as the FM3 instrument on the Aqua spacecraft. We determine the required magnitude of radiometric scaling by using spatially and temporally matched observations from these two instruments and describe the process to radiometrically scale SNPP/FM5 to Aqua/FM3 through the instrument spectral response functions. We also present validation results after application of this radiometric scaling and demonstrate the long-term consistency of the SNPP/FM5 record in comparison with the CERES instruments on Aqua and Terra. calibration; radiation budget; radiometric scaling
Su, Wenying; Liang, Lusheng; Wang, Hailan; Eitzen, Zachary A.Su, W., L. Liang, H. Wang, Z. A. Eitzen, 2020: Uncertainties in CERES Top-of-Atmosphere Fluxes Caused by Changes in Accompanying Imager. Remote Sensing, 12(12), 2040. doi: 10.3390/rs12122040. The Clouds and the Earth’s Radiant Energy System (CERES) project provides observations of Earth’s radiation budget using measurements from CERES instruments on board the Terra, Aqua, Suomi National Polar-orbiting Partnership (S-NPP), and NOAA-20 satellites. The CERES top-of-atmosphere (TOA) fluxes are produced by converting radiance measurements using empirical angular distribution models, which are functions of cloud properties that are retrieved from imagers flying with the CERES instruments. As the objective is to create a long-term climate data record, not only calibration consistency of the six CERES instruments needs to be maintained for the entire time period, it is also important to maintain the consistency of other input data sets used to produce this climate data record. In this paper, we address aspects that could potentially affect the CERES TOA flux data quality. Discontinuities in imager calibration can affect cloud retrieval which can lead to erroneous flux trends. When imposing an artificial 0.6 per decade decreasing trend to cloud optical depth, which is similar to the trend difference between CERES Edition 2 and Edition 4 cloud retrievals, the decadal SW flux trend changed from − 0.3 5 ± 0.18 Wm − 2 to 0.61 ± 0.18 Wm − 2 . This indicates that a 13% change in cloud optical depth results in about 1% change in the SW flux. Furthermore, different CERES instruments provide valid fluxes at different viewing zenith angle ranges, and including fluxes derived at the most oblique angels unique to S-NPP (>66 ∘ ) can lead to differences of 0.8 Wm − 2 and 0.3 Wm − 2 in global monthly mean instantaneous SW flux and LW flux. To ensure continuity, the viewing zenith angle ranges common to all CERES instruments (<66 ∘ ) are used to produce the long-term Earth’s radiation budget climate data record. The consistency of cloud properties retrieved from different imagers also needs to be maintained to ensure the TOA flux consistency. cloud properties; angular distribution model; climate data record; Earth’s radiation budget
Su, Wenying; Minnis, Patrick; Liang, Lusheng; Duda, David P.; Khlopenkov, Konstantin; Thieman, Mandana M.; Yu, Yinan; Smith, Allan; Lorentz, Steven; Feldman, Daniel; Valero, Francisco P. J.Su, W., P. Minnis, L. Liang, D. P. Duda, K. Khlopenkov, M. M. Thieman, Y. Yu, A. Smith, S. Lorentz, D. Feldman, F. P. J. Valero, 2020: Determining the daytime Earth radiative flux from National Institute of Standards and Technology Advanced Radiometer (NISTAR) measurements. Atmospheric Measurement Techniques, 13(2), 429-443. doi: https://doi.org/10.5194/amt-13-429-2020. Abstract. The National Institute of Standards and Technology Advanced Radiometer (NISTAR) onboard the Deep Space Climate Observatory (DSCOVR) provides continuous full-disk global broadband irradiance measurements over most of the sunlit side of the Earth. The three active cavity radiometers measure the total radiant energy from the sunlit side of the Earth in shortwave (SW; 0.2–4 µm), total (0.4–100 µm), and near-infrared (NIR; 0.7–4 µm) channels. The Level 1 NISTAR dataset provides the filtered radiances (the ratio between irradiance and solid angle). To determine the daytime top-of-atmosphere (TOA) shortwave and longwave radiative fluxes, the NISTAR-measured shortwave radiances must be unfiltered first. An unfiltering algorithm was developed for the NISTAR SW and NIR channels using a spectral radiance database calculated for typical Earth scenes. The resulting unfiltered NISTAR radiances are then converted to full-disk daytime SW and LW flux by accounting for the anisotropic characteristics of the Earth-reflected and emitted radiances. The anisotropy factors are determined using scene identifications determined from multiple low-Earth orbit and geostationary satellites as well as the angular distribution models (ADMs) developed using data collected by the Clouds and the Earth's Radiant Energy System (CERES). Global annual daytime mean SW fluxes from NISTAR are about 6 % greater than those from CERES, and both show strong diurnal variations with daily maximum–minimum differences as great as 20 Wm−2 depending on the conditions of the sunlit portion of the Earth. They are also highly correlated, having correlation coefficients of 0.89, indicating that they both capture the diurnal variation. Global annual daytime mean LW fluxes from NISTAR are 3 % greater than those from CERES, but the correlation between them is only about 0.38.
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. satellite data; diurnal cycle; global energy budget; remote sensing; climate model validation; exoplanet studies
Várnai, Tamás; Gatebe, Charles; Gautam, Ritesh; Poudyal, Rajesh; Su, WenyingVárnai, T., C. Gatebe, R. Gautam, R. Poudyal, W. Su, 2019: Developing an Aircraft-Based Angular Distribution Model of Solar Reflection from Wildfire Smoke to Aid Satellite-Based Radiative Flux Estimation. Remote Sensing, 11(13), 1509. doi: 10.3390/rs11131509. This study examines the angular distribution of scattered solar radiation associated with wildfire smoke aerosols observed over boreal forests in Canada during the ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) campaign. First, it estimates smoke radiative parameters (550 nm optical depth of 3.9 and single scattering albedo of 0.90) using quasi-simultaneous multiangular and multispectral airborne measurements by the Cloud Absorption Radiometer (CAR). Next, the paper estimates the broadband top-of-atmosphere radiances that a satellite instrument such as the Clouds and the Earth’s Radiant Energy System (CERES) could have observed, given the narrowband CAR measurements made from an aircraft circling about a kilometer above the smoke layer. This estimation includes both an atmospheric correction that accounts for the atmosphere above the aircraft and a narrowband-to-broadband conversion. The angular distribution of estimated radiances is found to be substantially different than the angular model used in the operational data processing of CERES observations over the same area. This is because the CERES model is a monthly average model that was constructed using observations taken under smoke-free conditions. Finally, a sensitivity analysis shows that the estimated angular distribution remains accurate for a fairly wide range of smoke and underlying surface parameters. Overall, results from this work suggest that airborne CAR measurements can bring some substantial improvements in the accuracy of satellite-based radiative flux estimates. aerosol; angular distribution model; smoke; wildfire; Cloud Absorption Radiometer
Kato, Seiji; Rose, Fred G.; Rutan, David A.; Thorsen, Tyler J.; Loeb, Norman G.; Doelling, David R.; Huang, Xianglei; Smith, William L.; Su, Wenying; Ham, Seung HeeKato, S., F. G. Rose, D. A. Rutan, T. J. Thorsen, N. G. Loeb, D. R. Doelling, X. Huang, W. L. Smith, W. Su, S. H. Ham, 2018: Surface Irradiances of Edition 4.0 Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) Data Product. J. Climate, 31(11), 4501–4527. doi: 10.1175/JCLI-D-17-0523.1. The algorithm to produce the Clouds and the Earth’s Energy System (CERES) Ed4.0 Energy Balanced and Filled (EBAF)-surface data product is explained. The algorithm forces computed top-of-atmosphere (TOA) irradiances to match with Ed4.0 EBAF-TOA irradiances by adjusting surface, cloud and atmospheric properties. Surface irradiances are subsequently adjusted using radiative kernels. The adjustment process is composed of two parts, bias correction and Lagrange multiplier. The bias in temperature and specific humidity between 200 hPa and 500 hPa used for the irradiance computation is corrected based on observations by Atmospheric Infrared Sounder (AIRS). Similarly, the bias in the cloud fraction is corrected based on observations by Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), and CloudSat. Remaining errors in surface, cloud and atmospheric properties are corrected in the Lagrange multiplier process. Ed4.0 global annual mean (January 2005 thorough December 2014) surface net shortwave (SW) and longwave (LW) irradiances, respectively, increases by 1.3 Wm-2 and decreases by 0.2 Wm-2 compared to EBAF Ed2.8 counterparts (the previous version), resulting increasing in net SW+LW surface irradiance by 1.1 Wm-2. The uncertainty in surface irradiances over ocean, land and polar regions at various spatial scales are estimated. The uncertainties in all-sky global annual mean upward and downward shortwave irradiance are, respectively, 3 Wm-2 and 4 Wm-2, and the uncertainties in upward and downward longwave irradiance are respectively, 3 Wm-2 and 6 Wm-2. With an assumption of all errors being independent the uncertainty in the global annual mean surface LW+SW net irradiance is 8 Wm-2.
Loeb, Norman G.; Doelling, David R.; Wang, Hailan; Su, Wenying; Nguyen, Cathy; Corbett, Joseph G.; Liang, Lusheng; Mitrescu, Cristian; Rose, Fred G.; Kato, SeijiLoeb, N. G., D. R. Doelling, H. Wang, W. Su, C. Nguyen, J. G. Corbett, L. Liang, C. Mitrescu, F. G. Rose, S. Kato, 2018: Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) Top-of-Atmosphere (TOA) Edition 4.0 Data Product. J. Climate, 31(2), 895–918. doi: 10.1175/JCLI-D-17-0208.1. The Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) top-of-atmosphere (TOA) Ed4.0 data product is described. EBAF Ed4.0 is an update to EBAF Ed2.8, incorporating all of the Ed4.0 suite of CERES data product algorithm improvements and consistent input datasets throughout the record. A one-time adjustment to SW and LW TOA fluxes is made to ensure that global mean net TOA flux for July 2005-June 2015 is consistent with the in-situ value of 0.71 W m–2. While global mean all-sky TOA flux differences between Ed4.0 and Ed2.8 are within 0.5 Wm-2, appreciable SW regional differences occur over marine stratocumulus and snow/sea-ice regions. Marked regional differences in SW clear-sky TOA flux occur in polar regions and dust areas over ocean. Clear-sky LW TOA fluxes in EBAF Ed4.0 exceed Ed2.8 in regions of persistent high cloud cover. Owing to substantial differences in global mean clear-sky TOA fluxes, the net cloud radiative effect in EBAF Ed4.0 is -18 Wm-2 compared to -21 Wm-2 in EBAF Ed2.8. We estimate the overall uncertainty in 1°x1° latitude-longitude regional monthly all-sky TOA flux to be 3 Wm-2 (1σ) for the Terra-only period and 2.5 Wm-2 for the Terra-Aqua period both for SW and LW. The SW clear-sky regional monthly uncertainty is estimated to be 6 Wm-2 for the Terra-only period and 5 Wm-2 for the Terra-Aqua period. The LW clear-sky regional monthly uncertainty is 5 Wm-2 for Terra-only and 4.5 Wm-2 for Terra-Aqua.
Loeb, Norman G.; Thorsen, Tyler J.; Norris, Joel R.; Wang, Hailan; Su, WenyingLoeb, N. G., T. J. Thorsen, J. R. Norris, H. Wang, W. Su, 2018: Changes in Earth’s Energy Budget during and after the “Pause” in Global Warming: An Observational Perspective. Climate, 6(3), 62. doi: 10.3390/cli6030062. This study examines changes in Earth’s energy budget during and after the global warming “pause” (or “hiatus”) using observations from the Clouds and the Earth’s Radiant Energy System. We find a marked 0.83 ± 0.41 Wm−2 reduction in global mean reflected shortwave (SW) top-of-atmosphere (TOA) flux during the three years following the hiatus that results in an increase in net energy into the climate system. A partial radiative perturbation analysis reveals that decreases in low cloud cover are the primary driver of the decrease in SW TOA flux. The regional distribution of the SW TOA flux changes associated with the decreases in low cloud cover closely matches that of sea-surface temperature warming, which shows a pattern typical of the positive phase of the Pacific Decadal Oscillation. Large reductions in clear-sky SW TOA flux are also found over much of the Pacific and Atlantic Oceans in the northern hemisphere. These are associated with a reduction in aerosol optical depth consistent with stricter pollution controls in China and North America. A simple energy budget framework is used to show that TOA radiation (particularly in the SW) likely played a dominant role in driving the marked increase in temperature tendency during the post-hiatus period. clouds; energy budget; global warming hiatus
Su, Wenying; Liang, Lusheng; Doelling, David R.; Minnis, Patrick; Duda, David P.; Khlopenkov, Konstantin V.; Thieman, Mandana M.; Loeb, Norman G.; Kato, Seiji; Valero, Francisco P. J.; Wang, Hailan; Rose, Fred G.Su, W., L. Liang, D. R. Doelling, P. Minnis, D. P. Duda, K. V. Khlopenkov, M. M. Thieman, N. G. Loeb, S. Kato, F. P. J. Valero, H. Wang, F. G. Rose, 2018: Determining the Shortwave Radiative Flux from Earth Polychromatic Imaging Camera. Journal of Geophysical Research: Atmospheres, 123(20), 11,479-11,491. doi: 10.1029/2018JD029390. The Earth Polychromatic Imaging Camera (EPIC) onboard Deep Space Climate Observatory (DSCOVR) provides 10 narrowband spectral images of the sunlit side of the Earth. The blue (443 nm), green (551 nm), and red (680 nm) channels are used to derive EPIC broadband radiances based upon narrowband-to-broadband regressions developed using collocated MODIS equivalent channels and CERES broadband measurements. The pixel-level EPIC broadband radiances are averaged to provide global daytime means at all applicable EPIC times. They are converted to global daytime mean shortwave (SW) fluxes by accounting for the anisotropy characteristics using a cloud property composite based on lower Earth orbiting satellite imager retrievals and the CERES angular distribution models (ADMs). Global daytime mean SW fluxes show strong diurnal variations with daily maximum-minimum differences as great as 20 Wm−2 depending on the conditions of the sunlit portion of the Earth. The EPIC SW fluxes are compared against the CERES SYN1deg hourly SW fluxes. The global monthly mean differences (EPIC-SYN) between them range from 0.1 Wm−2 in July to -4.1 Wm−2 in January, and the RMS errors range from 3.2 Wm−2 to 5.2 Wm−2. Daily mean EPIC and SYN fluxes calculated using concurrent hours agree with each other to within 2% and both show a strong annual cycle. The SW flux agreement is within the calibration and algorithm uncertainties, which indicates that the method developed to calculate the global anisotropic factors from the CERES ADMs is robust and that the CERES ADMs accurately account for the Earth's anisotropy in the near-backscatter direction. CERES; angular distribution model; radiation; DSCOVR; EPIC; Lagrange-1 point
Eitzen, Zachary A.; Su, Wenying; Xu, Kuan-Man; Loeb, Norman; Sun, Moguo; Doelling, David; Rose, Fred; Bodas-Salcedo, AlejandroEitzen, Z. A., W. Su, K. Xu, N. Loeb, M. Sun, D. Doelling, F. Rose, A. Bodas-Salcedo, 2017: Evaluation of a general circulation model by the CERES Flux-by-cloud type simulator. Journal of Geophysical Research: Atmospheres, 122(20), 10,655–10,668. doi: 10.1002/2017JD027076. In this work, we use the CERES FluxByCloudTyp data product (FBCTObs), which calculates TOA shortwave and longwave fluxes for cloud types defined by cloud optical depth (τ) and cloud top pressure (pc), and the CERES Flux-by-cloud type simulator (FBCTSim) to evaluate the HadGEM2-A model. FBCTSim is comprised of a cloud generator that produces subcolumns with profiles of binary cloud fraction, a cloud property simulator that determines the cloud type (τ, pc) for each subcolumn, and a radiative transfer model that calculates TOA fluxes. The identification of duplicate subcolumns greatly reduces the number of radiative transfer calculations required. In the Southern Great Plains region in January, February, and December (JFD) 2008, FBCTSim shows that HadGEM2-A cloud tops are higher in altitude than in FBCTObs, but also have higher values of OLR than in FBCTObs, leading to a compensating error that results in an average value of OLR that is close to observed. When FBCTSim is applied to the Southeast Pacific stratocumulus region in JJA 2008, the cloud tops are primarily low in altitude; however, the clouds tend to be less numerous, and have higher optical depths than are observed. In addition, the HadGEM2-A albedo is higher than that of FBCTObs for those cloud types that occur most frequently. FBCTSim is also applied to the entire 60° N to 60° S region, and it is found that there are both fewer clouds and higher albedos than observed for most cloud types, which represents a compensating error in terms of the shortwave radiative budget. CERES; 0321 Cloud/radiation interaction; 3337 Global climate models; 3394 Instruments and techniques; 3360 Remote sensing; model evaluation; Instrument simulator
Khlopenkov, Konstantin; Duda, David; Thieman, Mandana; Minnis, Patrick; Su, Wenying; Bedka, KristopherKhlopenkov, K., D. Duda, M. Thieman, P. Minnis, W. Su, K. Bedka, 2017: Development of multi-sensor global cloud and radiance composites for earth radiation budget monitoring from DSCOVR. doi: 10.1117/12.2278645. The Deep Space Climate Observatory (DSCOVR) enables analysis of the daytime Earth radiation budget via the onboard Earth Polychromatic Imaging Camera (EPIC) and National Institute of Standards and Technology Advanced Radiometer (NISTAR). Radiance observations and cloud property retrievals from low earth orbit and geostationary satellite imagers have to be co-located with EPIC pixels to provide scene identification in order to select anisotropic directional models needed to calculate shortwave and longwave fluxes. A new algorithm is proposed for optimal merging of selected radiances and cloud properties derived from multiple satellite imagers to obtain seamless global hourly composites at 5-km resolution. An aggregated rating is employed to incorporate several factors and to select the best observation at the time nearest to the EPIC measurement. Spatial accuracy is improved using inverse mapping with gradient search during reprojection and bicubic interpolation for pixel resampling. The composite data are subsequently remapped into EPIC-view domain by convolving composite pixels with the EPIC point spread function defined with a half-pixel accuracy. PSF-weighted average radiances and cloud properties are computed separately for each cloud phase. The algorithm has demonstrated contiguous global coverage for any requested time of day with a temporal lag of under 2 hours in over 95% of the globe.
Su, W.; Liang, L.; Miller, W. F.; Sothcott, V. E.Su, W., L. Liang, W. F. Miller, V. E. Sothcott, 2017: The effects of different footprint sizes and cloud algorithms on the top-of-atmosphere radiative flux calculation from the Clouds and Earth's Radiant Energy System (CERES) instrument on Suomi National Polar-orbiting Partnership (NPP). Atmos. Meas. Tech., 10(10), 4001-4011. doi: 10.5194/amt-10-4001-2017. Only one Clouds and Earth's Radiant Energy System (CERES) instrument is onboard the Suomi National Polar-orbiting Partnership (NPP) and it has been placed in cross-track mode since launch; it is thus not possible to construct a set of angular distribution models (ADMs) specific for CERES on NPP. Edition 4 Aqua ADMs are used for flux inversions for NPP CERES measurements. However, the footprint size of NPP CERES is greater than that of Aqua CERES, as the altitude of the NPP orbit is higher than that of the Aqua orbit. Furthermore, cloud retrievals from the Visible Infrared Imaging Radiometer Suite (VIIRS) and the Moderate Resolution Imaging Spectroradiometer (MODIS), which are the imagers sharing the spacecraft with NPP CERES and Aqua CERES, are also different. To quantify the flux uncertainties due to the footprint size difference between Aqua CERES and NPP CERES, and due to both the footprint size difference and cloud property difference, a simulation is designed using the MODIS pixel-level data, which are convolved with the Aqua CERES and NPP CERES point spread functions (PSFs) into their respective footprints. The simulation is designed to isolate the effects of footprint size and cloud property differences on flux uncertainty from calibration and orbital differences between NPP CERES and Aqua CERES. The footprint size difference between Aqua CERES and NPP CERES introduces instantaneous flux uncertainties in monthly gridded NPP CERES measurements of less than 4.0 W m−2 for SW (shortwave) and less than 1.0 W m−2 for both daytime and nighttime LW (longwave). The global monthly mean instantaneous SW flux from simulated NPP CERES has a low bias of 0.4 W m−2 when compared to simulated Aqua CERES, and the root-mean-square (RMS) error is 2.2 W m−2 between them; the biases of daytime and nighttime LW flux are close to zero with RMS errors of 0.8 and 0.2 W m−2. These uncertainties are within the uncertainties of CERES ADMs. When both footprint size and cloud property (cloud fraction and optical depth) differences are considered, the uncertainties of monthly gridded NPP CERES SW flux can be up to 20 W m−2 in the Arctic regions where cloud optical depth retrievals from VIIRS differ significantly from MODIS. The global monthly mean instantaneous SW flux from simulated NPP CERES has a high bias of 1.1 W m−2 and the RMS error increases to 5.2 W m−2. LW flux shows less sensitivity to cloud property differences than SW flux, with uncertainties of about 2 W m−2 in the monthly gridded LW flux, and the RMS errors of global monthly mean daytime and nighttime fluxes increase only slightly. These results highlight the importance of consistent cloud retrieval algorithms to maintain the accuracy and stability of the CERES climate data record.
Su, Wenying; Loeb, Norman G.; Liang, Lusheng; Liu, Nana; Liu, ChuntaoSu, W., N. G. Loeb, L. Liang, N. Liu, C. Liu, 2017: The El Niño-Southern Oscillation Effect on Tropical Outgoing Longwave Radiation: A Daytime Versus Nighttime Perspective. Journal of Geophysical Research: Atmospheres, 122(15), 7820–7833. doi: 10.1002/2017JD027002. Trends of tropical (30° N-30° S) mean daytime and nighttime outgoing longwave radiation (OLR) from CERES and AIRS are analyzed using data from 2003 to 2013. Both the daytime and nighttime OLR from these instruments show decreasing trends because of El Niño conditions early in the period and La Niña conditions at the end. However, the daytime and nighttime OLR decrease at different rates with the OLR decreasing faster during daytime than nighttime. The daytime-nighttime OLR trend is consistent across CERES Terra, Aqua observations, and computed OLR based upon AIRS and MODIS retrievals. To understand the cause of the differing decreasing rates of daytime and nighttime OLR, high cloud fraction and effective temperature are examined using cloud retrievals from MODIS and AIRS. Unlike the very consistent OLR trends between CERES and AIRS, the trends in cloud properties are not as consistent, which is likely due to the different cloud retrieval methods used. When MODIS and AIRS cloud properties are used to compute OLR, the daytime and nighttime OLR trends based upon MODIS cloud properties are approximately half as large as the trends from AIRS cloud properties, but their daytime-nighttime OLR trends are in agreement. This demonstrates that though the current cloud retrieval algorithms lack the accuracy to pinpoint the changes of daytime and nighttime clouds in the tropics, they do provide a radiatively-consistent view for daytime and nighttime OLR changes. The causes for the larger decreasing daytime OLR trend than that for nighttime OLR are not clear and further studies are needed. clouds; 0321 Cloud/radiation interaction; ENSO; outgoing longwave radiation
Wang, Hailan; Su, Wenying; Loeb, Norman G.; Achuthavarier, Deepthi; Schubert, Siegfried D.Wang, H., W. Su, N. G. Loeb, D. Achuthavarier, S. D. Schubert, 2017: The Role of DYNAMO In-situ Observations in Improving NASA CERES-like Daily Surface and Atmospheric Radiative Flux Estimates. Earth and Space Science, 4(4), 164–183. doi: 10.1002/2016EA000248. The daily surface and atmospheric radiative fluxes from NASA Clouds and the Earth's Radiant Energy System (CERES) SYN1deg Ed3A are among the most widely used data to study cloud-radiative feedback. The CERES SYN1deg data are based on Fu-Liou radiative transfer computations that use specific humidity (Q) and air temperature (T) from NASA Global Modeling and Assimilation Office (GMAO) reanalyses as inputs, and are therefore subject to the quality of those fields. This study uses in-situ Q and T observations collected during the Dynamics of the Madden-Julian Oscillation (DYNAMO) field campaign to augment the input stream used in the NASA GMAO reanalysis and assess the impact on the CERES daily surface and atmospheric longwave estimates. The results show that the assimilation of DYNAMO observations considerably improves the vertical profiles of analyzed Q and T over and near DYNAMO stations by moistening and warming the lower troposphere and upper troposphere and drying and cooling the mid-upper troposphere. As a result of these changes in Q and T, the computed CERES daily surface downward longwave flux increases by about 5 Wm-2, due mainly to the warming and moistening in the lower troposphere; the computed daily top-of-atmosphere (TOA) outgoing longwave radiation increases by 2-3 Wm-2 during dry periods only. Correspondingly, the estimated local atmospheric longwave radiative cooling enhances by about 5 Wm-2 (7-8 Wm-2) during wet (dry) periods. These changes reduce the bias in the CERES SYN1deg-like daily longwave estimates at both the TOA and surface, and represent an improvement over the DYNAMO region. This article is protected by copyright. All rights reserved. 1616 Climate variability; 3315 Data assimilation; 0434 Data sets; 7847 Radiation processes; CERES surface and atmospheric radiation estimation; DYNAMO in-situ observations; NASA GMAO reanalysis
Loeb, N. G.; Su, W.; Doelling, D. R.; Wong, T.; Minnis, P.; Thomas, S.; Miller, W. F.Loeb, N. G., W. Su, D. R. Doelling, T. Wong, P. Minnis, S. Thomas, W. F. Miller, 2016: Earth's Top-of-Atmosphere Radiation Budget. Reference Module in Earth Systems and Environmental Sciences. The top-of-atmosphere (TOA) Earth radiation budget (ERB) is a key property of the climate system that describes the balance between how much solar energy the Earth absorbs and how much terrestrial thermal infrared radiation it emits. This article provides an overview of the instruments and algorithms used to observe the TOA ERB by the Clouds and the Earth's Radiant Energy System (CERES) project. We summarize the properties of the CERES instruments, their calibration, combined use of CERES and imager measurements for improved cloud-radiation properties, and the approaches used for time interpolation and space averaging of TOA radiative fluxes. calibration; clouds; longwave; shortwave; broadband; CERES; climate; radiation budget; top-of-atmosphere; flux; Time interpolation
Loeb, Norman G.; Manalo-Smith, Natividad; Su, Wenying; Shankar, Mohan; Thomas, SusanLoeb, N. G., N. Manalo-Smith, W. Su, M. Shankar, S. Thomas, 2016: CERES Top-of-Atmosphere Earth Radiation Budget Climate Data Record: Accounting for in-Orbit Changes in Instrument Calibration. Remote Sensing, 8(3), 182. doi: 10.3390/rs8030182. The Clouds and the Earth’s Radiant Energy System (CERES) project provides observations of Earth’s radiation budget using measurements from CERES instruments onboard the Terra, Aqua and Suomi National Polar-orbiting Partnership (S-NPP) satellites. As the objective is to create a long-term climate data record, it is necessary to periodically reprocess the data in order to incorporate the latest calibration changes and algorithm improvements. Here, we focus on the improvements and validation of CERES Terra and Aqua radiances in Edition 4, which are used to generate higher-level climate data products. Onboard sources indicate that the total (TOT) channel response to longwave (LW) radiation has increased relative to the start of the missions by 0.4% to 1%. In the shortwave (SW), the sensor response change ranges from −0.4% to 0.6%. To account for in-orbit changes in SW spectral response function (SRF), direct nadir radiance comparisons between instrument pairs on the same satellite are made and an improved wavelength dependent degradation model is used to adjust the SRF of the instrument operating in a rotating azimuth plane scan mode. After applying SRF corrections independently to CERES Terra and Aqua, monthly variations amongst these instruments are highly correlated and the standard deviation in the difference of monthly anomalies is 0.2 Wm−2 for ocean and 0.3 Wm−2 for land/desert. Additionally, trends in CERES Terra and Aqua monthly anomalies are consistent to 0.21 Wm−2 per decade for ocean and 0.31 Wm−2 per decade for land/desert. In the LW, adjustments to the TOT channel SRF are made to ensure that removal of the contribution from the SW portion of the TOT channel with SW channel radiance measurements during daytime is consistent throughout the mission. Accordingly, anomalies in day–night LW difference in Edition 4 are more consistent compared to Edition 3, particularly for the Aqua land/desert case. calibration; earth radiation budget; Satellite; climate; Radiance
Corbett, J.; Su, W.Corbett, J., W. Su, 2015: Accounting for the effects of Sastrugi in the CERES Clear-Sky Antarctic shortwave ADMs. Atmos. Meas. Tech. Discuss., 8(1), 375-404. doi: 10.5194/amtd-8-375-2015. The Cloud and Earth's Radiant Energy System (CERES) Instruments on NASA's Terra, Aqua and Soumi-NPP satellites are used to provide a long-term measurement of the Earth's energy budget. To accomplish this, the radiances measured by the instruments must be inverted to fluxes by the use of a scene-type dependent angular distribution model (ADM). For permanent snow scenes over Antarctica, shortwave ADMs are created by compositing radiance measurements over the full viewing zenith and azimuth range. However, the presence of small-scale wind blown roughness features called sastrugi cause the BRDF of the snow to vary significantly based upon the solar azimuth angle and location. This can result in monthly regional biases as large as ±15 Wm−2 in the inverted TOA SW flux. In this paper we created a set of ADMs that account for the sastrugi effect by using measurements from the Multi-Angle Imaging Spectro-Radiometer (MISR) instrument to derive statistical relationships between radiance from different viewing angles. These ADMs reduce the monthly regional biases to ±5 Wm−2 and the monthly-mean biases are reduced by up to 50%. These improved ADMs are used as part of the next edition of the CERES data.
Su, W.; Corbett, J.; Eitzen, Z.; Liang, L.Su, W., J. Corbett, Z. Eitzen, L. Liang, 2015: Next-generation angular distribution models for top-of-atmosphere radiative flux calculation from CERES instruments: methodology. Atmos. Meas. Tech., 8(2), 611-632. doi: 10.5194/amt-8-611-2015. The top-of-atmosphere (TOA) radiative fluxes are critical components to advancing our understanding of the Earth's radiative energy balance, radiative effects of clouds and aerosols, and climate feedback. The Clouds and the Earth's Radiant Energy System (CERES) instruments provide broadband shortwave and longwave radiance measurements. These radiances are converted to fluxes by using scene-type-dependent angular distribution models (ADMs). This paper describes the next-generation ADMs that are developed for Terra and Aqua using all available CERES rotating azimuth plane radiance measurements. Coincident cloud and aerosol retrievals, and radiance measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS), and meteorological parameters from Goddard Earth Observing System (GEOS) data assimilation version 5.4.1 are used to define scene type. CERES radiance measurements are stratified by scene type and by other parameters that are important for determining the anisotropy of the given scene type. Anisotropic factors are then defined either for discrete intervals of relevant parameters or as a continuous functions of combined parameters, depending on the scene type. Significant differences between the ADMs described in this paper and the existing ADMs are over clear-sky scene types and polar scene types. Over clear ocean, we developed a set of shortwave (SW) ADMs that explicitly account for aerosols. Over clear land, the SW ADMs are developed for every 1° latitude × 1° longitude region for every calendar month using a kernel-based bidirectional reflectance model. Over clear Antarctic scenes, SW ADMs are developed by accounting the effects of sastrugi on anisotropy. Over sea ice, a sea-ice brightness index is used to classify the scene type. Under cloudy conditions over all surface types, the longwave (LW) and window (WN) ADMs are developed by combining surface and cloud-top temperature, surface and cloud emissivity, cloud fraction, and precipitable water. Compared to the existing ADMs, the new ADMs change the monthly mean instantaneous fluxes by up to 5 W m−2 on a regional scale of 1° latitude × 1° longitude, but the flux changes are less than 0.5 W m−2 on a global scale.
Su, W.; Corbett, J.; Eitzen, Z.; Liang, L.Su, W., J. Corbett, Z. Eitzen, L. Liang, 2015: Next-generation angular distribution models for top-of-atmosphere radiative flux calculation from CERES instruments: validation. Atmos. Meas. Tech., 8(8), 3297-3313. doi: 10.5194/amt-8-3297-2015. Radiative fluxes at the top of the atmosphere (TOA) from the Clouds and the Earth's Radiant Energy System (CERES) instrument are fundamental variables for understanding the Earth's energy balance and how it changes with time. TOA radiative fluxes are derived from the CERES radiance measurements using empirical angular distribution models (ADMs). This paper evaluates the accuracy of CERES TOA fluxes using direct integration and flux consistency tests. Direct integration tests show that the overall bias in regional monthly mean TOA shortwave (SW) flux is less than 0.2 Wm−2 and the RMSE is less than 1.1 Wm−2. The bias and RMSE are very similar between Terra and Aqua. The bias in regional monthly mean TOA LW fluxes is less than 0.5 Wm−2 and the RMSE is less than 0.8 Wm−2 for both Terra and Aqua. The accuracy of the TOA instantaneous flux is assessed by performing tests using fluxes inverted from nadir- and oblique-viewing angles using CERES along-track observations and temporally and spatially matched MODIS observations, and using fluxes inverted from multi-angle MISR observations. The averaged TOA instantaneous SW flux uncertainties from these two tests are about 2.3 % (1.9 Wm−2) over clear ocean, 1.6 % (4.5 Wm−2) over clear land, and 2.0 % (6.0 Wm−2) over clear snow/ice; and are about 3.3 % (9.0 Wm−2), 2.7 % (8.4 Wm−2), and 3.7 % (9.9 Wm−2) over ocean, land, and snow/ice under all-sky conditions. The TOA SW flux uncertainties are generally larger for thin broken clouds than for moderate and thick overcast clouds. The TOA instantaneous daytime LW flux uncertainties derived from the CERES-MODIS test are 0.5 % (1.5 Wm−2), 0.8 % (2.4 Wm−2), and 0.7 % (1.3 Wm−2) over clear ocean, land, and snow/ice; and are about 1.5 % (3.5 Wm−2), 1.0 % (2.9 Wm−2), and 1.1 % (2.1 Wm−2) over ocean, land, and snow/ice under all-sky conditions. The TOA instantaneous nighttime LW flux uncertainties are about 0.5–1 % (< 2.0 Wm−2) for all surface types. Flux uncertainties caused by errors in scene identification are also assessed by using the collocated CALIPSO, CloudSat, CERES and MODIS data product. Errors in scene identification tend to underestimate TOA SW flux by about 0.6 Wm−2 and overestimate TOA daytime (nighttime) LW flux by 0.4 (0.2) Wm−2 when all CERES viewing angles are considered.
Wang, Hailan; Su, WenyingWang, H., W. Su, 2015: The ENSO effects on tropical clouds and top-of-atmosphere cloud radiative effects in CMIP5 models. Journal of Geophysical Research: Atmospheres, 120(10), 4443–4465. doi: 10.1002/2014JD022337. The El Niño–Southern Oscillation (ENSO) effects on tropical clouds and top-of-atmosphere (TOA) cloud radiative effects (CREs) in Coupled Model Intercomparison Project Phase 5 (CMIP5) models are evaluated using satellite-based observations and International Satellite Cloud Climatology Project satellite simulator output. Climatologically, most CMIP5 models produce considerably less total cloud amount with higher cloud top and notably larger reflectivity than observations in tropical Indo-Pacific (60°E-200°E; 10°S-10°N). During ENSO, most CMIP5 models strongly underestimate TOA CRE and cloud changes over western tropical Pacific. Over central tropical Pacific, while the multi-model mean resembles observations in TOA CRE and cloud amount anomalies, it notably overestimates cloud top pressure (CTP) decreases; there are also substantial inter-model variations. The relative effects of changes in cloud properties, temperature, and humidity on TOA CRE anomalies during ENSO in the CMIP5 models are assessed using cloud radiative kernels. The CMIP5 models agree with observations in that their TOA shortwave CRE anomalies are primarily contributed by total cloud amount changes, and their TOA longwave CRE anomalies are mostly contributed by changes in both total cloud amount and CTP. The model biases in TOA CRE anomalies particularly the strong underestimations over western tropical Pacific are, however, mainly explained by model biases in CTP and cloud optical thickness (τ) changes. Despite the distinct model climatological cloud biases particularly in τ regime, the TOA CRE anomalies from total cloud amount changes are comparable between the CMIP5 models and observations, because of the strong compensations between model underestimation of TOA CRE anomalies from thin clouds and overestimation from medium and thick clouds. cloud; 0321 Cloud/radiation interaction; 4522 ENSO; cloud radiative effect; Global climate models; El Niño–Southern Oscillation
Su, W.; Corbett, J.; Eitzen, Z.; Liang, L.Su, W., J. Corbett, Z. Eitzen, L. Liang, 2014: Next-generation angular distribution models for top-of-atmosphere radiative flux calculation from the CERES instruments: methodology. Atmos. Meas. Tech. Discuss., 7(8), 8817-8880. doi: 10.5194/amtd-7-8817-2014. The top-of-atmosphere (TOA) radiative fluxes are critical components to advancing our understanding of the Earth's radiative energy balance, radiative effects of clouds and aerosols, and climate feedback. The Clouds and Earth's Radiant Energy System (CERES) instruments provide broadband shortwave and longwave radiance measurements. These radiances are converted to fluxes by using scene type dependent Angular Distribution Models (ADMs). This paper describes the next-generation ADMs that are developed for Terra and Aqua using all available CERES rotating azimuth plane radiance measurements. Coincident cloud and aerosol retrievals, and radiance measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS), and meteorological parameters from Goddard Earth Observing System (GEOS) data assimilation version 5.4.1 are used to define scene type. CERES radiance measurements are stratified by scene type and by other parameters that are important for determining the anisotropy of the given scene type. Anisotropic factors are then defined either for discrete intervals of relevant parameters or as a continuous functions of combined parameters, depending on the scene type. Compared to the existing ADMs, the new ADMs change the monthly mean instantaneous fluxes by up to 5 W m−2 on a regional scale of 1° latitude × 1° longitude, but the flux changes are less than 0.5 W m−2 on a global scale.
Su, Wenying; Loeb, Norman G.; Schuster, Gregory L.; Chin, Mian; Rose, Fred G.Su, W., N. G. Loeb, G. L. Schuster, M. Chin, F. G. Rose, 2013: Global all-sky shortwave direct radiative forcing of anthropogenic aerosols from combined satellite observations and GOCART simulations. Journal of Geophysical Research: Atmospheres, 118(2), 655–669. doi: 10.1029/2012JD018294. Estimation of aerosol direct radiative forcing (DRF) from satellite measurements is challenging because current satellite sensors do not have the capability of discriminating between anthropogenic and natural aerosols. We combine 3-hourly cloud properties from satellite retrievals with two aerosol data sets to calculate the all-sky aerosol direct radiative effect (DRE), which is the mean radiative perturbation due to the presence of both natural and anthropogenic aerosols. The first aerosol data set is based upon Moderate Resolution Imaging Spectroradiometer (MODIS) and Model for Atmospheric Transport and Chemistry (MATCH) assimilation model and is largely constrained by MODIS aerosol optical depth, but it does not distinguish between anthropogenic and natural aerosols. The other aerosol data set is based upon the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model, which does not assimilate aerosol observations but predicts the anthropogenic and natural components of aerosols. Thus, we can calculate the aerosol DRF using GOCART classifications of anthropogenic and natural aerosols and the ratio of DRF to DRE. We then apply this ratio to DRE calculated using MODIS/MATCH aerosols to partition it into DRF (MODIS/MATCH DRF) by assuming that the anthropogenic fractions from GOCART are representative. The global (60°N 60°S) mean all-sky MODIS/MATCH DRF is −0.51 Wm−2 at the top of the atmosphere (TOA), 2.51 Wm−2 within the atmosphere, and −3.02 Wm−2 at the surface. The GOCART all-sky DRF is −0.17 Wm−2 at the TOA, 2.02 Wm−2 within the atmosphere, and −2.19 Wm−2 at the surface. The differences between MODIS/MATCH DRF and GOCART DRF are solely due to the differences in aerosol properties, since both computations use the same cloud properties and surface albedo and the same proportion of anthropogenic contributions to aerosol DRE. Aerosol optical depths simulated by the GOCART model are smaller than those in MODIS/MATCH, and aerosols in the GOCART model are more absorbing than those in MODIS/MATCH. Large difference in all-sky TOA DRF from these two aerosol data sets highlights the complexity in determining the all-sky DRF, since the presence of clouds amplifies the sensitivities of DRF to aerosol single-scattering albedo and aerosol vertical distribution. clouds; aerosol; direct radiative effect; direct radiative forcing
Wang, Hailan; Su, WenyingWang, H., W. Su, 2013: Evaluating and understanding top of the atmosphere cloud radiative effects in Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) Coupled Model Intercomparison Project Phase 5 (CMIP5) models using satellite observations. Journal of Geophysical Research-Atmospheres, 118(2), 683-699. doi: 10.1029/2012JD018619. In this study, the annual mean climatology of top of the atmosphere (TOA) shortwave and longwave cloud radiative effects in 12 Atmospheric Model Intercomparison Project (AMIP)-type simulations participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) is evaluated and investigated using satellite-based observations, with a focus on the tropics. Results show that the CMIP5 AMIPs simulate large-scale regional mean TOA radiative fluxes and cloud radiative forcings (CRFs) well but produce considerably less cloud amount, particularly in the middle and lower troposphere. The good model simulations in tropical means, with multimodel mean biases of -3.6 W/m(2) for shortwave CRF and -1.0 W/m(2) for longwave CRF, are, however, a result of compensating errors over different dynamical regimes. Over the Maritime Continent, most of the models simulate moderately less high-cloud fraction, leading to weaker shortwave cooling and longwave warming and a larger net cooling. Over subtropical strong subsidence regimes, most of the CMIP5 models strongly underestimate stratocumulus cloud amount and show considerably weaker local shortwave CRF. Over the transitional trade cumulus regimes, a notable feature is that while at varying amplitudes, most of the CMIP5 models consistently simulate a deeper and drier boundary layer, more moist free troposphere, and more high clouds and, consequently, overestimate shortwave cooling and longwave warming effects there. While most of the CMIP5 models show the same sign as the multimodel mean, there are substantial model spreads, particularly over the tropical deep convective and subtropical strong subsidence regimes. Representing clouds and their TOA radiative effects remains a challenge in the CMIP5 models. radiative flux; cloud fraction; cloud radiative effect; global climate model; budget experiment; general-circulation models; impact; performance; relative humidity; surface; system
Corbett, J. G.; Su, W.; Loeb, N. G.Corbett, J. G., W. Su, N. G. Loeb, 2012: Observed effects of sastrugi on CERES top-of-atmosphere clear-sky reflected shortwave flux over Antarctica. Journal of Geophysical Research: Atmospheres, 117(D18), D18104. doi: 10.1029/2012JD017529. Determining the clear-sky top-of-atmosphere (TOA) albedo over snow from space requires knowledge of the bi-directional reflectance distribution function (BRDF), which itself is strongly influenced by the surface roughness of the snow. Sastrugi, a common element of surface roughness on Antarctica, tend to have a preferred azimuth direction, meaning the BRDF depends on the location and time of sampling. In this study we demonstrate that a sastrugi signal is present in the Clouds and the Earth's Radiant Energy System (CERES) reflectance measurements and TOA albedo estimates, leading to a spurious variation in instantaneous albedo as a function of solar azimuth of up to 0.08. By using the difference in flux between oblique and nadir views, we estimate the biases in monthly- and annual-mean 24-hour energy weighted clear-sky reflected TOA fluxes caused by sastrugi over Antarctica. At the grid box level, statistically significant monthly-mean biases of between ±15 Wm−2are found. For the entire Antarctic continent, monthly-mean biases are between 0.2 ± 0.9 Wm−2 to −1.7 ± 1.1 Wm−2 where a negative bias indicates the reflected flux is being underestimated. On an annual basis, the Antarctic bias is between −0.9 ± 1.1 Wm−2 and −1.0 ± 1.1 Wm−2. For the global annual mean clear-sky TOA flux, the bias caused by the presence of sastrugi is insignificant, −0.01 ± 0.02 Wm−2. By examining the anisotropy and the wind direction we infer that the negative TOA flux biases are likely to caused by sastrugi perpendicular to the solar azimuth whereas the positive TOA flux biases are likely to be caused by sastrugi parallel to the solar azimuth. CERES; albedo; 3359 Radiative processes; 0758 Remote sensing; 0736 Snow; Antarctica; sastrugi
Loeb, Norman G.; Kato, Seiji; Su, Wenying; Wong, Takmeng; Rose, Fred G.; Doelling, David R.; Norris, Joel R.; Huang, XiangleiLoeb, N. G., S. Kato, W. Su, T. Wong, F. G. Rose, D. R. Doelling, J. R. Norris, X. Huang, 2012: Advances in Understanding Top-of-Atmosphere Radiation Variability from Satellite Observations. Surveys in Geophysics, 33(3-4), 359-385. doi: 10.1007/s10712-012-9175-1. This paper highlights how the emerging record of satellite observations from the Earth Observation System (EOS) and A-Train constellation are advancing our ability to more completely document and understand the underlying processes associated with variations in the Earth’s top-of-atmosphere (TOA) radiation budget. Large-scale TOA radiation changes during the past decade are observed to be within 0.5 Wm−2 per decade based upon comparisons between Clouds and the Earth’s Radiant Energy System (CERES) instruments aboard Terra and Aqua and other instruments. Tropical variations in emitted outgoing longwave (LW) radiation are found to closely track changes in the El Niño-Southern Oscillation (ENSO). During positive ENSO phase (El Niño), outgoing LW radiation increases, and decreases during the negative ENSO phase (La Niña). The coldest year during the last decade occurred in 2008, during which strong La Nina conditions persisted throughout most of the year. Atmospheric Infrared Sounder (AIRS) observations show that the lower temperatures extended throughout much of the troposphere for several months, resulting in a reduction in outgoing LW radiation and an increase in net incoming radiation. At the global scale, outgoing LW flux anomalies are partially compensated for by decreases in midlatitude cloud fraction and cloud height, as observed by Moderate Resolution Imaging Spectrometer and Multi-angle Imaging SpectroRadiometer, respectively. CERES data show that clouds have a net radiative warming influence during La Niña conditions and a net cooling influence during El Niño, but the magnitude of the anomalies varies greatly from one ENSO event to another. Regional cloud-radiation variations among several Terra and A-Train instruments show consistent patterns and exhibit marked fluctuations at monthly timescales in response to tropical atmosphere-ocean dynamical processes associated with ENSO and Madden–Julian Oscillation. clouds; radiation budget; Geophysics/Geodesy; Astronomy, Observations and Techniques; Earth Sciences, general; Climate variability
Loeb, Norman G.; Su, WenyingLoeb, N. G., W. Su, 2010: Direct Aerosol Radiative Forcing Uncertainty Based on a Radiative Perturbation Analysis. J. Climate, 23(19), 5288-5293. doi: 10.1175/2010JCLI3543.1. Abstract To provide a lower bound for the uncertainty in measurement-based clear- and all-sky direct aerosol radiative forcing (DARF), a radiative perturbation analysis is performed for the ideal case in which the perturbations in global mean aerosol properties are given by published values of systematic uncertainty in Aerosol Robotic Network (AERONET) aerosol measurements. DARF calculations for base-state climatological cloud and aerosol properties over ocean and land are performed, and then repeated after perturbing individual aerosol optical properties (aerosol optical depth, single-scattering albedo, asymmetry parameter, scale height, and anthropogenic fraction) from their base values, keeping all other parameters fixed. The total DARF uncertainty from all aerosol parameters combined is 0.5–1.0 W m−2, a factor of 2–4 greater than the value cited in the Intergovernmental Panel on Climate Change’s (IPCC’s) Fourth Assessment Report. Most of the total DARF uncertainty in this analysis is associated with single-scattering albedo uncertainty. Owing to the greater sensitivity to single-scattering albedo in cloudy columns, DARF uncertainty in all-sky conditions is greater than in clear-sky conditions, even though the global mean clear-sky DARF is more than twice as large as the all-sky DARF. aerosols; Radiation budgets; radiative forcing; Surface observations
Su, Wenying; Bodas-Salcedo, Alejandro; Xu, Kuan-Man; Charlock, Thomas P.Su, W., A. Bodas-Salcedo, K. Xu, T. P. Charlock, 2010: Comparison of the tropical radiative flux and cloud radiative effect profiles in a climate model with Clouds and the Earth's Radiant Energy System (CERES) data. Journal of Geophysical Research: Atmospheres, 115(D1), D01105. doi: 10.1029/2009JD012490. An insightful link of model performance to the physical assumptions in general circulation models (GCMs) can be explored if assessment of radiative fluxes and cloud radiative effects go beyond those at the top of the atmosphere (TOA). In this study, we compare the radiative flux profiles (at surface, 500 hPa, 200 hPa, 70 hPa, and TOA) and cloud effect profiles (500 hPa, 200 hPa, and TOA) from HadGAM1, using Surface and Atmospheric Radiation Budget (SARB) data from Clouds and the Earth's Radiant Energy System (CERES) on the TRMM satellite over the tropics (30°S–30°N). Comparison at TOA reveals that HadGAM1 agrees well with CERES for mean cloud height but lacks in cloudiness. Comparing to its predecessor, HadAM3, HadGAM1 agrees better with observations in TOA LW cloud effects, net cloud effects, and the ratio of SW to LW cloud effects. Extending the comparison to multiple levels, we gain additional insight into the vertical differences in clouds: for clouds at heights below 500 hPa, HadGAM1 and CERES are in good agreement in terms of cloudiness, but HadGAM1 underestimates the average cloud height; for clouds between 500 and 200 hPa, HadGAM1 underestimates the cloudiness but overestimates the average cloud height; for clouds at heights above 200 hPa, HadGAM1 produces more clouds than in CERES. Stratifying the cloud effects by dynamic regimes, we find that HadGAM1 underestimates cloudiness and overestimates averaged cloud height in the convective regimes, but the opposite is true in the strong subsidence regimes. radiative flux; 0321 Cloud/radiation interaction; 1616 Climate variability; cloud radiative effect; 1626 Global climate models; global climate model
Su, Wenying; Loeb, Norman G.; Xu, Kuan-Man; Schuster, Gregory L.; Eitzen, Zachary A.Su, W., N. G. Loeb, K. Xu, G. L. Schuster, Z. A. Eitzen, 2010: An estimate of aerosol indirect effect from satellite measurements with concurrent meteorological analysis. Journal of Geophysical Research: Atmospheres, 115(D18), D18219. doi: 10.1029/2010JD013948. Many studies have used satellite retrievals to investigate the effect of aerosols on cloud properties, but these retrievals are subject to artifacts that can confound interpretation. Additionally, large-scale meteorological differences over a study region dominate cloud dynamics and must be accounted for when studying aerosol and cloud interactions. We have developed an analysis method which minimizes the effect of retrieval artifacts and large-scale meteorology on the assessment of the aerosol indirect effect. The method divides an oceanic study region into 1° × 1° grid boxes and separates the grid boxes into two populations according to back trajectory analysis: one population contains aerosols of oceanic origin, and the other population contains aerosols of continental origin. We account for variability in the large-scale dynamical and thermodynamical conditions by stratifying these two populations according to vertical velocity (at 700 hPa) and estimated inversion strength and analyze differences in the aerosol optical depths, cloud properties, and top of atmosphere (TOA) albedos. We also stratify the differences by cloud liquid water path (LWP) in order to quantify the first aerosol indirect effect. We apply our method to a study region off the west coast of Africa and only consider single-layer low-level clouds. We find that grid boxes associated with aerosols of continental origin have higher cloud fraction than those associated with oceanic origin. Additionally, we limit our analysis to those grid boxes with cloud fractions larger than 80% to ensure that the two populations have similar retrieval biases. This is important for eliminating the retrieval biases in our difference analysis. We find a significant reduction in cloud droplet effective radius associated with continental aerosols relative to that associated with oceanic aerosols under all LWP ranges; the overall reduction is about 1.0 μm, when cloud fraction is not constrained, and is about 0.5 μm, when cloud fraction is constrained to be larger than 80%. We also find significant increases in cloud optical depth and TOA albedo associated with continental aerosols relative to those associated with oceanic aerosols under all LWP ranges. The overall increase in cloud optical depth is about 0.6, and the overall increase in TOA albedo is about 0.021, when we do not constrained cloud fraction. The overall increases in cloud optical depth and TOA albedo are 0.4 and 0.008, when we only use grid boxes with cloud fraction larger than 80%. clouds; 0320 Cloud physics and chemistry; 0305 Aerosols and particles; aerosols; 3311 Clouds and aerosols
Xu, K. M.; Su, W. Y.; Eitzen, Z.Xu, K. M., W. Y. Su, Z. Eitzen, 2009: Use of CERES cloud and radiation data for model evaluation and cloud feedback studies. Proceedings of the 5th Wseas International Conference on Remote, 55-61.
Su, Wenying; Dutton, Ellsworth; Charlock, Thomas P.; Wiscombe, WarrenSu, W., E. Dutton, T. P. Charlock, W. Wiscombe, 2008: Performance of Commercial Radiometers in Very Low Temperature and Pressure Environments Typical of Polar Regions and of the Stratosphere: A Laboratory Study. J. Atmos. Oceanic Technol., 25(4), 558-569. doi: 10.1175/2007JTECHA1005.1. Abstract Characterizing the performance of ground-based commercial radiometers in cold and/or low-pressure environments is critical for developing accurate flux measurements in the polar regions and in the upper troposphere and stratosphere. Commercially available broadband radiometers have a stated operational temperature range of, typically, −20° to +50°C. Within this range, their temperature dependencies of sensitivities change less than 1%. But for deployments on high-altitude platforms or in polar regions, which can be much colder than −20°C, information on temperature dependency of sensitivity is not always available. In this paper, the temperature dependencies of sensitivities of popular pyranometers and pyrgeometers manufactured by Kipp and Zonen were tested in a thermal-vacuum chamber. When their body temperature is lowered to −60°C, pyranometer sensitivity drops by 4%–6% from the factory-default specification. Pyrgeometer sensitivity increases by 13% from the factory-default specification during a similar temperature change. When the chamber pressure is lowered from 830 to 6 hPa, the sensitivity decreases by about 2% for the pyranometer, and increases by about 2% for the pyrgeometer. Note that these temperature and pressure dependencies of sensitivities are specific for the instruments that were tested and should not be applied to others. These findings show that for measurements suitable for climate studies, it is crucial to characterize temperature and/or pressure effects on radiometer sensitivity for deployments on high-altitude platforms and in polar regions. temperature; instrumentation; Arctic; Pressure; Stratosphere
Su, Wenying; Schuster, Gregory L.; Loeb, Norman G.; Rogers, Raymond R.; Ferrare, Richard A.; Hostetler, Chris A.; Hair, Johnathan W.; Obland, Michael D.Su, W., G. L. Schuster, N. G. Loeb, R. R. Rogers, R. A. Ferrare, C. A. Hostetler, J. W. Hair, M. D. Obland, 2008: Aerosol and cloud interaction observed from high spectral resolution lidar data. Journal of Geophysical Research: Atmospheres, 113(D24), D24202. doi: 10.1029/2008JD010588. Recent studies utilizing satellite retrievals have shown a strong correlation between aerosol optical depth (AOD) and cloud cover. However, these retrievals from passive sensors are subject to many limitations, including cloud adjacency (or three-dimensional) effects, possible cloud contamination, uncertainty in the AOD retrieval. Some of these limitations do not exist in High Spectral Resolution Lidar (HSRL) observations; for instance, HSRL observations are not affected by cloud adjacency effects, are less prone to cloud contamination, and offer accurate aerosol property measurements (backscatter coefficient, extinction coefficient, lidar ratio, backscatter Angstrom exponent, and aerosol optical depth) at a fine spatial resolution ( 0305 Aerosols and particles; cloud; 3311 Clouds and aerosols; 3359 Radiative processes; aerosol
Loeb, Norman G.; Wielicki, Bruce A.; Su, Wenying; Loukachine, Konstantin; Sun, Wenbo; Wong, Takmeng; Priestley, Kory J.; Matthews, Grant; Miller, Walter F.; Davies, R.Loeb, N. G., B. A. Wielicki, W. Su, K. Loukachine, W. Sun, T. Wong, K. J. Priestley, G. Matthews, W. F. Miller, R. Davies, 2007: Multi-Instrument Comparison of Top-of-Atmosphere Reflected Solar Radiation. J. Climate, 20(3), 575-591. doi: 10.1175/JCLI4018.1. Abstract Observations from the Clouds and the Earth’s Radiant Energy System (CERES), Moderate Resolution Imaging Spectroradiometer (MODIS), Multiangle Imaging Spectroradiometer (MISR), and Sea-Viewing Wide-Field-of-View Sensor (SeaWiFS) between 2000 and 2005 are analyzed in order to determine if these data are meeting climate accuracy goals recently established by the climate community. The focus is primarily on top-of-atmosphere (TOA) reflected solar radiances and radiative fluxes. Direct comparisons of nadir radiances from CERES, MODIS, and MISR aboard the Terra satellite reveal that the measurements from these instruments exhibit a year-to-year relative stability of better than 1%, with no systematic change with time. By comparison, the climate requirement for the stability of visible radiometer measurements is 1% decade−1. When tropical ocean monthly anomalies in shortwave (SW) TOA radiative fluxes from CERES on Terra are compared with anomalies in Photosynthetically Active Radiation (PAR) from SeaWiFS—an instrument whose radiance stability is better than 0.07% during its first six years in orbit—the two are strongly anticorrelated. After scaling the SeaWiFS anomalies by a constant factor given by the slope of the regression line fit between CERES and SeaWiFS anomalies, the standard deviation in the difference between monthly anomalies from the two records is only 0.2 W m−2, and the difference in their trend lines is only 0.02 ± 0.3 W m−2 decade−1, approximately within the 0.3 W m−2 decade−1 stability requirement for climate accuracy. For both the Tropics and globe, CERES Terra SW TOA fluxes show no trend between March 2000 and June 2005. Significant differences are found between SW TOA flux trends from CERES Terra and CERES Aqua between August 2002 and March 2005. This discrepancy is due to uncertainties in the adjustment factors used to account for degradation of the CERES Aqua optics during hemispheric scan mode operations. Comparisons of SW TOA flux between CERES Terra and the International Satellite Cloud Climatology Project (ISCCP) radiative flux profile dataset (FD) RadFlux product show good agreement in monthly anomalies between January 2002 and December 2004, and poor agreement prior to this period. Commonly used statistical tools applied to the CERES Terra data reveal that in order to detect a statistically significant trend of magnitude 0.3 W m−2 decade−1 in global SW TOA flux, approximately 10 to 15 yr of data are needed. This assumes that CERES Terra instrument calibration remains highly stable, long-term climate variability remains constant, and the Terra spacecraft has enough fuel to last 15 yr. satellite observations; radiative forcing; Shortwave radiation
Su, Wenying; Charlock, Thomas P.; Rose, Fred G.; Rutan, DavidSu, W., T. P. Charlock, F. G. Rose, D. Rutan, 2007: Photosynthetically active radiation from Clouds and the Earth's Radiant Energy System (CERES) products. Journal of Geophysical Research: Biogeosciences, 112(G2), G02022. doi: 10.1029/2006JG000290. We describe a method that retrieves surface photosynthetically active radiation (PAR) and its direct and diffuse components from the Surface and Atmospheric Radiation Budget (SARB) product of Clouds and the Earth's Radiant Energy System (CERES). The shortwave spectrum in the SARB Edition 2 is calculated in 15 bands, 4 of which are used to develop the PAR, in conjunction with the look-up tables described in this paper. We apply these look-up tables to existing CERES Terra Edition 2 products. The new retrieved surface PAR is validated with LI-COR PAR measurements at seven Surface Radiation Budget Network (SURFRAD) sites using data from March 2000 to June 2005. The relative bias of retrieved all-sky PAR at the SURFRAD sites is 4.6% (positive sign indicating retrieval exceeds measurement), and 54% of the all-sky samples are within the ±10% uncertainty of the LI-COR PAR measurements. The satellite field-of-view (FOV) is more representative of the ground instrument FOV under clear conditions, so 89% of clear-sky retrievals are within the uncertainty of the LI-COR PAR measurements at SURFRAD sites with positive biases at most sites. The retrieved PAR is also validated at the Atmospheric Radiation Measurement (ARM) Southern Great Plains Central Facility (CF) site using data from October 2003 to June 2004 for those FOVs having both LI-COR and Rotating Shadowband Spectroradiometer (RSS) ground measurements; for this small domain, all-sky relative biases are again positive (1.9%) for LI-COR but negative (−4.2%) for RSS. The direct-to-diffuse ratio derived from CERES is smaller than that from RSS for both clear and cloudy conditions. CERES also retrieves the broadband shortwave insolation, and the relative biases for the broadband retrievals are much less than those for PAR at the above sites. It appears that some of the ground-based measurements of PAR do not have the fidelity of those for broadband shortwave insolation. 0360 Radiation: transmission and scattering; 3311 Clouds and aerosols; radiative transfer; PAR; 0428 Carbon cycling; carbon sequestration
Su, Wenying; Charlock, Thomas P.; Rose, Fred G.Su, W., T. P. Charlock, F. G. Rose, 2005: Deriving surface ultraviolet radiation from CERES surface and atmospheric radiation budget: Methodology. Journal of Geophysical Research: Atmospheres, 110(D14), D14209. doi: 10.1029/2005JD005794. We describe an algorithm that retrieves the surface UVB (280–315 nm) and UVA (315–400 nm) irradiances from the Surface and Atmosphere Radiation Budget (SARB) product of Clouds and the Earth's Radiant Energy System (CERES). The SARB product we use here routinely calculates the vertical profiles of shortwave, longwave, and window channel irradiances with inputs of retrievals from imagers collocated with CERES. The top of the atmosphere broadband irradiance from SARB is constrained by CERES broadband irradiance. The shortwave spectrum in the SARB calculation is divided into 15 bands, and the two ultraviolet spectral bands, band 5 (298.5–322.5 nm) and band 6 (322.5–357.5 nm), are used to generate surface UVB and UVA irradiances. In this study, we develop a set of ratio lookup tables to derive surface UVB and UVA irradiances from SARB band 5 and band 6 outputs. We show that the ratio of band 5 to UVB irradiance is sensitive to total column ozone, solar zenith angle, surface albedo, and the atmospheric profile in cloud-free conditions; in cloudy conditions, the ratio of band 5 to UVB irradiance is also sensitive to cloud optical depth and height. Additionally, we show that the ratio of band 6 to UVA irradiance is sensitive to solar zenith angle, surface albedo, and cloud optical depth. We also derive a UV index from the UVB irradiance. Our algorithm may be applied at any surface elevation or surface type, including snow and ice. Surface UV irradiances derived from the lookup table that we created agree well with those computed by the high-resolution, multistream radiative transfer code, with differences ranging from −10% to +4% for UVB and UVA irradiances. The relative differences for the UV index are higher, ranging from −26% to +16%. 3311 Clouds and aerosols; radiative transfer; 3359 Radiative processes; surface UV radiation; UV index
Su, Wenying; Charlock, Thomas P.; Rutledge, KenSu, W., T. P. Charlock, K. Rutledge, 2002: Observations of reflectance distribution around sunglint from a coastal ocean platform. Applied Optics, 41(35), 7369-7383. doi: 10.1364/AO.41.007369. A scanning spectral photometer is deployed on a rigid coastal ocean platform to measure upwelling solar radiances from the sea surface at nine elevation angles spanning 150° of azimuth. Measured radiance distributions at 500 nm wavelength have been compared with traditional model simulations employing the Cox and Munk distribution of wave slopes. The model captures the general features of the observed angular reflectance distributions, but: (a) the observed peak value of sunglint near the specular direction is larger than simulated, except for a very calm sea; the model-measurement differences increase with wind speed and are largest for low solar elevation; (b) the observed sunglint is wider than simulated. In contrast to some previous studies, our results do not show a clear dependence of the mean square sea-surface slope on stability (air-sea temperature difference). radiative transfer; Oceanic optics; Spectrometers and spectroscopic instrumentation
Su, Wenying; Mao, Jietai; Ji, Fei; Qin, YuSu, W., J. Mao, F. Ji, Y. Qin, 2000: Outgoing longwave radiation and cloud radiative forcing of the Tibetan Plateau. Journal of Geophysical Research: Atmospheres, 105(D11), 14863-14872. doi: 10.1029/2000JD900201. In order to study the energy balance and the cloud radiative forcing (CRF) of the Tibetan Plateau in detail, 2 years of GMS5 satellite data are employed to analyze the monthly mean outgoing longwave radiation (OLR) and CRF. It should be noted that the temporal resolution of GMS5 data is 1 hour, so the data can be used to study the diurnal variations of OLR. First, a method is presented to retrieve the OLR from split-window channels (10.5–11.5 and 11.5–12.5 μm) and the water vapor channel (6.5–7.0 μm) of GMS5. The method applies the discrete ordinates radiative transfer (DISORT) model together with the radiosonde profiles of the Tibetan Plateau to simulate radiances and fluxes of the three channels. A regression relationship is then developed to calculate the OLR from the observations of the three channels. Since the Tibetan Plateau is located nearly out of the effective observational range of the GMS5 satellite, the regression results of GMS5's split-window channels and water vapor channel are corrected by using simultaneously retrieved results from TIROS Operational Vertical Sounder (TOVS). The correlation coefficient of GMS5 and TOVS results is 0.8510, which is large enough for 1% significant level. The OLR distributions are calculated for the Tibetan Plateau using 2 years of GMS5 data and the regression and correction methods. The average of the OLR images for the same month and same time gives the monthly mean OLR distribution for each hour. The 24-hour OLR distributions of the same month are then averaged to yield the monthly mean OLR distribution for that month. Then our monthly mean OLR distributions are compared with the Clouds and the Earth's Radiant Energy System (CERES) results, and they are generally in good agreement with differences of 0312 Air/sea constituent fluxes; 0360 Radiation: transmission and scattering; 1610 Atmosphere; 1640 Remote sensing
