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Dr. Norman Loeb

Dr. Norman Loeb

Contact Information

NASA Langley Research Center
Mail Stop 420, Hampton, VA 23681-2199

Phone: 757-864-5688

Fax: 757-864-7996

Email: norman.g.loeb@nasa.gov

Education

Awards, Honors, and Positions

Publications

2020

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.; 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.
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.

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.
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
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.
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.
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.
Yu, Lisan; Jin, X.; Stackhouse, P. W.; Wilber, A. C.; Kato, S.; Loeb, N. G; Weller, R.Yu, L., X. Jin, P. W. Stackhouse, A. C. Wilber, S. Kato, N. G. Loeb, R. Weller, 2019: Global ocean heat, freshwater, and momentum fluxes.[in "State of the Climate in 2018"]. Bull. Amer. Meteor. Soc, 100(9), S81-84. doi: 10.1175/2019BAMSStateoftheClimate.1.

2018

Chen, Xiuhong; Huang, Xianglei; Dong, Xiquan; Xi, Baike; Dolinar, Erica K.; Loeb, Norman G.; Kato, Seiji; Stackhouse, Paul W.; Bosilovich, Michael G.Chen, X., X. Huang, X. Dong, B. Xi, E. K. Dolinar, N. G. Loeb, S. Kato, P. W. Stackhouse, M. G. Bosilovich, 2018: Using AIRS and ARM SGP Clear-Sky Observations to Evaluate Meteorological Reanalyses: A Hyperspectral Radiance Closure Approach. Journal of Geophysical Research: Atmospheres, 123(20), 11,720-11,734. doi: 10.1029/2018JD028850. Using the ground-based measurements from the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site and spectral radiance from the Atmospheric Infrared Sounder (AIRS) on National Aeronautics and Space Administration Aqua, we evaluate the temperature and humidity profiles from European Center for Medium Range Weather Forecasting ERA-Interim and Modern-Era Retrospective analysis for Research and Applications Version 2 reanalyses. Four sets of synthetic AIRS spectra are calculated using 51 clear-sky sounding profiles from the ARM SGP observations, the collocated AIRS L2 retrievals and the two reanalyses, respectively. A subset of AIRS channels sensitive to temperature, CO2, or H2O but not to other trace gases is chosen and further categorized into different groups according to the peak altitudes of their weighting functions. Synthetic radiances are then compared to the observed AIRS radiances for each group. For all groups, the observed AIRS radiances agree well with the synthetic ones based on the ARM SGP soundings or the AIRS L2 retrievals. The brightness temperature (BT) differences are within ±0.5 K. For two reanalyses, BT differences in all temperature-sensitive groups are generally within ±0.5 K; but the mean BT differences in all groups sensitive to both T and H2O are negative. Together, they suggest a wet bias in the free troposphere in both reanalyses. Moreover, such BT differences can be seen in the analysis of AIRS clear-sky radiances over the entire 30–40°N zone. A grid-search retrieval suggests that 9–30% reduction for reanalysis humidity between 200 and 800 hPa is needed to correct such wet bias. AIRS radiances; ARM soundings; reanalysis bias correction
Chepfer, H.; Noel, V.; Chiriaco, M.; Wielicki, B.; Winker, D.; Loeb, N.; Wood, R.Chepfer, H., V. Noel, M. Chiriaco, B. Wielicki, D. Winker, N. Loeb, R. Wood, 2018: The Potential of a Multidecade Spaceborne Lidar Record to Constrain Cloud Feedback. Journal of Geophysical Research: Atmospheres, 123(10), 5433-5454. doi: 10.1002/2017JD027742. Synthetic multidecadal spaceborne lidar records are used to examine when a cloud response to anthropogenic forcing would be detectable from spaceborne lidar observations. The synthetic records are generated using long-term cloud changes predicted by two Coupled Model Intercomparison Program 5 models seen through the COSP/lidar (CFMIP, Cloud Feedback Model Intercomparison Project, Observation Simulators Package) and cloud interannual variability observed by the CALIPSO (Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observations) spaceborne lidar during the past decade. CALIPSO observations do not show any significant trend yet. Our analysis of the synthetic time series suggests that the tropical cloud longwave feedback and the Southern Ocean cloud shortwave feedback might be constrained with 70% confidence with, respectively, a 20-year and 29-year uninterrupted lidar-in-space record. A 27-year record might be needed to separate the two different model predictions in the tropical subsidence clouds. Assuming that combining the CALIPSO and Earth-CARE (Earth Clouds, Aerosols and Radiation Explorer) missions will lead to a spaceborne lidar record of at least 16 years, we examine the impact of gaps and calibration offsets between successive missions. A 2-year gap between Earth-CARE and the following spaceborne lidar would have no significant impact on the capability to constrain the cloud feedback if all the space lidars were perfectly intercalibrated. Any intercalibration shift between successive lidar missions would delay the capability to constrain the cloud feedback mechanisms, larger shifts leading to longer delays. clouds; climate; space lidar
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
Loeb, Norman G.; Yang, Ping; Rose, Fred G.; Hong, Gang; Sun-Mack, Sunny; Minnis, Patrick; Kato, Seiji; Ham, Seung-Hee; Smith, William L.; Hioki, Souichiro; Tang, GuanglinLoeb, N. G., P. Yang, F. G. Rose, G. Hong, S. Sun-Mack, P. Minnis, S. Kato, S. Ham, W. L. Smith, S. Hioki, G. Tang, 2018: Impact of Ice Cloud Microphysics on Satellite Cloud Retrievals and Broadband Flux Radiative Transfer Model Calculations. J. Climate, 31(5), 1851–1864. doi: 10.1175/JCLI-D-17-0426.1. Ice cloud particles exhibit a range of shapes and sizes affecting a cloud’s single-scattering properties. Because they cannot be inferred from passive visible/infrared imager measurements, assumptions about the bulk single-scattering properties of ice clouds are fundamental to satellite cloud retrievals and broadband radiative flux calculations. To examine the sensitivity to ice particle model assumptions, three sets of models are used in satellite imager retrievals of ice cloud fraction, thermodynamic phase, optical depth, effective height and particle size, and in top-of-atmosphere and surface broadband radiative flux calculations. The three ice particle models include smooth hexagonal ice columns (SMOOTH), roughened hexagonal ice columns, and a two-habit model (THM) comprised of an ensemble of hexagonal columns and 20-element aggregates. While the choice of ice particle model has a negligible impact on daytime cloud fraction and thermodynamic phase, the global mean ice cloud optical depth retrieved from THM is smaller than SMOOTH by 2.3 (28%), and the regional root-mean-square-difference (RMSD) is 2.8 (32%). Effective radii derived from THM are 3.9 μm (16%) smaller than SMOOTH values and the RMSD is 5.2 μm (21%). In contrast, the regional RMSD in top-of-atmosphere (TOA) and surface flux between the THM and SMOOTH is only 1% in the SW and 0.3% in the LW when a consistent ice particle model is assumed in the cloud property retrievals and forward radiative transfer model calculations. Consequently, radiative fluxes derived using a consistent ice particle model assumption throughout provide a more robust reference for climate model evaluation compared to ice cloud property retrievals.
Smith, Natividad; Thomas, Susan; Shankar, Mohan; Priestley, Kory; Loeb, Norman; Walikainen, DaleSmith, N., S. Thomas, M. Shankar, K. Priestley, N. Loeb, D. Walikainen, 2018: Assessment of on-orbit variations of the Clouds and the Earth's Radiant Energy System (CERES) FM5 instrument. Earth Observing Missions and Sensors: Development, Implementation, and Characterization V, 10781, 1078119. doi: 10.1117/12.2324739. The Clouds and the Earth’s Radiant Energy System (CERES) mission is instrumental in monitoring changes in the Earth’s radiant energy and cloud systems. The CERES project is critical in guaranteeing the continuation of highly accurate Earth radiation budget Climate Data Records (CDRs). The CERES Flight Model-5 (FM-5) instrument, integrated onto the Suomi-National Polar-Orbiting Partnership (NPP) spacecraft, joined a suite of four CERES instruments deployed aboard NASA’s Earth Observing System (EOS) satellites Terra and Aqua. Each CERES instrument consists of scanning thermistor bolometer sensors that measure broadband radiances in the shortwave (0.3 to 5μm), total (0.3 to < 200 μm) and water vapor window (8 to 12 μm) regions. In order to ensure the consistency and accuracy of instrument radiances, needed for generating higher-level climate data products, the CERES project implements rigorous and comprehensive radiometric calibration and validation procedures. This paper briefly describes the trends observed in Edition-1 FM5 flux data products that are corrected for inflight gain changes derived from on-board calibration sources. The strategy to detect artifacts and correct for any sensor spectral response changes is discussed. Improvements and validation results of preliminary FM5 Edition-2 products will be compared with Terra and Aqua data products.
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; radiation; angular distribution model; DSCOVR; EPIC; Lagrange-1 point
Thorsen, Tyler J.; Kato, Seiji; Loeb, Norman G.; Rose, Fred G.Thorsen, T. J., S. Kato, N. G. Loeb, F. G. Rose, 2018: Observation-Based Decomposition of Radiative Perturbations and Radiative Kernels. J. Climate, 31(24), 10039-10058. doi: 10.1175/JCLI-D-18-0045.1. The Clouds and the Earth’s Radiant Energy System (CERES)–partial radiative perturbation [PRP (CERES-PRP)] methodology applies partial-radiative-perturbation-like calculations to observational datasets to directly isolate the individual cloud, atmospheric, and surface property contributions to the variability of the radiation budget. The results of these calculations can further be used to construct radiative kernels. A suite of monthly mean observation-based inputs are used for the radiative transfer, including cloud properties from either the diurnally resolved passive-sensor-based CERES synoptic (SYN) data or the combination of the CloudSat cloud radar and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar. The CloudSat/CALIPSO cloud profiles are incorporated via a clustering method that obtains monthly mean cloud properties suitable for accurate radiative transfer calculations. The computed fluxes are validated using the TOA fluxes observed by CERES. Applications of the CERES-PRP methodology are demonstrated by computing the individual contributions to the variability of the radiation budget over multiple years and by deriving water vapor radiative kernels. The calculations for the former are used to show that an approximately linear decomposition of the total flux anomalies is achieved. The observation-based water vapor kernels were used to investigate the accuracy of the GCM-based NCAR CAM3.0 water vapor kernel. Differences between our observation-based kernel and the NCAR one are marginally larger than those inferred by previous comparisons among different GCM kernels.
Weatherhead, Betsy; Wielicki, Bruce A.; Ramaswamy, V.; Abbott, Mark; Ackerman, Thomas; Atlas, Robert; Brasseur, Guy; Bruhwiler, Lori; Busalacchi, Antonio; Butler, James H.; Clack, Christopher T. M.; Cooke, Roger; Cucurull, Lidia; Davis, Sean; English, Jason M.; Fahey, David W.; Fine, Steven S.; Lazo, Jeffrey K.; Liang, Shunlin; Loeb, Norman G.; Rignot, Eric; Soden, Brian; Stanitski, Diane; Stephens, Graeme; Tapley, Byron; Thompson, Anne M.; Trenberth, Kevin E.; Wuebbles, DonaldWeatherhead, B., B. A. Wielicki, V. Ramaswamy, M. Abbott, T. Ackerman, R. Atlas, G. Brasseur, L. Bruhwiler, A. Busalacchi, J. H. Butler, C. T. M. Clack, R. Cooke, L. Cucurull, S. Davis, J. M. English, D. W. Fahey, S. S. Fine, J. K. Lazo, S. Liang, N. G. Loeb, E. Rignot, B. Soden, D. Stanitski, G. Stephens, B. Tapley, A. M. Thompson, K. E. Trenberth, D. Wuebbles, 2018: Designing the Climate Observing System of the Future. Earth's Future, 6(1), 80-102. doi: 10.1002/2017EF000627. Climate observations are needed to address a large range of important societal issues including sea level rise, droughts, floods, extreme heat events, food security, and fresh water availability in the coming decades. Past, targeted investments in specific climate questions have resulted in tremendous improvements in issues important to human health, security, and infrastructure. However, the current climate observing system was not planned in a comprehensive, focused manner required to adequately address the full range of climate needs. A potential approach to planning the observing system of the future is presented in this paper. First, this paper proposes that priority be given to the most critical needs as identified within the World Climate Research Program as Grand Challenges. These currently include seven important topics: Melting Ice and Global Consequences; Clouds, Circulation and Climate Sensitivity; Carbon Feedbacks in the Climate System; Understanding and Predicting Weather and Climate Extremes; Water for the Food Baskets of the World; Regional Sea-Level Change and Coastal Impacts; and Near-term Climate Prediction. For each Grand Challenge, observations are needed for long-term monitoring, process studies and forecasting capabilities. Second, objective evaluations of proposed observing systems, including satellites, ground-based and in situ observations as well as potentially new, unidentified observational approaches, can quantify the ability to address these climate priorities. And third, investments in effective climate observations will be economically important as they will offer a magnified return on investment that justifies a far greater development of observations to serve society's needs. climate observations; Climate Observing System Simulation Experiments; Value of Information; Economic Value; Grand Challenges; 1699 General or miscellaneous
Wong, T.; Kratz, D. P.; Stackhouse, P. W.; Sawaengphokhai, Parnchai; Wilber, A. C.; Gupta, S. K.; Loeb, N. GWong, T., D. P. Kratz, P. W. Stackhouse, P. Sawaengphokhai, A. C. Wilber, S. K. Gupta, N. G. Loeb, 2018: Earth Radiation Budget at Top-Of-Atmosphere [in “State of the Climate in 2017”].. Bull. Amer. Meteor. Soc, 99(8), S45-46. doi: 10.1175/2018BAMSStateoftheClimate.1.
Wong, T.; Smith, G. L.; Kato, S.; Loeb, N. G.; Kopp, G.; Shrestha, A. K.Wong, T., G. L. Smith, S. Kato, N. G. Loeb, G. Kopp, A. K. Shrestha, 2018: On the Lessons Learned From the Operations of the ERBE Nonscanner Instrument in Space and the Production of the Nonscanner TOA Radiation Budget Data Set. IEEE Transactions on Geoscience and Remote Sensing, 56(10), 5936-5947. doi: 10.1109/TGRS.2018.2828783. Monitoring the flow of radiative energy at top of atmosphere (TOA) is essential for understanding Earth's climate and how it is changing with time. The determination of TOA global net radiation budget using broadband nonscanner instruments has received renewed interest recently due to advances in both instrument technology and the availability of small satellite platforms. The use of such instruments for monitoring Earth's radiation budget was attempted in the past from satellite missions such as the Nimbus-7 and the Earth Radiation Budget Experiment (ERBE). This paper discusses the important lessons learned from the operation of the ERBE nonscanner instrument and the production of the ERBE nonscanner TOA radiation budget data set that have direct relevance to current nonscanner instrument efforts. uncertainty; atmospheric techniques; atmospheric measuring apparatus; atmospheric radiation; Earth; Extraterrestrial measurements; Instruments; Sea measurements; Meteorology; Atmospheric measurements; Satellite broadcasting; Data conversion; broadband nonscanner instruments; current nonscanner instrument efforts; Earth Radiation Budget Experiment; Earth's climate; energy measurement; ERBE nonscanner instrument; ERBE nonscanner TOA radiation budget data; important lessons; instrument technology; monitoring Earth's radiation budget; Nimbus-7; nonscanner TOA Radiation Budget data set; radiative energy; small satellite platforms; TOA global net radiation budget
Yu, L.; Jin, X; Kato, S.; Loeb, N. G; Stackhouse, P. W.; Weller, R. A.; Wilber, A. C.Yu, L., X. Jin, S. Kato, N. G. Loeb, P. W. Stackhouse, R. A. Weller, A. C. Wilber, 2018: Global ocean heat, freshwater, and momentum fluxes [in “State of the Climate in 2017”].. Bull. Amer. Meteor. Soc, 99(8), S81-84. doi: 10.1175/2018BAMSStateoftheClimate.1.

2017

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; model evaluation; 0321 Cloud/radiation interaction; 3360 Remote sensing; 3337 Global climate models; 3394 Instruments and techniques; Instrument simulator
Kratz, D. P.; Stackhouse, P.W.; Wong, T; Sawaengphokhai, P.; Wilber, A. C.; Gupta, S. K.; Loeb, N. G.Kratz, D. P., P. Stackhouse, T. Wong, P. Sawaengphokhai, A. C. Wilber, S. K. Gupta, N. G. Loeb, 2017: Earth radiation Budget at Top-of-Atmosphere [in “State of the Climate in 2016"]. Bull. Amer. Meteor. Soc., 97(8), S41-S42. doi: 10.1175/2017BAMSStateoftheClimate.1.
Liu, Chunlei; Allan, Richard P.; Mayer, Michael; Hyder, Patrick; Loeb, Norman G.; Roberts, Chris D.; Valdivieso, Maria; Edwards, John M.; Vidale, Pier-LuigiLiu, C., R. P. Allan, M. Mayer, P. Hyder, N. G. Loeb, C. D. Roberts, M. Valdivieso, J. M. Edwards, P. Vidale, 2017: Evaluation of satellite and reanalysis-based global net surface energy flux and uncertainty estimates. Journal of Geophysical Research: Atmospheres, 122(12), 6250–6272. doi: 10.1002/2017JD026616. The net surface energy flux is central to the climate system yet observational limitations lead to substantial uncertainty. A combination of satellite-derived radiative fluxes at the top of atmosphere (TOA) adjusted using the latest estimation of the net heat uptake of the Earth system, and the atmospheric energy tendencies and transports from the ERA-Interim reanalysis are used to estimate surface energy flux globally. To consider snowmelt and improve regional realism, land surface fluxes are adjusted through a simple energy balance approach at each grid point. This energy adjustment is redistributed over the oceans to ensure energy conservation and maintain realistic global ocean heat uptake, using a weighting function to avoid meridional discontinuities. Calculated surface energy fluxes are evaluated through comparison to ocean reanalyses. Derived turbulent energy flux variability is compared with the OAFLUX product and inferred meridional energy transports in the global ocean and the Atlantic are also evaluated using observations. Uncertainties in surface fluxes are investigated using a variety of approaches including comparison with a range of atmospheric reanalysis products. Decadal changes in the global mean and the inter-hemispheric energy imbalances are quantified and present day cross-equator heat transports are reevaluated at 0.22 ± 0.15 PW southward by the atmosphere and 0.32 ± 0.16 PW northward by the ocean considering the observed ocean heat sinks. uncertainty; 0399 General or miscellaneous; 0300 Atmospheric Composition and Structure; net surface energy flux; mass correction; land surface flux constraint; inter-hemispheric energy imbalance
Loeb, Norman G.; Wang, Hailan; Liang, Lusheng; Kato, Seiji; Rose, Fred G.Loeb, N. G., H. Wang, L. Liang, S. Kato, F. G. Rose, 2017: Surface energy budget changes over Central Australia during the early 21st century drought. International Journal of Climatology, 37(1), 159–168. doi: 10.1002/joc.4694. Satellite observations are used to investigate surface energy budget variability over central Australia during the early 21st century drought. Over a large expanse of open shrubland and savanna, surface albedo exhibits a multiyear increase of 0.06 during the drought followed by a sharp decline of 0.08 after heavy rainfall in 2010 broke the drought. The surface albedo variations are associated with increased normalized difference vegetation index (NDVI) during wet years before and after the drought and decreased NDVI during drought years. During the worst drought years (2002–2009), the surface albedo increase is most pronounced in the shortwave infrared region (wavelengths between 1 and 3 µm), implying soil moisture content variability is the likely cause of the albedo changes. At interannual timescales, surface albedo variability is associated with near-surface soil moisture, controlled by episodic precipitation events, whereas the multiyear increase in surface albedo is more closely linked with decreases in soil moisture in deeper surface layers. In addition to a higher surface albedo and lower soil moisture content during the drought, the observations show less evaporation, enhanced reflected shortwave radiation, increased upward emission of thermal infrared radiation, lower downwelling longwave (LW) radiation, reduced net total downward radiation, and higher sensible heating compared with the rainy period following the drought. Upward emission of thermal infrared radiation decreases sharply after the drought with increased surface evaporation. However, the surface energy budget changes during the worst drought years show a stronger relationship between upward emission of thermal radiation and reflected shortwave flux. During this period, evaporative fraction is extremely low and surface albedo is steadily increasing. In such extreme conditions, the surface albedo appears to modulate surface upward LW radiation, preventing it from getting too high. The change in upward LW radiation thus represents a negative feedback as it offsets further decreases in surface net radiation. radiation; albedo; energy budget; Precipitation; drought; Latent heat; Sensible heat
Smith, William L.; Hansen, Christy; Bucholtz, Anthony; Anderson, Bruce E.; Beckley, Matthew; Corbett, Joseph G.; Cullather, Richard I.; Hines, Keith M.; Hofton, Michelle; Kato, Seiji; Lubin, Dan; Moore, Richard H.; Segal Rosenhaimer, Michal; Redemann, Jens; Schmidt, Sebastian; Scott, Ryan; Song, Shi; Barrick, John D.; Blair, J. Bryan; Bromwich, David H.; Brooks, Colleen; Chen, Gao; Cornejo, Helen; Corr, Chelsea A.; Ham, Seung-Hee; Kittelman, A. Scott; Knappmiller, Scott; LeBlanc, Samuel; Loeb, Norman G.; Miller, Colin; Nguyen, Louis; Palikonda, Rabindra; Rabine, David; Reid, Elizabeth A.; Richter-Menge, Jacqueline A.; Pilewskie, Peter; Shinozuka, Yohei; Spangenberg, Douglas; Stackhouse, Paul; Taylor, Patrick; Thornhill, K. Lee; van Gilst, David; Winstead, EdwardSmith, W. L., C. Hansen, A. Bucholtz, B. E. Anderson, M. Beckley, J. G. Corbett, R. I. Cullather, K. M. Hines, M. Hofton, S. Kato, D. Lubin, R. H. Moore, M. Segal Rosenhaimer, J. Redemann, S. Schmidt, R. Scott, S. Song, J. D. Barrick, J. B. Blair, D. H. Bromwich, C. Brooks, G. Chen, H. Cornejo, C. A. Corr, S. Ham, A. S. Kittelman, S. Knappmiller, S. LeBlanc, N. G. Loeb, C. Miller, L. Nguyen, R. Palikonda, D. Rabine, E. A. Reid, J. A. Richter-Menge, P. Pilewskie, Y. Shinozuka, D. Spangenberg, P. Stackhouse, P. Taylor, K. L. Thornhill, D. van Gilst, E. Winstead, 2017: Arctic Radiation-IceBridge Sea and Ice Experiment: The Arctic Radiant Energy System during the Critical Seasonal Ice Transition. Bull. Amer. Meteor. Soc., 98(7), 1399-1426. doi: 10.1175/BAMS-D-14-00277.1. AbstractThe National Aeronautics and Space Administration (NASA)?s Arctic Radiation-IceBridge Sea and Ice Experiment (ARISE) acquired unique aircraft data on atmospheric radiation and sea ice properties during the critical late summer to autumn sea ice minimum and commencement of refreezing. The C-130 aircraft flew 15 missions over the Beaufort Sea between 4 and 24 September 2014. ARISE deployed a shortwave and longwave broadband radiometer (BBR) system from the Naval Research Laboratory; a Solar Spectral Flux Radiometer (SSFR) from the University of Colorado Boulder; the Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research (4STAR) from the NASA Ames Research Center; cloud microprobes from the NASA Langley Research Center; and the Land, Vegetation and Ice Sensor (LVIS) laser altimeter system from the NASA Goddard Space Flight Center. These instruments sampled the radiant energy exchange between clouds and a variety of sea ice scenarios, including prior to and after refreezing began. The most critical and unique aspect of ARISE mission planning was to coordinate the flight tracks with NASA Cloud and the Earth?s Radiant Energy System (CERES) satellite sensor observations in such a way that satellite sensor angular dependence models and derived top-of-atmosphere fluxes could be validated against the aircraft data over large gridbox domains of order 100?200 km. This was accomplished over open ocean, over the marginal ice zone (MIZ), and over a region of heavy sea ice concentration, in cloudy and clear skies. ARISE data will be valuable to the community for providing better interpretation of satellite energy budget measurements in the Arctic and for process studies involving ice?cloud?atmosphere energy exchange during the sea ice transition period.
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; ENSO; 0321 Cloud/radiation interaction; outgoing longwave radiation
Thampi, Bijoy; Wong, Takmeng; Lukashin, Constantin; Loeb, Norman GThampi, B., T. Wong, C. Lukashin, N. G. Loeb, 2017: Determination of CERES TOA fluxes using Machine learning algorithms. Part I: Classification and retrieval of CERES cloudy and clear scenes. J. Atmos. Oceanic Technol., 34(10), 2329–2345. doi: 10.1175/JTECH-D-16-0183.1. Continuous monitoring of the Earth radiation budget (ERB) is critical to our understanding of the Earth’s climate and its variability with time. The Clouds and the Earth’s Radiant Energy System (CERES) instrument is able to provide a long record of ERB for such scientific studies. This manuscript, which is first of a two-part paper, describes the new CERES algorithm for improving the clear/cloudy scene classification without the use of coincident cloud imager data. This new CERES algorithm is based on a subset of modern artificial intelligence (AI) paradigm called Machine Learning (ML) algorithms. This paper describes development and application of the ML algorithm known as Random Forests (RF) which is used to classify CERES broadband footprint measurements into clear and cloudy scenes. Results from the RF analysis carried using the CERES Single Scanner Footprint (SSF) data for the months of January and July are presented in the manuscript. The daytime RF misclassification rate (MCR) shows relatively large values (>30%) for snow, sea ice and bright desert surface types while lower values of (
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; DYNAMO in-situ observations; NASA GMAO reanalysis; CERES surface and atmospheric radiation estimation; 7847 Radiation processes
Yu, L.; Adler, R.; Huffman, G.; Jin, X.; Kato, S.; Loeb, N.; Stackhouse, P.; Weller, R.; Wilber, A.Yu, L., R. Adler, G. Huffman, X. Jin, S. Kato, N. Loeb, P. Stackhouse, R. Weller, A. Wilber, 2017: Ocean surface heat and momentum fluxes [In "State of the Climate in 2016"]. Bull. Amer. Meteor. Soc., 97(8), S75-S79. doi: 10.1175/2017BAMSStateoftheClimate.1.

2016

Dolinar, Erica K.; Dong, Xiquan; Xi, Baike; Jiang, Jonathan H.; Loeb, Norman G.Dolinar, E. K., X. Dong, B. Xi, J. H. Jiang, N. G. Loeb, 2016: A clear-sky radiation closure study using a one-dimensional radiative transfer model and collocated satellite-surface-reanalysis data sets. Journal of Geophysical Research: Atmospheres, 121(22), 2016JD025823. doi: 10.1002/2016JD025823. Earth's climate is largely determined by the planet's energy budget, i.e., the balance of incoming and outgoing radiation at the surface and top of atmosphere (TOA). Studies have shown that computing clear-sky radiative fluxes are strongly dependent on atmospheric state variables, such as temperature and water vapor profiles, while the all-sky fluxes are greatly influenced by the presence of clouds. NASA-modeled vertical profiles of temperature and water vapor are used to derive the surface radiation budget from Clouds and Earth Radiant Energy System (CERES), which is regarded as one of the primary sources for evaluating climate change in climate models. In this study, we evaluate the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) reanalyzed clear-sky temperature and water vapor profiles with newly generated atmospheric profiles from Department of Energy Atmospheric Radiation Measurement (ARM)-merged soundings and Aura Microwave Limb Sounder retrievals at three ARM sites. The temperature profiles are well replicated in MERRA-2 at all three sites, whereas tropospheric water vapor is slightly dry below ~700 hPa. These profiles are then used to calculate clear-sky surface and TOA radiative fluxes from the Langley-modified Fu-Liou radiative transfer model (RTM). In order to achieve radiative closure at both the surface and TOA, the ARM-measured surface albedos and aerosol optical depths are adjusted to account for surface inhomogeneity. In general, most of the averaged RTM-calculated surface downward and TOA upward shortwave and longwave fluxes agree within ~5 W/m2 of the observations, which is within the uncertainties of the ARM and CERES measurements. Yet still, further efforts are required to reduce the bias in calculated fluxes in coastal regions. 0360 Radiation: transmission and scattering; 0394 Instruments and techniques; 1640 Remote sensing; 1990 Uncertainty; 3359 Radiative processes; CERES SSF; clear-sky flux; MERRA-2; MLS; radiation closure; water vapor profile
Johnson, Gregory C.; Lyman, John M.; Loeb, Norman G.Johnson, G. C., J. M. Lyman, N. G. Loeb, 2016: Improving estimates of Earth's energy imbalance. Nature Climate Change, 6(7), 639-640. doi: 10.1038/nclimate3043. Atmospheric science; climate change; Physical oceanography
Kato, Seiji; Xu, Kuan-Man; Wong, Takmeng; Loeb, Norman G.; Rose, Fred G.; Trenberth, Kevin E.; Thorsen, Tyler J.Kato, S., K. Xu, T. Wong, N. G. Loeb, F. G. Rose, K. E. Trenberth, T. J. Thorsen, 2016: Investigation of the residual in column integrated atmospheric energy balance using cloud objects. J. Climate, 29(20), 7435–7452. doi: 10.1175/JCLI-D-15-0782.1. Observationally-based atmospheric energy balance is analyzed using Clouds and the Earth’s Radiant Energy System (CERES)-derived TOA and surface irradiance, Global Precipitation Climatology Project (GPCP)-derived precipitation, dry static and kinetic energy tendency and divergence estimated from ERA-Interim, and surface sensible heat flux from SeaFlux. The residual tends to be negative over tropics and positive over mid-latitudes. A negative residual implies that precipitation rate is too small, divergence is too large, or radiative cooling is too large. The residual of atmospheric energy is spatially and temporally correlated with cloud objects to identify cloud types associated with the residual. Spatially, shallow cumulus, cirrostratus, and deep convective cloud object occurrence are positively correlated with the absolute value of the residual. The temporal correlation coefficient between the number of deep convective cloud objects and individual energy components, net atmospheric irradiance, precipitation rate, and the sum of dry static and kinetic energy divergence and their tendency over western Pacific are, respectively, 0.84, 0.95, and 0.93. However, when all energy components are added, the atmospheric energy residual over tropical Pacific is temporally correlated well with the number of shallow cumulus cloud objects over tropical Pacific. Because shallow cumulus alters not enough atmospheric energy compared to the residual, these suggest 1) if retrieval errors associated with deep convective clouds are causing the column integrated atmospheric energy residual, the errors vary among individual deep convective clouds, and 2) it is possible that the residual is associated with processes in which shallow cumulus clouds affect deep convective clouds and hence atmospheric energy budget over tropical western Pacific.
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. broadband; calibration; CERES; climate; clouds; flux; longwave; radiation budget; shortwave; Time interpolation; top-of-atmosphere
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; climate; earth radiation budget; Radiance; Satellite
Loeb, Norman G.; Wang, Hailan; Cheng, Anning; Kato, Seiji; Fasullo, John T.; Xu, Kuan-Man; Allan, Richard P.Loeb, N. G., H. Wang, A. Cheng, S. Kato, J. T. Fasullo, K. Xu, R. P. Allan, 2016: Observational constraints on atmospheric and oceanic cross-equatorial heat transports: revisiting the precipitation asymmetry problem in climate models. Climate Dynamics, 46(9-10), 3239-3257. doi: 10.1007/s00382-015-2766-z. Satellite based top-of-atmosphere (TOA) and surface radiation budget observations are combined with mass corrected vertically integrated atmospheric energy divergence and tendency from reanalysis to infer the regional distribution of the TOA, atmospheric and surface energy budget terms over the globe. Hemispheric contrasts in the energy budget terms are used to determine the radiative and combined sensible and latent heat contributions to the cross-equatorial heat transports in the atmosphere (AHTEQ) and ocean (OHTEQ). The contrast in net atmospheric radiation implies an AHTEQ from the northern hemisphere (NH) to the southern hemisphere (SH) (0.75 PW), while the hemispheric difference in sensible and latent heat implies an AHTEQ in the opposite direction (0.51 PW), resulting in a net NH to SH AHTEQ (0.24 PW). At the surface, the hemispheric contrast in the radiative component (0.95 PW) dominates, implying a 0.44 PW SH to NH OHTEQ. Coupled model intercomparison project phase 5 (CMIP5) models with excessive net downward surface radiation and surface-to-atmosphere sensible and latent heat transport in the SH relative to the NH exhibit anomalous northward AHTEQ and overestimate SH tropical precipitation. The hemispheric bias in net surface radiative flux is due to too much longwave surface radiative cooling in the NH tropics in both clear and all-sky conditions and excessive shortwave surface radiation in the SH subtropics and extratropics due to an underestimation in reflection by clouds.
Stackhouse, P.W.; Wong, T; Kratz, D. P.; Sawaengphokhai, P.; Wilber, A. C.; Gupta, S. K.; Loeb, N. G.Stackhouse, P., T. Wong, D. P. Kratz, P. Sawaengphokhai, A. C. Wilber, S. K. Gupta, N. G. Loeb, 2016: Earth radiation Budget at Top-of-Atmosphere [in “State of the Climate in 2015"]. Bull. Amer. Meteor. Soc., 97(8), S41-S43. doi: 10.1175/2016BAMSStateoftheClimate.1.
von Schuckmann, K.; Palmer, M. D.; Trenberth, K. E.; Cazenave, A.; Chambers, D.; Champollion, N.; Hansen, J.; Josey, S. A.; Loeb, N.; Mathieu, P.-P.; Meyssignac, B.; Wild, M.von Schuckmann, K., M. D. Palmer, K. E. Trenberth, A. Cazenave, D. Chambers, N. Champollion, J. Hansen, S. A. Josey, N. Loeb, P. Mathieu, B. Meyssignac, M. Wild, 2016: An imperative to monitor Earth's energy imbalance. Nature Climate Change, 6(2), 138-144. doi: 10.1038/nclimate2876. The current Earth's energy imbalance (EEI) is mostly caused by human activity, and is driving global warming. The absolute value of EEI represents the most fundamental metric defining the status of global climate change, and will be more useful than using global surface temperature. EEI can best be estimated from changes in ocean heat content, complemented by radiation measurements from space. Sustained observations from the Argo array of autonomous profiling floats and further development of the ocean observing system to sample the deep ocean, marginal seas and sea ice regions are crucial to refining future estimates of EEI. Combining multiple measurements in an optimal way holds considerable promise for estimating EEI and thus assessing the status of global climate change, improving climate syntheses and models, and testing the effectiveness of mitigation actions. Progress can be achieved with a concerted international effort. climate change; Research data
Yu, L.; Adler, R.; Huffman, G.; Jin, X.; Kato, S.; Loeb, N.; Stackhouse, P.; Weller, R.; Wilber, A.Yu, L., R. Adler, G. Huffman, X. Jin, S. Kato, N. Loeb, P. Stackhouse, R. Weller, A. Wilber, 2016: Ocean surface heat and momentum fluxes [In "State of the Climate in 2015"]. Bull. Amer. Meteor. Soc., 97(8), S74-S80. doi: 10.1175/2016BAMSStateoftheClimate.1.

2015

Corbett, J. G.; Loeb, N. G.Corbett, J. G., N. G. Loeb, 2015: On the relative stability of CERES reflected shortwave and MISR and MODIS visible radiance measurements during the Terra satellite mission. Journal of Geophysical Research: Atmospheres, 120(22), 11,608–11,616. doi: 10.1002/2015JD023484. Fifteen years of visible, near-infrared, and broadband shortwave radiance measurements from Clouds and the Earth's Radiant Energy System (CERES), Multiangle Imaging Spectroradiometer (MISR), and Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on board NASA's Terra satellite are analyzed in order to assess their long-term relative stability for climate purposes. A regression-based approach between CERES, MODIS, and MISR (An camera only) reflectances is used to calculate the bias between the different reflectances relative to a reference year. When compared to the CERES shortwave broadband reflectance, relative drift between the MISR narrowbands is within 1% decade−1. Compared to the CERES shortwave reflectance, the MODIS narrowband reflectances show a relative drift of less than −1.33% decade−1. When compared to MISR, the MODIS reflectances show a relative drift of between −0.36% decade−1 and −2.66% decade−1. We show that the CERES Terra SW measurements are stable over the time period relative to CERES Aqua. Using this as evidence that CERES Terra may be absolutely stable, we suggest that the CERES, MISR, and MODIS instruments meet the radiometric stability goals for climate applications set out in Ohring et al. (2005). 1640 Remote sensing; 1694 Instruments and techniques; 3360 Remote sensing; 3394 Instruments and techniques; calibration; CERES; MISR; MODIS; Terra
Kato, Seiji; Loeb, Norman G.; Rutan, David A.; Rose, Fred G.Kato, S., N. G. Loeb, D. A. Rutan, F. G. Rose, 2015: Clouds and the Earth’s Radiant Energy System (CERES) Data Products for Climate Research. Journal of the Meteorological Society of Japan. Ser. II, 93(6), 597-612. doi: 10.2151/jmsj.2015-048. NASA’s Clouds and the Earth’s Radiant Energy System (CERES) project integrates CERES, Moderate Resolution Imaging Spectroradiometer (MODIS), and geostationary satellite observations to provide top-of-atmosphere (TOA) irradiances derived from broadband radiance observations by CERES instruments. It also uses snow cover and sea ice extent retrieved from microwave instruments as well as thermodynamic variables from reanalysis. In addition, these variables are used for surface and atmospheric irradiance computations. The CERES project provides TOA, surface, and atmospheric irradiances in various spatial and temporal resolutions. These data sets are for climate research and evaluation of climate models. Long-term observations are required to understand how the Earth system responds to radiative forcing. A simple model is used to estimate the time to detect trends in TOA reflected shortwave and emitted longwave irradiances. CERES; climate data; radiation budget
Liu, Chunlei; Allan, Richard P.; Berrisford, Paul; Mayer, Michael; Hyder, Patrick; Loeb, Norman; Smith, Doug; Vidale, Pier-Luigi; Edwards, John M.Liu, C., R. P. Allan, P. Berrisford, M. Mayer, P. Hyder, N. Loeb, D. Smith, P. Vidale, J. M. Edwards, 2015: Combining satellite observations and reanalysis energy transports to estimate global net surface energy fluxes 1985–2012. Journal of Geophysical Research: Atmospheres, 120(18), 9374–9389. doi: 10.1002/2015JD023264. Two methods are developed to estimate net surface energy fluxes based upon satellite-derived reconstructions of radiative fluxes at the top of atmosphere and the atmospheric energy tendencies and transports from the ERA-Interim reanalysis. Method 1 applies the mass-adjusted energy divergence from ERA-Interim, while method 2 estimates energy divergence based upon the net energy difference at the top of atmosphere and the surface from ERA-Interim. To optimize the surface flux and its variability over ocean, the divergences over land are constrained to match the monthly area mean surface net energy flux variability derived from a simple relationship between the surface net energy flux and the surface temperature change. The energy divergences over the oceans are then adjusted to remove an unphysical residual global mean atmospheric energy divergence. The estimated net surface energy fluxes are compared with other data sets from reanalysis and atmospheric model simulations. The spatial correlation coefficients of multiannual means between the estimations made here and other data sets are all around 0.9. There are good agreements in area mean anomaly variability over the global ocean, but discrepancies in the trend over the eastern Pacific are apparent. 0325 Evolution of the atmosphere; 1610 Atmosphere; 1630 Impacts of global change; 1635 Oceans; 1704 Atmospheric sciences; climate models; energy imbalance; satellite observations; surface heat flux
Loeb, N. G.; Wielicki, B. A.Loeb, N. G., B. A. Wielicki, 2015: SATELLITES AND SATELLITE REMOTE SENSING | Earth's Radiation Budget. Encyclopedia of Atmospheric Sciences (Second Edition), 67-76. Synopsis This article discusses the Earth's radiation budget and its role within the climate system. A brief summary of how Earth's radiation budget is determined from satellite observations is provided and the geographical, diurnal, and seasonal variations in its components are shown. The relationship between interannual variations in Earth's radiation budget and their relationship to natural fluctuations in the climate system such as the El Niño-Southern Oscillation are explored, as are the regional patterns of change during the past 12 years. This article also discusses the important role of clouds in modulating Earth's radiation budget at the top-of-atmosphere, surface, and within the atmosphere. Absorption; clouds; Diurnal; El Niño-Southern Oscillation; Emission; energy budget; Greenhouse effect; Interannual; radiation; Satellite
Rutan, David A.; Kato, Seiji; Doelling, David R.; Rose, Fred G.; Nguyen, Le Trang; Caldwell, Thomas E.; Loeb, Norman G.Rutan, D. A., S. Kato, D. R. Doelling, F. G. Rose, L. T. Nguyen, T. E. Caldwell, N. G. Loeb, 2015: CERES Synoptic Product: Methodology and Validation of Surface Radiant Flux. J. Atmos. Oceanic Technol., 32(6), 1121-1143. doi: 10.1175/JTECH-D-14-00165.1. AbstractThe Clouds and the Earth’s Radiant Energy System Synoptic (SYN1deg), edition 3, product provides climate-quality global 3-hourly 1° × 1°gridded top of atmosphere, in-atmosphere, and surface radiant fluxes. The in-atmosphere surface fluxes are computed hourly using a radiative transfer code based upon inputs from Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS), 3-hourly geostationary (GEO) data, and meteorological assimilation data from the Goddard Earth Observing System. The GEO visible and infrared imager calibration is tied to MODIS to ensure uniform MODIS-like cloud properties across all satellite cloud datasets. Computed surface radiant fluxes are compared to surface observations at 85 globally distributed land (37) and ocean buoy (48) sites as well as several other publicly available global surface radiant flux data products. Computed monthly mean downward fluxes from SYN1deg have a bias (standard deviation) of 3.0 W m−2 (5.7%) for shortwave and −4.0 W m−2 (2.9%) for longwave compared to surface observations. The standard deviation between surface downward shortwave flux calculations and observations at the 3-hourly time scale is reduced when the diurnal cycle of cloud changes is explicitly accounted for. The improvement is smaller for surface downward longwave flux owing to an additional sensitivity to boundary layer temperature/humidity, which has a weaker diurnal cycle compared to clouds. Climate records; radiative transfer; satellite observations; Surface fluxes
Smith, Doug M.; Allan, Richard P.; Coward, Andrew C.; Eade, Rosie; Hyder, Patrick; Liu, Chunlei; Loeb, Norman G.; Palmer, Matthew D.; Roberts, Chris D.; Scaife, Adam A.Smith, D. M., R. P. Allan, A. C. Coward, R. Eade, P. Hyder, C. Liu, N. G. Loeb, M. D. Palmer, C. D. Roberts, A. A. Scaife, 2015: Earth's energy imbalance since 1960 in observations and CMIP5 models. Geophysical Research Letters, 42(4), 1205–1213. doi: 10.1002/2014GL062669. Observational analyses of running 5 year ocean heat content trends (Ht) and net downward top of atmosphere radiation (N) are significantly correlated (r ~ 0.6) from 1960 to 1999, but a spike in Ht in the early 2000s is likely spurious since it is inconsistent with estimates of N from both satellite observations and climate model simulations. Variations in N between 1960 and 2000 were dominated by volcanic eruptions and are well simulated by the ensemble mean of coupled models from the Fifth Coupled Model Intercomparison Project (CMIP5). We find an observation-based reduction in N of − 0.31 ± 0.21 W m−2 between 1999 and 2005 that potentially contributed to the recent warming slowdown, but the relative roles of external forcing and internal variability remain unclear. While present-day anomalies of N in the CMIP5 ensemble mean and observations agree, this may be due to a cancelation of errors in outgoing longwave and absorbed solar radiation. 1616 Climate variability; 1626 Global climate models; 1635 Oceans; 4262 Ocean observing systems; 8408 Volcano/climate interactions; Net radiation; ocean uptake
Stanfield, Ryan E.; Dong, Xiquan; Xi, Baike; Del Genio, Anthony D.; Minnis, Patrick; Doelling, David; Loeb, NormanStanfield, R. E., X. Dong, B. Xi, A. D. Del Genio, P. Minnis, D. Doelling, N. Loeb, 2015: Assessment of NASA GISS CMIP5 and Post-CMIP5 Simulated Clouds and TOA Radiation Budgets Using Satellite Observations. Part II: TOA Radiation Budget and CREs. J. Climate, 28(5), 1842-1864. doi: 10.1175/JCLI-D-14-00249.1. AbstractIn Part I of this study, the NASA GISS Coupled Model Intercomparison Project (CMIP5) and post-CMIP5 (herein called C5 and P5, respectively) simulated cloud properties were assessed utilizing multiple satellite observations, with a particular focus on the southern midlatitudes (SMLs). This study applies the knowledge gained from Part I of this series to evaluate the modeled TOA radiation budgets and cloud radiative effects (CREs) globally using CERES EBAF (CE) satellite observations and the impact of regional cloud properties and water vapor on the TOA radiation budgets. Comparisons revealed that the P5- and C5-simulated global means of clear-sky and all-sky outgoing longwave radiation (OLR) match well with CE observations, while biases are observed regionally. Negative biases are found in both P5- and C5-simulated clear-sky OLR. P5-simulated all-sky albedo slightly increased over the SMLs due to the increase in low-level cloud fraction from the new planetary boundary layer (PBL) scheme. Shortwave, longwave, and net CRE are quantitatively analyzed as well. Regions of strong large-scale atmospheric upwelling/downwelling motion are also defined to compare regional differences across multiple cloud and radiative variables. In general, the P5 and C5 simulations agree with the observations better over the downwelling regime than over the upwelling regime. Comparing the results herein with the cloud property comparisons presented in Part I, the modeled TOA radiation budgets and CREs agree well with the CE observations. These results, combined with results in Part I, have quantitatively estimated how much improvement is found in the P5-simulated cloud and radiative properties, particularly over the SMLs and tropics, due to the implementation of the new PBL and convection schemes. climate models; Cloud parameterizations; Cloud radiative effects; Model comparison; Model evaluation/performance; Radiation budgets
Wong, T; Kratz, D. P.; Stackhouse, P.W.; Sawaengphokhai, P.; Wilber, A. C.; Gupta, S. K.; Loeb, N. G.Wong, T., D. P. Kratz, P. Stackhouse, P. Sawaengphokhai, A. C. Wilber, S. K. Gupta, N. G. Loeb, 2015: Earth radiation Budget at Top-of-Atmosphere [in “State of the Climate in 2014"]. Bull. Amer. Meteor. Soc., 96(7), S37-38. doi: 10.1175/2015BAMSStateoftheClimate.1.

2014

Allan, Richard P.; Liu, Chunlei; Loeb, Norman G.; Palmer, Matthew D.; Roberts, Malcolm; Smith, Doug; Vidale, Pier-LuigiAllan, R. P., C. Liu, N. G. Loeb, M. D. Palmer, M. Roberts, D. Smith, P. Vidale, 2014: Changes in global net radiative imbalance 1985–2012. Geophysical Research Letters, 41(15), 5588-5597. doi: 10.1002/2014GL060962. Combining satellite data, atmospheric reanalyses, and climate model simulations, variability in the net downward radiative flux imbalance at the top of Earth's atmosphere (N) is reconstructed and linked to recent climate change. Over the 1985–1999 period mean N (0.34 ± 0.67 Wm−2) is lower than for the 2000–2012 period (0.62 ± 0.43 Wm−2, uncertainties at 90% confidence level) despite the slower rate of surface temperature rise since 2000. While the precise magnitude of N remains uncertain, the reconstruction captures interannual variability which is dominated by the eruption of Mount Pinatubo in 1991 and the El Niño Southern Oscillation. Monthly deseasonalized interannual variability in N generated by an ensemble of nine climate model simulations using prescribed sea surface temperature and radiative forcings and from the satellite-based reconstruction is significantly correlated (r∼0.6) over the 1985–2012 period. Energy balance; radiative flux; climate model; 1610 Atmosphere; 1626 Global climate models; 1616 Climate variability; 1640 Remote sensing; Climate variability; satellite data; temperature; 1635 Oceans
Huang, Xianglei; Chen, Xiuhong; Potter, Gerald L.; Oreopoulos, Lazaros; Cole, Jason N. S.; Lee, Dongmin; Loeb, Norman G.Huang, X., X. Chen, G. L. Potter, L. Oreopoulos, J. N. S. Cole, D. Lee, N. G. Loeb, 2014: A Global Climatology of Outgoing Longwave Spectral Cloud Radiative Effect and Associated Effective Cloud Properties. J. Climate, 27(19), 7475-7492. doi: 10.1175/JCLI-D-13-00663.1. AbstractLongwave (LW) spectral flux and cloud radiative effect (CRE) are important for understanding the earth’s radiation budget and cloud–radiation interaction. Here, the authors extend their previous algorithms to collocated Atmospheric Infrared Sounder (AIRS) and Cloud and the Earth’s Radiant Energy System (CERES) observations over the entire globe and show that the algorithms yield consistently good performances for measurements over both land and ocean. As a result, the authors are able to derive spectral flux and CRE at 10-cm−1 intervals over the entire LW spectrum from all currently available collocated AIRS and CERES observations. Using this multiyear dataset, they delineate the climatology of spectral CRE, including the far IR, over the entire globe as well as in different climate zones. Furthermore, the authors define two quantities, IR-effective cloud-top height (CTHeff) and cloud amount (CAeff), based on the monthly-mean spectral (or band by band) CRE. Comparisons with cloud fields retrieved by the CERES–Moderate Resolution Imaging Spectroradiometer (MODIS) algorithm indicate that, under many circumstances, the CTHeff and CAeff can be related to the physical retrievals of CTH and CA and thus can enhance understandings of model deficiencies in LW radiation budgets and cloud fields. Using simulations from the GFDL global atmosphere model, version 2 (AM2); NASA’s Goddard Earth Observing System, version 5 (GEOS-5); and Environment Canada’s Canadian Centre for Climate Modelling and Analysis (CCCma) Fourth Generation Canadian Atmospheric General Circulation Model (CanAM4) as case studies, the authors further demonstrate the merits of the CTHeff and CAeff concepts in providing insights on global climate model evaluations that cannot be obtained solely from broadband LW flux and CRE comparisons. satellite observations; longwave radiation; Cloud radiative effects; Model evaluation/performance; General circulation models
Liu, C.; Yang, P.; Minnis, P.; Loeb, N.; Kato, S.; Heymsfield, A.; Schmitt, C.Liu, C., P. Yang, P. Minnis, N. Loeb, S. Kato, A. Heymsfield, C. Schmitt, 2014: A two-habit model for the microphysical and optical properties of ice clouds. Atmos. Chem. Phys. Discuss., 14(13), 19545-19586. doi: 10.5194/acpd-14-19545-2014. To provide a better representation of natural ice clouds, a novel ice cloud model containing two particle habits is developed. The microphysical and optical properties of the two-habit model (THM) are compared with both laboratory and in situ measurements, and its performance in downstream satellite remote sensing applications is tested. The THM assumes an ice cloud to be an ensemble of hexagonal columns and twenty-element aggregates, and to have specific habit fractions at each particle size. The ice water contents and median mass diameters calculated based on the THM closely agree with in situ measurements made during 11 field campaigns. In this study, the scattering, absorption, and polarization properties of ice crystals are calculated with a combination of the invariant imbedding T-matrix, pseudo-spectral time domain, and improved geometric-optics methods over an entire range of particle sizes. The phase functions, calculated based on the THM, show excellent agreement with counterparts from laboratory and in situ measurements and from satellite retrievals. For downstream applications in the retrieval of cloud microphysical and optical properties from MODIS observations, the THM presents excellent spectral consistency; specifically, the retrieved cloud optical thicknesses based on the visible/near infrared bands and the thermal infrared bands agree quite well. Furthermore, a comparison between the polarized reflectivities observed by the PARASOL satellite and from theoretical simulations illustrates that the THM can be used to represent ice cloud polarization properties.
Loeb, Norman G.; Rutan, David A.; Kato, Seiji; Wang, WeijieLoeb, N. G., D. A. Rutan, S. Kato, W. Wang, 2014: Observing Interannual Variations in Hadley Circulation Atmospheric Diabatic Heating and Circulation Strength. J. Climate, 27(11), 4139-4158. doi: 10.1175/JCLI-D-13-00656.1. AbstractSatellite and reanalysis data are used to observe interannual variations in atmospheric diabatic heating and circulation within the ascending and descending branches of the Hadley circulation (HC) during the past 12 yr. The column-integrated divergence of dry static energy (DSE) and kinetic energy is inferred from satellite-based observations of atmospheric radiation, precipitation latent heating, and reanalysis-based surface sensible heat flux for monthly positions of the HC branches, determined from a mass weighted zonal mean meridional streamfunction analysis. Mean surface radiative fluxes inferred from satellite and surface measurements are consistent to 1 W m−2 ( ENSO; satellite observations; Interannual variability; Atmospheric circulation; Cloud radiative effects; Energy budget/balance
Seidel, Dian J.; Feingold, Graham; Jacobson, Andrew R.; Loeb, NormanSeidel, D. J., G. Feingold, A. R. Jacobson, N. Loeb, 2014: Detection limits of albedo changes induced by climate engineering. Nature Climate Change, 4(2), 93-98. doi: 10.1038/nclimate2076. A key question surrounding proposals for climate engineering by increasing Earth's reflection of sunlight is the feasibility of detecting engineered albedo increases from short-duration experiments or prolonged implementation of solar-radiation management. We show that satellite observations permit detection of large increases, but interannual variability overwhelms the maximum conceivable albedo increases for some schemes. Detection of an abrupt global average albedo increase
Smith, G.L.; Priestley, K.J.; Loeb, N.G.Smith, G., K. Priestley, N. Loeb, 2014: Clouds and Earth Radiant Energy System: From Design to Data. IEEE Transactions on Geoscience and Remote Sensing, 52(3), 1729-1738. doi: 10.1109/TGRS.2013.2253782. The Clouds and the Earth's Radiant Energy System (CERES) project has instruments aboard the Terra and Aqua spacecraft that have provided a decade of radiation budget data. In October 2011, the CERES flight model 5 was placed in orbit on the NPOESS Preparatory Project spacecraft. Data from these instruments are being used to investigate the radiation balance of the Earth at various time and space scales and the role of clouds in this balance. The design and calibration, both on the ground and in-orbit, and operation of the instrument are discussed. Remote sensing; clouds; earth radiation budget; atmospheric measuring apparatus; atmospheric radiation; calibration; AD 2011 10; Aqua spacecraft; CERES flight model 5; CERES project instrument data; Earth radiation balance; NPOESS preparatory project spacecraft; Terra spacecraft; cloud and earth radiant energy system; cloud balance role; data design; ground calibration; ground design; in-orbit calibration; in-orbit design; instrument operation; radiation budget data; time-space scales; Earth; Extraterrestrial measurements; Instruments; Orbits; Space vehicles; Temperature measurement; Aqua; Clouds and the Earth's Radiant Energy System (CERES); Earth Observing System; NPOESS Preparatory Project (NPP); Terra

2013

Dessler, A. E.; Loeb, N.g.Dessler, A. E., N. Loeb, 2013: Impact of dataset choice on calculations of the short-term cloud feedback. Journal of Geophysical Research: Atmospheres, 118(7), 2821–2826. doi: 10.1002/jgrd.50199. Dessler [2010, hereafter D10] estimated the magnitude of the cloud feedback in response to short-term climate variations and concluded that it was likely positive, with an average magnitude of +0.50 ± 0.75 W/m2/K. This paper investigates the sensitivity of D10's results to the choice of clear-sky top-of-atmosphere flux (ΔRclear-sky), surface temperature (ΔTs), and reanalysis data sets. Most of the alternative ΔRclear-sky data sets produce cloud feedbacks that are close to D10, differing by 0.2–0.3 W/m2/K. An exception is the Terra SSF1deg ΔRclear-sky product, which produces an overall negative cloud feedback. However, a critical examination of those data leads us to conclude that that result is due to problems in the Terra ΔRclear-sky arising from issues with cloud clearing prior to July 2001. Eliminating the problematic early portion yields a cloud feedback in good agreement with D10. We also present an alternative calculation of the cloud feedback that does not require an estimate of ΔRclear-sky, and this calculation also produces a positive cloud feedback in agreement with D10. The various ΔTs data sets produce cloud feedbacks that differ by as much as 0.8 W/m2/K. The choice of reanalysis, used as a source of ΔRclear-sky or as adjustments for the cloud radiative forcing, has a small impact on the inferred cloud feedback. Overall, these results confirm the robustness of D10's estimate of a likely positive feedback. cloud feedback; energy budget
Doelling, David R.; Loeb, Norman G.; Keyes, Dennis F.; Nordeen, Michele L.; Morstad, Daniel; Nguyen, Cathy; Wielicki, Bruce A.; Young, David F.; Sun, MoguoDoelling, D. R., N. G. Loeb, D. F. Keyes, M. L. Nordeen, D. Morstad, C. Nguyen, B. A. Wielicki, D. F. Young, M. Sun, 2013: Geostationary Enhanced Temporal Interpolation for CERES Flux Products. J. Atmos. Oceanic Technol., 30(6), 1072-1090. doi: 10.1175/JTECH-D-12-00136.1.
Huang, Xianglei; Cole, Jason N. S.; He, Fei; Potter, Gerald L.; Oreopoulos, Lazaros; Lee, Dongmin; Suarez, Max; Loeb, Norman G.Huang, X., J. N. S. Cole, F. He, G. L. Potter, L. Oreopoulos, D. Lee, M. Suarez, N. G. Loeb, 2013: Longwave Band-By-Band Cloud Radiative Effect and Its Application in GCM Evaluation. J. Climate, 26(2), 450-467. doi: 10.1175/JCLI-D-12-00112.1. AbstractThe cloud radiative effect (CRE) of each longwave (LW) absorption band of a GCM’s radiation code is uniquely valuable for GCM evaluation because 1) comparing band-by-band CRE avoids the compensating biases in the broadband CRE comparison and 2) the fractional contribution of each band to the LW broadband CRE (fCRE) is sensitive to cloud-top height but largely insensitive to cloud fraction, thereby presenting a diagnostic metric to separate the two macroscopic properties of clouds. Recent studies led by the first author have established methods to derive such band-by-band quantities from collocated Atmospheric Infrared Sounder (AIRS) and Clouds and the Earth’s Radiant Energy System (CERES) observations. A study is presented here that compares the observed band-by-band CRE over the tropical oceans with those simulated by three different atmospheric GCMs—the GFDL Atmospheric Model version 2 (GFDL AM2), NASA Goddard Earth Observing System version 5 (GEOS-5), and the fourth-generation AGCM of the Canadian Centre for Climate Modelling and Analysis (CCCma CanAM4)—forced by observed SST. The models agree with observation on the annual-mean LW broadband CRE over the tropical oceans within ±1 W m−2. However, the differences among these three GCMs in some bands can be as large as or even larger than ±1 W m−2. Observed seasonal cycles of fCRE in major bands are shown to be consistent with the seasonal cycle of cloud-top pressure for both the amplitude and the phase. However, while the three simulated seasonal cycles of fCRE agree with observations on the phase, the amplitudes are underestimated. Simulated interannual anomalies from GFDL AM2 and CCCma CanAM4 are in phase with observed anomalies. The spatial distribution of fCRE highlights the discrepancies between models and observation over the low-cloud regions and the compensating biases from different bands. cloud forcing; Model evaluation/performance; Radiation budgets; Radiative fluxes; tropics
Kato, Seiji; Loeb, Norman G.; Rose, Fred G.; Doelling, David R.; Rutan, David A.; Caldwell, Thomas E.; Yu, Lisan; Weller, Robert A.Kato, S., N. G. Loeb, F. G. Rose, D. R. Doelling, D. A. Rutan, T. E. Caldwell, L. Yu, R. A. Weller, 2013: Surface Irradiances Consistent with CERES-Derived Top-of-Atmosphere Shortwave and Longwave Irradiances. J. Climate, 26(9), 2719-2740. doi: 10.1175/JCLI-D-12-00436.1. AbstractThe estimate of surface irradiance on a global scale is possible through radiative transfer calculations using satellite-retrieved surface, cloud, and aerosol properties as input. Computed top-of-atmosphere (TOA) irradiances, however, do not necessarily agree with observation-based values, for example, from the Clouds and the Earth’s Radiant Energy System (CERES). This paper presents a method to determine surface irradiances using observational constraints of TOA irradiance from CERES. A Lagrange multiplier procedure is used to objectively adjust inputs based on their uncertainties such that the computed TOA irradiance is consistent with CERES-derived irradiance to within the uncertainty. These input adjustments are then used to determine surface irradiance adjustments. Observations by the Atmospheric Infrared Sounder (AIRS), Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), CloudSat, and Moderate Resolution Imaging Spectroradiometer (MODIS) that are a part of the NASA A-Train constellation provide the uncertainty estimates. A comparison with surface observations from a number of sites shows that the bias [root-mean-square (RMS) difference] between computed and observed monthly mean irradiances calculated with 10 years of data is 4.7 (13.3) W m−2 for downward shortwave and −2.5 (7.1) W m−2 for downward longwave irradiances over ocean and −1.7 (7.8) W m−2 for downward shortwave and −1.0 (7.6) W m−2 for downward longwave irradiances over land. The bias and RMS error for the downward longwave and shortwave irradiances over ocean are decreased from those without constraint. Similarly, the bias and RMS error for downward longwave over land improves, although the constraint does not improve downward shortwave over land. This study demonstrates how synergetic use of multiple instruments (CERES, MODIS, CALIPSO, CloudSat, AIRS, and geostationary satellites) improves the accuracy of surface irradiance computations. Energy budget/balance; Radiation budgets; Radiative fluxes; radiative transfer
Li, J.-L. F.; Waliser, D. E.; Stephens, G.; Lee, Seungwon; L'Ecuyer, T.; Kato, Seiji; Loeb, Norman; Ma, Hsi-YenLi, J. F., D. E. Waliser, G. Stephens, S. Lee, T. L'Ecuyer, S. Kato, N. Loeb, H. Ma, 2013: Characterizing and understanding radiation budget biases in CMIP3/CMIP5 GCMs, contemporary GCM, and reanalysis. Journal of Geophysical Research: Atmospheres, 118(15), 8166-8184. doi: 10.1002/jgrd.50378. We evaluate the annual mean radiative shortwave flux downward at the surface (RSDS) and reflected shortwave (RSUT) and radiative longwave flux upward at top of atmosphere (RLUT) from the twentieth century Coupled Model Intercomparison Project Phase 5 (CMIP5) and Phase 3 (CMIP3) simulations as well as from the NASA GEOS5 model and Modern-Era Retrospective Analysis for Research and Applications analysis. The results show that a majority of the models have significant regional biases in the annual means of RSDS, RLUT, and RSUT, with biases from −30 to 30 W m−2. While the global average CMIP5 ensemble mean biases of RSDS, RLUT, and RSUT are reduced compared to CMIP3 by about 32% (e.g., −6.9 to 2.5 W m−2), 43%, and 56%, respectively. This reduction arises from a more complete cancellation of the pervasive negative biases over ocean and newly larger positive biases over land. In fact, based on these biases in the annual mean, Taylor diagram metrics, and RMSE, there is virtually no progress in the simulation fidelity of RSDS, RLUT, and RSUT fluxes from CMIP3 to CMIP5. A persistent systematic bias in CMIP3 and CMIP5 is the underestimation of RSUT and overestimation of RSDS and RLUT in the convectively active regions of the tropics. The amount of total ice and liquid atmospheric water content in these areas is also underestimated. We hypothesize that at least a part of these persistent biases stem from the common global climate model practice of ignoring the effects of precipitating and/or convective core ice and liquid in their radiation calculations. 1855 Remote sensing; 3337 Global climate models; CMIP3; CMIP5; radiation
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. aerosol; clouds; direct radiative effect; direct radiative forcing
Wen, Guoyong; Marshak, Alexander; Levy, Robert C.; Remer, Lorraine A.; Loeb, Norman G.; Várnai, Tamás; Cahalan, Robert F.Wen, G., A. Marshak, R. C. Levy, L. A. Remer, N. G. Loeb, T. Várnai, R. F. Cahalan, 2013: Improvement of MODIS aerosol retrievals near clouds. Journal of Geophysical Research: Atmospheres, 118(16), 9168–9181. doi: 10.1002/jgrd.50617. The retrieval of aerosol properties near clouds from reflected sunlight is challenging. Sunlight reflected from clouds can effectively enhance the reflectance in nearby clear regions. Ignoring cloud 3-D radiative effects can lead to large biases in aerosol retrievals, risking an incorrect interpretation of satellite observations on aerosol-cloud interaction. Earlier, we developed a simple model to compute the cloud-induced clear-sky radiance enhancement that is due to radiative interaction between boundary layer clouds and the molecular layer above. This paper focuses on the application and implementation of the correction algorithm. This is the first time that this method is being applied to a full Moderate Resolution Imaging Spectroradiometer (MODIS) granule. The process of the correction includes converting Clouds and the Earth's Radiant Energy System broadband flux to visible narrowband flux, computing the clear-sky radiance enhancement, and retrieving aerosol properties. We find that the correction leads to smaller values in aerosol optical depth (AOD), Ångström exponent, and the small mode aerosol fraction of the total AOD. It also makes the average aerosol particle size larger near clouds than far away from clouds, which is more realistic than the opposite behavior observed in operational retrievals. We discuss issues in the current correction method as well as our plans to validate the algorithm. 3-D; aerosol; clouds; MODIS

2012

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. 0736 Snow; 0758 Remote sensing; 3359 Radiative processes; albedo; Antarctica; CERES; sastrugi
Huang, Xianglei; Loeb, Norman G.; Chuang, HuiwenHuang, X., N. G. Loeb, H. Chuang, 2012: Assessing Stability of CERES-FM3 Daytime Longwave Unfiltered Radiance with AIRS Radiances. J. Atmos. Oceanic Technol., 29(3), 375-381. doi: 10.1175/JTECH-D-11-00066.1.
Kato, Seiji; Loeb, Norman G.; Rutan, David A.; Rose, Fred G.; Sun-Mack, Sunny; Miller, Walter F.; Chen, YanKato, S., N. G. Loeb, D. A. Rutan, F. G. Rose, S. Sun-Mack, W. F. Miller, Y. Chen, 2012: Uncertainty Estimate of Surface Irradiances Computed with MODIS-, CALIPSO-, and CloudSat-Derived Cloud and Aerosol Properties. Surveys in Geophysics, 33(3-4), 395-412. doi: 10.1007/s10712-012-9179-x. Differences of modeled surface upward and downward longwave and shortwave irradiances are calculated using modeled irradiance computed with active sensor-derived and passive sensor-derived cloud and aerosol properties. The irradiance differences are calculated for various temporal and spatial scales, monthly gridded, monthly zonal, monthly global, and annual global. Using the irradiance differences, the uncertainty of surface irradiances is estimated. The uncertainty (1σ) of the annual global surface downward longwave and shortwave is, respectively, 7 W m−2 (out of 345 W m−2) and 4 W m−2 (out of 192 W m−2), after known bias errors are removed. Similarly, the uncertainty of the annual global surface upward longwave and shortwave is, respectively, 3 W m−2 (out of 398 W m−2) and 3 W m−2 (out of 23 W m−2). The uncertainty is for modeled irradiances computed using cloud properties derived from imagers on a sun-synchronous orbit that covers the globe every day (e.g., moderate-resolution imaging spectrometer) or modeled irradiances computed for nadir view only active sensors on a sun-synchronous orbit such as Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation and CloudSat. If we assume that longwave and shortwave uncertainties are independent of each other, but up- and downward components are correlated with each other, the uncertainty in global annual mean net surface irradiance is 12 W m−2. One-sigma uncertainty bounds of the satellite-based net surface irradiance are 106 W m−2 and 130 W m−2. Astronomy, Observations and Techniques; Earth Sciences, general; Geophysics/Geodesy; Surface net irradiance; Surface radiative energy budget
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. Astronomy, Observations and Techniques; Climate variability; clouds; Earth Sciences, general; Geophysics/Geodesy; radiation budget
Loeb, Norman G.; Lyman, John M.; Johnson, Gregory C.; Allan, Richard P.; Doelling, David R.; Wong, Takmeng; Soden, Brian J.; Stephens, Graeme L.Loeb, N. G., J. M. Lyman, G. C. Johnson, R. P. Allan, D. R. Doelling, T. Wong, B. J. Soden, G. L. Stephens, 2012: Observed changes in top-of-the-atmosphere radiation and upper-ocean heating consistent within uncertainty. Nature Geoscience, 5(2), 110-113. doi: 10.1038/ngeo1375. Global climate change results from a small yet persistent imbalance between the amount of sunlight absorbed by Earth and the thermal radiation emitted back to space. An apparent inconsistency has been diagnosed between interannual variations in the net radiation imbalance inferred from satellite measurements and upper-ocean heating rate from in situ measurements, and this inconsistency has been interpreted as ‘missing energy’ in the system. Here we present a revised analysis of net radiation at the top of the atmosphere from satellite data, and we estimate ocean heat content, based on three independent sources. We find that the difference between the heat balance at the top of the atmosphere and upper-ocean heat content change is not statistically significant when accounting for observational uncertainties in ocean measurements, given transitions in instrumentation and sampling. Furthermore, variability in Earth’s energy imbalance relating to El Niño-Southern Oscillation is found to be consistent within observational uncertainties among the satellite measurements, a reanalysis model simulation and one of the ocean heat content records. We combine satellite data with ocean measurements to depths of 1,800 m, and show that between January 2001 and December 2010, Earth has been steadily accumulating energy at a rate of 0.50±0.43 Wm−2 (uncertainties at the 90% confidence level). We conclude that energy storage is continuing to increase in the sub-surface ocean. Atmospheric science; Climate science; Oceanography
Stephens, Graeme L.; Li, Juilin; Wild, Martin; Clayson, Carol Anne; Loeb, Norman; Kato, Seiji; L'Ecuyer, Tristan; Jr, Paul W. Stackhouse; Lebsock, Matthew; Andrews, TimothyStephens, G. L., J. Li, M. Wild, C. A. Clayson, N. Loeb, S. Kato, T. L'Ecuyer, P. W. S. Jr, M. Lebsock, T. Andrews, 2012: An update on Earth's energy balance in light of the latest global observations. Nature Geoscience, 5(10), 691-696. doi: 10.1038/ngeo1580. Climate change is governed by changes to the global energy balance. At the top of the atmosphere, this balance is monitored globally by satellite sensors that provide measurements of energy flowing to and from Earth. By contrast, observations at the surface are limited mostly to land areas. As a result, the global balance of energy fluxes within the atmosphere or at Earth's surface cannot be derived directly from measured fluxes, and is therefore uncertain. This lack of precise knowledge of surface energy fluxes profoundly affects our ability to understand how Earth's climate responds to increasing concentrations of greenhouse gases. In light of compilations of up-to-date surface and satellite data, the surface energy balance needs to be revised. Specifically, the longwave radiation received at the surface is estimated to be significantly larger, by between 10 and 17 Wm−2, than earlier model-based estimates. Moreover, the latest satellite observations of global precipitation indicate that more precipitation is generated than previously thought. This additional precipitation is sustained by more energy leaving the surface by evaporation — that is, in the form of latent heat flux — and thereby offsets much of the increase in longwave flux to the surface. View full text Atmospheric science; Climate science; hydrogeology and limnology; hydrology
Susskind, Joel; Molnar, Gyula; Iredell, Lena; Loeb, Norman G.Susskind, J., G. Molnar, L. Iredell, N. G. Loeb, 2012: Interannual variability of outgoing longwave radiation as observed by AIRS and CERES. Journal of Geophysical Research: Atmospheres, 117(D23), D23107. doi: 10.1029/2012JD017997. The paper examines spatial anomaly time series of outgoing longwave radiation (OLR) and Clear Sky OLR (OLRCLR) as determined using observations from CERES Terra and AIRS over the time period September 2002 through June 2011. We find excellent agreement of the two OLR data sets in almost every detail down to the 1° × 1° spatial grid point level. The extremely close agreement of OLR anomaly time series derived from observations by two different instruments implies high stability of both sets of results. Anomalies of global mean, and especially tropical mean, OLR are shown to be strongly correlated with an El Niño Index. These correlations explain that the recent global and tropical mean decreases in OLR over the time period studied are primarily the result of a transition from an El Niño condition at the beginning of the data record to La Niña conditions toward the end of the data period. We show that the close correlation of mean OLR anomalies with the El Niño Index can be well accounted for by temporal changes of OLR within two spatial regions, one to the east of, and one to the west of, the NOAA Niño-4 region. Anomalies of OLR in these two spatial regions are both strongly correlated with the El Niño Index as a result of the strong anticorrelation of anomalies of cloud cover and midtropospheric water vapor in these two regions with the El Niño Index. 1616 Climate variability; 1640 Remote sensing; AIRS; CERES; el nino; OLR
Wong, T. M.; Stackhouse Jr, PW; Kratz, D. P.; Wilber, A. C.; Loeb, N. GWong, T. M., P. Stackhouse Jr, D. P. Kratz, A. C. Wilber, N. G. Loeb, 2012: Earth Radiation Budget at Top-of-atmosphere [in "State of the Climate in 2011"]. Bull. Amer. Meteor. Soc., 93(7), S38-S40. doi: 10.1175/2012BAMSStateoftheClimate.1.

2011

Cole, Jason; Barker, Howard W.; Loeb, Norman G.; von Salzen, KnutCole, J., H. W. Barker, N. G. Loeb, K. von Salzen, 2011: Assessing Simulated Clouds and Radiative Fluxes Using Properties of Clouds Whose Tops are Exposed to Space. J. Climate, 24(11), 2715-2727. doi: 10.1175/2011JCLI3652.1. AbstractCoincident top-of-atmosphere (TOA) radiative fluxes and cloud optical properties for portions of clouds whose tops are exposed to space within several pressure ranges are used to evaluate how a GCM realizes its all-sky radiative fluxes and vertical structure. In particular, observations of cloud properties and radiative fluxes from the Clouds and the Earth’s Radiant Energy System (CERES) Science Team are used to assess the Canadian Centre for Climate Modeling and Analysis atmospheric global climate model (CanAM4). Through comparison of CanAM4 with CERES observations it was found that, while the July-mean all-sky TOA shortwave and longwave fluxes simulated by CanAM4 agree well with those observed, this agreement rests on compensating biases in simulated cloud properties and radiative fluxes for low, middle, and high clouds. Namely, low and middle cloud albedos simulated by CanAM4 are larger than those observed by CERES attributable to CanAM4 simulating cloud optical depths via large liquid water paths that are too large but are partly compensated by too small cloud fractions. It was also found that CanAM4 produces 2D histograms of cloud fraction and cloud albedo for low, middle, and high clouds that are significantly different than generated using the CERES observations. albedo; climate models; clouds; Optical properties; Radiative fluxes; Remote sensing
Kato, Seiji; Rose, Fred G.; Sun-Mack, Sunny; Miller, Walter F.; Chen, Yan; Rutan, David A.; Stephens, Graeme L.; Loeb, Norman G.; Minnis, Patrick; Wielicki, Bruce A.; Winker, David M.; Charlock, Thomas P.; Stackhouse, Paul W.; Xu, Kuan-Man; Collins, William D.Kato, S., F. G. Rose, S. Sun-Mack, W. F. Miller, Y. Chen, D. A. Rutan, G. L. Stephens, N. G. Loeb, P. Minnis, B. A. Wielicki, D. M. Winker, T. P. Charlock, P. W. Stackhouse, K. Xu, W. D. Collins, 2011: Improvements of top-of-atmosphere and surface irradiance computations with CALIPSO-, CloudSat-, and MODIS-derived cloud and aerosol properties. Journal of Geophysical Research: Atmospheres, 116(D19), D19209. doi: 10.1029/2011JD016050. One year of instantaneous top-of-atmosphere (TOA) and surface shortwave and longwave irradiances are computed using cloud and aerosol properties derived from instruments on the A-Train Constellation: the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite, the CloudSat Cloud Profiling Radar (CPR), and the Aqua Moderate Resolution Imaging Spectrometer (MODIS). When modeled irradiances are compared with those computed with cloud properties derived from MODIS radiances by a Clouds and the Earth's Radiant Energy System (CERES) cloud algorithm, the global and annual mean of modeled instantaneous TOA irradiances decreases by 12.5 W m−2 (5.0%) for reflected shortwave and 2.5 W m−2 (1.1%) for longwave irradiances. As a result, the global annual mean of instantaneous TOA irradiances agrees better with CERES-derived irradiances to within 0.5W m−2 (out of 237.8 W m−2) for reflected shortwave and 2.6W m−2 (out of 240.1 W m−2) for longwave irradiances. In addition, the global annual mean of instantaneous surface downward longwave irradiances increases by 3.6 W m−2 (1.0%) when CALIOP- and CPR-derived cloud properties are used. The global annual mean of instantaneous surface downward shortwave irradiances also increases by 8.6 W m−2 (1.6%), indicating that the net surface irradiance increases when CALIOP- and CPR-derived cloud properties are used. Increasing the surface downward longwave irradiance is caused by larger cloud fractions (the global annual mean by 0.11, 0.04 excluding clouds with optical thickness less than 0.3) and lower cloud base heights (the global annual mean by 1.6 km). The increase of the surface downward longwave irradiance in the Arctic exceeds 10 W m−2 (∼4%) in winter because CALIOP and CPR detect more clouds in comparison with the cloud detection by the CERES cloud algorithm during polar night. The global annual mean surface downward longwave irradiance of 345.4 W m−2 is estimated by combining the modeled instantaneous surface longwave irradiance computed with CALIOP and CPR cloud profiles with the global annual mean longwave irradiance from the CERES product (AVG), which includes the diurnal variation of the irradiance. The estimated bias error is −1.5 W m−2 and the uncertainty is 6.9 W m−2. The uncertainty is predominately caused by the near-surface temperature and column water vapor amount uncertainties. 0360 Radiation: transmission and scattering; 1610 Atmosphere; 1640 Remote sensing; aerosols; clouds; radiation; surface energy budget
Kratz, D. P.; Stackhouse, P.W.; Wong, T; Sawaengphokhai, P.; Wilber, A. C.; Loeb, N. G.Kratz, D. P., P. Stackhouse, T. Wong, P. Sawaengphokhai, A. C. Wilber, N. G. Loeb, 2011: Earth Radiation Budget at top-of-atmosphere in 'State of the Climate 2010'. Bulletin of the American Meterological Society, 92(6). doi: 10.1175/1520-0477-92.6.S1.
Smith, G. L.; Priestley, K. J.; Loeb, N. G.; Wielicki, B. A.; Charlock, T. P.; Minnis, P.; Doelling, D. R.; Rutan, D. A.Smith, G. L., K. J. Priestley, N. G. Loeb, B. A. Wielicki, T. P. Charlock, P. Minnis, D. R. Doelling, D. A. Rutan, 2011: Clouds and Earth Radiant Energy System (CERES), a review: Past, present and future. Advances in Space Research, 48(2), 254-263. doi: 10.1016/j.asr.2011.03.009. The Clouds and Earth Radiant Energy System (CERES) project’s objectives are to measure the reflected solar radiance (shortwave) and Earth-emitted (longwave) radiances and from these measurements to compute the shortwave and longwave radiation fluxes at the top of the atmosphere (TOA) and the surface and radiation divergence within the atmosphere. The fluxes at TOA are to be retrieved to an accuracy of 2%. Improved bidirectional reflectance distribution functions (BRDFs) have been developed to compute the fluxes at TOA from the measured radiances with errors reduced from ERBE by a factor of two or more. Instruments aboard the Terra and Aqua spacecraft provide sampling at four local times. In order to further reduce temporal sampling errors, data are used from the geostationary meteorological satellites to account for changes of scenes between observations by the CERES radiometers. A validation protocol including in-flight calibrations and comparisons of measurements has reduced the instrument errors to less than 1%. The data are processed through three editions. The first edition provides a timely flow of data to investigators and the third edition provides data products as accurate as possible with resources available. A suite of cloud properties retrieved from the MODerate-resolution Imaging Spectroradiometer (MODIS) by the CERES team is used to identify the cloud properties for each pixel in order to select the BRDF for each pixel so as to compute radiation fluxes from radiances. Also, the cloud information is used to compute radiation at the surface and through the atmosphere and to facilitate study of the relationship between clouds and the radiation budget. The data products from CERES include, in addition to the reflected solar radiation and Earth emitted radiation fluxes at TOA, the upward and downward shortwave and longwave radiation fluxes at the surface and at various levels in the atmosphere. Also at the surface the photosynthetically active radiation and ultraviolet radiation (total, UVA and UVB) are computed. The CERES instruments aboard the Terra and Aqua spacecraft have served well past their design life times. A CERES instrument has been integrated onto the NPP platform and is ready for launch in 2011. Another CERES instrument is being built for launch in 2014, and plans are being made for a series of follow-on missions. CERES; earth radiation budget; radiometry; Remote sensing
Szewczyk, Z. Peter; Priestley, Kory J.; Walikainen, Dale R.; Loeb, Norman G.; Smith, G. LouisSzewczyk, Z. P., K. J. Priestley, D. R. Walikainen, N. G. Loeb, G. L. Smith, 2011: Putting all CERES instruments (Terra/Aqua) on the same radiometric scale. Proc. SPIE, 8177, 817704-817704-11. doi: 10.1117/12.896897. Clouds and the Earth's Radiant Energy System (CERES) instruments are scanning radiometers on board the Terra and Aqua satellites since March of 2000 and June of 2002, respectively; hence, their continuous Earth's radiation budget dataset is more than a decade long. Since there are four CERES scanners in operation, it is important that their measurements are consistent. A focus of this paper is on placing two Aqua CERES sensors on the same radiometric scale as FM1 on Terra. The paper contains a description of radiation budget experiments that are used in this task, and a complete set of results. It is shown that one-time adjustments to gains and spectral response functions are sufficient in putting FM3 and FM4 on the same radiometric scale as FM1 at the beginning of their mission. The Edition 3 of ERBE-like data products use derived corrections for Aqua CERES sensors.
Zhao, Tom X.-P.; Loeb, Norman G.; Laszlo, Istvan; Zhou, MiZhao, T. X., N. G. Loeb, I. Laszlo, M. Zhou, 2011: Global component aerosol direct radiative effect at the top of atmosphere. International Journal of Remote Sensing, 32(3), 633-655. doi: 10.1080/01431161.2010.517790. The two-step approach of combining Clouds and the Earth's Radiant Energy System (CERES)/Moderate Resolution Imaging Spectroradiometer (MODIS) shortwave (SW) flux and aerosol optical thickness (AOT) at 0.55 μm with the component AOT fractions from the Goddard Space Flight Centre (GSFC)/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model to derive top of atmosphere (TOA) component aerosol direct radiative effect (ADRE) over the global cloud-free oceans proposed by the first author in a previous publication has been extended to cloud-free land areas for nearly global coverage. Validation has also been performed by comparing the ADRE computation with calculations from the Fu–Liou radiative transfer model at globally distributed AErosol RObotic NETwork (AERONET) sites by using the aerosol optical properties observed from AERONET and surface reflectance obtained from MODIS observations as the model inputs. The promising validation results provide support for extending the two-step approach from global clear-sky oceans to global clear-sky land areas. The global annual mean values of ADRE for clear-sky condition are +0.3 ± 0.2 W m−2 for black carbon, −1.0 ± 0.6 W m−2 for organic carbon; −2.3 ± 0.7 W m−2 for sulphate; −1.6 ± 0.5 W m−2 for dust; −2.2 ± 0.6 W m−2 for sea salt; −2.4 ± 0.8 W m−2 for anthropogenic aerosol; −4.5 ± 1.2 W m−2 for natural aerosol; and −6.8 ± 1.7 W m−2 for total aerosols. For global average cloudy skies, the all-sky values of component ADRE are about 42% of their clear-sky counterparts. The major sources of uncertainty in the estimates are also discussed.

2010

Bryan, Frank O.; Tomas, Robert; Dennis, John M.; Chelton, Dudley B.; Loeb, Norman G.; McClean, Julie L.Bryan, F. O., R. Tomas, J. M. Dennis, D. B. Chelton, N. G. Loeb, J. L. McClean, 2010: Frontal Scale Air–Sea Interaction in High-Resolution Coupled Climate Models. J. Climate, 23(23), 6277-6291. doi: 10.1175/2010JCLI3665.1. Abstract The emerging picture of frontal scale air–sea interaction derived from high-resolution satellite observations of surface winds and sea surface temperature (SST) provides a unique opportunity to test the fidelity of high-resolution coupled climate simulations. Initial analysis of the output of a suite of Community Climate System Model (CCSM) experiments indicates that characteristics of frontal scale ocean–atmosphere interaction, such as the positive correlation between SST and surface wind stress, are realistically captured only when the ocean component is eddy resolving. The strength of the coupling between SST and surface stress is weaker than observed, however, as has been found previously for numerical weather prediction models and other coupled climate models. The results are similar when the atmospheric component model grid resolution is doubled from 0.5° to 0.25°, an indication that shortcomings in the representation of subgrid scale atmospheric planetary boundary layer processes, rather than resolved scale processes, are responsible for the weakness of the coupling. In the coupled model solutions the response to mesoscale SST features is strongest in the atmospheric boundary layer, but there is a deeper reaching response of the atmospheric circulation apparent in free tropospheric clouds. This simulated response is shown to be consistent with satellite estimates of the relationship between mesoscale SST and all-sky albedo. Airndashsea interaction; albedo; Coupled models; Mesoscale systems; sea surface temperature; Wind stress
Huang, Xianglei; Loeb, Norman G.; Yang, WenzeHuang, X., N. G. Loeb, W. Yang, 2010: Spectrally resolved fluxes derived from collocated AIRS and CERES measurements and their application in model evaluation: 2. Cloudy sky and band-by-band cloud radiative forcing over the tropical oceans. Journal of Geophysical Research: Atmospheres, 115(D21), D21101. doi: 10.1029/2010JD013932. We first present an algorithm for deriving cloudy sky outgoing spectral flux through the entire longwave spectrum from the collocated Atmospheric Infrared Sounder (AIRS) and Cloud and the Earth's Radiant Energy System (CERES) measurements over the tropical oceans. The algorithm is similar to the one described in part 1 of this series of studies: spectral angular dependent models are developed to estimate the spectral flux of each AIRS channel, and then a multivariate linear prediction scheme is used to estimate spectral fluxes at frequencies not covered by the AIRS instrument. The entire algorithm is validated against synthetic spectra as well as the CERES outgoing longwave radiation (OLR) measurements. Mean difference between the OLR estimated in this way and the collocated CERES OLR is 2.15 W m−2 with a standard deviation of 5.51 W m−2. The algorithm behaves consistently well for different combinations of cloud fractions and cloud-surface temperature difference, indicating the robustness of the algorithm for various cloudy scenes. Then, using the Geophysical Fluid Dynamics Laboratory AM2 model as a case study, we illustrate the merit of band-by-band cloud radiative forcings (CRFs) derived from this algorithm in model evaluation. The AM2 tropical annual mean band-by-band CRFs generally agree with the observed counterparts, but some systematic biases in the window bands and over the marine-stratus regions can be clearly identified. An idealized model is used to interpret the results and to explain why the fractional contribution of each band to the broadband CRF is worthy for studying: it is sensitive to cloud height but largely insensitive to the cloud fraction. 1626 Global climate models; 3310 Clouds and cloud feedbacks; 3359 Radiative processes; band-by-band cloud radiative forcing; GCM evaluation; spectral fluxes
Lin, B.; Chambers, L.; P. Stackhouse Jr.; Wielicki, B.; Hu, Y.; Minnis, P.; Loeb, N.; Sun, W.; Potter, G.; Min, Q.; Schuster, G.; Fan, T.-F.Lin, B., L. Chambers, . P. Stackhouse Jr., B. Wielicki, Y. Hu, P. Minnis, N. Loeb, W. Sun, G. Potter, Q. Min, G. Schuster, T. Fan, 2010: Estimations of climate sensitivity based on top-of-atmosphere radiation imbalance. Atmos. Chem. Phys., 10(4), 1923-1930. doi: 10.5194/acp-10-1923-2010. Large climate feedback uncertainties limit the accuracy in predicting the response of the Earth's climate to the increase of CO2 concentration within the atmosphere. This study explores a potential to reduce uncertainties in climate sensitivity estimations using energy balance analysis, especially top-of-atmosphere (TOA) radiation imbalance. The time-scales studied generally cover from decade to century, that is, middle-range climate sensitivity is considered, which is directly related to the climate issue caused by atmospheric CO2 change. The significant difference between current analysis and previous energy balance models is that the current study targets at the boundary condition problem instead of solving the initial condition problem. Additionally, climate system memory and deep ocean heat transport are considered. The climate feedbacks are obtained based on the constraints of the TOA radiation imbalance and surface temperature measurements of the present climate. In this study, the TOA imbalance value of 0.85 W/m2 is used. Note that this imbalance value has large uncertainties. Based on this value, a positive climate feedback with a feedback coefficient ranging from −1.3 to −1.0 W/m2/K is found. The range of feedback coefficient is determined by climate system memory. The longer the memory, the stronger the positive feedback. The estimated time constant of the climate is large (70~120 years) mainly owing to the deep ocean heat transport, implying that the system may be not in an equilibrium state under the external forcing during the industrial era. For the doubled-CO2 climate (or 3.7 W/m2 forcing), the estimated global warming would be 3.1 K if the current estimate of 0.85 W/m2 TOA net radiative heating could be confirmed. With accurate long-term measurements of TOA radiation, the analysis method suggested by this study provides a great potential in the estimations of middle-range climate sensitivity.
Lin, Wuyin; Zhang, Minghua; Loeb, Norman G.Lin, W., M. Zhang, N. G. Loeb, 2010: Reply to Comments on “Seasonal Variation of the Physical Properties of Marine Boundary Layer Clouds off the California Coast”. J. Climate, 23(12), 3421-3423. doi: 10.1175/2010JCLI3483.1. clouds; marine boundary layer; North America; satellite observations; Seasonal 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
Stackhouse Jr, PW; Wong, T.; Loeb, N. G; Kratz, D. P.; Wilber, A. C.; Doelling, D. R.; Nguyen, L. CathyStackhouse Jr, P., T. Wong, N. G. Loeb, D. P. Kratz, A. C. Wilber, D. R. Doelling, L. C. Nguyen, 2010: Earth Radiation Budget at top-of-atmosphere [in "State of the Climate in 2009”]. Bull. Amer. Meteor. Soc., 91(7), S41. doi: 10.1175/BAMS-91-7-StateoftheClimate.
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%. 0305 Aerosols and particles; 0320 Cloud physics and chemistry; 3311 Clouds and aerosols; aerosols; clouds

2009

Lin, Wuyin; Zhang, Minghua; Loeb, Norman G.Lin, W., M. Zhang, N. G. Loeb, 2009: Seasonal Variation of the Physical Properties of Marine Boundary Layer Clouds off the California Coast. J. Climate, 22(10), 2624-2638. doi: 10.1175/2008JCLI2478.1. Abstract Marine boundary layer (MBL) clouds can significantly regulate the sensitivity of climate models, yet they are currently poorly simulated. This study aims to characterize the seasonal variations of physical properties of these clouds and their associated processes by using multisatellite data. Measurements from several independent satellite datasets [International Satellite Cloud Climatology Project (ISCCP), Clouds and the Earth’s Radiant Energy System–Moderate Resolution Imaging Spectroradiometer (CERES–MODIS), Geoscience Laser Altimeter System (GLAS), and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO)], in conjunction with balloon soundings from the mobile facility of the Atmospheric Radiation Measurement (ARM) program at Point Reyes and reanalysis products, are used to characterize the seasonal variations of MBL cloud-top and cloud-base heights, cloud thickness, the degree of decoupling between clouds and MBL, and inversion strength off the California coast. The main results from this study are as follows: (i) MBL clouds over the northeast subtropical Pacific in the summer are more prevalent and associated with a larger in-cloud water path than in winter. The cloud-top and cloud-base heights are lower in the summer than in the winter. (ii) Although the lower-tropospheric stability of the atmosphere is higher in the summer, the MBL inversion strength is only weakly stronger in the summer because of a negative feedback from the cloud-top altitude. Summertime MBL clouds are more homogeneous and are associated with lower surface latent heat flux than those in the winter. (iii) Seasonal variations of low-cloud properties from summer to winter resemble the downstream stratocumulus-to-cumulus transition of MBL clouds in terms of MBL depth, cloud-top and cloud-base heights, inversion strength, and spatial homogeneity. The “deepening–warming” mechanism of Bretherton and Wyant for the stratocumulus-to-trade-cumulus transition downstream of the cold eastern ocean can also explain the seasonal variation of low clouds from the summer to the winter, except that warming of the sea surface temperature needs to be taken as relative to the free-tropospheric air temperature, which occurs in the winter. The observed variation of low clouds from summer to winter is attributed to the much larger seasonal cooling of the free-tropospheric air temperature than that of the sea surface temperature. clouds; satellite observations; marine boundary layer; North America; Seasonal variability
Loeb, Norman G.; Wielicki, Bruce A.; Doelling, David R.; Smith, G. Louis; Keyes, Dennis F.; Kato, Seiji; Manalo-Smith, Natividad; Wong, TakmengLoeb, N. G., B. A. Wielicki, D. R. Doelling, G. L. Smith, D. F. Keyes, S. Kato, N. Manalo-Smith, T. Wong, 2009: Toward Optimal Closure of the Earth's Top-of-Atmosphere Radiation Budget. J. Climate, 22(3), 748-766. doi: 10.1175/2008JCLI2637.1. Abstract Despite recent improvements in satellite instrument calibration and the algorithms used to determine reflected solar (SW) and emitted thermal (LW) top-of-atmosphere (TOA) radiative fluxes, a sizeable imbalance persists in the average global net radiation at the TOA from satellite observations. This imbalance is problematic in applications that use earth radiation budget (ERB) data for climate model evaluation, estimate the earth’s annual global mean energy budget, and in studies that infer meridional heat transports. This study provides a detailed error analysis of TOA fluxes based on the latest generation of Clouds and the Earth’s Radiant Energy System (CERES) gridded monthly mean data products [the monthly TOA/surface averages geostationary (SRBAVG-GEO)] and uses an objective constrainment algorithm to adjust SW and LW TOA fluxes within their range of uncertainty to remove the inconsistency between average global net TOA flux and heat storage in the earth–atmosphere system. The 5-yr global mean CERES net flux from the standard CERES product is 6.5 W m−2, much larger than the best estimate of 0.85 W m−2 based on observed ocean heat content data and model simulations. The major sources of uncertainty in the CERES estimate are from instrument calibration (4.2 W m−2) and the assumed value for total solar irradiance (1 W m−2). After adjustment, the global mean CERES SW TOA flux is 99.5 W m−2, corresponding to an albedo of 0.293, and the global mean LW TOA flux is 239.6 W m−2. These values differ markedly from previously published adjusted global means based on the ERB Experiment in which the global mean SW TOA flux is 107 W m−2 and the LW TOA flux is 234 W m−2. satellite observations; Radiation budgets; Fluxes
Loeb, Norman G.; Wielicki, Bruce A.; Wong, Takmeng; Parker, Peter A.Loeb, N. G., B. A. Wielicki, T. Wong, P. A. Parker, 2009: Impact of data gaps on satellite broadband radiation records. Journal of Geophysical Research: Atmospheres, 114(D11), D11109. doi: 10.1029/2008JD011183. A simulated 30-year climate data record of net cloud radiative effect (defined as the difference between clear- and all-sky net top-of-atmosphere radiative flux) based on the first 5 years of Clouds and the Earth's Radiant Energy System (CERES) Terra measurements is created in order to investigate how gaps in the record affect our ability to constrain cloud radiative feedback. To ensure a trend estimate with an uncertainty small enough to constrain cloud radiative feedback to 25% of anthropogenic forcing in the next few decades, the absolute calibration change across the gap must be radiation; 1616 Climate variability; 3305 Climate change and variability; 0321 Cloud/radiation interaction; overlap; gaps
Myhre, G.; Berglen, T. F.; Hoyle, C. R.; Christopher, S.a.; Coe, H.; Crosier, J.; Formenti, P.; Haywood, J.m.; Johnsrud, M.; Jones, T.a.; Loeb, N.; Osborne, S.; Remer, L.a.Myhre, G., T. F. Berglen, C. R. Hoyle, S. Christopher, H. Coe, J. Crosier, P. Formenti, J. Haywood, M. Johnsrud, T. Jones, N. Loeb, S. Osborne, L. Remer, 2009: Modelling of chemical and physical aerosol properties during the ADRIEX aerosol campaign. Quarterly Journal of the Royal Meteorological Society, 135(638), 53-66. doi: 10.1002/qj.350. A global aerosol model with relatively high resolution is used to simulate the distribution and radiative effect of aerosols during the Aerosol Direct Radiative Impact Experiment (ADRIEX) campaign in August and September 2004. The global chemical transport model Oslo CTM2 includes detailed chemistry, which is coupled to aerosol partitioning of sulphate, nitrate and secondary organic aerosols. In accordance with aircraft observations the aerosol model simulates a dominance of secondary aerosols compared to primary aerosols in the ADRIEX study region. The model underestimates the aerosol optical depth (AOD) at 550 nm in the main region of the campaign around Venice. This underestimation mainly occurs during a 3–4 day period of highest AODs. At two AERONET (Aerosol Robotic Network) stations related to the ADRIEX campaign outside the Po valley area, the model compares very well with the observed AOD. Comparisons with observed chemical composition show that the model mainly underestimates organic carbon, with better agreement for other aerosol species. The model simulations indicate that the emission of aerosols and their precursors may be underestimated in the Po valley. Recent results show a large spread in radiative forcing due to the direct aerosol effect in global aerosol models, which is likely linked to large differences in the vertical profile of aerosols and aerosol absorption. The modelled vertical profile of aerosol compares reasonably well to the aircraft measurements as was the case in two earlier campaigns involving biomass burning and dust aerosols. The radiative effect of aerosols over the northern part of the Adriatic Sea agrees well with the mean of three satellite-derived estimates despite large differences between the satellite-derived data. The difference between the model and the mean of the satellite data is within 10% for the radiative effect. The radiative forcing due to anthropogenic aerosols is simulated to be negative in the ADRIEX region with values between − 5 and − 2 W m−2. Copyright © 2008 Royal Meteorological Society radiative forcing; aircraft measurements; secondary organic aerosols
Myhre, G.; Berglen, T. F.; Johnsrud, M.; Hoyle, C. R.; Berntsen, T. K.; Christopher, S. A.; Fahey, D. W.; Isaksen, I. S. A.; Jones, T. A.; Kahn, R. A.; Loeb, N.; Quinn, P.; Remer, L.; Schwarz, J. P.; Yttri, K. E.Myhre, G., T. F. Berglen, M. Johnsrud, C. R. Hoyle, T. K. Berntsen, S. A. Christopher, D. W. Fahey, I. S. A. Isaksen, T. A. Jones, R. A. Kahn, N. Loeb, P. Quinn, L. Remer, J. P. Schwarz, K. E. Yttri, 2009: Modelled radiative forcing of the direct aerosol effect with multi-observation evaluation. Atmos. Chem. Phys., 9(4), 1365-1392. doi: 10.5194/acp-9-1365-2009. A high-resolution global aerosol model (Oslo CTM2) driven by meteorological data and allowing a comparison with a variety of aerosol observations is used to simulate radiative forcing (RF) of the direct aerosol effect. The model simulates all main aerosol components, including several secondary components such as nitrate and secondary organic carbon. The model reproduces the main chemical composition and size features observed during large aerosol campaigns. Although the chemical composition compares best with ground-based measurement over land for modelled sulphate, no systematic differences are found for other compounds. The modelled aerosol optical depth (AOD) is compared to remote sensed data from AERONET ground and MODIS and MISR satellite retrievals. To gain confidence in the aerosol modelling, we have tested its ability to reproduce daily variability in the aerosol content, and this is performing well in many regions; however, we also identified some locations where model improvements are needed. The annual mean regional pattern of AOD from the aerosol model is broadly similar to the AERONET and the satellite retrievals (mostly within 10–20%). We notice a significant improvement from MODIS Collection 4 to Collection 5 compared to AERONET data. Satellite derived estimates of aerosol radiative effect over ocean for clear sky conditions differs significantly on regional scales (almost up to a factor two), but also in the global mean. The Oslo CTM2 has an aerosol radiative effect close to the mean of the satellite derived estimates. We derive a radiative forcing (RF) of the direct aerosol effect of −0.35 Wm−2 in our base case. Implementation of a simple approach to consider internal black carbon (BC) mixture results in a total RF of −0.28 Wm−2. Our results highlight the importance of carbonaceous particles, producing stronger individual RF than considered in the recent IPCC estimate; however, net RF is less different. A significant RF from secondary organic aerosols (SOA) is estimated (close to −0.1 Wm−2). The SOA also contributes to a strong domination of secondary aerosol species for the aerosol composition over land. A combination of sensitivity simulations and model evaluation show that the RF is rather robust and unlikely to be much stronger than in our best estimate.

2008

Huang, Xianglei; Yang, Wenze; Loeb, Norman G.; Ramaswamy, V.Huang, X., W. Yang, N. G. Loeb, V. Ramaswamy, 2008: Spectrally resolved fluxes derived from collocated AIRS and CERES measurements and their application in model evaluation: Clear sky over the tropical oceans. Journal of Geophysical Research: Atmospheres, 113(D9), D09110. doi: 10.1029/2007JD009219. Spectrally resolved outgoing thermal-IR flux, the integrand of the outgoing longwave radiation (OLR), has a unique value in evaluating model simulations. Here we describe an algorithm for deriving such clear-sky outgoing spectral flux through the entire thermal-IR spectrum from the collocated Atmospheric Infrared Sounder (AIRS) and the Clouds and the Earth's Radiant Energy System (CERES) measurements over the tropical oceans. On the basis of the predefined scene types in the CERES Single Satellite Footprint (SSF) data set, spectrally dependent ADMs are developed and used to estimate the spectral flux each AIRS channel. A multivariate linear prediction scheme is then used to estimate spectral fluxes at frequencies not covered by the AIRS instrument. The whole algorithm is validated using synthetic spectra as well as the CERES OLR measurements. Using the GFDL AM2 model simulation as a case study, applications of the derived clear-sky outgoing spectral fluxes in model evaluation are illustrated. By comparing the observed spectral fluxes and simulated ones for the year of 2004, compensating errors in the simulated OLR from different absorption bands are revealed, along with the errors from frequencies within a given absorption band. Discrepancies between the simulated and observed spatial distributions and seasonal evolutions of the spectral fluxes are further discussed. The methodology described in this study can be applied to other surface types as well as cloudy-sky observations and also to corresponding model evaluations. 1626 Global climate models; 3310 Clouds and cloud feedbacks; 3359 Radiative processes; clear-sky spectral flux; model evaluation
Loeb, Norman G.; Schuster, Gregory L.Loeb, N. G., G. L. Schuster, 2008: An observational study of the relationship between cloud, aerosol and meteorology in broken low-level cloud conditions. Journal of Geophysical Research: Atmospheres, 113(D14), D14214. doi: 10.1029/2007JD009763. Global satellite analyses showing strong correlations between aerosol optical depth and cloud cover have stirred much debate recently. While it is tempting to interpret the results as evidence of aerosol enhancement of cloud cover, other factors such as the influence of meteorology on both the aerosol and cloud distributions can also play a role, as both aerosols and clouds depend upon local meteorology. This study uses satellite observations to examine aerosol-cloud relationships for broken low-level cloud regions off the coast of Africa. The analysis approach minimizes the influence of large-scale meteorology by restricting the spatial and temporal domains in which the aerosol and cloud properties are compared. While distributions of several meteorological variables within 5° × 5° latitude-longitude regions are nearly identical under low and high aerosol optical depth, the corresponding distributions of single-layer low cloud properties and top-of-atmosphere radiative fluxes differ markedly, consistent with earlier studies showing increased cloud cover with aerosol optical depth. Furthermore, fine-mode fraction and Angstrom Exponent are also larger in conditions of higher aerosol optical depth, even though no evidence of systematic latitudinal or longitudinal gradients between the low and high aerosol optical depth populations are observed. When the analysis is repeated for all 5° × 5° latitude-longitude regions over the global oceans (after removing cases in which significant meteorological differences are found between the low and high aerosol populations), results are qualitatively similar to those off the coast of Africa. 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 3359 Radiative processes; aerosols; clouds; radiation
Marshak, Alexander; Wen, Guoyong; Coakley, James A.; Remer, Lorraine A.; Loeb, Norman G.; Cahalan, Robert F.Marshak, A., G. Wen, J. A. Coakley, L. A. Remer, N. G. Loeb, R. F. Cahalan, 2008: A simple model for the cloud adjacency effect and the apparent bluing of aerosols near clouds. Journal of Geophysical Research: Atmospheres, 113(D14), D14S17. doi: 10.1029/2007JD009196. In determining aerosol-cloud interactions, the properties of aerosols must be characterized in the vicinity of clouds. Numerous studies based on satellite observations have reported that aerosol optical depths increase with increasing cloud cover. Part of the increase comes from the humidification and consequent growth of aerosol particles in the moist cloud environment, but part comes from 3-D cloud-radiative transfer effects on the retrieved aerosol properties. Often, discerning whether the observed increases in aerosol optical depths are artifacts or real proves difficult. The paper only addresses the cloud-clear sky radiative transfer interaction part. It provides a simple model that quantifies the enhanced illumination of cloud-free columns in the vicinity of clouds that are used in the aerosol retrievals. This model is based on the assumption that the enhancement in the cloud-free column radiance comes from enhanced Rayleigh scattering that results from the presence of the nearby clouds. This assumption leads to a larger increase of AOT for shorter wavelengths, or to a “bluing” of aerosols near clouds. The assumption that contribution from molecular scattering dominates over aerosol scattering and surface reflection is justified for the case of shorter wavelengths, dark surfaces, and an aerosol layer below the cloud tops. The enhancement in Rayleigh scattering is estimated using a stochastic cloud model to obtain the radiative flux reflected by broken clouds and comparing this flux with that obtained with the molecules in the atmosphere causing extinction, but no scattering. 0305 Aerosols and particles; 0321 Cloud/radiation interaction; 0360 Radiation: transmission and scattering; aerosols; cloud adjacency; radiation
Menon, Surabi; Del Genio, Anthony D.; Kaufman, Yoram; Bennartz, Ralf; Koch, Dorothy; Loeb, Norman; Orlikowski, DanielMenon, S., A. D. Del Genio, Y. Kaufman, R. Bennartz, D. Koch, N. Loeb, D. Orlikowski, 2008: Analyzing signatures of aerosol-cloud interactions from satellite retrievals and the GISS GCM to constrain the aerosol indirect effect. Journal of Geophysical Research: Atmospheres, 113(D14), D14S22. doi: 10.1029/2007JD009442. Evidence of aerosol-cloud interactions is evaluated using satellite data from MODIS, CERES, and AMSR-E; reanalysis data from NCEP; and data from the NASA Goddard Institute for Space Studies climate model. We evaluate a series of model simulations: (1) Exp N, aerosol direct radiative effects; (2) Exp C, like Exp N but with aerosol effects on liquid-phase cumulus and stratus clouds; and (3) Exp CN, like Exp C but with model wind fields nudged to reanalysis data. Comparison between satellite-retrieved data and model simulations for June to August 2002 over the Atlantic Ocean indicate the following: a negative correlation between aerosol optical thickness (AOT) and cloud droplet effective radius (Reff) for all cases and satellite data, except for Exp N, a weak but negative correlation between liquid water path (LWP) and AOT for MODIS and CERES, and a robust increase in cloud cover with AOT for both MODIS and CERES. In all simulations, there is a positive correlation between AOT and both cloud cover and LWP (except in the case of LWP-AOT for Exp CN). The largest slopes are obtained for Exp N, implying that meteorological variability may be an important factor. On the basis of NCEP data, warmer temperatures and increased subsidence were found for less clean cases (AOT > 0.06) that were not well captured by the model. Simulated cloud fields compared with an enhanced data product from MODIS and AMSR-E indicate that model cloud thickness is overpredicted and cloud droplet number is within retrieval uncertainties. Since LWP fields are comparable, this implies an underprediction of Reff and thus an overprediction of the indirect effect. 0320 Cloud physics and chemistry; 0321 Cloud/radiation interaction; 3311 Clouds and aerosols; 3337 Global climate models; aerosol indirect effect; aerosol optical thickness; Cloud microphysics
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; 3311 Clouds and aerosols; 3359 Radiative processes; aerosol; cloud
Sun, Wenbo; Hu, Yongxiang; Loeb, N.G.; Lin, Bing; Mlynczak, M.G.Sun, W., Y. Hu, N. Loeb, B. Lin, M. Mlynczak, 2008: Using CERES Data to Evaluate the Infrared Flux Derived From Diffusivity Approximation. IEEE Geoscience and Remote Sensing Letters, 5(1), 17-20. doi: 10.1109/LGRS.2007.905198. Based on the diffusivity approximation theory, the infrared flux at the top of atmosphere (TOA) can be obtained by multiplying a factor of pi on the infrared radiance that was measured at a viewing zenith angle (VZA) of 53deg. This letter applies the diffusivity approximation on radiance measurements of the Clouds and the Earth's Radiant Energy System (CERES) to derive TOA infrared fluxes and compares these fluxes with the state-of-the-art CERES outgoing radiative fluxes. We find that the mean difference between the two kinds of instantaneous flux that were estimated at the window channel is 1 Wmiddotm-2, with a root-mean-square error of 1.7 Wmiddotm-2. This result shows that radiance measurement at a fixed VZA of 53 deg is a simple and effective method in the remote sensing of the infrared flux for satellite missions that monitor some specific climate processes and require longwave/window TOA fluxes, such as the Broad Band Radiometer instrument on EarthCARE; however, this approach may involve errors from an inhomogeneous scene or non-Lambertian emission of the surface. A careful design of the VZA and scan mode, such as a conical scan at 53deg, would produce much more convenient infrared flux measurements for the Earth-atmosphere system than other designs. atmospheric radiation; Broad Band Radiometer instrument; CERES data; climate processes; Clouds and the Earth's Radiant Energy System; Clouds and the Earth's Radiant Energy System (CERES); diffusivity approximation; diffusivity approximation theory; Earth-atmosphere system; EarthCARE; infrared flux; infrared radiance; nonLambertian emission; outgoing radiative fluxes; Remote sensing; root-mean-square error; satellite missions; top-of-atmosphere infrared fluxes; viewing zenith angle

2007

Loeb, N. G.; Kato, S.; Loukachine, K.; Manalo-Smith, N.; Doelling, D. R.Loeb, N. G., S. Kato, K. Loukachine, N. Manalo-Smith, D. R. Doelling, 2007: Angular distribution models for top-of-atmosphere radiative flux estimation from the Clouds and the Earth's Radiant Energy System instrument on the Terra satellite. Part II: Validation. J. Atmos. Oceanic Technol., 24(4), 564-584. doi: 10.1175/jtech1983.1. Errors in top- of- atmosphere ( TOA) radiative fluxes from the Clouds and the Earth's Radiant Energy System ( CERES) instrument due to uncertainties in radiance- to- flux conversion from CERES Terra angular distribution models ( ADMs) are evaluated through a series of consistency tests. These tests show that the overall bias in regional monthly mean shortwave ( SW) TOA flux is less than 0.2Wm(-2) and the regional RMS error ranges from 0.70 to 1.4 W m(-2). In contrast, SW TOA fluxes inferred using theoretical ADMs that assume clouds are plane parallel are overestimated by 3 - 4 W m(-2) and exhibit a strong latitudinal dependence. In the longwave ( LW), the bias error ranges from 0.2 to 0.4 W m(-2) and regional RMS errors remain smaller than 0.7 W m(-2). Global mean albedos derived from ADMs developed during the Earth Radiation Budget Experiment ( ERBE) and applied to CERES measurements show a systematic increase with viewing zenith angle of 4% - 8%, while albedos from the CERES Terra ADMs show a smaller increase of 1% - 2%. The LW fluxes from the ERBE ADMs show a systematic decrease with viewing zenith angle of 2% - 2.4%, whereas fluxes from the CERES Terra ADMs remain within 0.7% - 0.8% at all angles. Based on several months of multiangle CERES along- track data, the SW TOA flux consistency between nadir-and oblique- viewing zenith angles is generally 5% ( < 17 W m(-2)) over land and ocean and 9% ( 26 W m(-2)) in polar regions, and LW TOA flux consistency is approximate 3% ( 7 W m(-2)) over all surfaces. Based on these results and a theoretically derived conversion between TOA flux consistency and TOA flux error, the best estimate of the error in CERES TOA flux due to the radiance- to- flux conversion is 3% ( 10 W m(-2)) in the SW and 1.8% ( 3 - 5 W m(-2)) in the LW. Monthly mean TOA fluxes based on ERBE ADMs are larger than monthly mean TOA fluxes based on CERES Terra ADMs by 1.8 and 1.3 W m(-2) in the SW and LW, respectively.
Loeb, Norman G.; Wielicki, Bruce A.; Rose, Fred G.; Doelling, David R.Loeb, N. G., B. A. Wielicki, F. G. Rose, D. R. Doelling, 2007: Variability in global top-of-atmosphere shortwave radiation between 2000 and 2005. Geophysical Research Letters, 34(3), L03704. doi: 10.1029/2006GL028196. Measurements from various instruments and analysis techniques are used to directly compare changes in Earth-atmosphere shortwave (SW) top-of-atmosphere (TOA) radiation between 2000 and 2005. Included in the comparison are estimates of TOA reflectance variability from published ground-based Earthshine observations and from new satellite-based CERES, MODIS and ISCCP results. The ground-based Earthshine data show an order-of-magnitude more variability in annual mean SW TOA flux than either CERES or ISCCP, while ISCCP and CERES SW TOA flux variability is consistent to 40%. Most of the variability in CERES TOA flux is shown to be dominated by variations global cloud fraction, as observed using coincident CERES and MODIS data. Idealized Earthshine simulations of TOA SW radiation variability for a lunar-based observer show far less variability than the ground-based Earthshine observations, but are still a factor of 4–5 times more variable than global CERES SW TOA flux results. Furthermore, while CERES global albedos exhibit a well-defined seasonal cycle each year, the seasonal cycle in the lunar Earthshine reflectance simulations is highly variable and out-of-phase from one year to the next. Radiative transfer model (RTM) approaches that use imager cloud and aerosol retrievals reproduce most of the change in SW TOA radiation observed in broadband CERES data. However, assumptions used to represent the spectral properties of the atmosphere, clouds, aerosols and surface in the RTM calculations can introduce significant uncertainties in annual mean changes in regional and global SW TOA flux. 1610 Atmosphere; 1616 Climate variability; 1640 Remote sensing; albedo; radiative flux; Variability
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. radiative forcing; satellite observations; Shortwave radiation

2006

Bender, Frida a-M.; Rodhe, Henning; Charlson, Robert J.; Ekman, Annica M. L.; Loeb, NormanBender, F. a., H. Rodhe, R. J. Charlson, A. M. L. Ekman, N. Loeb, 2006: 22 views of the global albedo—comparison between 20 GCMs and two satellites. Tellus A, 58(3), 320-330. doi: 10.1111/j.1600-0870.2006.00181.x. A comprehensive comparison of characteristics of the planetary albedo (α) in data from two satellite measurement campaigns (ERBE and CERES) and output from 20 GCMs, simulating the 20th-century climate, is performed. Discrepancies between different data sets and models exist; thus, it is clear that conclusions about absolute magnitude and accuracy of albedo should be drawn with caution. Yet, given the present calibrations, a bias is found between different estimates of α, with modelled global albedos being systematically higher than the observed. The difference between models and observations is larger for the more recent CERES measurements than the older ERBE measurements. Through the study of seasonal anomalies and space and time distribution of correaltions between models and observations, specific regions with large discrepancies can be identified. It is hereby found that models appear to over-estimate the albedo during boreal summer and under-estimate it during austral summer. Furthermore, the seasonal variations of albedo in subtropical areas dominated by low stratiform clouds, as well as in dry desert regions in the subtropics, seem to be poorly simulated by the models.
Kato, Seiji; Loeb, Norman G.; Minnis, Patrick; Francis, Jennifer A.; Charlock, Thomas P.; Rutan, David A.; Clothiaux, Eugene E.; Sun-Mack, SzedungKato, S., N. G. Loeb, P. Minnis, J. A. Francis, T. P. Charlock, D. A. Rutan, E. E. Clothiaux, S. Sun-Mack, 2006: Seasonal and interannual variations of top-of-atmosphere irradiance and cloud cover over polar regions derived from the CERES data set. Geophysical Research Letters, 33(19), L19804. doi: 10.1029/2006GL026685. The daytime cloud fraction derived by the Clouds and the Earth's Radiant Energy System (CERES) cloud algorithm using Moderate Resolution Imaging Spectroradiometer (MODIS) radiances over the Arctic from March 2000 through February 2004 increases at a rate of 0.047 per decade. The trend is significant at an 80% confidence level. The corresponding top-of-atmosphere (TOA) shortwave irradiances derived from CERES radiance measurements show less significant trend during this period. These results suggest that the influence of reduced Arctic sea ice cover on TOA reflected shortwave radiation is reduced by the presence of clouds and possibly compensated by the increase in cloud cover. The cloud fraction and TOA reflected shortwave irradiance over the Antarctic show no significant trend during the same period. 1616 Climate variability; 3311 Clouds and aerosols; 3339 Ocean/atmosphere interactions; 3359 Radiative processes
Lee, Yong-Keun; Yang, Ping; Hu, Yongxiang; Baum, Bryan A.; Loeb, Norman G.; Gao, Bo-CaiLee, Y., P. Yang, Y. Hu, B. A. Baum, N. G. Loeb, B. Gao, 2006: Potential nighttime contamination of CERES clear-sky fields of view by optically thin cirrus during the CRYSTAL-FACE campaign. Journal of Geophysical Research: Atmospheres, 111(D9), D09203. doi: 10.1029/2005JD006372. We investigate the outgoing broadband longwave (LW, 5∼200 μm) and window (WIN, 8∼12 μm) channel radiances at the top of atmosphere (TOA) under clear-sky conditions, using data acquired by the Cloud and the Earth's Radiant Energy System (CERES) and Moderate-Resolution Imaging Spectroradiometer (MODIS) instruments on board the NASA Terra satellite platform. In this study, detailed analyses are performed on the CERES Single Scanner Footprint TOA/Surface Fluxes and Clouds product to understand the radiative effect of thin cirrus. The data are acquired over the Florida area during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers – Florida Area Cirrus Experiment (CRYSTAL-FACE) field program. Of particular interest is the anisotropy associated with the radiation field. Measured CERES broadband radiances are compared to those obtained from rigorous radiative transfer simulations. Analysis of results from this comparison indicates that the simulated radiances tend to be larger than their measured counterparts, with differences ranging from 2.1% to 8.3% for the LW band and from 1.7% to 10.6% for the WIN band. The averaged difference in radiance is approximately 4% for both the LW and WIN channels. A potential cause for the differences could be the presence of thin cirrus (i.e., optically thin ice clouds with visible optical thicknesses smaller than approximately 0.3). The detection and quantitative analysis of these thin cirrus clouds are challenging even with sophisticated multispectral instruments. While large differences in radiance between the CERES observations and the theoretical calculations are found, the corresponding difference in the anisotropic factors is very small (0.2%). Furthermore, sensitivity studies show that the influence due to a ±1 K bias of the surface temperature on the errors of the LW and WIN channel radiances is of the same order as that associated with a ±2% bias of the surface emissivity. The LW and WIN errors associated with a ±5% bias of water vapor amount in the lower atmosphere in conjunction with a ±50% bias of water vapor amount in the upper atmosphere is similar to that of a ±1 K bias of the vertical temperature profile. Even with the uncertainties considered for these various factors, the simulated LW and WIN radiances are still larger than the observed radiances if thin cirrus clouds are excluded. 0321 Cloud/radiation interaction; 0360 Radiation: transmission and scattering; CERES; cirrus clouds
Loeb, Norman G.; Sun, Wenbo; Miller, Walter F.; Loukachine, Konstantin; Davies, RogerLoeb, N. G., W. Sun, W. F. Miller, K. Loukachine, R. Davies, 2006: Fusion of CERES, MISR, and MODIS measurements for top-of-atmosphere radiative flux validation. Journal of Geophysical Research: Atmospheres, 111(D18), D18209. doi: 10.1029/2006JD007146. The Clouds and the Earth's Radiant Energy System (CERES), Multiangle Imaging Spectroradiometer (MISR), and Moderate-resolution Imaging Spectroradiometer (MODIS) instruments aboard the Terra satellite make critical measurements of cloud and aerosol properties and their effects on the Earth's radiation budget. In this study, a new multiangle, multichannel data set that combines measurements from all three instruments is created to assess uncertainties in instantaneous shortwave (SW) top-of-atmosphere (TOA) radiative fluxes inferred from CERES Angular Distribution Models (ADMs). MISR Level 1B2 ellipsoid-projected radiances from nine viewing directions in four spectral bands are merged with CERES by convolving the MISR radiances with the CERES Point Spread Function. The merged CERES-MISR data are then combined with the CERES Single Scanner Footprint TOA/Surface Fluxes and Clouds (SSF) product to produce the first merged CERES-MISR-MODIS data set. CERES and MISR data are used to generate narrow-to-broadband regression coefficients to convert narrowband MISR radiances to broadband SW radiances as a function of MODIS-based scene type. The regression uncertainty for all-sky conditions over ocean is approximately 4%. Up to nine SW TOA fluxes for every CERES footprint are estimated by applying the CERES Terra ADMs to each MISR angle. Assuming that differences along the line-of-sight from the different MISR angles are small, the consistency of the TOA fluxes provides an indication of the instantaneous TOA flux uncertainty. The overall relative consistency of all-sky ocean TOA fluxes is 6% (17 W m−2). When stratified by cloud type, TOA fluxes are consistent to 2–3% ( 1610 Atmosphere; 1640 Remote sensing; 3311 Clouds and aerosols; data fusion; radiative flux; top-of-atmosphere
Sun, Wenbo; Loeb, Norman G.; Davies, Roger; Loukachine, Konstantin; Miller, Walter F.Sun, W., N. G. Loeb, R. Davies, K. Loukachine, W. F. Miller, 2006: Comparison of MISR and CERES top-of-atmosphere albedo. Geophysical Research Letters, 33(23), L23810. doi: 10.1029/2006GL027958. The Clouds and the Earth's Radiant Energy System (CERES) and the Multi-angle Imaging SpectroRadiometer (MISR) on Terra satellite measure the Earth's top-of-atmosphere (TOA) albedo in broadband and narrowband, respectively. This study presents the first direct comparison of the CERES and MISR albedos. An algorithm for converting the MISR spectral albedos to broadband is derived. The MISR and CERES albedos for overcast ocean scenes are compared between 75°S–75°N for solar zenith angles ≤75°. For overcast 1° × 1° ocean regions, the relative differences and the relative root-mean-square (RMS) differences between the MISR and CERES albedos are ∼0.8% and ∼4.3%, respectively. Accounting for a ∼2.0% error in the MISR albedos due to narrow-to-broadband albedo conversion errors, the RMS difference between the MISR and CERES albedos due to angular distribution model (ADM) differences is estimated to be ∼3.8%. The remarkable consistency between the CERES and MISR albedos for overcast oceans suggests that both instrument teams have derived accurate corrections for the radiance anisotropy of cloud scenes. This consistency will strongly enhance the confidence in the temporal trends of cloud albedo measured by the CERES and have significant impact on climate studies. 0360 Radiation: transmission and scattering; 1640 Remote sensing; 1694 Instruments and techniques; albedo; broadband; CERES; MISR; spectral
Yu, H.; Kaufman, Y. J.; Chin, M.; Feingold, G.; Remer, L. A.; Anderson, T. L.; Balkanski, Y.; Bellouin, N.; Boucher, O.; Christopher, S.; DeCola, P.; Kahn, R.; Koch, D.; Loeb, N.; Reddy, M. S.; Schulz, M.; Takemura, T.; Zhou, M.Yu, H., Y. J. Kaufman, M. Chin, G. Feingold, L. A. Remer, T. L. Anderson, Y. Balkanski, N. Bellouin, O. Boucher, S. Christopher, P. DeCola, R. Kahn, D. Koch, N. Loeb, M. S. Reddy, M. Schulz, T. Takemura, M. Zhou, 2006: A review of measurement-based assessments of the aerosol direct radiative effect and forcing. Atmos. Chem. Phys., 6(3), 613-666. doi: 10.5194/acp-6-613-2006. Aerosols affect the Earth's energy budget directly by scattering and absorbing radiation and indirectly by acting as cloud condensation nuclei and, thereby, affecting cloud properties. However, large uncertainties exist in current estimates of aerosol forcing because of incomplete knowledge concerning the distribution and the physical and chemical properties of aerosols as well as aerosol-cloud interactions. In recent years, a great deal of effort has gone into improving measurements and datasets. It is thus feasible to shift the estimates of aerosol forcing from largely model-based to increasingly measurement-based. Our goal is to assess current observational capabilities and identify uncertainties in the aerosol direct forcing through comparisons of different methods with independent sources of uncertainties. Here we assess the aerosol optical depth (τ), direct radiative effect (DRE) by natural and anthropogenic aerosols, and direct climate forcing (DCF) by anthropogenic aerosols, focusing on satellite and ground-based measurements supplemented by global chemical transport model (CTM) simulations. The multi-spectral MODIS measures global distributions of aerosol optical depth (τ) on a daily scale, with a high accuracy of ±0.03±0.05τ over ocean. The annual average τ is about 0.14 over global ocean, of which about 21%±7% is contributed by human activities, as estimated by MODIS fine-mode fraction. The multi-angle MISR derives an annual average AOD of 0.23 over global land with an uncertainty of ~20% or ±0.05. These high-accuracy aerosol products and broadband flux measurements from CERES make it feasible to obtain observational constraints for the aerosol direct effect, especially over global the ocean. A number of measurement-based approaches estimate the clear-sky DRE (on solar radiation) at the top-of-atmosphere (TOA) to be about -5.5±0.2 Wm-2 (median ± standard error from various methods) over the global ocean. Accounting for thin cirrus contamination of the satellite derived aerosol field will reduce the TOA DRE to -5.0 Wm-2. Because of a lack of measurements of aerosol absorption and difficulty in characterizing land surface reflection, estimates of DRE over land and at the ocean surface are currently realized through a combination of satellite retrievals, surface measurements, and model simulations, and are less constrained. Over the oceans the surface DRE is estimated to be -8.8±0.7 Wm-2. Over land, an integration of satellite retrievals and model simulations derives a DRE of -4.9±0.7 Wm-2 and -11.8±1.9 Wm-2 at the TOA and surface, respectively. CTM simulations derive a wide range of DRE estimates that on average are smaller than the measurement-based DRE by about 30-40%, even after accounting for thin cirrus and cloud contamination. A number of issues remain. Current estimates of the aerosol direct effect over land are poorly constrained. Uncertainties of DRE estimates are also larger on regional scales than on a global scale and large discrepancies exist between different approaches. The characterization of aerosol absorption and vertical distribution remains challenging. The aerosol direct effect in the thermal infrared range and in cloudy conditions remains relatively unexplored and quite uncertain, because of a lack of global systematic aerosol vertical profile measurements. A coordinated research strategy needs to be developed for integration and assimilation of satellite measurements into models to constrain model simulations. Enhanced measurement capabilities in the next few years and high-level scientific cooperation will further advance our knowledge.Citation: Yu, H., Kaufman, Y. J., Chin, M., Feingold, G., Remer, L. A., Anderson, T. L., Balkanski, Y., Bellouin, N., Boucher, O., Christopher, S., DeCola, P., Kahn, R., Koch, D., Loeb, N., Reddy, M. S., Schulz, M., Takemura, T., and Zhou, M.: A review of measurement-based assessments of the aerosol direct radiative effect and forcing, Atmos. Chem. Phys., 6, 613-666, doi:10.5194/acp-6-613-2006, 2006.

2005

Diner, D. J.; Braswell, B. H.; Davies, R.; Gobron, N.; Hu, J. N.; Jin, Y. F.; Kahn, R. A.; Knyazikhin, Y.; Loeb, N.; Muller, J. P.; Nolin, A. W.; Pinty, B.; Schaaf, C. B.; Seiz, G.; Stroeve, J.Diner, D. J., B. H. Braswell, R. Davies, N. Gobron, J. N. Hu, Y. F. Jin, R. A. Kahn, Y. Knyazikhin, N. Loeb, J. P. Muller, A. W. Nolin, B. Pinty, C. B. Schaaf, G. Seiz, J. Stroeve, 2005: The value of multiangle measurements for retrieving structurally and radiatively consistent properties of clouds, aerosols, and surfaces. Remote Sensing of Environment, 97(4), 495-518. doi: 10.1016/j.rse.2005.06.006. Passive optical multiangle observations make possible the retrieval of scene structural characteristics that cannot be obtained with, or require fewer underlying assumptions than, single-angle sensors. Retrievable quantities include aerosol amount over a wide variety of surfaces (including bright targets); aerosol microphysical properties such as particle shape; geometrically-derived cloud-top heights and 3-D cloud morphologies; distinctions between polar clouds and ice; and textural measures of sea ice, ice sheets, and vegetation. At the same time, multiangle data are necessary for accurate retrievals of radiative quantities such as surface and top-of-atmosphere albedos, whose magnitudes are governed by structural characteristics of the reflecting media and which involve angular integration over intrinsically anisotropic intensity fields. Measurements of directional radiation streams also provide independent checks on model assumptions conventionally used in satellite retrievals, such as the application of 1-D radiative transfer theory, and provide data required to constrain more sophisticated, 3-D approaches. In this paper, the value of multiangle remote sensing in establishing physical correspondence and self-consistency between scene structural and radiative characteristics is demonstrated using simultaneous observations from instruments aboard NASA's Terra satellite (MISR, CERES, ASTER, and MODIS). Illustrations pertaining to the remote sensing of clouds, aerosols, ice, and vegetation properties are presented. (C) 2005 Elsevier Inc. All rights reserved.
Ignatov, Alexander; Minnis, Patrick; Loeb, Norman; Wielicki, Bruce; Miller, Walter; Sun-Mack, Sunny; Tanré, Didier; Remer, Lorraine; Laszlo, Istvan; Geier, ErikaIgnatov, A., P. Minnis, N. Loeb, B. Wielicki, W. Miller, S. Sun-Mack, D. Tanré, L. Remer, I. Laszlo, E. Geier, 2005: Two MODIS Aerosol Products over Ocean on the Terra and Aqua CERES SSF Datasets. J. Atmos. Sci., 62(4), 1008-1031. doi: 10.1175/JAS3383.1. Abstract Understanding the impact of aerosols on the earth’s radiation budget and the long-term climate record requires consistent measurements of aerosol properties and radiative fluxes. The Clouds and the Earth’s Radiant Energy System (CERES) Science Team combines satellite-based retrievals of aerosols, clouds, and radiative fluxes into Single Scanner Footprint (SSF) datasets from the Terra and Aqua satellites. Over ocean, two aerosol products are derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) using different sampling and aerosol algorithms. The primary, or M, product is taken from the standard multispectral aerosol product developed by the MODIS aerosol group while a simpler, secondary [Advanced Very High Resolution Radiometer (AVHRR) like], or A, product is derived by the CERES Science Team using a different cloud clearing method and a single-channel aerosol algorithm. Two aerosol optical depths (AOD), τA1 and τA2, are derived from MODIS bands 1 (0.644 μm) and 6 (1.632 μm) resembling the AVHRR/3 channels 1 and 3A, respectively. On Aqua the retrievals are made in band 7 (2.119 μm) because of poor quality data from band 6. The respective Ångström exponents can be derived from the values of τ. The A product serves as a backup for the M product. More importantly, the overlap of these aerosol products is essential for placing the 20+ year heritage AVHRR aerosol record in the context of more advanced aerosol sensors and algorithms such as that used for the M product. This study documents the M and A products, highlighting their CERES SSF specifics. Based on 2 weeks of global Terra data, coincident M and A AODs are found to be strongly correlated in both bands. However, both domains in which the M and A aerosols are available, and the respective τ/α statistics significantly differ because of discrepancies in sampling due to differences in cloud and sun-glint screening. In both aerosol products, correlation is observed between the retrieved aerosol parameters (τ/α) and ambient cloud amount, with the dependence in the M product being more pronounced than in the A product.
Kato, Seiji; Loeb, Norman G.Kato, S., N. G. Loeb, 2005: Top-of-atmosphere shortwave broadband observed radiance and estimated irradiance over polar regions from Clouds and the Earth's Radiant Energy System (CERES) instruments on Terra. Journal of Geophysical Research: Atmospheres, 110(D7), D07202. doi: 10.1029/2004JD005308. Empirical angular distribution models for estimating top-of-atmosphere shortwave irradiances from radiance measurements over permanent snow, fresh snow, and sea ice are developed using CERES measurements on Terra. Permanent snow angular distribution models depend on cloud fraction, cloud optical thickness, and snow brightness. Fresh snow and sea ice angular distribution models depend on snow and sea ice fraction, cloud fraction, cloud optical thickness, and snow and ice brightness. These classifications lead to 10 scene types for permanent snow and 25 scene types for fresh snow and sea ice. The average radiance over clear-sky permanent snow is more isotropic with satellite viewing geometry than that over overcast permanent snow. On average, the albedo of clear-sky permanent snow varies from 0.65 to 0.68 for solar zenith angles between 60° and 80°, while the corresponding albedo of overcast scenes varies from 0.70 to 0.73. Clear-sky permanent snow albedos over Antarctica estimated from two independent angular distribution models are consistent to within 0.6%, on average. Despite significant variability in sea ice optical properties with season, the estimated mean relative albedo error is −1.0% for very dark sea ice and 0.1% for very bright sea ice when albedos derived from different viewing angles are averaged. The estimated regional root-mean-square (RMS) relative albedo error is 5.6% and 2.6% when the sea ice angular distribution models are applied to a region that contains very dark and very bright sea ice, respectively. Similarly, the estimated relative albedo bias error for fresh snow is −0.1% for very dark snow scenes and 0.1% for very bright snow scenes. The estimated regional RMS relative albedo error is 3.5% and 5.0% when angular distribution models are applied to a region that contains very dark and very bright fresh snow, respectively. These error estimates are only due to angular distribution model error and do not include the error caused by scene identification. 1610 Atmosphere; 1635 Oceans; 1640 Remote sensing; irradiance estimate; polar regions; Shortwave radiation
Loeb, Norman G.; Kato, Seiji; Loukachine, Konstantin; Manalo-Smith, NatividadLoeb, N. G., S. Kato, K. Loukachine, N. Manalo-Smith, 2005: Angular Distribution Models for Top-of-Atmosphere Radiative Flux Estimation from the Clouds and the Earth’s Radiant Energy System Instrument on the Terra Satellite. Part I: Methodology. J. Atmos. Oceanic Technol., 22(4), 338-351. doi: 10.1175/JTECH1712.1. Abstract The Clouds and Earth’s Radiant Energy System (CERES) provides coincident global cloud and aerosol properties together with reflected solar, emitted terrestrial longwave, and infrared window radiative fluxes. These data are needed to improve the understanding and modeling of the interaction between clouds, aerosols, and radiation at the top of the atmosphere, surface, and within the atmosphere. This paper describes the approach used to estimate top-of-atmosphere (TOA) radiative fluxes from instantaneous CERES radiance measurements on the Terra satellite. A key component involves the development of empirical angular distribution models (ADMs) that account for the angular dependence of the earth’s radiation field at the TOA. The CERES Terra ADMs are developed using 24 months of CERES radiances, coincident cloud and aerosol retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS), and meteorological parameters from the Global Modeling and Assimilation Office (GMAO)’s Goddard Earth Observing System (GEOS) Data Assimilation System (DAS) V4.0.3 product. Scene information for the ADMs is from MODIS retrievals and GEOS DAS V4.0.3 properties over the ocean, land, desert, and snow for both clear and cloudy conditions. Because the CERES Terra ADMs are global, and far more CERES data are available on Terra than were available from CERES on the Tropical Rainfall Measuring Mission (TRMM), the methodology used to define CERES Terra ADMs is different in many respects from that used to develop CERES TRMM ADMs, particularly over snow/sea ice, under cloudy conditions, and for clear scenes over land and desert.
Loeb, Norman G.; Manalo-Smith, NatividadLoeb, N. G., N. Manalo-Smith, 2005: Top-of-Atmosphere Direct Radiative Effect of Aerosols over Global Oceans from Merged CERES and MODIS Observations. J. Climate, 18(17), 3506-3526. doi: 10.1175/JCLI3504.1. Abstract The direct radiative effect of aerosols (DREA) is defined as the difference between radiative fluxes in the absence and presence of aerosols. In this study, the direct radiative effect of aerosols is estimated for 46 months (March 2000–December 2003) of merged Clouds and the Earth’s Radiant Energy System (CERES) and Moderate Resolution Imaging Spectroradiometer (MODIS) Terra global measurements over ocean. This analysis includes the contribution from clear regions in both clear and partly cloudy CERES footprints. MODIS–CERES narrow-to-broadband regressions are developed to convert clear-sky MODIS narrowband radiances to broadband shortwave (SW) radiances, and CERES clear-sky angular distribution models (ADMs) are used to estimate the corresponding top-of-atmosphere (TOA) radiative fluxes that are needed to determine the DREA. Clear-sky MODIS pixels are identified using two independent cloud masks: (i) the NOAA/National Environmental Satellite, Data, and Information Service (NESDIS) algorithm that is used for inferring aerosol properties from MODIS on the CERES Single Scanner Footprint TOA/Surface Fluxes and Clouds (SSF) product (NOAA SSF); and (ii) the standard algorithm that is used by the MODIS aerosol group to produce the MODIS aerosol product (MOD04). Over global oceans, direct radiative cooling by aerosols for clear scenes that are identified from MOD04 is estimated to be 40% larger than for clear scenes from NOAA SSF (5.5 compared to 3.8 W m−2). Regionally, differences are largest in areas that are affected by dust aerosol, such as oceanic regions that are adjacent to the Sahara and Saudi Arabian deserts, and in northern Pacific Ocean regions that are influenced by dust transported from Asia. The net total-sky (clear and cloudy) DREA is negative (cooling) and is estimated to be −2.0 W m−2 from MOD04, and −1.6 W m−2 from NOAA SSF. The DREA is shown to have pronounced seasonal cycles in the Northern Hemisphere and large year-to-year fluctuations near deserts. However, no systematic trend in deseasonalized anomalies of the DREA is observed over the 46-month time series that is considered.
Myhre, G.; Stordal, F.; Johnsrud, M.; Diner, D. J.; Geogdzhayev, I. V.; Haywood, J. M.; Holben, B. N.; Holzer-Popp, T.; Ignatov, A.; Kahn, R. A.; Kaufman, Y. J.; Loeb, N.; Martonchik, J. V.; Mishchenko, M. I.; Nalli, N. R.; Remer, L. A.; Schroedter-Homscheidt, M.; Tanré, D.; Torres, O.; Wang, M.Myhre, G., F. Stordal, M. Johnsrud, D. J. Diner, I. V. Geogdzhayev, J. M. Haywood, B. N. Holben, T. Holzer-Popp, A. Ignatov, R. A. Kahn, Y. J. Kaufman, N. Loeb, J. V. Martonchik, M. I. Mishchenko, N. R. Nalli, L. A. Remer, M. Schroedter-Homscheidt, D. Tanré, O. Torres, M. Wang, 2005: Intercomparison of satellite retrieved aerosol optical depth over ocean during the period September 1997 to December 2000. Atmos. Chem. Phys., 5(6), 1697-1719. doi: 10.5194/acp-5-1697-2005. Monthly mean aerosol optical depth (AOD) over ocean is compared from a total of 9 aerosol retrievals during a 40 months period. Comparisons of AOD have been made both for the entire period and sub periods. We identify regions where there is large disagreement and good agreement between the aerosol satellite retrievals. Significant differences in AOD have been identified in most of the oceanic regions. Several analyses are performed including spatial correlation between the retrievals as well as comparison with AERONET data. During the 40 months period studied there have been several major aerosol field campaigns as well as events of high aerosol content. It is studied how the aerosol retrievals compare during such circumstances. The differences found in this study are larger than found in a previous study where 5 aerosol retrievals over an 8 months period were compared. Part of the differences can be explained by limitations and deficiencies in some of the aerosol retrievals. In particular, results in coastal regions are promising especially for aerosol retrievals from satellite instruments particularly suited for aerosol research. In depth analyses explaining the differences between AOD obtained in different retrievals are clearly needed. We limit this study to identifying differences and similarities and indicating possible sources that affect the quality of the retrievals. This is a necessary first step towards understanding the differences and improving the retrievals.
Sun, Wenbo; Loeb, Norman G.; Lin, BingSun, W., N. G. Loeb, B. Lin, 2005: Light Scattering by an Infinite Circular Cylinder Immersed in an Absorbing Medium. Applied Optics, 44(12), 2338-2342. doi: 10.1364/AO.44.002338. Analytic solutions are developed for the single-scattering properties of an infinite dielectric cylinder embedded in an absorbing medium with normal incidence, which include extinction, scattering and absorption efficiencies, the scattering phase function, and the asymmetry factor. The extinction and scattering efficiencies are derived by the near-field solutions at the surface of the particle. The normalized scattering phase function is obtained by use of the far-field approximation. Computational results show that, although the absorbing medium significantly reduces the scattering efficiency, it has little effect on absorption efficiency. The absorbing medium can significantly change the conventional phase function. The absorbing medium also strongly affects the polarization of the scattered light. However, for large absorbing particles the degrees of polarization change little with the medium’s absorption. This implies that, if the transmitting lights are strongly weakened inside the particle, the scattered polarized lights can be used to identify objects even when the absorption property of the host medium is unknown, which is important for both active and passive remote sensing. Atmospheric scattering; Oceanic optics; Scattering, stimulated
Wielicki, Bruce A.; Wong, Takmeng; Loeb, Norman; Minnis, Patrick; Priestley, Kory; Kandel, RobertWielicki, B. A., T. Wong, N. Loeb, P. Minnis, K. Priestley, R. Kandel, 2005: Changes in Earth's Albedo Measured by Satellite. Science, 308(5723), 825-825. doi: 10.1126/science.1106484. NASA global satellite data provide observations of Earth's albedo, i.e., the fraction of incident solar radiation that is reflected back to space. The satellite data show that the last four years are within natural variability and fail to confirm the 6% relative increase in albedo inferred from observations of earthshine from the moon. Longer global satellite records will be required to discern climate trends in Earth's albedo.
Zhang, M. H.; Lin, W. Y.; Klein, S. A.; Bacmeister, J. T.; Bony, S.; Cederwall, R. T.; Del Genio, A. D.; Hack, J. J.; Loeb, N. G.; Lohmann, U.; Minnis, P.; Musat, I.; Pincus, R.; Stier, P.; Suarez, M. J.; Webb, M. J.; Wu, J. B.; Xie, S. C.; Yao, M.-S.; Zhang, J. H.Zhang, M. H., W. Y. Lin, S. A. Klein, J. T. Bacmeister, S. Bony, R. T. Cederwall, A. D. Del Genio, J. J. Hack, N. G. Loeb, U. Lohmann, P. Minnis, I. Musat, R. Pincus, P. Stier, M. J. Suarez, M. J. Webb, J. B. Wu, S. C. Xie, M. Yao, J. H. Zhang, 2005: Comparing clouds and their seasonal variations in 10 atmospheric general circulation models with satellite measurements. Journal of Geophysical Research: Atmospheres, 110(D15), D15S02. doi: 10.1029/2004JD005021. To assess the current status of climate models in simulating clouds, basic cloud climatologies from ten atmospheric general circulation models are compared with satellite measurements from the International Satellite Cloud Climatology Project (ISCCP) and the Clouds and Earth's Radiant Energy System (CERES) program. An ISCCP simulator is employed in all models to facilitate the comparison. Models simulated a four-fold difference in high-top clouds. There are also, however, large uncertainties in satellite high thin clouds to effectively constrain the models. The majority of models only simulated 30–40% of middle-top clouds in the ISCCP and CERES data sets. Half of the models underestimated low clouds, while none overestimated them at a statistically significant level. When stratified in the optical thickness ranges, the majority of the models simulated optically thick clouds more than twice the satellite observations. Most models, however, underestimated optically intermediate and thin clouds. Compensations of these clouds biases are used to explain the simulated longwave and shortwave cloud radiative forcing at the top of the atmosphere. Seasonal sensitivities of clouds are also analyzed to compare with observations. Models are shown to simulate seasonal variations better for high clouds than for low clouds. Latitudinal distribution of the seasonal variations correlate with satellite measurements at >0.9, 0.6–0.9, and −0.2–0.7 levels for high, middle, and low clouds, respectively. The seasonal sensitivities of cloud types are found to strongly depend on the basic cloud climatology in the models. Models that systematically underestimate middle clouds also underestimate seasonal variations, while those that overestimate optically thick clouds also overestimate their seasonal sensitivities. Possible causes of the systematic cloud biases in the models are discussed. 1620 Climate dynamics; 1626 Global climate models; 3310 Clouds and cloud feedbacks; 3337 Global climate models; climate models; cloud modeling; seasonal variation of clouds

2004

Inamdar, Anand K.; Ramanathan, V.; Loeb, Norman G.Inamdar, A. K., V. Ramanathan, N. G. Loeb, 2004: Satellite observations of the water vapor greenhouse effect and column longwave cooling rates: Relative roles of the continuum and vibration-rotation to pure rotation bands. Journal of Geophysical Research: Atmospheres, 109(D6), D06104. doi: 10.1029/2003JD003980. The Clouds and the Earth's Radiant Energy System (CERES) instrument on board the Tropical Rainfall Measuring Mission (TRMM) satellite provides, for the first time, a large-scale (40 S to 40 N) data set for the atmospheric greenhouse effect and the column-averaged longwave (LW) radiative cooling rates in the broadband (5–100 microns) and the window (8–12 microns) regions. We demonstrate here that the separation into the window and the nonwindow (5–8 microns and 12–100 microns) fluxes provides the first global-scale data set to exhibit the sensitivity of the atmospheric greenhouse effect to vertical water vapor distribution. The nonwindow greenhouse effect varies linearly with the logarithm of column water vapor amount weighted with the atmospheric pressure, while the window component varies quadratically with the water vapor partial pressure. The column cooling rates range from about −170 to −210 W m−2 for the nonwindow region. The window cooling rates are only about 10% to 20% of the above range and approach rapidly to near-zero values for surface temperatures less than 288 K. The nonwindow component of the greenhouse effect and cooling rates are shown to be more sensitive to upper troposphere water vapor, while the window greenhouse effect and cooling rates are shown to be more sensitive to the lower troposphere water vapor amount. In addition, the data reveal that in tropical regions, with warm sea surface temperatures (greater than 297 K) and elevated upper tropospheric water vapor amounts, the continuum emission in the window region leads to enhanced cooling of the column, while the rotational bands in the nonwindow region lead to a net decrease in the longwave cooling of the atmospheric column. 1640 Remote sensing; 1694 Instruments and techniques; 3314 Meteorology and Atmospheric Dynamics: Convective processes; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; instruments and techniques; radiative processes; Remote sensing
Loukachine, Konstantin; Loeb, Norman G.Loukachine, K., N. G. Loeb, 2004: Top-of-atmosphere flux retrievals from CERES using artificial neural networks. Remote Sensing of Environment, 93(3), 381-390. doi: 10.1016/j.rse.2004.08.005. The Clouds and the Earth's Radiant Energy System (CERES) instruments on the Terra spacecraft provide accurate shortwave (SW), longwave (LW) and window (WN) region top-of-atmosphere (TOA) radiance measurements from which TOA radiative flux values are obtained by applying Angular Distribution Models (ADMs). These models are developed empirically as functions of the surface and cloud properties provided by coincident high-resolution imager measurements over CERES field-of-view. However, approximately 5.6% of the CERES/Terra footprints lack sufficient imager information for a reliable scene identification. To avoid any systematic biases in regional mean radiative fluxes, it is important to provide TOA fluxes for these footprints. For this purpose, we apply a feedforward error-backpropagation Artificial Neural Network (ANN) technique to reproduce CERES/Terra ADMs relying only on CERES measurements. All-sky ANN-based angular distribution models are developed for 10 surface types separately for shortwave, longwave and window TOA flux retrievals. To optimize the ANN performance, we use a partially connected first hidden neuron layer and compact training sets with reduced data noise. We demonstrate the performance of the ANN-based ADMs by comparing TOA fluxes inferred from ANN and CERES anisotropic factors. The global annual average bias in ANN-derived fluxes relative to CERES is less than 0.5% for all ANN scene types. The maximum bias occurs over sea ice and permanent snow surfaces. For all surface types, instantaneous ANN-derived TOA fluxes are self-consistent in viewing zenith angle to within 9% for shortwave, 3.5% and 3% longwave daytime and nighttime, respectively. Artificial neural network; radiation budget; Top-of-atmosphere flux
Smith, G. Louis; Wielicki, Bruce A.; Barkstrom, Bruce R.; Lee, Robert B.; Priestley, Kory J.; Charlock, Thomas P.; Minnis, Patrick; Kratz, David P.; Loeb, Norman; Young, David F.Smith, G. L., B. A. Wielicki, B. R. Barkstrom, R. B. Lee, K. J. Priestley, T. P. Charlock, P. Minnis, D. P. Kratz, N. Loeb, D. F. Young, 2004: Clouds and Earth radiant energy system: an overview. Advances in Space Research, 33(7), 1125-1131. doi: 10.1016/S0273-1177(03)00739-7. The Clouds and Earth radiant energy system (CERES) instrument was first flown aboard the TRMM spacecraft whose 35° inclination orbit allowed for the collection of radiation budget data over all local times, i.e. all solar zenith angles for the latitude range. Moreover, this instrument has gathered the only bidirectional radiance data covering all local times. An additional quartet of CERES instruments are now operating in pairs on both the TERRA and AQUA spacecrafts. Thus far, these instruments have collected several years of Earth radiation budget observations and continue to operate. For each of the TERRA and AQUA spacecrafts, one CERES instrument operates in a cross-track scan mode for the purpose of mapping the Earth’s outgoing longwave radiation and reflected solar radiation. The other operates in an azimuthal rotation while scanning also in zenith angle for the purpose of gathering measurements for the angular distribution of radiance from various scene types, to improve the computation of fluxes from radiance measurements. The CERES instruments carry in-flight calibration systems to maintain the measurement accuracy of 1% for measured radiances. In addition to retrieving fluxes at the top of the atmosphere, the CERES program uses data from other instruments aboard the spacecraft to compute the radiation balance at the surface and at levels through the atmosphere. Aqua; CERES; Earth observation system; radiation budget; Terra
Sun, Wenbo; G Loeb, Norman; Fu, QiangSun, W., N. G Loeb, Q. Fu, 2004: Light scattering by coated sphere immersed in absorbing medium: a comparison between the FDTD and analytic solutions. Journal of Quantitative Spectroscopy and Radiative Transfer, 83(3–4), 483-492. doi: 10.1016/S0022-4073(03)00101-8. A recently developed finite-difference time domain scheme is examined using the exact analytic solutions for light scattering by a coated sphere immersed in an absorbing medium. The relative differences are less than 1% in the extinction, scattering, and absorption efficiencies and less than 5% in the scattering phase functions. The definition of apparent single-scattering properties is also discussed. Absorbing medium; Coated sphere; Light scattering
Sun, Wenbo; Loeb, Norman G.; Kato, SeijiSun, W., N. G. Loeb, S. Kato, 2004: Estimation of instantaneous TOA albedo at 670 nm over ice clouds from POLDER multidirectional measurements. Journal of Geophysical Research: Atmospheres, 109(D2), D02210. doi: 10.1029/2003JD003801. An algorithm that determines the 670-nm top-of-atmosphere (TOA) albedo of ice clouds over ocean using Polarization and Directionality of the Earth's Reflectance (POLDER) multidirectional measurements is developed. A plane-parallel layer of ice cloud with various optical thicknesses and light scattering phase functions is assumed. For simplicity, we use a double Henyey-Greenstein phase function to approximate the volume-averaged phase function of the ice clouds. A multidirectional reflectance best-fit match between theoretical and POLDER reflectances is used to infer effective cloud optical thickness, phase function and TOA albedo. Sensitivity tests show that while the method does not provide accurate independent retrievals of effective cloud optical depth and phase function, TOA albedo retrievals are accurate to within ∼3% for both a single layer of ice clouds or a multilayer system of ice clouds and water clouds. When the method is applied to POLDER measurements and retrieved albedos are compared with albedos based on empirical angular distribution models (ADMs), zonal albedo differences are generally smaller than ∼3%. When albedos are compared with those on the POLDER-I ERB and Cloud product, the differences can reach ∼15% at small solar zenith angles. 0360 Radiation: transmission and scattering; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; albedo; angular distribution model; ice clouds; POLDER multidirectional measurement

2003

Haywood, Jim; Francis, Pete; Osborne, Simon; Glew, Martin; Loeb, Norman; Highwood, Eleanor; Tanré, Didier; Myhre, Gunnar; Formenti, Paola; Hirst, EdwinHaywood, J., P. Francis, S. Osborne, M. Glew, N. Loeb, E. Highwood, D. Tanré, G. Myhre, P. Formenti, E. Hirst, 2003: Radiative properties and direct radiative effect of Saharan dust measured by the C-130 aircraft during SHADE: 1. Solar spectrum. Journal of Geophysical Research: Atmospheres, 108(D18), 8577. doi: 10.1029/2002JD002687. The physical and optical properties of Saharan dust aerosol measured by the Met Office C-130 during the Saharan Dust Experiment (SHADE) are presented. Additional radiation measurements enable the determination of the aerosol optical depth, τaerλ, and the direct radiative effect (DRE) of the mineral dust. The results suggest that the absorption by Saharan dust is significantly overestimated in the solar spectrum if standard refractive indices are used. Our measurements suggest an imaginary part of the refractive index of 0.0015i is appropriate at a wavelength λ of 0.55 μm. Different methods for determining τaerλ=0.55 are presented, and the accuracy of each retrieval method is assessed. The value τaerλ=0.55 is estimated as 1.48 ± 0.05 during the period of heaviest dust loading, which is derived from an instantaneous DRE of approximately −129 ± 5 Wm−2 or an enhancement of the local planetary albedo over ocean of a factor of 2.7 ± 0.1. A comparison of the DRE derived from the C-130 instrumentation and from the Clouds and the Earth's Radiant Energy System (CERES) instrument on the Tropical Rainfall Measuring Mission (TRMM) satellite is presented; the results generally showing agreement to within a factor of 1.2. The results suggest that Saharan dust aerosol exerts the largest local and global DRE of all aerosol species and should be considered explicitly in global radiation budget studies. 0305 Aerosols and particles; 0360 Radiation: transmission and scattering; 1640 Remote sensing; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; aerosols; aircraft measurements; mineral dust; radiation balance; radiative forcing; Saharan dust
Kato, Seiji; Loeb, Norman G.Kato, S., N. G. Loeb, 2003: Twilight Irradiance Reflected by the Earth Estimated from Clouds and the Earth's Radiant Energy System (CERES) Measurements. J. Climate, 16(15), 2646-2650. doi: 10.1175/1520-0442(2003)016<2646:TIRBTE>2.0.CO;2. Abstract The upward shortwave irradiance at the top of the atmosphere when the solar zenith angle is greater than 90° (twilight irradiance) is estimated from radiance measurements by the Clouds and the Earth's Radiant Energy System (CERES) instrument on the Tropical Rainfall Measuring Mission (TRMM) satellite. The irradiance decreases with solar zenith angle from 7.5 W m−2 at 90.5° to 0.6 W m−2 at 95.5°. The global and daily average twilight irradiance is 0.2 W m−2, which is three orders of magnitude smaller than the daily and global average reflected irradiance at the top of the atmosphere. Therefore, the twilight irradiance can be neglected in global radiation budget estimate. The daily average twilight irradiance, however, can be more than 1 W m−2 at polar regions during seasons when the sun stays just below the horizon for a long period of time.
Loeb, Norman G.; Loukachine, Konstantin; Manalo-Smith, Natividad; Wielicki, Bruce A.; Young, David F.Loeb, N. G., K. Loukachine, N. Manalo-Smith, B. A. Wielicki, D. F. Young, 2003: Angular Distribution Models for Top-of-Atmosphere Radiative Flux Estimation from the Clouds and the Earth's Radiant Energy System Instrument on the Tropical Rainfall Measuring Mission Satellite. Part II: Validation. Journal of Applied Meteorology, 42(12), 1748-1769. doi: 10.1175/1520-0450(2003)042<1748:ADMFTR>2.0.CO;2. Abstract Top-of-atmosphere (TOA) radiative fluxes from the Clouds and the Earth's Radiant Energy System (CERES) are estimated from empirical angular distribution models (ADMs) that convert instantaneous radiance measurements to TOA fluxes. This paper evaluates the accuracy of CERES TOA fluxes obtained from a new set of ADMs developed for the CERES instrument onboard the Tropical Rainfall Measuring Mission (TRMM). The uncertainty in regional monthly mean reflected shortwave (SW) and emitted longwave (LW) TOA fluxes is less than 0.5 W m−2, based on comparisons with TOA fluxes evaluated by direct integration of the measured radiances. When stratified by viewing geometry, TOA fluxes from different angles are consistent to within 2% in the SW and 0.7% (or 2 W m−2) in the LW. In contrast, TOA fluxes based on ADMs from the Earth Radiation Budget Experiment (ERBE) applied to the same CERES radiance measurements show a 10% relative increase with viewing zenith angle in the SW and a 3.5% (9 W m−2) decrease with viewing zenith angle in the LW. Based on multiangle CERES radiance measurements, 1° regional instantaneous TOA flux errors from the new CERES ADMs are estimated to be
Loeb, Norman G.; Manalo-Smith, Natividad; Kato, Seiji; Miller, Walter F.; Gupta, Shashi K.; Minnis, Patrick; Wielicki, Bruce A.Loeb, N. G., N. Manalo-Smith, S. Kato, W. F. Miller, S. K. Gupta, P. Minnis, B. A. Wielicki, 2003: Angular Distribution Models for Top-of-Atmosphere Radiative Flux Estimation from the Clouds and the Earth’s Radiant Energy System Instrument on the Tropical Rainfall Measuring Mission Satellite. Part I: Methodology. Journal of Applied Meteorology, 42(2), 240-265. doi: 10.1175/1520-0450(2003)042<0240:ADMFTO>2.0.CO;2. Abstract Clouds and the Earth's Radiant Energy System (CERES) investigates the critical role that clouds and aerosols play in modulating the radiative energy flow within the Earth–atmosphere system. CERES builds upon the foundation laid by previous missions, such as the Earth Radiation Budget Experiment, to provide highly accurate top-of-atmosphere (TOA) radiative fluxes together with coincident cloud and aerosol properties inferred from high-resolution imager measurements. This paper describes the method used to construct empirical angular distribution models (ADMs) for estimating shortwave, longwave, and window TOA radiative fluxes from CERES radiance measurements on board the Tropical Rainfall Measuring Mission satellite. To construct the ADMs, multiangle CERES measurements are combined with coincident high-resolution Visible Infrared Scanner measurements and meteorological parameters from the European Centre for Medium-Range Weather Forecasts data assimilation product. The ADMs are stratified by scene types defined by parameters that have a strong influence on the angular dependence of Earth's radiation field at the TOA. Examples of how the new CERES ADMs depend upon the imager-based parameters are provided together with comparisons with existing models.
Loukachine, Konstantin; Loeb, Norman G.Loukachine, K., N. G. Loeb, 2003: Application of an Artificial Neural Network Simulation for Top-of-Atmosphere Radiative Flux Estimation from CERES. J. Atmos. Oceanic Technol., 20(12), 1749-1757. doi: 10.1175/1520-0426(2003)020<1749:AOAANN>2.0.CO;2. Abstract The Clouds and the Earth's Radiant Energy System (CERES) provides top-of-atmosphere (TOA) radiative flux estimates from shortwave (SW) and longwave (LW) radiance measurements by applying empirical angular distribution models (ADMs) for scene types defined by coincident high-resolution imager-based cloud retrievals. In this study, CERES ADMs are simulated using a feed-forward error back-propagation (FFEB) artificial neural network (ANN) simulation to provide a means of estimating TOA SW and LW radiative fluxes for different scene types in the absence of imager radiance measurements. In all cases, the ANN-derived TOA fluxes deviate from CERES TOA fluxes by less than 0.3 W m−2, on average, and show a smaller dependence on viewing geometry than TOA fluxes derived using ADMs from the Earth Radiation Budget Experiment (ERBE). The ANN-derived TOA SW and LW fluxes show a significant improvement in accuracy over the CERES ERBE-like fluxes when compared regionally.

2002

Kato, Seiji; Loeb, Norman G.; Rutledge, C. KenKato, S., N. G. Loeb, C. K. Rutledge, 2002: Estimate of top-of-atmosphere albedo for a molecular atmosphere over ocean using Clouds and the Earth's Radiant Energy System measurements. Journal of Geophysical Research: Atmospheres, 107(D19), 4396. doi: 10.1029/2001JD001309. The shortwave broadband albedo at the top of a molecular atmosphere over ocean between 40°N and 40°S is estimated using radiance measurements from the Clouds and the Earth's Radiant Energy System (CERES) instrument and the Visible Infrared Scanner (VIRS) aboard the Tropical Rainfall Measuring Mission satellite. The albedo monotonically increases from 0.059 at a solar zenith angle of 10° to 0.107 at a solar zenith angle of 60°. The estimated uncertainty in the albedo is 3.5 × 10−3 caused by the uncertainty in CERES-derived irradiances, uncertainty in VIRS-derived aerosol optical thicknesses, variations in surface wind speed and variations in ozone and water vapor. The estimated uncertainty is similar in magnitude to the standard deviation of 0.003 that is derived from 72 areas which are divided by 20° latitude by 20° longitude grid boxes. The empirically estimated albedo is compared with the modeled albedo using a radiative transfer model combined with an ocean surface bidirectional reflectivity model. The modeled albedo with standard tropical atmosphere is 0.061 and 0.111 at the solar zenith angles of 10° and 60°, respectively. The empirically estimated albedo can be used to estimate the direct radiative effect of aerosols at the top of the atmosphere over oceans. 0305 Aerosols and particles; 1640 Remote sensing; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 4264 Ocean optics; aerosol radiative forcing; molecular atmosphere; ocean surface reflectance; planetary albedo
Loeb, Norman G.; Kato, SeijiLoeb, N. G., S. Kato, 2002: Top-of-Atmosphere Direct Radiative Effect of Aerosols over the Tropical Oceans from the Clouds and the Earth's Radiant Energy System (CERES) Satellite Instrument. J. Climate, 15(12), 1474-1484. doi: 10.1175/1520-0442(2002)015<1474:TOADRE>2.0.CO;2. Abstract Nine months of the Clouds and the Earth's Radiant Energy System (CERES)/Tropical Rainfall Measuring Mission (TRMM) broadband fluxes combined with the TRMM visible infrared scanner (VIRS) high-resolution imager measurements are used to estimate the daily average direct radiative effect of aerosols for clear-sky conditions over the tropical oceans. On average, aerosols have a cooling effect over the Tropics of 4.6 ± 1 W m–2. The magnitude is ≈2 W m–2 smaller over the southern tropical oceans than it is over northern tropical oceans. The direct effect derived from CERES is highly correlated with coincident aerosol optical depth (τ) retrievals inferred from 0.63-μm VIRS radiances (correlation coefficient of 0.96). The slope of the regression line is ≈−32 W m–2 τ–1 over the equatorial Pacific Ocean, but changes both regionally and seasonally, depending on the aerosol characteristics. Near sources of biomass burning and desert dust, the aerosol direct effect reaches −25 to −30 W m–2. The direct effect from CERES also shows a dependence on wind speed. The reason for this dependence is unclear—it may be due to increased aerosol (e.g., sea-salt or aerosol transport) or increased surface reflection (e.g., due to whitecaps). The uncertainty in the tropical average direct effect from CERES is ≈1 W m–2 (≈20%) due mainly to cloud contamination, the radiance-to-flux conversion, and instrument calibration. By comparison, uncertainties in the direct effect from the Earth Radiation Budget Experiment (ERBE) and CERES “ERBE-like” products are a factor of 3–5 times larger.
Loeb, Norman G.; Kato, Seiji; Wielicki, Bruce A.Loeb, N. G., S. Kato, B. A. Wielicki, 2002: Defining Top-of-the-Atmosphere Flux Reference Level for Earth Radiation Budget Studies. J. Climate, 15(22), 3301-3309. doi: 10.1175/1520-0442(2002)015<3301:DTOTAF>2.0.CO;2. Abstract To estimate the earth's radiation budget at the top of the atmosphere (TOA) from satellite-measured radiances, it is necessary to account for the finite geometry of the earth and recognize that the earth is a solid body surrounded by a translucent atmosphere of finite thickness that attenuates solar radiation differently at different heights. As a result, in order to account for all of the reflected solar and emitted thermal radiation from the planet by direct integration of satellite-measured radiances, the measurement viewing geometry must be defined at a reference level well above the earth's surface (e.g., 100 km). This ensures that all radiation contributions, including radiation escaping the planet along slant paths above the earth's tangent point, are accounted for. By using a field-of-view (FOV) reference level that is too low (such as the surface reference level), TOA fluxes for most scene types are systematically underestimated by 1–2 W m−2. In addition, since TOA flux represents a flow of radiant energy per unit area, and varies with distance from the earth according to the inverse-square law, a reference level is also needed to define satellite-based TOA fluxes. From theoretical radiative transfer calculations using a model that accounts for spherical geometry, the optimal reference level for defining TOA fluxes in radiation budget studies for the earth is estimated to be approximately 20 km. At this reference level, there is no need to explicitly account for horizontal transmission of solar radiation through the atmosphere in the earth radiation budget calculation. In this context, therefore, the 20-km reference level corresponds to the effective radiative “top of atmosphere” for the planet. Although the optimal flux reference level depends slightly on scene type due to differences in effective transmission of solar radiation with cloud height, the difference in flux caused by neglecting the scene-type dependence is less than 0.1%. If an inappropriate TOA flux reference level is used to define satellite TOA fluxes, and horizontal transmission of solar radiation through the planet is not accounted for in the radiation budget equation, systematic errors in net flux of up to 8 W m−2 can result. Since climate models generally use a plane-parallel model approximation to estimate TOA fluxes and the earth radiation budget, they implicitly assume zero horizontal transmission of solar radiation in the radiation budget equation, and do not need to specify a flux reference level. By defining satellite-based TOA flux estimates at a 20-km flux reference level, comparisons with plane-parallel climate model calculations are simplified since there is no need to explicitly correct plane-parallel climate model fluxes for horizontal transmission of solar radiation through a finite earth.
Priestley, K. J; Wielicki, B. A; Green, R. N; Haeffelin, M. P. A; Lee, R. B; Loeb, N. GPriestley, K. J., B. A. Wielicki, R. N. Green, M. P. A. Haeffelin, R. B. Lee, N. G. Loeb, 2002: Early radiometric validation results of the CERES Flight Model 1 and 2 instruments onboard NASA's Terra Spacecraft. Advances in Space Research, 30(11), 2371-2376. doi: 10.1016/S0273-1177(02)80278-2. The CERES Flight Model 1 and 2 instruments were launched aboard NASA's Earth Observing System (EOS) Terra Spacecraft on December 18, 1999 into a 705 Km sun-synchronous orbit with a 10:30 a.m. equatorial crossing time. These instruments supplement measurements made by the CERES Proto Flight Model (PFM) instrument launched aboard NASA's Tropical Rainfall Measuring Mission (TRMM) spacecraft on November 27, 1997 into a 350 Km, 38-degree mid-inclined orbit. An important aspect of the EOS program is the rapid archival and dissemination of datasets measured by EOS instruments to the scientific community. On September 22, 2000 the CERES Science Team voted to archive the Edition 1 CERES/Terra Level 1b and Level 2 and 3 ERBE-Like data products. These products consist of instantaneous filtered and unfiltered radiances through temporally and spatially averaged TOA fluxes. CERES filtered radiance measurements cover three spectral bands including shortwave (0.3 to 5 μm), total (0.3 to <100 μm) and an atmospheric window channel (8 to 12 μm). The current work summarizes both the philosophy and results of validation efforts undertaken to quantify the quality of the Terra data products as well as the level of agreement between the Terra and TRMM datasets.
Satheesh, S. K.; Ramanathan, V.; Holben, B. N.; Moorthy, K. Krishna; Loeb, N. G.; Maring, H.; Prospero, J. M.; Savoie, D.Satheesh, S. K., V. Ramanathan, B. N. Holben, K. K. Moorthy, N. G. Loeb, H. Maring, J. M. Prospero, D. Savoie, 2002: Chemical, microphysical, and radiative effects of Indian Ocean aerosols. Journal of Geophysical Research: Atmospheres, 107(D23), 4725. doi: 10.1029/2002JD002463. Extensive and long-term multistation measurements of aerosol properties and radiative fluxes were carried out in the haze plume off the South Asian continent. These experiments are carried out at Kaashidhoo Climate Observatory (KCO) (4.95°N, 73.5°E), Minicoy (8.5°N, 73.0°E), and Trivandrum (8.5°N, 77.0°E). In addition, the top of the atmosphere fluxes were measured simultaneously by the CERES radiation budget instrument. Long-term observations (more than 15 years) over Trivandrum show that there is a gradual increase in aerosol visible optical depth from ∼0.2 in 1986 to ∼0.4 in 1999. Pre- and post-monsoon aerosol characteristics are examined to study the seasonal variations. The impact of aerosols on short-wave radiation budget is estimated using direct observations of solar radiation using several independent ground-based radiometers and satellite data as well as from modeled aerosol properties. It was observed that “excess absorption” is not needed to model diffuse fluxes. The lower atmospheric heating due to absorbing aerosols was as high as ∼20 W m−2 which translates to a heating rate perturbation of ∼0.5°K/day. The effect of aerosol mixing state (internally and externally) on aerosol forcing appears to be negligible. A sensitivity study of the effect of aerosols over land in contrast to that over the ocean shows an enhancement in lower atmosphere heating by about 40% simultaneous with a reduction of ∼33% in surface cooling. Increasing sea-surface winds increase aerosol cooling due to increased sea salt aerosol concentrations, which can partly offset the heating effect due to absorbing aerosols. 0305 Aerosols and particles; 1610 Atmosphere; 1704 Atmospheric sciences; 4801 Aerosols; aerosols; chemical composition; climate; radiative forcing
Sun, Wenbo; Loeb, Norman G.; Fu, QiangSun, W., N. G. Loeb, Q. Fu, 2002: Finite-difference time-domain solution of light scattering and absorption by particles in an absorbing medium. Applied Optics, 41(27), 5728-5743. doi: 10.1364/AO.41.005728. The three-dimensional (3-D) finite-difference time-domain (FDTD) technique has been extended to simulate light scattering and absorption by nonspherical particles embedded in an absorbing dielectric medium. A uniaxial perfectly matched layer (UPML) absorbing boundary condition is used to truncate the computational domain. When computing the single-scattering properties of a particle in an absorbing dielectric medium, we derive the single-scattering properties including scattering phase functions, extinction, and absorption efficiencies using a volume integration of the internal field. A Mie solution for light scattering and absorption by spherical particles in an absorbing medium is used to examine the accuracy of the 3-D UPML FDTD code. It is found that the errors in the extinction and absorption efficiencies from the 3-D UPML FDTD are less than ∼2%. The errors in the scattering phase functions are typically less than ∼5%. The errors in the asymmetry factors are less than ∼0.1%. For light scattering by particles in free space, the accuracy of the 3-D UPML FDTD scheme is similar to a previous model [Appl. Opt.38, 3141 (1999)]. Atmospheric scattering; Numerical approximation and analysis; Oceanic optics; Particles; Scattering, particles; Water

2001

Buriez, Jean-Claude; Doutriaux-Boucher, Marie; Parol, Frédéric; Loeb, Norman G.Buriez, J., M. Doutriaux-Boucher, F. Parol, N. G. Loeb, 2001: Angular Variability of the Liquid Water Cloud Optical Thickness Retrieved from ADEOS–POLDER. J. Atmos. Sci., 58(20), 3007-3018. doi: 10.1175/1520-0469(2001)058<3007:AVOTLW>2.0.CO;2. Abstract The usual procedure for retrieving the optical thickness of liquid water clouds from satellite-measured radiances is based on the assumption of plane-parallel layers composed of liquid water droplets. This study investigates the validity of this assumption from Advanced Earth Orbiting Satellite–Polarization and Directionality of the Earth's Reflectances (ADEOS–POLDER) observations. To do that, the authors take advantage of the multidirectional viewing capability of the POLDER instrument, which functioned nominally aboard ADEOS from November 1996 to June 1997. The usual plane-parallel cloud model composed of water droplets with an effective radius of 10 μm provides a reasonable approximation of the angular dependence in scattering at visible wavelengths from overcast liquid water clouds for moderate solar zenith angles. However, significant differences between model and observations appear in the rainbow direction and for the smallest observable values of scattering angle (Θ < 90°). A better overall agreement would be obtained for droplets with an effective radius of about 7–8 μm for continental liquid water clouds. On the other hand, changing the water droplet size distribution would not lead to a significant improvement for maritime situations. When horizontal variations in cloud optical thickness are considered by using the independent pixel approximation (IPA), a small improvement is obtained over the whole range of scattering angles but significant discrepancies remain for Θ < 80°, that is for large solar zenith angles in the forward-scattering direction. The remaining differences between various models based on the plane-parallel radiative transfer and POLDER observations are thought to be due to variations in cloud shape.
Chambers, L. H.; Wielicki, B. A.; Loeb, N. G.Chambers, L. H., B. A. Wielicki, N. G. Loeb, 2001: Shortwave Flux from Satellite-Measured Radiance: A Theoretical Study over Marine Boundary Layer Clouds. Journal of Applied Meteorology, 40(12), 2144-2161. doi: 10.1175/1520-0450(2001)040<2144:SFFSMR>2.0.CO;2. Abstract Earth radiation budget measurements, important to climate monitoring and to validating climate models, require that radiances measured by satellite instruments be converted to hemispherical flux. This paper examines that problem theoretically, using inhomogeneous cloud models constructed from Landsat scenes of marine boundary layer clouds. The spherical harmonics discrete ordinates method (SHDOM) code is applied to the model scenes to compute full two-dimensional radiation fields, which then simulate measured radiances. Inversion to flux is performed by several different methods, including plane-parallel table lookup and empirical angular distribution models with three different ways of determining scene identification, to examine error sources and relative magnitudes. Using a simple plane-parallel table lookup results in unacceptably large flux bias errors of 11%–60%, depending on the orbital viewing geometry. This bias can be substantially reduced, to no more than 6%, by using empirical angular distribution models. Further improvement, to no more than 2% flux bias error, is obtained if known biases in optical-depth retrievals are taken into account when building the angular models. Last, the bias can be further reduced to a fraction of a percent using scene identification based on multiple views of the same area. There are limits, however, to the reduction in the instantaneous error with this approach. Trends in the flux error are also identified, in particular an equator-to-pole trend in the flux bias. Given the importance of satellite measurements for determining heat transport from equator to pole, this consistent bias should be kept in mind, and efforts should be made to reduce it in the future.
Loeb, Norman G.; Priestley, Kory J.; Kratz, David P.; Geier, Erika B.; Green, Richard N.; Wielicki, Bruce A.; Hinton, Patricia O’Rawe; Nolan, Sandra K.Loeb, N. G., K. J. Priestley, D. P. Kratz, E. B. Geier, R. N. Green, B. A. Wielicki, P. O. Hinton, S. K. Nolan, 2001: Determination of Unfiltered Radiances from the Clouds and the Earth’s Radiant Energy System Instrument. Journal of Applied Meteorology, 40(4), 822-835. doi: 10.1175/1520-0450(2001)040<0822:DOURFT>2.0.CO;2. Abstract A new method for determining unfiltered shortwave (SW), longwave (LW), and window radiances from filtered radiances measured by the Clouds and the Earth’s Radiant Energy System (CERES) satellite instrument is presented. The method uses theoretically derived regression coefficients between filtered and unfiltered radiances that are a function of viewing geometry, geotype, and whether cloud is present. Relative errors in instantaneous unfiltered radiances from this method are generally well below 1% for SW radiances (std dev ≈0.4% or ≈1 W m−2 equivalent flux), less than 0.2% for LW radiances (std dev ≈0.1% or ≈0.3 W m−2 equivalent flux), and less than 0.2% (std dev ≈0.1%) for window channel radiances. When three months (June, July, and August of 1998) of CERES Earth Radiation Budget Experiment (ERBE)-like unfiltered radiances from the Tropical Rainfall Measuring Mission satellite between 20°S and 20°N are compared with archived Earth Radiation Budget Satellite (ERBS) scanner measurements for the same months over a 5-yr period (1985–89), significant scene-type dependent differences are observed in the SW channel. Full-resolution CERES SW unfiltered radiances are ≈7.5% (≈3 W m−2 equivalent diurnal average flux) lower than ERBS over clear ocean, as compared with ≈1.7% (≈4 W m−2 equivalent diurnal average flux) for deep convective clouds and ≈6% (≈4–6 W m−2 equivalent diurnal average flux) for clear land and desert. This dependence on scene type is shown to be partly caused by differences in spatial resolution between CERES and ERBS and by errors in the unfiltering method used in ERBS. When the CERES measurements are spatially averaged to match the ERBS spatial resolution and the unfiltering scheme proposed in this study is applied to both CERES and ERBS, the ERBS all-sky SW radiances increase by ≈1.7%, and the CERES radiances are now consistently ≈3.5%–5% lower than the modified ERBS values for all scene types. Further study is needed to determine the cause for this remaining difference, and even calibration errors cannot be ruled out. CERES LW radiances are closer to ERBS values for individual scene types—CERES radiances are within ≈0.1% (≈0.3 W m−2) of ERBS over clear ocean and ≈0.5% (≈1.5 W m−2) over clear land and desert.
Zhou, Y. P.; Rutledge, K. C.; Charlock, T. P.; Loeb, N. G.; Kato, S.Zhou, Y. P., K. C. Rutledge, T. P. Charlock, N. G. Loeb, S. Kato, 2001: Atmospheric corrections using MODTRAN for TOA and surface BRDF characteristics from high resolution spectroradiometric/angular measurements from a helicopter platform. High-resolution spectral radiance measurements were taken by a spectral radiometer on board a helicopter over the US Oklahoma Southern Great Plain near the Atmospheric Radiation Measurements (ARM) site during August 1998. The radiometer has a spectral range from 350 nm to 2500 nm at 1 nm resolution. The measurements covered several grass and cropland scene types at multiple solar zenith angles. Detailed atmospheric corrections using the Moderate Resolution Transmittance (MODTRAN) radiation model and in-situ sounding and aerosol measurements have been applied to the helicopter measurements in order to retrieve the surface and top of atmosphere (TOA) Bidirectional Reflectance Distribution Function (BRDF) characteristics. The atmospheric corrections are most significant in the visible wavelengths and in the strong water vapor absorption wavelengths in the near infrared region. Adjusting the BRDF to TOA requires a larger correction in the visible channels since Rayleigh scattering contributes significantly to the TOA reflectance. The opposite corrections to the visible and near infrarred wavelengths can alter the radiance difference and ratio that many remote sensing techniques are based on, such as the normalized difference vegetation index (NDVI). The data show that surface BRDFs and spectral albedos are highly sensitive to the vegetation type and solar zenith angle while BRDF at TOA depends more on atmospheric conditions and the vi ewing geometry. Comparison with the Clouds and the Earth's Radiant Energy System (CERES) derived clear sky Angular Distribution Model (ADM) for crop and grass scene type shows a standard deviation of 0.08 in broadband anisotropic function at 25 degrees solar zenith angle and 0.15 at 50 degrees solar zenith angle, respectively.

2000

Loeb, Norman G.; Parol, Frédéric; Buriez, Jean-Claude; Vanbauce, ClaudineLoeb, N. G., F. Parol, J. Buriez, C. Vanbauce, 2000: Top-of-Atmosphere Albedo Estimation from Angular Distribution Models Using Scene Identification from Satellite Cloud Property Retrievals. J. Climate, 13(7), 1269-1285. doi: 10.1175/1520-0442(2000)013<1269:TOAAEF>2.0.CO;2. Abstract The next generation of earth radiation budget satellite instruments will routinely merge estimates of global top-of-atmosphere radiative fluxes with cloud properties. This information will offer many new opportunities for validating radiative transfer models and cloud parameterizations in climate models. In this study, five months of Polarization and Directionality of the Earth’s Reflectances 670-nm radiance measurements are considered in order to examine how satellite cloud property retrievals can be used to define empirical angular distribution models (ADMs) for estimating top-of-atmosphere albedo. ADMs are defined for 19 scene types defined by satellite retrievals of cloud fraction and cloud optical depth. Two approaches are used to define the ADM scene types. The first assumes there are no biases in the retrieved cloud properties and defines ADMs for fixed discrete intervals of cloud fraction and cloud optical depth (fixed-τ approach). The second approach involves the same cloud fraction intervals, but uses percentile intervals of cloud optical depth instead (percentile-τ approach). Albedos generated using these methods are compared with albedos inferred directly from the mean observed reflectance field. Albedos based on ADMs that assume cloud properties are unbiased (fixed-τ approach) show a strong systematic dependence on viewing geometry. This dependence becomes more pronounced with increasing solar zenith angle, reaching ≈12% (relative) between near-nadir and oblique viewing zenith angles for solar zenith angles between 60° and 70°. The cause for this bias is shown to be due to biases in the cloud optical depth retrievals. In contrast, albedos based on ADMs built using percentile intervals of cloud optical depth (percentile-τ approach) show very little viewing zenith angle dependence and are in good agreement with albedos obtained by direct integration of the mean observed reflectance field (

1999

Loeb, Norman G.; Hinton, Patricia O'Rawe; Green, Richard N.Loeb, N. G., P. O. Hinton, R. N. Green, 1999: Top-of-atmosphere albedo estimation from angular distribution models: A comparison between two approaches. Journal of Geophysical Research: Atmospheres, 104(D24), 31255-31260. doi: 10.1029/1999JD900935. Empirical angular distribution models (ADMs) are commonly used to convert satellite-measured radiances to top-of-atmosphere (TOA) radiative fluxes. This study compares two methods of developing ADMs: (1) the radiance pairs method (RPM), which composits ratios of near-simultaneous radiance measurements over the same scene to construct the ADMs; (2) the sorting-into-angular-bins (SAB) method, which estimates ADM anisotropic factors from the ratio of the mean radiance in each angular bin to the mean flux determined by direct integration of the mean radiances. Theoretical simulations and analyses of measurements from the CERES (Clouds and Earth's Radiant Energy System) satellite instrument show that the RPM method provides a better estimate of the true mean ADM for a population of scenes, while the SAB method is better suited for top-of-atmosphere flux estimation. The CERES results also show that a variable field of view size with viewing zenith angle can cause an ≈10% (relative) change in estimated all-sky mean albedo with viewing zenith angle. 1620 Climate dynamics; 1640 Remote sensing; 1694 Instruments and techniques; 3359 Meteorology and Atmospheric Dynamics: Radiative processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 4504 Air/sea interactions
Satheesh, S. K.; Ramanathan, V.; Li-Jones, Xu; Lobert, J. M.; Podgorny, I. A.; Prospero, J. M.; Holben, B. N.; Loeb, N. G.Satheesh, S. K., V. Ramanathan, X. Li-Jones, J. M. Lobert, I. A. Podgorny, J. M. Prospero, B. N. Holben, N. G. Loeb, 1999: A model for the natural and anthropogenic aerosols over the tropical Indian Ocean derived from Indian Ocean Experiment data. Journal of Geophysical Research: Atmospheres, 104(D22), 27421-27440. doi: 10.1029/1999JD900478. The physical, chemical and radiative properties of aerosols are investigated over the tropical Indian Ocean during the first field phase (FFP) of the international Indian Ocean Experiment. The FFP was conducted during February 20 to March 31, 1998. The results shown here are from the Kaashidhoo Climate Observatory (KCO), a new surface observatory established on the tiny island of Kaashidhoo (4.965°N, 73.466°E) in the Republic of Maldives. From simultaneous measurements of aerosol physical, chemical, and radiative properties and the vertical structure from lidar, we have developed an aerosol model which, in conjunction with a Monte Carlo radiative transfer model, successfully explains (within a few percent) the observed solar radiative fluxes at the surface and at the top of the atmosphere. This agreement demonstrates the fundamental importance of measuring aerosol physical and chemical properties for modeling radiative fluxes. KCO, during the northeast monsoon period considered here, is downwind of the Indian subcontinent and undergoes variations in the aerosol visible optical depth τν from ∼0.1 to 0.4, with a monthly mean of ∼0.2. Lidar data suggest that the aerosol is confined largely to the first 3 kms. Sulfate and ammonium contribute ∼29% to τν; sea-salt and nitrate contributes ∼17%; mineral dust contributes ∼15%; and the inferred soot, organics, and fly ash contribute 11%, 20%, and 8% respectively. We estimate that anthropogenic sources may contribute as much as 65% to the observed τν. We consider both an externally and an internally mixed aerosol model with very little difference between the two in the computed radiative forcing. The observed scattering coefficients are in the upper range of those reported for other oceanic regions, the single-scattering albedos are as low as 0.9, and the Angstrom wavelength exponents of ∼1.2 indicate the abundance of submicron aerosols. In summary, the data and the model confirm the large impact of anthropogenic sources. The surface global fluxes (for overhead Sun) decrease by as much as 50 to 80 W m−2 owing to the presence of the aerosols, and the top of the atmosphere fluxes increase by as much as 15 W m−2, thus indicating that anthropogenic aerosols are having a large impact on the tropical Indian Ocean. 0345 Pollution: urban and regional; 1610 Atmosphere; 1836 Hydrological cycles and budgets; 1866 Soil moisture; 3359 Meteorology and Atmospheric Dynamics: Radiative processes