Clouds And Earth's Radiant Energy System Research Articles

Comparison of CERES-MODIS cloud microphysical properties with surface observations over Loess Plateau

To enhance the utility of satellite-derived cloud properties for studying the role of clouds in climate change and the hydrological cycle in semi-arid areas, it is necessary to know their uncertainties. This paper estimates the uncertainties of several cloud properties by comparing those derived over the China Loess Plateau from the MODerate-resolution Imaging Spectroradiometer (MODIS) on Terra and Aqua by the Clouds and Earth׳s Radiant Energy System (CERES) with surface observations at the Semi-Arid Climate and Environment Observatory of Lanzhou University (SACOL). The comparisons use data from January 2008 to June 2010 limited to single layer and overcast stratus conditions during daytime. Cloud optical depths (τ) and liquid water paths (LWP) from both Terra and Aqua generally track the variation of the surface counterparts with modest correlation, while cloud effective radius (re) is only weakly correlated with the surface retrievals. The mean differences between Terra and the SACOL retrievals are −4.7±12.9, 2.1±3.2μm and 30.2±85.3gm−2 for τ, re and LWP, respectively. The corresponding differences for Aqua are 2.1±8.4, 1.2±2.9μm and 47.4±79.6gm−2, respectively. Possible causes for biases of satellite retrievals are discussed through statistical analysis and case studies. Generally, the CERES-MODIS cloud properties have a bit larger biases over the Loess Plateau than those in previous studies over other locations.

An Efficient Method of Estimating Downward Solar Radiation Based on the MODIS Observations for the Use of Land Surface Modeling

Solar radiation is a critical variable in global change sciences. While most of the current global datasets provide only the total downward solar radiation, we aim to develop a method to estimate the downward global land surface solar radiation and its partitioned direct and diffuse components, which provide the necessary key meteorological inputs for most land surface models. We developed a simple satellite-based computing scheme to enable fast and reliable estimation of these variables. The global Moderate Resolution Imaging Spectroradiometer (MODIS) products at 1° spatial resolution for the period 2003–2011 were used as the forcing data. Evaluations at Baseline Surface Radiation Network (BSRN) sites show good agreement between the estimated radiation and ground-based observations. At all the 48 BSRN sites, the RMSE between the observations and estimations are 34.59, 41.98 and 28.06 W∙m−2 for total, direct and diffuse solar radiation, respectively. Our estimations tend to slightly overestimate the total and diffuse but underestimate the direct solar radiation. The errors may be related to the simple model structure and error of the input data. Our estimation is also comparable to the Clouds and Earth’s Radiant Energy System (CERES) data while shows notable improvement over the widely used National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) Reanalysis data. Using our MODIS-based datasets of total solar radiation and its partitioned components to drive land surface models should improve simulations of global dynamics of water, carbon and climate.

Dispersion of the Nabro volcanic plume and its relation to the Asian summer monsoon

Abstract. We use nighttime measurements from the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite, together with a Lagrangian trajectory model, to study the initial dispersion of volcanic aerosol from the eruption of Mt. Nabro (Ethiopia/Eritrea) in June 2011. The Nabro eruption reached the upper troposphere and lower stratosphere (UTLS) directly, and the plume was initially entrained by the flow surrounding the Asian anticyclone, which prevails in the UTLS from the Mediterranean Sea to East Asia during boreal summer. CALIPSO detected aerosol layers, with optical properties consistent with sulfate, in the lower stratosphere above the monsoon convective region in South and Southeast Asia within 10 days of the eruption. We show that quasi-isentropic differential advection in the vertically sheared flow surrounding the Asian anticyclone explains many of these stratospheric aerosol layers. We use Meteosat-7 data to examine the possible role of deep convection in the Asian monsoon in transporting volcanic material to the lower stratosphere during this time, but find no evidence that convection played a direct role, in contrast with claims made in earlier studies. On longer timescales, we use CALIPSO data to illustrate diabatic ascent of the Nabro aerosol in the lower stratosphere at rates of ~ 10 K per month for the first two months after the eruption, falling to ~ 3 K per month after the Asian anticyclone dissipates. Maps of stratospheric aerosol optical depth (AOD) show local peaks of ~ 0.04–0.06 in July in the region of the Asian anticyclone; we find associated estimates of radiative forcing small, ~ 5–10% of those reported for the eruption of Mt. Pinatubo in 1991. Additionally, we find no clear response in outgoing shortwave (SW) flux due to the presence of Nabro aerosol viewed in the context of SW flux variability as measured by CERES (Clouds and Earth Radiant Energy System).

Investigation of negative cloud radiative forcing over the Indian subcontinent and adjacent oceans during the summer monsoon season

Abstract. Radiative properties of clouds over the Indian subcontinent and nearby oceanic regions (0–25° N, 60–100° E) during the Asian summer monsoon season (June–September) are investigated using the Clouds and Earth's Radiant Energy System (CERES) top-of-the-atmosphere (TOA) flux data. Using multiyear satellite data, the net cloud radiative forcing (NETCRF) at the TOA over the Indian region during the Asian monsoon season is examined. The seasonal mean NETCRF is found to be negative (with its magnitude exceeding ~30 Wm−2) over (1) the northern Bay of Bengal (close to the Myanmar–Thailand coast), (2) the Western Ghats and (3) the coastal regions of Myanmar. Such strong negative NETCRF values observed over the Indian monsoon region contradict the assumption that near cancellation between LWCRF and SWCRF is a generic property of all tropical convective regions. The seasonal mean cloud amount (high and upper middle) and corresponding cloud optical depth observed over the three regions show relatively large values compared to the rest of the Indian monsoon region. Using satellite-derived cloud data, a statistical cloud vertical model delineating the cloud cover and single-scattering albedo was developed for the three negative NETCRF regions. The shortwave (SW), longwave (LW) and net cloud radiative forcing over the three negative NETCRF regions are calculated using the rapid radiative transfer model (RRTM) with the cloud vertical model as input. The NETCRF estimated from CERES observations show good comparison with that computed using RRTM (within the uncertainty limit of CERES observations). Sensitivity tests are conducted using RRTM to identify the parameters that control the negative NETCRF observed over these regions during the summer monsoon season. Increase in atmospheric water vapor content during the summer monsoon season is found to influence the negative NETCRF values observed over the region.

Point response function of the Clouds and Earth Radiant Energy System scanning radiometer

An overview of work related to the point response function (PRF) of the Clouds and Earth Radiant Energy System (CERES) scanning radiometer is presented. The aspects of the CERES design that affect the PRF are described, and then the design of the PRF is explained. The PRF was designed by shaping the field of view so as to minimize the blur plus alias errors of the radiance field reconstructed from the CERES measurements. The design is conducted in the Fourier domain. The PRF can then be computed by transforming the resulting transfer function to the physical domain. Alternatively, the PRF can be computed in the physical plane. The PRF of each model of the CERES instrument has been tested in the Radiation Calibration Facility by use of a PRF source and compared well with prediction. CERES instruments are aboard the Terra, Aqua, and Suomi-NPP spacecraft. In orbit, lunar observations are used to validate the PRF. These results showed nominal performance except for the longwave window channel of flight model 2, for which a region of anomalously high sensitivity was found.

위성자료를 이용한 2001-2010년 동안의 동아시아 지역 에어로졸 직접복사강제력 분석

The shortwave aerosol direct radiative forcing (SWARF) was analyzed using the Clouds and Earth's Radiant Energy System (CERES) data in the East Asian region from 2001 to 2010. In the Yellow Sea and the Korean Peninsula, located in the leeward side of China, significantly negative high SWARF at the top of atmosphere (TOA) occurs due to the long-range transport of anthropogenic (e.g. sulphate) and natural aerosols (e.g. mineral dust) from the East Asian continent. Conversely, eastern China has much higher levels of SWARF at the surface (SFC) due to anthropogenically emitted aerosol than in the Yellow Sea and the Korean Peninsula. Since the radiative forcing of aerosols in the atmosphere are different in type, aerosol types were classified into sea salt+sulphate, smoke, sulphate and dust by using satellite data. The analysis on the SWARF by the classified aerosol types indicated that sulphate occupies a predominant portion of the atmosphere in the Yellow Sea and the Korean Peninsula in the summer. In particular, the annual averages of the summer TOA SWARF increased in the Yellow Sea and the Korean Peninsula from 2001 to 2010.

Estimation of aerosol direct radiative effects for all-sky conditions from CERES and MODIS observations

Satellite observations have shown the global average of the aerosol direct radiative effect (DRE) at the top of the atmosphere to be approximately −5.0Wm−2. Although there is a general consensus on this quantity, it is essentially biased toward clear-sky conditions. To circumvent this limitation, the present study introduces a new method for retrieving the global DRE of aerosol over the region of 60°S–60°N for all-sky conditions (both clear and cloudy skies). The all-sky DRE was calculated on a monthly basis by combining the measured DRE for a clear sky and the simulated DRE for a cloudy sky in 1°×1° grids. For the measured clear-sky DRE, we employed aerosol, cloud, and radiation fluxes from the Cloud and Earth's Radiant Energy System (CERES) instrument and the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Terra satellite for May 2000–December 2005. For the simulated cloudy-sky DRE, we performed radiative transfer modeling with the MODIS cloud properties in addition to the aerosol optical properties independently estimated in this study that include asymmetry factor and single scattering albedo. The results show that the global mean±standard deviation of DRE for the all-sky scene is −3.1±1.0Wm−2, which is weaker than that for the clear-sky only. This is in good agreement with the global estimates from previous studies based on different methods. The main advantage of our method is near-real-time estimation of monthly global all-sky DRE that has physical consistency with the CERES data.

Top of Atmosphere Flux from the Megha-Tropiques ScaRaB

One of the important payloads on-board the joint Indo- French Megha-Tropiques satellite is the Scanner for Radiation Budget (ScaRaB). It is dedicated for monitoring the Earth Radiation Budget (ERB) parameters at Top of Atmosphere (TOA). In this article, details of the algorithm used for computing two important ERB components, namely TOA reflected shortwave and emitted longwave fluxes from ScaRaB radiance measurements are presented along with preliminary crosssatellite validation results. The ScaRaB flux computation algorithm is similar to the one used in the ERB Experiment. The maximum likelihood estimation algorithm is used for identification of different Earth scenes and cloud types. First, the raw radiances are corrected for spectral filtering effects followed by implementation of scene-type dependent angular correction to deduce shortwave and longwave fluxes. The instantaneous TOA flux data derived from ScaRaB radiance measurements are compared with similar data available from Clouds and Earth's Radiant Energy System (CERES) onboard Aqua and Terra satellites. Preliminary comparison confined to two months period (September- October 2012) using the two satellites suggests that the ScaRaB data are in good agreement with the CERES data. The bias-corrected root mean square difference in ScaRaB longwave flux is 4.7 and 5.3 Wm -2 with respect to CERES on-board Aqua and Terra satellites respectively. For ScaRaB shortwave flux, it is 25.9 Wm -2 and 25.5 Wm -2 with respect to CERES onboard Aqua and Terra satellites respectively. A detailed comparison of ScaRaB TOA flux data with more than one-year of CERES data is already initiated. Results from the preliminary comparison exercise suggest that the ScaRaB data can be used with confidence for ERB studies.

The Canadian Fourth Generation Atmospheric Global Climate Model (CanAM4). Part I: Representation of Physical Processes

The Canadian Centre for Climate Modelling and Analysis (CCCma) has developed the fourth generation of the Canadian Atmospheric Global Climate Model (CanAM4). The new model includes substantially modified physical parameterizations compared to its predecessor. In particular, the treatment of clouds, cloud radiative effects, and precipitation has been modified. Aerosol direct and indirect effects are calculated based on a bulk aerosol scheme. Simulation results for present-day global climate are analyzed, with a focus on cloud radiative effects and precipitation. Good overall agreement is found between climatological mean short- and longwave cloud radiative effects and observations from the Clouds and Earth's Radiant Energy System (CERES) experiment. An analysis of the responses of cloud radiative effects to variations in climate will be presented in a companion paper. [Traduit par la rédaction] Le Centre canadien de la modélisation et de l'analyse climatique (CCmaC) a mis au point la quatrième génération du modèle canadien de circulation générale de l'atmosphère (CanAM4). Le nouveau modèle comprend des paramétrisations physiques passablement modifiées comparativement à son prédécesseur. En particulier, le traitement des nuages, des effets radiatifs des nuages et des précipitations a été modifié. Les effets directs et indirects des aérosols sont calculés à l'aide d'un schéma d'aérosols en bloc. Nous analysons des résultats de simulation pour le climat général du jour présent en mettant l'accent sur les effets radiatifs des nuages et les précipitations. Nous trouvons un bon accord général entre la moyenne climatologique des effets radiatifs des nuages pour les courtes et les grandes longueurs d'onde et les observations de l'expérience CERES (Clouds and Earth's Radiant Energy System). Une analyse de la réponse des effets radiatifs des nuages aux variations du climat sera présentée dans un article connexe.

Improved estimates and understanding of global albedo and atmospheric solar absorption

This study integrates available surface‐based and satellite observations of solar radiation at the surface and the top of the atmosphere (TOA) with a comprehensive set of satellite observations of atmospheric and surface optical properties and a Monte Carlo Aerosol‐Cloud‐Radiation (MACR) model to estimate the three fundamental components of the planetary solar radiation budget: Albedo at the TOA; atmospheric solar absorption; and surface solar absorption. The MACR incorporates most if not all of our current understanding of the theory of solar radiation physics including modern spectroscopic water vapor data, minor trace gases, absorbing aerosols including its effects inside cloud drops, 3‐D cloud scattering effects. The model is subject to a severe test by comparing the simulated solar radiation budget with data from 34 globally distributed state‐of‐the art BSRN (Baseline Surface Radiation Network) land stations which began data collection in the mid 1990s. The TOA over these sites were obtained from the CERES (Cloud and Earth's Radiant Energy System) satellites. The simulated radiation budget was within 2 Wm−2for all three components over the BSRN sites. On the other hand, over these same sites, the IPCC‐2007 simulation of atmospheric absorption is smaller by 7–8 Wm−2. MACR was then used with a comprehensive set of model input from satellites to simulate global solar radiation budget. The simulated planetary albedo of 29.0% confirms the value (28.6%) observed by CERES. We estimate the atmospheric absorption to be 82 ± 8 Wm−2 to be compared with the 67 Wm−2 by IPCC models as of 2001 and updated to 76 Wm−2by IPCC‐2007. The primary reasons for the 6 Wm−2 larger solar absorption in our estimates are: updated water vapor spectroscopic database (∼1 Wm−2), inclusion of minor gases (∼0.5 Wm−2), black and brown carbon aerosols (∼4 Wm−2), the inclusion of black carbon in clouds (∼1 Wm−2) and 3‐D effect of clouds (∼1 Wm−2). The fundamental deduction from our study is the remarkable consistency between satellite measurements of the radiation budget and the parameters (aerosols, clouds and surface reflectivity) which determine the radiation budget. Because of this consistency we can account for and explain the global solar radiation budget of the planet within few Wm−2.

On the determination of the global cloud feedback from satellite measurements

Abstract. A detailed analysis is presented in order to determine the sensitivity of the estimated short-term cloud feedback to choices of temperature datasets, sources of top-of-atmosphere (TOA) clear-sky radiative flux data, and temporal averaging. It is shown that the results of a previous analysis, which suggested a likely positive value for the short-term cloud feedback, depended upon combining all-sky radiative fluxes from NASA's Clouds and Earth's Radiant Energy System (CERES) with reanalysis clear-sky forecast fluxes when determining the cloud radiative forcing (CRF). These results are contradicted when ΔCRF is derived using both all-sky and clear-sky measurements from CERES over the same period. The differences between the radiative flux data sources are thus explored, along with the potential problems in each. The largest discrepancy is found when including the first two years (2000–2002), and the diagnosed cloud feedback from each method is sensitive to the time period over which the regressions are run. Overall, there is little correlation between the changes in the ΔCRF and surface temperatures on these timescales, suggesting that the net effect of clouds varies during this time period quite apart from global temperature changes. Given the large uncertainties generated from this method, the limited data over this period are insufficient to rule out either the positive feedback present in most climate models or a strong negative cloud feedback.

A technique using principal component analysis to compare seasonal cycles of Earth radiation from CERES and model computations

A method for quantitatively comparing the seasonal cycles of two global data sets is presented. The seasonal cycles of absorbed solar radiation (ASR) and outgoing longwave radiation (OLR) have been computed from an eight‐year data set from the Clouds and Earth's Radiant Energy System (CERES) scanning radiometers and from a model data set produced by the NASA Goddard Space Flight Center Global Modeling and Assimilation Office. To compare the seasonal cycles from these two data sets, principal component (PC) analysis is used, where the PCs express the time variations and the corresponding empirical orthogonal functions (EOFs) describe the geographic variations. Ocean has a long thermal response time compared to land, so land and ocean are separated for the analysis. The root‐mean square values for the seasonal cycles of ASR and OLR are extremely close for the two data sets. The first three PCs are quite close, showing that the time responses and magnitudes over the globe are very similar. The agreement between the two sets of PCs is quantified by computing the matrix of inner products of the two sets. For ASR over land, the first PCs of CERES and the model agree to better than 99.9%. The EOF maps are similar for most of the globe, but differ in a few places, and the agreement of the EOF maps is likewise quantified. Maps of differences between the annual cycles show regions of agreement and disagreement.

Assessing regional scale predictions of aerosols, marine stratocumulus, and their interactions during VOCALS-REx using WRF-Chem

Abstract. This study assesses the ability of the recent chemistry version (v3.3) of the Weather Research and Forecasting (WRF-Chem) model to simulate boundary layer structure, aerosols, stratocumulus clouds, and energy fluxes over the Southeast Pacific Ocean. Measurements from the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) and satellite retrievals (i.e., products from the MODerate resolution Imaging Spectroradiometer (MODIS), Clouds and Earth's Radiant Energy System (CERES), and GOES-10) are used for this assessment. The Morrison double-moment microphysics scheme is newly coupled with interactive aerosols in the model. The 31-day (15 October–16 November 2008) WRF-Chem simulation with aerosol-cloud interactions (AERO hereafter) is also compared to a simulation (MET hereafter) with fixed cloud droplet number concentrations in the microphysics scheme and simplified cloud and aerosol treatments in the radiation scheme. The well-simulated aerosol quantities (aerosol number, mass composition and optical properties), and the inclusion of full aerosol-cloud couplings lead to significant improvements in many features of the simulated stratocumulus clouds: cloud optical properties and microphysical properties such as cloud top effective radius, cloud water path, and cloud optical thickness. In addition to accounting for the aerosol direct and semi-direct effects, these improvements feed back to the simulation of boundary-layer characteristics and energy budgets. Particularly, inclusion of interactive aerosols in AERO strengthens the temperature and humidity gradients within the capping inversion layer and lowers the marine boundary layer (MBL) depth by 130 m from that of the MET simulation. These differences are associated with weaker entrainment and stronger mean subsidence at the top of the MBL in AERO. Mean top-of-atmosphere outgoing shortwave fluxes, surface latent heat, and surface downwelling longwave fluxes are in better agreement with observations in AERO, compared to the MET simulation. Nevertheless, biases in some of the simulated meteorological quantities (e.g., MBL temperature and humidity) and aerosol quantities (e.g., underestimations of accumulation mode aerosol number) might affect simulated stratocumulus and energy fluxes over the Southeastern Pacific, and require further investigation. The well-simulated timing and outflow patterns of polluted and clean episodes demonstrate the model's ability to capture daily/synoptic scale variations of aerosol and cloud properties, and suggest that the model is suitable for studying atmospheric processes associated with pollution outflow over the ocean. The overall performance of the regional model in simulating mesoscale clouds and boundary layer properties is encouraging and suggests that reproducing gradients of aerosol and cloud droplet concentrations and coupling cloud-aerosol-radiation processes are important when simulating marine stratocumulus over the Southeast Pacific.

CERES Edition-2 Cloud Property Retrievals Using TRMM VIRS and Terra and Aqua MODIS Data—Part II: Examples of Average Results and Comparisons With Other Data

Cloud properties were retrieved by applying the Clouds and Earth's Radiant Energy System (CERES) project Edition-2 algorithms to 3.5 years of Tropical Rainfall Measuring Mission Visible and Infrared Scanner data and 5.5 and 8 years of MODerate Resolution Imaging Spectroradiometer (MODIS) data from Aqua and Terra, respectively. The cloud products are consistent quantitatively from all three imagers; the greatest discrepancies occur over ice-covered surfaces. The retrieved cloud cover (~59%) is divided equally between liquid and ice clouds. Global mean cloud effective heights, optical depth, effective particle sizes, and water paths are 2.5 km, 9.9, 12.9 μm , and 80 g·m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , respectively, for liquid clouds and 8.3 km, 12.7, 52.2 μm, and 230 g·m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> for ice clouds. Cloud droplet effective radius is greater over ocean than land and has a pronounced seasonal cycle over southern oceans. Comparisons with independent measurements from surface sites, the Ice Cloud and Land Elevation Satellite, and the Aqua Advanced Microwave Scanning Radiometer-Earth Observing System are used to evaluate the results. The mean CERES and MODIS Atmosphere Science Team cloud properties have many similarities but exhibit large discrepancies in certain parameters due to differences in the algorithms and the number of unretrieved cloud pixels. Problem areas in the CERES algorithms are identified and discussed.

Development of empirical angular distribution models for smoke aerosols: Methods

[1] Using broadband shortwave radiance measurements from the Clouds and Earth Radiant Energy System (CERES) sensors onboard the Terra and Aqua satellites, empirical angular distribution models (EADM) are constructed for smoke aerosols. These EADMs are constructed for smoke aerosols emitted during the biomass burning season (August-October), in South America. All available years (2000–2008) of both rotating azimuth plane and cross-track radiance data from CERES have been utilized. Aerosol scenes are identified using coincident aerosol optical thickness retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS). The new EADMs are used to estimate top-of-atmosphere (TOA) shortwave flux for cloud free scenes. The CERES clearly shows the angular dependence of shortwave radiance on smoke aerosol optical thickness. A comparison of TOA shortwave fluxes estimated from the new smoke EADM with the existing CERES TOA shortwave fluxes shows that the CERES fluxes are higher (lower) for aerosol optical thickness less (greater) than 0.3, largely due to the use of aerosol optical thickness in characterizing the new EADMs developed in this study. Empirical ADMs for smoke aerosols over land are developed for the first time in this study, and our results demonstrate that large amounts of aerosols emitted during biomass burning activities contribute to the anisotropy of the radiance distribution at the TOA. Therefore, it is imperative to include aerosol information in the angular distribution models, especially now that more than a 10 year record of Terra data is available.

Clouds and Earth Radiant Energy System (CERES), a review: Past, present and future

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.

Comparison of satellite‐derived TOA shortwave clear‐sky fluxes to estimates from GCM simulations constrained by satellite observations of land surface characteristics

AbstractClear‐sky, upwelling shortwave flux at the top of the atmosphere $\left(S_{\rm {TOA}}^{\uparrow}\right)$, simulated using the atmospheric and land model components of the Community Climate System Model 3 (CCSM3), is compared to corresponding observational estimates from the Clouds and Earth's Radiant Energy System (CERES) sensor. Improvements resulting from the use of land surface albedo derived from Moderate Resolution Imaging Spectroradiometer (MODIS) to constrain the simulations are also examined. Compared to CERES observations, CCSM3 overestimates global, annual averaged $S_{\rm {TOA}}^{\uparrow}$ over both land and oceans. However, regionally, CCSM3 overestimates $S_{\rm {TOA}}^{\uparrow}$ over some land and ocean areas while underestimating it over other sites. CCSM3 underestimates $S_{\rm {TOA}}^{\uparrow}$ over the Saharan and Arabian Deserts and substantial differences exist between CERES observations and CCSM3 over agricultural areas. Over selected sites, after using ground‐based observations to remove systematic biases that exist in CCSM computation of $S_{\rm {TOA}}^{\uparrow}$, it is found that use of MODIS albedo improves the simulation of $S_{\rm {TOA}}^{\uparrow}$. Inability of coarse resolution CCSM3 simulation to resolve spatial heterogeneity of snowfall over high altitude sites such as the Tibetan Plateau causes overestimation of $S_{\rm {TOA}}^{\uparrow}$ in these areas. Discrepancies also exist in the simulation of $S_{\rm {TOA}}^{\uparrow}$ over ocean areas as CCSM3 does not account for the effect of wind speed on ocean surface albedo. This study shows that the radiative energy budget at the TOA is improved through the use of MODIS albedo in Global Climate Models. Copyright © 2010 Royal Meteorological Society

Cloud Detection in Nonpolar Regions for CERES Using TRMM VIRS and Terra and Aqua MODIS Data

Objective techniques have been developed to consistently identify cloudy pixels over nonpolar regions in multispectral imager data coincident with measurements taken by the Clouds and Earth's Radiant Energy System (CERES) on the Tropical Rainfall Measuring Mission (TRMM), Terra, and Aqua satellites. The daytime method uses the 0.65-, 3.8-, 10.8-, and 12.0-mum channels on the TRMM Visible and Infrared Scanner (VIRS) and the Terra and Aqua MODIS. The VIRS and Terra 1.6-mum channel and the Aqua 1.38- and 2.1-mum channels are used secondarily. The primary nighttime radiances are from the 3.8-, 10.8-, and 12.0- mum channels. Significant differences were found between the VIRS and Terra 1.6-mum and the Terra and Aqua 3.8-mum channels' calibrations. Cascading threshold tests provide clear or cloudy classifications that are qualified according to confidence levels or other conditions, such as sunglint, that affect the classification. The initial infrared threshold test classifies ~43% of the pixels as clouds. The next level seeks consistency in three (two) different channels during daytime (nighttime) and accounts for roughly 40% (25%) of the pixels. The third tier uses refined thresholds to classify remaining pixels. For cloudy pixels, ~ 4% yield no retrieval when analyzed with a cloud retrieval algorithm. The techniques were applied to data between 1998 and 2006 to yield average nonpolar cloud amounts of ~ 0.60. Averages among the platforms differ by <0.01 and are comparable to surface climatological values, but roughly 0.07 less than means from two other satellite analyses, primarily as a result of missing small subpixel and thin clouds.

The Annual Cycle of the Energy Budget. Part II: Meridional Structures and Poleward Transports

Abstract Meridional structure and transports of energy in the atmosphere, ocean, and land are evaluated holistically for the mean and annual cycle zonal averages over the ocean, land, and global domains, with discussion and assessment of uncertainty. At the top of the atmosphere (TOA), adjusted radiances from the Earth Radiation Budget Experiment (ERBE) and Clouds and Earth’s Radiant Energy System (CERES) are used along with estimates of energy storage and transport from two global reanalysis datasets for the atmosphere. Three ocean temperature datasets are used to assess changes in the ocean heat content (OE) and their relationship to the net upward surface energy flux over ocean (FoS), which is derived from the residual of the TOA and atmospheric energy budgets. The surface flux over land is from a stand-alone simulation of the Community Land Model forced by observed fields. In the extratropics, absorbed solar radiation (ASR) achieves a maximum in summer with peak values near the solstices. Outgoing longwave radiation (OLR) maxima also occur in summer but lag ASR by 1–2 months, consistent with temperature maxima over land. In the tropics, however, OLR relates to high cloud variations and peaks late in the dry monsoon season, while the OLR minima in summer coincide with deep convection in the monsoon trough at the height of the rainy season. Most of the difference between the TOA radiation and atmospheric energy storage tendency is made up by a large heat flux into the ocean in summer and out of the ocean in winter. In the Northern Hemisphere, the transport of energy from ocean to land regions is substantial in winter, and modest in summer. In the Southern Hemisphere extratropics, land − ocean differences play only a small role and the main energy transport by the atmosphere and ocean is poleward. There is reasonably good agreement between FoS and observed changes in OE, except for south of 40°S, where differences among several ocean datasets point to that region as the main source of errors in achieving an overall energy balance. The winter hemisphere atmospheric circulation is the dominant contributor to poleward energy transports outside of the tropics [6–7 PW (1 petawatt = 1015 W)], with summer transports being relatively weak (∼3 PW)—slightly more in the Southern Hemisphere and slightly less in the Northern Hemisphere. Ocean transports outside of the tropics are found to be small (&amp;lt;2 PW) for all months. Strong cross-equatorial heat transports in the ocean of up to 5 PW exhibit a large annual cycle in phase with poleward atmospheric transports of the winter hemisphere.

An Observational Estimate of Inferred Ocean Energy Divergence

Abstract Monthly net surface energy fluxes (FS) over the oceans are computed as residuals of the atmospheric energy budget using top-of-atmosphere (TOA) net radiation (RT) and the complete atmospheric energy (AE) budget tendency (δAE/δt) and divergence (∇ · FA). The focus is on TOA radiation from the Earth Radiation Budget Experiment (ERBE) (February 1985–April 1989) and the Clouds and Earth’s Radiant Energy System (CERES) (March 2000–May 2004) satellite observations combined with results from two atmospheric reanalyses and three ocean datasets that enable a comprehensive estimate of uncertainties. Surface energy flux departures from the annual mean and the implied annual cycle in “equivalent ocean energy content” are compared with the directly observed ocean energy content (OE) and tendency (δOE/δt) to reveal the inferred annual cycle of divergence (∇ · FO). In the extratropics, the surface flux dominates the ocean energy tendency, although it is supplemented by ocean Ekman transports that enhance the annual cycle in ocean heat content. In contrast, in the tropics, ocean dynamics dominate OE variations throughout the year in association with the annual cycle in surface wind stress and the North Equatorial Current. An analysis of the regional characteristics of the first joint empirical orthogonal function (EOF) of FS, δOE/δt, and ∇ · FO is presented, and the largest sources of uncertainty are attributed to variations in OE. The mean and annual cycle of zonal mean global ocean meridional heat transports are estimated. The annual cycle reveals the strongest poleward heat transports in each hemisphere in the cold season, from November to April in the north and from May to October in the south, with a substantial across-equatorial transport, exceeding 4 PW in some months. Annual mean results do not differ greatly from some earlier estimates, but the sources of uncertainty are exposed. Comparison of annual means with direct ocean observations gives reasonable agreement, except in the North Atlantic, where transports from the ocean transects are slightly greater than the estimates presented here.