A 3D cloud‐construction algorithm for the EarthCARE satellite mission

Cloud and aerosol effects have a significant impact on the atmospheric radiation budget in the tropical Atlantic because of the spatial and temporal extent of desert dust and smoke from biomass burning in the atmosphere. The influences of African dust and smoke aerosols on cloud radiative properties over the tropical Atlantic Ocean were analyzed for the month of July for 3 years (2006–2008) using colocated data collected by the Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) and Clouds and the Earth's Radiant Energy System (CERES) instruments on the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and Aqua satellites. Aerosol layer height and type can be accurately determined using CALIOP data through directly measured parameters such as optical depth, volume depolarization ratio, attenuated backscatter, and color ratio. On average, clouds below 5 km had a daytime instantaneous shortwave (SW) radiative flux of 270.2 ± 16.9 W/m2 and thin cirrus clouds had a SW radiative flux of 208.0 ± 12.7 W/m2. When dust aerosols interacted with clouds below 5 km, as determined from CALIPSO, the SW radiative flux decreased to 205.4 ± 13.0 W/m2. Similarly, smoke aerosols decreased the SW radiative flux of low clouds to a value of 240.0 ± 16.6 W/m2. These decreases in SW radiative flux were likely attributed to the aerosol layer height and changes in cloud microphysics. CALIOP lidar observations, which more accurately identify aerosol layer height than passive instruments, appear essential for better understanding of cloud‐aerosol interactions, a major uncertainty in predicting the climate system.

The Clouds and the Earth's Radiant Energy System (CERES) is part of NASA's Earth Observing System (EOS), CERES objectives include the following. (1) For climate change analysis, provide a continuation of the Earth Radiation Budget Experiment (ERBE) record of radiative fluxes at the top-of-the-atmosphere (TOA), analyzed using the same techniques as the existing ERBE data. (2) Double the accuracy of estimates of radiative fluxes at TOA and the Earth's surface. (3) Provide the first long-term global estimates of the radiative fluxes within the Earth's atmosphere. (4) Provide cloud property estimates collocated in space and time that are consistent with the radiative fluxes from surface to TOA. In order to accomplish these goals, CERES uses data from a combination of spaceborne instruments: CERES scanners, which are an improved version of the ERBE broadband radiometers, and collocated cloud spectral imager data on the same spacecraft. The CERES cloud and radiative flux data products should prove extremely useful in advancing the understanding of cloud-radiation interactions, particularly cloud feedback effects on the Earth's radiation balance. For this reason, the CERES data should be fundamental to the ability to understand, detect, and predict global climate change. CERES results should also be very useful for studying regional climate changes associated with deforestation, desertification, anthropogenic aerosols, and ENSO events. This overview summarizes the Release 3 version of the planned CERES data products and data analysis algorithms. These algorithms are a prototype for the system that will produce the scientific data required for studying the role of clouds and radiation in the Earth's climate system.

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.

Satellite aerosol remote sensing entered a new era with the deployment of advanced satellite imaging instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS) on the NASA Terra and Aqua satellites. These new instruments provide the opportunity to learn more about aerosol properties than was possible using the simpler NOAA Advanced Very High Resolution Radiometer (AVHRR), which has been used to retrieve aerosol optical thickness for more than 20 years. Combining historical AVHRR and the more advanced MODIS aerosol retrievals to form a long‐term aerosol data record is critical for studying aerosol climate forcing. To achieve this objective, it is necessary to build a connection and establish consistency between the two retrievals through a careful evaluation of the two retrieval methods applied to the same data. As a first step in this effort, this paper exploits the potential of the Clouds and the Earth's Radiant Energy System (CERES) Single‐Scanner Footprint (SSF) data set that includes aerosol products derived from Terra MODIS data at the same locations using both the multichannel MODIS and the two‐channel AVHRR aerosol retrieval algorithms. The analysis examines the differences in the results seen over oceans on a global scale. It was found in a global mean sense that advancement in the aerosol retrieval over ocean from the MODIS algorithm relative to the AVHRR method is realized mostly in the improvement of the aerosol size parameter (ASP) rather than in the aerosol optical thickness (AOT). However, regional differences were observed in both AOT and ASP retrieved from the MODIS and AVHRR algorithms. These are examined further in the second part of this two‐part paper. Cloud contamination and surface roughness appear to affect both aerosol retrievals, effects that need further investigation.

[1] The Earth Clouds, Aerosols and Radiation Explorer (EarthCARE) mission developed by the European Space Agency and the Japan Aerospace Exploration Agency addresses the need to improve the understanding of the interactions between cloud, aerosol, and radiation processes. The broadband radiometer (BBR) instrument on board the EarthCARE spacecraft provides measurements of broadband reflected solar and emitted thermal radiances at the top of atmosphere (TOA) over the along-track satellite path at three fixed viewing zenith angles. The multiangular information provided by the BBR, combined with the spectral information from the EarthCARE's multispectral imager (MSI) can be exploited to construct accurate thermal radiance-to-flux conversion algorithms on the basis of radiative transfer modeling. In this study, the methodology to derive longwave (LW) fluxes from BBR and MSI data is described, and the performance of the LW BBR angular models is compared with the Clouds and the Earth's Radiant Energy System (CERES) Terra flux retrievals in order to evaluate the reliability of the BBR synthetic models when applied to satellite-based radiances. For this purpose, the BBR methodology proposed in this work is adapted to the CERES and the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument specifications, and new LW angular models for CERES are developed. According to plane-parallel simulations, the BBR LW flux uncertainty caused by flux inversion could be reduced up to 0.4 W m−2. The intercomparison between CERES BBR-like adapted and CERES original angular models is performed over a BBR-like database of CERES true along track, and the averaged instantaneous retrievals agree to within 2 W m−2.

Abstract. The Moderate Resolution Imaging Spectroradiometer (MODIS) C6 L3, Clouds and the Earth's Radiant Energy System (CERES) Edition-4 L3 products, and the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis data are employed to systematically study aerosol–cloud correlations over three anthropogenic aerosol regions and their adjacent oceans, as well as explore the effect of retrieval artifacts and underlying physical mechanisms. This study is confined to warm phase and single-layer clouds without precipitation during the summertime (June, July, and August). Our analysis suggests that cloud effective radius (CER) is positively correlated with aerosol optical depth (AOD) over land (positive slopes), but negatively correlated with aerosol index (AI) over oceans (negative slopes) even with small ranges of liquid water path (quasi-constant). The changes in albedo at the top of the atmosphere (TOA) corresponding to aerosol-induced changes in CER also lend credence to the authenticity of this opposite aerosol–cloud correlation between land and ocean. It is noted that potential artifacts, such as the retrieval biases of both cloud (partially cloudy and 3-D-shaped clouds) and aerosol, can result in a serious overestimation of the slope of CER–AOD/AI. Our results show that collision–coalescence seems not to be the dominant cause for positive slope over land, but the increased CER caused by increased aerosol might further increase CER by initializing collision–coalescence, generating a positive feedback. By stratifying data according to the lower tropospheric stability and relative humidity near cloud top, it is found that the positive correlations more likely occur in the case of drier cloud top and stronger turbulence in clouds, while negative correlations occur in the case of moister cloud top and weaker turbulence in clouds, which implies entrainment mixing might be a possible physical interpretation for such a positive CER–AOD slope.

The Clouds and the Earth's Radiant Energy System (CERES) instrument has scanning thermistor bolometers that measure broadband radiances in the shortwave (0.3 - 5.0 micron), total (0.3 - >100 micron) and 8 -12 micron water vapor window regions. On November 27, 1997, the CERES Protoflight model (PFM) instrument was launched aboard the Tropical Rainfall measuring Mission (TRMM) spacecraft. In December 1998, the CERES Flight models I and II (FM1 and FM2) instruments are scheduled for launch on the Earth Observing System-AM 1 (EOS-AM1) platform. The instrument generally operates in three scan modes; crosstrack normal, rotating azimuth normal and rotating azimuth short modes, while measuring the earth reflected and emitted radiances. The sensor measurements have shown a dependency on observation geometry during each of these scan modes of operation. At each elevation observation angle, the zero radiance offsets of the sensors were measured on the ground using end caps (low emittance aluminum targets) and a constant radiance reference (CRR) source, consisting of a curved strip blackbody. On-orbit, offsets were determined from observations of cold space (3 degree K blackbody). This paper describes the procedures and facilities used to determine the zero radiance offsets. The offset values calculated from ground and in-flight data for TRMM sensors, as well as the ground measurements for the FM1 and FM2 sensors are presented.

Data for the investigation of Clouds and the Earth's Radiant Energy System (CERES) began with the launch of the CERES instrument on the Tropical Rainfall Measuring Mission (TRMM) and continues with two CERES instrument on the EOS Terra satellite. The new instruments will sample regions poleward of the surface viewable from TRMM, and will thus place CERES in a position to contribute global observations of reflected sunlight and emitted terrestrial fluxes, beyond what could be observed from the TRMM equatorial orbit. During the initial observations from Terra, the new CERES instruments have undergone the same kind of initial checkout as the instruments on TRMM, as well as more detailed intercomparisons between the three CERES instruments now in orbit. Beyond the classic measurements of fluxes at the top of the Earth's atmosphere, CERES will also produce new observations that combine radiances from sister instruments on TRMM and Terra, namely VIRS and MODIS, to produce much more reliable retrievals of cloud properties that will provide new insights into the cloud-radiative feedback that remains one of the largest uncertainties in our understanding of the Earth's climate.

The Edition 2 (Ed2) cloud property retrieval algorithm system was upgraded and applied to the MODerate-resolution Imaging Spectroradiometer (MODIS) data for the Clouds and the Earth's Radiant Energy System (CERES) Edition 4 (Ed4) products. New calibrations for solar channels and the use of the 1.24-μm channel for cloud optical depth (COD) over snow improve the daytime consistency between Terra and Aqua MODIS retrievals. Use of additional spectral channels and revised logic enhanced the cloud-top phase retrieval accuracy. A new ice crystal reflectance model and a CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -channel algorithm retrieved higher ice clouds, while a new regional lapse rate technique produced more accurate water cloud heights than in Ed2. Ice cloud base heights are more accurate due to a new cloud thickness parameterization. Overall, CODs increased, especially over the polar (PO) regions. The mean particle sizes increased slightly for water clouds, but more so for ice clouds in the PO areas. New experimental parameters introduced in Ed4 are limited in utility, but will be revised for the next CERES edition. As part of the Ed4 retrieval evaluation, the average properties are compared with those from other algorithms and the differences between individual reference data and matched Ed4 retrievals are explored. Part II of this article provides a comprehensive, objective evaluation of selected parameters. More accurate interpretation of the CERES radiation measurements has resulted from the use of the Ed4 cloud properties.

Clear‐sky outgoing longwave radiation (OLR) is computed using the Atmospheric and Environmental Research (AER), Inc., Rapid Radiative Transfer Model (RRTM) for comparison with the observations of the Clouds and the Earth's Radiant Energy System (CERES) for both ocean and land scenes. CERES clear‐sky OLR is in agreement with RRTM model calculations to 0.2% accuracy using best estimate radiosondes (BE) launched coincident with NASA Aqua overpasses at the Atmospheric Radiation Measurement Southern Great Plains (SGP) site and 0.8% using retrieved profiles of temperature, water vapor, ozone, and surface parameters from the Atmospheric Infrared Sounder (AIRS) on the Aqua platform. A partial flux analysis using AIRS radiances implies an accuracy for the RRTM model in the far infrared of 0.4% (about 0.5 W/m2) for wave numbers less than 650 cm−1 (wavelengths greater than 15.4 μm). CERES minus model biases over clear‐sky ocean are similar to previously published results. Ordering the results according to the magnitude of the measured minus model mean bias for nighttime, tropical, ocean gives: +0.57 ± 1.9 W/m2 (Dessler/Fu‐Liou), +0.83 ± 1.5 W/m2 (Huang/MODTRAN5), +1.6 ± 1.6 W/m2 (Moy/RRTM), +3.7 ± 2.1 W/m2 (Dessler/Chou). Comparison of observed minus modeled OLR over land are included in this study. Excluding nonfrozen ocean, a mean difference over land of +2.0 W/m2 for nighttime cases and +1.0 W/m2 for daytime cases is found where the land classes are weighted inversely by their standard error. The nighttime bias is quite consistent across all the land classes. The daytime bias shows less consistency with a tendency toward larger CERES minus AIRS RRTM OLR bias for the land classes with smaller vegetation fraction. Comparison of clear‐sky CERES and AIRS RRTM OLR over cold snow‐/ice‐covered surfaces (mainly in the polar regions) is complicated by the use of the MODIS cloud mask in the identification of the clear CERES footprints used in the comparison. Clear scenes over cold surfaces can be identified more reliably in the daytime, for which the comparison between CERES and AIRS RRTM is better than 1.2 W/m2 indicating good agreement.

Clouds and the Earth's Radiant Energy System (CERES) Flight Model 5 (FM5) instrument is designed to continue the long-term monitoring of the Earth's radiation budget. Flight Model 5, the sixth of the CERES instrument was launched aboard the NPP spacecraft on October 2011 and it has started the Earth-viewing measurements on January 26, 2012. The CERES instrument with the three scanning sensors measure radiances in 0.3 to 5.0 micron region with Shortwave sensor, 0.3 to > 100 microns with Total sensor and 8 to 12 micron region with Window sensor. The prelaunch accuracy goal for the CERES instrument measurements is to have the emitted longwave radiances within 0.5% and the shortwave radiances within 1.0%. An accurate determination of the radiometric gains and spectral responsivity of CERES FM5 sensors was accomplished through rigorous calibrations using the primary sources. Post-launch evaluation of the sensor performance consists of sensor calibrations with the on-board sources and the solar diffuser called Mirror Attenuator Mosaic (MAM). Several validation studies utilising targets such as tropical ocean and deep convective clouds are performed as part of the CallVal protocol. This paper covers the overall performance of the CERES-FM5 instrument. The post-launch calibration and the validation results from the instrument are presented.

Some applications of data from the Clouds and the Earth's Radiant Energy System (CERES) scanning radiometer require the use of the point response function (PRF), which describes the influence of radiance from each point on the measurement. A radiance source for the measurement of the PRF of the CERES instruments was built and installed into the Radiometric Calibration Facility, in which the CERES instruments have been calibrated. The design and application of the PRF source and the computation of the PRF from these measurements are described. In order to compare the PRF based on measurements with the theoretical PRF, it is necessary to account for the finite size of the beam from the source. The use of the PRF source and the analysis of the data are demonstrated by application to the FM-5 instrument. The measured results compare well with theory for the CERES instruments and are presented for FM-5.

Background &amp; Objectives: Renewable energy generation systems are highly sensitive to climate. For example, clouds have a significant influence on solar power generation systems. They in turn are impacted by atmospheric aerosols which act as cloud condensation nuclei. Aerosols are both directly emitted from anthropogenic (e.g., power plants, transportation systems, industrial facilities) and natural sources (e.g., windblown dust, sea salt, forest fires), and form in the atmosphere. They can either inhibit or promote cloud formation, and/or precipitation, and thus are likely to play a significant role in altering the hydrological cycle, and perhaps electricity generation from hydroelectric, solar, and wind power systems. Integration of renewable energy systems within existing power generation infrastructure systems remains a challenging task as well. The objective of this study is to use cutting-edge satellite imaging technology and observations and coupled models to identify atmospheric variables and processes that impact solar power generation systems in Qatar and the Middle East. Methods: We will employ data from the Aerosol Robotic Network (AERONET) in situ measurements, Moderate Resolution Imaging Spectroradiometer (MODIS) satellite, and the Clouds and the Earth's Radiant Energy System (CERES) scanner. We will also assess the potential impact of future changes in atmospheric composition, clouds, and radiation on solar power generation systems. For this purpose, we will employ version 5.0 of the Community Multiscale Air Quality (CMAQ) modeling system, and the Weather Research and Forecasting (WRF) model. Results: The research will provide a set of model and satellite-based maps showing the spatial and temporal distribution of aerosols over the region, potentially assisting analysis aimed at identifying sites for solar power generation systems in Qatar. Conclusions: The research project will help establish the knowledge infrastructure that relies on computational science and space technology to ensure that Qatar continues on the path of economic prosperity through effective integration of emerging technologies with existing infrastructure.

The semi‐direct effects of dust aerosols are analyzed over eastern Asia using 2 years (June 2002 to June 2004) of data from the Clouds and the Earth's Radiant Energy System (CERES) scanning radiometer and MODerate Resolution Imaging Spectroradiometer (MODIS) on the Aqua satellite, and 18 years (1984 to 2001) of International Satellite Cloud Climatology Project (ISCCP) data. The results show that the water path of dust‐contaminated clouds is considerably smaller than that of dust‐free clouds. The mean ice water path (IWP) and liquid water path (LWP) of dusty clouds are less than their dust‐free counterparts by 23.7% and 49.8%, respectively. The long‐term statistical relationship derived from ISCCP also confirms that there is significant negative correlation between dust storm index and ISCCP cloud water path (CWP). These results suggest that dust aerosols warm clouds, increase the evaporation of cloud droplets and further reduce the CWP, the so‐called semi‐direct effect. The semi‐direct effect may play a role in cloud development over arid and semi‐arid areas of East Asia and contribute to the reduction of precipitation.

We describe a method to determine broadband albedo globally over land viewed by the Clouds and the Earth's Radiant Energy System (CERES) scanning radiometers on board the TRMM, Terra, and Aqua satellites. This albedo is used as a surface boundary condition for a fast radiation transfer code in the Surface and Atmospheric Radiation Budget (SARB) subsystem of the CERES processing scheme. Cloudy sky surface albedo is estimated from derived clear sky values. Clear sky surface albedo is assessed by comparing the CERES/SARB‐based surface albedo with the bidirectional reflectance distribution function (BRDF)–based surface albedo supplied by the MODIS land surfaces group. The SARB method employs broadband observations at the top of atmosphere (TOA) and assumes relative spectral shape of surface albedo. The MODIS group uses higher spatial resolution observations in several shortwave window channels to retrieve spectral surface albedos and then scales up to broadband surface albedo. Comparisons over snow‐free land show good agreement between the two independent products on the scale of the CERES footprint. Biases run approximately 0.005 absolute or 0.02 relative with SARB albedo, generally lower than MODIS. We find little dependence on view geometry and slight functional dependence on aerosol optical depth. The value selected for a priori surface spectral albedo is important, but not critical, when retrieving broadband surface albedo with broadband TOA data. However, based on calculations, aerosol forcing to TOA flux changes in spectral albedo shape can affect aerosol forcing for as much as would a 15% absolute change in the original broadband surface albedo.