Abstract
Reflected shortwave (SW) solar radiations at the top of atmosphere from Clouds and the Earth’s Radiant Energy System (CERES), Modern Era-Retrospective analysis for Research and Applications version 2 (MERRA-2), and ECMWF Reanalysis 5th Generation (ERA5) are examined to better understand their differences in spatial and temporal variations (seasonal and diurnal cycle timescale) with respect to the observations from the Earth Polychromatic Imaging Camera (EPIC) on the Deep Space Climate Observatory (DSCOVR) satellite. Comparisons between two reanalyses (MERRA-2 and ERA5) and EPIC reveal that MERRA-2 has a generally larger deviation from EPIC than ERA5 in terms of the SW radiance and diurnal variability in all seasons, which can be attributed to larger cloud biases in MERRA-2. MERRA-2 produces more ice/liquid water content than ERA5 over the tropical warm pool, leading to positive SW biases in cloud and radiance, while both reanalyses underestimate the observed SW radiance from EPIC in the stratus-topped region off the western coast of US/Mexico in the boreal summer. Himalaya/Tibet region in the boreal spring/summer and the midlatitude Southern Hemisphere in the boreal winter are the regions where MERRA-2 and ERA5 deviate largely from EPIC, but their deviations have the opposite sign. Vertical structures of cloud ice/liquid water content explain reasonably well these contrasting differences between the two reanalyses. As two independent observations, CERES and EPIC agree well with each other in terms of the SW radiance maps, showing 2–3% mean absolute errors over the tropical midlatitudes. The CERES-EPIC consistency further confirms that the reanalyses still have challenges in representing the SW flux and its global distribution. In the CERES-EPIC observation differences, CERES slightly overestimates the diurnal cycle (as a function of local solar time) of the observed EPIC irradiance in the morning and underestimates it in the afternoon, while the opposite is the case in the reanalyses.
Highlights
IntroductionThere have been considerable improvements in data assimilation techniques and satellite observations to produce realistic radiative fluxes, but deficiencies in the reanalysis models still prevent them from accurately representing the top of atmosphere (TOA) radiation fluxes, especially the reflected shortwave (SW) flux
Geographical distributions of top of atmosphere (TOA) upward SW fluxes (Fsw ) and their seasonal change are compared for Clouds and the Earth’s Radiant Energy System (CERES), MERRA-2, and ECMWF Reanalysis 5th Generation (ERA5) in 2017
The recent versions of the Goddard Earth Observing System (GEOS) model have significantly reduced the biases in cloud and upward SW flux in regions such as the tropical western Pacific warm pool, where the biases were positive
Summary
There have been considerable improvements in data assimilation techniques and satellite observations to produce realistic radiative fluxes, but deficiencies in the reanalysis models still prevent them from accurately representing the TOA radiation fluxes, especially the reflected shortwave (SW) flux. Further improvements are needed for a more accurate representation of the upward SW flux in the models This has been a great challenge, since uncertainties of the TOA radiative energy in the reanalysis can be induced by data assimilation techniques [13,14], and by deficiencies in model radiation schemes [15,16] and cloud schemes [17,18] that compute the radiative fluxes and cloud properties from the assimilated dynamical and thermodynamic structures
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