Evaluation of Model-Predicted Top-of-Atmosphere Radiation and Cloud Parameters over Africa with Observations from GERB and SEVIRI

Abstract

This study compared the Regional Atmospheric Climate Model version 2 (RACMO) with satellite data by simultaneously looking at cloud properties and top-of-atmosphere (TOA) fluxes. This study used cloud properties retrieved from Spinning Enhanced Visible and Infrared Imager (SEVIRI) data and TOA shortwave and longwave outgoing radiative fluxes measured by one of the Geostationary Earth Radiation Budget (GERB) sensors. Both SEVIRI and GERB resolve the diurnal cycle extremely well with 96 images per day. To test the physical parameterizations of the model, RACMO was run for a domain-enclosing Africa and part of the surrounding oceans. Simulations for July 2006, forced at the lateral boundaries by ERA-Interim reanalyses, show generally accurate positioning of the various cloud regimes but also some important modelobservation differences, which the authors tried to reduce by altering model parameterizations. These differences are as follows: 1) TOA albedo differences in clear-sky regions like the Sahara and southern Africa. These differences were considerably reduced by prescribing the surface albedo from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data. 2) A considerable overestimation of outgoing longwave radiation within the continental ITCZ caused by the fact that modeled cirrus clouds are far too thin. 3) Underestimation by the model of cloud cover, condensed water path and albedo of the stratocumulus fields off the coast of Angola. The authors reduced these underestimations by suppressing the amount of turbulent mixing above the boundary layer, by prescribing droplet radii derived from SEVIRI data, and by assuming incloud horizontal homogeneity for the radiation calculations. 4) Overestimation by the model of the albedo of the trade wind cumulus fields over the Atlantic Ocean. This study argues that this overestimation is likely caused by a model overestimation of condensed water path. In general, the analyses demonstrate the power of the simultaneous evaluation of the TOA fluxes and cloud properties.

Radiation budget biases in AMIP5 models over the East Asian monsoon region

“…However, subgrid‐scale radiation parameterization and its different representations in climate models introduce notable uncertainties in radiation‐related processes (e.g., cloud radiative feedback and aerosol radiative effect) [ Oreopoulos et al ., ; Shindell et al ., ; Stephens , ]. Over the past several decades, a great deal of attention has been paid to the performance of climate models in simulating the RB at the TOA [ Allan et al ., ; Anantharaj et al ., ; Greuell et al ., ; Harshvardhan et al ., ], within the atmosphere [ Wild , , ], and at the surface [ Bodas‐Salcedo et al ., ; Freidenreich and Ramaswamy , ; Garratt , ; Garratt and Prata , ; Gutowski et al ., ; Li et al ., ; Morcrette , ; Wild , , Wild et al ., , , , ]. Previous studies have also addressed the combination of all of the above components [ Kiehl et al ., ; Li et al ., ; Wild , , Wild et al ., , ; Wild and Roeckner , ].…”

“…With the assistance of surface-based radiation observations and radiative transfer models, a picture of global annual mean energy budget, referred to as global energy flows, can be drawn to provide the overall understanding of energy distribution within the climate system, despite a number of uncertainties [Kiehl and Trenberth, 1997;Stephens et al, 2012;Stevens and Schwartz, 2012;Trenberth et al, 2009;Wild et al, 2013]. simulating the RB at the TOA [Allan et al, 2007;Anantharaj et al, 2010;Greuell et al, 2011;Harshvardhan et al, 1989], within the atmosphere [Wild, 2000a[Wild, , 2000b, and at the surface [Bodas-Salcedo et al, 2008;Freidenreich and Ramaswamy, 2011;Garratt, 1994;Garratt and Prata, 1996;Gutowski et al, 1991;Li et al, 1997;Morcrette, 2002b;Wild, 2005, 2001, 1995a, 1995b. Previous studies have also addressed the combination of all of the above components [Kiehl et al, 1998;Li et al, 2013;Wild, 2008, Wild et al, 2013Wild and Roeckner, 2006].…”

Rainfall retrievals over West Africa using SEVIRI: evaluation with TRMM-PR and monitoring of the daylight time monsoon progression

“…Similar to the rain forest 25 region, rain rates decrease during daytime from 6 to 3 mm h −1 . This decrease in rainfall is tied with a decrease in the CWP diurnal cycle, as noted by Greuell et al (2010). The decrease in CWP and rainfall may be related to a typical diurnal cycle of MCSs with a maximum during nighttime.…”

Evaluation of rainfall retrievals from SEVIRI reflectances over West Africa using TRMM-PR and CMORPH

“…These process studies are useful to evaluate among others the cloud, rainfall, and land surface-atmosphere interaction predictions of regional climate models (see e.g. the work of Greuell et al, 2010 andvan Meijgaard, 2009). …”