Is the cloud absorption of solar radiation still underestimated notably by current model-based reanalyses?

Abstract

Cloud absorption of solar radiation strongly influences Earth’s radiation balance and climate change. Whether numerical models underestimate this absorption compared with observations has long been a highly debated issue in cloud–radiation research. Using state-of-the-art model-derived reanalyses, NCEP CFSv2, ECMWF ERA5, and NASA MERRA2, and the latest collocated satellite-surface observation in 2012–2023, we reinvestigate this controversial issue. The results demonstrate the observed cloud absorption of solar radiation still notably exceeds the modeled (regardless of model products), but their discrepancy has dropped a lot, particularly for NCEP CFSv2 and ECMWF ERA5. While a further investigation is needed, the reduced discrepancy may reflect the progress of shortwave radiation schemes in models, notably the integration of Rapid Radiative Transfer Model for General Circulation Models (RRTMG) and the Monte Carlo Independent Column Approximation (McICA). Additionally, it is noteworthy that there is not a perfect approach to obtaining the observed cloud absorption, and particularly the water vapor difference between clear and cloudy skies will often result in its unrealistic overestimation. If the impact from the water vapor difference is corrected, NCEP CFSv2, ECMWF ERA5, and NASA MERRA2 underestimate globally-mean cloud absorption by approximately 8.26, 14.50 and 16.51 W/m², respectively.