An evaluation of cloud vertical structure in three reanalyses against CloudSat/cloud-aerosol lidar and infrared pathfinder satellite observations

Abstract

Cloud fraction is a great source of uncertainty in current models. By utilizing cloudiness fields from CloudSat/cloud-aerosol lidar and infrared pathfinder satellite observations (CALIPSO), the three widely used reanalyses including the Interim ECWMF Re-Analysis (ERA-Interim), Japanese 55-yar Reanalysis (JRA-55), and the Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) are assessed for their representation of cloudiness. Results show all three reanalyses can basically capture the cloud horizontal pattern and vertical structure as in CloudSat/CALIPSO, yet the magnitude is markedly underestimated, in particular for JRA-55 and MERRA-2. Besides, all reanalyses struggle to simulate the mid-level clouds at low latitudes. In addition to these common deficiencies, the three reanalyses have their own distinctive behaviors and differ from one another. While ERA-Interim and JRA-55 show better performance for low-level clouds in the tropics, they exhibit remarkable underestimation for high-level clouds. On the contrary, MERRA-2 succeeds in representing high-level clouds but dramatically underestimates the low and mid-level clouds at low latitudes. As a measure of subgrid-scale variability of moisture, the derived “critical relative humidity (RHc)” from CloudSat/CALIPSO exhibits distinctive vertical structures at different latitudes, it is thus speculated that poor specification or parameterization of RHc is responsible for these bias behaviors.