PNNL

Abstract

The accurate representation of interactions between clouds and planetary boundary layer (PBL) is a persistent challenge in climate models, critical for simulating surface energy budget. The emergence of kilometer-scale Global Storm Resolving Models (GSRMs) offers the potential for enhanced details of PBL processes in these complex interactions. This study evaluates the representation of PBL-coupled and decoupled clouds in nine GSRMs simulations against extensive field observations by the Department of Energy Atmospheric Radiation Measurement (ARM) program, across six sites encompassing diverse regimes such as tropical land, midlatitude continent and ocean. By differentiating coupling based on the relative positions between clouds and PBL, our analysis focuses on the simulation of PBL height, cloud frequency, position and vertical extent. The GSRMs generally exhibit commendable agreement with observed cloud structures and PBL diurnal cycles across different ARM sites. Compared to the relatively consistent representation of decoupled clouds, discrepancies are observed in the simulation of coupled clouds, particularly in areas of intense convection, e.g., over tropical rain forest and mountainous regions. These biases are probably associated with the models' tendency to underestimate boundary layer humidity and the frequency of coupled clouds within different ranges of PBL heights. This study underscores the importance for improved representation of boundary layer convections within these high-resolution global models.