Improving Representation of Tropical Cloud Overlap in GCMs Based on Cloud-Resolving Model Data

摘要

The decorrelation length (Lcf) has been widely used to describe the behavior of vertical overlap of clouds in gene-ral circulation models (GCMs); however, it has been a challenge to associate Lcfwith the large-scale meteorological conditions during cloud evolution. This study explored the relationship between Lcfand the strength of atmospheric convection in the tropics based on output from a global cloud-resolving model. Lcftends to increase with vertical ve-locity in the mid-troposphere (w500) at locations of ascent, but shows little or no dependency on w500at locations of descent. A representation of Lcfas a function of vertical velocity is obtained, with a linear regression in ascending re-gions and a constant value in descending regions. This simple and dynamic-related representation of Lcfleads to a significant improvement in simulation of both cloud cover and radiation fields compared with traditional overlap treatments. This work presents a physically justifiable approach to depicting cloud overlap in the tropics in GCMs.