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

The decorrelation length (Lcf) has been widely used to describe the behavior of vertical overlap of clouds in general circulation models (GCMs); however, it has been a challenge to associate Lcf with the large-scale meteorological conditions during cloud evolution. This study explored the relationship between Lcf and the strength of atmospheric convection in the tropics based on output from a global cloud-resolving model. Lcf tends to increase with vertical velocity in the mid-troposphere (w500) at locations of ascent, but shows little or no dependency on w500 at locations of descent. A representation of Lcf as a function of vertical velocity is obtained, with a linear regression in ascending regions and a constant value in descending regions. This simple and dynamic-related representation of Lcf leads 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.

Citation: Jing, Xianwen, Hua Zhang, Masaki Satoh, and Shuyun Zhao. 2018. "Improving Representation of Tropical Cloud Overlap in GCMs Based on Cloud-Resolving Model Data". Journal of Meteorological Research 32, 233–245. https://doi.org/10.1007/s13351-018-7095-9