Intercomparison of the phase partitioning of water in mixed-phase clouds among global climate models

Description

Clouds are one of the major components of the Earth’s energy budget. The magnitude of the radiative influence of clouds on the Earth’s surface is highly dependent on the cloud water phase. It is well known that the magnitude and spatial distribution of the liquid water path (LWP) and ice water path (IWP) simulated by different global climate models (GCMs) have large differences and do not compare well with satellite observations. Modeling the phase partitioning between cloud liquid water and ice has been a challenging topic due to the unknowns in ice nucleation, growth, and ice-nucleating particles as well as the challenges related to the satellite retrievals. Although there have been numerous climate model inter-comparison studies, none of these studies concentrate particularly on the phase partitioning of cloud water. In this study, we aim to investigate the influence of ice nucleation mechanisms on the model predicted differences in the phase partitioning of cloud water using six different GCMs. We perform two sets of sensitivity simulations, one with default model ice nucleation mechanisms and the other with each model’s default ice nucleation replaced with a prescribed ice nucleation mechanism. We find that although the parameterization of ice nucleation leads to differences in cloud water phase among different GCMs, it is not the main factor leading to differences in model results.