Impact of detrained cumulus on climate simulated by the Community Atmosphere Model Version 5 with a unified convection scheme

Abstract

Cumulus elements generated by detraining convective condensate - detrained cumulus - are added to the Community Atmosphere Model Version 5 (CAM5) combined with a Unified Convection Scheme (UNICON). Instead of evaporating convective liquids detrained into clear portions, we diagnosed a new detrained cumulus that is horizontally nonoverlapped with cumulus and stratus in each layer by assuming a steady state balance between the detrainment rate of cumulus condensates and the dissipation rate of detrained condensates by entrainment mixing with environmental air. The addition of detrained cumulus was found to substantially improve the simulation of low-level clouds and the associated shortwave cloud radiative forcing, particularly in the subtropical trade cumulus regime. In addition to the mean climate, successful simulations of the diurnal cycle of precipitation, Madden-Julian Oscillation, and Kelvin wave were also well maintained.