Abstract
Realistic large-scale diurnal marches of precipitation in various regions in the global tropics over both land and ocean were successfully simulated in an atmospheric general circulation model (AGCM) developed in collaboration by the Center for Climate System Research, the National Institute for Environmental Studies, and the Frontier Research Center for Global Climate (CCSR/NIES/FRCGC), with a resolution of T106, and was forced with prescribed sea surface temperatures. This is an outstanding performance of the diurnal cycle simulated in the AGCM with similar resolution.
Comparison analyses with the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) and Precipitation Radar (PR) data revealed that an implementation of the relative humidity (RH) threshold to the prognostic Arakawa-Schubert (AS) cumulus parameterization significantly improved the diurnal variation of precipitation especially in its large-scale marches. It was suggested that the cloud-layer RH threshold lead to a tighter coupling between free-tropospheric gravity waves and cumulus convection compared to the original prognositic AS, with which convection is more obedient to the boundary-layer warming.
