A Numerical Study of a Mesoscale Convective System during TOGA COARE. Part I: Model Description and Verification

Abstract

A 16-h numerical simulation of the growing and mature stages of the 15 December 1992 Tropical Ocean Global Atmosphere Coupled Ocean?Atmosphere Response Experiment (TOGA COARE) mesoscale convective system (MCS) is performed to demonstrate the predictability of tropical MCSs when initial conditions and model physical processes are improved. The MCS began with two entities S1 and S2, which developed and eventually merged to form a large anvil cloud. To obtain a realistic simulation of the MCS, the initial moisture field in the operational European Centre for Medium-Range Weather Forecasts (ECMWF) analysis is improved, based on previous findings. The deep column ascent and surface potential temperature dropoff (SPTD) are implemented into the initiation mechanism of the Kain?Fritsch cumulus parameterization scheme (KF CPS). Other refinements to the KF CPS include the introduction of the accretion process in the formation of convective rain and the detrainment of rain and ice particles at the cloud top. With the improved initial conditions and model physics, the modeled MCS shows many features similar to the observations, including the evolution of the anvil cloud fraction, the three convective onsets at three different times during the growing stage, and the characteristics of two deep convective lines during the mature stage. A series of sensitivity tests indicates that the SPTD is largely responsible for the successful prediction of the life cycle of the MCS, while inclusion of the deep column ascent criterion yields a better timing for the onset of the mature stage. The effects of modifying the initial moisture field are also investigated.