Simulation of the South China Sea Summer Monsoon Onset

Generally speaking, the South China Sea summer monsoon (SCSSM) onset marks the arrival of the East and Southeast Asian summer monsoon and the beginning of the major rainy season in these regions. Therefore, the correct simulation of SCSSM has a significant implication. General Circulation Models (GCMs) have limitations in reproducing regional details because of the relatively low spatial resolution and simple representation of physical processes. Hence many studies tends to use air-sea coupled model and regional climate model to simulate the seasonal variations and anomalies of the East Asian monsoon.As an important energy source for atmospheric motion, cumulus convection plays a key role in determining the structure of temperature and moisture in the atmosphere. With the development of numerical model, different cumulus parameterization schemes have been designed and applied in the numerical weather forecasting models and the simulations of atmospheric general circulation. Many studies show that the choices of different cumulus parameterization schemes may have significant influences on the simulations of synoptic and climate systems, therefore the choice of the cumulus parameterization scheme has been one of the important problems in the modeling research. With the high-resolution regional climate model of China National Climate Center (RegCM_NCC), four cumulus parameterization schemes (Kuo, Grell, MFS, Betts-Miller) are adopted to carry out a series of sensitivity experiments on the SCSSM onset in 1998. The results indicate that the model is very sensitive to the choice of convective parameterization schemes. It seems that the Kuo cumulus scheme simulates the process of the SCSSM onset reasonably well, which can reproduce the onset timing and dramatic changes before and after the SCSSM onset, especially the upper and lower level flow patterns. For the amount of precipitation and location of the subtropical high, there are still some biases between the simulations and the observations, including the location of the subtropical high simulated further north and east, the precipitation amount over the South China Sea too little as well as the range of precipitation too narrow. The ensemble results are obviously superior to any single cumulus parameterization scheme and the obvious improvement is mainly on the simulation of precipitation over the South China Sea.