南海夏季风爆发的数值模拟

Simulation of the South China Sea Summer Monsoon Onset

利用高分辨率的区域气候模式(RegCM-NCC)对南海夏季风爆发进行模拟研究。研究表明:该模式对积云对流参数化方案的选择十分敏感,其中以Kuo积云参数化方案为最好,可以比较成功地模拟出南海夏季风的爆发时间、爆发前后高、低层风场的剧烈变化以及季风与季风雨带的向北推进。然而该方案对于雨量和副热带高压位置的模拟,与观测相比尚存在一定的偏差,主要表现为副热带高压位置模拟偏北、偏东;南海地区的降水量模拟偏少、降水范围偏小。此外,采用4种参数化方案(Kuo,Grell,MFS,Betts-Miller)集成的结果在某种程度上要优于单个方案的结果,这种改善主要体现在对南海地区季风爆发后降水的模拟上。

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.