南海夏季风爆发时期的大气环流变化特征

利用美国国家环境预报中心和气象研究中心的42年模式再分析资料,采用合成分析的方法,考察了南海夏季风爆发时期环流季节变化的特征.研究发现:尽管采用不同指标确定的南海夏季风爆发时间在有的年份差别很大,但各种不同指标对应的南海夏季风爆发时期大气环流的变化具有某些共同的特征.通过对各种指标确定夏季风爆发时间一致年份的大气环流特征分析表明,延伸到南海北岸附近地区的海上锋区对流加热和孟加拉湾北部陆地上的对流加热、沿东亚近海向西太平洋推进的冷空气是控制南海夏季风爆发的主要因素.对南海夏季风爆发早与爆发晚的年份的合成环流特征进一步表明:爆发早的年份,影响东亚附近海区的冷空气势力和南海南部的对流活动相对强,而爆发晚的年份,冷空气和南海南部的对流活动的影响要相对弱的多.日本本岛南部黑潮海区因冷空气激发的对流活动对南海夏季风的爆发也有重要的影响.

The Variation Characteristics in the Summer Monsoon Onset over the South China Sea

The characteristics of atmospheric circulation during summer monsoon onset over the South China Sea (SCS) are studied using the NCEP/NCAR reanalysis data from 1958 to 1999. It is found that, there are remarkable differences in the average onset times determined by various indices although for certain years, common variation characteristics do exist during the onset stage. In normal years, the onset time of summer monsoon over the SCS is approximately in the fourth pentad of May. The heating in the south of the SCS near the Equator, along with the cold front from the coastal region of the northern SCS to the northwestern Pacific, over the continent north of the Bay of Bangle, and the cold front itself act together, leading to the onset of the summer monsoon. In early monsoon onset years , the convection in the south of the SCS and the cold air over the northwestern Pacific is stronger than they are in normal years. While in late monsoon onset years , the convection region is shifted northwestward to the eastern Indian Ocean, and the cold air over the northwestern Pacific is weaker than in normal years. From the viewpoint of predicting the onset of summer monsoon over the SCS, once the location of convection area near the equator in the south of the SCS persists, the arrival of cold front may probably indicate the setup of summer monsoon over the SCS. While the persistent location of convection over the eastern Indian Ocean may imply that the summer monsoon will be late, the convection induced by the cold front over the Krushio may contribute more to the summer monsoon onset over the SCS.