南海西南季风爆发日期及其影响因子

利用1950～1999年NCEP全球格点日平均资料,在总结南海西南季风爆发前后850 hPa大气环流特征的基础上,提出了一个较为客观的确定南海西南季风爆发日期的大气环流方法.在与1980～1991年其他多种指标确定的爆发日期比较后,作者认为该大气环流方法所确定的爆发日期基本合理,并给出了1950～1999年各年南海西南季风爆发的日期.通过合成对比分析和相关分析发现,前期热带太平洋地区海温异常分布是影响南海西南季风爆发早晚的重要因素.菲律宾以东洋面海温偏高,赤道太平洋中部偏东地区海温偏低,可以使低层西太平洋副高减弱、高层中东太平洋洋中槽加深,印度洋热带地区偏西风偏强,印度洋-太平洋热带地区Walker环流偏强,为热带对流在孟加拉湾-南海地区发展提供了有利的环境.在孟加拉湾南部偏西气流的作用下,南海地区对流活动较为容易发展起来,低层较弱的西太平洋副热带高压也容易较早地撤出南海上空,使得南海西南季风较早爆发.反之亦然.

A Study of Southwest Monsoon Onset Date over the South China Sea and Its Impact Factors

By using the 1950-1999 NCEP daily averaged reanalyzed data and based on the major atmosphere characteristics at 850 hPa during southwest monsoon onset in the South China Sea (SCS), it is suggested an objective atmospheric circulation way to define the onset dates of SCS southwest monsoon. After compared to the onset dates defined by different indexes. We believe that the onset dates defined by the atmospheric circulation way are reasonable. The onset dates of the SCS southwest monsoon from 1950~ 1999 are given. It is found by compositive analyses and correlation analyses that the prophase distribution of the tropical Pacific SST is an important impact factor for the SCS monsoon onset. The higher SST in the eastern ocean of the Philippine and lower SST in the eastern area of the central equator Pacific will lead to a weaker western Pacific high in the lower layer, deeper oceanic trough of the central and eastern Pacific in higher layer, stronger westerly in tropical Indian Ocean, stronger Walker circulation in the region of the Indian-Pacific Ocean. They give the suitable conditions for convection development in the Bay of Bengal and the South China Sea. Under the effect of the strong westerly in the Bay of Bengal, it is easier and earlier that the convection in the SCS develops and the weaker western subtopic high extracts from the SCS, resulting in the earlier onset of the SCS monsoon, and vice versa.