南海夏季风异常及其对南海与周边地区的大气和海洋要素的影响

通过对南海夏季风异常年夏季南海及周边地区主要海-气要素场的对比分析,得到以下主要结论:强、弱季风年夏季南海及周边地区的主要海-气要素都表现出明显的差异。强季风年夏季南海中南部地区低层西风加强、高层东风加强,以南海北部为中心存在气旋性距平环流,上升运动增强。相应地,南海及我国东南沿海地区对流和降水增强,而长江中下游地区降水偏少。弱季风年则表现出与强季风年几近相反的分布特征。此外,强季风年西太平洋副热带高压较弱季风年位置明显偏东、强度明显偏弱。与对流和降水的分布相对应,强、弱季风年夏季南海及周边地区大气热源状态的分布也表现出明显的差异,差别最显著的区域正是在南海及周边地区。在强季风年,西起孟加拉湾东至菲律宾以东的洋面上为较明显的热源增强区,而弱季风年则为明显的热源减弱区。此外,强、弱季风年,南海海域的海面高度、海洋环流、海表温度等表征海洋状况的要素分布也明显不同,分布形势几近相反。海温作为重要的外源强迫,不仅对季风环流的形成有重要作用,而且明显受到季风异常的影响,进而对局地的天气气候产生重要的滞后影响。

Anomalies of the South China Sea summer monso on and their influence on the atmospheric and oceanic elements over the South China Sea as well as its adjacent regions

Based on the comparative analysis of the major air-sea elements over the South China Sea(SCS) and its adjacent regions during the anomalous years of South China Sea summer monsoon(SCSSM),the fundamental results were obtained.In the summer of the strong SCSSM year,the westerly in the low level and easterly in the upper level over the middle and southern part of the SCS enhanced,the cyclonic anomaly circulation existed over the northern part of the SCS,the ascending motions strengthened.Correspondingly,the convections and precipitation enhanced over the SCS and the coastal areas of China,whereas the precipitation decreased over the middle and lower reaches of the Changjiang River valley.While in the weak SCSSM year,the distributions of the above mentioned meteorological elements appeared nearly different.In the Strong SCSSM year,the position and strength of the subtropical high over the western Pacific Ocean was obviously farther east and weak than normal.Correspondingly the distributions of the convections,precipitation,and the atmospheric heat sources over the SCS and its adjacent regions between the strong and weak SCSSM year appeared quite different.The most significant difference was located at the SCS and its adjacent regions.In the strong SCSSM year,the obvious enhanced heat sources appeared over the regions from the Bay of the Bengal to the area to the east of the Philippines.Whereas in the weak SCSSM year,the heat sources over these regions weakened.Also,the distributions of the sea surface height,ocean circulation,sea surface temperature and so on which reflected the ocean conditions were apparently different between the strong and weak SCSSM year.As an important forcing factor,sea surface temperature not only plays an important role in the formation of the monsoonal circulation,but also was greatly affected by the monsoon anomalies.Further,it would make a significant impact on weather and climate over the local region.