南海夏季风建立、活跃和中断期的特征

根据欧洲中心(ECMWF)1979～1993年15年风资料和GMS 卫星观测的黑体辐射云顶温度TBB资料,取南海地区伴有强对流的西风/偏西南风建立作为南海夏季风爆发的标志,对南海夏季风爆发的特征和夏季风活动过程进行了分析.表明南海夏季风爆发平均日期在5月16日左右,但年际变化显著,最晚是6月上旬.有些年份在4月下旬会出现短暂的伴有强对流的西南风,而在6月初出现第二次强西南风爆发,第二次爆发才是真正的夏季风爆发.南海夏季风爆发前,在北纬1 5°N以北的南海地区往往会先出现强西南风,这是由于北方冷空气南下引起冷锋前两风加强,或者由于南海副热带高压的加强或北移引起的西风加强,不能称作真正的南海夏季风爆发.季风爆发以后,南海季风活动有显著的活跃和中断变化,在季风爆发至8月20日期间,平均中断1～2次/a,中断时间约1 5 d/a.

The Onset of the Summer Monsoon over the South China Sea and Its Active and Break Periods

Based on the ECMWF reanalysis data from 1979- 1993 and TBB data of CMS, an analysis on the onset of the summer monsoon over the South China Sea (SCS) is made. It is found the mean onsel dale is on the 16th of May. There is marked inlerannal variation of the onset day, the earliest day is in the beginning of May, and the latest onsel day is in beginning of June. In some years in the last ten days of April ihere appears marked south west How over the SCS, but the south west How only persists for more than a shorl period, and the easterly flow reappears. In the beginning of June the true onset appears. From the end of April to the middle of May before the onsel, in the SCS there appears strong south west flow to the north of 15N. These strong westerly flow are due to the soulhward advance of cold front or due to the strenglhening of the subtropical high in the SCS, and the westerly How can not be treated as the onset of the SCS summer monsoon. After the onset, there are active and break period of the south west summer monsoon flow, the average break period is about 15 days in each year.