赤道涡旋与南海夏季风爆发

文中应用１９７９－１９９５年共１７ａ的８５０ｈＰａ风场资料和ＮＯＡＡ卫星的ＯＬＲ资料，分析了南海夏季风爆发的特征。证实南海夏季风爆发，落后于同纬度的中南半岛和菲律宾岛屿地区。但在南海的东部和西部，季风爆发几乎是同时的，具有某种驻波的特征。文中还证实，大多数年份的４，５月间在１０５°Ｅ附近有赤道涡旋形成，这个涡旋引导它上游的赤道西风或南半球西风进入南海南部，为南海的季风爆发创造有利条件。这种涡旋不活跃的年份，季风爆发往往偏晚。它们之间可能存在某种联系。４月中旬，这个涡旋的形成和１０５°Ｅ越赤道气流的初步建立是同时的。进入５月份，这支越赤道气流逐渐加强。南海夏季风的活动与这支气流可能关系密切。如果称位于１０５°Ｅ附近的赤道涡旋为东亚的爆发涡旋，它显然与南亚季风的情况有较大差别。南亚的爆发涡旋与季风爆发的关系是直接的，而在东亚，则是间接的，这也说明了东亚季风比南亚季风更具有复杂性。

EQUATORIAL VORTEX AND THE ONSET OF SUMMER MONSOON OVER SOUTH CHINA SEA

The characteristics of summer monsoon onset in the South China Sea (SCS) were investigated based on 17 years (1979-1995) NMC wind data and OLR data from NOAA. It is proved that the onset of summer monsoon occurs later in SCS region than in Indo-China peninsula and island areas of Philippines. But the summer monsoon in the eastern part of SCS onsets almost at the same time as that in the western part of SCS. This simultaneity has somewhat standing wave feature. It is also confirmed that in most years there is a equatorial vortex forming near 105°E in April or May and the vortex leads the equatorial westerly in its upper reaches and the westerly in the Southern Hemi-sphere to the southern part of SCS. This creats a favorable condition for onset of the SCS summer monsoon. In the years when the equatorial vortex is unactive, the summer monsoon in the SCS onsets late. There is some relationship between the equatorial vortex and the onset date of SCS summer monsoon. Inearly April, the forming of the vortex and the preliminary building of cross-equatorial flows at 105°E is simult aneous. In May, these cross-equatorial flows enhance gradually and the activity of SCS summer monsoon may be closely associated with these flows. If the 105°E equatorial vortex is called onset vortex of East Asia, it is sure that this vortex is different from that of South Asia. In South Asia the onset vortex relates with monsoon onset directly, but in East Asia it does indirectly. So this also shows that East Asia Monsoon is more complicated than Indian Monsoon.