南海夏季风爆发的气候特征

THE CLIMATIC CHARACTERISTICS OF SUMMER MONSOON ONSET OVER SOUTH CHINA SEA

关键词:  南海夏季风爆发  热带对流  赤道西风

Key words:  Onset of summer monsoon over SCS  Tropical convection  Equatorial westerly

摘要:

首先以南海区域平均的候平均OLR值下降至235W/m²,同时纬向风由东转成西为定义标准确定南海季风从1979到1994年间爆发的平均日期是5月第4候,然后对16年(1979-1994年)的OLR场、风场及θ_se场的时段叠加合成图进行了分析,认为南海夏季风的建立是南海-西太平洋系统所造成。南海夏季风爆发前后,南海地区环流系统最显着的特征是低层西太平洋副高脊减弱东撤;高层南亚高压从10°N的菲律宾北跳到15°N以北的中南半岛;位势不稳定和热带对流的演变呈现海洋上的爆发晚于大陆和岛屿地区的特征,只是位势不稳定的变化超前深对流的发展。而爆发前后,周围地区对南海的最直接影响来自南海上游70-90°E赤道西风的加强和北抬东伸,同时索马里越赤道气流的加强和阿拉伯海高压的北撤,通过影响赤道西风也间接影响到南海。

Abstract:

According to the definition criterion of this paper,the mean onset time of the South China Sea Summer Monsoon(SCSSM) from 1979 to 1994 is the Fourth pentad of MAY. The composite analyses of 16 years of OLR,wind field and θ_se field show that the onset of SCSSM is caused by tthe SCS Western Pacific System,In the lower troposphere,the weakening and retreating eastward of the Subtropical High in SCS region is the outstanding feature of SCS circulation system around the onset time of SCSSM.At the same time,the moving northwestward of the SCS High is the characteristics of SCS circulation systems in the upper troposphere.The evolution of potential instability and tropical deep convection develops earlier over the continent and island areas than over the sea,and the developing of potential instability is earlier than that of deep convection.The strengthening and the stretching eastward of 70-90° E equatorial westerly at the upper reaches of SCS region has direct effect on the onset of SCSSM.Meanwhile the enhancement of Somali cross equatorial flow and the retreating northward of Arabian High affect the onset of SCSSM indirectly through producing effect on the tropical westerly.