4～5月南亚高压在中南半岛上空建立过程特征及其可能机制

Characteristics of the South Asia High Establishment Processes above the Indo-China Peninsula from April to May and Their Possible Mechanism

利用NCEP/NCAR再分析资料,发现菲律宾群岛以东洋面上空反气旋在4月第5候分裂成位于中南半岛上空的西部中心和仍位于菲律宾以东洋面上空的东部中心两部分,其中位于中南半岛上空的反气旋中心加强后形成南亚高压。中南半岛高空反气旋生成加强和菲律宾群岛以东洋面高空反气旋减弱消亡的同时发生是4～5月南亚高压在中南半岛上空建立过程的主要特征,其主要促发因子是亚洲南部大气非绝热加热状态的改变。事实上,随着对流沿亚澳"大陆桥"北移和中南半岛对流建立,中南半岛上升运动加强,高空辐散加剧,西部中心在中南半岛南部生成,南亚高压初步建立。随后,菲律宾群岛以东洋面上热源突然东撤至150°E以东,中南半岛热源成为主导,在加热区东面对流层高层激发出气旋式环流,造成西太平洋高压在120°E附近分裂。之后,孟加拉湾-中南半岛夏季风建立,孟加拉湾-中南半岛对流加强,在深对流作用下,中南半岛上空释放大量潜热,上升运动进一步加强,西部中心加强北抬。同时,南海对流开始加强,其释放的潜热加热会在加热区东部的对流层高层激发出正涡度变率,令东部中心减弱消亡,南亚高压在中南半岛上空完全建立。

In terms of the NCEP/NCAR daily-mean reanalysis data （1975-2005）, it is found that the upper troposphere anti-cyclone to the east of the Philippines break into two portions, the west anticyclone is above the Indo-China Peninsula （ICP） while the east one still stays above the ocean to the east of the Philippines. The South Asia high （SAH） forms by the reinforcement of the west anticyclone. The formation and strengthening of the ICP upper anticyclone and the weakening and vanishment of the anticyclone above the ocean to the east of the Philippines occur simultaneously, which composes the chief characteristics of the SAH establishment processes above the ICP from April to May, while the primary impact factor of the processes is the variation of the diabatic heating condition on the south of the Asian continent. With the northward propagation of the convection along the Asian-Australian ＂Land Bridge＂ and the buildup of the ICP convection, the upward motion over the ICP and the upper troposphere divergence strengthen, so that west center forms and the SAH establishes initially. Whereafter the heat source which has been on the ocean to the east of the Philippines withdraws eastward to the east of 150°E suddenly, the ICP heat source becomes the leader, which stimulates a cyclonic circulation to the east of the heating zone in the upper troposphere that results in the abruption of the SAH near 120°E. Then because of the strengthen of the BOB-ICP convection and the establishment of the BOB-ICP summer monsoon （BOB is short for Bay of Bengal）, a great deal of latent heat is released above the ICP, which makes the vertical motion enhance so that the west center intensifies and moves northward. The South China Sea （SCS） convection begins strengthening at the same time, and the released latent heating can stimulate the upper-level positive vorticity variety, which makes the east center weaken and disappear, and the SAH establishes completely above the ICP.