夏季青藏高原500hPa高压活动期间大气加热状况与大气环流特征

由于青藏高原500hPa层出现高压系统的活动,使高原大气产生“上高下高”的气压场结构,从而东亚大气环流也发生某些相应的变化。本文统计分析了高原500hPa高压的散度与垂直速度分布、高原大气热源的演变和100hPa层涡度、纬向风以及经圈环流的变化等。结果认为,由于夏季高原500hPa高压的活动,使高原上空垂直上升运动和对流加热受到抑制,100hPa南亚高压强度减弱、位置北抬、有向西部型过渡的特征。高原北侧西风急流减弱,东风急流南支与北支合并后位于原北文东风急流位置以南,侵入高原南麓的西南季风减弱。与此同时,孟加拉湾上空上升运动有所增强,其对流加热对维持东风急流乃至南亚季风将起重要作用。

THE CHARACTERISTICS OF THE ATMOSPHERIC HEATING AND THE ATMOSPHERIC CIRCULATION IN SOUTHEAST ASIA DURING THE ACTIVE PERIODS OF 500 hpa HIGH PRESSURE OVER THE QINGHAI-XIZANG PLATEAU IN SUMMER

In this paper,the distribution of the divergence and the vertical velocity of 500 hpa high and the evolution of the atmospheric heat source over the Qinghai-Xizang Plateau are computed,and the variation of the vorticity, the zonal flow at 100 hpa level and the vertical meridional cell are also analyzed. The results are as follows:A notable descending motion produced due to divergence in the lower troposphere and convergence in the upper troposphere exsists in the 500 hpa high over the QinghaiXizang Plateau in summer. DUring the active periods of 500 hpa high, the convective heating will be restrained, and the heat sink appears in the atmosphere over the Qinghai-Xizang Plateau. As a result, the 100 hpa south Asia High is weakened and will likely transform from east pattern to west pattern, and its long axis moves northward. Furthermore, the westerly jet situated north of the Qinghai--Xizang Plateau is weakened, the northern branch and the southern branch of easterly jet situated south of QinghaiXizang Plateau are weakened and merged into a single whole, so the southwest monsoon intruded into food of the Qinghai-Xizang Plateau is weakened too. On the contrary, the ascending motion situated over the Bay of Bengal is developed into stronger. Its convective heating will play an important role in the maintenance of the easterly jet and the south Asia monsoon.