2009年夏季西太平洋副热带高压北抬原因初探

利用数值模式再分析数据和常规观测资料,分析研究2009年6-8月西太平洋副热带高压(以下简称副高)连续5次北抬至偏北位置,且异常稳定维持,造成江淮流域干旱少雨(空梅)之缘由.通过合成、相关等分析方法探讨西风带、副热带、热带主要大气环流系统之间的相互影响和作用,并利用全型涡度方程探讨副高北抬和强度维持的主要机制.结果表明:(1)西风带波动的传播与副高变化关系密切,西太平洋副高的北抬过程起始于中段副高(140°～160°E)强度加强;(2)副高北抬之前孟加拉湾东部有明显的对流活动,对于副高的北抬和加强有一定的指示意义,而副高南侧的对流活动与副高北抬之间是一种伴随关系;(3)涡度场变化分析可知,副高北抬的关键因素是中高纬度槽脊变化引起的东亚沿海负涡度的增加.

The Study of Northward Jump of Subtropical High over the Western Pacific in Summer 2009

Using the reanalysis data derived from numerical model and the routine observation data, the mutual influence and interaction between the significant circulation systems in the westerlies, subtropics and tropical area during the summer of 2009 were studied by composite and correlation analysis. The complete form of vertical vorticity tendency equation was used to explore the dynamic mechanism for the northward jump and strength maintenance of the subtropical high. The study reveals that the variance of the subtropical high is closely related to the propagation of the westerly wave, and the jump of the west Pacific subtropical high starts at the strengthening of the middle part of subtropical high (140°-160°E); Severe convection over the Bay of Bengal occurred previous to the northward jump of the subtropical high, which has indicative significance to the forecast of the jump and strengthening of the subtropical high. Nevertheless, the convective activities south to the subtropical high have accompanying relationships with the northward jump of subtropical high; meanwhile, from the perspective of dynamic mechanism, the key factor of northward jump of the subtropical high is the variance of the vorticity over East Asia coastal areas, which is caused mainly by the movement of the trough and ridge in middle high latitudes.