1958～2000年6月连续性暴雨的特征分析

RESEARCH ON THE REASON OF THE DOUBLE RAIN-BANDS’ FORMING IN A SUSTAINING STORM RAINFALL OF SOUTH CHINA

利用1958～2000年6月的43年间我国长江以南各站的逐日降水资料,对连续性暴雨过程进行了区域划分和统计,并以此为依据作了初步的分析。分析发现6月份我国南方暴雨发生频繁,且华南、江南可同时有连续性暴雨过程存在,并得出了我国6月份连续性暴雨的基本特征以及年代际的变化规律,认为1990年代以后连续性暴雨增加明显。最后以1994、1998、2005年6月发生我国南方的连续性暴雨为例,初步探讨了连续性暴雨中华南、江南双雨带发展的基本规律和形成机制,指出产生连续性暴雨的大尺度背景场与南亚高压和高空急流的稳定维持有关。

Analysis of a sustaining storm rainfall in southern China in June 2005 reveals that when the quasi-longitudinal South Asia High ridge line is stable around 22°N and the quasi-longitudinal upper jet axis maintains around 35°N, it is beneficial for the growth of sustaining storm rainfall in southern China and for the forming of double rain-bands between 22 - 28 °N. The forming of northern rain-band is related to the divergence field of South Asia High. The Gravity Inertial Wave Instability of transversal waves may exist in the northern rain-band and the mixed Vortex Rossby Wave Instability may exist in the southern rain-band. The transformation of baroclinic potential vorticity to barotropic potential vorticity results in the increase of vorticity in lower layers and leads to the precipitation. The transformation of barotropic potential vorticity to baroclinic potential vorticity also happens in lower layers of the southern rain-band. The decrease of barotropic potential vorticity may also result in the increase of positive vorticity and it is beneficial for the development of precipitation.