陕西一次远距离台风持续性暴雨的成因分析

利用MICAPS实况观测、卫星云图TBB、地面气象自动观测资料,对2010年7月16—18日陕西一次持续性暴雨天气过程进行诊断分析,结果表明:500 hPa大陆高压,副热带高压稳定维持使得两高之间低值系统稳定少动,宽广的低压底部不断有短波槽携带冷空气东移南下,与两高之间的低值区合并,Conson台风在登陆和减弱的过程中在南海及附近地区维持较长的时间,低层从台风东侧至陕西建立了温湿能通量的能量输送通道,把台风东侧的温湿能沿副热带高压外围偏南风向陕西输送,暴雨位于低层温湿能等值线密集处;条件性对称不稳定与对流不稳定是此次暴雨发展与维持的重要机制,高层湿位涡大值区向下伸展,对暴雨起到增幅的作用。暴雨产生在地面湿静力温度线密集区略偏向于高能中心一侧。

Mechanism analysis of a far distant typhoon and persistent heavy rain process in Shaanxi province

By using routine observational, satellites and surface automatic observational data,far distant typhoon and heaviest rainfall process of Shaanxi in 2010 were analyzed. The conclusions are as follows. Low-pressure system between 500 hPa mainland high pressure and subtropical high pressure maintained stably and the short-wave cold troughs at the broad bottom of low-pressure moved continuously to south, and merged into low-pressure system situated between two high-pressure; furthermore, typhoon "Conson" located in the South China Sea for long time and the southerly jet near the center of typhoon extended northwardly and arrived at Shaanxi through the ridge line of the subtropical high over western Pacific, which caused persistent heavy rain in Shaanxi province. The transportation channels of water vapor and enthalpy at 850 hPa between the typhoon and Shaanxi was established and the warmer and wetter atmosphere was carried toward Shaanxi continuously. Heavy rains occurred in the overlapped area of upward motion, which locates in two circulations, and in dense belt line of enthalpy at 850 hPa. Convective instability and conditional symmetric instability are the important mechanism for development and maintenance of heavy rains. When big value area of moist potential vorticity at high level spreads downward, heavy rains become stronger. Heavy rains fall in dense belt of moist static temperature line, and they are slightly biased towards high-energy center side.