登陆热带气旋在鄱阳湖区的活动特征及原因分析

鄱阳湖流域是受登陆热带气旋（简称TC）影响最为频繁的内陆地区之一。利用中国气象局热带气旋年鉴资料、地面观测资料、中国气象局一日两次的常规探空资料以及NCEP/NCAR一日四次的2.5°×2.5°再分析资料，研究了过鄱阳湖TC的活动特征及其影响。首先统计1949~2012年进入鄱阳湖区域61个TC的活动特征发现，平均而言进入鄱阳湖地区的TC具有移速减慢，强度衰减变缓及降水增幅特征。大尺度环流场分析表明，登陆进入鄱阳湖区的TC处于太平洋副热带高压和东亚大陆高压之间的鞍形场中，引导气流减弱，水平风垂直切变减小，有利于其移速减慢、衰减减缓以及降水累计。几个典型TC个例的观测分析发现，TC降水降低了鄱阳湖区浅层土壤温度和低层大气温度及其日较差，但增加了土壤和空气湿度。鄱阳湖区域下垫面较高的地面热量有利于TC维持。而湖区对流有效位能在TC进入后明显降低，说明TC触发了该区域对流有效位能释放，有利于其降水增幅。

Characteristics of Landfalling Tropical Cyclone Activities over the Poyang Lake Basin and Mechanisms Analysis

The Poyang Lake basin is one of the inland areas in China that are under the most frequent influences of post-landfall tropical cyclones (TC). The interaction between TC and the underlying surface over this region is investigated using the TC best track data, surface and sounding observations and global meteorological re-analysis data. Statistical analysis of the data from 1949-2012 shows that the moving speed of TC reduced once they entered the Poyang Lake basin and their decaying rate became lower while the associated precipitation increased. Analysis of large-scale circulation indicates that TC entering Poyang Lake basin were located at the "saddle region" formed between the Pacific subtropical high and East Asian continental high. The weakened steering flow and reduced vertical shear of horizontal winds in the "saddle region" are favorable for the slowing of TC movement and decaying rate and precipitation increase. Several typical TC cases are selected to further examine the condition changes in the underlying surface during periods of TC influence. It is found that both the top layer soil temperature and lower atmosphere temperature decreased with reduced diurnal variations, while the soil water content and air humidity increased obviously due to the rainfall induced by TC. Relatively large heat storage over the Poyang Lake basin is favorable for the maintaining of TC. The convective available potential energy (CAPE) decreased significantly over this region under the impact of TC, indicating that TC triggered the release of CAPE and thus increased rainfall.