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.