环境场对东海登陆热带气旋陆地路径的影响

EFFECT OF ENVIRONMENTAL FIELD ON TROPICAL CYCLONE TRACK AFTER LANDFULL FROM EAST CHINA SEA

采用合成分析的方法,对比分析了在华东南部沿海登陆,维持较短陆地路径和维持较长陆地路径的两类热带气旋的环境场变化,结果表明:环境场对登陆热带气旋的陆地路径的维持有重要影响。当西北太平洋副热带高压迅速加强西伸;中低层低压环流迅速减弱;中低层环境热力条件差,海洋水汽输送中断;高层水平流场呈纬向型,青藏高原反气旋环流相对较弱而西北太平洋副热带高压反气旋环流强大,中纬带西风急流强大时,环境场的配置使热带气旋周围的高层水平辐散弱并衰减,低层水平辐合弱并衰减,热带气旋的对流被抑制,仅能维持较短路径很快就减弱消亡。反之,当西北太平洋副热带高压减弱东退,西风槽南压;低层低压环流长时间维持;中低层环境热力条件好,海洋水汽输送通畅;高层水平流场呈经向型,青藏高原反气旋环流相对强大而西北太平洋副热带高压反气旋环流减弱东退,中纬带西风急流较弱,低空东南风急流强大时,环境场的配置使热带气旋周围高层水平辐散强并维持,低层水平辐合强并维持,热带气旋的对流通畅,能维持较长生命史和较长的路径。

A composite study is performed on the tropical cyclone making landfall on the southern part of Eastern China coast. The environmental features are compared between the tropical cyclones filling shortly after landfall and those surviving long after that. It is concluded that, for long-lived landfall tropical cyclones, there are weakening and eastward shrinking of the western North Pacific subtropical high, southward shifting of the westerly trough, long-lived low pressure circulation at low level, favorable thermo-dynamical condition at mid- and low- levels, sufficient water vapor transportation, meridional upper-level flow, strong Tibetan anti-cyclonic circulation, weak westerly jet, and strong low-level southeasterly jet. In such an environment, the whole level upward motion, upper-level divergence and low-level convergence can all be strong and sustain quite a long time, resulting in a long-lived tropical cyclone. And vice versa.