环境场对近海热带气旋突然增强与突然减弱影响的对比分析

COMPARATIVE ANALYSIS OF THE INFLUENCE OF ENVIRONMENT FIELD ON RAPID INTENSIFYING AND WEAKENING OF TROPICAL CYCLONES OVER OFFSHORE WATERS OF CHINA

采用动态合成分析法对近海突然加强(RITC)和突然减弱(RWTC)两类热带气旋(TC)的环境场进行对比分析。研究表明:(1)两类TC形势场差异较明显,且影响RITC的南亚高压比影响RWTC的南亚高压强。(2)突变前后RITC有充足水汽供应配合较强辐合及上升运动,TC不断获得水汽凝结释放的潜热,使得损耗的能量得到补充和加强,高层辐散突变后减弱,使得TC能量得以保存和聚集,暖心结构被不断增加的潜热能所加强,有利于TC强度的爆发。(3)RWTC突变前后中低层上升运动减弱,中低层辐合变化不大,且由于水汽供应不足,TC获得的凝结潜热不足以补充TC自身的能量损耗,并且高层的上升运动及辐散突变后均加强,这些均有利于TC中心高层暖心热量不断减少,从而促使TC强度快速减弱。

Through a comparative analysis of the influence of environment field on the rapid intensifying and weakening of tropical cyclones over the offshore waters of China by using the dynamic composite analysis technique, our study shows the following results. Firstly, the geopotential height fields of these two types of TCs are dramatically different; the South Asia high which influences the former type of TCs is much stronger than the one which affects the latter type. Secondly, the former type is related to the transportation of plentiful water vapor, strong convergence and ascending motion. Secondly, TCs are supplied with latent heat due to constant vapor condensation to make up the energy which is lost by friction or other factors. Upper-level divergence weakens, enabling the TC to collect and conserve sufficient energy while TC＇s warm-cored structure strengthens because of consecutive increase of latent heat, being favorable for the TC to strengthen explosively. Thirdly, across the time before and after rapid weakening of the TC, ascending motion decreases in the middle and low layers of the atmosphere but no significant changes are noted in the convergence of the two layers; due to the insufficient supply of water vapor, the latent heat energy supplied to the TC is not enough to make up its own energy loss, resulting in rapid weakening of TCs because of two other extra reasons, namely, upper-level ascending motion and divergence are getting stronger after the abrupt weakening of the TC so that the heat keeps decreasing in the warm core of the upper part of the TC center.