热带气旋过台湾岛引起的副中心特征分析

AN ANALYSIS ON THE FEATURES OF SECONDARY CENTER PRODUCED BY THE TROPICAL CYCLONES CROSSING TAIWAN

利用台湾地区的地面观测资料证实了中国气象局台风年鉴资料中有些热带气旋(TC)靠近或穿过台湾岛时,伴有副中心产生的记录是真实的。分析发现,这些副中心是由强度相对较弱的TC(近中心最大风速Vmax≤50 m/s)与台湾岛内的中央山脉相互作用产生,且主要分布在台湾岛的西北和西南侧,但在生成机制上两者应该有所不同:台湾西北侧的副中心处于偏东气流过中央山脉北部的背风侧,是由地形背风侧下击流的增温降压作用产生的,生成初期是具有暖心结构的次生低压;而西南侧的副中心由台湾海峡上空偏西气流受南部中央山脉阻挡后形成的次级涡旋发展而成,生成初期不具有暖心结构及低压中心。

Based on the surface observation in the island of Taiwan,it was proved credible that secondary centers （SCs） are formed when tropical cyclones （TCs） sweep around or pass over it,which is recorded in the typhoon year-book of China Meteorological Administration.These SCs often appear on the northwestern and southwestern parts of Taiwan＇s Central Mountain Range （CMR）,when weak （maximum tangential wind speed is less than 50 m/s） TC＇s circulation approaches Taiwan and interacts with the CMR.However,there should be different formation mechanisms for the SCs initiating on the northwestern and southwestern part of the island：the first one develops from a secondary low,which is primarily produced due to the downslope adiabatic warming by the easterly wind passing over the northern CMR,so it is a low-pressure and warm-core center at its early stage; the latter one develops from a secondary vortex,which is produced from the cyclonic airstream when the westerly wind over Taiwan Strait approaches the southern CMR and deflects northward on the southwestern Taiwan,so it has no low-pressure and warm-core center at its early stage.