台湾地形对台风Meranti(1010)经过海峡地区时迅速增强的影响研究

台风在趋近大陆过程中强度一般衰减, 但Meranti(1010)北上进入台湾海峡过程中却迅速加强, 且在登陆福建时达到最强。采用中国气象局台风资料、NCEP GFS 0.5°×0.5°再分析资料及台湾雷达资料, 结合中尺度数值模式WRF(The Weather Research and Forecasting Model)开展台湾地形敏感性试验, 研究Meranti进入台湾海峡过程中的结构变化及迅速加强机理。结果表明:台湾地形是Meranti迅速加强的一个重要影响因子。Meranti北上过程中, 一方面通过台湾岛地形分流作用及其背风坡效应在台湾海峡内诱生中尺度涡旋, 形成正负相间的涡度分布, 激发出与台风相关的扰动波列。地形强迫抬升及扰动波列可加强垂直运动和积云对流, 有利于台风对流发展。另一方面, 台湾地形还通过改变环境气流使台风高空辐散场加强, 环境风垂直切变减小, 形成有利于台风发展的环流背景。比较不同高度台湾地形试验中台风动能收支发现, 台湾地形激发的扰动波列和积云对流增强了次网格尺度系统与台风间能量的交换, 成为Meranti登陆前迅速加强的主要动能源。

Effect of Taiwan Topography on the Rapid Intensification of Typhoon Meranti (1010) Passing by the Taiwan Strait

Tropical cyclone (TC) intensity usually decays when it approaches a coastline. However, typhoon Meranti (1010) underwent rapid intensification after entering the Taiwan Strait and reached its peak just before landfall. Based on the best track data provided by Shanghai Typhoon Institute, China Meteorological Administration, the National Centers for Environmental Prediction Global Forecast System reanalysis grid data with 0.5°×0.5° horizontal resolution and Doppler radar observation data from "the Taiwan Central Weather Bureau" combined with a set of numerical sensitivity experiments by the Weather Research and Forecasting mesoscale numerical model, a study was performed to investigate the mechanisms of structure change and rapid intensification of Meranti (1010) after entering the Taiwan Strait. Results indicate that the topography of Taiwan offered a vital advantage for structural change and rapid intensification of Meranti. When moving northward, two mesoscale vortexes occurred over the Taiwan Strait, which resulted in a disturbance wave train of vertical vorticity alternative distribution in positive and negative values due to the shunting and leeward slope effects of Taiwan island topography. The disturbance wave trains were associated with the typhoon and strengthened the vertical motion, which was beneficial for the convection development of Meranti. Moreover, by adjusting the environmental atmospheric circulation, Taiwan topography also helped to provide a favorable environment for TC development, with stronger divergence in the upper troposphere and smaller environmental vertical wind shear. A comparison of kinetic energy budgets of TC in sensitivity experiments indicated that the disturbance wave trains and severe cumulus convection aroused by Taiwan topography enhanced the kinetic energy exchange from a subgrid scale system to a TC system to become a major kinetic energy resource for the rapid intensification of Meranti.