1998-2009年间台风不活跃期间热带云团活动分析

热带云团是台风生成的前兆，虽然一些研究将近20 a来台风不活跃与大尺度环境场相联系，但是还没有人分析台风不活跃期热带云团的活动特点。本文利用目前仅有的1989-2009年全球热带云团资料，分析了西北太平洋热带云团近20 a的变化特征。1998年以后西北太平洋台风生成减少主要发生在7-10月，集中在南海（13～23°N，110～120°E）和西北太平洋台风活动区域的东部（13～23°N，145～170°E）。热带云团除1月外各月都有增加的趋势，特别是与台风生成显著减少区域相联系的热带云团活动具有显著的增加趋势。通过对NCEP/NCAR再分析资料分析发现，1998年后热带云团活动增加与环境风垂直切变增加有关，而增强的垂直切变不利于台风生成。

Analysis of tropical cloud clusters in typhoon inactive periods during 1998-2009

In this paper, the activity features of tropical cloud clusters in typhoon inactive periods were analyzed. By using the data of global tropical cloud clusters during 1989-2009, the variation features of tropical cloud clusters over the western North Pacific in recent 20 years were studied. The downward trend of typhoon genesis mainly occurred in July-October after 1998 over South China Sea(13-23°N, 110-120°E) and the eastern part of northwestern Pacific (13-23°N, 145-170°E). The tropical cloud cluster shows an increasing trend in each individual month except January. Especially the activities of the tropical cloud clusters over the regions where typhoon significantly decreases have a remarkable increasing trend. Analysis with NCEP/NACR reanalysis dataset shows that the increase of tropical cloud cluster activities after 1998 can be correlated obviously with the stronger vertical wind shear which is disadvantageous to the generation of typhoon.