西北太平洋热带气旋频数异常与五类主要大尺度环流型的关系

Relationship between the anomalous frequency of tropical cyclone genesis over the western North Pacific and five major large-scale circulation patterns

利用Yoshida and Ishikawa(2013)提出的一套客观分类方法对1979—2013年夏季(5—10月)共796个热带气旋(Tropical Cyclone,TC)生成前的大尺度环流背景场进行了分型,主要包括了季风切变线型(monsoon Shear Line,SL)、季风涡旋区(monsoon Gyre,GY)、季风辐合区(monsoon Confluence Region,CR)、东风波(Easterly Wave,EW)和热带气旋生成诱发的罗斯贝波扰动(Preexisting Tropical Cyclone,PTC)五大类大尺度环流型,其中SL、CR、GY与季风环流型紧密相关联。统计结果显示,大部分热带气旋生成与季风槽环流有关,并分析了五类环流型扰动下TC生成的位置及强度特征。基于分型结果可知,PTC环流型的异常增强和季风槽环流型的异常减弱是导致TC异常增加和异常减少的主要因素。并初步给出了可能的物理成因。

In this study,the environment of 796 tropical cyclones genesis(TCG)from 1979 to 2013 is assessed,via the categorization system developed by Yoshida and Ishikawa(2013),into five flow large-scale circulation patterns:monsoon shear line(SL),monsoon confluence region(CR),monsoon gyre(GY),easterly wave(EW)and preexisting tropical cyclone(PTC).The SL,CR and GY are related to the circulation pattern of monsoon trough among them.It is shown that most of the tropical cyclones are associated with circulation pattern of monsoon trough(such as SL-41%,CR-20%and GY-6%),and the TCG location and strength characteristics of TCs with each pattern is discussed.Based on the classification results,is found that the anomalies of the circulation pattern related to the monsoon trough and PTC are the main causes of the abnormal TCG frequency,and the possible physical origin thereof is given preliminarily.