大尺度环流系统对西北太平洋变性TC频数影响的气候诊断分析

Climate diagnostic analysis of effect of large-scale circulation on extratropical transition of tropical cyclones over Western North Pacific Ocean

基于中国热带气旋年鉴资料,从气候学角度出发,对西北太平洋TC(热带气旋)发生温带变性的频数与大尺度环流系统间的关系进行了诊断和分析。研究发现变性TC多发生于夏、秋两季,通过对NCEP月平均再分析资料的500hPa高度场进行EOF分解,发现西北太平洋TC变性的频数与65°N附近强冷高压系统在夏、秋两季都存在着正相关关系,且相关性在秋季高于夏季;与30°N附近强副热带高压系统存在负相关关系,夏季副热带高压系统的作用更大;与30°N以南西北太平洋多台风活动区域的弱低压存在显著的负相关,低压越弱,对流越弱,则TC的生成数越少,其中发生变性的TC数也会减少。500hPa高度场EOF分解的第一特征向量所对应的时间函数分布在20世纪70年代中期前后出现了反号,较好地对应了变性TC年频数的年际变化趋势,70年代中期之前变性TC呈总体偏多,之后变性TC的频数总体偏少,呈明显下降趋势。

In the perspective of climatology the statistical analysis of the typhoon data of 1961 -2000 from Typhoon Annuals of Shanghai Typhoon Institute is made in order to detect the effects of the large-scale circulation systems on the Extratropical Transition （ET） of tropical cyclones （TC） over Western North Pacific Ocean. It is found that most ET TC over western North Pacific Ocean occurs in summer and autumn, especially in the transition period from summer to autumn. The correlation and EOF analysis are further calculated on the 500hPa geo-potential height, and the strong correlation between ET, TC and large-scale circulation systems, such as cold wave, can be identified. The number of ET TC correlates with middle-and high-latitude cold high pressure center positively, and correlates with weak tropical low pressure negatively. The number of ET TC is higher than average before the middle of 1970＇s last century and has a decreasing trend since that time, which is consistent with the spatial and temporal distribution of the large scale circulation systems.