西北太平洋热带气旋生成数在1990年代中期发生突变的气候环境特征分析

CLIMATIC CHARACTERISTICS OF ABRUPT CHANGE ON TROPICAL CYCLONE NUMBER IN THE MID-1990S OVER NORTH WESTERN PACIFIC

利用CMA热带气旋(TC)最佳路径资料和NCEP再分析资料,分析1949—2013年西北太平洋(包括南海)TC生成数的变化特征,发现在1995年前后发生由偏多到偏少的显著突变。对影响TC生成的主要气候环境要素场进行对比分析表明,在1995年之后,虽然赤道西太平洋海表温度偏高,热带太平洋为类La Ni?a的异常海温型,但垂直上升运动减弱、对流层纬向风垂直切变幅度增大、海平面气压升高,均不利于TC的生成,其综合影响导致TC数目显著减少。对1995年前后两个时期TC生成多、少典型年份海洋大气环境场的对比分析表明,1995年以前热带海洋表面温度对TC生成有相对重要的影响,而1995年以后风场环境对TC生成的影响作用更重要。

Based on the CMA tropical cyclone （TC） best track data and NECP reanalysis dataset, variation characteristics of the number of TC from 1949 to 2013 over north western Pacific （including the South China Sea） are analyzed. We found that the TC number has changed abruptly from more to less around 1995. Comparative analysis shows that environmental factors, which are necessary for the formation of TC, also changed after mid-1990s. After 1995, sea surface temperature in the western equatorial Pacific is above normal, and there is a La Nifia-like pattern in the tropical Pacific. However, in the same period, vertical upward movement decreases, vertical shear of tropospheric east wind increases, and sea level pressure rises, all of which are unfavorable to TC＇s generation and work together to decrease TC numbers significantly. In addition, in two separate periods before and after 1995, we also compared oceanic and atmospheric environment of typical years when more and less TCs occur respectively. The analysis results show that, SST in the tropical Pacific has a relatively important effect on TC＇s formation before 1995, but the influence of the wind environment is more prominent in the generation of TC after 1995.