北印度洋热带气旋月季变化特征及成因分析

Monthly characteristics of tropical cyclone in the North Indian Ocean

采用美国联合台风警报中心(JTWC)提供的北印度洋1977年至2008年热带气旋(TC)资料、NOAA提供提供的1977—2008年月平均海表面温度(SST)资料、逐日的高度场(HGT)资料和NCEP提供1982—2008年全球再分析资料,对北印度洋热带气旋的月季变化的双峰结果进行分析,结果表明:500 hPa流场上热带辐合带的北进南退和500hPa高度场上南亚高压季节性进退跟双峰结构的季节变化有很好的对应关系。此外,海温的季节性变化和季风的爆发对热带气旋的月季变化有很大的影响,海温较高的时期,热带气旋发生频数较多,反之依然。当季风爆发时,存在着强的垂直风切变,不利于热带气旋的生成。正是这些综合因素,才造成了北印度洋热带气旋的双峰结构。

Based on the data of tropical cyclone in the North Indian Ocean from 1977 to 2008 from JTWC, the monthly SST and daily HGT from NOAA, and the global reanalysis data from 1982 to 2008 from NCEP, the dou- ble peak character of tropical cyclone over the North Indian Ocean is analyzed. The results show that： （1） the po- sition of flow field in the 500 hPa Intertropical Convergence Zone （ITCZ） well explained seasonal changes of tropical cyclone, as well as the seasonally changes of South Asia High in the 500 hPa according to the changes of tropical cyclone; （2） the seasonal variation of SST and the outbreak of the Monsoon show their impacts on occur- ring frequency of tropical cyclone, which means that high SST and weak vertical wind shear were in favor of the tropical cyclone frequency; （3）When the Monsoon broke out, the strong wind vertical shear was not conducive to the formation of tropical cyclone. Considering all the factors of above, they are the factors that led to the double peak structure of the tropical cyclone in the North Indian Ocean.