印度洋海温异常对西北太平洋台风的影响及机制研究

基于近40 a NCEP/NCAR再分析月平均高度场、风场、涡度场、垂直速度场以及NOAA重构的海面温度（sea surface temperature，SST）资料和美国联合台风预警中心（Joint Typhoon Warning Center， JTWC）热带气旋最佳路径资料，利用合成分析方法，研究了前期春季及同期夏季印度洋海面温度同夏季西北太平洋台风活动的关系。结果表明：1）前期春季印度洋海温异常（sea surface temperature anoma1y，SSTA）尤其是关键区位于赤道偏北印度洋和西南印度洋地区对西北太平洋台风活动具有显著的影响，春季印度洋海温异常偏暖年，后期夏季，110°～180°E的经向垂直环流表现为异常下沉气流，对应风场的低层低频风辐散、高层辐合的形势，这种环流形势使得低层水汽无法向上输送，对流层中层水汽异常偏少，纬向风垂直切变偏大，从而夏季西北太平洋台风频数偏少、强度偏弱，而异常偏冷年份则正好相反。2）春季印度洋异常暖年，西北太平洋副热带高压加强、西伸；而春季印度洋异常冷年，后期夏季西北太平洋副热带高压减弱、东退，这可能是引起夏季西北太平洋台风变化的另一原因。

Effect of Indian Ocean SSTA on typhoon in western North Pacific and its mechanism

Based on the NCEP/NCAR reanalysis data of monthly mean geopotential height, wind, vorticity, and vertical velocity, NOAA reconstructed sea surface temperature (SST) of the Indian Ocean, and the best track dataset from Joint Typhoon Waming Center (JTWC) at a 6-h interval from 1979 to 2018, the relationship between the Indian Ocean SST in the preceding spring and the concurrent summer and the summer typhoons over western North Pacific is investigated using synthetic analysis. The results are shown below. 1) The Indian Ocean sea surface temperature anomaly (SSTA) in the preceding summer, especially when the key region is located at the Indian Ocean north of the equator and the southwest Indian Ocean, has significant effects on typhoons over western North Pacific. In the years of abnormally high SST in spring over the Indian Ocean, in the later summer, the meridional vertical circulation between 110°E and 180 °E shows abnormal downdraft, corresponding to the circulation of low-level wind divergence and upper-level wind convergence, which stops the upward transport of low-level water vapor. In addition, due to the abnormally less water vapor in the middle troposphere and abnomally larger vertical shear of zonal wind, the summer typhoons over western North Pacific present characteristics of lower frequency and weaker intensity. A reverse situation is indicated in the abnormally cold years. 2) In the abnormally wam years of spring over the Indian Ocean, the western North Pacific subtropical high is strengthened and extends westward; while in the abnormally cold years, the western North Pacific subtropical high is weakened and goes eastward in the later summer, which is another probable reason for the changes of summer typhoons over western North Pacific.