8月中国登陆台风降水与对流层高层西风急流关系的初步研究

THE PRELIMINARY RESEARCH ON THE RELATIONSHIP BETWEEN LANDFALL TYPHOON RAINFALL OVER CHINA AND EAST ASIAN WESTERLY JET STREAM IN AUGUST

采用中国气象局及美国台风联合警报中心整编的1954—2013年best-track热带气旋资料、中国大陆743站逐日降水数据和美国国家环境预报中心及大气研究中心(NCEP/NCAR)的再分析资料,研究登陆中国的台风降水特征及其与对流层高层西风急流的关系。结果表明:8月登陆台风降水对中国东南沿海地区的影响明显,福建、浙江的登陆台风降水占同期降水的30%左右,局部地区达到40%。基于降水与200 hPa纬向风的显著相关区定义的东亚西风急流指数(EAWJI),描述了西风急流位置的经向移动。EAWJI与台风降水具有显著的负相关,即EAWJI出现负异常时,急流位置偏北,中国登陆台风降水增加,反之急流位置偏南、降水减少。急流位置偏北,西太平洋台风活动区域的对流层纬向风出现东风异常,有利于台风登陆中国,且登陆位置较常年偏北,登陆台风数较常年偏多,台风登陆后维持时间较常年偏长;在中国大陆及东部沿海附近,纬向风垂直切变为异常的东风切变、对流层低层相对涡度增强及水汽输送增大均有利于台风登陆后的维持,从而使登陆台风降水增加。

The relationship between landfall typhoon rainfall over China and East Asian westerly jet stream in the troposphere was analyzed based on the tropical cyclone （TC） best-track data from the China Meteorological Administration and, the Joint Typhoon Warning Center, daily precipitation data in 743 stations of China and the NCEP/NCAR Reanalysis data from 1954 to 2013. The result shows that the landfall typhoon rainfall mainly effects the precipitation over southeast coastal region of China in August. The landfall typhoon rainfall proportion in Fujian, Zhejiang was about 30% of all precipitation in August, at some places this proportion could reach 40%. The East Asian westerly jet index （EAWJI） based on precipitation and 200 hPa zonal wind significant correlation area, described the meridional move of westerly jet. EAWJI and typhoon rainfall has a significant negative correlation with EAWJI. That is to say, when negative anomaly appears, jet shows up in northern position, Chinese landfall typhoon rainfall increase; whereas jet shows up in southern position, typhoon rainfall decreased. When the of jets jumped northward, there would be easterly anomaly of tropospheric zonal wind in The Western Pacific typhoon activity area, which made it easy for the typhoons to land China and made the location of landing further north, the number of landfall typhoons more and the living time longer. The easterly shear of vertical zonal wind, the increasing relative vorticity and more water vapor transport in the lower troposphere of China's Mainland and near the east coast were helpful to maintain the landfall typhoon, so that the landfall typhoon rainfall increased.