盛夏中国弱台风大暴雨事件的可预报性

Predictability of Weak Typhoon Heavy Rainfall Event in China during the Midsummer

盛夏是我国台风的多发时期,而台风降水是我国降水的重要组成部分,一般认为台风登陆减弱后,其伴随的强风暴雨灾害也会随之减弱,但有时也会出现台风强度减弱而其带来的降水却反而达到大暴雨等级的现象,本文定义这种现象为“弱台风大暴雨”降水事件,即热带气旋2分钟平均近中心最大风速不足32.7 m/s (即未达到台风强度),且单站单日降水量超过100 mm (即达到大暴雨等级)的热带气旋降水事件。对盛夏中国“弱台风大暴雨”事件的年际变化及其可预报性进行了探究,结果表明:前期海表温度场巴伦支海异常增暖导致海冰减少,使得冷空气活动偏南,同时配合前期印度洋偶极子正位相导致的夏季越赤道气流增强,南海地区西南季风携带大量水汽输送北上,使我国降水量增加。而前期拉尼娜型海表温度信号与西太平洋副热带高压的减弱相配合导致影响我国的台风增多,强度偏弱,诱发“弱台风大暴雨”事件。

Typhoon occurs the most frequently in midsummer over China,and typhoon precipitation is an important part of precipitation in China.It is generally believed that after landing typhoon weakened,the accompanying strong storms and rainfalls will also be weakened.However,sometimes heavy rainstorm appears while the typhoon intensity weakens.This paper defines the“weak typhoon heavy rainfall”event,that is,the tropical cyclone does not reach the typhoon-class intensity(averaged wind speed of the tropical cyclone in 2 minutes is less than 32.7 m/s),and daily precipitation at each station exceeds 100 mm(the heavy rainstorm level).And by exploring the predictability and interannual variation of WTHRE,the results show that the abnormal warmth of the Barents Sea in the early sea temperature field caused the sea ice to decrease,which made the cold air activity southward,and cooperated with the positive phase of the previous IOD,which leads the cross-equatorial airflow enhanced in summer and a large amount of vapor transport northward carried with the South summer monsoon,which increases the precipitation in China.The combination of the La Niña-SST signal in the background field of the PDO cold phase and the weakening of the West Pacific subtropical high caused the increase of typhoon affecting China with weak intensity,which induced the WTHRE.