东亚夏季风对中国内地夏季热带气旋降水的影响

Impact of East Asian summer monsoon on summer tropical cyclone precipitation in China's mainland

利用中国内地格点降水资料和热带气旋最佳路径数据集提取热带气旋降水,在线性去除ENSO信号后,研究东亚夏季风对中国内地夏季热带气旋降水的影响。结果表明,1979—2019年,中国内地6—8月热带气旋降水与东亚夏季风指数呈现显著的正相关,相关系数达到0.53。东亚夏季风的减弱,使得西北太平洋大部分海域对流层低层的正涡度和气旋环流增强、中层的湿度正异常和垂直上升运动增强、垂直风切变减弱,有利于热带气旋的生成和发展;同时,在西北太平洋热带气旋的主要生成区对流层中层呈现气旋环流异常,因此中国内地沿海地区存在东风异常,有利于引导热带气旋移向中国内地,使得中国内地夏季热带气旋降水增加。研究结果说明东亚夏季风可通过调制影响热带气旋生成和路径的大尺度环境场,进而与中国内地夏季热带气旋降水的年际变化相联系。

Based on the grid-point precipitation data and the best track dataset of tropical cyclones,this study extracts the tropical cyclone precipitation(TCP)in China's mainland and reveals a significant effect of the East Asian summer monsoon on the TCP in China's mainland after removing El Niño Southern Oscillation(ENSO)signals.The results show that during the period 1979—2019,the TCP in China's Mainland from June to August shows a significant positive correlation of 0.53 with the East Asian summer monsoon index.The weakening of the East Asian summer monsoon has resulted in the enhancement of the positive vorticity and cyclonic circulation in the lower troposphere,positive moisture anomalies in the middle layer,and vertical upward motion,and the weakening of the vertical wind shear over most of the NW Pacific,which is favorable to the generation and development of tropical cyclones.Meanwhile,there is an anomalous mid-tropospheric cyclone over the main TC genesis region in the Northwestern Pacific ocean,meaning that an easterly anomaly dominates the coastal regions of China's mainland,which is favorable for TC movement towards China's mainland,resulting in an increase in the summer TCP in China's mainland.Therefore,by modulating the large-scale environmental fields which affects the frequency of TC genesis and TC track,the East Asian summer monsoon can be connected with the interannual variation of the summer TCP in China's mainland.