1994年印度洋偶极子对两广地区后汛期降水异常的影响机理

利用1979—2017年中国地面气象台站2 400站中广东省和广西壮族自治区（简称两广地区）174站的逐日降水资料、英国Hadley中心的逐月海表温度资料、NCEP/NCAR逐月再分析资料，分析了1994年华南后汛期（7—9月）期间印度洋偶极子（Indian Ocean Dipole，IOD）对两广降水极端正异常的影响机理。结果表明，1994年的正位相IOD事件引起了两广地区后汛期偏多，影响机制主要为两方面：一方面，IOD东极子区域海温负异常时，水汽沿着印度北部-孟加拉湾北部-中南半岛-两广地区和孟加拉湾中部-中南半岛-两广地区的异常水汽输送通道向两广地区输送，使得两广地区水汽异常辐合；另一方面，IOD东极子区域海温异常偏低时，该地区对流层低层异常辐散、高层异常辐合、存在异常下沉运动，两广地区对流层低层异常辐合、高层异常辐散、受异常上升运动控制。上述物理机制共同作用，导致1994年后汛期两广地区降水极端正异常。

The influence mechanism of the Indian Ocean Dipole on precipitation anomaly during the post-flood season over the Guangdong-Guangxi region in 1994

In this paper,based on the daily precipitation data of 174 stations in Guangdong Province and Guangxi Zhuang Autonomous Region(hereinafter collectively referred to as the Guangdong-Guangxi region) at a total of 2 400 China surface meteorological stations from 1979 to 2017,monthly sea surface temperature data of the Hadley Center in the UK and monthly NCEP/NCAR reanalysis data,the influence mechanism of the Indian Ocean Dipole(IOD) on the extreme positive anomaly of precipitation in southern China during the late flood season (July-September) of 1994 is analyzed.The study results show that the positive IOD event in 1994 can affect the above-normal precipitation over Guangdong-Guangxi region during post-flood season.In addition,when the sea surface temperature in the tropical southeastern Indian Ocean(eastern pole of IOD) is negative,water vapor is transported to the Guangdong-Guangxi region along the abnormal water vapor transport channels in the northern part of India,northern part of the Bay of Bengal,central part of the Bay of Bengal,central part of the Central South Peninsula,and two parts of the Bay of Bengal,resulting in an abnormal convergence of water vapor in the Guangdong-Guangxi region.At the same time,when the SST anomaly in the eastern pole of IOD is low,the anomalous convergence of the lower troposphere and anomalous divergence of the upper troposphere in the Guangdong-Guangxi region will then be controlled by the anomalous upward motion,which will result in meridional vertical circulation.The above physical mechanisms work together,thereby leading to extreme positive precipitation anomalies in the Guangdong-Guangxi region in the flood season after 1994.