Abstract:

The precipitation anomaly in the first half of July in southern China has an important impact on the double cropping rice production and social economy in China. Based on daily precipitation data from 2400 national meteorological stations in China, the daily reanalysis data with a resolution of 2.5°×2.5°and the six-hourly reanalysis data with a resolution of 1°×1°from National Centers for Environmental Prediction/National Center for Atmospheric Research(NCEP/NCAR)in July from 1981 to 2010 and 2019, the causes of precipitation anomaly in southern China in the first half of July in 2019 was analyzed by using ageostrophic wet \mathit{Q}-vector. The results are as follows: (1) The abnormal precipitation in the southern China occurred under the conditions that the south Asia high in the high-level was eastward and southward, the west Pacific subtropical high was significantly strong and westward and southward in the mid-level, and the geopotential height field in South China and the south of the Yangtze River was weak (cyclonic circulation anomaly) in the low-level in the first half of July in 2019. (2) The diagnosis of ageoserophic wet \mathit{Q}-vector showed that the upward movement corresponding to abnormal precipitation was mainly caused by the strong diabatic heating, and the diabatic heating was mainly induced by strong convergence of water vapor flux in the middle and low level. (3) The larger horizontal gradient of sea surface temperature (SST) in the equatorial western Pacific was favorable to strengthen the cross-equatorial flow, forming a zonal circulation similar to Walker cell over the north of the equator, and its descending branch was conducive to occurrence of anticyclonic circulation anomaly near the Bay of Bengal and the Philippines, and increasing the northward water vapor transport from the Bay of Bengal and the South China Sea. It was found that the change of SST horizontal gradient in the western equatorial Pacific would affect wind field and water vapor flux in the southern China by affecting the cross-equatorial flow, and then affect the precipitation in the first half of July in the southern China.

Key words: precipitation anomaly in the southern China, ascending motion, ageostrophic wet \mathit{Q}-vector

摘要：

7月上半月我国南方地区降水异常对我国双季稻生产和社会经济有着重要影响。利用1981—2010年及2019年7月中国区域约2400个国家地面气象站逐日降水量资料、美国国家环境预报中心和大气研究中心(National Centers for Environmental Prediction/National Center for Atmospheric Research，NCEP/NCAR)提供的分辨率为2.5°×2.5°的逐日及分辨率为1°×1°的逐6 h再分析资料，利用非地转湿 \mathit{Q}矢量诊断分析2019年7月上半月我国南方降水异常的成因。结果表明：2019年7月上半月南方地区的异常持续性降水发生在高层南亚高压偏南偏东、中层西太平洋副热带高压偏强偏南偏西、低层江南华南地区位势高度场偏弱(气旋性环流异常)的环境下;用非地转湿 \mathit{Q}矢量对上升运动进行诊断发现2019年7月上半月南方地区异常持续性降水对应的上升运动主要由非绝热加热造成，且强盛的非绝热加热又主要由中低层强盛的水汽通量辐合造成;赤道西太平洋较大的海温水平梯度有利于越赤道气流的加强，在赤道以北形成一个类似Walker cell的纬向环流，其下沉支有利于孟加拉湾至菲律宾一带出现反气旋环流异常，增加孟加拉湾和南海向北的水汽输送。对2019年7月上半月我国南方地区异常降水的研究发现，赤道西太平洋的海温水平梯度变化会通过影响越赤道气流来影响我国南方地区风场及水汽通量，进而影响我国南方地区7月上半月的降水。

关键词: 南方降水异常, 上升运动, 非地转湿 \mathit{Q}矢量