1979—2019年云贵高原夏季区域性极端日降水事件的异常环流特征

CIRCULATION ANOMALIES OF REGIONAL DAILY PRECIPITATION EXTREMES OVER YUNNAN-GUIZHOU PLATEAU DURING BOREAL SUMMERS OF 1979-2019

利用中国气象局国家气象信息中心整编的站点观测资料和NCEP/NCAR逐日再分析资料,对云贵高原1979—2019年夏季区域性极端日降水事件的异常环流进行了分析。云贵高原99%分位上的夏季(6—8月)极端日降水事件(以下简称降水事件)降水阈值为20.0 mm/d,在近41年里共发生了35次降水事件,其中7月上旬发生次数最多,7月下旬次之,8月中旬最少;35次降水事件中有4次为热带气旋系统影响,降水中心位于广西西南部及沿海地区,中心值超过75 mm,其余31次的降水中心主要集中在贵州中南部和广西北部,且降水中心强度明显低于热带气旋系统所带来的强度;受欧亚大陆中纬度(30~50°N)地区的纬向扰动波列和低纬地区异常垂直环流圈控制,云贵高原上空对流层中建立了深厚的异常上升运动,配合500 hPa副热带地区的异常反气旋式环流将南海和孟加拉湾的水汽输送至云贵高原并在当地沿地形辐合抬升,为云贵高原极端降水的形成提供有利的动力条件和水汽条件,同时周边地区异常冷却所带来的加热场梯度还进一步加强了云贵高原上空的气流入流,更加有利于强降水的产生和维持。此外,降水事件还与乌拉尔山至我国东北地区的低值系统活动和源自北大西洋及热带低纬地区的波扰能量传播有关。

Based on daily precipitation observations and NCEP/NCAR reanalysis data,the circulation anomalies of regional daily precipitation extremes(RDPEs)at or above the 99th percentile over Yunnan-Guizhou Plateau during boreal summers of 1979—2019 are investigated by using composite analysis.Our results suggest that there were 35 RDPEs in recent 41 years which mostly occurred in early July and the least in mid-August and the threshold for RDPEs was 20.0 mm/d.Among the 35 RDPEs,four were affected by tropical cyclone systems,and their precipitation centers were mainly in southwestern Guangxi and the southern coastal areas of Guangxi with more than 75 mm precipitation at the center.The precipitation centers of the other 31 RDPEs were mainly in central and southern Guizhou and northern Guangxi,and the intensity of the precipitation center was significantly weaker than that of the RDPEs affected by tropical cyclone systems.Due to zonal wave train disturbance in the mid-latitude area(30~50°N)of Eurasia and abnormal vertical circulation in the low-latitude area,a deep abnormal upward movement occurred in the troposphere of the Yunnan-Guizhou Plateau,which,together with the abnormal anticyclonic circulation at 500 hPa,led to the water vapor transport from the South China Sea and Bay of Bengal to the Yunnan-Guizhou Plateau,providing favorable dynamic conditions and water vapor conditions for the formation of precipitation extremes over the Yunnan-Guizhou Plateau.At the same time,the gradient of heating field caused by abnormal cooling in the surrounding areas strengthened the inflow of air flow,further facilitating the formation and maintenance of precipitation extremes.Moreover,the RDPEs were also related to the activities of low value systems from the Ural Mountains to northeastern China and the propagation of wave disturbance energy from the North Atlantic and low-latitude areas in the tropics.