2022年广西罕见龙舟水的大尺度环流成因分析

Analysis of the Causation of Large-scale Circulation Associated with a Rare“Dragon-boat Rain”in 2022 in Guangxi

利用NCEP大气再分析资料、广西降雨量资料,对2022年广西罕见龙舟水的大尺度环流成因进行了分析,结果表明:2022年龙舟水期间高层欧亚中高纬地区高压脊异常偏强,引导冷空气持续南下影响华南地区,副热带西风急流强度偏强、位置偏南,南亚高压强度偏强、位置偏东,在广西上空构成了有利于垂直运动的环流配置。中层西太平洋副热带高压强度偏弱,西段脊线位置偏南,导致水汽输送偏南。低层索马里越赤道气流异常偏强,南海夏季风爆发偏早,前沿位置偏南,水汽收支在华南地区较常年偏多40%。在多个大尺度环流系统异常特征共同作用下,广西发生了大范围持续性暴雨天气。

With the use of NCEP atmospheric reanalysis and rainfall amount data of Guangxi,this work analyzes and studies the causation of the large-scale circulation associated with a rarely seen“Dragon-boat Rain”(a concentrated period of heavy rain)in the Region in 2022.The results are shown as follows.Dur-ing the rain,the ridge of an upper-level high pressure was anomalously stronger over the mid-and high-lati-tude parts of the Eurasian continent,steering cold air to move southward continually to affect south China.Compared with the usual state,a westerly jet stream was stronger and located more southward,and a major high in South Asia was stronger and more eastward located,forming a circulation allocation that was favora-ble for vertical ascending motion.At the middle level,a subtropical high was weaker over the west Pacific and the western section of its ridge was more southward located,resulting in water vapor reaching areas more southward.At the low level,a cross-equatorial air current was anomalously stronger over Somalia,and sum-mer monsoon had an earlier onset over the South China Sea with a more southward frontal edge so that the water vapor budget was 40%more than the average year for south China.Due to the combined effects of a-nomalous characteristics of these multiple large-scale circulation systems,a widespread and sustained heavy rain weather took place in Guangxi.