“23·7”华北极端强降水特征和水汽条件研究

The characteristics and research on the water vapor condition of the

中文关键词:  “23·7”华北极端强降水，水汽条件，环流异常，水汽输送，地形作用

英文关键词:The “23?7” extreme rainstorm in North China, Water vapor condition, Circulation anomalies, Water vapor transport, Topography effect

中文摘要:

      利用地面气象站降水资料和ERA5再分析资料，对2023年7月29日—8月1日华北极端强降水的特征和水汽条件进行研究。结果表明，本次“23·7”华北极端强降水具有降水时间长、累计降水量大的特征，表现出显著极端性。降水主要位于太行山和燕山山前，最大降水中心与山脉走向基本一致，呈带状分布。极端强降水期间存在显著的环流异常，偏北的副热带高空急流、异常偏北的西太平洋副热带高压是此次极端强降水的关键环流；北上的台风“杜苏芮”残余环流、台风“卡努”和低空急流等是此次极端强降水的主要影响天气系统。此次极端强降水的水汽条件存在显著的阶段性特征，7月29日08时—31日08时主要降水区域低层辐合、高层辐散和上升运动强烈，低层气旋式风场发展深厚，水汽由台风“杜苏芮”残余环流近距离输送及其与“卡努”接力输送，并以前者为主，京津冀地区整层水汽处于净流入状态，最大水汽净流入量达1.5×108 kg/s；7月31日08时—8月1日08时上升运动、对流层低层辐合和高层辐散均显著减弱，低层气旋式风场厚度收缩，“杜苏芮”残余环流消亡，仅由台风“卡努”远距离输送水汽，京津冀地区内整层水汽处于净流出状态，最大水汽净流出量为5×107 kg/s。太行山和燕山地形的阻挡作用使得水汽辐合中心长时间滞留，同时其摩擦作用可能有利于山前上升运动增强，对本次极端强降水提供了有利条件。

英文摘要:

      The characteristics and the water vapor condition of the extreme rainstorm in North China from July 29 to August 1 in 2023 were investigated based on the surface meteorological observation precipitation data and the ERA5 reanalysis data. It is found that, the “23?7” extreme rainstorm in North China has the characteristics of long precipitation time and large cumulative precipitation, exhibiting significant extremes. The precipitation was mainly located in front of the Taihang Mountain and Yanshan Mountain. The maximum precipitation center was basically consistent with the direction of the mountains and was distributed in a strip. There were significant circulation anomalies during the extreme rainstorm. The northerly subtropical high-altitude jet stream, the abnormally northerly western Pacific subtropical high pressure were the key circulation of the extreme rainstorm, and the northward remnant circulation of Typhoon Doksuri, Typhoon Khanun and the low-altitude jet stream were main weather systems affecting on the extreme rainstorm. The water vapor conditions of the extreme rainstorm have obvious phase features. From 08:00 on July 29 to 08:00 on July 31, low-level convergence, high-level divergence and upward motion were strong in the main precipitation area, and the low-level cyclonic wind field developed deeply. Water vapor was transported at close range by the remnant circulation of Typhoon Doksuri and its relay transport with Typhoon Khanun, with the former being the main source. The entire layer of water vapor in the Beijing-Tianjin-Hebei region was in a net inflow state, with the maximum net inflow reaching 1.5×108 kg/s. From 08:00 on July 31 to 08:00 on August 1, the ascending motion, lower-tropospheric convergence and upper-level divergence were significantly weakened, the thickness of the low-level cyclonic wind field shrank, and only Typhoon Khanun transported water vapor over long distances. The entire layer of water vapor in the Beijing-Tianjin-Hebei region was in a state of net outflow, with the maximum net outflow reaching 5×107 kg/s. The blocking effect of the terrain of Taihang Mountains and Yanshan Mountains causes the water vapor convergence center to remain for a long time, while its frictional effect may strengthen the upwelling movement in front of the mountain, providing favorable conditions for this extreme heavy rainfall.