“21·7”河南极端降水的远距离台风作用分析

Analysis on the Influence of Distance Typhoon on the Extreme Precipitation in July 2021 in Henan

利用常规气象观测、中央气象台台风定位报、HYSPLIT模式和欧洲中心ERA5逐小时再分析等资料,对2021年7月1922日河南极端降水过程中远距离台风的作用进行了诊断分析。结果表明:此次特大暴雨是南亚高压、副热带高压、黄淮地区低涡或切变线和双台风远距离水汽能量输送共同作用造成的罕见极端降水。南亚高压东边界东扩、日本附近副热带高压稳定维持,以及位于河南的中尺度低涡或切变线,为极端降水的发生奠定了基础。远距离台风“烟花”和“查帕卡”双双与河南建立水汽通道,并维持72 h之久,使大量的水汽和能量通过低空东南急流或偏南气流源源不断地向河南输送,成为此次极端降水的关键因素。1921日暴雨区低层925 hPa的水汽主要来自“烟花”单通道输送;850 hPa和700 hPa水汽均源自“烟花”和“查帕卡”双台风双通道输送,850 hPa上“烟花”对水汽的贡献大于“查帕卡”的贡献,而700 hPa两台风贡献相当。由于中低层维持长时间的水汽和能量的输送,致使暴雨区强降水时段低层一直保持高温高湿状态。低层高温高湿,一是加强了暴雨区的对流不稳定,二是在不稳定能量释放后可重建对流不稳定层结,从而导致了特大暴雨的连续出现。此外,925 hPa水汽通量大值区、水汽通量散度负值中心与逐12 h强降水中心演变具有较好的对应关系。925 hPa弱冷空气侵入使暴雨加剧,强降水位于假相当位温等值线密集区。

This paper analyzes the role of distance typhoon in the extreme rainstorm in Henan on 1922 July,2021 based on the conventional meteorological observation,typhoon information provided by National Meteorological Center of CMA,Lagrangian trajectory model HYSPLIT v4.9 and ECMWF ERA5 reanalysis dataset.The results are as follows:The extremely severe rainfall this time was rarely seen in history,caused by the joint actions of the South Asia high,subtropical high,Huang-Huai vortex/shear line and long-distance water vapor energy transport of binary typhoons.The eastward extension of South Asia high ridge line,the stable maintenance of the subtropical high near Japan and the meso-scale Huang-Huai vortex/shear line in Henan lay a solid foundation for the extreme precipitation.The distance typhoons“In-Fa”and“Cempaka”both established water vapor channels with Henan and kept them for 72 hours so that a large amount of water vapor and energy were continuously transported to Henan through low-level southeast jet or southerly air flow,which became the key factor of this extreme precipitation.Analysis found that the 925 hPa water vapor in the extreme rainstorm area from the 19th to 21st mainly came from the single-channel transport of“In-Fa”.The water vapor at 850 hPa and 700 hPa were from the double-channel transport of“In-Fa”and“Cempaka”.The contribution of“In-Fa”to the 850 hPa moisture was greater than that of“Cempaka”,while their contribution to the waster vapor at 700 hPa was similar.Because of the long-term transport of water vapor and energy in the middle and low levels,the lower troposphere remained in the state of high temperature and high humidity in the extreme rainstorm area during the period of heavy precipitation.So high temperature and humidity not only strengthened the convective instability in the rainstorm area,but also helped reconstruct the convective instability stratification after the unstable energy was released,ensuring the continuous occurrence of severe rainfall.In addition,the 925 hPa large-value water vapor flux and the negative center of water vapor flux divergence corresponded well with the evolution of the 12 h severe rainfall centers.The severe precipitation was located in the dense isoline area of 925 hPa pseudo equivalent potential temperature and the intrusion of 925 hPa weak cold air exacerbated the rainstorm.