Analysis and Model Verification of Extreme rainfall Processes in Huabei of China in 2023

From July 29 to August 1, 2023, extreme heavy rainfall occurred in the Chinese HUABEI region. Heavy rainstorm occurred in the most areas of Beijing, Tianjin and Hebei province. The daily precipitation of 14 national meteorological observatories  exceeded the historical extreme value. The process intensity exceeded the three extreme rainstorm processes in the history of HUABEI region. Studying the causes of extreme heavy precipitation in HUABEI and evaluating the predictive performance of the model for extreme heavy precipitation is beneficial for improving the application and forecasting ability of the model. This article analyzes the weather scale characteristics and anomalies of this precipitation process from factors such as height field, wind field, divergence field, vorticity field, and water vapor. The dynamic and thermal structure of the vortex and the cause of the upper level continental high  are analyzed using the method of cyclone phase space map and full type vorticity equation. Finally, the predictive ability of the model for extreme precipitation is tested. The following main conclusions have been drawn:(1) The precipitation process is divided into two stages. Before the 31st, it was caused by the residual vortex circulation of the "Dussuri", with strong precipitation intensity and range. After the 31st, it was formed by the convergence of the easterly jet on the west side of the subtropical high pressure and its interaction with the terrain. Precipitation was mainly concentrated in the northern part of China, with weaker rainfall intensity compared to the previous period.(2) The key impact systems of this process are the 200hPa high trough and continental high pressure, the 500hPa blocking high pressure, and the residual circulation of the low-level "Dussuri". The divergence in front of the 200hPa high altitude trough is beneficial for maintaining upward movement in the North China region; At 500hPa, there is a blocking high pressure in the northern and eastern parts of North China, which is conducive to the maintenance of low-level vortex systems. The "Dussuri" convergence circulation is the triggering system of the process.(3) The water vapor conditions during this process were exceptionally good, mainly consisting of three water vapor transport paths: the southerly water vapor transport of the South China Sea monsoon, the eastward water vapor transport of the residual circulation of "Dussuri", and the southeast water vapor transport path of typhoon "Kanu".(4) During the northward movement, the residual vortex of the Dussuri maintains a quasi symmetric and warm center structure, with weak cold advection in the upper level of the vortex on the 30th.(5) The uneven vertical distribution of condensation latent heat heating generates negative vorticity in the upper troposphere, ensuring the stable maintenance of continental high pressure.(6) In global model forecasting, the CMA model cannot report a blocking high pressure above 96 hours of time. The EC deterministic model can predict heavy precipitation processes within a 120 hour time frame, and the ensemble forecast can have a predictable time frame of up to 7 days.