Mechanisms of Persistent Extreme Rainfall Event in North China, July 2023: Role of Atmospheric Diabatic Heating

During 29th July–1st August in 2023, a persistent heavy rainfall event (“23·7” event) hit North China causing severe floods, enormous infrastructure damage, and large economy loss. Observational analysis shows that the extremely large accumulation of precipitation and long duration of this event are closely related to a slowly moving landfall typhoon “Dusuari” over North China due to the blocking effect of an anomalous high over the mid-high latitude Asia. The anomalous southeasterly flow induced by the typhoon “Dusuari” and another typhoon “Khanun” over the East China Sea jointly built a highly efficient channel of water vapor supply from southern oceans toward North China. A water vapor budget analysis indicates that precipitation of this event is mainly caused by the dynamic process involving strong ascending motion. Accompanying strong water vapor transportation and convergence over North China, large amount of latent heat is released in the middle and the lower troposphere. The physical mechanisms of heavy rainfall-induced diabatic heating in maintaining the precipitation over North China is further investigated using statistical analysis and numerical experiments. On one hand, the latent heating released by heavy rainfall induces significant uplifting flows which causes more precipitation. On the other hand, the heavy rainfall-induced diabatic heating contributes to the enhancement of the westward extension of high-pressure dam over mid-high latitude through a regional meridional circulation. This strengthened high-pressure dam sustained the cyclonic circulation of “Dusuari” over North China, leading to continuous heavy rainfall there.