Regulatory Factors of the Morning Peak of Summer Regional Precipitation Events Over the Middle and Lower Yangtze River Basin, China

Abstract The diurnal variation of regional precipitation events (RPE) over the Middle and Lower Yangtze River Basin (MLYRB) significantly affects human activities and serves as a key reference for weather forecasting. Here, the diurnal variation of summer RPE over MLYRB under two monsoonal synoptic types and their regulatory factors have been addressed. Results indicate that the morning peak of RPE is closely associated with the southwesterly low‐level jet (SLLJ) and western Pacific subtropical high (WPSH). Specifically, SLLJ begins to accelerate at night driven by the ageostrophic wind, facilitating the development of the precipitation system. Subsequently, the morning westward expansion of WPSH provides large‐scale circulation forcing, leading to the strongest lower‐tropospheric convergence and mid‐tropospheric ascending motion over MLYRB, thereby generating the morning peak of RPE. Additionally, RPE are accompanied by significant frontogenesis, and deformation frontogenesis plays a more significant role than divergence frontogenesis in regulating the morning peak of RPE.