Multiscale Processes of Heavy Rainfall over East Asia in Summer 2020: Diurnal Cycle in Response to Synoptic Disturbances

Abstract Multiscale processes from synoptic disturbances to diurnal cycles during the record-breaking heavy rainfall in summer 2020 were examined this study. The consisted of eight episodes, each lasting about 5 days, and associated with two types disturbances. Type-1 episodes featured a northwestward extending western Pacific subtropical high (WPSH), while Type-2 had approaching midlatitude troughs southward retreat WPSH. Each episode 2–3 occurrences nocturnal low-level jets (NLLJs), close association intense early morning. NLLJs formed partly due geostrophic wind by increased pressure gradients under both also driven ageostrophic that veered maximum southerlies at late night boundary-layer inertial oscillation. amplitudes remarkably after onset which WPSH provided strong daytime heating solar radiation. By contrast, less changed episodes. strengthened mesoscale mean ascent, net moisture flux convergence, convective instability elevated warm moist air, led upscale growth MCSs northern terminus LLJ midnight. MCSs-induced Meiyu rainband was re-established Central China variations. findings highlight regional winds response can strongly regulate activities downscaling manner, thus produce rainfall.