Mechanism Analysis of a Wintertime Extreme Persistent Heavy Rainfall Event in Hainan Island

Abstract

AbstractExtremely persistent heavy rainfall (EPHR) events frequently occur in southern China, but its mechanisms of initiation and maintenance are not well understood, leading to difficulties in accurately forecasting. Thus, we investigated a typical EPHR case that occurred on Hainan Island on 14 December 2013 (UTC) using convection‐resolving WRF simulation and multi‐source observations. Results revealed that the intrusion of the cold surge, the formation of the quasi‐stationary mesoscale perturbed vortex (MPV) caused by deflected southerly winds and northeasterly winds, and local topographic forcing are three crucial factors for this EPHR event. Firstly, the invasion of cold surge provides a favorable thermal condition for strong convection, as the CAPE around Wanning city substantially increases during the invasion, greatly enhancing atmospheric instability. Secondly, the event is triggered around 06:00 UTC due to the low‐level convergence of easterly and northeasterly winds. The confrontation of easterly and northeasterly winds forms an MPV in the middle boundary layer, which plays an important role in the maintenance of strong convection. In the following hours, the easterly airflow is continuously deflected northward, but its southerly wind components are largely balanced by the northerly counterpart from the cold surge, so the MPV remained quasi‐stationary until 18:00 UTC, resulting in persistent heavy rainfall in Wanning city. Finally, the sensitivity experiments show that topographic blocking and friction effects also play a decisive role in this EPHR process. Overall, this study fully illustrates the special formation mechanism of a wintertime EPHR event, deepening the mechanistic understanding of EPHR events.