皖北一次特大暴雨过程中边界层急流日变化特征 及其对暴雨形成的影响分析

利用多普勒雷达风廓线产品、ERA5再分析资料和WRF模式,分析了2018年6月27日皖北一次特大暴雨过程中边界层急流的日变化特征及其对特大暴雨形成的作用。结果表明:特大暴雨发生期间存在边界层急流,急流最强达到了18 m·s^-1,强降水主要发生在急流快速增强的时段;急流前部的边界层辐合线是对流的触发因子,强降水落区位于急流核前部。急流为对流系统加强提供水汽和能量,且边界层急流和雷暴高压对峙使对流系统稳定少动,在对流系统西侧激发新的对流单体,有利于特大暴雨的发生;此次过程中天气系统的影响时间主要决定了强降水的落区,而边界层急流的日变化决定了强降水发生的时间段;边界层急流在夜间具有超地转特征,午后具有次地转特征,地转偏差和水平平流作用是导致夜间边界层急流增强的主要原因。

Analysis of diurnal variation characteristics of the boundary layer jet during an extremely heavy rainstorm in northern Anhui and its impact on rainstorm formation

Based on Doppler radar wind profile products, ERA5 reanalysis data and WRF model simulations,an extremely heavy rainstorm occurred on the night of June 27, 2018 in northern Anhui were analyzed. The diurnal variation characteristics of the boundary layer jet during the rainstorm and its impact on rainstorm formation are investigated. During the heavy rainstorm, a boundary layer jet with a maximum wind speed of 18 m·s^-1 is observed. Heavy rainfall mainly occurs along with the rapid intensification of the jet. The convection can be triggered by the boundary layer convergence line at the front of the jet core where the heavy rainfall appears, and the boundary layer jet can provide moisture and energy for the strengthening of the convective system. Besides, the confrontation between the boundary layer jet and thunderstorm high makes the convective system more stable, and this situation favors the continuously triggering of convective cells to the west, which is conducive to the occurrence of heavy rainfall. During this rainstorm, the precipitation area is mainly determined by the influence time of the weather system, while the time of precipitation occurrence is determined by the diurnal variation of the boundary layer jet. The boundary layer jet exhibits a super-geostrophic feature in the night and sub-geostrophic feature in the afternoon, andthe enhancement of the boundary layer jet in the night can attribute to geostrophic departure and associated horizontal advections.