重庆西部一次突发性山地暴雨中的爬流、绕流作用及湿位涡分析

Flow over and flow around effects and analysis of moist potential vorticity in a sudden mountain rainstorm in western Chongqing

摘要:

利用国家气象观测站降水量资料、FY-4A卫星云图资料和ERA5再分析资料,针对2023年7月26-28日发生在重庆西部地区的一次暴雨过程,通过爬流、绕流分解原理重点探讨地形激发的爬流与绕流对此次暴雨过程的动力作用,并以湿位涡为切入点分析了此次暴雨过程中热力特征,得到如下几点结论:(1)此次暴雨主要发生在夜间,呈现出[1]“双峰”态发展,持续时间长、强度大且覆盖范围广。中尺度对流系统(MCS)控制重庆西部地区,同时高原涡、西南涡共存以及台风“杜苏芮”的北上和其残余环流的输送作用为暴雨提供充足的水汽条件,从而促进降水强度增强并持续。(2)爬流运动对此次暴雨的贡献相较绕流运动更为显著,爬流分量强度与降水强度随时间的发展趋势、分布范围基本一致,爬流引起的垂直运动对大气抽吸效应具有增幅作用。(3)湿位涡正压分量(MPV1)和斜压分量(MPV2)在暴雨形成过程中均具有重要指示意义,对流层中低层MPV1负值区和MPV2正值区与降水区皆有较好的对应,特别是MPV1负值中心、MPV2正值中心强度变化与降水强度变化趋势吻合。

Abstract:

Based on the precipitation data from the national meteorological observatory, the FY-4A satellite cloud map data and the ERA5 reanalysis data for a rainstorm that occurred in the western part of Chongqing from July 26 to 28, 2023, through the principle of the decomposition of the creeping and circling currents to explore the dynamics of flow over and flow around currents inspired by the topography and to analyze the thermal characteristics of the rainstorm process by using moist potential vorticity as the entry point, the following conclusions are obtained: (1) The rainstorm mainly occurred at night and developed in a “bimodal” pattern with long duration, high intensity and wide coverage. The mesoscale convective system (MCS) controlled western Chongqing, while the coexistence of Tibetan Plateau vortics and southwestern vortex, as well as the northward movement of super typhoon Doksuri and the transport of its residual circulation provided sufficient water vapor for the rainstorm, thus promoting the enhancement of the intensity of precipitation and its persistence. (2) The contribution of the flow over current movement to the rainstorm is more significant than that of the cirrus movement, and the development trend and distribution range of the flow over current intensity and precipitation intensity over time are basically the same, and the vertical movement caused by the flow over current has an increase in atmospheric suction effect. (3) The positive pressure component (MPV1) and the oblique pressure component (MPV2) of the moist potential vorticity have important significance in the process of rainstorm formation, and the negative MPV1 and positive MPV2 zones in the middle and lower troposphere correspond well with the precipitation zone, especially the intensity changes of the negative MPV1 and positive MPV2 centers match the trend of the changes of the precipitation intensity.