江淮梅雨期持续性暴雨和极端强降水事件的位涡比较分析
Comparative analysis of potential vorticity between persistent rainstorm and extreme intense rainfall events during the Yangtze-Huaihe Meiyu period
毛江玉 1赵雪洁 2刘屹岷 1何编 1吴国雄1
作者信息
- 1. 中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室(LASG),北京 100029
- 2. 中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室(LASG),北京 100029;苏州市职业大学数理部,苏州 215104
- 折叠
摘要
基于我国气象台站观测降水数据和欧洲中期天气预报中心(ECMWF)第五代大气再分析资料(ERA5),从位势涡度(位涡)强迫垂直运动的角度,揭示了江淮梅雨期持续性暴雨和极端强降水事件的动力学机制及差异.基于改进的两种事件定义方法,识别出1979-2020年梅雨区共发生了24次持续性暴雨事件及24次极端强降水事件.事件合成分析表明,持续性暴雨事件最强雨带主要位于长江及其以南地区,而极端强降水事件最强雨带则位于长江及其以北地区.持续性暴雨事件与热带大气低频振荡密切相关,其中南亚高压偏东、西北太平洋副热带高压偏西,因而高空偏南的西风急流附近具有高值位涡的干冷空气向南和向低空入侵,在中低层与西南暖湿气流辐合并形成梅雨锋区.极端强降水事件更大程度地取决于偏北的西风急流南侧的高空辐散及位涡强迫的强冷空气.对于极端强降水事件位涡收支的定量诊断表明,在强降水达到峰值及之前,高层负的位涡倾向主要由负的垂直位涡平流所导致,而中低层正的位涡倾向则主要取决于垂直非绝热加热的位涡制造和垂直位涡平流.结合典型个例的垂直速度分解,进一步证实梅雨区上空水平位涡平流随高度增加的垂直分布激发的上升运动分量在极端强降水事件起着重要作用.
Abstract
In this study,based on the rainfall measurements from weather stations over China and atmospheric reanalysis products from the fifth-generation European Centre for Medium-Range Weather Forecasts(ECMWF)reanalysis(ERA5)during the period of 1979-2020,the dynamic mechanisms and differences of persistent rainstorm(PRS)events and extreme intense rainfall(EIR)events over the Yangtze-Huai-he Meiyu domain(YMD)are revealed from the perspective of potential vorticity(PV)-forced vertical motion.According to the improved defi-nitions of PRS and EIR events,24 PRS events and 24 EIR cases are identified over the YMD during the Meiyu period from 1979 to 2020.Composite analyses for the two types of events demonstrate that the most intense rainband of PRS events is mainly located in the Yangtze Riv-er and over the southern regions of it,while for the EIR,the most intense rainband is located in the Yangtze River and over the northern re-gions of it.The PRS events are found to be closely related to tropical atmospheric intraseasonal oscillation,during which the upper-tropo-spheric South Asian high extends more eastward,while the northwestern Pacific subtropical anticyclone in the lower and middle troposphere shifts more westward.Thus,the dry and cold air with high-PV around the upper-tropospheric westerly jet located more southward latitudes tends to intrude equatorward and downward,converging with the warm and moist air from the southwest in the lower and middle troposphere to form Meiyu front.However,the EIR events are more dependent to a greater extent on the upper-tropospheric divergence on the southern side of the westerly jet located more northward latitudes and PV-forced downward-intruding cold air.The quantitative diagnoses of PV bud-get for EIR events show that before and during the peak of intense rainfall,the net negative PV tendency in the upper troposphere is mainly dominated by the negative vertical PV advection,while the positive PV tendency in the middle and lower troposphere is mainly caused by the PV generation due to the vertically non-uniform diabatic heating and vertical PV advection.The vertical velocity decomposition of a typical EIR event further demonstrates that the component of ascending velocity forced by the vertical increase of horizontal PV advection plays an important role in triggering the EIR event.
关键词
江淮梅雨/持续性暴雨/极端强降水/位涡Key words
Yangtze-Huaihe Meiyu/persistent rainstorm/extreme intense rainfall/potential vorticity引用本文复制引用
基金项目
国家自然科学基金项目(42288101)
国家自然科学基金项目(42175076)
广东省基础与应用基础研究重大项目(2020B0301030004)
出版年
2024
NETL
NSTL
万方数据