“7·20”郑州特大暴雨的多模式对比及高分辨率区域模式预报分析

Multi-model comparison and high-resolution regional model forecast analysis for the “7·20” Zhengzhou severe heavy rain

摘要:

7月20日郑州遭遇特大暴雨，郑州站单日降水量（552.5 mm）和1 h降水量（201.9 mm）皆打破了该站建站以来的历史纪录。本文采用地面降水观测、静止卫星观测、再分析资料和数值模式预报数据对此次过程开展了多模式预报偏差原因分析和江苏省精细化天气分析和预报系统（Precision Weather Analysis and Forecasting System，PWAFS）的极端强降水预报能力分析。主要结论：1）此次暴雨过程因副热带高压西伸与台风”烟花”加强使二者之间的东风急流加强，并叠加地形的抬升作用而引起，前者提供了大尺度水汽条件，后者提供了局部动力条件；2）欧洲中期天气预报中心（European Center for Medium-range Weather Forecasts，ECMWF）模式和美国国家环境预报中心全球预报系统（Global Forecast System，GFS）的降水落区较好，中心略偏北，但强度显著偏低。PWAFS模式预报的降水量级高于全球模式，且具有沿地形分布的特征，但存在降水位置偏西和降水范围更为孤立等问题。3）结合再分析资料和PWAFS预报，对应此次强降水区域，7月20日白天存在中低层切变发展成闭合低压系统的过程，为对流发展提供了动力条件。

Abstract:

The "7·20" Zhengzhou severe heavy rain broke the Zhengzhou observed station's 1-hour precipitation record (201.9 mm) as well as the daily precipitation record (552 mm).In addition, there was a catastrophic rainfall process that left hundreds dead and dozens missing.High intensity, wide-coverage, and terrain-specific distribution were characteristics of this severe rainfall.This study used gauge precipitation observations, geostationary satellite observations, reanalysis data, and multiple numerical model forecasts to analyze the models' forecast deviations and Jiangsu Precision Weather Analysis and Forecasting System's (PWAFS) ability in forecasting extreme rainfall events.Here are the main conclusions:1) The heavy rain was caused by a strengthened easterly flow between the westward extended subtropical high and typhoon "In-fa", combined with a topographic lift.2) In terms of heavy rain, the European Center for Medium-range Weather Forecasts (ECMWF) and the Global Forecast System(GFS) performed well, but the precipitation center was slightly northerly biased and the intensity was noticeably lower than observation.PWAFS had a better performance in precipitation intensity forecasting and a distribution pattern along the terrain.However, PWAFS shows isolated rain centers that are biased to the west.3) Based on the PWAFS forecasts and reanalysis data, it was found that on 20 July over the heavy rain area, a shear line eventually developed into a deep low-pressure system, which provided favorable dynamic conditions for convective development.