2021年7月河南极端暴雨事件的位涡诊断和精细化预报

Potential Vorticity Analysis and Fine Forecast of Extreme Rainstorm Event in Henan Province in July 2021

2021年7月17~22日,河南省发生一次大范围极端暴雨事件。本文利用ERA5再分析资料,基于湿位涡和倾斜涡度发展理论对此次暴雨过程进行诊断分析,并考察高分辨率全球模式天机系统及欧洲中期天气预报中心业务预报系统对此次降水过程的预报能力。结果表明此次事件是中高—低纬系统相互作用、协同影响的结果。18~19日,来自中高纬度的高湿位涡沿倾斜的湿等熵面自对流层中高层向下入侵,降温和相对湿度增加,导致河南省西北部高涡度带的形成及对流层低层倾斜湿等熵面在河南省北部建立。20日受低纬台风的影响南风增强,沿倾斜湿等熵面的上滑运动增强,导致相对涡度迅猛发展,强降水发生。天机系统对此次强降水过程的预报能力较欧洲中期天气预报中心的业务预报系统好,能为业务部门提前发布预警信号提供科学支撑。湿位涡和倾斜涡度发展理论是暴雨的诊断及预报的有力理论基础,在再分析资料及模式预报数据中与降水强度、降水落区及雨带的移动均有很好的对应。

During 17–22 July 2021,a large-scale extreme rainstorm occurred in Henan Province.In this study,ERA5 reanalysis data were used to examine the heavy rainfall process based on the theory of moist potential vorticity and slantwise vorticity development.The forecast capabilities of the high-resolution global model Tianji system and the Integrated Forecast System(IFS)of ECMWF(European Centre for Medium-Range Weather Forecasts)were also investigated.The results show that this event results from the interaction and synergistic influence between the middle-high and low-latitude systems.From 18 to 19 July,the high moist potential vorticity in the middle and high latitudes intruded downward from the middle and upper troposphere along the slantwise moist isentropic surfaces.Together with the cooling and increased relative humidity,this led to the formation of the high vorticity zone in northwestern Henan Province and the establishment of the slantwise moist isentropic surfaces in the lower troposphere in northern Henan Province.On 20 July,a low-latitude typhoon strengthened the southerly wind and enhanced the up-sliding movement along the slantwise moist isentropic surface,resulting in the rapid development of relative vorticity and heavy rainfall.The Tianji system can forecast this heavy rain process better than IFS and can provide scientific support for the meteorological departments to issue early warnings.Moist potential vorticity and slantwise vorticity development theory are powerful theoretical bases for heavy rain analysis and forecast,which are well related to precipitation intensity,position,and movement in reanalysis and model forecast data.