2020年7月4日豫西北大暴雨数值分析

Numerical Analysis of a Cloudburst on July 4th 2020 in Northwest Henan

为了研究2020年7月4日豫西北地区的一次大暴雨发展过程,本文应用常规观测资料、欧洲气象中心ERA5再分析资料以及探空资料,利用常规观测资料对豫西北地区此次降水的环流背景、影响系统进行天气学分析;利用再分析资料以及探空资料对此次降水的水汽条件、动力条件和不稳定能量等方面进行数值分析。结果表明:1) 此次大暴雨过程中高纬地区为“两槽一脊”的环流形势,西槽后引导冷空气经新疆地区南压,与暖湿空气交汇,促进不稳定能量释放。豫西北地区上游短波槽发展,有正的相对涡度平流,使局地涡度增加。低层辐合,高层辐散的高低空配置,有利于垂直上升运动加强,且强度超过0.8 Pa/s,为大暴雨天气提供了动力条件。2) 此次降水过程水汽充足,来自孟加拉湾以及我国南海的暖湿气流在华南地区汇合,受副高脊线以及小高压影响,不断向豫西北地区输送。3) 降水过程期间,豫西北地区是假相当位温高值区,河南省以南的高值区,通过豫中地区向北输送不稳定能量。垂直剖面图上,500 hPa为分界点,且假相当位温分布密集。500 hPa以上,假相当位温递增,大气层结稳定;500 hPa以下,地面至600 hPa附近,假相当位温递减,且∆θse600-850达到了−36℃,不稳定能量较强。4) 探空资料中,对流有效位能(Convective Available Potential Energy, CAPE)先增大而后减小,对流抑制能量(Convective Inhibition, CIN)逐渐增大,两个物理量的值在大暴雨过程前后变化明显,表明了此次大暴雨过程中能量的积聚情况,对暴雨的发生发展有一定的指示作用。

In order to study the development process of a cloudburst in northwest Henan province on July 4th, 2020, in this paper, the general observation data, the ERA5 reanalysis data of the European meteorological center and the sounding data were used. Synoptic analysis was made on the circulation background and influence system of the cloudburst in the northwest of Henan province by using general observation data;numerical analysis was made on the water vapor condition, dynamic condition and unstable energy of the process by using the reanalysis data and sounding data. The results showed that: 1) The circulation pattern of “Two troughs and one ridge” in the high latitude area, the cold air at the rear of the western trough would pass through the south of Xinjiang region and converged with the warm and humid air to promote the release of unstable energy. There was positive relative vorticity advection in the upper short-wave troughs in northwest Henan, which increased the local vorticity. The low level convergence and high level divergence were favorable for strengthening the vertical ascending motion, and the intensity was more than 0.8 Pa/s, which provided the dynamic condition for heavy rain. 2) The moisture was sufficient. The warm and humid air from Bay of Bengal and South China Sea converged in South China, and under the influence of the western Pacific subtropical high and the high-pressure system in northwest Henan, it continuously transported water vapor to northwest Henan. 3) In the process of precipitation, the northwest area of Henan province was the high value area of pseudo-equivalent potential temperature;south of Henan province was also a high-value region of pseudo-equivalent potential temperature, sending unstable energy northward through central Henan. On the vertical section, 500 hPa level was the boundary point, and the distribution of pseudo-equivalent potential temperature was dense. Above 500 hPa level, the pseudo-equivalent potential temperature increased and the atmospheric stratification was stable;below 500 hPa, ground to near 600 hPa, the pseudo-equivalent potential temperature decreased, ∆θse600-850 reached −36˚C, and the unstable energy was strong. 4) In the sounding data, CAPE and CIN changed obviously before and after the process, which indicated the energy accumulation during the heavy rain process, which had indication for the occurrence and development of heavy rain.