四川盆地春季一次罕见区域性大风过程特征及成因分析

Analysis of characteristics and mechanism of a rare regional gale event in the Sichuan Basin during Spring

摘要

四川盆地地形特殊、大风事件少见，对其特征及具体成因认识尚不充分。利用加密气象观测站、探空、X 波段相控阵雷达、S 波段雷达及拼图、ERA5 再分析等资料，对 2022 年 4 月 11—12 日四川盆地一次罕见区域性大风过程特征及成因进行分析，并对强雷暴大风落区的可预报性和 X 波段雷达的应用进行了探究。结果表明：(1) 高空槽东移携带干冷空气叠加在低层暖脊之上，配合地面冷锋和辐合线，为强对流的发生提供了有利的环境条件。(2) 过程极大风速的空间分布具有明显的地域差异。四川盆地北部大风强度偏弱，多为 8~9 级，但分布广泛；盆地中部一线，大风强度最强，达 11~13 级，且呈西北-东南线状；而盆地南部的大风站数极少，但强度仍可达 12 级。(3) 大风强度和分布特征与其成因直接相关。盆地北部受天气尺度冷锋过境影响，形成大范围混合性大风；盆地南部暖湿气流北上触发对流，出现强且分散的雷暴大风；而中部一线，冷暖空气交汇触发飑线等强烈对流天气，强下沉有效位能造成的对流下沉支与密度流共同作用，形成西北—东南向线状分布的大风。(4) 此次强雷暴大风精细落区具有一定的可预报性，地面 3 h 负变压区能表征冷锋前暖平流强度，并提前 1~2 h 指示较周边地区更强的对流风暴发生位置。(5) X 波段相控阵雷达可观测到直接造成重庆中心城区雷暴大风的 γ 中尺度对流风暴精细演变过程，大风出现前主体回波前侧新生单体的雷达反射率因子质心在 10 min 内快速下降，该特征可提前 10~20 min 预警雷暴大风。

Abstract

Due to the special topography and rare gale events in the Sichuan Basin, its characteristics and mechanism are not fully understood. Using the meteorological observation station data, sounding data, X-band phased array radar, S-band radar and its mosaic, the fifth-generation European Centre for Medium-Range Weather Forecasts reanalysis data (ERA5), this study analyzes the characteristics and mechanism of a rare regional gale event occurring in the Sichuan Basin on April 11-12 2022, and further explores the predictability of strong gale locations and application of X-band radar. The results are as follows. (1) The eastward-moving upper-level trough brings dry and cold air which overlays a low-level warm ridge, aligning with the ground cold front and convergence line to create favorable conditions for deep convection. (2) The distribution of gales exhibits evident regional variations. In the northern Sichuan Basin, gale intensity is relatively weak, mostly force 8-9, but widely distributed. In the central basin, intensity is the strongest, reaching force 11-13 scale and distributed in a northwest-southeast linear pattern. In the southern basin, only a few stations recorded gales, yet the intensity exceed force 12. (3) The intensity and distribution characteristics of gales are directly linked to their formation mechanisms. The northern basin experienced mixed-type gusts due to the passage of synoptic-scale cold fronts. The northward intrusion of warm and moist airflow into the southern basin triggered convection, producing strong and scattered thunderstorm gusts. In the central basin, the convergence of warm and cold air leads to severe convection such as a squall line. The combined effects of convective downdrafts caused by the downdraft convective available potential energy and density currents form a northwest-southeast linear distribution of gusts. (4) The precise locations of these thunderstorm wind gusts show some predictability. The three-hour negative ground pressure variation areas indicate the intensity of warm advection ahead of the cold front and provide a 1-2-hour advance indication of the potential locations of stronger convective storms are more likely than in surrounding areas. (5) X-band phased array radar provides detailed observations of γ-mesoscale convective storms that directly caused the wind gusts in Chongqing. Observations reveal that prior to the onset of wind gusts, the radar reflectivity centroid of the new cell rapidly descends within 10 minutes, which allows for a 10-20-minute lead time to issue warnings for severe thunderstorm wind gusts.

关键词

雷暴大风 / 强对流 / X 波段相控阵雷达 / 3 h 变压

Key words

thunderstorm wind gust / severe convection / X-band phased array radar / 3-hour pressure variation

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基金资助

重庆市科技局技术创新与应用发展专项重点项目(CSTB2023TIAD-KPX0065)

四川省科技厅科技计划项目(2023YFS0430)

中国气象局复盘总结专项(FPZJ2023-108)

高原与盆地暴雨旱涝灾害四川省重点实验室开放研究基金项目(SZKT202206)

重庆市气象局创新团队项目(ZHCXTD-202003)