东北冷涡背景下三类区域性强对流天气过程时空分布和环境特征对比分析

Spatiotemporal distributions and environmental characteristics of three types of regional severe convective weather processes associated with the Northeast China cold vortex

  • 摘要: 东北冷涡是造成中国暖季强对流的重要天气尺度系统之一。为对比东北冷涡与不同类型强对流过程的时空关系及其环境特征差异,基于欧洲中期天气预报中心第5代大气再分析数据和中国国家气象信息中心提供的逐时大风、降水观测资料,筛选了2017—2021年4—9月东北冷涡背景下9例雷暴大风型、9例强降水型以及8例混合型强对流天气过程,通过动态合成开展了分析研究。结果表明:(1)三类强天气过程相对于冷涡的时空分布差异明显:雷暴大风型过程,超过70%的雷暴大风出现在冷涡中心的西南部或南部;而混合型过程,超过70%的大风出现在冷涡中心的东南部或南部;混合型和强降水型过程中,短时强降水均主要出现在冷涡中心南部或东南部,但后者发生在冷涡东南部的比例更高;雷暴大风型和强降水型过程主要出现在东北冷涡的发展和成熟阶段,而混合型过程主要发生在东北冷涡的成熟阶段。(2)三类强天气过程的环流形势和环境条件差异显著。雷暴大风型过程多出现在5—6月,一般对应的东北冷涡更深厚,等温线更密集,大气环境偏干,存在气温垂直递减率大和强风垂直切变条件,雷暴大风多发生在冷涡南侧的锋区附近,对流层中、高层受干冷空气控制,叠加在低层比较浅薄的暖湿空气之上有利于大气层结条件不稳定的增强,降水粒子蒸发降温形成的下沉气流和地面冷池,叠加锋区辐合更有利于形成区域性地面强风;而强降水型过程多集中在7—8月,对应的东北冷涡强度较弱,等温线较稀疏,强降水一般出现在锋前靠近暖区一侧的强层结不稳定区域内,对应水汽充沛、整层暖湿的环境条件,中低层温差较小,风垂直切变较弱。混合型过程对应的月份和冷涡强度与强降水型过程更接近,水汽、高低层温差以及风垂直切变等环境条件介于上述两类过程之间,但下沉对流有效位能在三类过程中表现为最大。总体来看,相较于中国中、低海拔地区雷暴大风和短时强降水的环境特征而言,东北冷涡背景下的强天气过程对应更强的深层风垂直切变,具有更强的天气尺度动力强迫。

     

    Abstract: Northeast China cold vortex is one of the important synoptic-scale systems that causes severe convective weather in the warm season in China. In order to compare and analyze the spatiotemporal relationship between Northeast China cold vortex system and different types of severe convective weather processes and their environmental characteristics, based on the Fifth Generation Atmospheric Reanalysis Product of European Centre for Medium-Range Weather Forecasts and hourly precipitation and wind data provided by the National Meteorological Information Centre of China, severe convective weather processes including nine thunderstorm wind gust, nine heavy precipitation and eight hybrid type processes associated with Northeast China cold vortex from April to September of 2017—2021 are screened out. Comparative analysis is carried out by dynamic synthesis approach. The results are as follows: (1) Differences in the spatiotemporal distribution of the three types of severe weather processes and Northeast China cold vortex system are significant. In the thunderstorm wind gust processes, more than 70% of thunderstorm wind gusts occur in the southwest or south of the cold vortex center. However, in the hybrid type processes, more than 70% of thunderstorm wind gusts occur in the southeast or south of the cold vortex center. More than 75% of the heavy precipitation events occur in the south to southeast of the cold vortex center in both the hybrid type processes and heavy precipitation processes, but a higher proportion of the latter occur in the southeast of the cold vortex. Processes of thunderstorm wind gust and heavy precipitation mainly occur in the development and maturity stages of the Northeast China cold vortex, while hybrid processes mainly occur in the maturity stage. (2) The characteristics of circulation patterns and environmental conditions of the three types of severe weather processes are significantly different. Thunderstorm wind gust processes are concentrated from May to June, generally corresponding to a stronger cold vortex, denser 500 hPa isotherms, a drier atmosphere, a larger vertical temperature lapse rate and stronger vertical wind shear. Thunderstorm wind gusts mostly occur near the front area. The cold and dry advection in the middle troposphere superimposing on the shallow warm and wet air in the lower layer is conducive to the growth of unstable stratification in the frontal zone. Meanwhile, the downdraft formed by evaporation and cooling of precipitation particles couples with the convergence in the frontal zone, leading to the formation of regional surface wind gusts. Heavy precipitation processes are concentrated from July to August, corresponding to a weaker cold vortex and sparsely distributed isotherms. Heavy precipitation generally occurs in the region of strong unstable stratification near the warm sector ahead of the front, which corresponds to an environment with more water vapor content, smaller temperature differences between middle and low layers and weaker vertical wind shear. The time period and cold vortex intensity corresponding to the hybrid type processes are closer to that of the heavy precipitation processes, and the conditions of water vapor, vertical temperature lapse rate and vertical wind shear are between those for the above two types of processes, but DCAPE is the largest in the three types of processes. However, compared with the environmental characteristics of thunderstorm wind gusts and short-term heavy precipitation in the middle and low altitudes of China, the three types of severe weather processes under the background of the Northeast China cold vortex correspond to stronger deep vertical wind shear condition, indicating that the cold vortex system provides strong synoptic scale dynamic forcing.

     

/

返回文章
返回