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华北夏季中尺度对流系统西行过程的特征分析

Analysis of characteristics of mesoscale convective systems westward propagation process during summer in North China

  • 摘要: 华北地区夏季中尺度对流系统(mesoscale convective system, MCS)西行过程常伴随暴雨等强对流天气,往往给当地带来严重气象灾害。为了解MCS西行的基本特征,利用红外亮温数据和逐小时融合降水产品(combined precipitation, COMB),统计分析了华北地区2008—2018年6—8月MCS西行过程的特征。结果表明:(1) 华北夏季MCS西行的主要移动方向为西-西南向,频数从午后开始显著增长,峰值出现在17—18时(北京时,下同),08时最低。(2) 将MCS西行过程按降水强度分为一般强度降水过程和短时强降水过程,对比分析发现短时强降水MCS过程的活跃区域主要集中在河北南部、河南北部以及山东的中西部地区;而一般强度降水MCS过程的活跃区域较为分散。(3) 短时强降水MCS过程的云顶亮温较低,云顶面积较大,降水率平均值为34 mm·h−1,累积降水量的大值区位于太行山山脉东部的陡峭迎风坡、泰山山脉,以及山脉与平原的过渡地带;一般强度降水过程的云顶亮温较高,云顶面积较小,平均降水强度为8.7 mm·h−1,大值中心位于华北西部吕梁山附近,是因为MCS西行频数较多的缘故。专门针对MCS西行的研究是对MCS理论的补充,能够为华北暴雨的预警预报和防灾减灾提供理论参考。

     

    Abstract: In North China, the westward movement of summer mesoscale convective systems (MCS) is often accompanied by severe convective weather such as heavy rainfall, frequently causing significant meteorological disasters. To understand the basic characteristics of the westward-moving MCS, the infrared brightness temperature data and the hourly combined precipitation products (COMB) were used to analyze the statistical characteristics of the westward-moving MCS during the summer season from June to August during 2008-2018 in North China. The results are as follows. (1) The main moving direction of MCS during summer in North China is west-southwest. The frequency begins to increase significantly in the afternoon, peaks around 17:00-18:00 (BJT) in the evening, and has the lowest occurrence probability at 08:00. (2) The westward-moving MCS are classified into moderate-intensity precipitation and short-duration heavy precipitation according to precipitation intensity. A comparative analysis reveals that the active areas of short-duration heavy precipitation MCS processes are mainly concentrated in southern Hebei, northern Henan, and the central and western regions of Shandong; while the active areas of moderate-intensity precipitation MCS processes are relatively scattered. (3) The cloud-top brightness temperature of short-duration heavy precipitation MCS processes is relatively low, with a large cloud-top area and an average precipitation rate of 34 mm·h−1. The areas with large cumulative precipitation are located in the steep windward slopes on the eastern side of the Taihang Mountains, the Taishan Mountains, and the transition zones between mountains and plains. The cloud-top brightness temperature of moderate-intensity precipitation processes is relatively high, with a small cloud-top area, and an average precipitation intensity is 8.7 mm·h−1. The large-value center is located near the Lvliang Mountains in western North China, due to the relatively high frequency of MCS moving westward. This is a specialized study on westward-moving MCS, which serves as a valuable supplement to MCS theory and provides a theoretical reference for early warning, forecasting, and disaster prevention related to heavy rainfall in North China.

     

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