CHARACTERISTICS OF THUNDERSTORM ACTIVITY IN THE NORTHWEST PACIFIC BASED ON LIGHTNING CLUSTERING METHOD
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摘要: 利用2010—2018年全球闪电定位网(WWLLN)观测资料, 采用基于闪电密度的空间聚类算法(DBSCAN)建立了西北太平洋地区雷暴数据集, 研究了该区域雷暴的时空分布特征, 并进行海陆差异对比。研究结果表明, 在合理设定DBSCAN参数阈值的条件下, 基于WWLLN闪电聚类的雷暴与天气雷达观测在时空分布和过程演变上具有一致性。西北太平洋区域的日均雷暴数为3 869, 雷暴的闪电密集区平均面积为557.91km2, 平均延展尺度为31.99 km, 平均闪电频次为33 str/(h·thu)。在空间分布上, 东南亚沿海地区与热带岛屿的雷暴活动最强, 南海的雷暴活动强于深海。距离海岸线越近的海域其雷暴面积越大。在季节分布上, 整个区域雷暴活动在夏季(6—8月)达到全年最强, 南海雷暴活动6月达到峰值, 而日本东部近海海域的雷暴活动则在冬季达到最强。我国内陆南方地区雷暴3月开始显著增多, 雷暴平均面积达到最大, 但雷暴平均闪电频次5月才达到峰值。在日变化方面, 陆地雷暴活动呈现典型的单峰型特征, 大部分雷暴发生在午后及傍晚。海洋雷暴日变化则较为平缓, 南海具有其独特的雷暴日变化特征。Abstract: Based on lightning data from the World Wide Lightning Location Network(WWLLN) from 2010 to 2018, and the algorithm of Density-Based Spatial Clustering of Application with Noise(DBSCAN), this study establishes a thunderstorm dataset of the Northwestern Pacific. The temporal and spatial distribution characteristics of thunderstorms in this region are studied, and the characteristics of thunderstorms over land and ocean are compared. The results show that when the parameter thresholds of the DBSCAN algorithm are reasonably performed, the temporal and spatial distribution and evolution of thunderstorms based on WWLLN lightning clusters are consistent with the observations of weather radars.The average daily number, the average area of lightning cluster, the average extension scale, and the average lightning frequency of thunderstorms in the Northwestern Pacific region are 3869, 557.91 km2, 31.99 km, and 33 str/(h · thu), respectively. In terms of spatial distribution, thunderstorm activities are the most intense in the coastal areas of Southeast Asia and tropical islands. In addition, thunderstorm activities in the South China Sea are stronger than that in the deep ocean. The average area of offshore thunderstorms increases with the shortening of its distance from the coastline. As for seasonal variation, thunderstorm activities throughout the region reach their peak in summer(June to August) with the peak of that over the South China Sea in June, while thunderstorm activities off the coast of eastern Japan reach their peak in winter. In the southern part of China's inland areas, thunderstorm activities begin to increase significantly in March and the average area of thunderstorms reaches its maximum at that time; however, the average lightning frequency of thunderstorms reaches its peak in May. In terms of diurnal variation, the distribution of continental thunderstorm activities is typical unimodal, and most thunderstorms occur in the afternoon and evening. The diurnal variation of marine thunderstorms is relatively moderate, and a unique diurnal pattern can be found in the thunderstorm activities in the South China Sea.
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Key words:
- thunderstorm /
- lightning /
- WWLLN /
- DBSCAN /
- Northwestern Pacific
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表 1 雷暴特征参量
特征参量 定义 单位 雷暴发生时间 聚类成该雷暴闪电的开始时间 年月日时 雷暴位置 聚类成该雷暴闪电的质心位置 经纬度 雷暴面积 聚类成该雷暴闪电的最小外接凸多边形的面积 km2 雷暴延展尺度 聚类成该雷暴闪电中相距最远的2个闪电之间的距离 km 雷暴闪电频次 单位时间内聚类成该雷暴中的闪电数 str/h -
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