基于LLS的陕西省近10年地闪时空分布特征

基于2005—2015年闪电观测和NCEP再分析资料，对陕西省地闪时空分布及气候环流特征进行统计分析。结果表明，近10年来陕西地闪呈波动上升趋势，平均12.8万次/a，平均密度为0.67 fl/(km2·a)，负闪占总地闪93.7%。每年3月地闪开始逐渐活跃，年平均强度最大；8月地闪最活跃，盛夏总频次超过全年的75%。陕西地闪频次日变化呈单峰型，峰值在16—17时，下午至前半夜活跃；对应时段在延安周边地区的闪电密集区东移南压明显。陕北地闪日变化幅度明显偏大，关中峰值时段偏晚其他地方约3 h，陕南地闪夜发性明显。陕西地闪主要分布在黄土高原东侧、南侧和秦巴山脉南麓的迎风坡，正闪主要位于陕北和陕南西部局地。相比其他省市，陕西地闪密度明显偏小，但平均强度偏大。陕西地闪活动与西太平洋副热带高压的南北进退变化基本一致，随着季节变化而出现北跳、扩大和迅速消散过程。春季闪电主要位于陕南；初夏陕北南部至渭北明显增多；盛夏闪电最强，北部闪电中心区东移至黄河沿线，关中闪电频次增幅远大于陕北、陕南；夏末闪电迅速消散。陕西盛夏闪电主要包括4种气候类型，不同类型的环流特征差异显著。25 °N以北、80~100 °E附近关键区青藏高压强盛、陕西周边温度槽落后高度槽、相对明显的不稳定层结条件是盛夏闪电活跃的有利环流背景。 

SPATIAL AND TEMPORAL DISTRIBUTION CHARACTERISTICS OF CLOUD-TO-GROUND LIGHTNING DURING THE LAST DECADE IN SHAANXI PROVINCE BASED ON LLS

Based on the cloud-to-ground (CG) lightning data from 2005 to 2015 probed by Lightning Location System (LLS) in Shaanxi province and NCEP reanalysis data, the spatial and temporal distribution characteristics of lightning and circulation characteristics are analyzed the first time by comparing with other regions in China. The results show that CG lightning in Shaanxi has a fluctuating rising tendency during the 10 years, and the annual average frequency is 128 000, the CG lightning average density is 0.67 fl/(km2·a) and negative frequency is about 93.7% of the total. Lightning is gradually active from March and its monthly average intensity reaches the annual maximum. The number of CG lightning in midsummer accounts for 75% of the annual total and reaches the maximum in August. CG lightning in Shaanxi is active from afternoon to midnight and high-density areas around Yan'an move eastward and southward obviously. Daily variation of CG lightning frequency peaks during 16:00-17:00, and the amplitude of daily variation in the northern part is obviously larger than in other areas. Daily peak time of CG lightning in Guanzhong is 3 hours later than in other areas. CG lightning is relatively active at night in southern Shaanxi than in other areas. Concentrated CG lightning areas in Shaanxi are mainly distributed in the east and south sides of Loess Plateau, and south sides of Qinling and Bashan Mountains, all of which are windward slopes and altitude gradients are high. Lightning activity area moves northward, and expands and decays quickly with season, which are significant in Shaanxi, and the trend of which is consistent with climatic change of West Pacific Subtropical High. Spring CG lightning is mainly located in the southern part of the province. Lightning reduced significantly in the south and increased obviously in the south part of Northern Shaanxi and Weibei during early summer. During midsummer, active areas and intensity reach annual maximum and the northern lightning center moves eastward to the Yellow River. Meanwhile, increasing amplitude of monthly frequency in Guanzhong is much larger than in other parts. Lightning dissipates rapidly in late summer. Based on monthly change modes of lightning density during midsummer in Shaanxi, there are mainly four climate types to describe the temporal and spatial characteristics, and the features of the four types have significant difference. The circulation characteristics, including Tibetan High near the critical region around north to 25 °N and from 80~100 °E, a temperature trough lagging behind a height trough in the areas surrounding Shaanxi and relatively obvious unstable stratification, are favorable to lightning during midsummer.