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北京地区正地闪时间分布及波形特征
Temporal Distribution and Waveform Characteristics of Positive Cloud-to-ground Lightning in Beijing Area
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摘要: 为了给雷电防护及机理研究提供必要的基础数据，利用闪电定位资料和电场快慢变化资料，对北京地区正地闪的时间分布规律及波形特征进行了统计分析。结果表明：北京地区正地闪分布随月份而不同，较大频次出现在5—7月，较高比例出现在春、秋季（3—5月和10—11月）；而一天内的正、负地闪分布具有反对应关系，正地闪在傍晚（15:00—21:00，北京时）具有较大的频次和较高的比例，且该比例随闪电频次增大而呈减少的趋势；正地闪多为单次回击，多回击正地闪数占正地闪总数的3.89%；正地闪波形上升沿时间分布范围为5~28 μs，平均为11.55 μs，慢前沿时间分布在2.8~23.6 μs之间，平均值为9.41 μs，慢前沿幅度与回击峰值比为53%，过零时间为43.97 μs，负反冲深度均值为20.75%，辐射场归一化到100 km的回击场强峰值为13.66 V/m；正地闪连续电流持续时间平均值为113 ms，具有连续电流的正地闪比例高达69.2%，其中48.7%具有长连续电流过程。Abstract: The temporal distribution and waveform characteristics for positive cloud to ground lightning (PCG) vary in different regions. The research on characteristics of PCG in Beijing Area is still not enough up to now. Based on the lightning location data from March to November in 2004 and 2005, the temporal distribution of PCG in Beijing Area is analyzed. The waveform characteristics are also investigated using the data of electric field change. The results show that from May to July there are more PCG happening than other seasons in Beijing Area. The PCG occupies 55.3% of all lightning events from March to May and from October to November, while the percentage of PCG is only 10.88% for the whole year. On the other hand, the distribution of PCG in Beijing also changes with time in a day, with a high frequency of PCG and a large percentage up to 16.2% during 15:00—21:00. It's also found that the temporal distribution is inverse correlation between PCG and negative cloud to ground lightning (NCG) in a day. There is a decreasing tendency of PCG lightning with an increase of cloud to ground (CG) lightning. For most of PCG there is only one return stroke and the percentage of PCG with multiple return strokes is only 3.89%. The PCG with multiple return strokes mainly occurs in May and November and during 15:40—17:20 in a day. The waveform parameters and the characteristics of continuing current are given by statistics. The rising time of return stroke is between 5—28 μs, with a mean value of 11.55 μs. The time of slow front is between 2.8—23.6 μs with 9.41 μs on average. The ratio between the amplitude of slow front and the peak of return peak is 53%. The time of recovering to zero is 43.97 μs and the depth of the dip is 20.75%. The average value of return stroke peak after being normalized to 100 km is 13.66 V·m-1. Most of PCG contain continuing current process. The percentage of PCG with continuing current is 69.2%, 48.7% of which lead to long continuing current. The average lasting time of continuing current is 113 ms.
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图 2 2004, 2005年3-11月平均地闪频次分布图
Fig. 2 The distribution of cloud-to-ground lightning from March to November in 2004 and 2005
图 5 多回击正地闪日分布规律
Fig. 5 Daily distribution of PCG lightning with multiple return strokes
图 7 正地闪参数统计图（a）上升沿时间，（b）慢前沿时间，（c）过零时间，（d）回击峰值，（e）慢前沿峰值比，（f）负反冲深度
Fig. 7 Waveform parameters of PCG lightning (a) rise time, (b) slow front time, (c) the time of recovering to zero, (d) the peak of return stroke, (e) the ratio between the amplitude of slow front and stroke peak, (f) the depth of the dip
图 8 电场慢变化曲线上的连续电流
Fig. 8 Continuing current in the curve of slow electric field change
表 1 正、负地闪分布统计
Table 1 Distribution of positive and negative cloud-to-ground lightning
表 2 连续电流统计表
Table 2 Statistics of continuing current
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