广州地区地闪放电过程的观测及其特征分析

Observations of the Cloud-to-ground Lightning Discharge Process and Analysis on Its Characteristic in Guangzhou

为了比较系统地认识和理解地闪放电的特征,利用高速摄像机和闪电电磁场观测设备对广州地区的地闪放电过程进行了光、电、磁综合观测。分析结果表明:1)地闪预击穿过程由呈双极性的大脉冲簇组成,80%以上的脉冲的初始极性与其后的回击极性相同;2)负地闪首次回击前的下行梯级先导均表现出较多的分叉,平均发展速度为105 m/s量级,在向下发展过程中速度增加,通道亮度也逐渐增强;3)当下行先导接近高建筑物时,在高建筑物上常常激发产生出多个上行先导,不管是上行连接先导还是上行未连接先导,均可以发展传输上百m,甚至达到几百m,2维平均发展速度均在104～105 m/s量级;4)72%的负地闪具有多次回击,且有3次回击的比例最高,约为25%,回击之间的时间间隔主要在100ms之内,但最大可达500ms;5)在人工触发闪电中直接测量的回击电流峰值在6.67～31.93kA之间;6)65%的负地闪含有连续电流过程,41%的回击后跟随有连续电流,连续电流的持续时间在1～358ms之间;7)连续电流中的M分量持续时间主要集中在3ms以内,相邻M分量之间的时间间隔主要分布在0～10ms之间,2/3的第1个M分量起始时间与回击起始时间之间的时间间隔<2ms。

The cloud-ground lightning（CG） discharge processes in Guangzhou were observed in both optical and electromagnetic aspects by using high speed cameras and electric field change measurements for systematically investigating the characteristics of CG.According to the observation results and analysis on them,conclusions are carried out as follows.1） Both positive and negative CG＇s pre-breakdown processes were composed of large bi-polar pulse bursts,and 80% of the pulses have the same initial polarity as that of the following return strokes.2） A downward stepped leader before the first return-stroke（RS） of negative flashes present significant branches,and its average developing speed is the order of magnitude of 105 m/s.As a downward leader develops,the development can speed up and the luminosity of the leader channel mostly increases at the same time.3） When a downward leader gets closer to a tall building,several upward leaders will be initiated.The upward leaders,connected or not,can have lengths over 100 m or even several hundreds,with an average 2D developing velocity of around 104～105 m/s.4） About 72% of negative CG discharges produce multiple RSs,among which the largest proportion（approximately 25%） are three-times RSs.The interval between RSs is mainly no longer than 100 ms,but its maximum value is up to 500 ms.5） The peak current of RS directly measured in altitude-triggered lightning varies from 6.67 kA to 31.93 kA.6） 65% of negative CG contains continuous current and 41% RS is followed by continuous current,of which the duration ranges from 1 ms to 358 ms.7） The duration of M-component involved in continuous currents is mainly shorter than 3 ms,and interval between adjacent M-components is mainly 0～10 ms.2/3 of the interval between the first M-component and the RS initiation is shorter than 2 ms.