广东一次雷暴过程负地闪先导的电学特征分析

CHARACTERISTICS OF THE ELECTRIC FIELDS PRODUCED BY NEGATIVE LEADER IN ONE THUNDERSTORM IN GUANGDONG

利用 0 .0 8μs时间分辨率的大容量慢天线电场变化测量系统在广东从化地区一次雷暴过程中观测得到的 44次负地闪电场变化波形 ,对负地闪回击前 2 0 0 μs内的先导电场变化波形进行了分析。发现负地闪首次回击前的先导电场变化波形 ,按最后一个先导脉冲与相应回击间电场变化特征大致可分为三类。通常负地闪先导过程由若干脉冲式变化组成 ,首次回击前先导脉冲间的平均时间间隔为 1 5.8μs(均方差 5.3μs) ;继后回击前直窜 -梯级先导脉冲间的平均时间间隔为 9.4μs(均方差 5.5μs)。首次回击前最后一个先导脉冲与首次回击间的平均时间间隔为 1 2 .7μs(均方差 7.8μs) ,最后一个先导脉冲幅值与回击峰值之比的平均值为0 .1 (均方差 0 .0 4 ) ,且两者之间有很好的相关性 ,并用回击传输线模式对这一关系进行了解释。

Characteristics of the electric fields produced by stepped and dart stepped leaders 200 μs just prior to the return strokes in negative lightning discharges to ground during a thunderstorm process have been analyzed by using data from broad band slow antenna with system of time resolution 0.08 μs in Conghua area near Guangzhou. It has been found that the electric field produced by stepped leader could be divided into three types based on their characteristics between the last leader pulse and the return stroke for 44 negative ground lightning discharges. The average time interval between the successive leader pulses prior to the first return strokes was 15.8 μs, with a standard deviation of 5.3 μs, and that of dart stepped leader pulses prior to the successive return strokes was 9.4 μs with a standard deviation of 5.5 μs. The average time interval between the last leader pulse and the first return strokes was 12.7 μs, with a standard deviation of 7.8 μs. The ratio of the amplitude of the last leader pulse to that of the return stroke was 0.1, with a standard deviation of 0.04. A correlation between the amplitude of the last leader pulse and the return stroke radiation field peak has been observed. The correlation is interpreted by using the transmission line model of return stroke.