人工触发闪电实验中初始电流脉冲辐射磁场的观测与模拟

Observation and Simulation of Magnetic Fields Radiated by Initial Current Pulses in Rocket-triggered Lightning

为了进一步了解人工引雷初始阶段正先导的电磁辐射特征,利用2014年夏季山东人工触发闪电实验中的5次实验数据分析了磁场脉冲序列的特征,并利用基于Heidler函数模拟结果作为输入电流的传输线模式对单个磁场脉冲进行了模拟。磁场脉冲可根据幅值和半峰值宽度的明显差异分成两种类型,即脉冲型脉冲和波纹型脉冲;两类脉冲的脉冲间隔相当,表明其产生机制一致。由于波纹型脉冲对应的电流脉冲在通道底部的电流测量中较难识别,因此本文仅模拟脉冲型脉冲,结果表明其是由先导电流脉冲沿着钢丝通道向下传输时辐射产生;利用模拟结果对不同磁场分量(即感应场与辐射场)的研究发现,在火箭发展高度为152 m的情况下,当观测距离为200 m时感应场与辐射场分量相当,当观测距离<40 m时,感应场对总磁场峰值的贡献超过80%,当观测距离>500 m时,辐射场对总磁场峰值的贡献>80%。

In order to analyze the sequence of magnetic pulses during the initial stage of rocket-triggered lightning, we used the measurement data for five classical triggering lightning flashes during the Shandong Artificial Triggered Lightning Experiment （SHATLE） in August of 2014 to statistically analyze these pulses. We applied a transmission-line model to calculate the magnetic field by fitting the measured initial current pulse with Heidler function. The results show that these magnetic pulses can be classified into two categories with distinct differences in magnitude and timescale, namely impulsive pulses and ripple pulses, but the inter-pulse interval is similar, which indicates that the mechanism of generation is probably the identical for both types. The current pulses associated with the ripple pulses are usually difficult to discern in the conventional current measurement at the channel base, so we simulate the single impulsive pulse only and the simulation result is in good agreement with the measurement, which indicates that the sequence of magnetic pulses is radiated by leader current pulses propagating along the triggering wire. The relationship between individual components （i.e., induction field and radiation field） and the total magnetic field shows that, in the case of rocket height at 152 m above ground, when the observation distance is less than 40 m, the induction field contributes more than 80% to the peak magnetic field. When the distance is greater than 500 m, the radiation field contributes over 80% to the peak magnetic field.