用远场辐射场反演云闪放电参数

用地面电磁场遥感闪电放电参数无论是在实际应用还是理论研究中都具有重要意义。文中基于电流传输线模式 ,提出了一种用单站远场VLF/LF辐射场反演云内放电参数的简便方法。当传输线电流从底部传播到顶部的时间只有几微秒时 ,整个传输线的VLF/LF辐射可以近似成偶极子辐射 ,即远场辐射场与电流的时间变化率和传输线长度的乘积成正比。因此 ,对远场辐射场做时间积分就能获得完整的电流矩波形 (上升沿有所加宽 ) ,而且传输线模式中的重要参数 ,电流从底部传播到顶端经历的时间 ,也可以近似地用辐射场时间积分幅度与辐射场幅度之比来估计。这一方法具有估计云闪双极性大脉冲辐射过程的放电参数的潜力。

EVALUATION OF INCLOUD LIGHTNING DISCHARGE PARAMETERS FROM REMOTE ELECTROMAGNETIC FIELDS

It is of practical and theoretical importance to retrieve incloud lightning discharge parameters from far radiation fields, since these parameters are inaccessible by direct measurements. In this article a simple technique is presented to derive these parameters from remote electromagnetic field measured at a single site based on Transmission Line Model. The time for the current to travel from the bottom to the top of the transmission line channel is only of several microseconds, the transmission line current tends to produce the remote electromagnetic field in VLF/LF band approximately as the same way as the current dipole does, that is, the field is linear to the current derivative multiplied by the channel length. Therefore by recording the remote electromagnetic field and making the time integral one can obtain the full waveform of the current movement (current multiplied by channel length), except that its rise would be slightly broadened. The current waveform will be further extracted from the current movement waveform under assumption of the channel length. Furthermore, the time for the current to travel from bottom to top of the channel can also be estimated from the amplitude ratio of the remote radiation field to its time integral, which will help to estimate alternately the traveling velocity of the current(assuming the channel length) or the channel length(assuming the current velocity). This method provides a potential tool to evaluate incloud lightning discharge parameters from lightning bipolar radiation fields.