中高层(60-120km)大气电参数非线性效应对地闪回击电磁场传播的影响

Effects of the nonlinear atmospheric electric parameters at the high altitudes on the propagation of lightning return stroke electromagnetic field

基于麦克斯韦方程组,通过综合考虑电子热效应和电离、吸附效应的非线性变化,利用二维时域有限差分算法(2D FDTD),建立了对流层-中高层大气电动力耦合模式,分析了中高层大气电参数的非线性效应对地闪回击电磁场传播的影响。结果表明,对微秒量级的地闪回击辐射场而言,在60 km以下,由于弛豫时间为毫秒量级,不需要考虑电参数的非线性效应。而在60 km以上的空间,由于弛豫时间快速减小至小于微秒量级,必须考虑电参数非线性效应带来的影响。如果考虑中高层大气电参数非线性效应,距地面90 km高度处地闪回击辐射场峰值明显减小,其中,垂直电场受影响最明显,场峰值最大可减小75%左右,而水平电场受影响相对较小。因为垂直电场脉冲持续时间为几百微秒,而水平电场脉冲持续时间仅为几十微秒,电磁场脉冲持续时间越长,受微秒量级中高层大气电介质弛豫时间的影响越大。

In order to investigate the effect of the nonlinear atmospheric electric parameters at high altitudes on the propagation of lightning return stroke electromagnetic field, the upper troposphere atmospheric electric-coupling model is performed by u- sing the 2D Finite-Difference Time-Domain method, considering the electronic thermal effect, ionization and absorption effect in the Maxwell＇s equations. For the lightning return stroke field within the initial microseconds times, our simulated results show that the effect of the nonlinear atmospheric electric parameters below 60 ＇kin altitude can be ignored while it has to be considered above 60 km altitude, because the relaxation time below 60 km altitude is about several milliseconds, however, it is less than 1 ms above 60 km altitude. It is found that the nonlinear effect of the atmospheric electric parameters reduces the vertical field peak value more significantly than the horizontal electric field, and the peak value of the vertical electric field can be reduced by 75~ or so. Because the vertical electric field lasts hundreds of microseconds while the horizontal electric field is only tens of mi- croseconds, the longer the time of the field pulse continues, the more attenuation of the field peak will be made due to the re- laxation time within several microseconds.