Effect Of The Nonlinear Atmospheric Electric Parameters At High Altitudes On The Propagation Of Lightning Return Stroke Electromagnetic Field

The calculation of electric field is mostly in free space, without taking into account the atmospheric electrical conductivity at high altitudes. For inverting of the lightning current triggering discharge phenomenon at high altitudes, this could lead to a large uncertainty.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 troposphere-upper atmosphere electric-coupling model is performed by using2D Finite-Difference Time-Domain method, considering the electronic thermal effect, ionization and absorption effect in Maxwell’s equations. Furthermore, we extend semi-analytical model and simulate the optical emissions produced in elves. The main results are as follows:(1)Firstly, we analyze the range and intensity of the effect of the nonlinear atmospheric electric parameters on the propagation of lightning return stroke electromagnetic field. For the lightning return stroke field within the initial microseconds times, our simulated results show that the effect of the nonlinear atmospheric electric parameters below60km altitude can be ignored while it has to be considered above60km altitude, because the relaxation time below60km altitude is about several or tens milliseconds, however, it is less than1ms above60km 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 is reduced by about3times. The longer time of the field wave, the more attenuation of the field peak due to the relaxation time within several microseconds.(2)Moreover, we extend the semi-analytical model presented by Yashunin. It is noted that the semi-analytical model not only can predict the lightning vertical field, but also the horizontal electric field with a satisfied accuracy in the small region with a radius ranging from r=5km to30km at a height of z=80km above the lightning strike point. Compared with the results in free space, the nonlinear effect of the atmospheric electric parameters has a relatively little effect on the radiated field component, however, it have much effect on the electrostatic and induction component. For example, the induction field component in the conducting nonlinear medium decreases by about43%, compared with that in free space. The induction field is larger than the radiation field component within the radius r=25km at a height of z=80km above the lightning strike point. Also, it is worthy noting that the so-called induction field component is relative and different according to different approaches.(3)We simulate the temporal and spatial evolution of the optical emissions produced in elves. The simulated results show that the duration is about1ms, the horizontal radius is up to300km, the height is between80-100km. The characteristic of the simulated results is consistent with the observed results.