The electrodynamic responses of the atmosphere and ionosphere to the lightning discharge

The purpose of this study was to use the complete set of Maxwell's equations to simulate the electromagnetic response of the atmosphere and the ionosphere during and after the lightning discharge. A three-dimensional numerical model is used to calculate the quasistatic electric field over the 10 ms-2 s range. The model contains an isotropic conductivity profile below 70 km and an anisotropic conductivity profile from 70 km-150 km (different latitudes, day/night conditions have been considered), a time-varying charge distribution (representing the thunderstorm source function), and a perfectly conducting ground surface. Both vertical and horizontal transient electric fields and upward Maxwell currents in the ionosphere have been calculated for a vertical discharge. The results show that the relaxation time of the electric field due to the lightning discharge, which is no longer than epsilon(0)/sigma, will decrease with an increase of the altitude of observation and have little change with the horizontal distance from the lightning discharge. It also shows that the Maxwell current from the thundercloud spreads out to the ionosphere during a time interval of several milliseconds following the lightning discharge. This current flows along directions both parallel and perpendicular to the geomagnetic field lines and mainly propagates horizontally above 70 km. A good agreement between the simulation results and the measurement data has been achieved. These results show the importance of the use of the complete set of Maxwell's equations and the inclusion of an anisotropic ionospheric conductivity in the lightning response simulation. The conclusion of this paper also may help to explain some of the long-standing controversies between measurements and theoretical predictions. (C) 1998 Elsevier Science Ltd. All rights reserved.