New model simulations of the global atmospheric electric circuit driven by thunderstorms and electrified shower clouds: The roles of lightning and sprites

Several processes acting below, in and above thunderstorms and in electrified shower clouds drive upward currents which close through the global atmospheric electric circuit, These are all simulated in a novel way using the software package PSpice. A moderate negative cloud-to-ground lightning discharge from the base of a thunderstorm increases the ionospheric potential above the thundercloud by 0.0013%. Assuming the ionosphere to be an equipotential surface, this discharge increases the current flowing in the global circuit and the fair-weather electric field also by 0.0013%. A moderate positive cloud-to-ground lightning discharge from the bottom of a thunderstorm decreases the ionospheric potential by 0.014%. Such a discharge may trigger a sprite, causing the ionospheric potential to decrease by similar to 1 V. The time scales for the recovery of the ionospheric potential are shown to be similar to 250 s, which is of the same order as the CR time constant for the global circuit. Knowing the global average rate of lightning discharges, it is found that negative cloud-to-ground discharges increase the ionospheric potential by only similar to 4%, and that positive cloud-to-ground discharges reduce it by similar to 3%. Thus, overall, lightning contributes only similar to 1%-an almost insignificant proportion-to maintaining the high potential of the ionosphere. It is concluded that the net upward current to the ionosphere due to lightning is only similar to 20 A. Further, it is concluded that conduction and convection currents associated with "batteries" within thunderclouds and electrified shower clouds contribute essentially equally (similar to 500 A each) to maintaining the ionospheric potential. (C) 2007 Elsevier Ltd. All rights reserved.