Effects of lightning and sprites on the ionospheric potential, and threshold effects on sprite initiation, obtained using an analog model of the global atmospheric electric circuit

A quantitative model of the global atmospheric electric circuit has been constructed using the PSpice electrical engineering software package. Currents (similar to 1 kA) above thunderstorms and electrified rain/shower clouds raise the potential of the ionosphere (presumed to be an equipotential surface at 80 km altitude) to similar to 250 kV with respect to the Earth's surface. The circuit is completed by currents flowing down through the fair-weather atmosphere in the land/sea surface and up to the cloud systems. Using a model for the atmospheric conductivity profile, the effects of both negative and positive cloud-to-ground (CG) lightning discharges on the ionospheric potential have been estimated. A large positive CG discharge creates an electric field that exceeds the breakdown field from the ionosphere down to similar to 74 km, thereby forming a halo, a column sprite, and some milliseconds later, from similar to 67 km down to similar to 55 km at similar to 60 ms after the discharge, a carrot sprite. Estimates are made of the return stroke current and the thundercloud charge moment change of a +CG discharge required to exceed the threshold breakdown field, or the threshold field for creating and sustaining negative or positive streamers. The values for breakdown at 80 km altitude are 35 kA and 350 C. km, (Coulomb. kilometers), respectively, and those at 70 km altitude are 45 kA and 360 C. km, respectively. The different temporal and spatial developments of the mesospheric electric field distinguishing between column and carrot sprites agree with the latest deductions from recent observations. The current flowing in the highly conducting sprite reduces the ionospheric potential by similar to 1 V.