A model of the stratiform thundercloud and sudden changes in the electric field accompanying a lightning discharge

A numerical model of a stratiform thundercloud and transient electrical pro cesses in the atmosphere accompanying a lightning discharge is presented. T he cloud layers are modeled as three coaxial charged disks and electrostati c images. The thickness and radii of the disks and the altitude of the lowe r disk are free parameters. The attitudes of the remaining disks and charge densities before a lightning stroke are calculated. The latter are equal t o 0.8-4.5 nC m(-3) a disk thickness of 500 m. The results of the calculatio n of sudden changes in the electric field strength at the cloud axis up to an altitude of 90 km are given for a set of values of free parameters. At a positive lightning stroke, the field strength at an altitude of 16 km can reach -17.4 kV/m. Such a field was obtained at an altitude of the lower clo ud layer of 5 km and a radius of 10 km, which is similar to the observed va lues [Marshall et al., 1995a, 1995b, 1996]. It has been shown that the fiel d sudden changes above stratiform clouds caused by the intracloud lightning strokes or positive cloud-to-ground lightning strokes are insufficient for the initiation of a usual breakdown in thermal electrons but can exceed th e runaway threshold for background relativistic electrons leading to the de velopment of an electron avalanche and the specific discharge form [Gurevic h et al., 1992].