Lateral corona currents from the return stroke channel and the slow field change after the return stroke in a lightning discharge

Abstract

Following Bruce the field change after the return stroke of a lightning discharge has been considered as due to the lateral corona currents from the return stroke channel. (The relatively slow field change after the return stroke has reached the cloud had been called the c-field change by Appleton and Chapman. Later Schonland called it the Re change. This usually lasts for about 3 msec after the onset of the return stroke.) It was Pierce and Wormell who pointed out that when the return stroke, effectively at ground potential, would shoot up along the core of the sheath of negative charge formed during the leader stroke, the potential difference between the return stroke and the leader sheath would not be far different from the potential of the main negative charge of the cloud with respect to the ground. This high potential difference would cause lateral corona currents to flow. In the present paper the fall of the leader sheath potential due to the corona current flow with time has been taken into account, and an expression for the total corona at any instant has been given. Subtracting the corona current from the return stroke current at any instant, the effective return stroke current contributing to the observed electric field change has been obtained, and the change in the radiated electric field has been derived from the time derivative of the effective dipole current moment. The computed change of the radiated field during the return stroke and after agrees well with what is usually observed.