TIME-AVERAGED CURRENT ANALYSIS OF A THUNDERSTORM USING GROUND-BASED MEASUREMENTS

The amount of upward current provided to the ionosphere by a thunderst orm that appeared over the Kennedy Space Center (KSC) on July 11, 1978 , is reexamined using an analytic equation that describes a bipolar th understorm's current contribution to the global circuit in terms of it s generator current, lightning currents, the altitudes of its charge c enters, and the conductivity profile of the atmosphere. Ground-based m easurements, which were obtained from a network of electric field mill s positioned at various distances from the thunderstorm, were used to characterize the electrical activity inside the thundercloud. The loca tion of the lightning discharges, the type of lightning, and the amoun t of charge neutralized during this thunderstorm were computed through a least squares inversion of the measured changes in the electric fie lds following each lightning discharge. These measurements provided th e information necessary to implement the analytic equation, and conseq uently, a time-averaged estimate of this thunderstorm's current contri bution to the global circuit was calculated. From these results the am ount of conduction current supplied to the ionosphere by this small th understorm was computed to be less than 25% of the time-averaged gener ator current that flowed between the two vertically displaced charge c enters.