What directs a lightning flash towards ground?

Abstract

In this paper we attempt to show that the necessary condition to create a lightning ground flash is the generation of a vertical conducting channel below the main negative charge centre. The probability of such an event increases if frequent breakdown takes place between the negative charge centre and the lower positive charge centre (LPCC). Analysis of electromagnetic field signatures produced by ground flashes in Sweden show pronounced radiation during the preliminary breakdown process. Such strong pulses are rarely found in tropical thunderstorms in Sri Lanka. We attribute these signatures to preliminary breakdown between the main negative charge centre and the LPCC and argue that meteorological conditions which favour the production of strong LPCC's are more likely to be found at mid and high latitudes than in the tropics, thus explaining why there is a greater probability of lightning flashes striking the ground in these regions.