Lightning Observations in Finland and Theoretical Calculation of the Lightning Electromagnetic Pulse

Abstract

This paper deals with lightning observations made in Finland by lightning flash counters for thirty years and by an LLP lightning location system since 1984. Estimation of flashes per unit area based on counter data cannot yet be performed since the operational range of the counters is unknown, being somewhere between 17 and 45 km. The counters seem to record more flashes than the LLP system does. A reason could be the low conductivity of the earth in Finland, which might deform the electromagnetic signal emitted by a lightning stroke too much during the propagation to pass the acceptance criteria of the LLP system. Signals incident on a LLP direction finder have been recorded, and theoretical calculations were started. The latter work also discussed in this paper has, however, so far only concerned a perfectly conducting earth thus giving no answer to the question of the effect of the low conductivity.