Characteristics of cloud to ground lightning flashes

Abstract

A detailed study on the characteristics of cloud-to-ground lightning flashes over Sweden was carried out for the period 1987 to 2000 using the data obtained from the Swedish lightning locating network. Results are presented by analysing over half a million lightning ground flashes. The average variation of the annual mean of the total number of flashes was found to be 37%. About 12% of the cloud to ground flashes were positive flashes and their average variation about the annual mean was 26%. The average peak currents were fairly constant over the years with variations as little as 4% for negative flashes and 5% for positive flashes. The average peak current values for negative and positive flashes were –29.90 kA and +63.97 kA respectively. A correlation between the mean monthly flash count and percentage of positive flashes was seen. A similar relationship is seen with the mean monthly flash count and the peak currents for both polarities. In general, high flash density and high peak currents were observed in the southern part of Sweden where most of the major cities are located. Flash densities exceeding 0.4 flashes km-2 was observed for several large cities. The maximum flash rate of 32 flashes hr-1 within a 10 km radius was seen in Jönköping (14.18 E, 57.78 N) in the Province of Småland.