Diurnal variations in lightning activity over Swaziland as observed from Space: 1998-2006

Abstract

Lightning phenomena have recently gained a lot of interest among researchers mainly due to its impact on the human and natural environment. The thermodynamics of lightning and its distribution on the landscape are, therefore, under intense investigation in many part of the world, mainly in the developed world. In this report, nine years of lightning data (January 1998 to December 2006) from the Lightning Imaging Sensor on board the Tropical Rainfall Measuring Mission (TRMM) satellite was used to analyse the diurnal frequency of lightning frequency over Swaziland, a country characterized by a complex terrain. Through geographic information systems analysis of the lightning flash counts, which was corrected for detection efficiency and instrument view time, was analysed to reveal diurnal patterns in lightning activity across the four climatic seasons and the country’s four eco-climatic (physiographic) zones. Results showed a pronounced evidence of bimodal peaks, mainly in summer (52%) and autumn (28%), during the late afternoon and evening (1400 and 2000 hours), accounting for 60% of the total hourly flashes, and a second peak during the late evening hours (2200-0000 hours), which were found to be for 27% of the hourly total. The time of maximum lightning frequently occurred mainly over the elevated areas of the Highveld) (37%), Middleveld (32%) and Lowveld (24%), resulting from updrafts caused by topographic lifting. This suggests the presence of convective development and stratiform precipitation according to the local and meso-scale circulation weather system affecting the country. The installation of a ground-based system is recommended, as this would further improve the understanding of the spatial and temporal dynamics of lightning in Swaziland. 1 Swaziland National Trust Commission, P.O. Box 100, Lobamba H107, Swaziland