Ground Strike Point Density Map of South Africa

Abstract

South Africa's flash density map is derived from an IEC 62858 compliant Lightning Location System (LLS) known as the Southern African Lightning Detection Network (SALDN) owned and operated by the South African Weather Service (SAWS). The Ground Flash Density (GFD) parameter has been widely used to depict the lightning risk across the country to inform effective lightning protection. However, the spatial and temporal flash clustering technique characterises a flash consisting of multiple strokes with only the parameters of the first return stroke and therefore assumes a single Ground Strike Point (GSP) per flash. The GFD parameter thus does not account for possible multiple GSPs per flash as evident from ground-truth data in a form of high speed camera observations. The GFD parameter may therefore be underestimating the amount of lightning risk. This paper proposes a new South African GSP density map, using the same lightning dataset from the IEC 62858 compliant SALDN to estimate the associated lightning risk. The GSP parameter and consequently the GSP map is derived from a GSP clustering algorithm with a proven success rate of upto 90%. In this paper, the GFD has been derived from SALDN data between July 2007 and July 2016, the GSPs have been estimated using a GSP clusturing algorithm in MATLAB ®, where strokes of a flash within 150 m and overlapping error ellipses form a GSP. The results show a mean of 1.81 GSPs per flash with the highest difference between GFD and GSPs depicted around the high altitude areas of Mpumalanga and Kwazulu Natal provinces.