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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

The influence of terrain elevation on lightning density in South Africa

Bhavika, Bhikha 10 March 2010 (has links)
M.Sc. / Lightning data are used in various applications from risk management to weather forecasting providing valuable insight to everyday operations. In South Africa, the South African Weather Services (SAWS) commissioned a new lightning detection network in February 2006. The nineteen-sensor network spread across South Africa overcomes previous disadvantages to lightning detection by providing wider coverage, higher detection efficiencies and better spatial resolution. This study investigated the influence of terrain elevation on lightning density in South Africa using data from the SAWS lightning detection network. Data incorporating one year from February 2006 to January 2007 were analysed using Geoinformatic Information System (GIS) programmes. The study incorporated two phases of analysis. The first included an evaluation of lightning climatology and the influence of elevation on lightning density for the whole of South Africa. The second phase, using four sub-regions of South Africa, included evaluation of local influences of elevation, slope and aspect on lightning density, for a period restricted to one month, December, during the peak lightning season. Lightning density was found to be highest over high topographic regions of the Highveld and escarpment regions. Enhanced lightning activity occurs over the eastern coast and over the Indian Ocean adjacent to the KwaZulu Natal coast. Diurnal variations in lightning activity indicate the influence of solar radiation on convective thunderstorm development with peaks occurring during the late afternoon and early evening. Results of the influence of elevation on lightning density over the country of South Africa, indicate that lightning density increases with elevation up to a maximum of 1 800 m decreasing thereafter, in contrast to literature reports indicating maximum activity at 1 200 m elevation. This result was found throughout the year except for winter months where thunderstorms are dominated by frontal activity. Lightning density in all four sub-regions was found to increase with elevation up to approximately 1 500 m and decrease thereafter. Diurnal patterns of lightning activity in all regions indicate the dominance of convective thunderstorms. Slope and aspect was found to be influential in certain regions but mostly as a secondary factor influencing thunderstorm development. Lightning density in South Africa is influenced to a great degree by terrain elevation especially over the highly elevated regions of the Highveld and Escarpment. This work contains the first comprehensive analysis of lightning frequency distributions from the new (2006) SAWS lightning detection network, and the first significant update of lightning distribution over southern Africa since 1975.

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