Abstract
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.