Initial steps in the development of a comprehensive lightning climatology of South Africa
Date
2009-07-08T07:14:57Z
Authors
Gill, Tracey
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Abstract
The summer rainfall region of South Africa is dominated by convective thunderstorm
development from October to March. The result is that lightning is a common event over most
of the country during this time. The South African Weather Service (SAWS) installed a stateof-
the-art Lightning Detection Network (LDN) in late 2005 in order to accurately monitor
lightning across South Africa. Data from this network for 2006 was utilised in order to
develop an initial climatology of lightning in South Africa. Analyses were performed of
lightning ground flash density, flash median peak current and flash multiplicity on a 0.2° grid
across South Africa. The highest ground flash density values were found along the eastern
escarpment of the country, extending onto the high interior plateau. There is a general
decrease in flash density from east to west, with almost no lightning recorded on the west
coast of the country. The regions of highest flash density recorded the highest percentages of
negative polarity lightning. The percentage of positive lightning was higher in the winter
months, as was the median peak current of lightning of both polarities. The median peak
current distribution displayed distinct bands of current values oriented in northwest to
southeast bands across the country. The bands of higher median peak current correspond to
the regions to the rear of the interior trough axis in areas dominated by stratiform cloud
development and were more dominant in the mid summer months. The highest flash
multiplicity was recorded in the regions of highest flash density. Along the southern
escarpment, on the eastern side of South Africa, flash multiplicity values exceeded 3 flashes
per square kilometer. The highest flash multiplicity of negative polarity lightning was
recorded in the spring and early summer. Throughout the year, the percentage of single stroke
flashes for positive lightning is high. Topography and the position of the surface trough have
a very strong influence on the ground flash density and median peak current distributions, but
not on the flash multiplicity distribution. The results from the analyses of the three lightning
variables were then combined to determine risk indexes of high intensity lightning and of
positive polarity lightning. The eastern part of South Africa is at extreme risk from both large
amounts of lightning and from positive polarity lightning, whereas the regions in the northwest of the country that are dominated by mining are at extreme risk from mainly positive polarity lightning.
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Keywords
Lightning, Climate, South Africa