Lightning Activity Over Legon and its Application to Rainfall Estimation

Abstract

Lightning is an important component in the global electric circuit of the earth. It is a leading cause of outages in electric power and telecommunication systems, of forest fires and of delays in aircraft missions. A lightning sensor operating at a radio frequency of300 kHz was constructed ~d used to study the occurrence of lightning in and around the University of Ghana campus during thunderstorms. Rainfall figures during each thunderstorm were also recorded. Data was collected over a period of two and half months (from May 13 to August 2, 200S). It was observed that the number of strikes correlated with the amount of rainfall, a larger number of lightning strikes being associated with a greater amount of rainfall. Polynomials of various degrees were fit to the data and the cubic polynomial (y = 2E-05x3 - 0.0037~ + 0.42S7x - 2.3078) was found to yield the best compromise between correlation coefficient and coverage of the amount of rainfall (y) and the number of lightning strikes (x) during the study period. The experiment can be used to estimate the amount of rainfall (y) if the number of lightning strikes (x) during a thunderstonn is known assuming that there was rainfall during the period. A similar analysis perfonned on lightning flash rate and rainfall amount did not indicate a strong correlation. The maximum number of lightning strikes recorded during the study period was 200 ± 1 and this occurred on the night of May ]S, 200S when most parts of Accra were flooded. Coincidentally, a maximum of 117.3 ± 0.1 mm rain was recorded on the same day at Legon. The minimum number of lightning strikes for the study period was 15 ± occurred on June 13,2008. On that day, the amount of rainfall was 15.2 ± 0.1 mm.