Characterization of the Lightning Activity over Tropical Africa

E. E. AVILA; M. G. NICORA; R. E. BÜRGESSER

Congreso; America Geophysical Union, Meeting of the Americas; 2013

Three zones have been long recognized as major components of the global electrical circuit: Africa, South America and the Maritime Continent. These three zones stand out in all global maps of lightning activity with Africa dominating over the other two. There is a great deal of work related to the lightning activity over Africa with a clear agreement that it is mainly concentrated in the tropics. In the tropical region, the Congo Basin shows the highest lightning activity followed by the Gulf of Guinea in the west and by the Ethiopian Highlands in the north-east. In this work, the lightning flash rate over tropical Africa was analyzed using lightning data of two independent lightning detection systems, the World Wide Lightning Location Network (WWLLN) and the Lightning Imaging Sensor (LIS). Spatial and time distributions of lightning activity were studied using different spatial and temporal scales. The lightning activity over this region presents a pattern with a localized center of high lightning activity located on the western foot of the Albertine Rift. This center is located between [0°; -3°] of latitude and [27°; 29°] of longitude and presents a flash rate density exceeding 100 flashes km-2 yr-1. Results seem to indicate that the topographic relief forces air upwards that further enhances thunderstorm development and can subsequently lead to an increase in lightning activity. The Congo Basin shows high surface air temperature, low values of the cloud top temperature and substantial annual rainfall. The low amplitude in the lightning annual variations that we found is consistent with the low annual variation of temperatures in the region and with a rainy season lasting almost all year long. The diurnal cycle observed is consistent with global observation for tropical region with a peak in flash rate in the late afternoon (local time) and with the rainfall diurnal cycle. Significant lightning activity was also found over Lake Victoria which presents similar daily variation in flash rate as the Congo Basin and a diurnal lightning activity without a marked cycle. The lightning activity found is consistent with the daily and diurnal convection activity present over the lake.