Estimation of sprite occurrences in Central Africa

Abstract

Extremely low-frequency magnetic field disturbances from intense positive lightning discharges are compared to the convective cloud cover in central Africa, derived from infrared brightness temperatures recorded on board the geostationary satellite Meteosat during April 1998. The mean diurnal variation of the positive lightning charge moment is well correlated with the mean diurnal variation of the cloud cover at ∼ 11.5 km height and constrains the mean lightning channel length. The daily integrated positive cloud to ground charge transfer exhibits a pronounced day to day variability which is well correlated with the cloud cover at ∼ 15.5 km height, related to the charging of the thundercloud ∼ 4 hours prior to the maximum cloud to ground charge transfer. The cloud cover area is used to calculate an effective cloud volume which is related to the cloud to ground charge transfer via the charge density. This charge density is used to determine promising locations for optical sprite observations in the central Congo basin and Cameroon with ∼ 69 estimated sprite occurrences during an average night.