The thunderstorm activity in South Africa, Europe, and parts of America was monitored in Pretoria, South Africa (1980--1987), at the von-Neumayer station, Antarctica (1983--1986), and in Bonn, Germany (1989--1990), by the analysis of very low frequency sferic pulses coming from cloud-to-ground return strokes. A single-station method was used that derives the geographical coordinates of the position of thunderstorms entirely from the sferics' wave forms (Volland-Heydt technique). The seasonal variation of thunderstorm activity was measured over southern continental Africa and over the adjacent ocean regions. While continental Africa exhibits the well-known maximum in (southern) summer, activity peaks occur in April along the coast of Angola and in May over the warm Agulhas current south of Africa. The mean thunderstorm activity in Africa did not change over the last decade. A case study was performed to compare sferics data with synoptic thunderstorm data. It shows the advantage of the sferics measurements, in particular, over the oceans, where few synoptic weather stations exist.

A comparison with METEOSAT infrared data, from which cloud-top temperatures can be derived, showed that in the tropics of continental Africa, cloud-top temperatures below 225 K are a necessary, but not a sufficient condition that these clouds are thunderclouds. In the temperate regions of Africa and Europe, thunderclouds generally correlate well with cloud-top temperature below 245 K. A thundercloud index has been inferred from the METEOSAT infrared data and has been correlated with the sferics data. This index works well in temperature regions but much less so in the tropics. ¿ American Geophysical Union 1992