Development and field evaluation of a lightning earth-flash counter

The lightning-flash counters of the 1950s were difficult to calibrate as far as their range was concerned, and their discrimination against inter- and intracloud flashes (now referred to as cloud flashes) was found to be poor. Research in South Africa over the past fifteen years was thus concentrated on improving the response of counters to earth flashes and on their calibration. This resulted in the development of a 10 kHz counter, which, over a long period, has a better than 90% response to earth flashes in a subtropical area where cloud flashes predominate, and, furthermore, has an effective range to earth flashes of almost 20 km, which has been reliably measured. Some 400 counters were installed throughout southern Africa, and the earth-flash density has been determined over a seven-year period. This indicates some significant differences with the previously measured distribution of thunderstorm days. Comparisons have been undertaken with other counters, notably the 500 Hz counter developed in Queensland, Australia, which, together with the 10 kHz counter, have been adopted as standard international counters of CIGR¿¿.