Remote sensing of thunderstorm activity by means of VLF sferics

The results of a three-month observational period (June–August 1981) during sunlit hours (9:00–15:00 GMT) with VLF sferics at the two stations Tel Aviv, Israel, and Pretoria, South Africa, are presented and compared with rainfall data for the European-African area, with two lability indices of thunderstorm prediction, and with synoptic thunderstorm reports for the same time interval. The locations of thunderstorm centers on the continents determined from the sferics stations compare reasonably well with the distribution of rainfall, indicating that the VLF sferics method is a useful measure of rainfall, particularly in remote regions with inadequate coverage of observing stations. The lability index of Showalter (1953) appears to be rather qualitative for the prediction of thunderstorm occurrence, and any fine structure in the distribution of thunderstorm centers as seen in the sferics data is lost. The same is true of the synoptic reports of thunderstorm days. A new lability index has been developed. This index leads to a more detailed structure of thunderstorm prediction, which is consistent with the sferics data.