A Possible Cause for Preference of Super Bolt Lightning Over the Mediterranean Sea and the Altiplano

Abstract

Exceptionally high-energy lightning strokes >106 J (X1000 stronger than average) in the very low-frequency band between 5 and 18 kHz, also known as superbolts (SB), occur mostly during winter over the North-East Atlantic, the Mediterranean Sea, and over the Altiplano in South America. Here we compare the World-Wide Lightning Location Network database with meteorological and aerosol data to examine the causes of lightning stroke high energies. Our results show that the energy per stroke increases sharply as the distance between the cloud's charging zone (where the cloud electrification occurs) and the surface decreases. Since the charging zone occurs above the 0°C isotherm, this distance is shorter when the 0°C isotherm is closer to the surface. This occurs either due to cold air mass over the ocean during winter or high surface altitude in the Altiplano during summer thunderstorms. Stroke energy decreases with the warm phase of the cloud, as proxied by the cloud base temperature, and increases with a more developed cloud, as proxied by the cloud top temperature, but to a much lesser extent than the distance between the surface and 0°C isotherm. Aerosols play no significant role. It is hypothesized that a shorter distance between the charging zone and the ground represents less electrical resistance that allows stronger discharge currents.