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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 super bolts (SB), occur mostly during winter over the North Atlantic, the Mediterranean Sea, and over the Altiplano in South America. This study compares the World-Wide Lightning Location Network (WWLLN) database with meteorological and aerosol data to examine the causes that determine lightning stroke energies. Our results show that the energy per stroke increases sharply as the distance between the 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. It occurs either due to cold air mass over the ocean during winter, or high surface altitude in the Altiplano during summer thunderstorms. Stroke energy increases also with storm intensity as related to lower cloud top temperature, but to a much lesser extent than the distance between the surface and 0 °C isotherm. Another factor that slightly affects the energy is the contribution of more supercooled water to the charging zone. Aerosols play no significant role in the clouds with cool base temperatures. It is hypothesized that a shorter distance between the charging zone and the ground represents less electrical resistance, allowing stronger discharge currents.
