Global Distribution of Superbolts

We use World Wide Lightning Location Network (WWLLN) data on the radiated radio frequency electromagnetic energy per stroke to identify the upper tip of the global lightning stroke energy distribution. The mean stroke energy is about 1,000 J per stroke in the very low frequency band between 5 and 18 kHz, while the distribution used in this paper is limited to strokes in that band above 1 MJ, about 3 orders of magnitude above the mean. It is shown that these energies are representative of the tip of the optical distribution, first identified by Turman (1977) above 10 GW per stroke, which he termed “superbolts.” The distribution peaks globally in the Northern Hemisphere winter (November–February) with most superbolts being found in the North Atlantic west of Europe, the winter Mediterranean Sea, and a strong local maximum over the Andes in South America. We identify regions with somewhat fewer superbolts in the North Pacific east of Japan in winter, along the equator of the Atlantic and Indian Oceans and south of South Africa. We find very few superbolts during April–October each year. While superbolts are scattered around the globe, the local occurrence peaks do not coincide with the usual three main lightning “chimneys.” Unlike the distribution of all normal global lightning, we find superbolts predominantly over the oceans and seas, with fewer over the continents, just the opposite of all global lightning.