The sea-land ratio of extremely strong cloud-to-ground lightning is significantly smaller than previously estimated

Previous studies, based on satellite optical data and VLF network observations, determined that lightning superbolts (SBs) that have exceptionally high peak currents occur predominantly over the oceans. Satellite measurements were categorized according to optical intensity out of which the highest 1% were categorized as SBs and occurred predominantly over the NW Pacific near the coast of Japan. In contrast, VLF measurements were categorized according to their energy, out of which the highest 0.001% of the cloud-to-ground lightning strikes (CG) were categorized as SBs and occurred predominantly over the oceans (>90%) and during the wintertime of the northern hemisphere.

This study analyzed the spatial-temporal distribution of 3.8·10⁹ CG strokes observed during 2018-2023 by the Earth Networks Total Lightning Network (ENTLN). It was determined that the proportion of high peak current (I_peak) CG over the oceans compared to land was greater than 1 starting at PC>80 kA and no more than ~2 for PC=180-310 kA. Above 200-kA, 67% of the CG occurred over the oceans. The percent of PC>200 kA from the total CG (PC>2 kA) is ~0.3%. The percent of the total CG is 0.001% at PC~935 kA, where the sea-to-land ratio is only ~1.2. Over the annual cycle, CG with PC>200 kA was not observed at all during the months of May-September in both hemispheres, while during the rest of the year, most of the events over land occurred in the southern hemisphere at a ratio of 4.4:1 relative to the northern hemisphere, while over the oceans there was a 1:1 ratio between hemispheres. Finally, the hourly distribution of CG over land with PC>200 kA is consistent with the shape of the Carnegie curve as determined for lightning in general in previous studies. The hourly distribution over the oceans exhibits a higher number of events from midnight until 06:30 local time and is relatively constant and low throughout the daytime until 17:30 and afterward increases up to the midnight maximum frequency. These results demonstrate the small contribution of CG with PC>200 kA over the oceans to the atmospheric electric field variations in the Carnegie curve.