A University of Washington study maps the location and timing of “superbolts” — bolts that release electrical energy of more than 1 million Joules, or a thousand times more energy than the average lightning bolt, in the very low frequency range in which lightning is most active. Results show that superbolts tend to hit the Earth in a fundamentally different pattern from regular lightning, for reasons that are not yet fully understood.
The study was published Sept. 9 in the Journal of Geophysical Research: Atmospheres, a journal of the American Geophysical Union.
“It’s very unexpected and unusual where and when the very big strokes occur,” said lead author Robert Holzworth, a UW professor of Earth and space sciences who has been tracking lightning for almost two decades.
Holzworth manages the World Wide Lightning Location Network, a UW-managed research consortium that operates about 100 lightning detection stations around the world, from Antarctica to northern Finland. By seeing precisely when lightning reaches three or more different stations, the network can compare the readings to determine a lightning bolt’s size and location.
The network has operated since the early 2000s. For the new study, the researchers looked at 2 billion lightning strokes recorded between 2010 and 2018. Some 8,000 events — four millionths of a percent, or one in 250,000 strokes — were confirmed superbolts.
“Until the last couple of years, we didn’t have enough data to do this kind of study,” Holzworth said.
The authors compared their network’s data against lightning observations from the Maryland-based company Earth Networks and from the New Zealand MetService.
The new paper shows that superbolts are most common in the Mediterranean Sea, the northeast Atlantic and over the Andes, with lesser hotspots east of Japan, in the tropical oceans and off the tip of South Africa. Unlike regular lightning, the superbolts tend to strike over water.