New studies shine light on bright lightning superbolts

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AGU press contact:
Lauren Lipuma, +1 (202) 777-7396, [email protected]

Contact information for the researchers:
Michael Peterson, Los Alamos National Laboratory, [email protected]

Los Alamos National Laboratory press contact:
Laura Mullane, +1 (505) 412-7733, [email protected]

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WASHINGTON—Two new studies looking at the brightest lightning events on Earth have investigated how these rare superbolts originate and find they are distinct from normal lightning flashes. The new findings could help scientists better understand these mysterious strokes and inform safety efforts, such as public advisories and engineering guidance.

The studies analyzed lightning events spotted by orbiting satellites. The authors found the brightest superbolts were more than 1,000 times brighter than typical lightning. One lightning stroke even exceeded 3 terawatts of power – thousands of times stronger than ordinary lightning detected from space.

The research sheds light on an ongoing debate among scientists about how these energetic lightning flashes originate. The new studies propose superbolts typically result from rare positively charged cloud-to-ground events, rather than the more common negatively charged cloud-to-ground events characteristic of most lightning.

Understanding these extreme events tells scientists about what lightning is capable of, said Michael Peterson, a remote-sensing scientist at Los Alamos National Laboratory in Los Alamos, New Mexico. Peterson is lead author of both studies published in AGU’s Journal of Geophysical Research: Atmospheres, which advances the understanding of Earth’s atmosphere and its interaction with other components of the Earth system.

Superbolts were first reported in 1977, based on optical brightness measurements made by the Vela satellite and initially described as lightning flashes 100 times brighter than typical lightning. Since that time, however, there has been an ongoing debate as to whether these observations represent phenomena distinct from ordinary lightning. The viewing angle of a satellite, for example, could affect the observed brightness of a lightning event.

“When you see a lightning flash from space, it will look a lot dimmer than if you were to see it from ground level because the clouds block some of the light,” Peterson said.

The new studies complement the 1977 report. One study used data captured by the Geostationary Lightning Mapper, a detector on a satellite that remains centered over the Americas, from January 2018 through January 2020. The authors added up signals detected on the cameralike sensor to calculate the total brightness for lightning flashes.

They classified superbolts as lightning 100 times brighter than average and detected about 2 million strokes — 0.32% of all lightning events — above this threshold. The researchers identified clusters of the absolute brightest events –1,000 times brighter or more than ordinary lightning – in the central United States, the La Plata basin in South America and coastal regions of Central America. The brightest flashes also corresponded with positively charged cloud-to-ground events, as captured by radio-frequency lightning sensors on the ground.

These brightest signals corresponded to megaflash events, which can extend over long distances. “It could be that a strike nearby you, in clear air, was actually from a stroke that started hundreds of kilometers away,” said Robert Holzworth, an atmospheric and space physicist at the University of Washington in Seattle, who was not involved with the new research. Holzworth co-authored a 2019 study on superbolts, using data from the World Wide Lightning Location Network, which detects radio waves emitted during lightning strikes. New world records for lightning extent (709 kilometers or 442 miles) and duration (16.73 seconds) were established from megaflashes identified by Peterson earlier this year.

The second study relied on data from the FORTE satellite, which detects the maximum, rather than total, brightness of lightning events. The researchers analyzed data from 1997 to 2010 and identified about 20,000 events that could be classified as superbolts that produced at least 100 gigawatts of power. For comparison, as of September 2020, all the solar panels in the United States have a total capacity of 85 gigawatts. Of the brightest superbolts, about 1,000 had a maximum output over 350 gigawatts and largely corresponded with positive cloud-to-ground strokes.

Positively charged lightning events, which involve positive charges traveling from clouds down to the ground, make up less than 5 percent of all lightning and are typically stronger than negatively charged cloud-to-ground strokes. Positive lightning can occur when storms build up large amounts of charge, such as over oceans. Consistent with this, the brightest superbolts detected in the new study were often found in oceanic storms, particularly during the winter and near Japan and in the Mediterranean Sea.

There are differences in the hotspots identified by the earlier analysis by Holzworth et al. and those described in the new work, potentially because of differences in detection by radio waves versus optical brightness. Future studies, such as those using high-resolution Lightning Mapping Arrays, could capture lightning events more thoroughly and provide additional details of superbolt physics.

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