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Every so often, the Earth reminds us that it is able to release a furious energy.
Case in point: Scientists have just detected a new extreme in hotspots of lightning activity called “superbolt” – intense lightning that glows up to 1,000 times brighter than typical lightning.
The observations come from researchers at the US Los Alamos National Laboratory, which used satellites to measure extreme lightning events. The results require a rethinking of what constitutes a superbolt and shed new light on how and where superbolts originate.
“We want[ed] to see what the borders are [of superbolts] they really are, “said atmospheric scientist Michael Peterson The Washington Post. “It’s about how big and brilliant they can get.”
Superbolts were first detected by satellite data in the 1970s, being described as lighting that exceeds the bolt mean by a factor of 100 or more.
Since then, atmospheric scientists have debated what really counts as a superbolt, because measurements made by different instruments can vary.
“When you see a flash from space, it will look much dimmer than if you saw it from ground level because clouds block some of the light,” Peterson said, explaining how satellite measurements can differ from ground-based detectors.
There is also the question of whether the superbolts are supercharged by some unique phenomenon, or whether they are just bigger, brighter shots than the usual lightning variety.
“Understanding these extreme events is important because it tells us what lightning is capable of,” said Peterson, who has detected some record-breaking lightning strikes in recent years, including a 2018 megaflash (long-lasting lightning) that has spread to about 700 kilometers (440 miles) across the sky and lasted nearly 17 seconds.
In a new study, Peterson and his colleague Erin Lay analyzed data collected by NASA’s Geostationary Lightning Mapper, a detector tied to meteorological satellites and sent into orbit to record lightning, day and night, over the Americas and adjacent oceans every two. milliseconds.
Unlike ground-based monitoring systems, which detect radio waves, GLM measures the total brightness (optical energy) of lightning strikes within clouds, in the clouds, plus lightning striking the ground.
(Michael Peterson / Los Alamos National Laboratory)
Above: A nearly 7-second superbolt captured by the Geostationary Lightning Mapper in the southeastern United States in February 2019.
The researchers sifted through two years of data for lightning that shone 100 times brighter than a typical lightning bolt detected from space and found about 2 million events intense enough to be called superbolts – about one in 300 lightning events.
Note that it is possible, however, that some superbolts appeared brighter than other attacks if they were on the edge of a storm cloud and the satellite tracker had a cloudless view.
When the researchers raised the level of lightning events at least 1,000 times brighter than normal lightning, they identified the critical points of the superbolt’s energy activity.
The brightest cases were concentrated in the central United States and in the Rió de La Plata basin, which embraces Uruguay, Paraguay and parts of Argentina and Brazil.
However, the GLM detector may not have captured every single superbolt. Although the satellites are fixed in the Americas, from Alaska in the north to the southern tip of Argentina, GLM measures the strongest lightning, but not necessarily the strongest, if it is shorter than 2 milliseconds.
“[U]singing total energy to the screen for the brightest lightning cases will miss short-lived but extremely powerful optical pulses, “the study authors write in their paper.
There was significant overlap, however, with the superbolts identified by the Los Alamos researchers in a second study, which ranked the superbolts based on their peak power, in the same way that these extreme events were initially defined.
In the second study, the researchers analyzed 12 years of data from another satellite and counted the lightning strikes as a superbolt if they produced 100 gigawatts of power. For comparison, that’s more power in one bolt than all solar panels in the US combined.
“Lightning even exceeded 3 terawatts of power, thousands of times stronger than normal lightning detected from space,” Peterson said.
By combining satellite data with ground-based measurements, the researchers also found that superbolts are indeed a different type of lightning.
The most powerful superbolts (producing more than 350 gigawatts of power) are the result of rare positively charged cloud-to-ground events, rather than negatively charged cloud-to-ground events, which characterize most lightning strikes.
The results also showed that superbolts often occur on the ocean and tend to spark from megaflashes, which extend hundreds of miles horizontally from tip to tail.
‘Ocean storm systems, particularly during winter, and particularly those located in Japan, have been shown to produce these intense superbolts,’ explain the researchers in the second article.
This is somewhat in line with the results of a 2019 study, which found superbolts formed primarily on oceans and seas, although that research found most of the superbolts in the North Atlantic, west of Europe.
Hence, the question is by no means resolved. Atmospheric scientists must continue to compare measurements from different ground and orbiting instruments to understand the differences between them and to better characterize extreme lightning events.
“It will be an important undertaking by the atmospheric electricity community to reconcile the maximum events recorded by the various optics and [ground-based radio-frequency] tools and then come to a consensus on what is – and what is not – a superbolt, “the researchers write.
The two documents were published here and here in Journal of Geophysical Research: Atmospheres.
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