From time to time the Earth reminds us that it is capable of releasing angry energy.
Case in point: Scientists have just discovered a new extreme in hot spots of lightning activity called ‘superbolts’: intense lightning strikes that shine up to 1,000 times brighter than typical lightning strikes.
The observations come from researchers at Los Alamos National Laboratory in the US, who used satellites to measure the extreme lightning strikes. The results force a rethink of what a superbolt is, and shed new light on how and where superbolts form.
“We want[ed] to see what the boundaries are [of superbolts] be real, ”said atmospheric scientist Michael Peterson The Washington Post. “It’s about how big and how bright they can get.”
Superbolts were first detected from satellite data in the 1970s and are described as lighting that exceeds average bolts by a factor of 100 or more.
Since then, atmospheric scientists have been debating what really counts as a superbolt, as measurements from different instruments can vary.
“When you see a lightning bolt from space, it looks much fainter than if you saw it from the ground, because the clouds block some of the light,” Peterson said, explaining how satellite measurements can differ from on. ground based detectors. .
There is also the question of whether superbolts are fueled by a unique phenomenon, or whether they are just bigger, brighter strikes of the usual lightning variant.
“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 mega-flash (sustained lightning strike) that stretched over 700 kilometers. (440 miles) across the sky and lasted almost 17 seconds.
In a new study, Peterson and his colleague Erin Lay analyzed data collected by NASA’s Geostationary Lightning Mapper, a detector attached to weather satellites and orbiting Earth to record lightning flashes, day and night, over America and the adjacent oceans every two milliseconds.
Unlike ground-based monitoring systems, which detect radio waves, the GLM measures the total brightness (optical energy) of lightning strikes in clouds, between clouds, plus lightning strikes on the ground.
Above: A nearly 7-second superbolt captured by the Geostationary Lightning Mapper over the southeastern United States in February 2019.
The researchers combed two years of data for lightning strikes that shone 100 times brighter than a typical lightning bolt detected from space, and found about 2 million events intense enough to be called a superbolt – about one in every 300 lightning strikes .
However, keep in mind that it is possible that some superbolts appeared brighter than others if they were on the edge of a storm cloud and the satellite detector had a cloud-free view.
When the researchers raised the bar for lightning events that were at least 1,000 times brighter than a regular lightning strike, they identified key hot spots of energetic superbolt activity.
The most radiant cases were concentrated in the central United States and in the Rió de La Plata Basin, which stretches across Uruguay, Paraguay and parts of Argentina and Brazil.
However, the GLM detector may not have captured every superbolt. Although the satellites are fixed on America, from Alaska in the north to the southernmost tip of Argentina, GLM measures the most energetic lightning bolts, but not necessarily the most powerful flashes, if they are shorter than 2 milliseconds.
“[U]sing total energy to screen for the brightest lightning events will lack short but extremely powerful optical pulses, ”the study authors write in their paper.
However, there was significant overlap with superbolts identified by Los Alamos researchers in a second study, in which superbolts were classified based on their peak power – in the same way that these extreme events were first defined.
In the second study, the researchers analyzed 12 years of data from another satellite and counted lightning strikes as superbolts when they produced 100 gigawatts of power. In comparison, that’s more power in one bolt than all solar panels in the US combined.
In fact, a lightning strike was more than 3 terawatts of power – thousands of times stronger than ordinary lightning detected from space, Peterson said.
By combining satellite data with ground measurements, the researchers also found that superbolts are indeed a different kind of lightning.
The most powerful superbolts (producing over 350 gigawatts of power) were the result of rare positively charged cloud-to-earth events, rather than negatively charged cloud-ground events, which are characteristic of most lightning strikes.
The results also showed that super bugs are common over the ocean and tend to spark from mega-flashes, which extend horizontally for hundreds of miles from tip to tail.
“Oceanic storm systems, especially during the winter, and especially those around Japan, have been found to produce these intense superbolts,” the researchers explain in the second paper.
This is somewhat in line with the results of a 2019 study that found superbolts formed mainly over the oceans and seas, although that study found most superbolts in the North Atlantic Ocean, west of Europe.
So the issue is far from resolved. Atmospheric scientists must continue to compare measurements from different ground and orbit instruments to understand the differences between them and to better characterize extreme lightning strikes.
“It will be an important undertaking of the atmospheric electricity community to discover the top events generated by the various optical and [ground-based radio-frequency] instruments and then come to a consensus on what is and what is not a superbolt, ”the researchers write.
The two articles are here and here in it Journal of Geophysical Research: Atmospheres.