Every now & then, Earth reminds us it’s capable of releasing some furious energy.
The observations come from researchers at US Los Alamos National Laboratory, who used satellites to find the extreme lightning events. The results forced a rethink on what constitutes a superbolt and shed new light on how & where superbolts originate.
“We want to ascertain what the boundaries (of superbolts) really are,” atmospheric scientist Michael Peterson said. “It’s about how big & the way bright they will get.”
Superbolts were first detected from a satellite data in the 1970s. Being described as lighting that outshines average bolts by an element of 100 or more.
Since then, atmospheric scientists are debating what really counts as superbolt because measurements taken by different instruments can be different.
“When you see a lightning flash from space, it’ll look tons dimmer than if you used to see it from ground level because the clouds block a number of the light,” Peterson said, explaining how satellite measurements can differ from ground-based detectors.
There’s also the question arise that whether superbolts are supercharged by some unique phenomenon or if they’re just bigger & brighter strikes of the standard lightning variety.
“Understanding these extreme events is vital because it tells us what lightning is capable of,” said Peterson, who has detected some record-breaking lightning strikes in recent years including one 2018 megaflash (long-duration lightning burst) that stretched some 700 Km across the sky & lasted nearly 17 seconds.
In a new study, Peterson & his colleague Erin Lay analysed data collected by NASA’s Geostationary Lightning Mapper, a detector strapped to weather satellites & sent into orbit to record flashes of lightning, day & night, over America and the adjacent oceans every 2 milliseconds.
Unlike ground-based monitoring systems which detect radio waves, the GLM measures the entire brightness (optical energy) of lightning bolts in clouds between clouds plus lightning that strikes the bottom.
The researchers combed data of two years for lightning strikes that shone 100 times brighter than a typical bolt detected from space & located about 2 million events intense enough to be called a superbolt, roughly one in every 300 lightning events.
It’s possible though that some superbolts appeared brighter than other strikes, if they were on the fringes of a cloud & the satellite detector had a cloud free view.
When researchers raised the bar to lightning events at least of 1,000 times brighter than a standard lightning strike & they identified key hotspots of energetic superbolt activity.
However, the GLM detector won’t have captured every single superbolt. Although the satellites are fixated on the Americas from Alaska in the north to Argentina’s southern tip, GLM measures the most energetic lightning bolts but not necessarily the foremost powerful flashes, if they happen to be shorter than two milliseconds.
“Using total energy to screen for the brightest lightning cases will miss short-duration yet extremely powerful optical pulses,” the study authors wrote in their paper.
There was significant overlap, however, with superbolts identified-by Los Alamos researchers in a second study, which classified superbolts by their peak power, the similar way these extreme events had first been defined.
In second study, researchers analysed 12 years of data from another satellite & counted lighting strikes as superbolts, if they produced 100 gigawatts of power. For comparison, that’s more power in 1 bolt than all the solar panels in the US combined.
“One lightning stroke even exceeded 3 terawatts of power, thousands of times stronger than ordinary lightning detected from space,” Peterson said.
Combining satellite data with ground-based measurements, researchers also found that superbolts are indeed a different type of lightning.
The most powerful superbolts (producing more than 350 gigawatts of power) resulted from rare charged cloud to ground events, instead of negatively charged cloud-to-ground events which characterizes most lightning strikes.
The results also showed that superbolts often occur over the ocean & have a tendency to spark from megaflashes, which stretch many miles horizontally from tip to tail.
“Oceanic storm systems, particularly during the winter & particularly those located around Japan are shown to supply these intense superbolts,” researchers explain in the second paper.
This somewhat aligns with results from a 2019 study which found that superbolts mainly formed over the oceans & seas, although that research detected most superbolts in the North Atlantic, west of Europe.
So, matter is by no means settled. Atmospheric scientists keep comparing measurements from different ground-based & orbiting instruments to know differences between them & to better characterise extreme lightning events.
“It’ll be an important undertaking by atmospheric electricity community to reconcile the top-events recorded by the various optical & ground-based radio frequency instruments. Then come to a consensus on what is & what is not, a superbolt,” researchers wrote.
The two papers were published in the Journal of Geophysical Research: Atmospheres.