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World record 477-mile-long lightning ‘megaflash’ confirmed over U.S.

The World Meteorological Organization also certified a flash over South America that lasted a record 17 seconds

Lightning image from the Geostationary Lightning Mapper on NOAA's GOES-16 satellite from April 29, 2020. (NOAA)
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The World Meteorological Organization announced on Monday that it had confirmed two new mind-blowing lightning “megaflash” records. The findings, which come after careful data-checking and rigorous certification processes, include one record event that occurred over the Lower 48 states.

On April 29, 2020, a sprawling mass of strong to severe thunderstorms produced a 477.2-mile-long lightning strike over the southern United States. It stretched from near Houston to southeast Mississippi, a distance equivalent to that between Columbus, Ohio, and New York City.

The record beats out a 440-mile-long megaflash that occurred over southern Brazil on Halloween of 2018.

The WMO also identified a new world record for the long-lasting lightning flash. It lit up the skies over Uruguay and northern Argentina for 17.1 seconds on June 18, 2020, surpassing a 16.73-second flash recorded over northern Argentina on March 4, 2019.

“These are extraordinary records from single lightning flash events,” wrote Randall Cerveny, rapporteur of Weather and Climate Extremes for WMO, in a statement.

On the previous record: World record lightning ‘megaflash’ in South America — 440 miles long — confirmed

What are megaflashes?

Megaflashes dwarf ordinary lightning strikes. As Earth dwellers, we’re accustomed to seeing what’s going on near the ground, including conventional cloud to ground lightning bolts. Hundreds or thousands such strikes might accompany a run-of-the-mill thunderstorm on a summer’s afternoon.

Megaflashes are different. They’re enormous. They snake through regions of high electric field and can travel for hundreds of miles while lasting more than 10 seconds. Since most storm clouds are fewer than 10 miles high, lightning can’t grow terribly long in the vertical direction. But megaflashes have plenty of space to sprawl in the horizontal.

Where lightning hit the most in the U.S. in 2021

All megaflashes accompany MCSs, or mesoscale convective systems. MCSs are clusters of thunderstorms that often rage overnight and can occupy an area the size of several states, last for hours and stretch 750 miles or more end-to-end. They’re a staple of the spring and early summer across the southern and central United States, and are also common in Brazil, Argentina and Uruguay. South America’s “Altiplano,” or high Andean Plateau, also brews prolific lightning-producing storms.

Megaflashes crawl through the clouds but can produce or induce ground connections at various points. Sometimes MCSs merge, leading to amplified and more chaotic electric fields that can also be supportive of megaflashes. Covering so much real estate means megaflashes flicker for an extended duration.

How are megaflashes detected?

While atmospheric electrodynamicists had long since theorized about the existence of megaflashes, the scale and duration of said flashes was not well-understood until recently. Conventional lightning detection arrays, which rely on a network of ground-based sensors that detect a strike’s electromagnetic field and use multistation triangulation to determine its location, are most effective in plotting cloud to ground discharges.

“Detecting these extreme lightning events is very difficult due to their exceptional rarity and scale,” wrote Michael J. Peterson of the Space and Remote Sensing Group at Los Alamos National Laboratory, in an email. “Your sensor has to be in just the right place at perfectly the right time to be able to see it — and the instrument has to be capable of measuring something as large as a megaflash. Most sensors historically have fallen short of these requirements.”

That changed with the Nov. 19, 2016, launch of the GOES East weather satellite, soon followed by GOES West. Both peer down on North America from 22,236 miles above Earth and have “Geostationary Lighting Mappers,” or instruments that are able to discern the infrared signal associated with a lightning flash. That allows for the tracking of cloud-to-cloud and intracloud flashes from above.

Similar satellite-mounted devices existed before GOES East and West but were only able to scan smaller swaths and for shorter time windows. In fact, GOES satellites’ geostationary lightning mappers capture one image every two milliseconds; Europe and China will be deploying similar space-born sensors in the coming years.

How common are megaflashes?

There’s reason to believe megaflashes may be more common than once believed. Now that scientists are able to spot and resolve them over North America, they’re able to begin constructing a catalogue of events.

One particularly impressive discharge, which eventually spanned 300 miles but was not evaluated by the WMO, occurred on the morning of Oct. 23, 2017. A thunderstorm was raging near Thackerville, Okla., a little more than an hour’s drive north of the Dallas-Fort Worth Metroplex. A lightning strike illuminated skies near the Red River — Oklahoma’s southern border — at 12:13 a.m.

At the same time, the landscape was also aglow near Burlington, Kansas; the same massive 300 mile-long lightning bolt had illuminated an area four times larger than the state of Connecticut.

“Now that we have a robust record of these monster flashes, we can begin to understand how they occur and appreciate the disproportionate impact that they have,” Peterson wrote in the WMO release. He served as the lead author of the WMO’s report.

The organization has also been keeping tabs on other lightning records and used the latest announcement as an opportunity to underscore the importance of lightning safety. Any time thunder can be heard, an individual is close enough to be struck by lightning.

“The only lightning-safe locations are substantial buildings that have wiring and plumbing; not structures such as at a beach or bus stop,” wrote Ron Holle, a lightning specialist. “As these extreme cases show, lightning can arrive within seconds over a long distance, but they are embedded within larger thunderstorms, so be aware.”

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Just the beginning

With a new generation of detection capabilities rolling out and proliferating around the world, lightning scientists expect there’s much more waiting to be discovered.

“I don’t think we know for sure just how big megaflashes can get,” wrote Chris Vagasky, a lightning specialist at Vaisala, in an email. “Before we had the Geostationary Lightning Mapper, the longest length and the longest duration flashes were measured using Lightning Mapping Arrays. Those records were more than doubled by [these records].”

Vagasky noted that, even with scheduled satellite launches upcoming, “we’ll still be missing portions of Southeast Asia, like Indonesia, Malaysia, and Singapore, and we’ll be missing much of Australia.” That leaves out an enormous area that could be home to megaflashes.

Peterson agrees.

“It is likely that these records of 768 km and 17.102 s are not the final word on extreme lighting,” he wrote in his email.

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