A massive bolt of lightning that lit up the sky from Dallas to Kansas City, Mo., in October 2017 is officially the longest single flash ever recorded.
A reanalysis of satellite data collected during the storm revealed that this megaflash spanned 829 kilometers and lasted 7.39 seconds, says Michael Peterson, an applied physicist at Georgia Tech in Atlanta. A study describing the event was published online July 31 in the Bulletin of the American Meteorological Society.
Megaflashes are relatively rare, happening in only about 1 in 1,000 thunderstorms across the Americas. But any given one can pack a punch, Peterson says. They’re long, complex discharges of electricity that don’t just shunt energy from cloud to cloud, but from cloud to ground as well. While typical lightning strikes the ground for mere microseconds, these massive bolts do so for up to 100 milliseconds, potentially infusing energy into a tree or other target. That can also make them powerful triggers for wildfires.
The 2017 cloud-to-cloud record-breaker spawned from a massive thunderstorm system that swept across the U.S. Midwest. It also sparked at least 116 cloud-to-ground spikes along its length.
Megaflash hot spots include the U.S. Midwest and southeastern South America, site of the previous record-holder, a 709-kilometer-long bolt over parts of Brazil and Argentina. That lightning still holds the record for longest duration, at 17 seconds.
Researchers hope that satellites “staring” — in geostationary orbit, that is — continuously at such hot spots will help uncover why these flashes occur.
“They have the same ingredients as ordinary lightning, but with a twist,” Peterson says. The convective heart of thunderstorms can contain many rain and ice particles, which are sent aloft to different heights due to updrafts. Each particle can carry a charge, and when they collide, the charge transfers, forming lightning.
There’s a limit to how high these particles can rise: Thunderstorm cells don’t tend to kick them up higher than 11 kilometers, the upper boundary of Earth’s troposphere, or lowest atmospheric layer. “When they can’t go up anymore, they go out,” creating the potential for an epic flash, Peterson says. “There are these massive, horizontally large, charged layers that are vertically as thin as a sheet of paper. And these layers are key ingredients for megaflashes.”
Understanding how giant bolts of lightning form is an active area of research, he adds. “A single strike can potentially impact a lot of people. It’s the most impactful kind of lightning we have on Earth,” Peterson says. “It’s the kind of lightning we want to get a good handle on to keep people safe.”