Lightning flash measuring 768 kilometres is the longest ever recorded

The world’s longest lightning flashes – both in terms of the distance covered and duration – have been measured from space and confirmed by the World Meteorological Organization (WMO).

One of the flashes occurred in the southern US in April 2020 and had a length of about 768 kilometres, or the distance from London to Hamburg in Germany, which is 60 kilometres longer than the previous record set in Brazil in 2018.

The second flash was measured in June 2020. It straddled the Uruguay-Argentina border, and lasted for 17 seconds, longer than any other flash ever detected.

“We now have clear proof that single lightning events can last 17 seconds,” says Randall Cerveny at Arizona State University. “This is important to scientists because it improves our understanding of the dynamics of lightning: how, where and, importantly, why lightning occurs the way it does.”

The flashes were seen in thunderstorm hotspots, in the Great Plains of North America and the Río de la Plata basin in South America, respectively. The geography of the areas makes them prone to relatively large convective systems, which can cause individual thunderstorms to combine into massive weather systems that trigger extreme lightning strikes.

The flash that spanned the southern US would have been difficult to measure with conventional ground-based equipment, so meteorologists turned to lightning mappers on geostationary satellites, which have a far wider field of view.

“We have had this type of lightning-detection and mapping equipment in orbit only for a handful of years, and through it, we are learning much more about mega-flashes,” says Cerveny.

Although the flashes were both detected in 2020, it is only now that the WMO has certified the events as having the respective longest distance and longest duration on record.

According to Graeme Marlton at the Met Office, UK, there was a long process of double-checking instruments, cross-checking observations and verification from a panel of experts before the events could be recorded as world record lightning flashes.

With both flashes occurring in 2020, it might seem to indicate that lightning is becoming more extreme, but it could simply be that improved imaging capabilities allowed both records to be broken so recently. “Only once several years of these extreme events have been recorded will we be able to assess whether they are becoming more common,” says Marlton. However, climate change does appear to be increasing the frequency of lightning across Earth.

While the lightning strikes measured didn’t make ground contact, their length and duration are still an important reminder of how far lightning can strike from its parent region, says Cerveny. Any time that you hear thunder, says Cerveny, you should find a lightning-safe place, such as a substantial building or a fully enclosed metal-topped vehicle.