3 months ago
35
A crackling monster strike that spanned the equivalent distance between Sydney and Melbourne has been confirmed as the largest lightning flash on record by the World Meteorological Organisation (WMO).
The flash stretched 829 kilometres through a chaotic complex of thunderstorms across the Great Plains in America, from eastern Texas to Kansas City. The “megaflash” beat the previous record by 61 kilometres and covered the distance of a 90-minute flight in seconds.
This lightning storm over the US, captured by NOAA satellites, produced a record-breaking megaflash in 2020. Now another megaflash, uncovered during the reanalysis of a 2017 storm, has beaten that record.Credit: NOAA
Scientists are rethinking safety implications as meteorologists get a better handle on these colossal, rarely captured electric events.
“Lightning is a source of wonder but also a major hazard that claims many lives around the world every year,” WMO Secretary-General Celeste Saulo said.
“These new findings highlight important public safety concerns about electrified clouds, which can produce flashes which travel extremely large distances and have a major impact on the aviation sector and can spark wildfires.”
Megaflashes are a single discharge of lightning at least 100 kilometres long. The flashes shoot horizontally through a type of storm called a mesoscale convective system, which is a massive cluster of circulating thunderstorms.
Lightning in normal storms travels only a few kilometres.Credit: Nick Moir
Ice crystals, super-cooled water droplets, and hail-like lumps collide and exchange electrons within thunderstorms, resulting in positively and negatively charged regions with clouds.
That can generate an electric charge which leaps between oppositely charged parts of a thunderstorm as intra-cloud lightning, or towards the ground as a strike that’s hotter than the sun.
In a mesoscale storm, the generation of charge happens on a massive scale.
The huge systems unleash megaflashes due to “expansive electrified clouds that discharge at sufficiently low rates to facilitate single horizontal flashes spanning extraordinary distances”, according to the American Meteorological Society.
Satellite image of the record lightning flash spanning 829 kilometres.Credit: WMO
Because megaflashes travel so far and fast, they undermine the “30-30 rule” taught in the US, where lightning is considered dangerous if the time between a flash of light and thunder is less than 30 seconds. For a normal storm, 30 seconds between the flash and thunder would mean the storm is about 10 kilometres away. A normal lightning strike wouldn’t reach that far.
A megaflash storm, however, can send bolts many hundreds of kilometres from the main charge-generating region, putting unsuspecting people at risk.
An average megaflash unleashes five to seven ground strikes on average as it zigzags through the clouds, according to lightning scientist Michael J. Peterson, who was the lead author of the research identifying the record-breaking flash.
Loading
“These statistics demonstrate that there is no safe location below an electrified cloud that is producing megaflashes, and current lightning safety guidance is not always sufficient to mitigate megaflash hazards,” Peterson, from Georgia Tech Research Centre, wrote in Earth Interactions.
Scientists have only recently gained the ability to measure megaflashes thanks to space-based mapping technology and geostationary satellites now permanently trained on storm hotspots such as the Great Plains.
Meteorologists discovered the new record-breaking megaflash by reanalysing data from a 2017 storm.
Mesoscale storm systems capable of summoning megaflashes also occur in Australia, often in the north.
The Examine newsletter explains and analyses science with a rigorous focus on the evidence. Sign up to get it each week.
Most Viewed in National
Loading
