Lightning bolt 829 kilometres long breaks record for biggest ever

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.

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.

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“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.

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