Robert Holzworth’s World Wide Lightning Location Network can detect every bolt of lightning that hits the Earth. Comprised of 100 sensors spread across the globe from Finland to Antarctica, the network can pick up the pulses of electromagnetic energy created and dissipated by lightning strikes. In doing so, it is capable of determining exactly where a strike took place to within roughly five kilometres.
This particular detection network has been in place since the early 2000s and now Holzworth and his team at the University of Washington finally have enough data to analyse a particularly dramatic lightning phenomenon – the superbolt.
Nine years’ worth of data was needed for this task for one reason in particular – superbolts are extremely rare. Defined by the team as a bolt that, at its peak, releases electrical energy of more than one million joules, or a thousand times more energy than the average lightning bolt (the overall energy in the strike would be far higher), they occurred only once out of every 250,000 bolts detected. In total, the researchers looked at around two billion lightning strikes recorded between 2010 and 2018. Some 8,000 events – four-millionths of a per cent – were supersized.
Several discoveries followed this initial finding. ‘It is very unexpected and unusual where and when the very big strikes occur,’ says Holzworth. He is referring to the fact that while 90 per cent of normal lightning occurs over land, around 80 per cent of the superbolts were found to occur over water, though some of these strikes did occur very close to land, with the English coast featuring prominently. In general, superbolts were found to be most common in the northern hemisphere, in the Mediterranean Sea, the northeast Atlantic and over the Andes.
What’s more, the time of year for superbolts doesn’t follow the rules for typical lightning. Regular lightning hits in the summer, but superbolts strike both hemispheres between the months of November and February. The reasons for these differences are still unknown. While the team has a theory that it could be related to sunspots or cosmic rays, it is still too early to say for sure.
It is also not known what effect a superbolt would actually have if one was to break ranks and hit land. Would the devastation be a thousand times worse than a lesser bolt? ‘The short answer to the question is we don’t know,’ says Holzworth. ‘Because we haven’t really captured individual superbolts where we could say it destroyed three trees instead of one. Or it killed five people instead of none.’
Nevertheless, he does add that optical data captured in a different study coincides to some extent with this new analysis. This means that a particularly bright and dramatic-looking bolt of lightning could just be a superbolt. Or, as Holzworth says: ‘If you were standing around on the ground watching it, you would say, oh, there was a big one.’
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