Anyone who has watched a lightning storm knows that lightning is one of nature's most awe-inspiring phenomena.
According to the U.K. Met Office, lightning strikes the planet up to four billion times a year. It's more than just a light show, as it helps to keep Earth's electrical balance in check, aids in fixing nitrogen, and even helps to clear the atmosphere of pollutants.
Some lightning strikes work harder than others. While most lightning flashes measure 2 to 3 miles in length, some bolts larger than our heads can be heard above our heads, forking their way across hundreds of miles of sky. How big can lightning get? Should we be concerned about these bolts?
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When there is a strong positive charge in one region of the cloud and a strong negative charge in another, there is electrical force between them.
Don MacGorman is a physicist and senior researcher at the National Severe Storms Laboratory in Oklahoma.
As the electric force grows, it breaks down the air's insulation power, which keeps areas of different charge separated from each other. The electrons in the air are knocked loose from their atoms and molecules by the excessive electrical force. MacGorman told Live Science that the process is called an electron avalanche and it is what we mean when we say the air breaks down.
This creates a hot channel in the air that acts like a wire, with the ends growing outward towards the positive and negative charges that caused the breakdown. The growing channel eventually connects the positive and negative charges, and when it does, it creates a huge electric current.
MacGorman said that it was a giant spark that had grown through the cloud.
Sometimes the lower region of a cloud doesn't have enough charge to stop the channel. The lightning bolt is stretching downward. As it does so, it draws an upward spark from the ground to meet it, triggering a lightning flash with huge electric currents that transport some of the storm's charge to the ground. The cloud-to-ground channels are what most of us think of when we think of lightning.
What factors limit the bolts' size? For decades, researchers have been trying to answer this question. The maximum extent of a flash is limited by the height of a storm cloud, which is about 20 km from the ground.
There is more room to play with an extensive cloud system. The heavyweights work here.
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Myron Ligda used radar to detect a flash that spanned more than 100 miles. It was recognised as the longest lightning flash ever recorded. Researchers have been able to measure larger flashes thanks to technology.
A 200 mile bolt over Oklahoma was identified in 2007. In October of last year, a huge flash of lightning illuminated the skies above Texas, Oklahoma and Kansas. A group of researchers published a study in the Bulletin of the American Meteorological Society about the mega flash that hit three states.
The flash has been surpassed. A lightning bolt over Brazil was later found to have spanned more than 700 km. The skies broke the record on April 29, 2020 with a mega flash that stretched from Texas to Mississippi, covering 476 miles.
Satellites record many of the record-breaking flashes that lightning has traditionally been observed from. MacGorman is an author of a study about the record-breaking lightning flash in October of last year.
Even with these exciting visual insights, researchers are still unsure of the precise mechanics that underpin such lengthy electrical illuminations. Large scale wind flows that enable that system to be tied together to persist for a long time are certain processes that are required.
Christopher Emersic, a research fellow who studies thunderstorm electrification at the University, said that the mega flashes appear to be a continuous sequence of discharges in very close succession.
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He thinks that if a cloud system is charged across a large area, a series of discharges can fall like dominoes.
The larger the parent cloud, the more opportunity there is for the discharge to continue propagating.
MacGorman said that storms can get larger than the ones we have measured from.
With more sophisticated detection tools, it is likely that lightning hunters will find even larger bolts that break current records and increase our awareness of these immense natural feats.
Despite the apocalyptic picture they paint, mega flashes are not necessarily more dangerous than regular lightning.
Because the cloud systems from which they originate are so vast, it can be difficult to predict mega flash strikes.
It is possible that in a warming world there will be an increase in the types of storms that give rise to megaflashes.
MacGorman estimates that mega flashes make up less than 1% of lightning flashes. Even though researchers like him will go on hunting, they will discover even bigger monsters for us to marvel at.
Live Science originally published it on December 14, 2019.
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