Apr 14, 2025 04:07 PM
https://www.sciencefocus.com/planet-eart...ng-weirder
EXCERPTS: . . . We’ve certainly tried to get to the bottom of it and, over the years, the quest to understand lightning has inspired many strange, and in some cases productive, endeavours. [...] That’s not to say we’re still entirely in the dark about it, though. We do know that lightning is a large-scale discharge of electrical energy. It can discharge from clouds towards the ground, within clouds or even from clouds upwards into space.
That charge is built up as tiny particles of hail, ice and water move through the turbulent environment within a thundercloud. When they bump into each other, they knock electrons free and transfer charge from one particle to another – much like rubbing a balloon against your head can create a static charge that makes your hair stand on end.
Typically, small, positively charged ice crystals tend to get carried upwards to the top of the cloud, while heavier, negatively charged lumps of wet hail drift down towards the bottom. The resulting polarisation generates an electric field.
At the same time, a pool of positive charge builds up on Earth’s surface below the storm cloud. It’s now essentially a giant battery in the sky, but instead of the batteries containing a few volts that we’re accustomed to using in our homes, this cloud battery consists of a hundred million volts.
Once the electric field becomes great enough, a lightning channel forms and dissipates the electric field. The lightning channel is “very narrow, very hot and extremely conductive of electricity. It almost behaves like a wire in the cloud,” says Prof David Smith, who specialises in atmospheric science and astrophysics at the University of California, Santa Cruz, in the US.
We’re most familiar with lightning that travels from clouds to the ground, but around 75 per cent of lightning actually happens within the storm cloud. That’s because the electric field within the clouds is much stronger than the one between the clouds and Earth’s surface.
But wherever it comes from, there’s still a fundamental question we can’t answer: how does lightning start?
Part of the reason we still don’t fully understand how lightning forms is that it’s extremely difficult to study. “It’s happening up in a cloud, which is a very hostile place,” says Smith. “And in the moments before a strike, when lightning is forming, it’s shrouded from sight by clouds.”
It’s very dangerous to fly directly through a storm cloud and most planes can’t reach altitudes high enough to fly above them, so researchers have largely been restricted to studying lightning from the ground below or from above, in space.
And that’s not all. The very act of trying to study lightning risks disrupting the conditions needed to create it. “An aeroplane is a big piece of metal and when you put that in the cloud, you’re disturbing the electrical environment that you want to explore,” Smith says.
Because we can’t easily get inside a storm cloud to study lightning directly, much of the research into it relies on measuring lightning indirectly. Light and radio waves, for example, are created when electrical charges move – giving scientists clues as to where lightning is forming.
A common method to study lightning as it forms uses a technique called radio interferometry, which detects the radio waves using antennae at ground level. Scientists can use this approach to triangulate the location of electrical discharges inside thunderclouds to within a few tens of meters. But it doesn’t tell them exactly what’s triggering the lightning.
Another method in the lightning scientists’ toolkit is creating artificial lightning in a specialised laboratory. “The advantage of using a laboratory is that it’s very controllable and repeatable,” says Dr Daniel Mitchard, a particle physicist at Cardiff University’s Lightning Laboratory. In other words, researchers can collect measurements that would be nearly impossible in real clouds due to the unpredictable nature of lightning.
“You can put a lot of instrumentation very close to that lightning arc to measure things like energy and temperatures,” Mitchard explains.
However, artificial lightning strikes are “as destructive as they are in real life,” he says. “So, we can’t be anywhere near [the generated lightning] when it goes off. You can’t look at it because it’ll blind you. You have to wear ear protection, because we also produce the thunder – and it’s all within a shielded room.”
Only in the last 30 years or so have we had the technology to study lightning clouds from above – using space shuttles and satellites – and this has opened new avenues of research and reinvigorated the quest to understand how lightning forms.
A key player in the mystery of how lightning starts is the fact that air is an extremely good insulator – in other words, it doesn’t readily conduct electricity. So, an enormous electric field is needed to overcome that insulating power and create lightning that can jump gaps spanning several kilometres.
Scientists have calculated the size of the electric field needed (known as the ‘breakdown threshold’), but when they’ve measured the electric fields inside thunderclouds, they don’t come anywhere close to that threshold.
“You’ve got millions of lightning flashes a day and yet you never seem to see an electric field big enough to actually make a spark,” says Joseph Dwyer, professor of physics and astronomy at the University of New Hampshire, in the US. “It’s one of the biggest mysteries in the atmospheric sciences.”
Scientists have proposed a number of explanations for this apparent contradiction... (MORE - missing details)
EXCERPTS: . . . We’ve certainly tried to get to the bottom of it and, over the years, the quest to understand lightning has inspired many strange, and in some cases productive, endeavours. [...] That’s not to say we’re still entirely in the dark about it, though. We do know that lightning is a large-scale discharge of electrical energy. It can discharge from clouds towards the ground, within clouds or even from clouds upwards into space.
That charge is built up as tiny particles of hail, ice and water move through the turbulent environment within a thundercloud. When they bump into each other, they knock electrons free and transfer charge from one particle to another – much like rubbing a balloon against your head can create a static charge that makes your hair stand on end.
Typically, small, positively charged ice crystals tend to get carried upwards to the top of the cloud, while heavier, negatively charged lumps of wet hail drift down towards the bottom. The resulting polarisation generates an electric field.
At the same time, a pool of positive charge builds up on Earth’s surface below the storm cloud. It’s now essentially a giant battery in the sky, but instead of the batteries containing a few volts that we’re accustomed to using in our homes, this cloud battery consists of a hundred million volts.
Once the electric field becomes great enough, a lightning channel forms and dissipates the electric field. The lightning channel is “very narrow, very hot and extremely conductive of electricity. It almost behaves like a wire in the cloud,” says Prof David Smith, who specialises in atmospheric science and astrophysics at the University of California, Santa Cruz, in the US.
We’re most familiar with lightning that travels from clouds to the ground, but around 75 per cent of lightning actually happens within the storm cloud. That’s because the electric field within the clouds is much stronger than the one between the clouds and Earth’s surface.
But wherever it comes from, there’s still a fundamental question we can’t answer: how does lightning start?
Part of the reason we still don’t fully understand how lightning forms is that it’s extremely difficult to study. “It’s happening up in a cloud, which is a very hostile place,” says Smith. “And in the moments before a strike, when lightning is forming, it’s shrouded from sight by clouds.”
It’s very dangerous to fly directly through a storm cloud and most planes can’t reach altitudes high enough to fly above them, so researchers have largely been restricted to studying lightning from the ground below or from above, in space.
And that’s not all. The very act of trying to study lightning risks disrupting the conditions needed to create it. “An aeroplane is a big piece of metal and when you put that in the cloud, you’re disturbing the electrical environment that you want to explore,” Smith says.
Because we can’t easily get inside a storm cloud to study lightning directly, much of the research into it relies on measuring lightning indirectly. Light and radio waves, for example, are created when electrical charges move – giving scientists clues as to where lightning is forming.
A common method to study lightning as it forms uses a technique called radio interferometry, which detects the radio waves using antennae at ground level. Scientists can use this approach to triangulate the location of electrical discharges inside thunderclouds to within a few tens of meters. But it doesn’t tell them exactly what’s triggering the lightning.
Another method in the lightning scientists’ toolkit is creating artificial lightning in a specialised laboratory. “The advantage of using a laboratory is that it’s very controllable and repeatable,” says Dr Daniel Mitchard, a particle physicist at Cardiff University’s Lightning Laboratory. In other words, researchers can collect measurements that would be nearly impossible in real clouds due to the unpredictable nature of lightning.
“You can put a lot of instrumentation very close to that lightning arc to measure things like energy and temperatures,” Mitchard explains.
However, artificial lightning strikes are “as destructive as they are in real life,” he says. “So, we can’t be anywhere near [the generated lightning] when it goes off. You can’t look at it because it’ll blind you. You have to wear ear protection, because we also produce the thunder – and it’s all within a shielded room.”
Only in the last 30 years or so have we had the technology to study lightning clouds from above – using space shuttles and satellites – and this has opened new avenues of research and reinvigorated the quest to understand how lightning forms.
A key player in the mystery of how lightning starts is the fact that air is an extremely good insulator – in other words, it doesn’t readily conduct electricity. So, an enormous electric field is needed to overcome that insulating power and create lightning that can jump gaps spanning several kilometres.
Scientists have calculated the size of the electric field needed (known as the ‘breakdown threshold’), but when they’ve measured the electric fields inside thunderclouds, they don’t come anywhere close to that threshold.
“You’ve got millions of lightning flashes a day and yet you never seem to see an electric field big enough to actually make a spark,” says Joseph Dwyer, professor of physics and astronomy at the University of New Hampshire, in the US. “It’s one of the biggest mysteries in the atmospheric sciences.”
Scientists have proposed a number of explanations for this apparent contradiction... (MORE - missing details)
