There are few sights and sounds more able to instill us with delicious, jellifying terror than a full-blooded lighting storm. There are 16 million across the globe every year. But how do they form and how do they work? To find out, we look at 10 different types of electrical discharge from the small-scale to the gut-wrenchingly huge – and maybe gain a new appreciation, tinged with fearful awe, of what happens when Mother Nature turns the lights on.
Cloud To Ground Lightning
(Image via: Warren Tyrer)
How do you make lightning? Easy. All you need is a couple of hundred cubic miles of air, a large space above it (40,000 vertical feet is a nice number), and a massively powered heat-engine – say, the Earth. Ready? Take your air and steadily heat it up. As it rises, it will cool and condense into droplets of water vapour in fluffy, opaque clumps. Congratulations – you are now the proud owner of a bouncing baby cumulonimbus.
(Image via: Richard Fisher)
Now for the science bit. For reasons that are by no means clear, some parts of the cloud shed electrons and other parts gain them – in other words your storm-cloud gains an electrical charge, the top becoming positive and the base negative. Where you have opposite charges, you have an electrical field between them. Excitement all round. But all this fun isn’t limited to the sky – thanks to the rules of electrostatic induction, the ground gains an equal and opposite charge to the nearest part of the cloud lying overhead. Now you have perfect conditions for a bridging spark of truly epic proportions.
(Image via: jfyffe)
Once the field is strong enough, the air ionizes into plasma, a far better conductor of electricity. This happens unevenly, forming “paths” of plasma through the storm that provide crooked lines of least resistance for lightning – these are known as step leaders. In a fraction of the blink of an eye, step leaders fan down through the cloud and out the bottom, branching downwards like the roots of a tree. As this truly wondrous high-speed footage shows, all it takes is for one of these faintly glowing channels to connect with the ground…and ZAP. You just made lightning. Safety announcement: since it is hotter than the surface of the Sun (a toasty 30,000 °C), be sure to take a few steps back – not that you have time, as a lightning bolt travels at 130,000 miles an hour.
Ground to Cloud Lightning
(Image via: zoutedrop)
Sometimes the ground will give lightning a helping hand – an upward-pointing thread of positively-charged plasma called a streamer. All objects on the ground will create their own streamers (including human bodies) which attempt to meet the downward-traveling step leaders halfway. When these streamers are of an unusual size, they become the dominating leaders and the resulting bolt of lightning will travel upwards. The taller the object, the more likely it is that one of its streamers will attract or emit a lightning bolt – which is why it is good practice to avoid trees in a storm.
Cloud to Cloud Lightning
(Image via: Thrutheeyes)
But why go as far as the ground? Clouds can earth themselves (for want of a better word) by firing bolts between their oppositely-charged regions, either as intracloud lightning or the much rarer intercloud variety (from one cloud to another).
(Images via: NOAA Photo Library / Wikimedia Commons and CrankyPK)
If you’re watching a thunderstorm, most of the light show is intracloud lightning. Aircraft pilots are particularly wary of intercloud bolts for one very good reason – they shoot across their flightpaths.
(Image via: Louie Jerome / Wikimedia Commons)
It seems ludicrous to describe something moving at 36 miles a second as “crawling”, but that is what anvil lightning does – spreading horizontally across the sky, giving the eye just enough time to discern its movement.
(Image via: Yeeta)
A particularly dangerous variety of anvil lightning is the “bolt from the blue” – a strike that moves horizontally away and out from the cloud before curling back down to earth, sometimes appearing out of a blue sky. As it originates in the positively-charged upper regions of a cloud, this is a form of positive lightning – massively charged and extremely hazardous.
(Image via: Disaster Strikes)
Ribbon lightning is lighting that gets blown sideways by the wind. No, really. Remember, lightning follows the paths of ionized air particles – and if the wind is strong enough, these particles will scud sideways, parallel to the observer. Any further lightning bolts will also appear to have been blown by the wind.
(Image via: Weatherfriend)
What we regard as a discrete flash of lightning is usually a flurry of bolts in both directions – and ribbon lightning (looking for all the world like bad camerawork) is the result of the afterimage of displaced return strokes of lightning registering on the human eye or digital CCD.
(Image via: © 2009 Andy Nixon – www.andynix.za.net)
Weirder still (and rarely captured on film) is bead lightning, the result of the lightning trail cooling down and breaking up into a string of bright, often spherical sections, visible for anything up to a second. It is not known if this is a product of standard irregularities in the path of the lightning, or if some atmospheric factor is malforming the lightning itself.
Sprites, Jets and Elves
(Image via: Sprites And Jets)
If anything illustrates how little we understand electrical storms, it is what happens above the clouds. They have been anecdotally recorded for decades, but it was only in 1994 that cameras first captured proof of the existence of a bizarre, colorful family of electrical discharge. We have termed them jets, sprites and elves – and they have modern science somewhat flummoxed.
(Image via: Wikimedia Commons)
Red sprites (and yes, that is their actual color) appear to be intense directed explosions of high-energy electrons triggered by positive lightning or cosmic radiation. They burst upwards at relativistic speed, almost too quick for the naked eye, to a height of almost 100 km. And…that is about all we know, so far. If you can bear the accompanying music, watch them in action here.
(Image via: Anomalies Unlimited)
Some people argue there’s no such thing. Other people post their YouTube videos and stand by them to the bitter end. But whether it truly exists or not, ball lightning has polarized (sorry) popular imagination ever since the above photo by a Japanese student started circulating. Until it is definitively captured on film or reproduced in the lab, it remains a case for Mulder and Scully.
St. Elmo’s Fire
(Images via: Captain James Ashby and Martin Popek)
Thanks to the late great John Hughes, everyone has heard the name – but what exactly is it? For the answer, we go back to the effect of electrical charge upon the air in a thundercloud. When grounded objects start to accumulate charge, they ionize the surrounding air and turn it to plasma, accompanied by an eerie blue glow and a flicker of small-scale electrical discharges. Remember that plasma makes it much easier for lightning to strike? Then you’ll know why St Elmo’s Fire is a very bad thing to encounter on your travels – and why this video of a commercial flight passing near a thunderstorm is not for the faint-hearted.
(Image via: Thunderbolts)
Lastly we come to a manifestation of lightning where everything comes together and anything goes. When volcanoes erupt, they unleash lightning storms of staggering ferocity. Talking of the eruption of Vesuvius in 79 AD (and the destruction of Pompeii), Pliny the Younger wrote: “behind us were frightening dark clouds, rent by lightning twisted and hurled, opening to reveal huge figures of flame.”
(Image via: geekologie)
The mechanics of volcanic lightning aren’t yet known – it seems likely that water vapour released from magma forms a localized, super-concentrated form of storm cloud, unleashing a terrifyingly accelerated bout of electrical activity. Whatever the underlying causes, it’s clear that while the best advice for avoiding standard lightning is to get somewhere safe and crouch in a ball, if it’s volcanic lightning- you get out of there fast. Some storms aren’t meant to be weathered by mere mortals.