What’s more than ten kilometres (6 miles) long, five times hotter than the surface of an average star and packs in more strokes per second than an over-zealous teenage boy who’s just discovered the joy of internet porn?
Yeah, I know. The picture kind of gives it away doesn’t it?
I have had a complete love affair with thunderstorms for as long as I can remember. I think they are the most awe-inspiring and yet paradoxical demonstration of nature’s prodigious temper and seductive grace. In the space of an hour, the sky can go from an azure blue to the colour of dark slate as giant cumulonimbus clouds broil and swell with latent energy.
Thunderstorms generate all kinds of severe weather: torrential downpours, vicious winds, hail, microbursts and even tornadoes. But they indirectly owe their very name to the one weather feature that claims the lives of, on average, 55 people every year in the United States: lightning!
Shocking Statistics
Source: Global distribution of lightning April 1995 – February 2003 from the combined observations of the NASA OTD (4/95-3/00) and LIS (1/98-2/03) instruments.
Approximately 8 million bolts of lightning strike the Earth every single day, starting 10,000 forest fires annually. In the United States, over 300,000 insurance claims are made against lightning damage every year and the bill for this damage is a staggering $400,000,000.
Yes. Thunderstorms are seriously dangerous systems. I shouldn’t have to tell you that and yet countless golfers are killed by lightning every year. Could there be anything less intelligent than standing in the middle of a wide open space during a thunderstorm with a metal rod in your hand pointed at the sky? With five billion joules of energy surging through a single lightning bolt – enough energy to illuminate a 100 watt bulb for three months – you are picking a fight you simply cannot win.
Against all logic, according to the U.S. National Weather Service, lightning STILL kills more people than tornadoes AND hurricanes combined. What is this madness?
It’s Electricity!
Thunderstorms are extremely busy weather systems. Within a storm cell, legions of water vapour particles are whipped, flung and tumbled around by complex air circulations. Storms themselves are powered by strong updrafts of hot, moist air. This air cools and condenses as it rises through the heights of the lower atmosphere, becoming dense. It consequently loses its upward momentum and sinks and spills out of the rear of the thunderstorm (check out the diagram below).
Photo Credit: “Thunderstorm formation” by NOAA T-storm-mature-stage.jpg. Licensed under Public Domain via Wikimedia Commons
Together, these motions form a continuous cycle of updrafts and downdrafts, which provides the storm system the energy it needs to electrocute golfers, whip cows into the air and blow Dorothy and her dog, Toto, into a parallel reality.
How does this explain what lightning is? Well, it brings us a lot closer to understanding cloud polarization. OMG. What does that mean?
Clouds Can be Bi-Polar Too
Just like batteries, molecules and certain members of your family, clouds too can become bi-polar. Within a thunderstorm, legions of water vapour particles get swirled around violently by the turbulent air circulations. But there are two predominant movements of air in a single cell storm system: hot moist air going up and colder drier air going down.
The water vapour particles being swept up into the cloud smash into those going down and these collisions, while totally invisible to us, are violent enough to cause the descending water particles to literally tear electrons off of the ascending water particles. Electrons are negative. So you see there is a gradual separation of charge within a thundercloud as the descending water particles become negatively charged and the rising water particles (having had an electron or two pilfered from their orbitals) become positively charged.
Credit: Earth Science Australia
As a result of particle motions within a thunderstorm, the lower cloud regions become negatively charged and the upper cloud regions positively charged. A positive charge is induced in the ground immediately below the thunderstorm in response to storm’s electric field.
The story doesn’t end here: the polarization of the thundercloud has an effect on its environment, namely, the surface of the Earth and the various objects on it. An electrical field swells outwards from the cloud, caressing the electrons belonging to Earth’s atoms, seducing them into moving. Those who studied physics will remember, electron movement = charge.
The presence of such a massive reservoir of negative charge immediately above the Earth’s surface repels its negatively charged electrons (like repels like), causing an opposing positive charge to build up. In other words, trees, poles, buildings and your head actually develop a static positive charge in the seconds prior to lightning strike. This is probably why people who have been struck by lightning and have lived to tell the tale say that they felt their hair stand on end just before they become a living conductor for 1,000,000,000 volts of electricity.
Zap!
At some critical juncture, nature notices the thunderstorm’s complete disregard for her love of equilibrium and so a raging streak of electricity discharges between the negative and positively-charged cloud regions. Or the negatively charged lower cloud regions and the positively charged ground immediately below it. And ZAP! You get lightning!
I can feel the cogs of your mind over-heating. So, if you aren’t quite happy with this explanation, then watch the movie Thor. While it doesn’t provide any scientific explanation on lightning genesis whatsoever, Chris Hemsworth is so beautiful you will forget your intellectual torment immediately *swoon*
Guys… you can enjoy watching Natalie Portman at her career low. In a lab coat.
I know I did.
Thunder, Contrary to Kindergarten Mythology, is Not God’s Fart
In spite of my illuminating explanations above – coupled with your homework to watch Thor – the exact physics of lightning generation are not entirely understood. Thunder, on the other hand, is and its explanation makes for a very interesting story. You may want to remember this so you can impress a future date with it…
When lightning tears out of a cloud, the air in the discharge channel heats up from ambient air temperature to a toasty 28,000°C or 50,000°F. That’s approximately five times hotter than the surface of our Sun. And all of this happens in as little as 90 microseconds. I know, right? A yawning chasm of a time denomination.
The problem is, you can’t heat anything up from 10°C to 28,000°C in this short amount of time without some kind of catastrophic consequence. So when lightning shows the ill social etiquette of doing so, the air expands violently, generating a shockwave that explodes outwards from the discharge channel. This shockwave travels faster than the speed of sound – it’s supersonic – so we can’t actually hear it. Dogs probably could, but you’ll have to ask one to be certain.
With distance from the discharge channel, this shockwave slows down and as it does it falls within our audio range. That’s when we hear thunder. I have heard that if you stand close enough to lightning you won’t actually hear it, because the shockwave is supersonic. While this makes sense in theory, human trials are pending. It also explains why, when a storm is very close, the lightning makes a sharp cracking explosive sound while, when further away, you hear the thunder as a low sexy rumble.
Class Dismissed: Your Take-Home Message
More people die of lightning injuries in Florida than anywhere else in America and perhaps even the world. While I’m aware that they have an amazing water world playground at their feet, they also have the highest lightning strike density in the entirety of the United States. Perhaps y’all should bear that in mind the next time you go wind surfing in an electrical storm.
Regardless of where you live, however, if you value your life then don’t swim, don’t bath, don’t chat on a land line, don’t play golf, don’t stand under a tree and don’t go running around like Julie Andrews in a thunderstorm. Otherwise, it won’t just be music the hills are alive with.
Oh, and enjoy the show! Isn’t nature spectacular?
Like Why? Because Science‘s Facebook page to receive sexy doses of science on the daily!
Wander Woman Thea 
