Six striking facts about lightning
Lightning is the stuff of myths and legends and may have even provided the first spark for life on Earth.
There's nothing like a dramatic interplay of lightning and thunder for atmosphere and fear, but is it really true that lighting never strikes twice? And what does lightning have to do with volcanoes?
'Don't worry, lightning never strikes twice'
Unfortunately for anyone whose house had been struck by lightning (or who uses this expression to suggest a negative event is unlikely to re-occur) the exact opposite is true. Some areas and places are simply more prone to being hit by lightning.
"The geographic conditions that lead to the storm coming through and causing lightning are fixed — the mountains are there, the buildings are there," says Dr Karl Kruszelnicki.
"So, you're more likely to have lightning hit the same place more than once."
ABC weatherman Graham Creed agrees.
"These days lightning rods get hit multiple times and other things such as large trees or overly metallic rocks can become lightning attractors," he says.
The world record for a person being struck by lightning is held by American Roy C Sullivan, an ex-park ranger who survived being struck seven times. Many people thought he was a human conductor, but his job just happened to mean he spent a lot of time outdoors in a national park where there were a lot of lightning storms, says Dr Karl.
Lightning can occur 'out of the blue'
The concept of a shocking 'bolt from the blue' is based on reality. Lightning can indeed move well in advance of a storm and hit the ground without any obvious warnings.
"Lightning can travel up to 16 kilometres ahead of a thunderstorm," says Creed.
Dr Karl tells the story of a jet at a United States Air Force base that was refuelling on a sunny, cloudless day. But there was a storm on the horizon.
"Then bingo, it sent a lightning bolt to the aeroplane and blew up the fuel vapour and killed a bunch of people," he says.
Lightning comes out of the ground as well as down from the sky
It may look like there's just one bolt zig-zagging towards the ground, but there's actually a bolt that leaps up to meet it. It's just that the bolt from the ground is so fast that we can't see it.
Even though our eyes don't catch it, this answering bolt is much bigger than the one from the clouds, in every way!
Like sexual tension, electrical tension wants to be relieved.Dr Karl Kruszelnicki
"The one coming down is maybe centimetres across and carrying tens of thousands of amps," says Dr Karl "and it's moving at a 150 kilometres per second, and that's slow."
As this bolt coming down gets within 25 to 60 metres off the ground there is so much electrical tension between the ground and the bolt that an answering bolt rises from the Earth to meet it.
"And this bolt coming up is about a metre across," says Dr Karl, "and instead of 10,000 amps you've got a million amps. And instead of 150 kilometres a second, 150,000. So you don't see it. But you can photograph it with an ultra-high speed camera."
Sparking ice causes lightning
Recently, we've discovered the actual mechanism that results in lightning, and it seems that two different types of ice are to blame.
"In your fridge you have two sorts of ice," says Dr Karl. "There's the hard, chunky stuff in the ice tray and the soft, feathery crap around the freezer."
When there is a strong updraft, these different types of ice can form high up in a storm cloud, even in the tropics.
"If you have these two different types of ice hitting each other then they will form sparks, and build up the massive electrical charge, and then you get the lightning," says Dr Karl.
A global survey of thunderstorms that counted lightning flashes and correlated them with the volume of ice crystals, confirmed that ice is present in lightning all across the globe.
Volcanoes and solar winds can cause lightning
Volcanic eruptions can result in particularly spectacular lightning bolts.
Although the phenomenon is fairly common and has been photographed since the 1940s, when Mount Vesuvius erupted in Italy, it is not found in all types of volcanic eruptions, says Dr Adele Crozier of Geosciences Australia.
"It's mostly associated with explosive volcanism," she says.
The lightning strikes don't occur as part of a normal thunderstorm, but instead take place within the eruption column and are caused by charged ash particles. However, scientists still don't know exactly what causes them.
At the other end of the spectrum of spectacular eruptions there's evidence that high-energy particles in the solar wind may influence thunderstorms.
UK researchers found a significant increase in lightning bolts in the 40 days after the Earth passed through dense streams of high-speed solar wind.
"Cosmic rays, tiny particles from across the universe accelerated to close to the speed of light by exploding stars, have been thought to play a part in thundery weather down on Earth, but our work provides new evidence that similar, if lower energy, particles created by our own Sun also affect lightning," says Dr Chris Scott of the University of Reading.
Ball lightning really exists
Ball lightning is perhaps the most bizarre type of lightning that we know of (and yes, there are several other types of lightning, including positive and negative lightning, and intra-cloud lightning.)
These weird glowing grapefruit-sized balls of almost any colour appear to float in the air, and move slowly through walls, nosing around rooms. They've even been known to invade high-flying jets and scare the living daylights out of the passengers.
It's a phenomenon that's been reported for hundreds of years and has baffled scientists for most of that time.
However, scientists from the Australian National University and CSIRO may have finally solved the mystery.
They suggest ball lightning is a kind of leftover effect of a lightning strike. The theory is that some of the positive and negative charged particles (ions) left in the wake of a strike could accumulate on the outside of non-conducting surfaces such as a window, instead of dissipating as they normally do (either by recombining or travelling to the ground).
"These ions pile up and produce an electrical field which penetrates the glass," says Dr John Lowke of CSIRO.
The electric field ionises gas molecules in the air, which release light. So ball lightning may be nothing more than a ball of glowing gas.