Lightning Dangerous Earth

It's a tornado!

Look at that!

Our planet is home to some spectacular natural wonders.

THUNDERCLAP

Yet exactly how and why they form is still a mystery.

But now, new camera technologies are revealing

their inner workings in stunning detail.

My name is Dr Helen Czerski

and I'll be looking at how these extraordinary images

are transforming our understanding of the natural world.

In this programme, we look at the latest scientific insights

into the hottest natural phenomenon on Earth - lightning.

Lightning is one of the most dramatic natural spectacles

on the planet but we still don't fully understand it.

Exactly what triggers it and why there are more lightning strikes

in some places than others is a mystery.

Now, cameras are seeing what our eyes can't -

from discovering the secrets of rare upward lightning

in super high speed...

..to capturing vast electrical bursts,

spreading kilometres above thunderstorms.

We can now capture, on camera, the complex processes

crucial to understanding this unpredictable force of nature.

Lightning strikes our planet over 30 times a second.

And each strike is five times hotter than the surface of the sun.

Now that so many of us carry cameraphones...

..we're capturing just how dangerous this force of nature can be.

LOUD THUNDERCLAP

Oh, my God! Whoa!

In Sydney, drivers had a lucky escape

when a lightning-hit tree crashed into their path.

-Is that guy OK? Whoa!

-He's all right.

In Newcastle, a lightning bolt set this house on fire.

And these holidaymakers were lucky to walk away with their lives.

THUNDERCLAP

Oh! Oh, my God! I felt it! I felt it!

So, how and why is the planet we live on

plagued by these vast electrical bolts?

Considering that lightning strikes somewhere on Earth

three million times every single day,

it's slightly surprising that we don't know very much

about the details of what triggers it.

But we do know the big picture,

which is that lightning is basically a giant electric static discharge.

It's just like when you touch a car, maybe on a cold, dry day,

and you feel an electric shock.

It's exactly the same thing but on a much bigger scale.

And I can demonstrate the principle with this machine here,

which is a Van de Graaff generator, one of the workhorses of physics.

If I switch it on...

There's a positive electric charge building up

on the large metal sphere

and a negative electric charge building up on the small one.

And when that charge gets big enough...

SPARK CRACKLES ..we get a spark,

really clear spark. There we go. SPARKS CONTINUE TO CRACKLE

And this is what's happening when there's a bolt of lightning.

THUNDERCLAP

In both cases, the spark we're seeing is an electrical discharge

travelling through the air.

And the sound is lightning's own sonic boom - thunder...

THUNDERCLAP

..created by the hot air rapidly expanding.

In the Van de Graaff generator, I'm creating the charge artificially.

In a thundercloud, scientists think that the charge builds up

when ice crystals of different sizes collide.

The heavier, usually negatively-charged crystals,

move to the bottom of the cloud.

Just like in a battery, opposite charges are trapped.

So, on the ground below the cloud, a positive charge builds up.

Here, the two steel balls represent the positive Earth

and the negative base of the cloud.

Between the two, the electric field grows stronger and stronger.

The problem is, air is an electrical insulator.

Charge can't travel through it very easily.

However, if you get enough negative charge and enough positive charge,

eventually, it builds up so much that the air actually breaks down.

The air molecules break down and form a little tube

that the electric charge can travel through.

SPARKS CRACKLE Ooh! So, on a small scale,

this is almost exactly what's happening

in these big thunderclouds,

where you get these huge bolts of lightning.

THUNDERCLAPS

The detail of exactly how the electrical charge travels

through the air is still being worked out.

Lightning moves at speeds of over 150,000 kilometres a second,

so it's only with the invention of new camera techniques

that scientists have really been able to see what's going on.

Rapid City, South Dakota,

is in the heart of America's thunderstorm zone.

Here, meteorologist Tom Warner uses specialist high-speed cameras

to film lightning at up to 100,000 frames per second.

When you view a flash in real time,

it's like seeing a title of a book. You can see there was a flash there

that reached the ground and maybe it flickered a little bit,

but that's all you know.

You come and record the same flash with these high-speed cameras,

it's like a novel.

It tells a unique story every time you play it back. Incredible.

Tom keeps the cameras constantly recording during a storm.

Once he triggers, it saves just the previous few seconds of footage,

but that's enough.

THUNDERCLAP

These images show each stage of a lightning strike.

It starts with a fleeting stroke, called a stepped leader,

normally invisible to the naked eye.

Here, we see it branching downwards

until one of the forks makes contact with the ground,

producing the far brighter and faster return stroke.

This is the powerful channel of electrical current

we usually see as lightning.

The entire process takes around one-hundredth of a second.

So, it's only by slowing it down many hundreds of times

that it becomes visible.

Lightning is so fast that studying its form is only possible

with photographic advances.

Historically, our understanding of it

has gone hand in hand with camera technology.

Before photography,

the most common way of depicting lightning

was in the form of a zigzag.

The problem for meteorologists was that they didn't believe

that zigzag lightning appeared in nature.

This is the first known photograph of lightning, dated 1847.

Early pictures like this reveal that each split-second bolt

was a complex pattern of different shapes.

One of the first photographers to use the camera

for the scientific investigation of lightning

was a railroad photographer named William Jennings.

He suspected that zigzag lightning was not the true form of lightning

and he sought to show that lightning comes in a range

of different forms and shapes.

This one shows lightning behind the clouds.

In this case, it wanders across the sky

and doesn't even touch the ground.

And in this one, we have parallel discharges.

But normal photography couldn't capture

how a split-second stroke changed over time.

A big problem with early lightning photography

was capturing the high-speed movement of the lightning flash.

To solve this problem, a British physicist,

Charles Vernon Boys, invented a lightning camera.

The concept was ingenious. It was to move the lenses.

They didn't have film that was high-speed enough to capture,

but with the system of rotating lenses,

it was possible to capture the evolution of the flash

as it evolved, and spread it across the film.

This 1941 movie shows how this innovative camera

revealed lightning's multiple flashes.

-MOVIE SOUNDTRACK:

-Our eyes saw only this.

-THUNDERCLAP

-But here are some surprises,

revealed by the Thunderbolt Hunters' ultra high-speed cameras.

What appeared as a single flash

was, in reality, a series of strokes.

High-speed photography has come a long way since then,

revealing the evolution of a lightning strike beat by beat.

But Tom Warner's cameras have also captured something unexpected -

remarkable images of a rare form of lightning that travels upward.

Most lightning discharges down from the sky

through the pathways of ionised air, called leaders.

But this footage reveals lightning travelling up into the clouds.

When I played this for the first time, I was just blown away.

It was just amazing to see it.

What's extraordinary is that most of this upward lightning

is caused by us...

..set off by the transmission towers, wind turbines and high-rises

that now litter our urban landscapes.

Naturally occurring upward lightning is rare.

But these tall structures create intense electric fields,

concentrated at their tips, whenever there's a storm cloud overhead.

Tom's videos have revealed that during a storm,

these intense electric fields discharge

as ground to cloud strikes.

These towers experience up to 100 times more

of these upward lightning strikes

than they do regular downward lightning,

so there's a far greater chance of damage.

Lightning that's caused by human activity is nothing new

and it can have near-catastrophic consequences.

Kennedy Space Center sits in the heart

of America's lightning capital, Florida.

THUNDERCLAP

On November 14th, 1969, they launched the Apollo 12 moon mission.

It had been a stormy day,

but the countdown proceeded as normal to blast-off.

-FLIGHT COMMS:

-'Houston, good trajectory...'

But just seconds after takeoff, warning lights started flashing

and electrical circuits began to malfunction.

-COMMS:

-'What happened here, we had everything in the world drop out.

'I'm not sure if we've been hit by lightning.'

Well, power went up through

what was a fairly weak electric field

and actually magnified that electric field as it went up through it.

THUNDERCLAPS

By magnifying the small electric field of the storm cloud,

Apollo 12 triggered its own bolt of lightning.

Only quick thinking and a backup computer saved the mission.

It almost shut Apollo down.

It was only because they had lots of redundant systems

that they were able to escape.

It was very, very close to losing the mission

and losing the astronauts.

Space rockets aren't the only aircraft at risk from lightning.

We all come a lot closer to lightning strikes

than we might imagine.

Whoa!

Because every commercial airliner is struck by lightning

on average once a year.

This clip, filmed by an eyewitness in London,

shows the hair-raising moment

a bolt of lightning seems to travel right through the plane.

So, how do planes withstand

being struck by millions of volts of electricity?

It turns out they're behaving like giant Faraday cages.

Faraday cages are named after Michael Faraday

because he did the experiments, back in 1836,

that demonstrated this principle.

And it's all to do with what happens when you have a hollow object

that's made of a conducting material,

so that's normally a metal.

If you bring that close to an electric field,

the charges can travel right around the outside of your hollow container

without ever going near the inside.

It's a bit of physics used to dramatic effect

by high-voltage entertainers, like this.

This performer is wearing a Faraday cage

and that's why he can reach out

and touch these strong electric discharges

without it hurting him at all.

So, the electric field is very strong here

but, instead of going through the performer,

it travels around the outside of his conducting suit

and will reach the ground without ever touching his body.

So, he's completely protected

because he's inside the Faraday cage.

And this is what happens in a plane.

The metal tube of the plane acts as a Faraday cage

so, that when it gets struck by lightning,

the electric charge travels around the outside and onwards,

without ever going anywhere near the passengers,

the flight controls or anything else inside the plane.

If we look back at the clip of the London flight,

you can see how the lightning travels harmlessly

from wing tip to wing tip and the plane keeps flying.

The planes we fly on are safe because they're made of metal

but now, to make aircraft lighter and more efficient,

manufacturers are starting to move over to carbon fibre.

The problem is that carbon fibre doesn't conduct electricity

nearly as well, making the planes more vulnerable to lightning.

At the Cobham Research Centre in Oxfordshire,

scientist Stephen Haigh is testing a solution.

If you design an aircraft,

you have to demonstrate it's safe from lightning.

It's a real threat and you make sure you're protected it against it.

Stephen and a team of engineers shoot artificial lightning bolts

through different materials

to see just what happens when a plane is struck.

First, they test a panel made of aluminium,

the material most planes in the air today are still made of.

Primarily, the concern is to make sure

that we don't have any puncture of this skin

during the lightning attachment.

Some of these panels are, effectively, wing skin panels

covering the fuel tank, so what you don't want

is any possibility of ignition of a fuel vapour within the tank.

With the help of a massive high-current generator,

they're able to recreate the worst that nature might throw at it.

This is mimicking a severe lightning strike, actually.

Much more severe than that you'd normally expect

but that's the way you qualify an aircraft -

you know, go for the worst case.

-OK, good to go?

-Yep.

OK.

MACHINE WHIRRS

EXPLOSION

100,000 amps causes quite a strike, but has it punctured the panel?

So, you can see a little bit of surface damage, loss of the paint.

No puncture though. It's not a problem. That's a good result.

Next, they put in one of the new carbon fibre panels.

MACHINE WHIRRS

EXPLOSION

It seems to be much more damaged,

but is it?

Much of the damage is due to the fact

there's a really thick paint layer on this panel,

so you can see it's just been peeled off.

But, actually, the physical damage to the panel is quite small.

In order to protect the plane,

a layer of conductive material has been added.

To protect the carbon,

there's a very thin weave of copper mesh over here,

which gives it the lightning protection.

That's protected the carbon fibre underneath.

Just like the aluminium planes, this thin layer of metal mesh,

embedded in the carbon fibre, acts as a Faraday cage,

keeping the inside of the plane safe from harm.

Work like this ensures all the planes in our skies

will keep flying, even if they're struck by lightning.

THUNDERCLAP

A lightning strike can be up to one billion volts

and when there's no Faraday cage to conduct the heat away,

the effect can be devastating.

These are as close as you can get to actually holding lightning.

It's called a fulgurite and this was formed in the Western Sahara

when a lightning bolt struck the desert sand

and it heated the sand up so much, it fused it into glass,

so at least 2,000 degrees C.

And the lovely thing about it is all these stunning details on here.

You can see the shape of the lightning bolt,

because that's what's left behind in glass.

And if lightning can do this to sand,

you can only imagine what it would do

to something much more vulnerable...

..like a human being.

Around one in ten people struck by lightning are killed,

most from cardiac arrest.

But a surprising number survive the intense heat.

I picked up the backpack with one hand

and went to grab the pitchfork and the lights went out.

Where I laid, the grass was totally burned.

The whole length of my body was burned.

I felt as though I was completely on fire.

I didn't see any fire or smoke or anything,

but just from the inside out of me,

it just felt like I was just...on fire.

THUNDERCLAP

So, what does happen when lightning hits a human body

and why do most people survive?

The answer may lie with the surface of the human skin.

It's thought that people who survive lightning may be partly protected

if there's a thin layer of sweat or rainwater on their skin.

By coating this mannequin in water

and striking it with 30,000 amps of lab-generated lightning,

we can replicate the effect.

MACHINE BUZZES

ELECTRICAL CRACKLE

MACHINE BUZZES

ELECTRICAL CRACKLE

The layer of water conducts the lightning

around the surface of the body,

protecting the internal organs from harm.

It may save your life, but the resulting burns can be severe.

One of the things we see with the burns that do occur with lightning,

are not really caused by the lightning

so much as they're caused by what lightning is doing

on the surface of the body -

turning the rainwater or sweat into steam

and then that causes a burn. So, for instance,

if you've got a cotton T-shirt on,

the steam can escape readily through that,

but if you've got a leather jacket on,

it will hold the steam in longer, so you'll end up with a deeper burn.

One of the things that we see

when the sweat or the rainwater's turned into steam,

is a tremendous expansion, obviously,

of the water into the steam.

Shoes can actually be blown off because you've got wet socks,

sweaty socks, and that turns into a vapour explosion

within the closed space of the shoe

and can actually blow the shoe apart.

ELECTRICAL CRACKS

Being struck by lightning can also leave behind feathery tattoos,

known as Lichtenberg figures.

Just as lightning branches out,

searching for the most conductive path through the air,

on a person, it creates these dramatic marks,

as the discharge travels across the surface of the skin.

A normal bolt of lightning is powerful enough,

but what about an electrical discharge up to 80km wide?

For years, pilots reported seeing vast flashes of light,

spread across the sky but they were so faint and so brief

that no-one was sure if they even existed.

It wasn't until 1989, that a scientist,

trying out a new low-light camera,

accidentally caught the first ever image of one.

What he'd captured was a rare event called a sprite.

Like lightning, these are immense discharges of electricity,

but they form high in the atmosphere, above storms.

INDISTINGUISHABLE FLIGHT COMMUNICATIONS

Now, this team of scientists are setting out on an expedition

to try and capture them on high-speed cameras,

in order to discover more.

Sprites dwarf normal lightning

and yet they're so faint and so fleeting, they're barely visible.

The real difference is how brief the sprites last.

Normal lightning can last,

if you count all the strokes together, maybe half a second.

Sprites are a lot shorter in duration -

one one-thousandth of a second.

If they succeed, these will be the first ever high-speed images

of sprites from the air.

But sprites are so faint,

they have to keep their plane in near-total darkness

and use low-light intensifiers on the cameras

as they approach the thunderstorm.

We're headed to Mississippi, right now, and then, past that,

we're going to head over toward Little Rock, Arkansas,

and then we're going to go straight out toward Des Moines, Iowa.

About two hours to get there.

We'll have four hours to loiter around the storms

for the sprite to... Pictures at the back, then two hours back home,

so we'll be airborne about eight hours tonight.

At 15,000 metres up, their plane is now high in the atmosphere.

With me flying at this altitude, it's the clarity of the air,

because the visibility is forever.

With a thunderstorm in full swing,

these should be perfect sprite conditions.

It looks to me like we're getting all the lightning on our backside

right now, so is it possible to turn, say, ten degrees to the left?

The cameras are ready to trigger at super-high speed.

10,000 frames a second, 50 microsecond inauguration time.

Gain is 60,500.

-Elevation is minus four.

-Go again.

Finally, they see something.

Sprite.

I think it was probably outside the field of view, I'm not sure.

But it slips through their fingers. They set up to try again.

We're now at minus four degrees elevation.

-Sprite.

-We're looking. Yeah, we got it.

It looks like there's two of them I think he got.

Finally, they have success.

The high-speed cameras have caught this elusive phenomenon

in all its glory.

A vast column of light 30km tall, dwarfing the city below.

Thanks to footage like this,

scientists now know these astonishing displays

almost always follow a powerful lightning strike.

As the strike discharges,

it sends huge amounts of electrical charge to the Earth,

temporarily increasing the electrical field

in the middle atmosphere and creating these giant sparks -

an event so brief and so faint,

it's almost invisible to the naked eye, finally revealed.

You and I live on seconds or minutes or maybe even years of timescales,

and sprites are one one-thousandth of a second.

That makes you realise how different the world can be.

To give you a sense of scale,

a normal lightning bolt is about the diameter of my thumb.

But a sprite can be up to 80km wide.

New discoveries are being made all the time.

I've got some very special footage here.

It's taken from the International Space Station

and it's video looking down on the top of a thunderstorm,

so there's lots of flashes of lightning.

If I stop it at just the right moment...

we'll see something very special.

And here it is.

It's a blue jet. It's much brighter than a sprite.

It's the first time it's been filmed from space.

It's a huge electrical discharge,

going from the top of the thunderstorm out into space.

And we don't know very much about what these are or how they form,

but now that we have this sort of footage,

we stand a very good chance of answering those questions.

Lightning is one of the deadliest natural forces on Earth,

striking our planet at random millions of times every day.

There are still many secrets to be revealed

but, thanks to new camera technologies,

we're getting closer than ever before

to understanding this spectacular phenomenon.