Operation Cloud Lab: Secrets of the Skies - Learning Zone


Operation Cloud Lab: Secrets of the Skies - Learning Zone

A team of scientists takes to the skies in an airship to explore Earth's atmosphere.


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One of the world's largest airships is taking

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a team of scientists and adventurers on a unique expedition

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a voyage deep into one of the most mysterious

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and precious environments on earth - the atmosphere.

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So we have this dynamic bubble of air constantly moving,

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constantly changing,

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and that's what we are here with Cloud Lab to explore.

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This quest is taking the team coast to coast

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across America to discover the many surprising ways

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in which the atmosphere shapes our world.

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It's difficult to imagine,

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but the skies are home to a vast ocean of water. Yet it is beyond

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our reach, suspended all around us as an invisible, vaporous gas.

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Only once it is transformed into clouds does it become liquid water.

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It's this deceptively simple transformation of water,

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from gas to liquid,

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that ultimately brings water from the sea to the Earth's land surfaces

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by generating 1.4 trillion tonnes of rainfall every day.

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Yet clouds are as mysterious as they are beautiful.

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How can such delicate, ephemeral structures carry so much water?

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To begin to understand exactly how much water clouds carry,

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meteorologist Felicity Aston wants to try something

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that's never been attempted before.

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So what would be really great,

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I don't know if it's going to be possible or not,

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but what would be really great is if we could weigh a cloud -

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see how heavy it is, and work out how much water is in one of those clouds.

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But to do that, we've got to get up there.

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So we've got to do a bit of cloud hunting.

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Energy from the sun evaporates water from the sea

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into the air above.

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When this moist air is warm enough,

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it starts to rise in a column of air known as a thermal.

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As it rises, it gets colder,

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and cold air can't hold as much water as warm air.

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So you get to a certain level, when it's cold enough,

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when all that water from the sea starts to re-materialise as tiny,

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little droplets of water.

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That is the birth of a cloud.

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OK - that's the one I want. That one.

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It'll be really great to go right through the middle

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and right into the heart of it.

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Atmospheric chemist Dr Jim McQuaid primes the instrumentation.

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So we have a... There's a laser beam here.

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So this is one instrument we've got, it is called a LiDAR.

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The LiDAR, a kind of light radar, will measure the cloud's dimensions

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by emitting a laser and analysing the light reflected back.

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A second probe will measure the exact size

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and density of the individual droplets of liquid

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as the airship passes through the cloud.

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OK, Jim, are you ready?

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OK.

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So I'm picking up cloud droplets now.

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The humidity has gone up to 100%.

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Wow, so that cloud was nearly a kilometre long.

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So, Jim, have you got an idea of how wide the cloud was?

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200 metres across.

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So we are going to assume it was as tall as it was wide,

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because it looked like a fairly solid elliptical shape,

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so we just use a simple formula to work out the volume of the cloud.

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How wide was it - 200 metres?

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20 million...

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-20 million?

-Cubic metres.

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In that small, compact cloud. 20 million cubic metres.

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To calculate the cloud's weight,

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they factor in the size and density of the water droplets within it.

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The weight per cubic metre is about...say the average is 0.2.

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-0.2g per cubic metre.

-Per cubic metre.

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OK. So we times 0.2 by 20 million.

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Yes...

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So that small cloud weighed four tonnes. That's incredible.

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It is.

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The experiment has revealed that even a small

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cumulus cloud converts large amounts of vapour to liquid water.

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The average cumulus is 50 times larger than the one the team

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have measured, so it carries around 200 tonnes of water.

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But the greatest water bearers are cumulonimbus clouds.

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Up to ten times more dense than cumulus cloud, and measuring,

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on average, 1,000 times larger, these can weigh one million tonnes.

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At any one point in time, the world's clouds hold

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an astonishing 129 billion tonnes of water in the sky.

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The team want to investigate how the rain cycle works.

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It all comes down to the little understood process

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that causes raindrops to form.

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Rain doesn't form easily, which people in the UK

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and, frankly, people in Florida,

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are going to think is a bit odd, because it rains a lot,

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but you need a little catalyst - a nucleus - to help raindrops form.

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It's a bit like a grain of sand at the heart of a pearl.

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Normally, tiny particles like dust or sea-salt

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suspended in clouds do the job.

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But a new idea has emerged suggesting that rain drops could be

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seeded by another kind of particle.

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Life, in the form of bacteria.

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Micro-biologist Dr Chris Van Tulleken

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wants to know whether that's the case.

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Often, the first thing to form around particles are ice crystals,

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because high up inside clouds

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temperatures can be well below freezing.

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Those crystals of ice act like a magnet, attracting water vapour

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and growing rapidly.

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When they are big enough and heavy enough they fall -

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and as they fall, they melt to become rain.

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So Chris is mounting an experiment to find out which is

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the best at producing ice.

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Is it dust or bacteria?

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So we've got three rows of drops here.

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We've got the first row, near me,

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that's pure water, and then the second row has mineral dust in it

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and the third row has a bacteria that we know does live in clouds.

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And we are just going to drop the temperature on this plate

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and see which freezes more easily.

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So we are below... We are below freezing.

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It's funny, isn't it? So we talk about freezing as zero,

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but it's actually really hard to get water to freeze.

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In fact, pure water doesn't freeze until well below zero.

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There needs to be impurities in the water for it to

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freeze at higher temperatures.

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It's minus eight, almost minus eight and a half.

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Nothing's frozen yet.

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There you go. There, there.

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But that was only the bacterial ones.

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None of the mineral ones have frozen.

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Only when it is two degrees colder does the mineral dust

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finally start to freeze.

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Ah, those... At almost minus 11,

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some of the mineral ones are going.

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Not only has the experiment demonstrated that ice

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forms around bacteria,

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but that it does so at a higher temperature than around dust.

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So, the bacterial protein is more efficient than the mineral,

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the main mineral that we think causes rain,

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and, to me, the key thing is here - bacteria have evolved a protein -

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they've made something that helps water freeze, that helps ice form.

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The experiment raises the intriguing possibility that

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bacteria will make clouds rain more readily.

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So, knowing whether a cloud is a home to bacteria or not could help

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forecasters predict if it's going to rain.

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This is Gulf Shores, Alabama.

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It's an important staging post for a number of different migratory

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bird species, all of which are trying to escape the approaching

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American winter.

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They are resting up here before the most perilous

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part of their journey to South and Central America.

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The 600-mile flight across the Gulf of Mexico.

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Cloud Lab's Andy Torbet is joining a group of scientists

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tracking the migration patterns of the birds that depart from here.

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They're on a dawn raid to catch and then tag some.

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-And you'll check them every...?

-30 minutes.

-OK.

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The question they're trying to answer is do the birds time

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their departures to take advantage

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of favourable atmospheric conditions?

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Now is an ideal time to test the idea.

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A cold front, a mass of cooler air, has just swept through the region,

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bringing with it torrential rain.

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But now conditions have improved.

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I really wanted to see a humming bird.

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-They just seem so delicate.

-Yeah, they are very delicate.

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That's why we put them in the bags instead of the boxes,

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just for purely that reason.

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The birds are caught between two conflicting pressures.

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On the one hand, winter is coming,

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and they have to move before food becomes scarce.

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On the other, if they get their timing wrong,

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they may find themselves fighting head winds.

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So he's making a spot there to attach the transmitter.

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The birds, in this case, a hummingbird,

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are fitted with radio transmitters to track their departure.

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How much does that weigh?

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It weighs about 4% of the bird's body mass.

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It may look invasive,

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but the procedures have been honed over many years.

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So where will you be picking up the data from that transmitter?

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From the towers that we have here on the peninsula that

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will pick up the signal when the bird departs across the Gulf of Mexico.

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-Do you want to let him go?

-Oh, yes, please.

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-OK, how do I hold him?

-Open your hand.

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OK - then hold the wings?

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And if you just let your hands go

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he can just fly off or maybe with a little encouragement.

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-OK.

-Good luck, little one.

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There he goes. Wow! Pretty impressive.

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That was brilliant.

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Now all they can do is wait and see if the birds use the better weather

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to make the crossing that evening.

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We put radio tags on some birds to see

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whether they actually made it across the gulf,

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and three of the birds that we tagged made the journey.

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And it took them between 16 and 24 hours.

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-Wow!

-But it just showed that they were able to make that journey.

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The tagged hummingbirds and thrushes departed that same evening

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and reached their destination.

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The passage of the cold front led to an improvement in the weather,

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and delivered a tail-wind that the birds seem to have exploited.

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And the data Felicity has gathered suggests

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they are not the only birds

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that take advantage of a change in the wind.

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This is national radar data, so any of the green,

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red and yellow signals you can see - that's bad weather that was

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sitting right on top of you and pinning all those birds down.

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But then as that front moves across,

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there's a sudden explosion of these sort of rosette blue colours.

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And nobody knew what they were at first,

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but now they know that it's biological matter showing up

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on the radar - so that is the birds leaving - it shows up on the radar.

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And if I just let this play, you can

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see that over the whole country, as fronts move across,

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behind the fronts you'll see this sudden explosion of birds leaving.

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After the passage of a front,

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many millions of birds take to the skies in an attempt to reduce

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the energy required to make their migration.

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It really just shows how important these weather fronts

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are for the birds.

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They have to fly in air that's following these cold fronts along.

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And just seeing it on this level shows that these weather fronts

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you know, they are vital for movement.

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Not just on a small scale but on a global scale.

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The Cloud Lab team want to explore a surprising

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consequence of human impact upon the atmosphere.

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The apparent increase in the frequency

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and intensity of hurricanes.

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They've arrived at New Orleans.

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In 2005, this was the scene of the deadliest hurricane to hit

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the United States in more than half a century.

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Hurricanes have battered these shores

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since long before there were human settlements.

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It's a consequence of the particular geography in this area.

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THUNDER ROLLS

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As water is evaporated into the sky to form clouds,

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it brings with it vast amounts of heat energy.

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In the warm, shallow waters of the Gulf, that process takes place

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with such intensity that it can help to generate a hurricane.

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We already know that the sea surface temperatures,

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drive the hurricanes, they're the hurricane fuel.

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And so if we look at a graph of sea surface temperatures,

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we can see that there's a very obvious, upward trend,

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so temperatures are getting warmer and warmer, decade after decade.

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And that's what's driving not only more hurricanes but worse hurricanes.

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So what I'd like to know now is what's driving that upward

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trend in temperature.

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There's a newly emerging idea that the temperature

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of the Gulf may be influenced by pollutants in the atmosphere.

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So we've come to an area that has a lot of heavy industry

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and also one of the busiest shipping lanes in the US,

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because here we are likely to see what impact that's

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having on the clouds that are forming in this area.

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Clouds have an important effect on sea temperatures

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because of the way they block out the sun's heat.

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But the extent to which they block the sun depends upon what

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they're made from, because polluted clouds have different

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properties compared to clean clouds.

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What we'd now like to do is to try

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and get into some of these clouds over here.

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-We're looking for a dirty cloud.

-Dirty, yep.

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Well, not dirty, but something that's either over

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-this shipping channel or over the oil refineries.

-OK.

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Jim detects methane and carbon dioxide -

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important markers for other pollutants.

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The high levels of pollution

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mean there are more particles on which the cloud droplets can form.

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And that has an important knock-on effect.

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This is the size distribution and the average

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is about six microns, and that's quite small,

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whereas in the cleaner clouds

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which we've flown through in Florida, the average size is more like ten.

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Right. So we are seeing more small droplets

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-than you would in a clean cloud.

-Yes.

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In dirty clouds you have more and smaller particles,

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so they are going to be denser clouds, there's more droplets.

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The consequences of this are far-reaching.

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The clouds here are dirty clouds and because they are

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thicker and denser, they are blocking out more sunlight than clean clouds.

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So they are having a net cooling effect

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on the climate underneath them.

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-So dirty clouds are cooling down temperatures.

-Yes.

-Right.

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It seems that polluted clouds cool the world's oceans.

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And yet sea surface temperatures are on the rise.

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Fuelling hurricanes.

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Felicity calls upon the one piece of data that can make

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sense of this confusing picture.

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The way in which pollution levels

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have changed over the past few decades.

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What I'm thinking is that the period when the atmosphere

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was at its dirtiest.

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And if you look at these hurricane seasons...

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..it's pretty much the same period of time

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as when there were less hurricanes.

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-So it's possible that pollution is suppressing hurricanes.

-Yeah.

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It's an extraordinary idea,

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that higher levels of pollution in the past might have been suppressing

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hurricanes because polluted clouds were cooling the world's oceans.

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But environmental legislation has improved air quality

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across America.

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So there are fewer of these dense, polluted clouds.

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As a result, the seas have slowly warmed up again.

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So, what we are saying is that by cleaning up

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our atmosphere...we have allowed there to be more hurricanes.

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So we are not seeing an upward trend in hurricanes.

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What we have seen in past decades, when the air was dirty,

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was a suppression in hurricanes. What we are seeing

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at the moment is a return to the natural state of things, a return

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to the normal number of hurricanes you would expect to find in a season.

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The airship is approaching the desert city of Phoenix, Arizona,

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where the team want to answer a question about human impact

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upon the atmosphere.

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Can cities make their own weather?

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So I've been looking at historical data

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and you can see that Phoenix in the last 100 years has gone

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from being really a small, agricultural settlement

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into a large, urban city.

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In the same period of time, there has been a distinct change

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in the amount of rainfall in the city.

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There are areas of Phoenix that have had up to

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a 12% increase in the amount of rainfall,

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which is really significant,

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and it looks like there might be a correlation between the two.

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So we want to see

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if we can unravel how the city might be creating its own weather.

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The rain that falls here has followed the same

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cycle for millennia.

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Every summer, warm, moist air is swept up from the oceans to

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the south.

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As this air meets the hot desert, variations in the landscape

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drive pockets of air upwards as thermals.

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Where the moisture cools, condenses,

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and ultimately falls in sudden downpours of rain.

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This process should make rainfall across the region fairly random.

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But something appears to be concentrating it upon the city.

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To see why, Felicity is going to start by surveying

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temperatures in Phoenix and the surrounding desert.

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I took several readings of the surface temperature

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and I was getting between 37 and 38 degrees centigrade.

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So, it's pretty hot down there, it's soaking up all the heat from the sun.

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For the city to be concentrating rainfall,

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it needs to be hotter than the desert,

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driving extra thermal activity.

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I'm getting a real variety in surface temperatures.

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So if I take a reading from the road or a car park, it's pretty

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much the same surface temperature as in the desert,

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but if I point the camera at a garden or a swimming pool or a roof top,

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then it's a lot less.

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So, on average, the surface temperature here will overall

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be a lot less than the desert.

0:25:440:25:46

The city is a little cooler than the surrounding desert.

0:25:480:25:51

So there's no evidence for the increased

0:25:510:25:53

thermal activity that can explain the rainfall.

0:25:530:25:56

As the day wears on, that picture soon changes.

0:26:050:26:09

See, look, look, look, look, see the city.

0:26:160:26:19

-Yeah.

-It's hotter than the desert.

0:26:190:26:21

OK, yeah, you can see definitely the boundary.

0:26:210:26:24

So that's the desert cooling down and that's the hot city.

0:26:250:26:29

That's a really nice example of it.

0:26:290:26:31

Whilst the natural landscape has quickly cooled,

0:26:360:26:39

the camera reveals the city to have remained warm.

0:26:390:26:42

They've identified an effect called the urban heat island.

0:26:450:26:48

Earlier today, we measured the ground temperature of the suburbs

0:26:510:26:55

to be 24, 25 degrees,

0:26:550:26:56

and see, I'm measuring, 23, 22 -

0:26:580:27:02

I mean it's still as hot as when we measured it in the middle of the day.

0:27:020:27:05

The city surfaces are continuing to radiate

0:27:080:27:11

the energy of the sun they absorbed earlier in the day.

0:27:110:27:14

The question is whether the urban heat island is generating thermals.

0:27:160:27:20

If it is, they should be able to detect

0:27:220:27:25

an increase in temperature at altitude from the airship.

0:27:250:27:28

So, I've just had a look at the temperatures

0:27:310:27:33

and this is the temperature going down and that's going down simply

0:27:330:27:36

because the sun's going down - you know, we're turning the heater off.

0:27:360:27:39

So this is the temperature over the desert

0:27:390:27:42

and this is the temperature over the city.

0:27:420:27:45

Oh, wow, so this is where we hit the city?

0:27:450:27:47

-Yeah.

-So we've got this big parcel of warm air sitting

0:27:470:27:50

over the city.

0:27:500:27:53

It makes a lot of logical sense that that air is going to start rising and

0:27:540:27:58

that's going to start convection and the consequence of that is weather.

0:27:580:28:02

So the increased rainfall in Phoenix could be caused by

0:28:060:28:10

the urban heat island effect.

0:28:100:28:12

It generates thermals over the city,

0:28:130:28:16

that force air upward, where it begins to cool.

0:28:160:28:19

That in turn can cause the vapour to condense and form rain,

0:28:200:28:24

concentrated here upon Phoenix.

0:28:240:28:27

So we've found the connection we were looking for,

0:28:300:28:32

between cities, and the increased rainfall that Phoenix has been

0:28:320:28:37

experiencing in the last 100 years.

0:28:370:28:39

And the really exciting thing about that is that we've

0:28:390:28:42

hard evidence that human beings are creating their own weather.

0:28:420:28:47