Archives for May 2011

d ~ 388'492'800 km: day 151

Image © NASA JPL Ocean Surface Topography Team. (La Nina is shown in this Ocean Surface Topography Mission (OSTM)/Jason-2 satellite image of the Pacific Ocean, based on the average of 10 days of data centered on Dec. 26, 2010. The image depicts places where the Pacific sea-surface height is higher (warmer) than normal as yellow and red, while places where the sea surface is lower (cooler) than normal are shown in blue and purple. Green indicates near normal conditions)

It's easy to forget how large our planet is. If you were to start anywhere on the Equator and follow it around the planet, you'd pass 25,000 miles of mountains, forests, deserts and ocean (mostly ocean) before you arrived back at your starting point. And when you got back, covered in sand, salt, tropical insects and the odd bird dropping, it would be hard to imagine that the weather over a full third of that enormous distance is all connected. But that's what El Niño and La Niña represent - two extreme states of one huge system that covers a third of the Equator.

Digesting that fact might stretch the brain a bit, but it doesn't stop there. The atmosphere and the ocean are equal partners in all this. When the airflow across all those 10,000 miles of the Equator changes, the flow of millions of tonnes of ocean water changes too. Today, we can see that a huge change in the flow of all this air and water is about to happen - a period of La Niña conditions is giving way to "neutral" conditions. But what does that mean?

Let's start in the atmosphere near South America. High up, there's cold dry air travelling eastwards from Australia. It hits the Andes, and it sinks. That pushes down on the air that was already there and this lower air is pushed back westwards along the Equator to Australia. So we have a giant conveyer belt of air that is travelling west along the Equator at the ocean surface. If you blow sideways on a hot cup of tea, you'll see that you push the surface tea away from you, and this is what happens in the ocean. The water at the surface of the ocean is pushed along to the west. But what takes its place? The answer is cold water from deeper down in the ocean, so in normal conditions, the water right at the South American coast is cold, because all the warm water is being pushed along towards Australia. This is a "neutral" state.

El Niño happens when that westwards flow of air weakens, and so the warm water can slosh back towards South America. This is where the name "El Niño" came from - it's what Peruvian fishermen called the warm water that sporadically appeared off their coast. When this happens, the cold water never reaches the surface. La Niña conditions are the opposite - the westwards winds get even stronger, and push the warm water even further west. It's a bit like a giant water seesaw. This enormous system of air and water switches between these two states every few years, but we can't really predict when it's going to happen.

During El Niño years, there can be droughts in Australia and Indonesia, and whole ecosystems can be disrupted because the nutrient-rich cold water never reaches the ocean surface. In La Niña years, there is really strong rainfall in Australia and much less rain in South America.

Image © NASA JPL

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

Just like we were excited to hear about NASA STEREO satellites capturing 3D images of the Sun, back in february - recent developments in the study of the universe has got us talking about astronomy developments once again.

Image © CfA click for larger image

It took over 10 years to complete but the 2MASS Redshift survey (2MRS) conducted by the Harvard-Smithsonian Center for Astrophysics, was revealed yesterday at the 218th meeting of the American Astronomical Society, by Karen Masters (University of Portsmouth, UK).

CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Our fascination with astronomy, like with many other people, couldn't have been put more precisely than by Karen's statement at the press release - "I think it speaks to our desire to understand our place in the universe...I wouldn't be happy if we didn't have a complete map of the Earth. It's nice to have a complete map of where we live."

(From CfA press release)
The 2MRS mapped in detail areas previously hidden behind our Milky Way to better understand the impact they have on our motion. The motion of the Milky Way with respect to the rest of the universe has been a puzzle ever since astronomers were first able to measure it and found it couldn't be explained by the gravitational attraction from any visible matter.

2MRS chose galaxies to map from images made by the Two-Micron All-SkySurvey (2MASS). This survey scanned the entire sky in three near-infrared wavelength bands. Near-infrared light penetrates intervening dust better than visible light, allowing astronomers to see more of the sky. But without adding redshifts, 2MASS makes only a 2-D image.

Some of the galaxies mapped had previously-measured redshifts, and Huchra started painstakingly measuring redshifts for the others in the late 1990s using mainly two telescopes: one at the Fred Lawrence Whipple Observatory on Mt. Hopkins, AZ, and one at the Cerro Tololo Inter-American Observatory in Chile. The last observations were completed by 2MRS observers on these telescopes shortly after Huchra's death in October 2010.

The 2MASS Redshift Survey began measuring the galaxies' redshifts, one by one, using two telescopes in Arizona and Chile. A galaxy's light is redshifted, or stretched to longer wavelengths, by the expansion of the universe. The farther the galaxy is from Earth, the greater its redshift, so redshift measurements yield galaxy distances - the vital third dimension in a 3-D map.

(Full CfA press release)

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

d ~ 373'056'000 km: day 145

(AccuWeather.com Senior meteorologist and severe weather expert, Henry Margusity, offers the Meteorological Madness blog including detailed analysis of severe weather across the US. Accuweather creates more than 600 weather videos a day and is a hub for all things weather).

The Joplin tornado will go down in the record books as one of the 10 deadliest tornadoes on record. So why has it been so active?

One of the theories is the strong La Nina that occurred. The La Nina is the colder than normal waters in the southern Pacific. That area of colder water has caused a shift in the jet stream that has resulted in a wild and extreme weather pattern across the United States since the winter, recent trends have shown the La Nina has weakened but the residual affects on the Jet Stream are still causing extreme weather in the form of tornadoes. It will take another month or so for the weather pattern to finally shift to one that is not as extreme.

While it's unclear as to what has caused the extreme weather, one thing is sure, the severe weather season will go down in the record books for the United States.

Below is a list of tornado FAQs, offering a quick reference of tornado records and stats.

Tornado Statistics

• How many tornadoes hit the U.S. yearly?
Tornado reporting methods have changed a lot in the last several decades, so the officially recorded tornadoes are believed to be incomplete. Although the actual average is unknown, recent trends indicate the number is around 1,300. This year the number of tornadoes is 1151 reports which is on pace for a record season.

• How many people are killed by tornadoes every year?
On average, about 60 people are killed by tornadoes every year, most from flying or falling debris. This year, 482 people have been killed by tornadoes.

• What were the top 10 deadliest U.S. tornadoes in the Past? (pending final totals from the Apr 27, 2011 and May 22, 2011 tornadoes)
1. Mar 18, 1925, Tri-State (MO/IL/IN), 695 deaths
2. May 6, 1840, Natches, MS, 317 deaths
3. May 27, 1896, St. Louis, MO, 255 deaths
4. Apr 5, 1936, Tupelo, MS, 216 deaths
5. Apr 6, 1936, Gainesville, GA, 203 deaths
6. Apr 9, 1947, Woodward, OK, 181 deaths
7. Apr 24, 1908, Amite, LA / Purvis, MS, 143 deaths
8. Jun 12, 1899, New Richmond, WI, 117 deaths
9. May 22, 2011, Joplin, MO 116 deaths (pending final totals)
10. Jun 8, 1953, Flint, MI, 115 deaths
11. May 11, 1953, Waco, TX, 114 deaths

• What city has been hit by the most tornadoes?
Oklahoma City. The exact count is not known, but the total is more than 100.

• Which city/town holds the most tornado fatalities in a single city or town?
Murphysboro, IL - at least 234 people lost their lives during the March, 1925 "Tri-state" tornado.

• What was the deadliest U.S. tornado day?
The Dixie Alley tornado outbreak on Apr 27, 2011 set a record of 335 deaths.

• What was the biggest outbreak of tornadoes?
On Apr 3 and 4, 1974, 147 tornadoes touched down in 13 states.
April 25-28, 2011 may exceed this number once the final number of tornadoes is counted. So far 492 tornado reports.

• What was the biggest known tornado?
The Hallam, Nebraska tornado of May 22, 2004 had the peak width of nearly two and a half miles, which is close to the maximum size for tornadoes.

• What was the strongest tornado? What is the highest wind speed in a tornado?
Tornado wind speeds have only been recorded in weaker ones, since violent tornadoes could destroy weather instruments. The highest winds that have ever been found during a tornado were about 302 mph near Bridge Creek, OK on May 3, 1999.

• What were the costliest tornadoes?
On Jun 8, 1966, the Topeka, KS tornado had a cost of about $1,680,136,978 in 2010 dollars.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

d ~ 370'483'200 km: day 144

Another Icelandic volcano has erupted and ash is back in the headlines. But have you noticed the odd trajectory of the ash cloud? The Met Office has issued maps of where the ash will get to in the next few days and the plume is doing something very strange.

Image © Met Office

Before you curse the winds delivering powdered volcano to the UK, bear in mind that those winds are only bringing half the plume. The rest of it is on its way round the north of Norway to Russia. Why would a massive cloud of floating glass fragments split into two like that?

Wind happens because air is getting pulled by gravity, accelerated by the Coriolis effect and pushed about by pressure differences. For example, where cold polar air touches warm air near the top of the troposphere, the associated pressure difference and the spin of the Earth cause a rapid eastwards wind that we call the jet stream. But the air just above and below that experiences different forces and may be doing slightly different things.

Look up into the sky today and think about where that air might have come from. It turns out that seven days ago the air that is now 1.5 km above the UK was 5km up above the north of Russia, and it travelled to us via Greenland, slowly losing height along the way. The air that is 3km above me today was close to ground level over the mid-Atlantic only two days ago, and it's been rising pretty rapidly since then. We are connected to the rest of the planet by the air above us.

The direction and speed of the air changes with height, and the large patterns like the jet stream only tell part of the story. Hot air balloonists use this complexity to change direction - they can't steer left or right, but they can go up or down to join an airstream which is going in the direction that they want.

So the answer to our question about the ash cloud is that the wind over Iceland is going in different directions at different heights. The plume currently reaches 10-15 km above the surface. The ash that gets up above 8 km has joined a northwards wind which is taking it away over the Arctic ocean. But below 8 km there is a different air stream, carrying the other half of the plume towards us.

Most of the time, we don't see the complexity in our atmosphere because air is transparent. The ash cloud is letting us trace one tiny segment of the air flow around our planet. For me, part of the beauty the atmosphere is that it's always changing. This time, the volcanic eruption and the movement of the atmosphere have lined up to cause problems for travellers. But it won't last long, and the travellers will soon be on their way again. In the mean time, enjoy being able follow part of our atmosphere on its journey around the globe.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

d ~ 367'910'400 km: day 143

Here's an interesting clip we wanted to share - highlighting why Iceland has a high amount of active volcanoes. From the 2009 BBC series 10 things you didn't know about... - Professor Iain Stewart discusses Iceland's unique geometry, including how the massive 1963 eruption created one of the youngest islands: the volcanic island of Surtsey off the southern coast of Iceland.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

d ~ 360'192'000 km: day 140

Scientists have worked tirelessly to better understand the makings of a tornado and projects such as VORTEX II or the TWISTEX team, the first to get an inside view of a tornado, are regarded highly in their field.

The objective of this research is a better understanding of how tornadoes are generated and why one supercell drops a tornado and another doesn't, in order to increase tornado warning lead times and improve the validity of data amongst other things.

Storm chasers are keen on photographing and filming these storms as well as understanding how they work. But as May draws to a close and we move eventually into what is regarded the last month of 'tornado season' - we want to know who are the ultimate storm chasers and why?

Being a non chaser myself it has been fascinating speaking with experienced chasers. But do these type of 'responsible' chasers get enough credit? Or does the limelight shine only on chasers who risk their lives to get the shot?

Which brings me on to the level of risk and the assumption that chasers have a desire for destruction. Tornadoes are categorized by their level of intensity, ranging from a category F0 (minor damage) to an F5 (total damage) on the Fujita scale. It's no secret that some chasers would love to see an F5 tornado. But because you want to see a huge funnel whizzing at speeds of 261-318 miles per hour, doesn't automatically mean you want the destruction that is part and parcel of it. There's definitely a fine line there.

Leave a comment and let the team know who you think ranks at the top. A lot of names are flying about, to name a few - Roger Edwards, Chuck Doswell, Reed Timmer, Stuart Robinson, Paul Knightly of UK weather world, and Paul Sherman of Netweather - the list is endless. But what we really want to know is what makes the legends, legends?

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

Image © Derbyshire harrier/Flickr

d ~ 357'029'600 km: day 139

I've been trying to identity this cloud. With my cloud spotter bible firmly beside me, this photo had me stumped for a while. It looks like a cross between rapunzel's hair hanging down the tower and a twisted rope, not very scientific descriptions I agree - but this 'cloud' is not easy to identify.

Image © Derbyshire harrier/Flickr

It was spotted in the UK by one of our 23 Degrees observers, and my initial thought was that it was a contrail, which are visible trails of condensed water vapour made by the exhaust of aircraft engines. The tell tale signs of the contrail are long, ropey strands of cloud that are heading in a different direction to the rest of the atmosphere. That's usually an indicator that something other than the atmosphere created it. However this one doesn't look like a classic contrail.

I decided to ask for a second opinion from John Hammond at the Met Office and he told me that if there is sufficient moisture in the atmosphere, condensation trails can last for some time. Because the trail appears to stop as it runs into a veil of Cirrostratus cloud he thinks the cloud is shielding it and that's changing its appearance. So it's just a contrail playing tricks with my eyes.

The photos don't scream out contrail, maybe just whisper it, and it's because of that sniff of doubt perhaps you'd like to comment on it. What do you think it is? Remember that you too can add your weird and wonderful weather phenomena photos to the 23 Degrees photo pool and we can decipher here.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

Image © NASA

d ~ 349'900'800 km : day 136

In Antarctica, it's getting colder. The sun last shone on the south pole in March, and the tilt of our planet means that each day complete darkness swallows up a bit more of the continent. Since there's no incoming energy from the sun, the land and the ocean can only cool down. And it's at this time of year in the south that an innocuous little fact, one that most of us take entirely for granted, quietly makes the huge Southern Ocean a much more hospitable place for almost all marine life.

Ice floats. Icebergs, ice cubes, ice on a freezing river... they all float. And this is weird, because when most substances freeze they get more dense and so the bits that are frozen solid will sink to the bottom of the unfrozen liquid. Water has the quirk that when it freezes, the molecules form a rigid crystal structure with gaps between the atoms that weren't there before. The consequence is that ice is less dense than the water it froze from, and so it floats.

If frozen water sank, just imagine what would happen. Ponds, lakes and the oceans would freeze from the bottom up. There would be nowhere warm and protected under the ice for living things to hide, and the water would just keep freezing upwards until there was no liquid left. All water-based life would have much more of a struggle to survive.

As it is, ice actually acts as an insulating lid, keeping the water below it warm. Heat is lost from the liquid water surface about a hundred times faster than from the ice surface, so less heat is lost overall from an ice-covered ocean. At this time of year, sea ice is growing rapidly in the Antarctic, and it's as if the ocean is responding to the cold by growing itself a blanket. Every year in the Antarctic, 19 million square kilometers of sea ice is formed, and each summer almost all of it melts.

This ice is also a bit like a floating pantry. Lots of algae and krill live on the bottom of it, and these are an important source of food for fish and other Antarctic life.

Sea ice is amazing stuff. It's different to icebergs - those are huge lumps of ice that have fallen off glaciers into the ocean. Sea ice is the ocean freezing at its surface, thickening into large mobile slabs as the winter season goes on. My favourite thing about this ice is that even though the ocean is salty, sea ice isn't. As the water freezes, the salt molecules are squeezed out, first into little brine pockets and later (especially if the ice lasts more than one year) into the ocean. You could hack off a bit of multi-year sea ice, stick it in your drink and never notice its salty origins.

So when you look at ice cubes jostling around in your glass this summer, think about the ice on the other side of the world, jostling around Antarctica in the dark. It's keeping a huge amount of extra heat in the Southern Ocean until the sun comes back, and all just because it floats.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

Kate Humble and the 23 Degrees team are back after filming the break up of the ice at Alexandra Falls in Hay River in the northern territories of Canada. This was a job for people with strong nerves and infinite patience.

You see the problem with filming weather phenomena is that you never quite know when they are going to happen. It's true scientists can track weather events like storms with radar and satellites but even then, it can change direction at the last minute and you will miss it.

It's the same with filming the ice break up. The scientists have been taking readings, comparing the ice build up with previous years, but this kind of prediction is not an exact science, so they can only narrow it down to a rough window that they think it will break up in. This year all was going to plan and they thought it would go in late April; we mobilized in the UK to head out, but then there were a few cold days so they had to start again with their predictions and we had to postpone our flights.

At times it can be very frustrating, because the team have to work out when's the right time to go. If they head out too early, they'd be hanging around waiting and waiting, and would not be able to afford to stay long enough to get the collapse of the frozen waterfall. Head out too late and the break up could happen while they were 35,000 feet over the Atlantic.

As it happens the team got it just right and arrived in good time with the scientists saying it would break up in the next few days of their arrival. Then it was a waiting game, a case of heading out to the frozen waterfall and listening for the first cracks. On our first day of filming not much happened and after ten hours of waiting they headed back to base praying it wouldn't happen overnight in the dark.

On the second day of filming after several hours of waiting and nothing happening, the Assistant Producer had to head off for another bit of important filming. 5 minutes after she left the falls started to break up. Two months of planning, days of waiting and she missed the lot. However the director had had his cameras trained on the falls and got the collapse in all its glory.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

Day 134: 231 days remaining

Last week Kate and the 23 Degrees production team were in Northern Canada filming the Hay River ice break up. Here's Kate's video blog whilst on location.

To read more on the team's trip in Northern Canada, read Series Producer Stephen Marsh's blog on the Arctic and ice break up.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

Day 130: 235 days remaining

The tropical depression Bebeng (international name Aere), has been upgraded to a tropical storm and hit the eastern Catanduanes province in the Philippines.

The storm generated wind speeds of above 90 km/hr and has officially kicked off 2011's Pacific typhoon season. The storm is still active and according to the Central Weather Bureau it's generating winds at the center of around 18 meters per second with gusts of 25 meters per second. It's heading northeast at between 25 to 32km/hr towards Basco, Batanes but is expected to be downgraded back to a depression by 13th May as it continues to move north into colder waters.

The latest reports from Reuters suggest that 15 people have died and around 100,000 forced to leave their homes by the strong winds, fierce rain and flash floods. The storm has also caused millions of pounds of damage to farms and crops.

Image © Central Weather Bureau

The Philippines are prone to typhoons and get hit by around 20 each year. So what is it about the Philippines that make them a target for such a high number? Well it's all down to location. The Philippines are located in the tropics surrounded by warm seas, which power the storms. And they are far enough away from the equator for the Coriolis Effect to cause the powerful winds to spin in the developing storm.

For more on typhoons read BBC broadcast Meteorologist Peter Gibbs post on Cyclone Yasi and Coriolis effect.

If you live in the area affected by Tropical storm Aere or know of someone affected, do get in contact with us.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

Day 129: 236 days remaining

As if we needed a reason to remind you about Earth's orbit around the Sun, here's another chance for us to let you know about some cool planetary science. We don't orbit the sun alone - there are seven other planets, a dwarf planet and countless other asteroids and bits of space debris. And they all journey around the Sun on their own orbits. But this week something special is happening - several planets are going to be in close proximity to each other and are aligned in what's called "conjunction". And if you get up early you might just catch them.

Anyone up just before dawn looking at the sky, might get a glimpse of Mars, Jupiter, Venus, and Mercury. Although many millions of miles apart, from down here on Earth these four planets will appear as a close cluster in the sky. If you manage to catch this, or have already got a shot of it, then please don't keep it to yourself, no really, let us know. And if you missed it then there's a few more chances this week - at least until 12th May.

What can you expect to see? For tomorrow you should be able to see with the naked eye Jupiter and Venus within close proximity, so it's fair to say this is a rare sighting. You will most likely need to be up for around 5am (GMT), but I have been informed it's worth the fewer hours of sleep. Here's an example of what you might get to see, taken by Alan Dyer on 7th May:

Image © Alan Dyer San Pedro de Atacama

The photo above as with other great shots of this sighting were sent through to NASA Space weather. The photo shows from top to bottom, Venus (the brightest), Mercury (to the right), Jupiter and Mars (just below and the faintest).

Let the 23 Degrees team know if you plan on sky watching this week and send in your photos. Good luck and remember to set that alarm clock.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

Image © Jeff Schmaltz MODIS Land Rapid Response Team NASA

d ~ 324'172'800 km: day 126

Brush fire, bush fire, forest or wild fire - they all refer to the same phenomenon.

In the past week wild fires have swept across parts of the West Highlands in Scotland. But even more recently the situation became more severe when Fife Fire and Rescue reported that a wildfire had broken out in the central belt, the most heavily populated region of Scotland located south of the Highlands.

Wild fires have also ravaged other areas of the UK. Northern Ireland, northwest England and Berkshire have all been struck by these destructive fires. The natural causes of wildfires can range from lightning to volcanic eruptions to spontaneous combustion - but the recent wildfires in the UK may have been started deliberately by members of the public. However the warmest April since records began, leading to an unusually long period of dry conditions certainly played a key role in spreading the fires.

With rainfall well below average in the past two months, the combination of "spring's longer daylight hours and really prolonged dry weather means that any moisture that has been left has evaporated quickly" says Matt Dobson at Meteogroup. This creates the prefect conditions for fires to take hold and strong southeast breeze fanning the flames helped spread the fires.

Wild fires can occur in all parts of the world apart from Antarctica and are most common in spring and summer. In winter there are fewer long dry periods "evaporation rates are very low and you will remember that everywhere stays very damp after it has rained" says Matt Dobson at Meteogroup, so the fires don't spread.

Fortunately a respite from the fires may be on the way. The next few days should see "an increase in rain and thunderstorm and hopefully an end to the current conditions". Which is good news for the fire-fighters and the forests.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

d ~ 319'027'200 km: day 124

The layer of air that we live in is dynamic, constantly moving around, heating up or cooling down, and transporting water and heat around the planet. All of this happens because the sun doesn't heat the Earth evenly (you get less solar energy at the poles than at the equator). The tilt of the Earth means that the heating pattern changes throughout the year, and this is why we have seasons. Our word for what the local air is doing right now is "weather", and it's an incredibly important aspect of our environment. Considering that we spend our lives wading around in this ocean of air, it's not surprising that almost all our senses are affected when it changes.

We take for granted that we can see clouds, hear rain and feel warm winds, but it turns out that our noses are also a good tool for monitoring the weather. So what is it that we can smell?

First of all, it turns out that the local air pressure and humidity can affect how well you can smell at all. Surprisingly, this has only recently been studied properly, but your sense of smell is sharper when the pressure is higher and when it's more humid. You know those fresh spring mornings that just smell "clean"? Actually, it's just that the cold dry air means that you are not really smelling much at all. All the icky smells are still there, but you are happily oblivious. Ignorance is bliss when it comes to spring mornings. The flip side of this is that you can tell when it's humid (and therefore when it might rain) because the smell of everything becomes more intense.

The smell that most people associate with the weather is a really strong earthy smell that you get just before and during summer showers. The smell is a chemical called geosmin (literally "Earth smell"), and it's found in a particular type of soil bacteria called actinomycetes. These bacteria produce spores when they're dried out, and when it rains, these spores are kicked up so that they become airborne. Storm showers are often associated with localized strong winds, so these winds can blow this smell to you before the rain actually arrives. It's like a bacterial weather forecast, even if the message only arrives a few minutes before the rain itself. This is also why the earthy smell isn't as strong in cities - you may notice more intense general smells (because it's humid), but there's less geosmin around.

Lightning also has a smell associated with it. The electrical breakdown of air helps ozone to form, and this has a distinctive metallic smell. Ozone is a molecule made up of three oxygen atoms (normal oxygen molecules only have two oxygen atoms), and it's very reactive so it doesn't last long.

And of course, what you can smell may tell you where the wind is coming from. For example, the smell of the sea tells you that the air has come from the coast. So next time you're out and about, sniff the air. You'll be directly sensing the type of air that you're living in on that particular day, and there may be some clues to the larger-scale weather patterns passing through your local area.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?

d ~ 316'454'400: day 123

The 23 Degrees team are heading back out to Northern Canada on the edge of the Arctic Circle. The last time we were out there it was mid-winter and it was 35 degrees below zero. That's seriously cold. On that trip we were learning why Yellowknife was the coldest city in America, and why mid-January is the coldest period in the northern hemisphere. This time we are there to discover what happens when the Sun warming rays finally reach this northern territory.

We are travelling to the Hay River which flows towards the Great Slave Lake. During winter the Hay river is a major highway linking Yellowknife with the outside world. The frozen river becomes a three-lane highway for the ice road truckers to ship in supplies. But from April the days are getting longer and more and more solar energy is arriving, warming the ice. Now for most rivers this is not a big deal, the ice melts and the river flows. But not the Hay River because unusually it flows south to north, and that makes a big difference. Because of the planet's tilt the warming Sun's rays hit the headwaters of the river in the south first, while downstream in the north there's little sun so it stays really cold. This means that the upstream part of the river thaws first while the downstream section of the river stays frozen.

Once the ice upstream melts and breaks up it starts to flow north towards the Great Slave Lake. When it gets there the great lumps of ice smash into the frozen lake - sometime creating huge pile-ups of ice. If these ice dams are big enough they can block off the flow of water, which then spreads into the surrounding tundra. That can be very bad news for the inhabitants of Hay River, the last time it happened the town was flooded.

Kate Humble and the Team are going filming with scientists and local experts who are monitoring the break up of the ice in an attempt to see if there will be a flood. One indicator of how bad the ice break up is going to be is the Alexandra Falls. Right now the 35-metre waterfall is frozen solid but soon it's going to melt, with a serious crash.

In a brief moment hundreds of tonnes of ice will splinter and fall, and the whole waterfall will collapse. The incredible cascade of water and ice will only last for a short time but it signals the start of a tense period for the locals and the scientists. For the next few days they will closely monitor the ice break up to assess how much ice will hit the Slave Lake and how much flooding might occur.

The 23 Degrees team will be there watching the break up and relaying back updates on this incredible spectacle.

• Bookmark with:
• del.icio.us |
• Digg |
• Reddit
• - What's this?