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East Coast America Update: The Beauty of Snowflakes

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Helen Czerski Helen Czerski | 09:41 UK time, Friday, 21 January 2011

d ~ 54'028'800 km: day 21 of Earth's orbit

 

On Monday, the 23 degrees team travelled to New York to investigate the effects of Lake Effect Snow. Here, presenter Helen Czerski gives us her account of the trip...

We arrived in snowy Oswego, New York around 9am on Monday, and at the beginning nobody noticed the falling snow. Everyone was busy thinking about camera angles, where to park the radar truck and how many layers to wear. After a while there was a pause, and somebody held out their snow-covered arm and said, “That’s incredible”. And it was. Every single snowflake that had fallen on his sleeve was picture-perfect, and we realized that every snowflake we could find had a flawless six-sided branching structure. The snowflakes looked exactly like snowflakes, and we just couldn’t stop looking at them.

It was weird because we all realized at the same moment that what we all knew as a snowflake, the pretty shape that you see on Christmas cards and on winter jumpers, was something we had never actually seen before. In the UK, the temperature doesn’t go very far below freezing and the snowflakes that bump into each other in the air tend to be a bit wet, so they break and stick together. What we see are clumps of broken bits from lots different snowflakes, and it’s easy to miss the six-sided symmetry of the individual crystals. But where we were filming in up-state New York, the temperature was far lower (around -15C) and the snowflakes hadn’t bumped into each other much, so nothing had spoiled the stunning crystal structures.

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Unspoiled snowflakes are beautiful things. But if this is just frozen water, why don’t we see our ice trays full of snowflakes? The answer is that in the right conditions, water can go from being water vapour to solid ice without passing through liquid water in between, and that’s what happens inside snow clouds. There are water molecules floating in the air around the growing snowflakes, and if they bump into the crystal, they can stick to it and freeze straight away. They might also bump into it and then float off again. The shape all depends on how easy it is for a water molecule in the air to get to and stick to each different part of the snowflake.

In your ice tray, all the water in each ice cube compartment has to freeze in a fixed shape because it has nowhere else to go - it’s liquid and it has to stay in the ice tray. The beautiful dendrite snowflakes that we saw branch out because the water molecules don’t have to freeze wherever they land, and because they’re more likely to land in some places than others. The stickiest places change with time, and depend on the tiny variations in temperature and humidity as the flake travels through the snow cloud. The precise conditions at each time in the journey control exactly how the newest bits are growing. And so, as you go from the middle of a snowflake outwards, you’re reading its own autobiography about the place it grew up.

To read more on snowflakes and what determines their shape, take a look at meteorologist Chris Westbrook's account of its extraordinary transformation from water vapour to intricate snowflakes.

Helen Czerski is co-presenter of 23 Degrees

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