Thursday, October 21, 2010

Down in the valley....valley so some geology....hear the wind blow....

It's been a windy few days here in Taylor Valley, but that's a good thing!

Most people associate wind and cold with "wind chill." This is the perception that weather feels colder on a windy day. Wind chill cools you down because it replaces the warm air right around your body or clothes with cold air (wearing windproof clothing like we do here helps reduce the feeling of wind chill greatly).

Interestingly, wind chill was first studied scientifically by Paul Siple. Siple was a Boy Scout on one of Admiral Byrd's Antarctic expeditions, and went on to become a major figure in Antarctic history. (It's part of his legacy that a Boy Scout and a Girl Scout are annually rotated through the Antarctic bases--you never know who will have the next big idea!).

So why is wind a good thing here? Oddly enough, it depends on which way the wind is blowing. When the wind blows down-valley, it means that the air mass is coming off the polar plateau (where the ice cap is). This air is very cold and very dry. As it descends into the valley from high on the plateau, the wind suddenly finds that it's at a higher pressure than it was before (in the same way that air pressure is low on a mountain top, and high at the base of a mountain--there's more more atmosphere above you at the base of the mountain, squeezing down on the air around you, resulting in a higher air pressure).

This squeezing of the wind (an increase in pressure) raises its temperature. This is the ideal gas law at work in nature (it's also the same phenomenon that you observe when you pump up a bike tire or a basketball--by raising the pressure inside, the air in the tire or ball warms up, too).

So, since I got here, the temperature has been hovering around -25*C (-13*F) (did I mention that it's spring time here?). Once the wind started blowing yesterday, the temperature raced up to -10*C (14*F), and even pushed -5*C (23*F) for a couple of hours. Down right balmy.

Nice weather means that it's time to be outside working, though. More about the permafrost soon!

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