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The Anemometer
Mon Dec 13, 2004
Listen in RealAudio 
The Mount Washington Observatory is noted in the weather world for measuring the
highest surface wind speed on the planet. Did you ever wonder how we measure that
wind? Hi, I’m Bryan Yeaton, and this is The Weather Notebook.
The general device that clocks wind speed is called an anemometer. But there are
several types. Probably the one with which you are most familiar has three cups that
spin around. The rotational speed of the cups is converted to the displayed
reading—be it in miles per hour, kilometers per hour, or meters per second.
Another classic type of anemometer is the swinging plate, or pressure plate. This is
the one you can find for about seven bucks in the science gadget store. The wind
exerts its force against a flat plate affixed to a pivot; a stronger wind will push the plate
higher up on a scale.
A sonic anemometer uses sound waves to determine wind speed. Sound is beamed
between prongs a few inches apart, and the wind will actually change the speed of the
sound waves to a known extent. A hot-wire device works in a similar manner, where
the wind will cool a heated wire, and the amount of energy it takes to keep the wire at a
certain temperature can be converted into a wind speed.
Atop Mount Washington, the highest winds are measured with a pitot tube. Wind gets
squeezed through a small nozzle in the tube, and that pressure reads out on a chart in
our weather room. Icing on the summit is often so severe that we have to clear up to a
foot an hour off our instruments. For that, we use another specialized weather service
tool, called a "crowbar."
The Weather Notebook is funded by Subaru of America, and the Lyndon State College
Meteorology program.
Today's Links
Lyndon State College
http://www.lsc.vsc.edu/
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