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Catching the wind

Matt Erdmann, of Madison, takes advantage of the wind as he kiteboards at Olbrich Park along the shore of Lake Monona in January. The wind is simply air in motion, flowing from high atmospheric pressures to low pressures.

AMBER ARNOLD, STATE JOURNAL ARCHIVES

Q: What is the cause of strong winds?

A: The wind is simply air in motion, flowing from high atmospheric pressures to low pressures.

Moving anything requires a force. The strong winds we experienced this past weekend were due to a strong pressure gradient force.

A pressure gradient is how fast atmospheric pressure changes over distance. So, when pressure changes rapidly over a small distance, the pressure gradient force is large. Strong winds almost always result from large pressure gradients. Recently, southern Wisconsin has been under the influence of a weather pattern that has strong pressure gradients and thus strong winds.

The Coriolis force pulls the wind to the right so that in the Northern Hemisphere winds blow counterclockwise around low pressure systems and clockwise around high pressure ones. So, if you put your back to the wind, lower pressure is to the left.

What the wind is blowing over can also influence the wind speed. Over the open lakes, the wind will be faster than through a stand of trees, where it will be slowed by friction. In the presence of buildings, the air can be funneled between buildings and pick up speed.

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During this time of the year, thunderstorms also can cause strong winds. Rain falling from a thunderstorm evaporates underneath the cloud, cooling the air beneath it. This cold heavy air plunges to the surface and “splashes” against the ground like a bucket of cold water. The air then rushes sideways resulting in strong winds.

These “microbursts” are capable of producing winds of more than 100 mph, causing significant damage while lasting for only five to 15 minutes.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.

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