Weather Whys; Coriolis

This is weather-wise. In the northern hemisphere, if you stand with your back to the wind, lower pressure will be to your left, and high pressure will be to your right. That rule of thumb is called Bies-Ballett's Law, after the 19th century Dutch meteorologist who discovered it. But the laws of physics tell us air should flow from areas of high pressure to areas of low pressure. Why then do we see the wind blowing between the pressure centers instead of directly from one to the other? As it turns out, there are other forces acting on the wind which keep it from flowing straight from high to low pressure. One of the most important is what's called the Coriolis force. Imagine a merry-go-round with a dartboard mounted on its edge facing the center. You're standing on the opposite edge across from the dartboard. The merry-go-round stopped, you throw a few darts. Given a reasonable amount of skill, it's not too hard to land most of the darts on the board.

But then the merry-go-round begins to rotate in a counter-clockwise direction. Just as before, you throw a few darts, but now they seem to swing far to the right of their target. That's because the merry-go-round moves the dartboard out of the path of your throw. To you, it seems the dart curves away because you're rotating with the merry-go-round. To an observer on the ground, your throw looks straight. Similarly, the earth rotates under a moving stream of air, making the wind appear to curve. In the northern hemisphere, the deflection is toward the right. The air stream is being pushed that direction by the Coriolis effect and is pushed to the left by the pressure gradient force. Those two forces achieve a balance, and the wind flow is centered between them. Otherwise is produced by KGOU Radio at the University of Oklahoma in cooperation with the School of Meteorology and the Center for Analysis and Prediction of Storms. For weather-wise, I'm Drew Barlow.