by Evan Becker on April 19th, 2004

Evan Becker

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Is it true that tornados spin clockwise in the northern hemisphere and counterclockwise in the southern? If so, why?

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  • by Redneck Savant on January 13th, 2009

    Redneck Savant

    YES! But there are exceptions.

    In answer - I once watched a satellite feed of several storm systems forming over the equator. From the photos, it was quite apparent that each storm system had a rotation to it (clockwise in the northern hemisphere, and counterclockwise in the southern). The reason storm systems rotate this way is complex, but you can understand it simply - by putting your hand out the window of a moving car. You feel the air resistance. When you move with the wind, you feel less resistance, against the wind - you feel more. The formation of these storm systems works in much the same way - only the system is your hand and the earth is the car.

    So, there is more resistance toward rotation counterclockwise in the northern hemisphere, and visa-versa for the southern. Yes, it is possible to go against that resistance, but even though this may happen on a small scale at times (tornados) - you will not likely ever witness one on a large scale (hurricane or the whole storm system). I know, speaking of a tornado as small scale seems a bit odd - but this is the WHOLE WORLD we are talking about - and it's spin is powerful beyond belief. 900 miles per hour at the equator - where most storm systems form. Can you imagine putting your hand out the window at 900MPH? Of course the weather is affected by that!

    A small object will feel less resistance to the wind, a bigger one will feel more. That's why some tornados can spin the other way - but storm systems don't. The bigger it is, the more resistance to opposing the spin of the earth it will have.

    I don't know if the following is under a specific scientific theory - but think about this for a second:

    The earth spins faster at the equator than the poles (the speed of an object in rotation increases the farther it is from the center of rotation). If I have a storm system 100 miles wide - then the side closest to the equator MUST be spinning faster than the side farther from the equator. It is precisely that difference in speed that causes storm systems to rotate in the first place. As faster air moves by, it creates a vacume of sorts, drawing in the slower air from much like an airplane wing is designed to create lift.

    To summarize - Most tornados do IN FACT rotate CW in the Northern, and CCW in the Southern Hemispheres. The reason for this is the Earth's rotation - and it's effect on the weather (the corolis effect).

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