Stormy Weather

Hurricanes, Monsoons, and Tropical Storms

What is the Coriolis effect?

Named after French mathematician scientist Gustave Coriolis (1792–1843), who first explained it in 1835, the Coriolis effect refers to the way objects appear to move in a curving or circular pattern when observed from a point of view position that is rotating. Imagine yourself standing next to a playground carousel. Two of your friends are riding on opposite sides of the carousel as it spins around. One friend holds a ball and tries to roll it to the person on the other side, but as he does so, the ball seems to veer to one side and roll off the carousel. To your point of view (as you stand off to the side), however, the ball rolled in a straight line, but it did not reach your other friend because as the ball moved across the carousel moved beneath it and the intended receiver was no longer in the original position.

Now imagine the Earth as it spins on its access. Above the Earth, suspended in the atmosphere, is a forming hurricane. The air around the hurricane is moving toward the eye, which is where the lowest air pressure is. However, as the air moves toward the eye, it is deflected to the right (in the Northern Hemisphere) by the Earth’s spin, or to the left (in the Southern Hemisphere). This causes the hurricane clouds to rotate counterclockwise in the North and clockwise in the South.


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