If you’re taking a spring trip to Paris this year, take a sharp look at the Eiffel Tower. Above the top of the arches and the metal lattice work, the names of famous scientists are embossed, visible from the ground below. One of them is Gustave-Gaspard de Coriolis. Working in the early 1800’s as a mechanical engineer, he developed important theories on the function of machines, billiard games, and especially the explanation of wind directions around the world.
Even today, it’s not easy to visualize what became known as the Coriolis Effect. It’s caused by Earth’s rotation. Large bodies of air or water seem to move in a curve or even a circle. Tourists often ask (and even check) if the water in Australian bathroom drains rotates in the opposite direction than it does here. I don’t really care. Besides, at my house some drains rotate clockwise and some go counterclockwise. The bath water gets its spin from the shape of the sink, not Earth’s rotation.
But on a scale of hundreds of miles, the Coriolis Effect is a major controller of windflow. Hurricanes, Typhoons and Cyclones are all the same type of circular storm. They don’t develop at the equator because there’s no Coriolis effect there. You can imagine standing at the equator, looking east (in the direction that the earth is turning). On both sides, the globe’s curvature is dropping away from you. Walk ahead in a straight line, and you’re going along the center of the ball. But stand some way to the left (the North Pole in this example). Earth’s curvature rises at right and drops to the left. To walk in a straight line, you need to climb a bit to the right. Retracing your footsteps, you’ve made a right-hand curve. It’s the opposite if you step to the right side, or south, of the equator. Keeping your steps in a straight line will have you walk in a left-turning curve.
Hurricanes develop in the warm subtropics. As soon as they build up wind during their early stages as tropical depressions, the Coriolis effect makes the air start to turn. The stronger the windflow, the steeper the curve. Finally, once the windspeeds exceed 75mph, there’s the familiar pattern that Gustave Coriolis described: circular storms turning counterclockwise north of the equator, but clockwise in the southern hemisphere.
Rudi Kiefer, Ph.D., is a professor at Brenau University, teaching physical and health sciences on Brenau’s Georgia campuses and in China. His column appears Sundays and at gainesvilletimes.com.