Why Do Hurricanes Spin?

The Coriolis Effect

Hurricanes spin clockwise in the Southern Hemisphere and counterclockwise in the Northern Hemisphere. Wind moves from high-pressure systems to low-pressure systems. Its spin is a result of the Coriolis Effect. But what is the Coriolis Effect?

The globe makes one full rotation every 24 hours, thus, it moves with a constant angular velocity. Though the globe and everything on it spins with a constant angular velocity, every point of the globe moves with a different linear velocity. Let’s take a point on the equator and compare it to a point that is closer to the North Pole. Point 1 is closer to the equator and Point 2 is closer to the North Pole. Both are rotating at the same pace, but the distance they must travel are different. The circle which Point 2 is on has a much smaller circumference than the larger circle. In order to rotate at the same speed, the points must be travelling at different linear velocities. If we take a snapshot during this rotation, we would see that the Point 1 would travel faster in a straight line than Point 2. Therefore, the farther out from the center of the Earth something it, the faster it travels linearly. So what does this have to do with the Coriolis Effect?

Travelling in the hemispheres

Let’s say Superman visits Florida and wants to throw a baseball to Wonder Woman in New York. Superman is standing when he throws the baseball and Wonder Woman is standing to catch it. He throws it straight towards her only to find out that it didn’t land in New York, but rather the Atlantic Ocean! How can this be? Superman is moving at a greater linear velocity than Wonder Woman because he is closer to the equator. When he throws the ball, it is moving faster than Wonder Woman and actually lands ahead of the intended destination! Wonder Woman gets in her invisible jet and flies over to Washington to see if she can throw it to Superman more accurately. Thankfully, she has a spare ball. She lands and throws it to Superman. Much to her dismay, it never reaches him. It lands instead in the Gulf of Mexico! In Washington, she is moving more slowly than Superman is in Florida and the ball lands behind Florida. In the Northern Hemisphere, travelling objects tend to shift to the right of the destination.

For hurricanes, imagine that the baseball is a high-pressure system (Point 1) and the destination is a low-pressure system (Point 2). The apparent deflection to Point 3 reflects the rotational motion of the hurricane.

The same logic applies to the Souther Hemisphere. At a point south of the destination, a thrown ball will have less linear velocity than the destination and will fall to the left of it. A ball thrown at a point north of the destination, a thrown ball will have a higher linear velocity than the destination and will fall to the left of it. In the Southern Hemisphere, travelling objects tend to shift to the left of the destination.

What about aircraft?

One would be observant to question if and how aircraft would take this into consideration. If a flight leaves Miami, Florida and is heading to Albany, New York, it would have to correct for the Coriolis Effect or it would fly into the ocean, right? Yes and no. There are many flight corrections a pilot makes during flight. The most significant effect is wind speed. Corrections made by the pilot inadvertently take the Coriolis Effect into account. Overall, it is not something for which a pilot makes a direct correction, but instead a peripheral correction.

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