Coriolis Effect and Hurricanes
A hurricane, also called a typhoon or cyclone, is a common name for a tropical cyclone, which is a spinning storm system originating over water having wind speeds of over 118 km/hour or 73 miles/hour! The storms are known for their low pressures and spiral shape, and they most often form over warmer waters and bring heavy rains.
If you look up some pictures of weather systems online, you can see the characteristic “eye” shape of these storms. This is due to the Corilois Effect, which is the deflecting of objects (in this case, air) when considered in a rotating frame of reference, like the spin of the Earth. Gaspard-Gustave Coriolis developed a mathematical model for this type of force in 1835 when studying water wheels.
Problem: Model the rotation of the Earth and the Coriolis Effect.
What will happen as you try to draw a straight line from the center of the Lazy Susan while it is spinning?
- Construction paper
- Lazy Susan
- An assistant
- Cut out a piece of paper that covers the top of the Lazy Susan. Tape it down so it does not slide off.
- Draw a dot in the center of the paper with a marker.
- Spin the Lazy Susan.
- Try to draw a straight line from the center of the paper to the outside of the circle. What happens?
- Try spinning the platform in the other direction or at different speeds. How does this affect the lines you try to draw?
- For the next activity, stand up and pick a spot towards the center of the room. You are going to be air at high pressure.
- Slowly move toward the center of the room, this is the low pressure.
- As you do this, have a friend or parent pull your sleeve 90° to your right. This models how a hurricane spins in the Northern Hemisphere. Can you guess how?
As the platform spins, the lines drawn from the center will curve around the paper.
Wind is created by the rushing of air from high pressure to low pressure; the greater the difference in pressure, the faster the wind moves. Between these points is a straight line. However, due to the rotation of the Earth, the wind is deflected and curves, giving us the Coriolis Effect. In the Northern Hemisphere, the rotation of the Earth deflects wind to the right so that it spins clockwise. Wind in the Southern Hemisphere spins counter-clockwise.
So why is it that hurricanes in each hemisphere have a tendency to spin in the opposite direction of the deflection of the wind? Something else is going on, and it has to do with the areas of low pressure created by this deflection.
In the activity you did at the end of the experiment, you demonstrated how wind moves from high pressure to low. In the Northern Hemisphere the Earth spins left underneath you, so the wind is directed to the right. As you approach the low pressure center and are continually pulled right, it will appear as you are rotating to the left. It is the opposite in the Southern Hemisphere: the Earth appears to be rotating right underneath you and winds are pushed left, causing the spin of cyclones to occur in the clockwise direction.
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