What is a tropical cyclone?
Tropical cyclones are violent storms that originate over oceans in tropical areas and move over to the coastal areas bringing about large scale destruction caused by violent winds, very heavy rainfall and storm surges. Tropical cyclones are called “hurricanes” in the Atlantic, the Caribbean and northeastern Pacific, “typhoons” in the western Pacific and “cyclones” in the Indian Ocean and “willy willies” in the sea around Australia.
Why don’t tropical cyclones form within 5° of the equator?
At the latitude of tropical cyclone development, the Coriolis force is weaker than in the midlatitudes. At upper levels in the atmosphere the Coriolis force balances the pressure gradient around a cyclone, and the magnitude of this “balancing act” is proportional to the wind speed. With a weaker Coriolis force, the winds must move faster to balance the pressure gradient. So, given a midlatitude cyclone and a tropical cyclone with equal central low pressures, winds around the tropical cyclone will be faster. As the latitude approaches the Equator, the Coriolis force continues to weaken and finally disappears. This explains why tropical cyclones do not form at latitudes between 5° N and 5° S. Without the Coriolis force, there is no mechanism to cause winds to revolve around a low-pressure center, so they do not converge to form cyclones.
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