What Causes a Cyclone?

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Cyclones, also known as hurricanes or typhoons, are primarily caused by high ocean temperatures, broad-scale wind systems and clustered thunderstorms, which liberate the heat energy from the ocean surface and transfer it to the cyclone. Ocean temperatures must be higher than 80 degrees Fahrenheit to a depth of at least 150 feet.

This heat from the ocean combines with the Earth’s rotation to create the cyclone’s spin and propulsion. As the cyclone moves across cooler waters, land or into unfavorable wind systems, it gradually begins to dissipate as it loses energy.

There are a number of additional atmospheric conditions that must be present in order for a cyclone to form, including moisture layers in the mid-troposphere, approximately 3 miles above the Earth’s surface, and low vertical wind shear between the Earth’s surface and the upper troposphere. Cyclones also need to be at least 310 miles from the equator, where the deflective Coriolis force of the planet’s rotation begins to take effect.

Depending on the caliber of these conditions, a cyclone’s center, or eye, can grow to be more than 62 miles in diameter, although 25 miles is more typical.

A cyclone’s severity is measured on a 5-point scale, ranging from Category 1, which have gales of between 56-78 kilometers per hour causing possible damage to trees and lightweight structures, to Category 5, which have very destructive winds of up to 173 miles per hour, causing widespread destruction and loss of life.