What is a typhoon?

A typhoon is a type of large storm system having a circular or spiral system of violent winds, typically hundreds of kilometers or miles in diameter. The winds spiral around a region of low atmospheric pressure. "Typhoon" is the name of these storms that occur in the Western Pacific. "Hurricane" is the name given to these storms in the Atlantic Ocean and Eastern Pacific. In the Indian Ocean, they are called "Tropical Cyclones". For stronger typhoons, a characteristic structure called the "eye" forms when the maximum wind speeds exceed about 85 miles per hour, or 140 kilometers per hour. The eye is a region of clear air with no clouds, and is a few tens of kilometers in diameter. The energy that powers typhoons comes from the evaporation of warm ocean water. The water vapor rises to the top of the typhoon along the sides of the eye, then condenses into clouds. Warmer ocean water produces more powerful typhoons, which can grow into "super typhoons".

The physics of typhoons depends on a balance between the low pressure at the center of the storm and the Coriolis force that comes from the rotation of the earth. Since the Coriolis force is zero at the Earth's equator, typhoons can only form at latitudes that are more than about 10 degrees north or south of the Earth's equator. Due to the Coriolis force, the winds in a typhoon spiral in the counter-clockwise direction in the northern hemisphere when observed from above. The winds spiral in the clockwise direction in the southern hemisphere.

Typhoons are measured on the Saffir-Simpson scale. Category 1 storms have the lowest wind speeds. Category 5 storms are the most powerful and have the highest wind speeds.

Contributing source: NOAA

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