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".