The centre of a cyclone is a calm area. It is called the eye of the storm. A large cyclone is a violently rotating mass of
air in the atmosphere, 10 to 15 km high. The diameter of the eye varies from 10 to 30 km . It is a region free of clouds and has light winds. Around this calm and clear eye , there is a cloud region of about 150 km in size. In this region there are high-speed winds (150–250 km/h) and thick clouds with heavy rain. Away from this region the wind speed gradually decreases. The formation of a cyclone is a very complex process.