Why do cyclones occur?
Cyclones are oceanic phenomena, which usually develop from a thunderstorm in the trough regions.
Cyclones are huge revolving storms caused by winds blowing around a central area of low atmospheric pressure.
Cyclones develop over warm seas near the Equator. Air heated by the sun rises very swiftly, which creates an area of very low pressure. As the warm air rises, it becomes loaded with moisture which condenses into massive thunderclouds. Cool air rushes in to fill the void that is left, but because of the constant turning of the Earth on its axis, the air is bent inwards and then spirals upwards with great force. The swirling winds rotate faster and faster, forming a huge circle which can be up to 2,000 km across. At the centre of the storm is a calm, cloudless area called the eye, where there is no rain, and the winds are fairly light.
As the cyclone builds up it begins to move. It is sustained by a steady flow of warm, moist air. The strongest winds and heaviest rains are found in the towering clouds. Winds around the eye can reach speeds of up to 200 km/h, and a fully developed cyclone pumps out about two million tonnes of air per second. This results in heavy rainfall.
Cyclones usually begin in tropical regions. In the northern hemisphere, cyclones are called hurricanes or typhoons and their winds blow in an anti-clockwise circle. In the southern hemisphere, these tropical storms are known as cyclones, whose winds blow in a clockwise circle.