What Is a Cyclone?

CYCLONES

What is a cyclone?
Cyclones are large revolving storms that are caused by winds blowing around a place of low atmospheric pressure. In the northern hemisphere, these huge storms 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, and always blow in an ant-clockwise circle.

How do cyclones occur?
Cyclones are caused over warm seas near the Equator. Air that is heated by the sun, rises very quickly, which creates areas of very low pressure. As the very warm air rises, it receives moisture, which condenses into huge thunderclouds. Cool air sweeps in to fill the void that is left, but due to the continuous turning of the Earth, the air is bent inwards and then spirals upwards with tremendous force. The swirling winds rotate faster and faster, causing a massive circle to form, which can be up to 2, 000 km across. In the very middle of the storm is a calm, cloudless area called the eye, where there is no rain, and the winds are quite light.

Where do cyclones occur?
Cyclones start in tropical regions, such as Northern Australia, South-East Asia and many Pacific islands. Northern Australia has around five cyclones every year, during the summertime wet season. In order for a cyclone to develop, the sea surface must be at least 26ºC.


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CYCLONE YASI

Where is Queensland?
Queensland is a state of Australia that occupies the north-eastern section of the mainland continent (see last page for map).

What happened and when?
Cyclone Yasi made landfall in northern Queensland in the early hours of 3rd February 2011. In Mission Beach, winds were recorded to have reached speeds of 290 km/h (180mph). Yasi left behind significant damage, ‘a scene of mass destruction’, as over half the buildings in Innisfail and Cardwell were damaged, 140, 000 houses were blacked out, drinking water was in short reply and one person was killed of...