Known variously as hurricane, typhoon or, meteorologically correctly, tropical cyclone, the cyclone weather system of low barometric pressure at its centre reaches the defining criticial intensity when it registers at least force 12 on the Beaufort Scale. In terms of speed this is around 100kmh or faster. Hurricanes may be more than 500km wide and often travel at up to 250kmh.
In the northern hemisphere the air circulates anticlockwise and in the southern hemisphere it circulates clockwise.
Hurricanes are the result of a huge differential in atmospheric pressure, caused by sea temperature variations. When the ocean warms to 26°C, huge volumes of water evaporate, with spiralling winds sweeping the moisture upwards to create large cumulonimbus clouds. The release of latent heat from the water vapour condensing into drops adds more warmth to the air, which accelerates the growth of the storm.
The spinning air creates cumulonimbus clouds, bringing torrential rain circulating around a low pressure centre, the eye. This low pressure can also cause the sea level to rise significantly, causing devastating flooding when the storm hits land.
The ocean origins explain why coastal areas of warm countries suffer greater numbers of hurricanes than elsewhere. Power in the wind quickly dies when it reaches land and its supply of fuel — humid air — is removed.
 |
|
|
|
|
|
|
|
|
|
|
|
|
 |
|
|||||||||||
 |
 |
 |
 |
 |
 |
 |
 |
|
||||
 |
|
|||||||||||
 |
 |
 |
|
|||||||||
 |
 |
|
||||||||||
 |
|
|||||||||||
 |
|
|||||||||||
 |
 |
|
||||||||||
 |
|
|||||||||||
 |
|
|||||||||||
 |
|
|||||||||||
 |
 |
|
||||||||||
 |
|
|||||||||||