CYCLONES
What is a Cyclone?
A cyclone is a system of rotating winds over a warm water area, spinning
inward to a low pressure center and generally causing stormy weather.
Structure of a Cyclone
 Eye: The centre or eye of a tropical cyclone is at the area of lowest
pressure and is characterized by little or no wind and often a
cloudless sky. In severe cyclones the eye usually shows up as a
circular hole in the central cloud mass.
 Eye Wall: Surrounding the eye is a wall of dense convective cloud
rising about 15 km into the atmosphere. This is the eye wall and is
where the most violent winds and heaviest rainfall occur.
 Spiral rain bands
Mayor cyclonic areas in the world
 North Atlantic
 North-East Pacific
 North-Central Pacific
 North-West Pacific
 North Indian Ocean
 South-West Indian Ocean
 Australian Region
 Southern Pacific
Areas affected by tropical cyclones
Tropical cyclones which occur in the Atlantic region and affect the
Caribbean and USA usually comprise less than 15% of global tropical
cyclone activity. Tropical cyclones also occur in various parts of the Pacific
Ocean, and can affect coastal regions of Mexico, south-east Asia, northeast Australia and the south Pacific islands. Those that form in the Indian
Ocean can affect India, Bangladesh, north-west Australia, some parts of
east Africa and Indian Ocean islands such as Mauritius and Madagascar.
In the northern hemisphere most tropical cyclones occur between June
and November with a peak in September. However, in the north-west
Pacific it is not unusual to have the occasional tropical cyclone outside of
this period. In the southern hemisphere the season usually lasts from
November to April. Tropical cyclones are occasionally observed in the
South Atlantic, but this is a very rare occurrence. The map above shows
the areas of the world affected by tropical cyclones.
How do cyclones form?
1. Sea water it’s at its hottest (27º or more).
2. Air above the sea surface is heated and the warm moist starts to
rise.
3. A deep center of low atmospheric pressure is made while the moist
rises.
4. Warm air spirals upward around the center of the cyclone, called the
`eye´.
5. Very dark and heavy clouds form and precipitate torrential rainfall
while in the `eye´ the weather is calm and dry.
Factors
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Water temperature at least 27º or more
Down to a depth of at least 160 ft.
Rapid cooling with height
High humidity
Low wind speed difference in a small area
Impacts
 A cyclone can be still powerful enough to destroy vehicles, buildings
and other structures and objects.
 They can even make them fly in the sky, turning loose debris into
fatal projectiles.
 Cyclones have caused 1.9 million deaths worldwide.
Some Famous Cyclones around the World
 Cyclone Yasi
Formed: 26 January 2011
Dissipated: 3 February 2011
 Cyclone Tracy
Formed: 21 December 1974
Dissipated: 26 December 1974
 Cyclone Larry
Formed: 18 March 2006
Dissipated 21 March 2006