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Cyclones
GMS satellite image on 9 January 1992 showing Typhoon Axel in the northwest
Pacific and Cyclones Mark and Betsy in the southwest Pacific. Bureau of
Meteorology
Following information taken from:
http://ntlapp.nt.gov.au/tracy//advanced/Met/cyclones.html (Australian
governmental department
and
mapsoftheworld.com
What are cyclones?
• A Cyclone is a closed area of circular rotating
fluid, clockwise in the Southern Hemisphere
and Counterclockwise in the Northern
Hemisphere
• It arises due to low atmospheric pressure
Types of cyclones:
• Cold core cyclones depends on the trough it is formed in
• Warm core cyclones forms in the upper level of the trough
• Extratropical cyclone is a totally different type of
atmospheric disaster, which lacks both tropical and polar
features. It is observed outside the tropical zone.
Extratropical cyclones are primarily centered around midlatitude.
• Polar low is relatively less severe in nature. It is very
common in north and south poles
• Mesocyclone is a special type of cyclonic whirlpool that
accompanies other severe weather conditions like
tornadoes, supercells and thunderstorm
Tropical cyclones
• Tropical cyclone depends on the warm core
storm system
• Most common form of cyclone
• Develops due to a low pressure center
• Occurs over warm oceans
• Comes with powerful current of air, heavy
rainfall and severe thunderstorms
Formation
1. Upward movement of warm air.
2. As the moist air moves up it comes in contact
with the cold air in the upper level of
atmosphere and gets condensed.
3. A powerful low-pressure cell is an essential
factor for tropical cyclone. A revolving draft
with a strong inward current leads to tropical
cyclone
• Based on its location and severity, tropical cyclone is classified as
1. typhoon,
2. tropical storm,
3. cyclonic storm,
4. tropical depression and
5. hurricane.
If the velocity of storm wind is not more than 60 kilometers per hour,
it is termed as tropical depression.
Tropical storms come with a speed of 60 to 110 kilometers pre hour.
Wind speed associated with tropical cyclones must be more than 100
kilometers per hour.
Tropical cyclones, which break out in the eastern part of North Pacific and
northern Atlantic regions are popularly known as hurricanes.
The same when occurs in the western part of North Pacific, it is termed as
typhoon.
Hurricanes
For a hurricane to form
• the temperature of ocean water should not be less than
26.5 degree Celsius.
• Moisture and heat developed from the water surface are
the main factors influencing the strength of hurricanes.
• As the land or ocean temperature falls, strength of
hurricane decreases.
For hurricane formation the relative humidity of the lower
and middle tropospheric level must also be very high.
Condensation of vapor reduces substantially due to high
relative humidity. This results in latent heat formation due
to increased precipitation.
• The foremost characteristic is that tropical cyclones are most violent of
all the atmospheric disturbances.
• The average speed is 120 kmph. Although it may vary from 32 kmph to
200 kmph or more. At times it reaches 400 kmph also.
• They have closed isobars. The pressure gradient is very sharp. More
closely spaced isobars represents greater velocity of the storm and
vice-versa. The pressure at the center is extremely low. The winds from
the surrounding area are drawn towards this low-pressure core called
the "eye" of the cyclone.
• Tropical cyclones develop over oceans and seas only. They are most
violent and vigorous over water. On landfall, their velocity decreases
due to friction, and as the source of energy is cut off, they dissipate
soon. Thus they affect the coastal areas only.
• The movement of tropical cyclone is affected by the prevailing wind
system. Normally they move from east to west under the influence of
trade winds.
• They are seasonal in nature and occur during a specific period of the
year only. In the Caribbean this is June to November