A cyclone is an atmospheric perturbation
in the aspect of a large cloud mass spiral bands, associated
with a very intense depression with swirling winds more than
In the southern hemisphere, the winds rotate in the direction
of clockwise in the cyclone. And the direction of rotation
is opposite in the northern hemisphere. The direction of rotation
of the wind around the depression is due to the rotation of
the Earth called CORIOLIS force
A cyclone is made with a "eye" of about
average diameter 20 to 50 km, but can reach 200 km according
to the cyclone. Closer one gets to the eye of the cyclone
more the temperature rises 50°F (10°C) higher
than the surrounding air in high altitude and from 32
to 35,6°F (from 0 to 2°C) higher than surface
air), more the pression is lower, the precipitation
is greater and become violent winds up to 155 mph (250
km/h) for the most intense cyclones, while when we are
in the eye winds are very low.
Tropical cyclones generally have a diameter of a
few hundred kilometers, but they can reach 1000 or even
1500 km and cloud structures can reach 20 km height.
Warm, moist air rises high altitude turning
eye of the cyclone and dry air down into the eye.
A video giving information on cyclones
AND CONDITONS OF FORMATION CYCLONES
there are several types and main mechanisms of
formations of cyclones :
Tropical cyclones form over warm
water in tropical seas and draw their energy from
the latent heat of condensation of water.
develop a tropical cyclone favourable conditions
are necessary : a depression must cross over ocean
heated more than 78,8°F
at least 60 meters depth and distant for more than
550 km from equator. This is from 5° latitude
that the Coriolis
force can act on the trigger initial vortex
as it is null at the equator. The force generated
by the earth's rotation causes wind deflection to
the east in the northern hemisphere. This allows
warm moist air to rise to 9.000
m. Then the atmospheric pressure decreases. With
the Coriolis force, the hot and humid air begins
to swirl. Water vapor forms clounds.
Gerater is the difference between the air temperature
low and high altitude, the more air is unstable,
creating violent thunderstorms.
Spiral, cold air descends and it warms and rises
a tropical cyclone reaches land or in cold water
the winds weaken as it is no longer powered by the
vapor of warm water.
A depression passes over an area of
water to more than
78,8°F (26°C). Warm and humid air rises up then is
winds lower altitudes. The pressure drops to the sea surface
and increases at the highest clouds to the tropopause, the
top of the
troposphere. The cold air descends it warms and
turns in a spiral around the depression forming in central
the eye of the tropical cyclone. So a cyclone is created.
Extra-tropical cyclones (winter storms)
occur in the middle latitudes of the Earth
and draw their energy from areas with heavy difference of
temperatures between the tropics and the poles. The majority
of their power is due to baroclinic processes. Their field
of temperature and humidity is asymmetric.
EPSILON, VINCE, DELTA of 2005 are called extra-tropical
cyclones according to the season and thus as the temperature
of the ocean was lower at 78,8°F (26°C).
entre les cyclones extra-tropicaux et
les cyclones tropicaux
october to march
summer / autumn
Location of storms
tropical and subtropical areas
Peak wind gusts
44-112 mph (20-50 m/s)
74-201 mph (33-90 m/s)
Life at a given
point in time
tidal waves, tornadoes
Extent of damage
many small damages
small and large damages
Subtropical cyclone are cyclones which both the characteristics
of tropical and extratropical cyclones. Their characteristics
of tropical cyclones is that they can have a warm heart. But
some have a cold heart. The strong winds in subtropical cyclones
is wider and far from the nucleus. These cyclones can have a
radius of maximum diameter 420.km.
Sometimes these subtropical systems are transformed into
storms or tropical cyclones as was the case with Hurricane Florence
in November 1994 in the Atlantic. They are formed at subtropical
latitudes so beyond the tropics, up to a latitude of 50°.
Polar cyclones are low pressure systems from 1000
that originate in high latitudes, areas where the thermal
contrast is significant as the border of the ice zone
with the open sea while that the very cold air goes at
altitude. They form there where the water is not too cold
and without ice in the northern seas: the Labrador Sea,
the Gulf of Alaska and the sea of Japan. But they are
also common on polar waters surrounding Antarctica. More
polar cyclones formed in the northern hemisphere than
in the southern hemisphere. About 15 polar cyclones per
winter occur in the Eurasian Arctic, Greenland and the
Canadian Arctic zone.
As tropical cyclones they turn in the opposite direction
to clockwise in the Northern Hemisphere. Polar cyclones
can give very localized conditions of blizzards.
Polar cyclone off the coast of the Iceland
AND DIRECTIONS CYCLONES
Cyclones can move thousands of
kilometres at an average speed of 12 to 15 mph (20
to 25 km/h). This speed is quite low in the phase
of genesis, but it gradually increases that they
stray tropical waters and head to the North (for
the northern hemisphere). Then their displacement
can be faster (700 to 1000 km per day).
This map shows the areas where
hurricanes hit more often and
their directions. As you can see it is all along the
(to 10° of latitude) they develop as the water
is hot enough.
here to see the track of tropical cyclone activity
In the northern Indian Ocean is from January to
March they develop. In the North Atlantic and North
Pacific, it is between June and September that tropical
cyclones form. In the South Pacific and the South
of the Indian ocean is from May to June and from October
to December that they form.
However, in the South Atlantic there is logically
not tropical cyclones that form as water is not warm
enough, and then because of the permanent presence
of a strong vertical wind shear in the troposphere
and the intertropical convergence zone which disrupts
But the 03/28/2004 a tropical cyclone was observed
for the first time in the South Atlantic and hit the
coast of southeastern Brazil with winds up to 93 mph
(150 km/h) and an average of 74 mph (120 km/h). This
cyclone known as Catarina was born as an extratropical
stage then is passed to the hybrid stage (warm air
at the centre in lower layers, cold air aloft) and
became a tropical cyclone at warm core (warm air at
the centre at all levels) where there is exchange
of energy between ocean-atmosphere.
Cyclone Catarina has hit Brazil,
this is a rare occurence
Régnier helped me correct mistakes, please
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Im not english speaker, some improprieties can
appear to english masters.
Could you help me reporting by mail any fault you
read. Thank you for all.