1. WelcomeWelcome
Prepared by
Priya.M
B.Ed Geography

2. CYCLONESCYCLONES

3. CYCLONESCYCLONES
Atmospheric Atmospheric systemsystem
of low barometric pressure accompanied by of low barometric pressure accompanied by
strong winds that rotate counter-clockwise instrong winds that rotate counter-clockwise in
the northern hemisphere and clockwise in thethe northern hemisphere and clockwise in the
southern hemisphere called 'cyclone' in thesouthern hemisphere called 'cyclone' in the
Indian ocean and southern Pacific, it is calledIndian ocean and southern Pacific, it is called
'hurricane‘.'hurricane‘.
The locational point of view Cyclones areThe locational point of view Cyclones are
classified into two principal types:classified into two principal types:
1.1. Temperate cyclonesTemperate cyclones
2.2. Tropical cyclonesTropical cyclones

4. Temperate cyclonesTemperate cyclones
oror
Extratropical cycloneExtratropical cyclone
Temperate cyclones are depressions causedTemperate cyclones are depressions caused
by the meeting of the warm tropical air and theby the meeting of the warm tropical air and the
cold polar air at latitudes 40 to 60 N and S.cold polar air at latitudes 40 to 60 N and S.
When cold polar air moves in a general westerlyWhen cold polar air moves in a general westerly
direction and warm tropical air moves in adirection and warm tropical air moves in a
general easterly direction, a wave develops. Thegeneral easterly direction, a wave develops. The
wave bulges into the cold air and gets larger.wave bulges into the cold air and gets larger.
Pressure at the tip of the wave falls and windsPressure at the tip of the wave falls and winds
blow around this low pressure point.blow around this low pressure point.

5. TYPES OF TEMPERATETYPES OF TEMPERATE
CYCLONESCYCLONES
Though temperate cyclone is are mainlyThough temperate cyclone is are mainly
originated due to convergence of twooriginated due to convergence of two
contrasting air masses in terms ofcontrasting air masses in terms of
temperature, pressure, and humidity but sometemperature, pressure, and humidity but some
local cyclones also form due to other reasonslocal cyclones also form due to other reasons
related to temperature variations andrelated to temperature variations and
consequent pressure differences.consequent pressure differences.
1.1. Dynamic cyclonesDynamic cyclones
2.2. Thermal cyclonesThermal cyclones
3.3. Secondary cyclonesSecondary cyclones

6. Dynamic cyclonesDynamic cyclones
Dynamic cyclones are, in fact, real temperateDynamic cyclones are, in fact, real temperate
cyclones because they are formed due tocyclones because they are formed due to
convergence of cold polar air masses and warmconvergence of cold polar air masses and warm
and moist maritime tropical air masses. Theseand moist maritime tropical air masses. These
cyclones affect the weather conditions of verycyclones affect the weather conditions of very
large areas in middle latitudes. Different frontslarge areas in middle latitudes. Different fronts
and sectors are fully developed in dynamicand sectors are fully developed in dynamic
cyclonescyclones..

7. Thermal CyclonesThermal Cyclones
Thermal cyclones are formed due toThermal cyclones are formed due to
development of low pressure centres on thedevelopment of low pressure centres on the
continents in summer in temperate regions andcontinents in summer in temperate regions and
as such winds blow from all direction towardsas such winds blow from all direction towards
the low pressure centres. Such thermallythe low pressure centres. Such thermally
induced temperate cyclones are stationary atinduced temperate cyclones are stationary at
their places of origin and different fronts are nottheir places of origin and different fronts are not
developed.developed.

8. Secondary cyclonesSecondary cyclones
Secondary cyclones are those whichSecondary cyclones are those which
develop due to passage of cold windsdevelop due to passage of cold winds
over warm sea after the occlusion of mainover warm sea after the occlusion of main
cyclone. They are short-lived and verycyclone. They are short-lived and very
weak.weak.

9. Shape, size and velocity of theShape, size and velocity of the
temperate cyclonestemperate cyclones
• Temperate cyclones are of different shapes e.g.Temperate cyclones are of different shapes e.g.
Circular, semi circular, elliptical, elongated or ‘V’Circular, semi circular, elliptical, elongated or ‘V’
shaped.shaped.
• Temperate cyclones also greatly vary in size andTemperate cyclones also greatly vary in size and
extent. Average large diameter of an idealextent. Average large diameter of an ideal
cyclones is about 1900km while short diametercyclones is about 1900km while short diameter
measures 1000km .measures 1000km .
• The temperate cyclones move east ward underThe temperate cyclones move east ward under
the influence of westerly winds.the influence of westerly winds.

10. Tropical CycloneTropical Cyclone
A type of low pressure system whichA type of low pressure system which
generally forms in the tropics. It is composed ofgenerally forms in the tropics. It is composed of
a large, rotating area of clouds, wind anda large, rotating area of clouds, wind and
thunderstorm activity. A tropical cyclone beginsthunderstorm activity. A tropical cyclone begins
as tropical depression, further intensifies to aas tropical depression, further intensifies to a
tropical storm, then becomes a tropical cyclonetropical storm, then becomes a tropical cyclone
when its maximum sustained winds reach 74when its maximum sustained winds reach 74
mph.mph.

11. Types of Tropical cycloneTypes of Tropical cyclone
It may be pointed out that tropical cyclonesIt may be pointed out that tropical cyclones
are so varied in size, weather conditions andare so varied in size, weather conditions and
their general characteristics that no two cyclontheir general characteristics that no two cyclon
are classify them into certain categories.are classify them into certain categories.
Generaly they are divided into 4 major types.Generaly they are divided into 4 major types.
1.1.Tropical disturbances or easterly wavesTropical disturbances or easterly waves
2.2.Tropical depressionTropical depression
3.3.Tropical stormsTropical storms
4.4.Hurricanes or typhoonsHurricanes or typhoons

12. Tropical disturbancesTropical disturbances
Tropical disturbances are migratory waveTropical disturbances are migratory wave
like cyclones and are associated with easterlylike cyclones and are associated with easterly
trade winds. They are also called easterlytrade winds. They are also called easterly
waves. A tropical cyclone is a storm systemwaves. A tropical cyclone is a storm system
characterized by a large low-pressure centercharacterized by a large low-pressure center
and numerous thunderstorms that produceand numerous thunderstorms that produce
strong winds.strong winds.

13. Tropical disturbancesTropical disturbances

14. Tropical depressionsTropical depressions
Once a group of thunderstorms has comeOnce a group of thunderstorms has come
together under the right atmospheric conditionstogether under the right atmospheric conditions
for a long enough time, they may organize into afor a long enough time, they may organize into a
tropical depression. Winds near the center aretropical depression. Winds near the center are
constantly between 20 and 34 knots (23 - 39constantly between 20 and 34 knots (23 - 39
mph).mph).

15. Tropical depressionsTropical depressions

16. Tropical stormsTropical storms
A A tropical stormtropical storm is an organized system of is an organized system of
strong thunderstorms with a defined surfacestrong thunderstorms with a defined surface
circulation and maximum sustained windscirculation and maximum sustained winds
between 17 metres per second and 32 metresbetween 17 metres per second and 32 metres
per second. At this point, the distinctive cyclonicper second. At this point, the distinctive cyclonic
shape starts to develop, although an eye is notshape starts to develop, although an eye is not
usually present.usually present.

17. Tropical stormTropical storm

18. Hurricane or typhoonHurricane or typhoon
A A hurricanehurricane or or typhoontyphoon is a system withis a system with
sustained winds of at least 33 metres persustained winds of at least 33 metres per
second or 74 miles per hour (119 km/h). Asecond or 74 miles per hour (119 km/h). A
cyclone of this intensity tends to develop an eye,cyclone of this intensity tends to develop an eye,
an area of relative calm at the center ofan area of relative calm at the center of
circulation. The eye is often visible in satellitecirculation. The eye is often visible in satellite
images as a small, circular, cloud-free spot.images as a small, circular, cloud-free spot.

19. HurricaneHurricane