Tropical Cyclones | Geography for UPSC 2024 (Pre & Mains) PDF Download

 Page 1


 
 
TROPICAL CYCLONES  
Tropical cyclones are violent storms that originate over oceans in tropical 
areas and move over to the coastal areas bringing about large scale 
destruction caused by violent winds, very heavy rainfall and storm surges.  
The conditions favourable for the formation and intensification of tropical 
storms are:  
(i) Large sea surface with temperature higher than 27° C;  
(ii)   Presence of the Coriolis force;  
(iii)  Small variations in the vertical wind speed;  
(iv)  A pre-existing weaklow-pressure area or low-level-cyclonic 
circulation;  
(v)  Upper divergence above the sea level system 
 
NOTE: 
 They are known as Cyclones in the Indian Ocean, Hurricanes in the 
Atlantic, Typhoons in the Western Pacific and South China Sea, and 
Willy-willies in the Western Australia.  
STRUCTURE OF TROPICAL CYCLONE  
Tropical cyclones originate and intensify over warm tropical oceans.  
The energy that intensifies the storm, comes from the condensation 
process in the towering cumulonimbus clouds, surrounding the centre of 
the storm.  
With continuous supply of moisture from the sea, the storm is further 
strengthened.  
On reaching the land the moisture supply is cut off and the storm 
dissipates.  
Page 2


 
 
TROPICAL CYCLONES  
Tropical cyclones are violent storms that originate over oceans in tropical 
areas and move over to the coastal areas bringing about large scale 
destruction caused by violent winds, very heavy rainfall and storm surges.  
The conditions favourable for the formation and intensification of tropical 
storms are:  
(i) Large sea surface with temperature higher than 27° C;  
(ii)   Presence of the Coriolis force;  
(iii)  Small variations in the vertical wind speed;  
(iv)  A pre-existing weaklow-pressure area or low-level-cyclonic 
circulation;  
(v)  Upper divergence above the sea level system 
 
NOTE: 
 They are known as Cyclones in the Indian Ocean, Hurricanes in the 
Atlantic, Typhoons in the Western Pacific and South China Sea, and 
Willy-willies in the Western Australia.  
STRUCTURE OF TROPICAL CYCLONE  
Tropical cyclones originate and intensify over warm tropical oceans.  
The energy that intensifies the storm, comes from the condensation 
process in the towering cumulonimbus clouds, surrounding the centre of 
the storm.  
With continuous supply of moisture from the sea, the storm is further 
strengthened.  
On reaching the land the moisture supply is cut off and the storm 
dissipates.  
 
 
The place where a tropical cyclone crosses the coast is called the landfall 
of the cyclone.  
The cyclones, which cross 20o N latitude generally, recurve and they are 
more destructive.   
A mature tropical cyclone is characterised by the strong spirally 
circulating wind around the centre, called the eye.  
The diameter of the circulating system can vary between 150 and 250 km. 
The eye is a region of calm with subsiding air.  
Around the eye is the eye wall, where there is a strong spiralling ascent of 
air to greater height reaching the tropopause.  
The wind reaches maximum velocity in this region, reaching as high as 
250 km per hour.  
Torrential rain occurs here. 
 From the eye wall rain bands may radiate and trains of cumulus and 
cumulonimbus clouds may drift into the outer region.  
The diameter of the storm over the Bay of Bengal, Arabian sea and Indian 
ocean is between 600 - 1200 km.  
The system moves slowly about 300 - 500 km per day.  
The storm peters out on the land 
 
RECURVING CYCLONES  
         The cyclones, which cross 20o N latitude generally, recurve and they 
are more destructive.   
Page 3


 
 
TROPICAL CYCLONES  
Tropical cyclones are violent storms that originate over oceans in tropical 
areas and move over to the coastal areas bringing about large scale 
destruction caused by violent winds, very heavy rainfall and storm surges.  
The conditions favourable for the formation and intensification of tropical 
storms are:  
(i) Large sea surface with temperature higher than 27° C;  
(ii)   Presence of the Coriolis force;  
(iii)  Small variations in the vertical wind speed;  
(iv)  A pre-existing weaklow-pressure area or low-level-cyclonic 
circulation;  
(v)  Upper divergence above the sea level system 
 
NOTE: 
 They are known as Cyclones in the Indian Ocean, Hurricanes in the 
Atlantic, Typhoons in the Western Pacific and South China Sea, and 
Willy-willies in the Western Australia.  
STRUCTURE OF TROPICAL CYCLONE  
Tropical cyclones originate and intensify over warm tropical oceans.  
The energy that intensifies the storm, comes from the condensation 
process in the towering cumulonimbus clouds, surrounding the centre of 
the storm.  
With continuous supply of moisture from the sea, the storm is further 
strengthened.  
On reaching the land the moisture supply is cut off and the storm 
dissipates.  
 
 
The place where a tropical cyclone crosses the coast is called the landfall 
of the cyclone.  
The cyclones, which cross 20o N latitude generally, recurve and they are 
more destructive.   
A mature tropical cyclone is characterised by the strong spirally 
circulating wind around the centre, called the eye.  
The diameter of the circulating system can vary between 150 and 250 km. 
The eye is a region of calm with subsiding air.  
Around the eye is the eye wall, where there is a strong spiralling ascent of 
air to greater height reaching the tropopause.  
The wind reaches maximum velocity in this region, reaching as high as 
250 km per hour.  
Torrential rain occurs here. 
 From the eye wall rain bands may radiate and trains of cumulus and 
cumulonimbus clouds may drift into the outer region.  
The diameter of the storm over the Bay of Bengal, Arabian sea and Indian 
ocean is between 600 - 1200 km.  
The system moves slowly about 300 - 500 km per day.  
The storm peters out on the land 
 
RECURVING CYCLONES  
         The cyclones, which cross 20o N latitude generally, recurve and they 
are more destructive.   
 
 
Tropical Cyclone (TC) Recurvature is the change in the cyclone's 
track from westward to eastward and poleward.  
 
 
Owing to the change in the influence of the wind systems from the 
deep easterlies of the tropics into the strong upper tropospheric 
westerlies of the mid-latitudes.  
Eg . Cylcone Okhi 
El-Nino Year – More favourable 
 
 
STAGES OF DEVELOPMENT OF A TROPICAL CYCLONE  
Tropical Depressions< Tropical Storms< Tropical Cyclones< Tornadoes  
THUNDERSTORMS AND TORNADOES 
Other severe local storms are thunderstorms and tornadoes. 
 They are of short duration, occurring over a small area but are violent. 
Thunderstorms are caused by intense convection on moist hot days.  
A thunderstorm is a well-grown cumulonimbus cloud producing thunder 
and lightening. 
Page 4


 
 
TROPICAL CYCLONES  
Tropical cyclones are violent storms that originate over oceans in tropical 
areas and move over to the coastal areas bringing about large scale 
destruction caused by violent winds, very heavy rainfall and storm surges.  
The conditions favourable for the formation and intensification of tropical 
storms are:  
(i) Large sea surface with temperature higher than 27° C;  
(ii)   Presence of the Coriolis force;  
(iii)  Small variations in the vertical wind speed;  
(iv)  A pre-existing weaklow-pressure area or low-level-cyclonic 
circulation;  
(v)  Upper divergence above the sea level system 
 
NOTE: 
 They are known as Cyclones in the Indian Ocean, Hurricanes in the 
Atlantic, Typhoons in the Western Pacific and South China Sea, and 
Willy-willies in the Western Australia.  
STRUCTURE OF TROPICAL CYCLONE  
Tropical cyclones originate and intensify over warm tropical oceans.  
The energy that intensifies the storm, comes from the condensation 
process in the towering cumulonimbus clouds, surrounding the centre of 
the storm.  
With continuous supply of moisture from the sea, the storm is further 
strengthened.  
On reaching the land the moisture supply is cut off and the storm 
dissipates.  
 
 
The place where a tropical cyclone crosses the coast is called the landfall 
of the cyclone.  
The cyclones, which cross 20o N latitude generally, recurve and they are 
more destructive.   
A mature tropical cyclone is characterised by the strong spirally 
circulating wind around the centre, called the eye.  
The diameter of the circulating system can vary between 150 and 250 km. 
The eye is a region of calm with subsiding air.  
Around the eye is the eye wall, where there is a strong spiralling ascent of 
air to greater height reaching the tropopause.  
The wind reaches maximum velocity in this region, reaching as high as 
250 km per hour.  
Torrential rain occurs here. 
 From the eye wall rain bands may radiate and trains of cumulus and 
cumulonimbus clouds may drift into the outer region.  
The diameter of the storm over the Bay of Bengal, Arabian sea and Indian 
ocean is between 600 - 1200 km.  
The system moves slowly about 300 - 500 km per day.  
The storm peters out on the land 
 
RECURVING CYCLONES  
         The cyclones, which cross 20o N latitude generally, recurve and they 
are more destructive.   
 
 
Tropical Cyclone (TC) Recurvature is the change in the cyclone's 
track from westward to eastward and poleward.  
 
 
Owing to the change in the influence of the wind systems from the 
deep easterlies of the tropics into the strong upper tropospheric 
westerlies of the mid-latitudes.  
Eg . Cylcone Okhi 
El-Nino Year – More favourable 
 
 
STAGES OF DEVELOPMENT OF A TROPICAL CYCLONE  
Tropical Depressions< Tropical Storms< Tropical Cyclones< Tornadoes  
THUNDERSTORMS AND TORNADOES 
Other severe local storms are thunderstorms and tornadoes. 
 They are of short duration, occurring over a small area but are violent. 
Thunderstorms are caused by intense convection on moist hot days.  
A thunderstorm is a well-grown cumulonimbus cloud producing thunder 
and lightening. 
 
 
 When the clouds extend to heights where sub-zero temperature prevails, 
hails are formed and they come down as hailstorm.  
If there is insufficient moisture, a thunderstorm can generate duststorms.  
A thunderstorm is characterised by intense updraft of rising warm air, 
which causes the clouds to grow bigger and rise to greater height. This 
causes precipitation.  
Later, downdraft brings down to earth the cool air and the rain.  
From severe thunderstorms sometimes spiralling wind descends like a 
trunk of an elephant with great force, with very low pressure at the 
centre, causing massive destruction on its way. Such a phenomenon is 
called a tornado.  
Tornadoes generally occur in middle latitudes.  
The tornado over the sea is called water sprouts.  
These violent storms are the manifestation of the atmosphere’s 
adjustments to varying energy distribution. 
 The potential and heat energies are converted into kinetic energy in these 
storms and the restless atmosphere again returns to its stable state.