PPT: Pressure Belts Notes | EduRev

UPSC: PPT: Pressure Belts Notes | EduRev

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 Page 1


• There are distinctly identifiable zones of 
homogeneous horizontal pressure regimes 
or ‘pressure belts’. On the earth’s surface, there 
are in all seven pressure belts.
• The seven pressure belts are :
• equatorial low,
• the sub-tropical highs,
• the sub-polar lows, and
• the polar highs.
Page 2


• There are distinctly identifiable zones of 
homogeneous horizontal pressure regimes 
or ‘pressure belts’. On the earth’s surface, there 
are in all seven pressure belts.
• The seven pressure belts are :
• equatorial low,
• the sub-tropical highs,
• the sub-polar lows, and
• the polar highs.
Equatorial Low Pressure Belt or ‘Doldrums’
• Lies between 10°N and 10°S 
latitudes.
• Width may vary between 5°N and 5°S 
and 20°N and 20°S.
• This belt happens to be the zone of 
convergence of trade winds from 
two hemispheres from sub-tropical high 
pressure belts.
• This belt is also called the Doldrums, 
because of the extremely calm air 
movements.
• The position of the belt varies with the 
apparent movement of the Sun.
Page 3


• There are distinctly identifiable zones of 
homogeneous horizontal pressure regimes 
or ‘pressure belts’. On the earth’s surface, there 
are in all seven pressure belts.
• The seven pressure belts are :
• equatorial low,
• the sub-tropical highs,
• the sub-polar lows, and
• the polar highs.
Equatorial Low Pressure Belt or ‘Doldrums’
• Lies between 10°N and 10°S 
latitudes.
• Width may vary between 5°N and 5°S 
and 20°N and 20°S.
• This belt happens to be the zone of 
convergence of trade winds from 
two hemispheres from sub-tropical high 
pressure belts.
• This belt is also called the Doldrums, 
because of the extremely calm air 
movements.
• The position of the belt varies with the 
apparent movement of the Sun.
Page 4


• There are distinctly identifiable zones of 
homogeneous horizontal pressure regimes 
or ‘pressure belts’. On the earth’s surface, there 
are in all seven pressure belts.
• The seven pressure belts are :
• equatorial low,
• the sub-tropical highs,
• the sub-polar lows, and
• the polar highs.
Equatorial Low Pressure Belt or ‘Doldrums’
• Lies between 10°N and 10°S 
latitudes.
• Width may vary between 5°N and 5°S 
and 20°N and 20°S.
• This belt happens to be the zone of 
convergence of trade winds from 
two hemispheres from sub-tropical high 
pressure belts.
• This belt is also called the Doldrums, 
because of the extremely calm air 
movements.
• The position of the belt varies with the 
apparent movement of the Sun.
Climate
• This belt is characterized by extremely low pressure with calm 
conditions.
• This is because of the absence of Surface winds since winds 
approaching this belt begin to rise near its margin. Thus, only 
vertical currents are found.
• As the larger part of the low pressure belt passes along the 
oceans, the winds obtain huge amount of moisture.
• Vertical winds (convection) carrying moisture 
form cumulonimbus clouds and lead to thunderstorms 
(convectional rainfall).
• Inspite of high temperatures, cyclones are not formed at 
the equator because of ‘zero’ coriolis force. (we will see more 
later)
Page 5


• There are distinctly identifiable zones of 
homogeneous horizontal pressure regimes 
or ‘pressure belts’. On the earth’s surface, there 
are in all seven pressure belts.
• The seven pressure belts are :
• equatorial low,
• the sub-tropical highs,
• the sub-polar lows, and
• the polar highs.
Equatorial Low Pressure Belt or ‘Doldrums’
• Lies between 10°N and 10°S 
latitudes.
• Width may vary between 5°N and 5°S 
and 20°N and 20°S.
• This belt happens to be the zone of 
convergence of trade winds from 
two hemispheres from sub-tropical high 
pressure belts.
• This belt is also called the Doldrums, 
because of the extremely calm air 
movements.
• The position of the belt varies with the 
apparent movement of the Sun.
Climate
• This belt is characterized by extremely low pressure with calm 
conditions.
• This is because of the absence of Surface winds since winds 
approaching this belt begin to rise near its margin. Thus, only 
vertical currents are found.
• As the larger part of the low pressure belt passes along the 
oceans, the winds obtain huge amount of moisture.
• Vertical winds (convection) carrying moisture 
form cumulonimbus clouds and lead to thunderstorms 
(convectional rainfall).
• Inspite of high temperatures, cyclones are not formed at 
the equator because of ‘zero’ coriolis force. (we will see more 
later)
Sub-Tropical High Pressure Belt or Horse Latitudes
• Formation
• After saturation (complete loss of moisture) at the ITCZ, the air moving 
away from equatorial low pressure belt in the upper troposphere 
becomes dry and cold.
• This dry and cold wind subsides at 30°N and S.
• So the high pressure along this belt is due to subsidence of air 
coming from the equatorial region which descends after becoming 
heavy.
• The high pressure is also due to the blocking effect of air at upper 
levels because of the Coriolis force.
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