ATMOSPHERIC PRESSURE
What is Air Pressure?
It is the force exerted on a
point on the Earth surface by the weight of air column above that point.
In
figure1 above, there is high
atmospheric pressure at point because, the air column above the point A (low
altitude area) is longer/larger and therefore, it exerts more force.
At
point B (high altitude area), there is a shorter/smaller air column above the
point, therefore there is lower atmospheric pressure.
Factors Influencing
Atmospheric Pressure
1.
Altitude
2.
Temperature
Variation
3.
Earth’s
Rotation
Altitude
Pressure
decreases with increase in altitude
High
altitude areas have a thin/shorter air column, which causes less force to the
area. This leads to a lower atmospheric pressure
Low
altitude areas have a thick/long air column, which causes more force to the
area. This leads to a higher pressure in the area.
Temperature Variation
Atmospheric
pressure reduces with increase in temperature.
When
temperature increases, air is heated, expands, becomes light and rises creating
a low pressure.
When
temperature decreases, air is cooled, contracts, becomes dense and descends
creating a high pressure.
Earth’s Rotation
Equatorial
areas rotate faster than polar areas which pushes air masses towards the
equator. The air is expands due to increased space at the equator and rises
creating a low pressure.
Air
from the polar areas towards the equator crosses longer latitudes and therefore
spreads out and rises up reducing pressure at 60◦N and 60◦S of the equator.
As
the air moves away from the poles, more air descends from the atmosphere. The
air is forced into a small area, leading to a higher pressure at poles.
Air
rising at the equator descends at latitude 30ᵒN and 30ᵒS. The air is thus
forced into areas of reducing/shorter latitudes, causing a higher pressure at
latitude 30ᵒN and 30ᵒS.
