ATMOSPHERIC PRESSURE AS AN ELEMENT OF WEATHER

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.