SHARE

# Forces acting on the moving air near the Earth’s surface

There are three forces acting on moving air near the Earth’s Surface. They are

2. Coriolis Force.
3. Forces of Friction.

## (1) Pressure gradient force (pgf)

Pressure Gradient Force is the basic activating force for the wind. I.e. it initiates the movement of air.

They are two types

1. Gentle Pressure Gradient (slow movement of wind).
2. Steep Pressure Gradient (Faster movement of wind).

Pressure Gradient Force attempts to take the air from high pressure zone to low pressure across the isobar in a perpendicular direction.

## (2) Coriolis Force

Because of earth rotation, all moving bodies on the earth appear to get deflect.

To account for that apparent deflection the scientists has proposed a force calledCoriolis law (named after French Mathematician – Gespard coriolis).

Ferrels Law states “the effect of Coriolis force on a moving body – there is an apparent deflection of moving body to its right in the Northern Hemisphere and to its left in the Southern Hemisphere.”

This Coriolis Force is negligible near the equator and it increases towards the pole.

The reason for this lies in the effect that the earth’s speed decreases as we more from Equator to the poles and the rate of this is decreases is a function of Latitude (rate increases  towards the pole).

## (3) Forces of Friction:

Speed decreases, modifies the direction. The Frictional drag of this Earth’s surface acts both to slowdown wind movement and to modify its direction of Flow.

#### Zone of Convergence of Air

Zone of Convergence of Air is a Zone where there is net in flow of air. A low pressure zone is a zone of convergence of air.

#### Zone of Divergence of Air

Zone of Divergence of Air is a zone where there is net out flow of air. A high pressure zone is a zone of divergent of air.

#### Cyclone and Anticyclone

A Cyclone is a wind system with a Low pressure at the centre, An anticyclone is wind system with a high pressure at the centre.