Introduction

• Two types of movement of air in the atmosphere
• Horizontal movement due to difference in pressure is called wind
• Balance out the uneven distribution of pressure over the globe
• Serves as means of transporting heat, moisture, and other properties from one part of the earth to other
• Vertical movement of air column is called current
• Significant for the formation of clouds, precipitations and various types of storms

Factor Affecting Wind Motion

a) Horizontal pressure gradient

• The direction of wind and its magnitude or velocity is greatly affected by the horizontal pressure difference (pressure gradient). The greater this difference, the greater the wind velocity; and direction is always from higher pressure towards lower pressure

b) Rotation of the earth / Coriolis force

• Coriolis force is an apparent and additional force caused by the earth’s rotation about its axis on a parcel of moving air.
• The Coriolis force is responsible for deflection of winds towards the right in the northern hemisphere and left in the southern hemisphere.

c) Frictional force

• frictional force tries to slow the air and also change its direction. Therefore, there seems the deflection in direction of wind and change in speed due to the frictional force offered by the materials on its direction

d) Centrifugal action of wind

• centrifugal force tends to pull the air outwards from the centre of curvature. But the curved path is maintained by inward acting force i.e. centripetal force.

Gradient wind:

• A wind moving along the isobars at such a velocity that the force due to pressure gradient is balanced by the deflective and centrifugal effect is called the gradient wind.
• In other words, it refers to the horizontal wind velocity in which balance is achieved between Coriolis force, pressure force and centrifugal force.

Geostrophic wind

• It is the theoretical (horizontal) wind that would result from an exact balance between the Coriolis effect and the pressure gradient force.
• The geostrophic wind is directed parallel to isobars.