We know that air is the mixture of oxygen, nitrogen, carbon dioxide, water vapour and dust particles. Air in motion is called the wind. Do you know how the wind blows?
When any place on the earth gets heated by the sun’s rays, the air of that place also gets heated. Due to this heating the air expands and hence its density decreases or it becomes lighter. The hot air, due to this lightness, goes up in the atmosphere. And this causes a decrease in atmospheric pressure in that area. Under such a condition air from high pressure cold regions rushes to that place to create an equilibrium. This movement of air is called the blowing of wind.
In the areas adjoining the sea, the earth becomes hot during the day. Due to this air becomes lighter and goes up in the atmosphere. To restore balance, cold air from the sea blows towards the land. During the night, a reverse movement takes place, that is, the earth becomes colder than the sea water and as such the air moves from the land towards the sea.
It is very hot in the regions surrounding the equator. It creates an equatorial belt of low pressure. So there is a constant upward movement of hot air from these regions. This hot air flows out to the north and south.
The rotation of the earth in its axis considerably affects the directions of the winds. The westerly winds are the direct result of the earth’s rotation from the west to the east. The spinning of the earth makes all in the northern hemisphere deflect towards the right and in the southern hemisphere, towards the left. Superimposed on the general wind systems are local winds. These are caused by temperature differentials associated with topographical features such as mountains and coastal belts. The presence of mountains also influences the wind direction. The mountains obstruct the winds and change their directions. The speed and direction of wind is measured by an instrument called an anemometer.