Causes of Wind

Winds can be broadly classified as planetary and local winds.

Planetary winds are caused due to greater solar heating of the earth’s surface near the equator as compared to solar heating near the northern or southern poles. It causes the hot air to rise from equator to poles in easterly direction and the cold air from poles flows back westerly to the equator near the earth’s surface. The direction of motion of these winds with respect to earth is affected by the rotation of the earth. In actuality, the phenomenon of wind direction and its magnitude is quite complex since it is affected by uneven layer of heating of air, frictional resistance, obstructions caused by mountains, buildings, trees etc.

Local winds  are caused due to differential heating of land and water in coastal areas. Due to solar radiations, the land mass surface becomes hotter than the water. It causes the air above the land to heat up and becomes hotter than the air above water since it is not heated fast, because part of heat is absorbed by water and partly to evaporate water.

Lighter hot air above the land rises up and the cooler air of higher density above sea water moves towards the land to replace the hot air. It causes shore breezes. At night the direction of breeze is reversed since the land mass cools to sky more rapidly than the mass of sea water.

Another mechanism of local winds is caused by the hills and mountain sides. The air during the day at higher slopes above the land heat ups more rapidly compared to the lower land surfaces. It causes the cooled air from land to move up along the slopes causing wind. The process is reversed at night where the cool heavy air from slopes flows downwards.