THE MOVEMENT OF AIR: WINDS
The movement of air is mainly caused by the differences in pressure and temperature. Warm air is lighter and it rises upwards, meanwhile, cold air is denser and hence it moves down to replace the warm air. This phenomenon is experienced as wind.
The movement of air across the earth determines the weather and climate of all regions. The sun’s radiation heats up the land, sea and the air. The land and water bodies also heat up the air, making it less dense. Here, hot air increases and creates a low pressure over that area and cold air sinks and creates a region of high pressure. Air, like all fluids, likes to maintain equal pressure. To do so, cold air from high-pressure areas flows into regions of lower pressure.
when air is heated by radiation from the heated land or water, it rises. But since land gets heated faster than water, the air over land would also be heated faster than the air over water bodies.
So, if we look at the situation in coastal regions during the day, the air above the land gets heated faster and starts rising. As this air rises, a region of low pressure is created and air over the sea moves into this area of low pressure. The movement of air from one region to the other creates winds. During the day, the direction of the wind would be from the sea to the land. At night, both land and sea start to cool. Since water cools down slower than the land, the air above water would be warmer than the air above land.
All these phenomena are the result of changes that take place in our atmosphere due to the heating of air and the formation of water vapour. Water vapour is formed due to the heating of water bodies and the activities of living organisms. The atmosphere can be heated from below by the radiation that is reflected back or re-radiated by the land or water bodies. On being heated, convection currents are set up in the air. In order to gain some understanding of the nature of convection currents.
When water bodies are heated during the day, a large amount of water evaporates and goes into the air. Some amount of water vapour also get into the atmosphere because of various biological activities. This air also gets heated. The hot air rises up carrying the water vapour with it. As the air rises, it expands and cools. This cooling causes the water vapour in the air to condense in the form of tiny droplets. This condensation of water is facilitated if some particles could act as the ‘nucleus’ for these drops to form around. Normally dust and other suspended particles in the air perform this function. Once the water droplets are formed, they grow bigger by the ‘condensation’ of these water droplets. When the drops have grown big and heavy, they fall down in the form of rain.