■ HEATING AND COOLING OF THE ATMOSPHERE □ Convection ◇ The | Upsc geography
■ HEATING AND COOLING OF THE ATMOSPHERE
□ Convection
◇ The transfer of heat energy through the movement of a mass of substance from one place to another place is called convection.
◇ The process of convection becomes effective only in fluids or gases because their internal mass motion activates convection of heat energy. The earth's surface gets heated after receiving heat energy (insolation) from the sun. Consequently, the air coming in contact with the warmer earth's surface also gets heated and expands in volume. Thus, warmer air becomes lighter and rises upward and a vertical circulation of air is set in. Conversely, the relatively colder air aloft becomes heavier because of contraction in volume and thus descends to reach the earth's surface. The descending air is warmed because of dry adiabatic rate and warm ground surface. This warm air again ascends because of increase in volume and decrease in density.
