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Convection

One way that heat is transferred through air is by convection. Convection of heat energy in the atmosphere involves the movement of air. Air is a poor conductor of energy, so convection is a major process of energy movement in the Earth’s atmosphere. In the atmosphere, convection occurs when a shallow layer of air in contact with a hot surface warms by conduction, acquires buoyancy (warmer air is less dense than colder air), and rises, taking with it the energy that it stores. As the Earth is heated by the Sun, bubbles of hot air called thermals rise upward from the warm surface.

In meteorology, convection refers primarily to atmospheric motions in the vertical direction. The term "advection" is sometimes used to refer to air motion in the horizontal direction. An air parcel will rise naturally if the air within the parcel is warmer than the surrounding air (like a hot air balloon). Therefore, if cool air is present aloft with warm air at lower levels, thermals can rise to great heights before losing their buoyancy.

Such convection processes in a large part dominate the world's weather, including the production of rain and snow, thunderstorms, hurricanes and frontal systems. When air convects it cools. If cooling is sufficient, the temperature of the rising air will fall below its dew point, releasing excess water vapour as clouds and ultimately precipitation.