Thermal

A thermal column (or thermal) is a column of rising air in the lower altitudes of Earth's atmosphere. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example of convection, specifically atmospheric convection. The Sun warms the ground, which in turn warms the air directly above it. Dark earth, urban areas, and roadways are good sources of thermals.

The warmer air near the surface expands, becoming less dense than the surrounding air. The lighter air rises and cools due to its expansion in the lower pressure at higher altitudes. It stops rising when it has cooled to the same temperature as the surrounding air. Associated with a thermal is a downward flow surrounding the thermal column. The downward-moving exterior is caused by colder air being displaced at the top of the thermal.

The size and strength of thermals are influenced by the properties of the lower atmosphere (the troposphere). Generally, when the air is cold, bubbles of warm air are formed by the ground heating the air above it and can rise like a hot air balloon. The air is then referred to as unstable. If there is a warm layer of air higher up, an inversion can prevent thermals from rising high and the air is said to be stable.

Thermal (disambiguation)

Thermal is an adjective related to heat. It may specifically refer to:

Places

See also