AskDefine | Define thermal

Dictionary Definition

thermal adj
1 relating to or associated with heat; "thermal movements of molecules"; "thermal capacity"; "thermic energy"; "the caloric effect of sunlight" [syn: thermic, caloric] [ant: nonthermal]
2 of or relating to hot a hot spring; "thermal water"
3 caused by or designed to retain heat; "a thermal burn"; "thermal underwear" n : rising current of warm air

User Contributed Dictionary




thermal (plural: thermals)



  1. pertaining to heat or temperature.
  2. (of fabric) providing efficient insulation so as to keep the body warm.

Derived terms


pertaining to heat or temperature
providing efficient insulation so as to keep the body warm

Extensive Definition

This article is about the atmospheric phenomenon. For other uses of the term thermal, see thermal (disambiguation).
A thermal column (or thermal) is a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and an example of convection. The Sun warms the ground, which in turn warms the air directly above it.
When a pool of warmer air accumulates, it expands and becomes lighter (less dense) than the surrounding air mass. The mass of lighter air will then rise, but as it does so it will cool due to expansion. This process will continue until at some height the pool of air will have cooled to the same temperature as the surrounding air, at this stage the air will stop rising. Also 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 thermal top.
The size and strength of thermals are influenced greatly by the properties of the lower atmosphere (the troposphere). Generally, when the air is cold, bubbles of warm air formed by the ground heating the air above it, can rise like a hot air balloon. The air is then said to be 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.
Thermals on the Sun typically form hexagonal prisms (Bénard cells).
Thermals are often indicated by the presence of visible cumulus clouds. When a steady wind is present thermals and their respective cumulus clouds can align in rows oriented with wind direction. Cumulus clouds formed by the rising air in a thermal as it cools and ascends, until the water vapor in the air begins to condense into visible droplets. The condensing water releases latent heat energy allowing the air to rise higher. Very unstable air can rise to great heights condensing large quantities of water and so forming showers or even thunderstorms.
Thermals are one of the many sources of lift used by soaring birds and gliders to soar.
A similar phenomenon can be seen in a lava lamp.

External links

thermal in Danish: Termik
thermal in German: Thermik
thermal in Spanish: Termal
thermal in Esperanto: Termiko
thermal in Italian: Corrente ascensionale
thermal in Hebrew: זרם אוויר חם
thermal in Hungarian: Termik
thermal in Dutch: Thermiek
thermal in Norwegian: Termikk
thermal in Norwegian Nynorsk: Termikk
thermal in Slovenian: Termika
thermal in Finnish: Termiikki
thermal in Swedish: Termik
thermal in Russian: Термик

Synonyms, Antonyms and Related Words

aestival, blood-hot, blood-warm, calid, equatorial, fire storm, genial, hot air, luke, lukewarm, mild, room-temperature, subtropical, summery, sunny, sunshiny, superheated air, temperate, tepid, thermic, toasty, tropical, unfrozen, warm, warm as toast, warmish
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