Thermal

Thermal

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.

The warmer air expands, becoming less dense than the surrounding air mass. The mass of lighter air rises, and as it does, it cools due to its expansion at lower high-altitude pressures. 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 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 reach the level of free convection (LFC) and thus 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.

ee also

*Hot tower
*Vertical draft
*Atmospheric thermodynamics

External links

* [http://cires.colorado.edu/~angevine/thermals_2006.htm What do thermals look like?] - "Thermal Structure and Behavior" by Wayne M. Angevine
* [http://bookergc.blogspot.com/2008/04/thermal-formation-and-decay.html Time-lapse video of clouds caused by thermals forming and decaying]


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  • thermal — thermal, ale, aux [ tɛrmal, o ] adj. • 1625; de thermes 1 ♦ Qui a une température élevée à la source et des propriétés thérapeutiques (⇒ thermes). Eaux thermales chargées de principes minéralisateurs. ⇒ minéral. Émanations thermales : sources,… …   Encyclopédie Universelle

  • Thermal — Ther mal, a. [L. thermae hot springs, fr. Gr. ?, pl. of ? heat, fr. ? hot, warm, ? to warm, make hot; perhaps akin to L. formus warm, and E. forceps.] 1. Of or pertaining to heat; warm; hot; as, the thermal unit; thermal waters. [1913 Webster]… …   The Collaborative International Dictionary of English

  • Thermal — (Экс ле Бен,Франция) Категория отеля: 2 звездочный отель Адрес: 2 rue Davat BP 519, 73105 Эк …   Каталог отелей

  • thermal — (adj.) 1756, having to do with hot springs, from Fr. thermal (Buffon), from Gk. therme heat, from PIE *ghwerm /*ghworm warm (Cf. L. fornax an oven, kiln, formus warm, O.E. wearm; see WARM (Cf. warm)). Sense of having to do with hea …   Etymology dictionary

  • thermal — ► ADJECTIVE 1) relating to heat. 2) (of a garment) made of a fabric that provides good insulation to keep the body warm. ► NOUN 1) an upward current of warm air, used by birds, gliders, and balloonists to gain height. 2) (thermals) thermal… …   English terms dictionary

  • thermal — [thʉr′məl] adj. [Fr < Gr thermē, heat: see WARM] 1. having to do with heat, hot springs, etc. 2. warm or hot ☆ 3. designating or of a loosely knitted material honeycombed with air spaces for insulation to help retain body heat [thermal… …   English World dictionary

  • Thermal — Thermal, warme Quellen betreffend od. dazu gehörig. Daher Thermalbäder, so v.w. Thermae …   Pierer's Universal-Lexikon

  • thermal — thermal, ale (tèr mal, ma l ) adj. Se dit des eaux médicinales dont la température habituelle excède 25° centigrades. •   Les matières en effervescence et les substances combustibles anciennement enflammées continuent de brûler ; et c est ce qui… …   Dictionnaire de la Langue Française d'Émile Littré

  • thermal — [adj] warm heated, hot, lukewarm, melting, roasting, scorching, sizzling, snug, summery, sweltering, thermic, toasty; concept 605 …   New thesaurus

  • Thermal — Coat – тепло и гидроизоляционный материал, для теплоизоляции трубопроводов жилых и промышленных конструкций. Коэффициент теплопроводности 0,001 вт/м град. Совмещает в себе гидроизоляцию, теплоизоляцию и покровный слой. [Щукина Е. Г.… …   Энциклопедия терминов, определений и пояснений строительных материалов

  • thermal — thermally, adv. /therr meuhl/, adj. 1. Also, thermic. of, pertaining to, or caused by heat or temperature: thermal capacity. 2. of, pertaining to, or of the nature of thermae: thermal waters. 3. designed to aid in or promote the retention of body …   Universalium

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