Thermal 354370 222023163 2008-06-27T05:17:29Z Closedmouth 372693 Reverted edits by [[Special:Contributions/68.185.92.221|68.185.92.221]] (using [[WP:HG|Huggle]]) [[Image:Thermal column.svg|thumb|Example of a thermal column between the ground and a cumulus]] :''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 [[density|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 [[power (physics)|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 [[temperature inversion|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 cloud|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 (soaring)|lift]] used by [[soaring birds]] and [[gliders]] to [[gliding|soar]]. A similar phenomenon can be seen in a [[lava lamp]]. ==See 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] [[Category:Aviation terminology]] [[Category:Severe weather and convection]] [[da:Termik]] [[de:Thermik]] [[es:Termal]] [[eo:Termiko]] [[it:Corrente ascensionale]] [[he:זרם אוויר חם]] [[hu:Termik]] [[nl:Thermiek]] [[no:Termikk]] [[nn:Termikk]] [[sl:Termika]] [[fi:Termiikki]] [[sv:Termik]] [[ru:Термик]]