thermal

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thermal Used as a noun, the term refers to air that rises in a column over some localized heat source; it rises through the atmospheric environment as a result of its reduced density. Intense heating over land (and particularly over some types of surface) results in adiabatic expansion and uplift. When thermals rise to condensation level, short-lived clouds (e.g. fair-weather cumulus) may form. Continued strong thermals can result in the growth of the cloud into large cumulus or cumulonimbus. When the upward growth reaches a stable layer, the cloud top may spread laterally.

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