Editing Lapse rate (section)

== Convection and adiabatic expansion ==
[[File:Emagram.GIF|thumb|350px|right|[[Emagram]] diagram showing variation of dry adiabats (bold lines) and moist adiabats (dash lines) according to pressure and temperature]]

As convection causes parcels of air to rise or fall, there is little heat transfer between those parcels and the surrounding air. Air has low [[thermal conductivity]], and the bodies of air involved are very large; so transfer of heat by [[heat conduction|conduction]] is negligibly small. Also, intra-atmospheric radiative heat transfer is relatively slow and so is negligible for moving air. Thus, when air ascends or descends, there is little exchange of heat with the surrounding air. A process in which no heat is exchanged with the environment is referred to as an [[adiabatic process]]. 

Air expands as it moves upward, and contracts as it moves downward. The expansion of rising air parcels, and the contraction of descending air parcels, are [[adiabatic process]]es, to a good approximation. When a parcel of air expands, it pushes on the air around it, doing [[Work (thermodynamics)|thermodynamic work]]. Since the upward-moving and expanding parcel does work but gains no heat, it loses [[internal energy]] so that its temperature decreases. Downward-moving and contracting air has work done on it, so it gains internal energy and its temperature increases.

Adiabatic processes for air have a characteristic temperature-pressure curve. As air circulates vertically, the air takes on that characteristic gradient, called the ''adiabatic lapse rate''. When the air contains little water, this lapse rate is known as the dry adiabatic lapse rate: the rate of temperature decrease is {{nowrap|9.8&nbsp;°C/km}} ({{nowrap|5.4&nbsp;°F}} per 1,000&nbsp;ft) (3.0&nbsp;°C/1,000&nbsp;ft). The reverse occurs for a sinking parcel of air.<ref name="DLA">{{cite book|last1=Danielson|first1=EW|last2=Levin|first2=J|last3=Abrams|first3=E|title=Meteorology|publisher=McGraw Hill Higher Education|year=2002|isbn=9780072420722}}</ref>

When the environmental lapse rate is less than the adiabatic lapse rate the atmosphere is stable and convection will not occur.<ref name=Goody/>{{rp|63}} The environmental lapse is forced towards the adiabatic lapse rate whenever air is convecting vertically.

Only the [[troposphere]] (up to approximately {{convert|12.|km|ft}} of altitude) in the Earth's atmosphere undergoes [[convection]]: the [[stratosphere]] does not generally convect.<ref>{{cite web|url=http://scied.ucar.edu/shortcontent/stratosphere-overview|title=The stratosphere: overview|publisher=UCAR|access-date=2016-05-02}}</ref> However, some exceptionally energetic convection processes, such as volcanic [[eruption column]]s and [[overshooting top]]s associated with severe [[supercell thunderstorms]], may locally and temporarily inject convection through the [[tropopause]] and into the stratosphere.

Energy transport in the atmosphere is more complex than the interaction between radiation and dry convection. The [[water cycle]] (including  [[evaporation]], [[condensation]], [[Deposition (aerosol physics)|precipitation]]) transports [[latent heat]] and affects atmospheric humidity levels, significantly influencing the temperature profile, as described below.