Editing Water vapor (section)

=== Condensation ===
[[File:Above the Clouds.jpg|thumb|Clouds, formed by condensed water vapor]]

Water vapor will only condense onto another surface when that surface is cooler than the [[dew point]] temperature, or when the [[saturation vapor pressure|water vapor equilibrium]] in air has been exceeded. When water vapor condenses onto a surface, a net warming occurs on that surface.<ref>{{Cite journal |last1=Held |first1=Isaac M. |last2=Soden |first2=Brian J. |title=Water vapor feedback and global warming |date=November 2000 |journal=Annual Review of Energy and the Environment|volume=25|issue=1|pages=441–475 |doi=10.1146/annurev.energy.25.1.441|issn=1056-3466}}</ref> The water molecule brings heat energy with it. In turn, the temperature of the atmosphere drops slightly.<ref>{{harvp|Schroeder|2000|p=19}}</ref> In the atmosphere, condensation produces clouds, fog and precipitation (usually only when facilitated by [[cloud condensation nuclei]]). The [[dew point]] of an air parcel is the temperature to which it must cool before water vapor in the air begins to condense. Condensation in the atmosphere forms cloud droplets.

Also, a net condensation of water vapor occurs on surfaces when the temperature of the surface is at or below the dew point temperature of the atmosphere. [[Deposition (meteorology)|Deposition]] is a [[phase transition]] separate from condensation which leads to the direct formation of ice from water vapor. [[Frost]] and snow are examples of deposition.

There are several mechanisms of cooling by which condensation occurs:
1) Direct loss of heat by conduction or radiation.
2) Cooling from the drop in air pressure which occurs with uplift of air, also known as [[Adiabatic process|adiabatic cooling]].
Air can be lifted by mountains, which deflect the air upward, by convection, and by cold and warm fronts. 
3) Advective cooling - cooling due to horizontal movement of air.