Adiabatic cooling

Adiabatic cooling
Adiabatic cooling occurs when one or more of three possible lifting agents – convective, cyclonic/frontal, or orographic – cause a parcel of air containing invisible water vapor to rise and cool to its dew point, the temperature at which the air becomes saturated. The main mechanism behind this process is adiabatic cooling.[13] As the air is cooled to its dew point and becomes saturated, water vapor normally condenses to form cloud drops. This condensation normally occurs on cloud condensation nuclei such as salt or dust particles that are small enough to be held aloft by normal circulation of the air.[14][15]

File:Cloud evolution in under a minute.ogv
Animation of cloud evolution from cumulus humilis to cumulonimbus capillatus incus
One agent is the convective upward motion of air caused by daytime solar heating at surface level.[14] Airmass instability allows for the formation of cumuliform clouds that can produce showers if the air is sufficiently moist.[16] On moderately rare occasions, convective lift can be powerful enough to penetrate the tropopause and push the cloud top into the stratosphere.[17]

Frontal and cyclonic lift occur when stable air is forced aloft at weather fronts and around centers of low pressure by a process called convergence.[18] Warm fronts associated with extratropical cyclones tend to generate mostly cirriform and stratiform clouds over a wide area unless the approaching warm airmass is unstable, in which case cumulus congestus or cumulonimbus clouds are usually embedded in the main precipitating cloud layer.[19] Cold fronts are usually faster moving and generate a narrower line of clouds, which are mostly stratocumuliform, cumuliform, or cumulonimbiform depending on the stability of the warm airmass just ahead of the front.[20]