Basics of Aircraft Icing Detection and Ice Protection
Physics of Clouds and Icing
Condensation of pure water vapor requires super-saturation of several hundred percent.
Since condensation nuclei are common in the atmosphere, supersaturation of more than 1% is rare.
The number of cloud condensation nuclei usually determines the number of droplets in a cloud.
Fixing the liquid water content (LWT), clouds forming in clean air have larger droplets than clouds forming in polluted air.
Pure liquid water can be cooled to about -40 C without freezing.
Since ice nuclei are rare in the atmosphere, supercooled liquid water (SLW) is ubiquitous.
SLW droplets freeze when contacting a solid such as aircraft airframe (contact nucleation), causing icing.