Ice nucleus

An ice nucleus is a particle which acts as the nucleus for the formation of an ice crystal in the atmosphere.

The presence of ice nuclei increase the temperature that ice will form in the atmosphere from around −42°C to about −10°C. There are many processes that can take place in the atmosphere to form ice particles, the simplest is by water vapor depositing directly onto the solid particle. The presence of an ice nucleus can also cause a previously supercooled water droplet to freeze through contact, immersion or dissolution within the water that would otherwise have stayed in the liquid phase at a given temperaturecite journal
author = Koop, T.
year = 2004
title = Homogeneous ice nucleation in water and aqueous solutions
volume = 218
issue = 11
pages = 1231–1258
url = http://cat.inist.fr/?aModele=afficheN&cpsidt=16233451
accessdate = 2008-04-07] .

Ice particles can have a significant effect on cloud dynamics. They are known to be important in the processes by which clouds can become electrified, which causes lightning. They are also known to be able to form the seeds for rain droplets.

Many different types of particulates in the atmosphere can act as ice nuclei, both natural and anthropogenic, including those composed of minerals, soot, organic matter and sulfate. However, the exact nucleation potential of each type varies greatly, depending on the exact atmospheric conditions. Very little is known about the spatial distribution of these particles, their overall importance on global climate through ice cloud formation and whether human activity has played a major role in changing these effects. However, snowflakes appear to be often formed around biological ice nucleators cite journal
author = Christner, Brent C.
coauthors = Morris, Cindy E.; Foreman, Christine M.; Cai, Rongman; Sands, David C.
year = 2008
title = Ubiquity of Biological Ice Nucleators in Snowfall
journal = Science
volume = 319
issue = 5867
pages = 1214

doi = 10.1126/science.1149757
pmid = 18309078] , typically bacterial cells cite journal
author = Sattler, B.
coauthors = Puxbaum, H.; Psenner, R.
year = 2001
title = Bacterial growth in supercooled cloud droplets
journal = Geophysical Research Letters
volume = 28
issue = 2
pages = 239–242
url = http://www.agu.org/pubs/crossref/2001.../2000GL011684.shtml
accessdate = 2008-04-07

doi = 10.1029/2000GL011684] .

Attempts to measure ice nucleation in the lab as recently as June 2007 show that biomass burning-dominated aerosols do not act as ice nuclei Fact|date=April 2008.

References

ee also

*Bergeron process
*Cloud condensation nuclei
*Nucleation
*Snow
*Supercooling