Editing Cloud physics (section)

=== Bergeron process ===
{{main|Bergeron process}}
The primary mechanism for the formation of ice clouds was discovered by [[Tor Bergeron]].  The Bergeron process notes that the [[saturation vapor pressure]] of water, or how much water vapor a given volume can contain, depends on what the vapor is interacting with.  Specifically, the saturation vapor pressure with respect to ice is lower than the saturation vapor pressure with respect to water.  Water vapor interacting with a water droplet may be saturated, at 100% [[relative humidity]], when interacting with a water droplet, but the same amount of water vapor would be supersaturated when interacting with an ice particle.<ref>{{cite web |author=Sirvatka, P. |title=Cloud Physics: The Bergeron Process |website=[[College of DuPage]] Weather Lab |url=http://weather.cod.edu/sirvatka/bergeron.html}}</ref>  The water vapor will attempt to return to [[Vapor–liquid equilibrium|equilibrium]], so the extra water vapor will condense into ice on the surface of the particle.  These ice particles end up as the nuclei of larger ice crystals.  This process only happens at temperatures between {{convert|0|C|F}} and {{convert|-40|C|F}}. Below {{convert|-40|C|F}}, liquid water will spontaneously nucleate, and freeze. The surface tension of the water allows the droplet to stay liquid well below its normal freezing point. When this happens, it is now [[supercooled liquid]] water.  The Bergeron process relies on super cooled liquid water (SLW) interacting with [[ice nuclei]] to form larger particles. If there are few ice nuclei compared to the amount of SLW, droplets will be unable to form.  A process whereby scientists seed a cloud with artificial ice nuclei to encourage precipitation is known as cloud seeding.  This can help cause precipitation in clouds that otherwise may not rain.  [[Cloud seeding]] adds excess artificial ice nuclei which shifts the balance so that there are many nuclei compared to the amount of super cooled liquid water.  An over seeded cloud will form many particles, but each will be very small.  This can be done as a preventative measure for areas that are at risk for [[hail]] storms.{{fact|date=January 2018}}