Formation of Ice Crystals
The most common way to form an ice crystal, starts with an ice nucleus in the cloud. Ice crystals can form from heterogeneous deposition, contact, immersion, or freezing after condensation. In heterogeneous deposition, an ice nucleus is simply coated with water. For contact, ice nuclei will collide with water droplets that freeze upon impact. During immersion, an ice nucleus will hit a water droplet and instantly freeze it. Water can also condense onto ice nuclei and then freeze.
Water will freeze at different temperatures depending upon the type of ice nuclei present. Ice nuclei cause water to freeze at higher temperatures than it would spontaneously. For pure water to freeze spontaneously, called homogenous nucleation, cloud temperatures would have to be -42 degrees Celsius. Here are some examples of ice nuclei:
| Ice Nuclei | Temperature to Freeze (degrees C) |
|---|---|
| Bacteria | -2.6 |
| Kaolinite | -4 |
| Silver Iodide | -7 |
| Vaterite | -9 |
Read more about this topic: Bergeron Process
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