What does “supersaturation with respect to ice” mean?
This is one of the very interesting fact about water: In order to change from gas to liquid, or liquid to solid, it needs to dissipate energy in form of heat. Reversly, when it goes from solid to liquid, or liquid to gas, it has to absorb energy in form of heat. The latter is the reason we perspire in order to cool down our skin. When water vapour rises in the atmosphere and cools down, it has to give away heat to condense. The problem is: those molecules are so small that they have virtually no mass. Therefore they can’t transfer that heat. If it then meets anything like a dust corn, it will become a water droplet. The same happens for water droplets becoming ice. In fact, it is said that water can be undercooled to minus 40 degrees Celsius before it freezes! This answers an interesting question: When the temperature is below freezing point, what are clouds made of: ice or water? The answer is: Both. Some molecules had a chance to freeze and some didn’t. It is when a water droplet mee
