Jack Frost is here, but what makes frost happen?
Ah Fall. The leaves, the change in the air, the frost. Frost is cool. Okay cold, but what I mean is that it looks cool. In fact the whole process of frost forming is really interesting.
So frost forms when the dew point (the temperature below which water comes out of the air) is below freezing. Now the interesting thing about frost is that it doesn’t form well (if at all) if it’s windy … even a light breeze can stifle frost from forming on surfaces. The next thing is that dew/frost settles down. For example, I park my car in the open in the driveway at the house. Lorraine parks hers under a tree. Past two mornings no frost on her car, lots on mine. The frost hits the branches first before it gets to her car!
The other interesting thing is when the dew point is above freezing but the temperature goes below freezing overnight. Then you get more of an ice than a frost on surfaces.
My favourite frost is hoar frost. That happens (if I understand it right) when there is a lot of water coming out of the air and the temperature doesn’t go far below freezing. Then you get that amazing snowy effect, almost fuzzy.
Those are the winter mornings that are awesome.
Tags: frost, frost formation, what is frost
4 Comments
The other thing about the dew point is that it is very tough for the temperature to go much below that point under normal circumstances. That is because the water has to give up energy to its surroundings when it precipitates out of the air.
Right! Duh, I should have remembered that. Yeah that phase change energy release was something that took me a while to get, but once we experience something like the an evening snow melt … well it’s pretty amazing.
Do dew and frost really settle down? Or do they form in place on a surface that has cooled through radiational cooling? That might explain why the car parked in the open has more frost — it’s loosing infrared radiation to the open sky, while the tree’s IR emission keeps the other car warmer.
Good question Andy … I’m pretty sure about it settling down, but great fodder for an experiment. Unfortunately we’re not going to have frost anytime soon round here. Any readers in colder climes wish to help?