eli5: cold air is denser thus sinks down. why chimney smoke goes down when its cold outside (and usually foggy)?
In: 3
As you mentioned, cold air is denser than hot air thus sinks. Hot smoke is less dense than cold smoke so it rises… but hot smoke is also denser than cold air, so it sinks.
What you might have witness or are seeing is a temperature inversion. This usually occurs at night or early morning with not much wind and no cloud cover. Coincidentally that’s when fog can occur as well. It seems to be more pronounced in winter for reasons unknown to me.
The way the atmosphere is heated is sun heats the crust, the crust heats the air that is touching it, and that hot air rises. The way the atmosphere is cooled is similar, the crust cools via radiation cooling (no clouds), and that cool crust cools the air that is touching it. However, cool air does not rise so you can end up with an inversion. Which is to say air is warmer above and the coldest air is found right at the surface.
Warm chimney smoke rises, it cools as it expands and comes in contact with the cold air around it. Eventually it cools enough that it is colder than the warmer inversion air above it. It no longer rises.
Here is a [beautiful picture](https://upload.wikimedia.org/wikipedia/commons/b/b9/SmokeCeilingInLochcarron.jpg) of it. [Another one.](https://nwdistrict.ifas.ufl.edu/phag/files/2018/04/temp-inversion-2.jpg) [Here](https://createarcticscience.files.wordpress.com/2013/03/eur_temp.jpg) is a temp chart for the arctic and it’s [associated picture.](https://createarcticscience.files.wordpress.com/2013/03/p1040360.jpg)
Latest Answers