It is colder in the hollows in winter than on the slopes of the mountains. Why?

The reason for the lower temperatures in the basins during the winter months than on the higher slopes is the physical property of the warm gas to rise higher. And the atmosphere, as you know, consists of several gaseous substances. As they heat up, they become lighter than the air on the slopes, and rise higher. Instead, cold and heavy air descends to the bottom of the basin from the surrounding slopes. Liquids have the same property, and therefore the water on the surface of the seas is always warmer than at depth.