Question

where does hot rising air get its heat from? Why does air get colder as it ascends, if it is getting closer to the sun? If this is because air is moving away from the earth (a possible source of heat) why is it that snow can be on the ground when ambient temperature is above freezing point? Water is a better conductor of heat than air is

Answer 1

a)The mechanism responsible for the rising of hot air is flotation: Hot air is less dense than cold air and hence air pressure will exert an upwards force, in the same way air rises in water. Now if cold air was magically unaffected by gravity, then it would not be able to exert pressure on the hot air and thus it would not rise.

The statement that "heat rises", by the way, is not universally true. Look at water. Here, it is the cold water that is less dense than warm water (at least in the temperature regime of importance to freezing). In winter, when water gets colder, the cold water raises to the top and eventually will freeze, while the water below remains liquid for the moment.

b) The reason it's actually colder is because, as you go up in the atmosphere, the Earth's atmosphere feels less pressure the higher up you go. So as the gas in the atmosphere rises it feels less pressure, which makes it expand. When the gas expands it does some work. And and if it's doing work, it must be losing some energy; and if it loses energy, its temperature must drop because we define temperature as the average energy of the particles. Therefore, if the energy of the particles is lower, the temperature must be lower.

C) Snow forms in the atmosphere, not at the surface. So snow can fall when surface temperatures are above freezing as long as atmospheric temperatures are below freezing and the air contains a minimum moisture level (the exact level varies according to temperature).