Warm air

typically speaking, air is less dense because it is "warmer" than other air. The reason is that as heat is added to air, the molecules become excited in a higher energy state. As the energy level rises, the molecules space themselves farther apart. Density is the measure of matter per unit volume. A less dense matter will rise (since we are talking about fluids here). So if you have a gas that is cold, but of a lower density, you will see it rise above a higher density gas. If you study the temperature and density profile of the earth's atmosphere, you will see that the temp does not uniformly get cooler or warmer. This is mostly due to the chemical composition of the air at different altitudes and how they react to the energy from the sun.

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I'm qite baffled with your answer, I thought thermo dymanics described updrafts and down drafts due to the heat equilibrilium? ..or maybe I'm just wrong about these teaching that contradicts everything you are saying.

The chemical composition of air changes a function of altitude as well. Air is more than just oxygen. Different gasses expand at different rates when heat is applied.

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Yes, pressuer is the key, what I said holds true for the Troposphere though.

In answering the OP's original question about cool air that is less dense, the full answer requires more nuance. That is all I am saying. Given a smaller view of a mostly homogeneous fluid like the troposphere, you are correct about equilibrium, but pressure equilibrium thermal equilibrium between two fluids.

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Uh uh! Didn't say pressure equilibrilium has anything to do with thermal equilibrilium, just that that factor also exist.

I think you're just having sport with me, but okay.

Two fluids can be in pressure equilibrium without being in thermal equilibrium.

You did not mention pressure equilibrium explicitly, but in speaking about pressure and temperature, it is directly implied by the relationships between the two.

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Okf for the sake of respect and peace, I'll just say your right.

Sorry, I'm not trying to be a pest. I'm an engineer and I struggle sometimes to leave things in the simplest of terms. The funny thing is that I'm frustrated because I'm actually leaving a whole lot out!

meh

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I understand your fustration, I'v played lots of RTS games and bashed n00bs, usually 1v3, they would then claim I was an expert, but the truth is they sucked which they would not accept and get offended. Having superior insight in a given subject often causes fustration when disussing with less educated people.