Eli5: If heat is energy, how does cold wind exist? How can air move (have cold gusts of wind) if it’s not hot? Where does the energy for movement of cold air come from?

Question

I asked this in school and the teacher thought I was trolling and didn’t answer me. It’s been like 20 years and I still think about it, it drives me crazy lol.

In: Planetary Science

Answer 1

Wind is caused by a difference in heat in a body of air. The easiest example is a flame because it’s a strong heat difference– the fire is very hot and the surrounding air is much cooler.

Heat is added to the air around the fire, which causes it to expand. The less dense air is squeezed upward by the cooler air– this is why fire and hot smoke tend to rise. That creates a momentary low-pressure area though, so cooler air moves in to replace it, and itself gets heated by the fire. This phenomenon is called convection.

That happens on a global scale because the sun doesn’t heat the earth evenly. Some places are hotter than others, which creates all sorts of high and low pressure zones in the atmosphere, so air is always blowing every which way as it moves to equalize the pressure. But of course it won’t achieve that because there will always be some sort of heat difference until maximum entropy, aka heat death.

There’s also the Coriolis force, which is the earth rotating and not completely taking the atmosphere with it. IIRC this is what causes the jet stream.