# [Physics] Is wind caused by differences in the atmospheric pressure or by differences in the atmospheric temperature or both

atmospheric sciencefluid dynamicspressuretemperaturethermodynamics

I have heard that "Wind is caused by differences of atmospheric pressure" and "Wind is caused by differences of atmospheric temperature" both but I don't know for case that doesn't follow one of this. I will simulate that case.

Case 1 : same temperature but different pressure

Each room has air inside and has same volume.

Case 2 : same pressure but different temperature

Each room has air inside and has same volume.

If I removed thin adiabatic wall instantly, which case does wind occurr or both ?

Movement of air (the wind) is caused by difference of pressure. Air moves from the areas with high pressure to areas with low pressure.

Well, as a result the pressure decreases in the area the air moves from and increases in the area the air moves to.

As a result the pressure would become equal and the wind would stop. But how come Earth's atmosphere has not reached equilibrium during it's billion years history and from time to time the wind does blow?

Even if at some moment the atmosphere is in equilibrium, because the Sun heats the air not evenly, the temperature (and the pressure) of some volumes of air would change and air masses would start moving.

In the second example, nothing would happen at the moment you remove the wall. Left half of gas would gradually heat up, right side would cool down. By the time equilibrium is reached concentration of gas in both halves will become equal ($1.5 n_0$), so there would be some net movement of gas from left to right, but that's not a wind.