Ah got it. I'm currently training for PPL so have been studying this among other things.
Entropy causing gasses to mix evenly is true... on a large enough timescale.
In reality any gas or fluid will form boundary layers between masses of the substance having different temperatures, moving at different speeds, or having other properties (eg salinity for a liquid).
When flying you can end up passing through these discontinuities - regions where the air is very turbulent on both sides of the boundary. You can also develop different amounts of lift in one air mass vs another due to density. The entire air mass itself may be moving in a different direction and/or at a different velocity on one side of the boundary vs the other.
In a small airplane the effect is more pronounced. On a bright sunny day near the ground I get negative G when passing over a small bit of water followed by positive G when passing over a hot parking lot. It is very obvious where there is a region of hotter less dense air rising vs cooler more humid air.
SO yes, the final answer is probably just in the land of "air pushing wings down". I'm content with that, going into deep fluid dynamics analysis is probably too much for me at the moment :) Thanks!
Entropy causing gasses to mix evenly is true... on a large enough timescale.
In reality any gas or fluid will form boundary layers between masses of the substance having different temperatures, moving at different speeds, or having other properties (eg salinity for a liquid).
When flying you can end up passing through these discontinuities - regions where the air is very turbulent on both sides of the boundary. You can also develop different amounts of lift in one air mass vs another due to density. The entire air mass itself may be moving in a different direction and/or at a different velocity on one side of the boundary vs the other.
In a small airplane the effect is more pronounced. On a bright sunny day near the ground I get negative G when passing over a small bit of water followed by positive G when passing over a hot parking lot. It is very obvious where there is a region of hotter less dense air rising vs cooler more humid air.