What would the wind be at 2000ft above the airfield?
A 270/10
B 270/20
C 210/05
D 210/ 10
It's a lousy question. The precision of such rules of thumb are insufficient to differentiate between A and B.
Is any of this happening in reality? Surely the coriolis effect, which is responsible for the altitude wind turning right relative to the surface wind, is still there at night?
It's more that the drag of the surface is responsible for turning the surface wind left relative to the geostrophic wind. With that in mind, a geostrophic wind of 270/20 and a geostrophic wind of 270/10 are both likely to result in a surface wind of 240/not-much.
I don't fly much at night but have never noticed any big difference in the winds aloft v. surface. What does happen is that both of them tend to be much weaker.
Like you I have relatively little experience at night, but tend to notice the effect. What tends to happen on a clear night is that the boundary layer is also thinner. So by the time you get to even 1000 ft, you get the full force of the geostrophic wind.