Originally Posted by
eckhard
Of course, the real atmosphere is untidy and non-uniform, especially close to the ground. Accelerations and turbulence take place, but we must try to keep a clear mind.
This is true in the real world, but the downwind turn myth holds that even in a non-turbulent uniform air mass, you will lose more airspeed in a turn to downwind than you will performing the same rate turn in calm air. So, the abstraction of a uniform airmass moving relative to the ground with no relative movement or air within the parcel is correct to address the fallacy. wind gradients, shear and vertical movement only serve to muddy the waters.