Formation of a classical superior mirage.

A ray ‘A’ from low down on the distant hillside can be strongly refracted across temperature (air density) gradients between the cold and warmer air.  It appears to the eye to come from above the real object.   Rays leaving farther up the hillside can reach the eye directly ‘B’ or by refraction at the cold-warm air boundary ‘C’.   the result is an inverted image of the hillside.   Extra refraction ‘D’ gives an erect image above the inverted one.

The Scottish hillside mirage is hard to disentangle.  Parts are inverted and others erect.   Mirages like this approach the appearance of a Fata Morgana.