10.13. Explanation of the superior mirage. (a) When warm, less dense air is above cool, dense air near the surface, light waves are bent so that objects appear to be higher than they actually are. (b) For a superior mirage, objects can be elevated and sometimes reversed.
10.14. Explanation of the inferior mirage. (a) When cool, dense air is above warm, less dense air, light waves are bent so that objects appear to be lower than they actually are. (b) Looking toward the ground one sees a patch of shiny water, while in reality one is viewing light from the blue sky that has been bent by the large change in density in the vertical.
(excerpts and images "Weather of the Pacific Northwest" courtesy UW Press)