"The phenomenon of the superior image mirage can produce results similar to those noted by Rowbotham and Blount. This would have required, on each occasion, temperature inversions in the atmosphere with an increase of eleven degrees Celsius per hundred metres of altitude. If the temperature range were less than this, the light would have been scattered skywards; if greater, the horizon itself would have appeared curved. Repetition of the exact atmospheric condition required for each of the many observations is unlikely."
"A superior mirage occurs when the air below the line of sight is colder than that above. This is called a temperature inversion, since it does not represent the normal equilibrium temperature gradient of the atmosphere. Since in this case the light rays are bent down, the image appears above the true object, hence the name superior."
Got that off some reference website. Thought I'd throw it into the mix