Lateral mirages, as these are called, are similar to the mirages made by hot roads that resemble reflections in water. In lateral mirages the air layers of different temperatures are stacked vertically rather than horizontally and the mirror image is close to (and overlapping) the hot wall.



It is not easy to picture mirage rays because they are almost straight and a scale diagram would be impossibly long and narrow. At lower left is an attempt. Distances from the wall are highly exaggerated to show the ray curvatures.

A ray from "a" that can reach the eye penetrates deeply into the warm/cold air boundary. The ray is refracted across the temperature gradients to curve back outwards from the wall so that it appears to come from "a' ". Rays from "b" reaching the eye do not approach the wall so closely and they are more gently refracted. The refracted rays appear to come from a second mirrored figure close to the wall.



The 'real' figure remains visible via almost undeviated rays from "a" and "b" that do not penetrate into the hot air layers. These are drawn very lightly