Shimmer
(Section 3.2.3.8)Definition: Shimmer: The apparent fluttering of objects at the Earth’s surface, when viewed in the horizontal direction.
Shimmer occurs chiefly over land when the surface is hot, usually when the Sun is shining brightly. It is caused by short-period fluctuations of the refractive index in the surface layers of the atmosphere as a result of the motion of small parcels of air. Shimmer may significantly reduce the visibility.