An inferior mirage is a mirage of an object visible below that object. Usually the mirage is mirrored upside-down as well. Apart from roads and land, inferior mirages can sometimes also be seen over lakes or oceans, since these surfaces are very extended and flat. Over Lake Markermeer and IJsselmeer in The Netherlands, for example, inferior mirages are quite common. The mirage makes the horizon look lifted up and inverted downwards; sometimes the mirage is compressed (stooping) or extended (looming), other times the mirage is a perfect mirror image. The mirage is formed due to the slight temperature gradient of the atmosphere: cold air over warm air causes refraction of light upwards - so you look down to see light coming from the horizon or sky. For lake mirages, the angle is very small (usually a few arc minutes). If the water of the lake is warm, like in autumn, mirages occur even more frequently.
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