Atmospheric
Optics
Svalbard Mirage
~ 80°50'N 22°16'W. Franz Kerschbaum saw this mirage while circumnavigating Svalbard.
Near the sea the terrain curves in on itself and mirrors. The "horrizon" is actually the lower edge of the mirage as evidenced (left) by its ragged appearance.
Images ©Franz Kerschbaum, shown with permission
An "inferior mirage", inferior not for any want of quality but because the mirage image is below the original object and inverted.
Inferior mirages are produced by refraction between a lower warm air layer and cold air above. Near Svalbard the lower layer was warmed by the sea. The sea here is on a tip of the Atlantic Gulf Stream.
The coastline lower parts are invisible because of the 'vanishing line' effect.
At left, two rays from the coast (A) reach the eye. The upper one , passing mainly through the colder air, is only slightly curved downwards towards the warmer air. The lower ray from (A) is strongly curved and appears to the eye to come from a the coast reflected by a mirror. Rays from point (B), lower down, do the same. Position (C) is different. Only one ray reaches the eye. Rays from lower down the coast cannot reach the eye at all and so those parts are invisible.
The level (C) is the level of the mirage vanishing-line. The 'real' view and inverted mirage view join at the vanishing line and the eye can see no details of the scene that are below it.
These pictures were taken fairly high up on a small ship, ~16m above the sea. That accounts for the high vanishing line. Mirages can change dramatically with camera or eye height - try it.
