Fata morgana
"Tout est prisme dans une atmosphère de particules glacées où l’air n’est que miroirs et petits cristaux. De là de surprenants mirages. Nombre d’objets vus à l’envers, pour un moment apparaissent la tête en bas. Les couches d’air qui produisent ces effets sont en révolution constante ; ce qui y devient plus léger monte à son tour et change tout ; la moindre variation de température abaisse, élève ; incline le miroir ; l’image se confond avec l’objet, puis s’en sépare, se disperse, une autre image redressée monte au-dessus, une troisième apparaît pâle, affaiblie, de nouveau renversée."
"Everything is prism in an atmosphere of icy particles where the air is only mirrors and small crystals. Hence surprising mirages. Many objects seen upside down, for a moment appear head down. The layers of air that produce these effects are in constant revolution; what becomes lighter then rises in its turn and changes everything; the slightest variation of temperature lowers, raises; tilts the mirror; the image merges with the object, then separates from it, disperses itself, another upright image rises above it, a third appears pale, weakened, reversed again."
Translated from Jules Michelet
Below is a fata morgana observed around Huvudskär in the Stockholm archipelago on 18 May 2018. Passing along the tip of the island, it becomes obvious that the band on the horizon extends very broadly. This is in fact a fata morgana, a mirage created when there is an inversion, a layer of cold air stuck at the surface of the sea, above which there is a duct of warmer air, which gets colder again at a higher altitude. These are the conditions for this phenomenon to appear, resulting in a stack one to several layers of inverted images, reflected at the interface of the air layers of different temperatures.
Below is an example of a double layer fata morgana observed on the same day.
Below is a series of fata morgana observed on 1st of July in lake Vänern, close to the island of Djurö.
The typical aspect of a fata morgana in our cold countries, is a reflection of the horizon on a cold layer of air which superimpose to the horizon line its inverted picture. On the picture above, you can see a line between the sea and the horizon, and the islands and vegetation on the horizon being replicated in an inverted way above the sea.
The two islands closer to us on the horizon (picture on right below) are not affected by the phenomenon.
As for the tip of the island below (picture on right), it is clear that it is not pointing above the sea level as it looks like. In fact, the inverted replication of the horizon line appears clearly when looking at the symmetrical pattern below the lighthouse or on the pole at the right of the lighthouse.
