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   Mock mirage, M-Mir, sunsets

Sunset at Pointe de la Torche , France imaged by Laurent Laveder (PhotoAstronomique.net) in August '04. The faint lines have been added to indicate layers of different temperature in the atmosphere. As the sun's image sinks through them it is miraged into fantastical ever changing shapes. The slices show descending erect images of the solar disk and ascending inverted images. Images ©Laurent Laveder, shown with permission.
 
A setting sun distorted and seemingly cut into horizontal slices is a sign that one or more temperature inversion layers are at work. The layers are sometimes made visible (1,2) by the dust and aerosol they trap and greater refraction.

Sunlight is refracted by the different density layers sometimes sufficiently strongly to produce mock-mirages (ray paths). The mirages are most apparent when the progress of the sinking sun is closely watched (eye care!). A single mock-mirage has two erect images and an inverted image. Sections of the sun will often be seen sinking and rising in the layers. Where an image is rising, we are seeing a section of an inverted solar disk.

Sometimes the temperature, and thus density, differences are so great that rays are trapped within layers. Ducting is said to occur and the trapped rays might travel large distances before escaping. Here are two ducted M-Mir sunsets 1,2.

Mock-mirage sunsets are very sensitive in their appearance to your height. You must be above the inversion layer but not necessarily physically very high because inversions can be very close the the land or sea surface. Two views of the same sunset are here 1,2.

The top of a mock-mirage sunset sometimes produces a single or even multiple green and blue flashes. These are less pronounced than the classical I-Mir flash and are more often photographed than observed by eye.