Moilanenbogen (EE77)

The Moilanen arc is a white V-shaped arc 9° above the sun. As early as 1975, Horst Gäbler (1921-2014) sketched an arc on the Fichtelberg in the Ore Mountains as part of an ice fog halo that was V-shaped approximately 10° above the sun. In November 1995, the Finn Jarmo Moilanen was finally able to photograph and measure this arc, which was later named after him. Karl Kaiser observed a similar arc in diamond dust in Schlägl, Upper Austria, on January 30, 1997. To this day, this phenomenon remains a mystery, mainly because it must be a crystal form that occurs only in ice fog and not in cirrus clouds, as this arc has never been observed there. Moreover, this crystal does not seem to produce any other "exotic" halos, as is the case with pyramidal ice crystals, for example. For a long time, it was assumed that it occurs exclusively on ice crystals that have grown from the condensation nuclei of snow cannons. These use enzymes for faster crystal growth, and it is assumed that under optimal conditions, crystals can form that do not occur in the wild or only rarely. Meanwhile, there are few observations from areas without snow cannons, such as on January 25, 2012 in Achsheim or on January 21, 2016 in Bremerhaven on the North Sea coast.

During the occurrence of the Moilanen arc, multiple searches for possible causative ice crystals were conducted, but without conclusive success so far. In the meantime, the arc can be simulated with a wedge-shaped crystal form with an inclination angle of 34°. However, whether this crystal form actually occurs in nature and whether it can especially float in the air in the necessary exact vertical alignment is questionable. Thus, the cause of the Moilanen arc is still not determined.