The image above shows an arc that points towards the bulge in sub-Kern. Its formation is unknown. We captured the arc first time on two occasions on the night of 6/7 January 2016 in Rovaniemi. The current case was photographed in Rovaniemi too, on the night of 28/29 November 2016.
Judging from the crossing of helic arc and (what appears to be) Hastings over the 46° halo, the lamp must be around 3.5 degrees below horizon. I made some quick simulations. The upper one has plates, randoms, and Parry. Plate shaped Parry crystals were used to get the relative intensity of the helic arc and Hastings somewhat comparable to the actual arcs. Simulation has also subanthelic arc, and it seems to be present in the photo, although it is quite broad and diffuse. The lack of Parry arc in the actual display is rather curious.
To make sure that the mystery arc is not some kind of anomalous singularly occurring Tricker, the lower simulation was made with added column oriented crystals. Sure enough, location of the Tricker does not match.
The bulge in sub-Kern seems itself also anomalous and appears to be associated with the mystery arc. The bulge has not been photographed in the numerous displays without this arc.
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