“Randomized Moilanen half circle halo“ observed again in Ore Mountain Range diamond dust hotspot

On the evening of November 27th, 2015, a group of German halo observers including myself drove on top of Mt. Klínovec to witness a diamond dust halo display both created by the moon and artificial light sources. In a car headlight beam, I detected the upper half of what seemed to be a circular halo of radius 12°-13° by stacking video frames. Because we could simultaneously observe a (traditional) Moilanen arc at the moon, and experienced a considerable wind strength, I suspected that the orientations of the Moilanen crystals got randomized at eye level due to near-ground turbulences.

More than 3 years later, on December 15th, 2018, several halo enthusiasts were attracted independently by favorable conditions and met by chance on the summit of Mt. Fichtelberg, about 4 km north of Mt. Klínovec. After nightfall, multiple halo species created by car headlights became visible, such as the 22° circular halo, 22° parhelia, upper and lower 22° tangent arcs, 46° circular halo, parhelic circle and traces of the Moilanen arc. About 19:30 CET, Andreas Möller recorded a video of the glittering 22° ring and Moilanen spots. A maximum stack of the individual frames revealed that again not the familiar upward bent V-shape was present here, but a downward-curved segment of (likely) a circle:

photographed and processed by Andreas Möller

In effect, this confirms the earlier observation, though it still is a matter of definition if this phenomenon should be regarded as an individual halo species. So far, visual observations have only given the impression of independent glints, with the circular shape being only accessible through more or less elaborate post-processing of video footage.

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