Moilanen arc observations from Davos

Moilanen arc in Davos. Photo: Bertram Radelow

This report describes halo displays including Moilanen arcs (MAs) which occurred in Davos from 2005 to 2017, caused by snow gun induced diamond dust. Four of them are discussed in more detail. The MAs are presented in relation to the degree of ripening of the diamond dust crystals, and with respect to the other halo types in the displays.

Davos is a world-renowned winter sport resort. Because of the decreasing amount of natural snow over the past decades, numerous snow guns have been installed. In the winter season 2017/18, more than 150 of them are running.

Snow guns produce artificial snow made from clumps of small ice spheres without any discernible hexagonal crystal structures. However, a part of the water spray is converted into microscopically small ice spheres which drift off. These will serve as condensation seeds for larger crystals, often in column shape, but also plates do occur.

Remarkably, MAs are preferably generated during the first stage of crystal growth. Full-ripe crystals produce only dull MAs or none at all.

Author: Bertram Radelow, Davos, Switzerland

Diamond dust halos on December 2nd, 2017 at the Fichtelgebirge

Concave and convexe Parry arc. Photos: Ruben Jakob

At the Fichtelgebirge, a low mountain range in northeastern Bavaria, there were similar halo phenomena as in the ore mountains circa 100km away (see article). In the morning, the high fog staunched and dissolved while passing the mountains. From afar, a very interesting cloud edge was seen at Mount Schneeberg (1051m above sea level). Shortly ahead Schneeberg, the temperature fell below -8 °C and rose to -5 °C in the fog. In the valley between the two mountains diamond dust was non-existent. I kept searching and trying to get out of the fog. Just in the village Grassemann (about 700m above sea level) there was a right parhelion and shortly afterwards a Supralateral arc visible above the fog. After 20 minutes, the fog suddenly came up to me and conjured a variety of halos in the sky. When I saw the concave and the convex Parry arc as well as the Moilanen arc distinctly, I was speechless. After that, the halo activity waned slowly. At 10 o’clock there were no more halos seen. The high fog broadened increasingly and the sun couldn’t shine through.

All in all, the following halo types were visible:
– 22°-halo
– Parhelia
– Upper tangent arc
– Upper and lower sun pillar
– Circumzenithal arc
– 46°-halo and Supralateral arc
– Fragment of parhelic circle
– Upper concave and convex Parry arcs
– Upper Tape arcs
– Heliac arc
– Subhelic arc
– Moilanen arc

Afterwards I drove to the top of Mount Ochsenkopf (1024m above sea level). There was a second halo show starting at 11.10 CET. However, expect of the right infralateral arc with the Tape arc, there were no further halo types.

Author: Ruben Jacob, Burgkunstadt, Germany

Diamond dust halos on December 2nd, 2017 at the rim of the Ore Mountains

Due to the inflow of polar air in the night of december 1st to 2nd there was fog formation in the valleys of the ore mountains. At the top of Fichtelberg (1214m above sea level) Claudia Hinz could observe the lower tangent arc and in parts also the submoon repeatedly in the lower sea of clouds. About 03.45 CET single shreds of clouds rose from the valley and forms an extensive halo phenomenon for 5 minutes as it is rare at the moon certainly. There was the 22°-halo, both parhelia, bright upper and lower tangent arcs, the complete light pillar, 46°-halo, supra- and infralateral arc, parhelic circle, submoon and both subparhelia. The evaluation of the photos revealed the Parry arc, the Lowitz arc on the left side and the upper and lower Tape arcs.

During the day Wolfgang Hinz took over the further observation at the rim of the ore mountains. At the sun the halo types changed quite fast, too. Several times the 16 visual observed halo types formed phenomena including 19 halos. Pictures showed two more halo types. Some halos lasted just for minutes, whereas the 22°-halo and the parhelia were there from 9.30 CET to 13.00 CET. But they appered earlier and continued towards the later afternoon. The Halos were observed on top of Fichtelberg and its surrounding area, at the border to Bohemia and at the Czech ski area Neklid, as well as on the way home in the mountain village Tellerhäuser.

All in all, the following halo types were observed:
– 22°-halo with both parhelia
– Upper and lower tangent arc
– Upper and lower sun pillar
– Circumzenital arc
– 46°-Halo
– Parhelic circle
– The left Lowitz arc shortly
– Left 120°-parhelia
– Supra- and infralateral arcs
– Parry arc
– Subsun
– Tape arc’s
– Trickers’s anthelic arc
– Heliac arc
– Moilanen arc (faint)
– Subhelic arc (Photo)
– Anthelion (Photo)

Author: Claudia and Wolfgang Hinz, Schwarzenberg, Germany

Diamond dust halos in Jena, Germany

On January 22nd 2017 I had the opportunity to witness a halo phenomenon in my home town for the first time.

The observation took place in Jena-Maua Germany (50°51’59.4″N 11°36’02.0″E) from 8:45-10:45 CET within about one kilometer. The maximum activity was observed between 10:15 and 10:45 CET.

We had a high-pressure weather situation with more and more lifting and dispelling fog (starting with 50m AGL) in the ‘Saale’-valley. Measured temperatures were about -10 to -6 degrees.

After recognizing the lower sun pillar besides the left Subparhelia in front of the fog boundary (seen from 300m height) I drove closer to the fog and found myself standing inside diamond dust (height 150m).

Between 9:45 and 10:45 the following types of halos have been witnessed: 22° halo, left and right parhelia, upper and lower tangent arcs, upper and lower sun pillar, Circumzenithal Arc, parhelic circle, Anthelion, left and right 120° parhelia, Supralateral arc, Parry arc, Subsun, left and right subparhelia, Tricker’s anthelic arc, Tapes arcs, Heliac arc and subhelic arc.

Uncertainties exist concerning the following observations: Lowitz arcs and Moilanen arc.

To sum up the best possibility of seeing this phenomenon was inside or near Jena-Maua – a small district of the city Jena which has some industry chimneys (compare the last photographs with the smoke trail). It seems legit to suppose that industrial fine particules conduced sublimation/condensation nucleus for the diamond dust development.

Author: Marco Rank, Jena, Thuringia, Germany

Thin plates in rotating Parry orientation as an explanation for the display on the night of 8/9 November, 2016, in Rovaniemi

8-9nov-taulukko-valmisIn an earlier post I told simulation attempts were not succesful for this display. Well, I really did not put that much effort into it. Now I have given it a fresh look and managed to get some succees.

The problem was the subhelic arc and anthelic arcs that could not be get rid of. In new simulations made with HaloPoint the subhelic arc issue is pretty much resolved and the anthelic arcs also play it low key.

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On some aspects of a display observed in Rovaniemi on the night of 9/10 November, 2016

This was a good no-hassle night of diamond dust hunt. The swarm was stationary and I didn’t have to pack up every 20 minutes to follow its whims. During the 6 hours of observing it was necessary to move only once. Also, both two locations were quite good concerning the light pollution. Especially the second place, where I wrapped it up in the morning ours, had a really dark segment which I used to light up the anthelic region.

As for the halos, the start of the night at around midnight was not so inspiring. As I arrived to the snow deposit area near the river, a sneak peek in beam revealed a run-of-the-mill plate display and I though it will just get worse because the temperatures were in the bad range, around -15 C. So I decided I might as well give some minutes for the half-moon display that had a smudge of Moilanen arc. In photographs it was transformed into a nice V-shape.

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A distinct Wegener but other reflection halos from column orientation lacking

58408_e6b1bf173a772112c7ee827c1b4a106fSpotlight displays are great in that almost every time you photograph them, you realize you understand halos less and less. This time the puzzle is: Why Wegener in the image above is so strong in comparison to other reflection halos? No subhelic arc is visible and neither there seems to be diffuse arc I think the spikes at the subanthelic point are lamp artefacts. Of course I can’t not say that for sure, but around the subanthelic point even weak stuff shows up easily to the eye, so had there been diffuse arcs, I should have noticed it. If we accept this, then, in addition to the Wegener, the only suggestion of column reflection halos is what looks like a short patch of Tricker arc cutting across the sub-Kern arc (see the simulation below for comparison).

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A possible new halo above Moilanen arc

average3A simple diamond dust display that I photographed on the 6th of this month in Rovaniemi, shows above the Moilanen arc another, weaker V-shape. As I uploaded the photo on Taivaanvahti, I was not conscious of the effect, it caught the sharp eye of Panu Lahtinen and Reima Eresmaa who commented on it. Then some photo processing made it stand out more clearly. The version above was worked by Nicolas Lefaudeux. It is a stack of 13 images taken during 125 seconds.

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A plate spotlight display on 5th November 2016

average-valmis6Showcasing the last winter’s spotlight displays is still under way, but fresh produce is already coming in. Here is the new crop that I harvested on the evening of 5th November in Rovaniemi. In the image above the lamp is around -6 degrees below the horizon and both parhelic and subparhelic circle are visible. Slight intensity enhancements in them on the side of the sky opposite to the lamp are suggestive of Liljequist parhelia. Included are also Sub-Kern and sub-120° parhelion. I did not spot sub-Kern this time, but the latter was quite discernible when running alongside the beam. As usual, it was a pale pillar of light in which no individual crystals were detectable – very different from the intense subparhelic circle patch towards the subanthelic point, which is always made of pure glitter.

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