Thursday, 3 December 2020

A big display from Sotkamo, Finland – with a possible new halo

 4x3, 2590-2592, 2608-2610, 2614-2616, 2623-2625

Two years ago the halo community got its latest novel multiple scattering halo in the supermassive Borlänge display: a halo that is both parhelion of the tangent arc and tangent arc of the parhelion.

It seems now we have a second case. On 25 November Sami Härmä photographed an impressive display in the Naapurivaara village of Sotkamo, Finland, and in the photos he published in Taivaanvahti people thought of seeing fuzzy spots reminiscent of the Borlänge parhelion-tangent arcs.

Single photos didn't respond well to enhancing, so it was good there were some with similar enough composition and taken with sufficient time between them to do stacks. These stacks seem indeed to confirm the presence of the parhelion-tangent arcs.

And there may be more. In the stacks both Wegener arc and uppervex Hastings arc materialized, and in addition to having the parhelion-tangent arc enhancements in the expected location on Wegener arc, it looks like the Hastings might have its own enhancements, too: a parhelion-Parry arc. This would be a novel halo, though in the light of this new wisdom, one might see it now also in the Borlänge display on the right side. 

If we consider the prospects of parhelion-Parry arc purely from the perspective of sun elevation, then the Sotkamo display comes out more favourably. That's because the lower sun elevation of 4.5 degrees in Sotkamo gives, all else being equal, a brighter Parry than the 6.0 degrees for those Magnus Edbäck photos of the Borlänge display in the link above.

At the end of this post are three photos that allow to compare the intensity of the Parry and tangent arcs in the Sotkamo display. While the tangent arc looks a bit brighter of the two, the difference may not be as big as in the Borlänge display, at least judging by the video by MrWhikked. The Edbäck photos might also be re-visited in this respect, the Parry and tangent arcs are washed white by processing in currently published versions of his photos.

A HaloPoint simulation of the display, arrows marking the parhelion-tangent arc and parhelion-Parry arc. I was not able to simulate the display's Ounasvaara arc and uppercave Parry arc with one Parry crystal population. Triangles were needed to get the former, tabulars the latter. The V-shape inside 22 halo is two multiple scattering halos superposed: tangent arc and Parry arc from subsun. Neither has been observed yet, the V in the Sotkamo display inside 22 halo is Moilanen arc. Fixed multiple scattering probability 0.7 was used.


A baffling detail is the weakling circumzenith arc. The apparent multiple scattering halos in this display need not only very bright tangent and Parry arcs, but also very bright parhelia. And very bright parhelia should translate to strong circumzenith arc. Actually, it is not just weak. The cza simply looks strange, as if made of two parts: a brighter stub embedded in the 46 supralateral arc, continued by a much fainter extension. And is there even a gap separating the two parts? Compare this to the normal looking Borlänge display cza.

Let's move on. Notable mentions in the Sotkamo display are of course the uppervex Hastings that is a great catch in a solar display, the third one on record, and the outstanding Ounasvaara arc (see the photos in Taivaanvahti), which is likewise the third known solar case. It was easily bright enough for visual, and Härmä indeed wrote me of having seen it with his eyes.

There have been other displays with monstrous Parry contribution, but this is the first time we get a wide photographic coverage of the sky of such a display. In the Borlänge display the video by MrWhikked gave us glimpses of what's going on elsewhere in the sky, providing valuable extra info, but it is nice to have photos now.

Härmä took many of his photos by bracketing three shots in quick succession. The stacks shown here are made of such separate sets. In the info under the photos for example 4x3 means four three image sets. For the record, the photo id numbers are also given. The two four set stacks (normal and flip stacked) were a bit of a stretch, there was quite a lot of distortion between the better matching two 2x3 sets from which I made them. That's why you see the helic arc duplicating towards edges. But in the center where it mattered for the multiple scattering halos the distortion is less. Folks with more technical prowess surely could do better work of Härmä's photos than I managed. Although the original raws are not publicly up for download, Härmä is happy to send the batch should anyone like to take a look. The photos were taken at 12:40-12:57 local time, exif gives an hour later time as the camera was in summer time.

The display occurred 6 km from the slopes. Härmä tells the temperature was around -7 C, right in the -5 to -10 C range where the most massive snow gun displays are forged. The fact that it was cloudy before the display appeared and that it was soon finished by clouds taking over again, tells this was a punch hole cloud display – particles from snow gunning turning a small area of low hanging stratus into ice crystals.           

                                         4x3 + flip stack, 2590-2592, 2608-2610, 2614-2616, 2623-2625


 2x3, 2590-2592, 2608-2610


2x3, 2614-2616, 2623-2625


 Brightness comparison of the tangent and Parry arc. The photos are picked from three of the four sets used in stacks.
Post corrected 6.12.2020. Replaced "infralateral" with "supralateral".


  1. This makes the south pole displays look weak. I think I see upper 46 Galle arc on the 46d halo

  2. Right, Michael, the brightening on the top of 46 halo must be Galle. Should have tried to include it in the simulation.

  3. I am so jealous Marko! I wished I lived near a ski resort and nearest one I know of is a couple hours away in Indiana and its called perfect north. I tell you if I was with you watching one of these displays I think would be in heaven. However I will make a small crystal swarm in my barn and let the xtals fall on a large plexiglas sheet and do some windshield type displays

    Also I had to get a new email since my other one the bowlturner one got hacked here is the new one:

  4. In 2018 I think I may have gotten a sub-CHA on the windshield of my dad's car. If you want to see pics send me email

  5. Wow that's out of this world! The Ounasvaara arc in the last set of stacks almost outshines the weak CZA! Congrats to all the lucky ones who witnessed this phenomenal display.

  6. Well just book a flight to Rovaniemi, Michael. I am happy to accommodate any serious chasers. Two persons makes the operation so much easier, especially when crystal sampling is involved. In one beam the max persons is two, but there can be two teams in their own cars to chase after the diamond dust, looking for the best locations. We have once tried this and it worked good. And we could even think about doing videos of those chases.

    1. I would Marko but because of the virus I don't think it would be a good idea. Also I am afraid of flying in a jet. I have the money and a passport but no vacation days and also the language would be a problem in some ways and plus having rent a car and all that its just too much money.

    2. True, this winter is not the time. There are probably restrictions for foreign arrivals. Maybe then the next winter. The car I have, that's not a problem, unless for some reason I don't have it next winter anymore. The lights I have too. Acebeam W30 and K75 plus the good old 75W hid.

    3. Did you copy my email? If so send me an email

  7. Interesting display. Riikonen could you call? It seems that i have lost your phone number.
    Best regards
    Marko Mikkilä

  8. I have lost your number too, Mikkilä. And apparently we don't have each others emails either. I'll ask from other core people who are better at preserving information, let's see if we can talk tomorrow.

  9. Excuse me for including myself into this discussion but I am extreamly interested in these phenomenons after witnessing what seem to be some of the more common halos and I have so many questions. Am I understanding this correctly that you can produce these events some how with your cars windshield and depending on your position or location while one is visible it is possible to see an even more complex set of arcs compared to witnessing it at another place?