Complex Halo Display, Borlänge, Sweden

On the 14th December 2018 at 12.30 UTC, Magnus Edbäck photographed an amazingly complex display in his home village of Utendal near Borlänge, Sweden comprising many extremely rare halos with at least one completely new halo form, a multiple scattering halo. Highlights include 46° contact arc, Hastings arc, extremely long Schulthess arcs and the rarely seen in daylight Ounasvaara arc. Like Marko Riikonen's 6th March 2017 Rovaniemi display, this one will go down in the annals of halo history and no doubt will be discussed and analysed for a long time to come. The two faint patches of light on either side of the 22° tangent arc are the new multiple scattering halo which at the time of writing has not been given a name. It is quite possible that the display was caused by snow guns in operation at the Romme Alpin ski centre situated about 12km away from Utendal.

Magnus has very kindly agreed to give an account of how he photographed the display.

"This is the story about my halo picture.

I was having lunch at my parents home when my mother asked me to look out to see how nice the sun was shining. At once I saw that this was not like any halo I had ever seen before. The sight of the sky was amazing. I then went to my home and grabbed the camera. My parents and I live next door to one another in Utendal, a small village outside Borlänge. I quickly checked that I had the appropriate lens, it was Samyang 14mm F2.8 that was on. The camera I used is a Canon 6D which I have modified with a Baader filter, mainly for use when I shoot the starry sky. From what I understand, the filter has no significance when shooting halo.

I went to a place on my parents courtyard where I could see as much of the display as possible. I quickly checked the settings on the camera, adjusted it to ISO200 and set the aperture to F8 to get a good depth of field. The day was quite cold (about 7 degrees below zero) and I was not wearing a jacket so I only took a few quick pictures (4pcs).

I then went back home to look at the pictures. On my way home, I also saw arcs to the north and I'm very sad that I did not take any photos of them. I quickly examined the images in Adobe Lightroom and picked an image that I uploaded to the Swedish astroforum www.astronet.se. I then went back to my parents to finish lunch.

Quite soon afterwards, I received comments on www.astronet.se by both Hans Bengtsson and Timo Karhula, who thought the display appeared to be something out of the ordinary. Hans thought I should send the image to Les Cowley and Timo thought I should publish it on www.taivaanvahti.fi. I received answers fairly quickly from both Les and www.taivaanvahti.fi. At 15:35 UTC 2018-12-14 I received mail from Marko Pekkola where he wrote:
"Congratulations Magnus of finding a new halo form in the sky in solar display! Several experts analysed this photo and Marko Riikonen identified one of the forms as the first multiple scattering halo of its kind.”  - Magnus Edbäck

Image processed by Nicolas Lefaudeux.

Image processed by Nicolas Lefaudeux.

Nicolas Lefaudeux has analysed and stacked the four raw files with background subtraction and produced these breathtakingly complex and beautiful processed images. The new halo is a multiple scattering [MS] halo, ie a "halo of a halo". These are extremely rare and can only appear in the brightest displays with very bright halos to forms.

This new halo is the uta of parhelion / parhelion of uta and it is the 5th MS halo form (after par of par, uta of uta, uta of pc/pc of uta, and cza of pillar). It requires both a very bright parhelion and a very bright uta to form. 

This uta of par/par of uta was the most likely MS halo form expected to be caught, because of its relative ease to appear in simulation and because it is not overlapped with other bright regular halos.

All images copyright Magnus Edbäck

Halos on 6th March 2017 in Rovaniemi

This display came into existence suddenly, when in the morning sun came out from behind a clear cut edge of a receding cloud area. Some points:

- Ounasvaara arc in a solar display
- There is a kind of extension to the Ounasvaara arc which makes it drop shaped. The extension is responsible for the narrow end of the drop near the helic arc. It seems to be present also in the first Ounasvaara arc display. It's caused by the same raypaths as Ounasvaara arc, but with an added basal face reflection.
- 120° arcs. Simulations say they are formed in Lowitz oriented crystals. The halo is not centered on 120° parhelia: it lies along a circle of 60 degree radius centered on the subanthelic point. It is made by raypaths that in plate oriented crystals give 120° parhelia and sub-120° parhelia.
- An uppervex Hastings in solar display. All the others – the spotlight ones – are indirect detections, because the lamp has always been at an elevation where Wegener and Hastings overlap.
- Helic arc is brighter than subanthelic arc. I could simulate this by lengthening the Parry crystals, but then the simulation went wrong in other ways too much. If we can't get this right, it kinda tells me we don't understand this display. I was told that I probably regret of not taking a crystal sample. It had not occurred to me, but once I was reminded, it was obvious that I should. In the simulation no column shaped crystals were used. It would have been of interest to see whether the crystal sample concurred.

This version was worked by Nicolas Lefaudeux

I also regret of photographing this with Nikon D3200 which is why we have to suffer all the artefacts. Not that there would have been any choice at the time, but about a month earlier I was offered a chance to borrow D800 for my halo hunts. I declined in fear of breaking it. A third regret, that was more personal and could have been easily avoided, was that I didn't have mirror with me and thus did not see many things. Didn't see, for example, the 120° arcs, Hastings / Wegener separation, both of which would have been visible easily with mirror. Spotting the 120° arcs in situ – that would have been something. 

The display occurred at around -17° C. You don't expect a major display at such temps in Finland. But sometimes they do occur, like was the case with Mikkilä's Kern display in 2007. Low supersaturations were in my mind the key here. They were low because the night was cloudy and thus the diamond dust could not have spawned before the morning when it started clearing up. And at that point, with the sun above horizon at such late time in the season, the air was not getting so much colder as for supersaturations to increase to the point of crapping the display (which is the usual scenario).

This post was modified on 15 Oct 2017 to replace the simulation with a new one. It has labels added to mark some of the features that seem to appear in the photos (sorry for the degree numbers having placed at the end of halo names, there is some glitch in Photoshop which forces this). Also, the parameter file was replaced becase I adjusted the parameters of the column oriented population a bit, increasing crystal h/d from 0.5 to 0.8 and making it a little more triangular. This more burned more fine grained simulation has gained features that are not seen in the images. Possibly with a better camera some of these could have been dug out from the display. 

The post was further modified on 21. Oct by adding "originals" of the stacks.

 

A singe frame from the very beginning of the series (added 11 Oct. 2017)

"Originals" of the stacks.

A major spotlight display with possible 4th Tape arc component

By Jarmo Moilanen, Marko Mikkilä and Marko Riikonen

On 23 November 2015, we were watching diamond dust halos develop under overcast skies in Rovaniemi. As we stood on a rectangular field a couple of hundred meters across, we followed halos slowly gather momentum in the spotlight beam, reaching climax when clouds were cleared away for a short while – and revealing at the same time also a lunar display. Here is an excerpt from Marko’s observation log written the next day:

“The display just adds gear. We are looking at beautiful subanthelic stuff, subanthelic arc, diffuse arc… It becomes monstrous when the cloud almost disappears. That is when we get also a moon display with full parhelic circle. No one seems to be in a rush to photograph the moon display. The beam display is sheer grotesquery. The laser scapel sharp, 100% pure glitter of the tangent arc and uppervex Parry.”

In the photos the lamp is 5-6 degrees below the horizon. In the image above, the most noteworthy feature perhaps is the slight intensity enhancement in the 46° infralateral arc, marked with arrows in the simulation below. These could be sings of the fourth, as of yet unobserved Tape arc component (raypath 14), which is highly unlikely to be ever seen in solar displays as it appears in simulations only when light is several degrees below the horizon. Although it is probably here, we would still hope for a better example from lower light elevations that would make it easier to identify.

Another feature of interest is the “Ounasvaara arc”, which in the photos looks like an odd continuation of circumnadir arc. This Parry orientation halo is visible particularly well in the two photos below, that, unlike the photo above, were taken off-beam, from underneath. Although off-beam images are not visually as appealing for their non-uniform lighting, the halos in the brightest part of the beam are enhanced in them.

We regret of not getting a visual of the Ounasvaara arc – judging from its intensity, it should have been easily visible to the eye. Well, something for the next time.

As usual, we also had a gasoline filled petri dish out to collect the crystals. No serious end cavities this time, which is in accordance with the observation log’s note of “100% pure glitter”.

At last we switched off the lamp to give the moon display the stage. However, by the time we got to it, the lunar halos were already starting to decline. In our next post we will show nevertheless the few photos that were taken.