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

Faint Kern arc, long Schulthess arcs and possible 46° contact arcs

On 12. November routine plate stuff prevailed over large areas around Rovaniemi. As I drove around, in one location my eye caught an uppervex Parry arc so I stopped to photograph. Visible was also circumzenith arc and even though it was far from dazzling, I aimed the lens at zenith with Kern in mind. After all, you have to account for the sun elevation upon judging how good the cza really is. Those bright at higher sun may lose much of their lustre at low sun. And the lower the sun, the better for Kern. In this case the sun was low: elevation at 1315 local time was 4.6 degrees.

As shown above, the attempt was not in vain: there really seems to be a full circle around zenith. True, the Kern is extremely faint and there are banded artefacts in the image, so one must be careful here. But the regular circle seems different from these artefacts.

The image above shows three versions of a stack of 21 photos taken during 1m 59s (sun has not been tracked in any part of the process). One is blue-minus-red image and two others are made with background removal technique with two different gaussian blur and median noise values. Nicolas Lefaudeux had instructed me on this method. It is also described on his site. The fourth image is a simulation made with HaloPoint.

Because of the Kern’s visibility display rather close to the noise threshold, it would probably be best to refrain from further analysis. But because I made the simulation anyway, let’s say that the Kern’s relatively uniform intensity seems to point at crystals towards triangular shape and I had to use quite extreme triangularity in simulation as depicted by the crystal figure below.



The display has also exceptionally long Schulthess arcs – they extend all the way to 46° halo. The Lowitz oriented population used to simulate them gives also 46° contact arcs. In the actual display 46° contact arcs may be visible too, but it is hard to say because the artefact bands are oriented in similar direction.

For reference, below is also a single image straight from camera. Enhancing it (not shown) seemed also give out Kern arc, but it was even closer to noise threshold than the stack. In any case, the diamond dust was so uniform stacking did not really bring that much benefit.

Simulation of reflected Lowitz arcs

Here is an attempt simulate the Jari Luomanen display of 22. January 2006. Reflected Lowitz arcs arise in the simulation from thin plate crystals tilting 10° about the Lowitz axis. Same crystal population also makes the crossing arcs below circumzenith arc - the 46° contact arcs. These are not seen in the photo, but it was not possible to make simulation without them appearing (46° contact arcs are still theoretical, no reliable observations are known). Some other, less serious problems are also evident in the simulation. Reflected Lowitz arcs, however, are well in accordance with the photograph.

Two more crystal populations were used. Oriented plates made parhelia and circumzenith arc and poorly oriented plates the 22° halo. Sun elevation was 7°. More details on the simulation are here. Simulation is made with HaloSim by Les Cowley and Michael Schroeder. Simulation files are here.