Tuesday, 18 February 2020

Intense Kern arc from China


After years of waiting, we finally have the very first Chinese Kern display, and it's a big one.

On the morning of Feb 14 2020, a blanket of natural, high quality diamond dust lingered above Siziwang Qi (Dorbod Banner), Inner Mongolia for about two hours (later reports suggest the display lasted the whole day), treating the locals with a jaw-dropping plate display.

© TIAN Xiangyang, shown with permission

Crystal density and quality were so high that parhelia, circumzenithal arc, parhelic circle, 120° parhelia and even Liljequist parhelia all look insanely bright in photos and videos. Such intensity undoubtedly made multi-scattering possible. 44° parhelia showed up very well in most locations despite the relatively high sun elevation. In the following photo, the sun had risen to 20° and the 44° parhelia were still there.

© YANG Yongqiang, shown with permission

The true highlight of the display, however, lurked near the zenith. The circumzenithtal arc appeared not only bright, but also as a full circle, even to unaided eyes. The Kern arc, finally!

While most observers’ attention were drawn to the low hanging gems near the horizon, some did bother to look up and documented Kern arc’s grand debut in China. These two untouched handphone photos below speak volumes about the arc’s top rate quality.

© ZHENG Dan, shown with permission

© TIAN Xiangyang, shown with permission

The following videos will give you an idea of how crazy the scene was:




Once the initial excitements died down, we began to wonder about the Kern arc’s true origin in this display. The arc appeared rather smooth and uniform all around and somewhat broader than the circumzenithal arc. Could this broad, diffuse appearance be attributed to multi-scattering?

With the help of Zhang Jiajie’s simulation program (https://github.com/LoveDaisy/ice_halo_sim/tree/master/cpp), we found out that multi-scattering is capable of noticeably enhancing the Kern arc for both regular and triangular plate crystals. Also note how the gaps in the regular plate Kern arc get filled and smoothened out by multi-scattering.

Simulation by ZHANG Jiajie, sun elevation at 13°

Simulation by ZHANG Jiajie, sun elevation at 13°

The multi-scattering enhancements above have at least two components:
  • A secondary circumzenithal arc created by parhelia, parhelic circle and 120° parhelia
  • A secondary parhelic circle created by the original, single-scattered circumzenithal arc
Below is a comparison between the Kern arc and the above two secondary rings. They do appear broad and diffuse as expected.

Simulation by ZHANG Jiajie, sun elevation at 13°, semi-triangular plate crystals with c/a = 0.3 are used

These rings, when integrated, can get brighter than the Kern arc in simulations, especially when crystals are thin. So theoretically it’s possible for them to overwhelm the Kern and become the main player. In reality though, co-existence might be the more reasonable answer.

Back to the display itself, Marko Riikonen commented in our email exchange that this display is almost a clone of the legendary 1970 Saskatoon display (http://www.thehalovault.org/2011/01/the-saskatoon-halo-display.html), in which the 44° parhelia were first photographed. According to Marko, visual sightings of the Kern arc were reported by the photographers but veracity of these reports has been much debated until recent years. Now that we have a repeat event with undeniable Kern arc presence, the Saskatoon chapter could probably be closed.

Best regards,
Jia Hao

18 comments:

  1. I noticed the sky inside the Kern is darker

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    1. Thanks for the input Michael. My bet is on the darker inside being normal sky gradient which reaches minimum at zenith. I could be wrong. Maybe the experts will have something to say about this.

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  2. Congratulations on a most marvellous observation; I'm so pleased that China has secured its first Kern sighting. You are very quickly becoming world leaders in serious halo research and your documentation is absolutely first rate. The fact that this display was captured on a phone camera emphasises just how good this display must have been.

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    1. Thanks Alec! We're really excited about this one. For years we've been assuming top tier diamond dust doesn't exist in China. Really glad to be proven wrong. Hope to see the next one soon : )

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  3. Yeah, the Saskatoon can finally rest in peace. First there was the 2007 stacked image by Marko Mikkil√§ that proved Kern arc is indeed real. Then arrived the 14 May and 24 June 2014 displays in Finland with their multiple scattering 22° parhelic circles, making it clear multiple scattering Kern must be possible as well. In December 2018 it was turn for the video by "MrWhikked" of the Borl√§nge display, where a brief glimpse of Kern arc is seen, removing any doubts there might have been as to the naked eye visibility of the halo. And now we have the Siziwang Qi with a Kern arc that was actually seen by ordinary folks. It also looks pretty much colorless, which is in line with the white Kern reported by Ripley and Saugier in Saskatoon.

    By now it is clear China gets some of the greatest displays. Every summer Lascar type stuff and over the top odd radius column arc displays appear in Chinese skies, with some insane traditional displays to boot. And all that is matched by their talented and enthusiastic people. The simulation software by Zhang Jiajie, once released, will expand what has been possible up until now. The dissection of the Kern arc at end of Jia Hao's post is a case in point. Seeing that simulation possibly hit me even harder than the Siziwang Qi display. We have been dreaming about such capability, and suddenly it is here.

    The high sun photo by Yang Yongqian invites comparison to the similar looking 18 October 2013 display in Levi, Finland by Antti Henriksson. I have thought 17 degrees moon altitude in the Levi display was already pretty high for 44 parhelia, but Siziwang Qi raised the bar three degrees more. I made simulations with HaloRay and expectedly significantly higher multiple scattering probability is needed to have 44 parhelia at these high elevations than, say, at 5 degree light source elevation. The Levi display has that funny feature under the CZA, I wonder if Yang Yongqian photo or some other photos would allow to check whether it was in Siziwang Qi as well.

    Levi display:
    https://www.taivaanvahti.fi/observations/show/19422

    regards,
    Marko Riikonen

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    1. Hey Marko I noticed the sky inside the Kern is darker and BTW: I got some of those halo arcs on ice surface on moms bird bath. I did not get any stills but I did get video and its on my youtube channel

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    2. Thanks for elaborating on the Saskatoon story and Kern arc's modern history!

      The Finnish moonlight display in that link is insane. I'd bet multi-scattered Kern arc was there too. And that feature below the CZA is really puzzling, looks weirdly sharp. The moon pillar seems to fade off on each end linearly so if it has anything to do with creating a ms CZA, the ms CZA probably shouldn’t look too sharp at its lower end? Too bad Yang Yongqiang's photos are taken with a phone camera too, just like all other photos we've received so far. None of these submissions survive serious post processing to compare with the Finnish case… Let’s hope some DSLR shots emerge someday.

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    3. Agh never mind I got the display replicated in Zhang's program. Letting pillar raypaths 1 and 2 go through multi-scattering picks that one up.

      https://drive.google.com/file/d/13HGmj3xm_KOGTe1BU3q6_yANfsqhIXs3/view?usp=sharing

      The arc's appearance and color in the simulation match the display quite well. The pillar in the Siziwang Qi display was also quite strong. Such a pity that no DSLR images are available. I suspect this arc is partially responsible for the CZA glow Nicolas mentioned in our email exchange.

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  4. Wow, what a simulation! And it is really eye candy to see again the MS contribution picked apart. You came up independently with the same explanation as Nicolas did at the time of this display. I was thinking it was some lens artefact, but Nicolas of course saw it for what it was and told it must be the cza of pillar.

    Michael, I think we might have in the past wondered on some photos about a possibly darker sky inside circumnadir arc. I just can't recall right at hand what photos those might have been. Maybe there is some unexpected darkness inside the Kern arc in the other photo here.

    Good to hear you got some surface arcs, too, Michael. I just bumped on to yet another observation of this stuff:

    http://home.eduhi.at/member/nature/met/atmoest/bilder2020/20200216.htm

    Now there will be some cold days in Finland so we will freeze water in our backyards. Petri Martikainen has already succeeded and gotten some nice photos of the regimented crystals. See this post of his:

    https://www.taivaanvahti.fi/observations/show/88544

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    1. I just played around with Zhang's program and created the following GIF showing pillar CZA's change with solar altitude.

      https://drive.google.com/open?id=1d9DtnhmPhdYLHlTH5dm2r7LOgx-1e4GA

      The lower limit of the arc stays at around 57° from horizon at all tested solar altitudes. You guys probably have already figured this out, that limit turns out to be the lower altitude limit of the original CZA. The lower pillar in the Finnish display probably stretched all the way to the horizon, feeding rays to ms crystals with incident angle down to 0°.

      I also tried applying USM to one of Yang Yongqiang's iPhone photos. The pillar CZA seems to be showing up a little below the original CZA, but I don't think it can be taken too seriously given the image's poor bit depth.

      https://drive.google.com/open?id=1xfcDdLDs8akaLm_ec359s8hue3Qd7ykV

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    2. Thanks again for this simulation, Jia. Yes, that's what Nicolas told, that it is CZA caused by the part of pillar at the horizon. Well, let's hope to have input from the man himself.

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  5. Congratulations to this outstanding display and the wonderful analysis!

    Alexander Haussmann

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  6. If I am not mistaken the Saskatoon display had 66d parhelia too?

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    1. Yes, Ripley and Saugier had drawn spots at around that location. They write: "These parhelia were visible only at the peak of the display and even then were quite faint. They presumably were parhelia of the other parhelia." I wonder what's the psychology behind those spots. Certainly they were not parhelia of the 44 parhelia. To me they were a factor that cast a shadow on their Kern arc report.

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  7. Parhelia of 120 parhelia come much easier in simulations than parhelia of 44 parhelia. So maybe they were looking at these. Or Liljequist parhelia, which are really prominent in some Siziwang Qi material.

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    1. Yeah the 120d parhelia were dazzling and the liljequist parhelia are probably the best to date. I just wonder what a spot light display would of looked like from these crystals

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  8. My thinking is that spotlight equalizes the displays because extent of the crystal swarm is not a factor. Maybe it would not have stood out so much.

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