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:

https://m.weibo.cn/5471509356/4471997029347233 

https://m.weibo.cn/5893589762/4471826476341170 

https://m.weibo.cn/5299394320/4471803969617073

https://m.weibo.cn/5703217900/4473449294440181

https://m.weibo.cn/6624168505/4472005455908200

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.blogspot.com/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

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

by Marko Riikonen

In the previous post of this display I discussed two photos taken towards the end of the hunt, just before twilight. Now it is time to look at the photos taken earlier, from midnight onwards at another location. Please mouse over or click the photos to remove the milky veil that the systems adds as default to them.

Of the several stacks that were photographed, I made simulations of two that are shown below. Unlike the morning photos, now only one stricly oriented Parry population was needed to the explain the display’s halos from c-axis horizontally oriented crystals. So here we have a pure case of uppervex Hastings and nothing reminescent of Wegener.

Except that a little detail strikes a dissonant chord. In the lamp side photo above an arc is touching the bottom of the 22° halo whereas the simulation gives an arc that is separated – the lowervex Parry. Thus the lower arc in the photo is suggestive of tangent arc and column orientation. But everything else – the presence of Tape arcs, the bright helic arc, lack of subhelic or 46° lateral arcs – shouts out loud this is pure Parry. So what is going on?

Well, even though spotlight displays have a highly 2D character, there is divergentness involved and halos may extend more towards the lamp than true 2D halos would. Look for example at the upper Tape arcs in the photo. They are deeply embedded into the 46° halo, although in simulation they are separated. In the photo they even seem to extend slightly inside the 46° halo. And in other displays upper tangent arc always pushes through the 22° halo towards the lamp (it may be a different thing with that halo, though, than with Parry). Even in solar displays various arcs can be glued to their circular rings despite simulations telling they should be separated.

So I would not quite yet scrap the pure Parry character of this display because of that little anomaly at the bottom of 22° halo. It is not the first time to be faced with this matter: we were wondering about it last winter in another potential Hastings case.

As for this lamp side view in general, it seemed not possible to get a satisfying match. For example, with all parameters that I tried, a secondary upper Tape arc (if letters are used to denote it, maybe it should be upper Tape arc B, instead of the Tape arc D that I used in an earlier post) was produced outside the primary. As for the Hastings, in the photo it is brightest near the lamp, then has an intensity drop just inside 46° halo before getting again a bit brighter outside. I could not reproduce this variation. I think there is going on something that is beyond the reach of the simulation software. In the simulation shown was used just one Parry population optimized to make a Hastings that is brightest near the lamp and vanishes outwards. The crystals were thin h/d 0.05 plates. Such a solution did not quite produce matching intensity distribution for the helic arc, and I am certainly not proposing this as final solution. The parameter table for the simulation is not given as I happened not to save it. Because in the photo there is Moilanen arc, I added it to the simulation too. Simulation light source elevation is -5 degrees.

Opposite to the lamp the view is very much Parryish, as shown below. In addition to simulation I have provided also a br version of the image because it makes it easier to distinquish the spikes of lamp artefacts from halos. It seems to show that inside the subanthelic arc there is no diffuse arcs, just artefacts. Another image further below also has the hallmarks of pure Parry.

In the sideview image below noteworthy is the very thin core of the sub-120° parhelion. It is as thin as the sun pillar above the Parry arc. In br version this core is better separated from the glow surrounding it. Further below are four other photos from the first part of the night.

 

 

Finally, I make a return to the anthelic region photo from second part of the night. Earlier I had shown only br version of the blue spots in Liljequist parhelia, but they come out also in “visible wavelengths”, as demonstrated by the extremely saturated version below. Noteworthy is also the dark area that seems to be confined by the shape of subanthelic arc even though the top of the subanthelic arc is not seen. This was something I raised up in an earlier post that discussed a display photographed by Marko Mikkilä.

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

By Marko Riikonen

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.

Then I switched on the sacred light, and to my delight, things improved soon. First to be noticed, when standing a little outside the beam, was an odd intensity threshold which materialized into a helic arc. “Hastgener” followed the suit, it was a beautiful colored arc of crystal glitter. And as I turned facing opposite to the lamp, higher up in the sky were glittering the two vertical parts of the subanthelic arc loop. Nothing much suggestive of column stuff was evident, neither visually nor from the camera display, so I was pretty sure the “Hastgener” must be a Hastings arc.

But was it? This post is about the two photos that I took towards the end of the night in the second location (which is another snow deposit site), where I moved after it got crappy at the first location. I have attempted to make a simulations of those two photos to test the issue, as shown below. While working on them, I also realized from the br image something of moderate interest: there are blue spots on both Liljequist and sub-Liljequist parhelia.

                            It was -20° C at the location where these photos were taken.

I got the best match for the display using two Parry populations in the HaloPoint software: one with strictly oriented crystals and other with 4 degree rotation. The contribution of these two populations are dissected in the image below, as well as of the other two populations used in the simulation. The 4 degree rotational population has an orientation that makes halos look like an intermediate between Parry and column. These two populations were necessary to make the subanthelic arc look right. It is actually quite typical that you have use about 4-5 degree rotating Parry crystals to simulate diamond dust displays. Earlier I have analysed one case from 2010 in Tampere.

Because of the need for rotating population, I would play is safe and say we don’t have a pure uppervex Hastings here, even though the display clearly has Parry domination over columns. The photos taken earlier in the night at the first location may have a cleaner Hastings, but I need to take a closer look at them.

Then to the colors of Liljequist parhelia. In the br version above of the image that points opposite to the camera there are visible blue spots of both Liljequist and sub-Liljequist parhelia. The flashing image below shows that the br image brightenings do not overlap with brightest parts of the Liljequist parhelia in visual image, but are a little further out towards the 120 parhelia. This is the location where the blue spots are seen also in the simulation.

The simulation shows also a narrow slice of reddish color further out from the anthelic point, at the very edge of Liljequist parhelia. The red is there because the fainter outer half of Liljequist parhelia away from anthelic point is made by parhelia which is rotated by 120 degrees (raypath 3567). In br the red color would make a dark spot, but it is not seen in the photos.

Everything said in the two paragraphs above applies also to the sub-stuff. The raypaths are the same, except for and added basal reflection.

So this observation of Liljequist parhelia blue spots adds to the growing list of various blue effects. The sub-Lilje blue spot we seem to have photographed already last winter on the night of 5/6 January, but normal Lilje blue spot is a new catch as far as I know. Other blue effects that have been photographed, in addition to the traditional parhelic circle blue spot, are blue circle, blue subsun and subanthelic arc blue spot. The latter has not been talked about, it is visible in my photo of a spotlight display from the night of 7/8 December 2008.

Correction: the subanthelic arc blue spot has been talked about in the comments section of the link above.

A plate spotlight display on 5th November 2016

By Marko Riikonen

Showcasing 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.

The display disappeared immediately when it got cloudy and there was nothing to be had for the rest of the night. What is not visible in any of the photos, but what was there many times during the display was the subanthelic diffraction pillar. Discovered by Marko Mikkilä in 2012, it is a quite basic feature in plate displays, but tends to come and go, never lasting long. So it is not necessarily captured by the camera unless you take it as your target.

The temperature was around -10 and -11 °C at the location. It is in a typical range of good plate stuff, not yet too cold.

Streetlight parhelic circle on video

By Nicolas Lefaudeux,  Marko Mikkilä,  Marko Riikonen and Jarmo Moilanen

The image above opens a video of parhelic circle under streetlight. There has been some question on whether the three dimensional character of divergent light halos shows up on video, but at least here the vortex effect of the parhelic circle is tangible.

Likewise, dimensional effect of parhelia is well visible in another video. At the end of the clip the camera is panned to show also the Liljequist and sub-Liljequist parhelia. One more video. Downloading gives better quality.

These were seen on the night of 6/7 January in Rovaniemi. Below are two more images from the night’s action.

Catching a divergent light halo effect predicted by simulations

Sometimes it is possible to make a deliberate attempt to photograph something predicted by simulations. On the night of 6/7 January we made such an attempt on the diffuse spots of light that in simulations are seen next to the divergent light subparhelion.

The effect is formed by a mixture of subparhelic circle raypaths, including 3157 raypath and sub-120° parhelion raypath. Its exact shape and position depends significantly on the crystal shape, like for the Liljequist parhelia.

To obtain an omnidirectional secondary light source that was bright enough we pointed the lamp directly to the snow surface. We took photos, looked at them more closely the next day, and there it was – those smudges of light predicted by simulations.

The photo above is actually from a slightly better case on the night of 18/19 January. Next to it is a simulation. Below is the one on the 6/7th.

Nicolas Lefaudeux / Marko Riikonen / Jarmo Moilanen / Marko Mikkilä