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

Project Kern Update

Just under a year ago, we launched Project Kern, the aim of the project being to “try to photograph as many Kern arcs as possible [in a twelve month period]…. to better understand their frequency and to ascertain whether they really are the rarest of the rare”. I am very pleased to announce that almost at the end of the allotted twelve month period of the project we have received our first Kern.

On 20th January 2018, Pasi Vormisto observed an excellent halo display whilst driving just outside the town of Nokia close to the city of Tampere in Finland. Upon finding a suitable parking spot, he managed to document the whole of the display and in so doing photographed several rare halo forms including Tape arcs and 44° parhelia. However, of great interest to us is the Kern arc which appeared in a couple of the frames. One of the characteristics of this particular example is how bright it appears to be. It is readily visible without any additional processing and one wonders whether it would have been visible to the naked eye or in a mirror. One might also speculate as to what kind of monster this would have become if a sequence of images had been taken on a tripod for later stacking. However, every credit must been given to Pasi for even remembering to photograph the area around the circumzenithal arc. All too often, observers become transfixed by all the ‘action’ occurring in the immediate vicinity of the sun.

So then, can we draw any tentative conclusions? I think the jury is still out, but on recent evidence it seems as though they are appearing once or twice per year. For example, in 2015, we had Eresmaa’s two UK Kerns and in 2016 we had Riikonen’s daylight Rovaniemi Kern. Of course, we don’t know how many actual Kerns there were that went unobserved/un-photographed. Although Project Kern is now drawing to a close, there is still time to add to our grand total of one. If it has taught us anything, it is the need to encourage as many observers as possible to routinely photograph the area around the zenith and better still to stack their images. In this way we may better understand their frequency and distribution.

All images copyright Pasi Vormisto.

44° parhelion in eastern Finland

Have secondary parhelia made their appearance already this winter somewhere? If not, then here is the first one. On 8 February Kai Kotivuori was skiing on the Pielinen lake, and took a couple of photos of a bright plate display. One photo was framed so that we can see also 44° parhelion. 

Following evening an anonymous observer was fishing burbot around the same area and took photos of a lunar display showing lowervex Parry. 

Next 44° parhelia - in Stockholm

I found very nice photo of diamond dust display (on 3. January 2006) with 44° parhelion. Photo is used with permission of Yvonne Primé. All photos of the display are here. See also updated list of 44° parhelia occurrences. Two other reports from the same day are here and here.

Simulation of 44° parhelion

Here is a simulation of the Jaakko Tähti 44° parhelion display. In order to produce 44° parhelion (left arrow) in the simulation, multiple scattering has been used for plate crystal population. Reflected Lowitz arcs (right arrow) as well as 22° halo are simulated with "normal" single scattering populations.

Photo and simulations are also found here. Simulation is made with program by Mika Sillanpää and Jarmo Moilanen.

Patrik Trncak notified me about another likely case of photographed 44° parhelion. It was documented by Matthew Hyde in Greenland in summer 2002.

44° parhelia, Minnesota

Jaakko Tähti is to be congratulated!

For completeness of the records, part of the Minnesota halos of 3rd January 2004 are shown here. The top image is 'as was' from the camera. Bright left and right hand 44° parhelia were visible in the display.

44° parhelion in Finland

Once thought to be an extremely rare halo, the 44° parhelia is now increasing it's appearances. The display on the right was photographed by Jaakko Tähti on 21. December 2005 at Viitasaari, Finland. To my knowledge, this is the eighth photographed occurrence of 44° parhelion. 

The formation of 44° parhelia differs from other halos in that it's not caused directly from sun rays, but from light rays of another halo - namely the common 22° parhelia. In other words, it is the parhelia of parhelia. Formation of 44° parhelia seem to require diamond dust conditions and very bright 22° parhelia. According to Jarmo Moilanen, also low sun elevation is essential to ensure there are enough ice crystals between the sun and observer. Here the sun elevation is 2°.

List of photographed occurrences of 44° parhelia: 

3 Dec 1970, Saskatoon, Canada, Earle Ripley (photos not shown)

23 Jan 2002, Vaala, Finland, Jarmo Moilanen (drawing shown)

June 2002, Greenland, Matthew Hyde

30 Dec 2002, Juva, Finland, Jari Piikki (drawing shown)

3 Jan 2004, Minnesota, USA 

21 Nov 2004, Teuva, Finland, Heikki Mahlamäki

21 Dec 2005, Viitasaari, Finland, Jaakko Tähti

3 Jan 2006, Stockholm, Sweden, Yvonne Primé