A possible rarity found on older diamond dust Moon display photos

The several past winters in the Czech Republic were very sub-par. Lots of work and not enough negative NAO resulted in bad conditions across the country.

Since another winter season is behind the door, I wanted to get ready a bit and started looking at older pictures to prepare me for what's ahead.

A quick look at an older diamond dust display from the beginning of 2019 left me speechless. I have found not only Moilanen, but also a possible Mikkilä arc (do we call it that?) as well. Sadly, the display was changing very rapidly and stacking proved to be non helpful. My wide lens is also at the end of its life, resulting in lots and lots of artifacts that makes discerning any low-vis arcs very hard.

Below is an unsharp-masked photo of the arc in question:

  

Apart from Moilanen and the mystery arc, there is a weak helic arc and some nice Lowitz arcs as well.

 

Let me know what you think of this. I'll leave you with a cold-feeling inducing shot of a later stage of the display.

 

 

Unprecedented high-quality 28° arc outbreak in China

The 28° arc outbreak in China just wouldn't stop.  Since my last post ( https://thehalovault.blogspot.com/2022/08/28-arc-spotted-4-times-within-one-week.html ), 16 more sightings were reported across multiple provinces as of Aug 27, meaning that a total of 20 cases occurred within the 20 day period between Aug 7 and 26. Such an intense outbreak is beyond our wildest dreams.

What makes this outbreak more monumental is the high average quality of cases. Multiple observers described the 28° arcs as 'very bright, as bright as the 24° and 35° plate arcs'. Visual detection of color in the arcs was also widely reported, which has been a real rarity in past years.

If we were to identify the climax of the outbreak, it has to be Aug 21 and 22. Within this busy 24 hours, bright and vivid 28° arcs, together with other high quality odd radius plate arcs, popped up every time the sun neared the horizon. The largely low-cloud and haze free skies gave enthusiasts in several provinces a rare opportunity to appreciate odd radius halos at their best.

Aug 21, evening:

The grand show started in Anhui and Jiangsu Province. LIU Qianyu in Anqing grabbed with his DSLR a series of textbook standard photos showcasing a typical sunset odd radius plate arc + 28° arc display.

Taken by LIU Qianyu in Anqing, Anhui Province. Camera photo. Single exposure.

300km away, LI Jiamin in Nanjing witnessed an equally splendid display. She also managed to take a time-lapse video of it.

Taken by LI Jiamin in Nanjing, Jiangsu Province. Mobile phone photo. Single exposure.

Aug 22, morning:

Less than 12 hours later in Nanjing, the 28° arc showed up again in the morning sky, bringing its  recurrence interval record in China from 3 days down to hours.

HAO Yanjun, one of our key community members, contributed by far our most comprehensive camera coverage of a 28° arc display. Despite not having a tripod available at the scene, he managed to follow the display for hours handholding his SONY mirrorless camera. 

Taken by HAO Yanjun in Nanjing, Jiangsu Province. Camera photo. 30 frame stack.

HAO's effort in maintaining a relatively consistent field of view and regular intervals while shooting clearly pays off in post processing. Stacking 30 frames yields a result beating all our past data. The BGR + B-R processed version of the stack turns out buttery smooth, almost like a simulation!

BGR and BGR+B-R version of HAO Yanjun's stack.

HAO's amazing captures have undoubtedly raised the bar to a whole new level, and will likely remain unchallenged for some time.

Aug 22, evening:

Hours later, the crystals drifted southwards to Jiangxi and Hunan Province. CHEN Junzhi in Ganzhou probably never anticipated his first 28° arcs to be this bright.

Taken by CHEN Junzhi in Ganzhou, Jiangxi Province. Mobile phone photo.

TANG Chaowen in Shaoyang was treated with something a bit different. The 28° arc he saw, while also bright and colorful, exhibits a prominent sunvex/comma shape. 

Taken by TANG Chaowen in Shaoyang, Hunan Province. Mobile phone photo.

Such peculiar appearance was first reported in the 2020 Pu'er display ( https://thehalovault.blogspot.com/2020/09/mysterious-sunvex-28arcs-in-yunnan-china.html ). Now TANG's capture provides solid evidence that the Pu'er case isn't a one-off outlier. Given that available theories are facing trouble explaining the shape, fresh ideas are much needed to crack the Chinese 28° arc mystery.

Jia Hao

28° arc spotted 4 times within one week in China

After a two year long no-show, the mysterious 28° arc finally makes its comeback in China, in a very dramatic way.

Between Aug 7 and 14, the arc was observed four times in three provinces, setting a new record.

Aug 14, Ningbo, Zhejiang Province

Photographed by LI Shengyu. Single exposure with no processing. Shown with permission.

BGR and B-R versions of the stacked image.

Very high quality set of capture by LI Shengyu. Stacking, BGR and B-R processing reveal the arc's weird sunvex comma shape, reminiscent of the 2020 Pu'er display ( https://thehalovault.blogspot.com/2020/09/mysterious-sunvex-28arcs-in-yunnan-china.html ).

Aug 13, Xi'an, Shanxi Province

Photographed by Aphelius. Shown with permission.

Enhanced by Aphelius. Shown with permission.

Seasoned sky watcher Aphelius sets China's northernmost (35°N) 28° arc sighting record with his brilliant Aug 13 observation. Xi'an is geographically considered a Northern China city, which means the 28° arc finally makes its debut in Northern China. It remains to be seen how much more north it can push in future.

Aug 10 and Aug 7, Renhuai, Guizhou Province

ZHANG Zhengqiang's second observation on Aug 10. Mobile phone photo. Shown with permission. 

BGR processed version.

ZHANG Zhengqiang's first observation on Aug 7. Mobile phone photo. Shown with permission.

BGR processed version.

Yet another new record, ZHANG Zhengqiang witnessed a repeat event merely two days after his first observation on Aug 7, from exactly the same location! The two displays almost look identical. Atmospheric condition during those few days must have been remarkably consistent.

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At the time of writing, there's still an ongoing odd radius plate arc outbreak in Southern China, which has lasted more than a month and shows no sign of stopping. Plate arcs are spotted almost everyday in (mostly) Southern China since late June. We shall reach well over 50 odd radius days in 2022. More 28° arc occurrences are likely on the way if the outbreak continues.

Jia Hao

Stacking comparison: Canon 80D vs. Nikon D7000

by Marko Riikonen and Petri Martikainen

One of us, Martikainen, was passing on May 25 though Joensuu where the other one, Riikonen, was staying, and we had decided to do a stacking comparison with our cameras weather allowing. It went swimmingly. There was high cloud from morning to the sun set and when we rendezvoused in the evening on a grassy field next to lake Pyhäselkä to set up tripods, cameras and blockers for the test, the display reached its peak.

Martikainen was photographing with Nikon D7000, Riikonen with Canon 80D. We both had Samyang 8 mm fisheye, though not the same model. Our blockers differed a bit. Martikainen had the blocker on a separate tripod, whereas Riikonen's was attached to the camera hot shoe.

We set identical iso, shutter speed and aperture. Then we took 136 photos every 5 seconds, at around 1/3 of the of way there was a little longer simultaneous break.

In postprocessing we harmonized the color temp and tint of raw's before turning them into 16 bit tiffs for stacking with Halostack in full size. As the 80D images are larger than D7000, the former's final stack was downsized to match the latter before we gave them identical application of the usual methods of usm, br and bgr.

Downsizing the 80D stack before the enhancements could make it lose some of its higher resolution advantage, so we made a test. Usm with a radius higher relative to the two cameras image size was applied to the 80D stack before downsizing and this was compared to the version where the 80D stack was first downsized and then usmed (with the smaller radius). There was zippo difference. So it seems ok to downsize the 80D images to D7000 scale before enhancements

The test showed D7000 as the better halo camera, something that Riikonen had suspected all along. We do not know how to characterize in proper terms the differences seen in the photo comparisons, but it seems like 80D has more problems with color noise.

Terminology:

usm = unsharp mask

br = blue minus red

gr = green minus red

bgr = background removal 

Original stack. Left 80D, right D7000

 

2 x usm (radius 25, 25)

 

3 x usm (radius 25, 25, 12.5)

 

br

 

br + bgr

gr

 

gr + bgr

 

bgr

100% detail (after D7000). Left D7000, right 80D. 2 x usm (radius 25, 25)

Double CZA, Kraków, Poland

On May 7, I was working on my programming side project. At about 17:15 local time (UTC+2h)

I was finally able to take a short break. I decided to get some fresh air on my balcony (facing south).The temperature was about 17-18°C and a substantial fraction of the visible sky was covered in rather thick clouds. The zenith area, however, was quite clear, except for a layer of nebulous cirrostratus clouds and some broken mid-level clouds. I could see a faint circumzenithal arc, so I went back inside and grabbed my camera. I took only three pictures of the CZA at 17:20, 17:21 and 17:22, before the arc disappeared completely. I noticed it was a little broader than usual, but I thought that maybe it had something to do with the solar altitude. At 18:30, I finished my work for the day and looked out of the window again. The CZA was back and I thought I could see a supralateral arc as well, so I took some more pictures. About 25 minutes later, thick clouds rolled in from the west and obscured the display. 

Since it wasn’t a particularly bright display, I didn’t think about it much until the next day when I began processing the photos I took over the last week. I was pleased to find CZA, supralateral and a suncave Parry arc (Apr 30) and another CZA + supralateral display (May 6), and then began to process the few photos that I’d taken on the previous day. The first one showed just a normal CZA, but in the second one I could see a faint rainbow smudge right under the CZA. At first, two things came to my mind: 46° halo and camera artifacts. Stellarium told me that the sun altitude was 25°. According to a chart I found on the internet, at this solar altitude the CZA should be quite narrow and the 46° halo should touch the CZA. Also, the arc in my pictures followed the shape of the CZA instead of curving downwards. I could see it in the third picture (taken in a slightly different direction) too, so I thought I could safely assume it was not an artifact or a lens flare. The rest of the photos I took later in the evening revealed a regular CZA, supralateral arc and a 46° halo – they looked completely different to the weird double arc. Then I remembered reading about an unusual type of halo related to the CZA before, but I couldn’t remember where, so I submitted my report to spaceweather.com in hope of it getting some attention there.

Meanwhile, I went on looking for the mysterious CZA phenomenon I read about earlier. I stumbled upon it a few days later, by accident. Someone had posted a link to a Halo Vault article on reddit describing a secondary CZA spotted in China. Then I found the report of A.F. Jensen. I was really excited when I realized that the second report fitted my observation quite well, so I decided to write you immediately. 

Lately, halos have been keeping my quite busy. I could see another CZA / supralateral / suncave Parry arc combo in the morning of May 14 and there is a nice 22° halo visible right now. Honestly, I can’t remember seeing that many displays in a row since I’ve seen my first one in May 2005!

                                                                                                                                         - Tomasz Adam

Peculiar Elliptical Halo in Suzhou, China

On Feb 5 a very strange case of elliptical halo was recorded by FU Lei from Suzhou, Anhui Province, China.

The short-lived elliptical halo in the display was sliced by the cloud bands into two segments, both exhibit a gradual increase in radius as the halo approaches the cloud bands' lower limits. Such behavior shall be explained by varying apex angles of responsible flat pyramidal crystals.

According to halo experts Marko Riikonen and Nicolas Lefaudeux, it's been long debated whether there's a 'preferred' apex angle in the elliptical halo theory. This particular case serves as strong evidence that there's probably no 'preferred' angle at all. Ellipses can sometimes behave like iridescent clouds - instead of a smooth water droplet size gradient, there is a gradient of crystal angle.

Jia Hao

(Almost) Solitary Parhelic Circle in Genhe, China

On Jan 8 WANG Jingxian from Genhe, China captured a very interesting diamond dust display in which the only prominent halo was a (almost) solitary parhelic circle.

According to WANG, the display had already passed its prime when the pictures were taken and the parhelic circle had faded somewhat. Except for a diffuse pillar and very weak parhelia, nothing else showed up throughout the display - no circumzenithal arc, no 120° parhelia, no upper tangent arc.

Solitary parhelic circle has been observed before in China, but not at such low solar altitude. Marko Riikonen later reminded us of a very nice photographically confirmed case by Jarmo Moilanen back in 2004. (hopefully Jarmo can visit this page and share his capture in the comments). Marko himself also witnessed a streetlight display in Oulu back in 2002 ( https://www.ursa.fi/ursa/viestinta/listat/halo-l/0543.html ) in which the parhelic circle and circumzenithal arc shined without parhelia.

Crystal samples from such displays are still much needed to pinpoint responsible crystals. Marko noted he saw stellar plates were falling on his sleeves during the Oulu display, and suggests such stellar shapes could theoretically be the cause of the absence of parhelia.  In the Genhe display where even the circumzenithal arc is missing, the crystals probably need to be more optically subpar, allowing only external reflections on vertical faces. Besides, as both Marko and JI Yun suggest, optically imperfect columns could also play a part.

Jia Hao