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, 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

Monday, 23 December 2019

Winter Solstice elliptical halo

I was outside working on the day of the Winter Solstice and saw AC clouds coming in and I anticipated elliptical halo and got my camera gear ready. Not too long afterward I saw ice crystals precipitating out the AC and using a telephone pole as a sun block got a small elliptical halo. It came and went twice. This I believe is my 2nd elliptical halo for the 2019 year.

Tuesday, 27 August 2019

28° arcs from Yunnan, China

Two rounds of week-long odd-radii outbreaks swept across southern China in July and August. The second outbreak turned out to be the more noteworthy one, involving predominantly Chengdu-like low sun plate displays ( http://www.thehalovault.org/2018/10/time-machine-chengdu-display-from-july.html ).

Zhong Zhenyu, a member of the Chinese skywatcher community chat group, went halo hunting with his DSLR on August 21 after being informed of the on-going outbreak in his area. The community's collective effort paid off and Zhong was treated with some great celestial rarities.

© Zhong Zhenyu, shown with permission.
Upon first glance, the scene immediately reminds us of the Chengdu display, with 3 colored arcs piling up to the right side of the sun. The arc in the middle possesses the same color separation as the other two, especially when USM is applied.

© Zhong Zhenyu, shown with permission. Unsharp mask applied.

B-R analysis later carried out by Nicolas Lefaudeux further confirms the arc's authenticity. The left-side component also shows up in the processed image. At this point it's quite clear that we've got the third confirmed sighting of 28° arcs in China.

Processed by Nicolas Lefaudeux.

Over the past few years, this type of weak, low sun odd radius plate displays occur rather frequently during summer monsoon over southern China. Now with 3 confirmed and 1 possible cases of 28° arcs within 3 years, chances of these plate displays involving exotic arcs may not be as slim as we expected.

Jia Hao

Sunday, 18 August 2019

Odd Radius Display, Southern Ohio, USA, 17th August 2019

On the evening of Saturday, 17th August 2019, I observed this complex pyramidal halo display. In total, I saw a faint 9d halo, lower 9d plate arc, bright 18d plate arc, 18d halo, upper and lower 24d plate arcs and a weak upper 23d plate arc. This display is very similar to the one I captured in 2017, the only difference being the one in 2017 the lower 9d plate arc was bright and colorful and in the present display it was weak.

Sunday, 28 July 2019

Possible 28° (plate) arc from Changsha, China

On July 1st, skywatcher Luo Wuping captured a decent odd radius plate display during sunset hours from Changsha, Hunan Province, China.

© Luo Wuping, shown with permission. 3 images stacked.

Upon first glance at his photos, we immediately noticed the display's striking similarities to the previous two Chinese displays involving 28° arcs ( http://www.thehalovault.org/2018/10/time-machine-chengdu-display-from-july.html and http://www.thehalovault.org/2018/09/28-plate-arc-captured-in-haikou-china.html ). The brightening between the left 35° and 24° plate arcs looks very much like the 28° arcs confirmed in previous cases and its position matches simulations.

© Luo Wuping, shown with permission. 3 images stacked with minor USM applied.

Unlike the Chengdu display, the brightening only appeared on one side of the sun. Uneven distribution of clouds/crystals might be at play here but the absence of the right side component definitely complicates the situation.

Typically B-R analysis on raw files resolves difficult cases like this (which worked well for the Hainan display). Unfortunately, only handphone photos are available at the time of writing, and the jpeg files turned out insufficient for serious image processing.

After discussions with Nicolas Lefaudeux and other halo experts, we reached the conclusion that it's safer to consider the case a possible one for now given the lack of solid evidence. Hopefully DSLR records of the event will surface some day in future.

Jia Hao

Thursday, 11 July 2019

Pyramidal halos 7-10-19

Before leaving for work yesterday, I saw some cirrus clouds moving in and in a short time later 18 and 23d halos along 18d plate arcs, and bright upper 23d arc appeared. The display went on for a while and when the sun was high enough, a bright and well-defined lower 23d plate arc formed. The lower 23d plate arc in this display is my best to date.

Thursday, 2 May 2019

Kern with subhelic arc in the UK

Berkshire (UK), 28 April 2019: Top left corner shows what's left after applying the gradient subtraction and stretching of histograms on a 38-frame average stack. Top right and bottom left, respectively, are with additional blue-minus-red subtraction and colour-channel enhancement. A HaloPoint simulation is included for reference at the bottom right corner.

While relaxing at home in the evening of a mostly cloudy day, a ray of light caught my eye and I checked the halo situation. In fragmented cirrus there was a mediocre circumzenithal arc (CZA) but not much more than that (my view towards the setting Sun is not that great). I took notice of the Sun being low in the sky so odds for Kern arc were on the rise: in the next moment I was setting up my DSLR to get some photos from my backyard.

CZA disappeared soon after I started shooting the first set of images, but it came back a few minutes later so I chose to do a re-run. Fortunately so, as the latter set turned out fruitful indeed in the post-processing.

The processed stack indicates presence of a faint Kern arc as an extension of CZA at the left. Slightly further to the left, there is a white arc that best matches the subhelic arc in the simulation. I think there is also a subtle suggestion of helic arc alongside of the subhelic, but this is less convincing. Furthermore, there are colored patches below the CZA approximately where 46° contact arcs would appear if there were Lowitz-oriented crystals in the mix. The simulation shown above is a synthesis of three distinct populations, including singly-oriented plates, singly-oriented columns, and Lowitz-oriented plate crystals.