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