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

4 comments:

  1. All three similar records found in China occurred at sunrise/sunset.If there is any reason make 28°arc disappear when the sun beyond about 5-10°altitude? we
    haven't reach any conclusion yet.

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  2. I am not sure if that is a 28d arc either. Lack of the right side component is making me think that this is just an area of crystal swarm intensification

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  3. 28 or not, it is good to have some halo news from China again.

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  4. I agree, shortly after arriving up North in Wisconsin I got a pyramidal halo with 9,18,22 and possibly 24d halos with 18d plate arcs

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