Discovered in a spotlight display in 2007, we now have the first case of a high cloud Ounasvaara arc. The halo came up in a big display that Leesa Brown photographed in Kissimmee, Florida, on 23 April this year. She took about 1200 photos between 18:12 and 19:04 and it's good she didn't stint on film, otherwise the narrow occurrence window for the Ounasvaara arc at 19:00-19:02 might have been missed. It helps also that she photographed wide enough to cover the sky high up beyond the circumzenith arc.
The same goes for the display's Kern arc, which visibility window (at least where you need not to guess whether it is there) was equally short at 18:38-18:39. While Kern arc has been photographed in high clouds a handful of times, this is only the second time that it is intense enough to appear in single images.
The display had also Lowitz arcs curving down from both Parry arcs, a highly unusual combo. Normally we see from Parry-Lowitz oriented crystals only the Lowitz arc associated with uppercave Parry arc, that is, the upper Lowitz arc. Sightings of the one associated with the uppervex Parry arc, the circular Lowitz arc, are very few. Actually, should anyone know such observations, it would be nice to hear.
And then there is an exemplary 46° contact arc straight above the sun. More often 46° contact arcs are seen in diamond dust, high cloud cases are very rarely encountered.
All and all, this display in Kissimmee on 23 April ranks among the top photographed high cloud halo complexes. Its uniformity and celestial span might have been a bit compromised, but the conglomerie of high rarities makes up for it.
We asked Leesa to give her first hand impressions of the display, here is what she wrote:
On Friday, April 23 2021, I had been out all day with a friend, doing
some nature photography. I kept seeing a lovely 22 degree halo, and bits
of other interesting sky phenomena, and snapped photos of them between
watching birds and other wildlife.
I got home around 6:00 pm, and
all I wanted to do was sit down and rest. But there was a halo and a
lovely display going on outside, so I did what any sky-loving
photographer would do - I dropped my stuff inside the door, and went
back outside to capture whatever I could.
When I'm photographing
displays like the one I saw that Friday night, my one overriding
feeling is always the same - wanting to turn to someone and say "Do you
SEE that??"
That's why I'm so happy to have found some of the
people I've met online since that day. My friends and family like the
photos of displays like these, but they don't truly understand the joy
of finding new arcs you've never seen before, or the beauty of seeing
these in person.
Birders call your first sighting of a particular species of bird a "lifer."
This display turned out to be more than that for me - probably a once in a lifetime event.
And
now, with the help of Marko Riikonen, Alec Jones, and a few others, I
can finally turn to the people reading this and say "Do you SEE that?"
I'm glad there's someone there to see it this time.
Thank you!
All Leesa's photos and the panoramas she made are in Google Drive should anyone like to take a look:
https://drive.google.com/
Color versions of the three panoramas above, plus one more panorama, are at the end of the post. The helic arc, which is largely lost in the b-r images, shows up nice in these versions. Also, the Kern arc can be discerned.
Finally, above is a simulation for the display's Ounasvaara arc stage. Two Parry
populations were needed to get it right. Ounasvaara arc needs triangular crystals, but such crystals make only uppervex Parry, not
uppercave Parry. So, another population of slightly tabular crystals was
necessary to summon up the latter. It is a bit strange combination of
Parry populations and probably does not reflect the full truth as the
unevenness of high clouds likely complicates things here. Arrows from
top down: Kern arc, Ounasvaara arc, 46° contact arc, upper Lowitz arc
and circular Lowitz arc.
The simulation was done with Samuli Vuorinen's Haloray software and then turned into b-r. There was a problem with the Parry halo intensities in the software, which is why the right side arm of the Ounasvaara arc is brighter than the left. Now I just heard from Vuorinen the bug has been fixed. The parameters are displayed below in the HaloPoint user interface as Haloray doesn't come with such at-a-glance view.
Addendum on 9 May 2021
The Kissimmee display just gets bigger. Reima Eresmaa spotted from the Kern arc stage panorama (28 DSC_7359b_stitch-2) also Hastings and Wegener arcs. Below is shown the single photo (DSC_7377) containing those arcs, compared to a simulation. Subhelic arc would be expected as well in this massive display and the white stripe under the Wegener arc looks like a potential candidate. But the otherwise pretty well matching simulation does not support this: the stripe is too high up in the photo. So unless I have made a mistake in correlating the simulation and the photo, it must be regarded as a wispy cloud strand. Sun elevation for the Haloray simulation is 16 degrees. Alec Jones enhanced the photo.
Hastings arc is always a great catch, probably no more than half a dozen high cloud cases are known.
Reima Eresmaa has worked a simulation that gives a good match with all halos, including subhelic arc. His simulation with the photo is added below. See more in comments.
