An attempt at high cloud 44° parhelion

High cloud 44° parhelion is still waiting for its capturer. A chance to try for one came on September 28 this year in Kontiolahti, Finland, when a cirrus floe containing a short-lived blinding parhelion moved out towards the appropriate position.

I had already camera snapping photos at 10s interval, but changed it to 4 seconds when I estimated the leading edge of the floe had reached about 44 degree distance from the sun. The b-r image above is 84 frame stack from the time it took for the floe to pass the 44-46 degree azimuth and shows indeed a dark spot indicative of red color. But it looks to be too far out for 44° parhelion when compared to the 46° halo in the image. Probably we are looking here just at a segment of 46° halo or 46° lateral arcs crossing, or both, but proper measurements using starfield may still be worth doing. 

Even if the result seems negative, it thought to share this to pay attention to situations where high cloud 44° parhelion might be a prospect. Below are other relevant images and some more info.

Bgr and usm versions.

At 13 degree sun elevation 44° parhelion is inside 46° halo, which is not the case with the spot in the observed display. The other half of the simulation has column and Parry population as the display had halos also from these crystals. Made with HaloPoint.

The short stage during which bright parhelion appeared in a cirrus floe. Photo interval is 10s.

Here is shown the first (top) and last (bottom) photo of the 84 frame stack (middle) from the period that it took for the floe (delineated) to pass 44-46 degree mark.

Uncropped versions of the 84 frame stack, br and usm. Notice the lacking of uppervex Parry. With regular hexagons at 13 degree sun it should be of equal brightness with the uppercave. In stacking, when sun is tracked at this solar elevation range, uppervex gets unfocused and uppercave focused relative to each other due to their sun elevation dependent movement which are in the opposite directions. But as the stack has only 0.5 degree sun elevation change (from 13.3 to 12.8 degrees) the effect should be negligible. Thus the absence of uppervex (or almost absence, there seems to be a ghostly suggestion of it in the image) tells of tabular crystals. A simulation with 0.7 1 1 0.7 1 1 shape modified crystal in HaloPoint reproduces the situation and this is what has been used in the simulation above (0.2 uniform deviation for the two faces). If somebody knows other similar Parry displays showing evidence of tabulars, I am happy to hear. I think I knew one, but have forgotten about it.

In Germany they had this display much better:

https://forum.meteoros.de/viewtopic.php?f=2&t=61567&sid=b6b52b267d966f7de49207b4e6863089

https://forum.meteoros.de/viewtopic.php?f=2&t=61570&sid=d1f3268f300beb1ff746ae83a13af46e

Marko Riikonen

Simulation-like 18° plate arcs and puzzling 22° arcs from airplane, China

On May 24, 2023, I witnessed a very high-quality case of 18° plate arcs while onboard a flight over Southwestern China. Due to my busy work schedule, it took me nearly two months to review and analyze the batch of photos I captured. Clearly, there were more surprises contained in them.

The 18° plate arcs are common in China (in the southern region during the summer), but high-quality occurrences are rare worldwide. In recent years, Chinese sky enthusiasts have explored and contributed numerous images of 18° halos. Some were quite bright, but without exception, they were all quite blurry, likely due to wobbly crystals and diffraction. Blurriness of these arcs might be a common feature since, in previous cases, they are almost always accompanied by the 23° plate arc, indicating the presence of thicker ice crystals, which may have difficulty maintaining low tilts in crystal orientations.

Therefore, when I witnessed this pair of remarkably clear V-shaped 18° plate arcs, I was surprised that such small tilts even exist under natural condition. The arcs were amazingly bright, outshining all other halos minus the sun pillar. In fact, I only noticed the 18° plate arcs and the sun pillar with my naked eyes. Other halos in the display were all picked up later photographically.

(The display lasted for less than a minute, during which I managed to capture six photos. In hindsight, I regret not taking more photos by tolerating the glare and adjusting the shooting angle less frequently to avoid reflections from the aircraft window. However, with the limited six photos I have, I was able to align and stack them to obtain a more complete halo phenomenon. Taking more photos might have further enhanced the final result.)

6-frame stack. Solar altitutde 9.8°.

Now let's move on to the other halos in the display. The lower 20° plate arc and the lower right 24° plate arc are clearly present in some of the photos. The 9° plate arc appears to be absent. In simulations, one can invoke nearly triangular ice crystals to weaken the arc till it gets overwhelmed by the bright sun pillar. However, it's also possible that the absence of the 9° plate arc is due to uneven distribution of ice crystals since the lower left 24° plate arc never showed up. The 35° plate arcs appear strong in simulations, but they were unfortunately obstructed by the wing and engines during the display.

What caught my attention even more are the arcs at the 22° positions. Initially, I thought the pair of tilted arcs outside the 18° plate arcs were 22° parhelia, distorted due to wide-angle lens effects. However, simulations show that the 22° parhelia should be closer to the sun and shouldn't tilt to such an extent.

So, what are these tilted arcs in the photos? They are neither regular crystal halos nor something generated by (3 0 -3 2) exotic crystals or cubic ice crystals. Their presence perplexes me.

B-R, BGR and other post processing work indicate these tilted arcs are actually the brightest spots on a pair of much longer, vertical, slightly sunvex arcs, resembling the appearance of the Lower Schulthess Arcs, also known as Lower Reflected Lowitz Arcs or Subparhelic Arcs.

BGR(background removed) version. 

B-R processed version. The vertical extent of the arcs becomes clear. Segments of 18°, 20° and 24° halos can also be seen.

The behaviour of Subparhelic Arcs/Reflected Lowitz Arcs/Schulthess Arcs has been a long-standing issue. It seems challenging to explain why they mostly appear as single or double arcs, rarely as triple arcs as shown in simulations. But in this case, there is an additional puzzle: why do these arcs have significantly enhanced bright spots near the 22° parhelia position?

I don't want to explain all the discrepancies with simulations as "uneven clouds" or other coincidental factors. During the one-minute long display, it remained remarkably stable - the Lower Schulthess Arcs/Lower Reflected Lowitz Arcs/Subparhelic Arcs were always present, and the aforementioned 22° bright spots were also consistently there, even though the clouds had undergone some changes.

I wish to hear the opinions of fellow researchers worldwide on this matter. I am hesitant to claim it as a puzzle, but I am not exactly sure what mechanisms created these arcs. After initial attempts at simulation, I found that Lowitz raypaths 8-2-1-6 and its multi-reflection derivatives such as 8-2-1-2-1-6 etc. produce a pair of arcs that resembles what I saw. If we artificially disallow conventional Lowitz raypaths and allow only the above mentioned multi-reflection paths, then Lowitz-oriented plates with moderate tilt such as 15° produce a relatively ok match. (Compared to the odd radii in the photos, the match is much poorer. Lowitz arcs' mismatch with simulations has been a long-standing issue and it seems this case is no exception).

Simulation showing only the Lowitz raypaths 8-2-1-6 and its multi-reflection derivatives such as 8-2-1-2-1-6 etc.

Comparison between the simulation and the real scene. Not the best match, but close.

To explain why only multi-reflection raypaths are present, it might be speculated that the ice crystals are extremely thin. Nicolas Lefaudeux's '100 hit' theory inspired me. Perhaps certain extremely thin plates allow for multiple internal reflections between basal faces, creating the observed halo while excluding the usual Lowitz arcs.

However, explaining why only Lower Schulthess Arcs/Lower Reflected Lowitz Arcs are present, and not the upper and middle ones, is much more difficult. Perhaps a specific mechanism exists that gets the Lowitz oriented crystals azimuthally locked so that its face 6 faces the observer, while still allowing the main axis to azimuthally rotate within a limited range of angles, thus selectively producing these two arcs? (Fully locking the main axis cannot produce satisfactory arcs. I have tested this). If such a thing is possible, this pair of arcs might deserve a specific name to distinguish them from Schulthess Arcs/Reflected Lowitz Arcs/Subparhelic Arcs. However, I still feel this is a far fetched explanation since there is no available literature indicating the existence of such a 'alternative' Lowitz orientation.

As I haven't obtained the posting access to HaloVault, my colleague JIA Hao has kindly helped me translate and post these observations (originally in Chinese). Also special thanks to ZHANG Jiajie for having multiple fruitful discussions with me on this topic. We look forward to more excellent explanations from the global community. 

JI Yun

Digging up old odd radius display for 28d spotting

Hello everyone,

after several talks with Alec, I decided to make some digging into my old odd radius halos displays to search for rare halos and find out some more 28d halo (and 13d halos too).

Here are some examples of what I found so far that might be interesting to submit here to your assessment. I hope you will find those cases interesting.

For some of them, I still have all the raw files of the sequence, for others, I kept few raw images, but for all of them (exposed here at least) I made various time-lapses to keep sequence in B-R rendering, colour rendering, stacked with 4 or 8 images each, like the one I presented earlier in this blog.

I will start with a sharp display of odd radius circular halos I got last year, in April, at the morning.
I'm not usually an early bird so I can miss some nice displays each year. For this one I got the chance to have the display still available to start a capture from my roof window. The center of my house is a stair tower which offer a nice blocking roof for the spot I am from. Therefore, with the shaprness of the display, the 9° ring was particularly well visible on B-R rendering before the sun comes out of the roof (because the diffusion of the light on the lens add noise up to the 9° ring area). There is a first image, B-R rendered from a sole raw image, to give a view of the sharpness of the event:

2022-04-20-SSE-[08h45à19h09]-bw-v4-crop-half-(1)
where we can see clearly 35°, 22°, 23°, 20° and 18° halos

Stacking with the above one as first image, with the 25 following images makes those odd radius halos more clear:

2022-04-20-SSE-[08h45à19h09]-bw-v4-crop-half-(1)-26s27-m
''-m'' stands for ''align manually'' in Registax 5, software I use to make my second processing of stacking if any.

Well, in the light of recent search for 28+° ring, this was one of my first tries even if I was expecting, like for the 13° halo, to find it when the rings are not sharp. But if you don't try, you won't find anything.
So there is a processing the the previous stack to enhance sharp halo first then eventually larger borders ones if any.

2022-04-20-SSE-[08h45à19h09]-bw-v4-crop-half-(1)-26s27-m-UsMl^n&m
''-UsM^n'' stands for Unsharp mask applied several times with various settings (m & n)
Do you see 28° ring ? Or could this be artefact due to unsharp masking ?

There is a folder on my drive, so you can take a look at the time-lapses of the day. As usual, better download it rather than viewing it as a Youtube video, to have a better video compression (as is the original one) Many years ago, I got a nice odd radius display at sunset, during a day of November 2014. The view is not ideal, as I placed my camera on the edge of a window, look south, with a wide angle rectangular lens, hence the distortion. (EoS 1200D + Sigma 8-16mm, set at 8mm). I was so amazed by the display I sent it to Nicolas Lefaudeux to have his expertise on the matter. And then he told me I caught the 28° halo, again (but I don't recall why this 'again') ;-) There is the display, B-R rendered, and unsharp masked.

1st of the odd radius sequence, after altostratus clouds went east, with unsharp mask done

And later in the sequence, after it vanished a first time, 28° ring was there again at the end, without unsharp mask applied [Stack]

Unfortunatly, I did not keep any raw file of this event.
There is a folder where are all the remainings.



And any old how, here are some I cannot say it is, but looks like there might be something there.... or not:

2015-03-07-[]-bw-[8-8]-UsM-[6-5]-UsM (16), Dole, Jura, France (and for the scary look of it!)

2017-03-11-[14h30à18h42]-bw-[8-8]-UsM-[8-4]-UsM (26)-7s7, Dole, Jura, France

2017-04-24-[13h57à20h36]-bw-[8-8]-UsM-[6-4]-UsM (18), Dole, Jura, France

2018-04-04-[18h39à19h19]-bw-[8-8]-UsM-14s14-USM, Pontarlier, Doubs, France

2018-04-09-[14h09à16h42]-bw-[8-8]-UsM-(21)_UsM-9s9-m, Jouhe, Jura, France

2019-05-23-[08h35à17h36]-bw-[8-8]-UsM-(20)_UsM-4s4, Jouhe, Jura, France

2020-04-17-[09h11à14h12]-bw-[8-4]-UsM-(153)-6s6-UsM, Jouhe, Jura, France

2021-02-16-[09h43à14h33]-bw-[8-4]-UsM-24fps(61)-6s6-UsM-histo-UsM, Jouhe, Jura, France

2022-04-11-[08h20à19h48]-bw-[4-2]-UsM-[2-2]-UsM(233)-9s9-UsM, Jouhe, Jura, France

2022-08-02-[09h32à18h09]-SSE-bw-[8-4]-UsM (305)-6s6-h9-h13-h18-h22-P23, Jouhe, Jura, France

2022-11-12-[14h09à16h09]-bw-[8-4]-UsM²-(40)-5s5-UsM-h35, Jouhe, Jura, France

And while browsing at all of those, I realized I got at least a dozen of 13° halos, with at least one with the Moon. Which could make a post after this one, for the record.

And a last one, not for the 28d spotting, but only because I like it a lot:

2021-05-23au24-[22h52à02h56]-bw-(152)-6s6-UsM-2s2-blr-UsM
Sharp odd radius halos with the Moon!, Jouhe, Jura, France

Now, a couple hours after starting this post, I think I may go get some rest ;-).

Greetings from France.
Nicolas R.

Time Machine: High Cloud Hastings Arc in China, 2012.02.22

The Hastings arc is among the rarest of all halos, even more so in high clouds. On Feb 22, 2012, XU Guodong was blessed with an outstanding display in Mohe, and became possibly the world's very first person to photograph a high cloud Hastings arc.

The display started in the morning and lasted for at least two hours till noon. XU happened to be on a road trip thus unable to document the event continuously from a fixed location. Most of his photos were taken at two stages of the display, when the sun was at around 15° and 22° respectively.

During the first stage, the typical sun-side Parry elements such as the Helic arc and Tape arcs were not particularly strong. However, the Hastings arc was fairly prominent and very easy to distinguish in unprocessed images. Had XU been equipped with the necessary halo knowledge, he would've recognize the arc at the scene with naked eyes.

Early stage of the display when the sun was at around 15°. 4-frame mosaic. Slightly enhanced. See if you can spot the Hastings arc.

Background subtracted version of the mosaic. The Hastings arc stands out nicely.

The original image to illustrate how prominent the Hastings was.

The display remained strong as the sun rose to 22° elevation, when XU made the second stop of his road trip. At this stage the Tape arcs improved a bit while the Helic arc disappeared. The Hastings arc, together with the Wegner arc, somewhat weakened but was still easily discernible in unprocessed images.

2-image mosaic. Slightly enhanced. Sun at around 22°.

Background subtracted version. Though weaker than during the first stage, the Hastings extends further towards the sun.

While the sky around the sun was jam-packed with great stuff, the opposite side was also very busy. The highlight absolutely goes to the loop-shaped Tricker arc. XU was very impressed by how the loop gradually shrinks in size as the sun rises.

Tricker arc (probably some Greenler and Trankle too) during XU's first stop. Sun at 15°.

Tricker arc during XU's second stop. 3-image mosaic. Sun at 22°. Note how the faint Subhelic arc goes above the 120° parhelia and then touches the upper end of the Tricker loop. The blue spot is quite strong too.

This display bears great significance in China's modern halo history. 10 years have passed and it still is unchallenged, and will likely remain so for a very long time.

Jia Hao

Odd radius display on sunset time, 2022-10-16 (Jouhe, France)

Often, when I see the clouds coming from west, I try to do a high cloud sunset to see if there is something to see (like sun pillar and sunvex halos).

this day, we had mosly contrails making here and there some ice halos from my position, but nothing unusual to catch the eye (furtive sundogs, 22° halos, upper tangent and maybe Lowitz buddies but too short in time to be exploitable) (Time-Lapse of part of the day in here, South-South-East Field of View). To find other halos at sunset, the exercice can be tricky, as the global backgroud turn progressivly to yellow then orange so the b-r rendering is more complicated, with adaptation to make in the last 30-45 mins before the end of sunset.
As I don't have automatized this, I find myself resigned to make one setting for the whole sequence to save time in my processings.
And sometimes, something catch my eye, as it did this last 16th of october, last year.
The three next images show 3 differents times of the event, with slightly different processings:

2022-10-16-[17h14à18h58]-NNW-bw-v1-[4-2]-UsM-(49)-5s5-histo-UsM-h20-h28?-h35

2022-10-16-[17h14à18h58]-NNW-bw-v2-[4-2]-UsM-(47)-7s7-UsM-histo

2022-10-16-[17h14à18h58]-NNW-bw-v2-[4-2]-UsM(56)-6s6-UsM-h28?-histo


If needed, I can provide the bw sequence, so you can see (as I do with VirtuaDub) the evolution of the display and distinguish the 28° halo with dynamic (back and forth) play on the sequence.

A sequence you will be able to see there (Version1 & Version2), but with the compression due to GoogleVideo. Again, all raw images are still in my possession, as I guess I might not be done with this display yet.

Sharp Lowitz & Parry display, in short time [2023-04-04]

Here are some nice ice halos at the passage of a particular layer of clouds, during a clear sky day (2023-04-04, from near Dole, Jura, France). This clouds layers gave an extraodinary sharp looking display of ice halos, as I rarely saw in 15 years of watching. I was then in the good spot at the right time, for this one. While I was taking care of my lawn, during a clear sky day, I saw some high altitude clouds coming from the north, and decided to take the bet I will have some ice halos, but I did not epected that kind of sharp halos. In all the below images, clouds are coming from the left (North-East).

On this first stack image, you can see the Wegener arc, with almost the part crossing the parhelic circle. There is also the 120° parhelion with reddish edge as well as on the circle.
Process is (as an example of how I do usually, for the image shown above,
named 2023-04-04-[14h57to15h37]-bw-[4-2]-UsM(11)-5s5-notrack-UsM.bmp):
→ B-R ( -bw ) rendering of all the images of the sequence ( -[14h57to15h37] ),
→ 11th stack ( (11) ) of the sequence with 4 images ( -[4 ),
→ then Unsharp mask on this stack ( -UsM ),
→ then a new stack (with Registax, without the track on the sun ( -notrack ))
→ of 5 ( -5s5 ) of last stacks (those ones taken every 2 images ( -2] ))
→ then one more Unsharp filter ( -UsM ) to end it.

Later, like 5-6 minutes later, the layer of clouds enter the 46° FoV from the sun, which gave the most impressive part of the display to me.

Here is one single image, with just B-R rendering (no UsM or what so ever).

Then 2 stack versions witht this image along with some before and after, to see more clearly the Lowitz & Parry display, (on the above one, we can see parts of 46° halo, but not in whiole, because of the hole in the clouds crossing the view... I guess)

and with the images when the clouds are on the side of the sun from my point of view. I even manage to watch clearly the circumscribed halo while i was cutting my lawn.
You can also see the left part of lower Parry arc tangent with the circumscribed halo.

A last part of the display, with clouds on the bottom left of the sun, to see the extension of the lower Lowitz and the extension of the left part of the Lower Parry, tangent to the circumscribed halo.
For this stack, a "min" function is applied during the stacking process, in order to keep the minimum value of each pixel while stacking, and try to make the black forms therefore the colored halos more visible.

A crop on the left sundog, to see the Lowitz crossing and the 2 Parry arcs.

I have not presented any colored versions, because of the heterogeneous form of the clouds mask the halos for this display.

Finally, a time-lapse of the display is available here, which a compilation of differents time-lapses (one for each processing type). From those images are extracted the previous posted here :
www.flickr.com/photos/gaukouphoto/52808574767/in/dateposted/

All images are taken with Canon EoS 6D + 8mm Samyang lens from my roof windows, South-South-East side.
Settings: 1/1000s, ISO100, f/9,4, 1 image every 12s.
Sun mean height is 47° at the time of the sequence.

Google Drive folder shared, with all the images presented here, and the time-lapse.
I still have all the raws of the sequence if needed too.

Odd Radius Display Including 13° Halo, Vilnius, Lithuania 18th March 2023

The display occurred on 18 of March and I observed it from Vilnius, Lithuania.

For the whole day, cirrostratus clouds covered the entire sky. The clouds were moving eastward and also sublimating.

I started observing at 10:25 EET. At that time there were already odd radius halos present: with the naked eye, you could definitely notice both the 9° and 18° halos.

At 11:45, only the 9° halo was present, and at 12:00 the odd radius halos disappeared. After that, and until around 17:00, there were a faint 22° halo and tangent arc visible.

I photographed the halos in raw format with a DSLR camera. After enhancing the images, a 35° halo became visible, but I was surprised the most to see a ring between 9° and 18° halos, which appeared to be a 13° halo. After sending the images to The Halo Vault, I got a confirmation about this from Nicolas Lefaudeux and the Halo Vault team.

Here are some pictures from the display, last two of them in the sequence were processed by Nicolas Lefaudeux:

(All images copyright Donatas Gražulis)

(Image processed by Nicolas Lefaudeux)

(Image processed by Nicolas Lefaudeux)

A similar feature appears in an older photograph that I took on 25 of June 2019. This is the only photo from that day that this appears in; it was taken with a phone:

- Donatas Gražulis