Double CZA spotted in Czechia

 

At the 19th of January 2021, Jarda Fous (the most active diamond dust observer in Czechia as of now) was planning a trip to Boží dar at Ore mountains where he managed to capture a doubled CZA. Temperature was oscillating between -10 and -8 degrees Celsius, low stratus clouds were hanging atop of the Neklid ski slope and snow guns were at full blast.
GPS coordinates are as follows: N 50°24.24398', E 12°56.31133'
All pictures were taken between 09:15 and 11:30 UTC. Doubled CZA was observed at 10:55 UTC. Jarda used Nikon D7200 with 8mm fisheye lens for wide angle images and Nikkor 18-105 f/3,5-5,6G ED VR for details.

At first, ice fog with low quality ice crystals only managed to conjure up a 22 degree halo with pahelia.

Later a whole myriad of halos developed - among the 22 degree halo and parhelia, a parhelic circle, colourful CZA with aforementioned doubling, 120 degree parhelia, upper tangent arc with uppercave Parry, upper Tape arcs, supralateral arc, 46 degree halo, Moilanen arc and helic arc could be seen as well. Kern was not observed, nor does it show on pictures and stacks.

Looking forward to all of your comments and remarks.

 

A clear 28° halo on snow surface

Sunshine has been a rare phenomenon in Finland this winter. On 16th January, the sky was finally clear and temperature had dropped to -25°C, so I headed to a nearby lakeshore to observe possible surface halos. There were indeed 22° and 46° halos visible on the snow, so I took a set of 335 photos by moving back and forth of a 50 m stretch of a road along the lake. The mirrored stack revealed that this was an odd radius display with 18°, 20°, 23° and 24° halos present. An interesting feature was that 22° and 23° halos were equally strong and well defined in the stack.

Two days later I got another chance to photograph surface halos in the same place. The temperature was -8°C. Only a modest 22° halo with some bright glints outside it were visible to naked eye, so I did not expect much from the stack. Nevertheless, I took 147 photos. This time the mirrored stack looked even better than two days ago: a strong 22° halo accompanied by several odd radius halos, including a clear 28° ring.

A comparison with the previous display (limited by blue frame in the photograph below) provided another surprise: the prominent ”22° halo” was in fact a 23° halo and 22° halo was missing. So this was an odd radius display with 18°, 20°, 23°, 24°, 28°, 35° and 46° halos. Although there are not many observations of 28° halo on surface yet, it seems probable that it is not as rare as has been thought. This gives some hope that a crystal sample can be obtained one day.

The strong 23° halo and the absence of 22° halo in this surface display is interesting. It means that the usual ”22° halo” on snow may in some rare instances be something else than it looks, but it is not easy to detect such cases from the abundance of common 22° halos. For example, the first observation of surface 28° halo on 7 April 2012 by Jari Luomanen and Marko Riikonen looks rather similar as the current one, and it may perhaps contain 23° halo instead of 22° halo (yellow frame below, photo Jari Luomanen). Although all photos in this collage were taken with Samyang 8 mm fisheye lens, the result should be viewed with caution due to the robust alignment.

Parhelic circle without parhelia

 

The two displays above have both a faint parhelic circle, but the one on the right has a notable omission: there are no parhelia. These photos (12 and 7 frame stacks of about 2 minute exposures) were taken in Rovaniemi on the night of 3/4 January, in different locations and 3 hours between them. In Taivaanvahti less heavily edited versions are shown.

With the moon at 33 degree elevation in the right hand image – which was the latter shot of the two – the parhelia should be far enough outside the 22° halo to avoid being masked by it (even with its puffed up form). It seems to me the only explanation for this solitary parhelic circle is to assume special plate oriented crystals that allow only for an external reflection. Below are two simulations to illustrate this. The simulation on the left has the hits limit at 100 for both plate and random populations, on the right for the plate population only one hit was allowed – an external reflection. This gives the parhelic circle without parhelia.

Should this be the correct explanation, one may still ask why the restriction to external reflection applies only to plate oriented and not to random oriented crystals. Maybe there is something else going on here that has not occurred to me. In 2017 my camera captured a similar case.

EDIT 25 Jan: Added above a third simulation to imitate a buffed up 22° halo. It has 22, 23, 24° halos of about equal brightness. The parhelia are still outside of this broad ring.

I include also two spotlight views from this night. They were taken before I photographed the lunar display in the left hand image. Odd radius halos are visible, 24° plate arcs and 35° halo. Temperature was -20 C. Some more photos are shown in Taivaanvahti. The apparent 9° stuff in the right hand lunar photo is probably an artefact, the appearance of these features seemed to depend on the values of image enhancement.

 

The camera is Canon 40D, the same one that I have been using since the start of the season. It is gone now, it broke when I was ready to photograph a great plate display the another night. Even if this camera leaves much to be desired, such as dynamic range, the line noise, not having an integrated intervalometer, it is quite good where artefacts are concerned. Serious color banding artefacts are not a problem with this body.

Streetlight halos in Lahti, 17 January 2021

After having spotted reasonably thick diamond dust from a distance while taking the sheepdog out, I spent good few hours outdoors observing and photographing divergent light halos in the surroundings of Pikku Vesijärvi park in Lahti, Southern Finland. As is generally the case in urban areas in this country, there were many lamp posts to choose from, but few of them provided any sort of darkish background for serious observing. Much of my time went into finding good spots and chasing the best swarm of ice crystals while also trying to avoid crowds of people. I found quite good conditions in the harbour area: very quiet this time of year but the lights along a boulevard are being kept switched on. For the best results I chose a lamp at the far end of the boulevard with nothing but a lake in the background.

Based on my visual observations, much of the display was dominated by singly-oriented column crystals with additional contributions from plate crystals at times. Temperature at the nearby Sopenkorpi weather station varied in the range of -7°C to -9°C.

The photo above is an unsharp-masked stack that consists of 10 individual 30 second exposures and covers some 10 minutes at around 9:15 pm local time. My interpretation of the photo is as follows:

• The Y-shape above the lamp is the divergent light version of the upper tangent arc.
• The horizontal arcs to the left and right of the lamp are the divergent parhelia.
• The vertical line pointing to the top of the frame is the superlamp.
• The curved lines pointing approximately to 11 and 1 positions from the lamp are the superparhelia.
• Of the pair of arcs at 10 and 2 positions from the lamp, the one that goes above the other is the helic arc.
  

Some uncertainty remains on the identification of the arc immediately below the helic arc. Nicolas Lefaudeux (personal communication) has kindly offered two possible explanations that are both supported by his atlas of divergent light halo simulations: Firstly, corresponding to a hypothesis of singly-oriented column crystals (and the interpretation that the Y-shaped arc indeed is the upper tangent arc), this arc would be the divergent light version of Wegener arc. For the other possibility, we replace the idea of singly-oriented column crystals by Parry orientation, which means that the Y-shape would come from the upper sunvex Parry arc. The oblique arc below the helic would then be divergent light Hastings arc, potentially with a contribution from Tape arc, as the two overlap in the simulation.

The relatively strong presence of helic arc provides some support to the Hastings/Tape option. On the other hand, from what I could see visually for the most parts of the display, I would feel uneasy to exclude the presence of singly-oriented crystals altogether. The smart-phone photo below illustrates my point: the sparkles above the floodlight make no resemblance to Parry, but instead look much like upper tangent arc. Therefore I feel that at least part of the intensity is likely to come from the Wegener option.

Subparhelia on hood of car on 1-10-21

 Got home from work and being it was cold I ten to want to go over to my dad's car and look for halos in the frost crystals. I went over to look and saw some beautiful subparhelia along with subparhelic circle as well. I removed the lens off of my LED flashlight here is what I got in the photos. I also got a weak sub-CZA but it was to weak to be photographed