Diamond dust season is about to begin, the hissing of guns at the Ruka resort may be heard already at the end of September. To get in the spirit, let's reach into the drawer and grab this display which appeared on the night of 7/8 February 2017 in Rovaniemi. At first it was bog-standard plate with CNA, sub-120, and sub-Lilje / subparhelic circle patch opposite to the lamp, but then it changed, giving these long subparhelic arcs. The lamp sits at the usual ~5 degrees below the horizon. The location is Sieriaapa bog some 6 km east from the ski center. This is the direction where the diamond dust most often heads to, guided by the prevailing wind and topography.
Friday, 18 September 2020
Friday, 4 September 2020
Jiří Kaňovský from Černotín, Czech Republic observed three separate halo complexes this August.
August 2nd, 2020 – bright odd radius halos
I (Jiří Kaňovský) was visiting my aunt when I’ve noticed a halo making cirrostratus cloud shield. It was obvious that what I saw were not classical halos, but odd radii ones. I was able to observe 9°, 18°, 20°, 22°, 23°, 24° and 35° halos. Near the end of the observation, a bright 23° parhelion joined the party.
August 10th, 2020 – classic halos with a twist
These halos were observed due to an extensive cirrus/cirrostratus cumulonimbogenitus shield from a previous thunderstorm activity. At the evening hours, some of the cirrus clouds began to sublimate. Among the classic halos like 22° halo, UTA, CZA, SLA and 22° parhelion, later image stacking revealed a bright spot near supposed 9° column arcs and a 24° halo or a 24° column arc as well.
August 24th, 2020 – almost invisible uppercave Parry
There was a surprise 14 days later in the form of a weak but nice halo complex. A 22° halo, parhelions, weak UTA and CZA were observed. Later image processing revealed a weak uppercave Parry and a hint of a supralateral arc.
All these observations are a part of an endeavour to bring an old project back to life – the Czech HOP (Halo Observation Project). After 10 years of inactivity, multiple people are joining again to work on the project so it could be a place for amateurs and “professionals” alike where they can share their photos of observed complexes.
Saturday, 27 June 2020
Wednesday, 17 June 2020
|© HUANG Qian, shown with permission. Single exposure.|
|© ZHOU Ling, shown with permission. Single exposure.|
Annotated version as follows:
The intensity of the display rivals the 2016 Chengdu display as the 28° arcs stand out even in smartphone photos above. 20°, 24° and 35° plate arcs in the photos are also quite well defined.
Unfortunately, like previous displays, no other exotic arcs are found in the photos we received from the community.
Now that we have a great and early start of the season, let's hope for more great stuff to come.
Monday, 15 June 2020
Friday, 12 June 2020
Wednesday, 10 June 2020
Only three days before the low-sun odd radius display ( http://www.thehalovault.org/2020/06/odd-radius-display-at-low-sun-in.html ), I observed a brief but intense display that included well-defined suncave Parry arc as the visual highlight. Shown above are the two 50-frame stacks that I managed to extract out of the display. Both cover five minutes and they are separated by another five-minute interval during which I was too busy to collect data. Solar elevation is 26° in the first (top panels) and 25° in the second (bottom).
Applying the usual background-subtraction on the average stacks (on the left) makes helic, Tape, and Lowitz arcs all stand out reasonably well in addition to the circumzenithal, supralateral, upper tangent, and Parry arcs. As the simulation (HaloPoint 2.0) in the top right-hand-side corner demonstrates, the anthelic arc close to the far left edge is Hastings rather than Wegener. Kern arc only appears in the second stack, coming out the clearest in the middle panel. Here, blue-minus-red colour subtraction is applied on top of the background subtraction. The bottom right corner is the average 50-frame stack without further processing.
Sunday, 7 June 2020
I made different versions of the stack that were adjusted with Photoshop. They are shown here in non-mirrored - mirrored pairs:
pair 1: double usm + HDR Toning
pair 2: background removal (BGR) + HDR Toning
pair 3: background removal (BGR) + HDR Toning. BGR with different values than for pair 2
pair 4: BR + BGR
It seems this was an odd radius display. A weak 24 halo appears to show up in pairs 2 and 4. Images also seem to have 35 halo. The most interesting thing, however, is the feature that looks like 28 halo. I measured it from BR image using a star field photo and the inner edge was at 27 plus some. Also, I measured the apparent 35 halo and got 35 degrees.
The night's lowest temp was at the sunrise, -7 C at the airport. Windy, clear skies overnight. Not quite the foggy, calm conditions that I have previously associated with surface odd radii. Unfortunately I forgot to take the microscope as I headed for the lake with bicycle. Realized this pretty soon after leaving my place, but didn't turn back.
This is not the first suspected surface 28 halo. On 7 April 2012 Jari Luomanen and I photographed on a small lake in Eastern Finland an odd radius display that by all looks has a 28 halo:
Friday, 5 June 2020
Hérincs did not photograph the crystals, but simulations that I made at the time suggested a possibility that crystals are all oriented exactly in the same way. This time we got the crystals under a microscope – first by Martikainen – and a wonderful landscape was revealed in which crystals were packed next to each other, and indeed locked in the same exact orientation. Below is one typical photo that I took.
The displays are formed when deposited rain water freezes over the night. In Hérincs case it was ponds that froze, in Tampere it was water freezing on lake ice. Martikainen also successfully performed his own freezing experiments in his backyard. I followed suit, this video shows one of these home made ice plates with a Hérincs type display.
On that plate we see distant spots, both white and colored. Some move along roughly horizontal plane as the plate is rotated, while others are more or less stationary. Below is a freeze frame from the video with some stationary spots marked.
The stationary spots could be seen as formed from raypaths similar to sub-120 parhelion and rotated subparhelion (120 degrees rotated subparhelion). The moving spots, in turn, would be made by raypaths similar to subparhelic circle. Below is an animation where azimuthally locked plate oriented crystal has been rotated in 1 degree steps. Similarities with what is going on in the rotated ice plate are apparent. The rotated subparhelion actually move too, but not much, similar to the normal subparhelion.
Concerning the colored moving spots (not including the subparhelia and rotated subparhelia), in simulations many of them arise from three-hit prism face ray paths plus basal face reflection. In Parry oriented crystals such ray paths make reflected Hastings arcs when the inner prism face reflection is from horizontal basal face. Below is a stacked segment of the video demonstrating how the moving spots draw out subparhelic circle when the plate is rotated, i.e. when the crystal is allowed to rotate azimuthally.
The distant white spots and colored subparhelia were seen also on lake ice as shown by this video. Below is a photo of the same situation. Both the colored and white spots were blindingly bright, you couldn't look at them at all, a heavy underexposure was necessary for the colors to not wash out.
In simulations cna spot can be off-set by tilting the crystal, as demonstrated below. The other spot is made by exactly horizontally oriented plates, the other one by plates tilted 10 degrees. So it looks like there are crystals on this particular patch at two tilting angles.
The white arcs are really parhelic circles. However, the column oriented crystals go only as far as explaining the geometry. As far as the microscopic examinations are believed, the crystals are always locked in the same exact orientation in each patch, and thus should only be able to make spots, not arcs (although it must be admitted that at least two separate orientations seems to be possible as evidenced by the doubled cna spot above). But I won’t say no more about this, as Petri Martikainen has been studying the problem, and will hopefully write his own post in the future.
In the simulations above it is seen that also a moving white spot from plate population is aligned with the white arc. Here is a video showing such white spots on white arcs in a real display. Below is a still frame.
The simulations must be taken only as a rough guide. Simulation software assume halos formed in singular crystals floating in the air, on the ice plate the situation is very different. The crystals are packed next to each other and the attachment of the crystals incapacitates some faces. Then there is the inner reflection from the bottom of the ice plate to be considered. It could be that a multiple scattering formation might better describe some features. Moreover, we have seen under the microscope some scattered crystals rising above the basic level of the packed crystals. These may explain features that look like they are consisting of separate crystals rather than being made of solid light. The circumnadir spot, for example, is in many displays visibly made of individual crystals.
I throw in also some simulations from randomly oriented crystals that show the area where any given raypath can make a halo spot in strictly regimented crystals if the orientation of the crystals only is right to light up the particular spot. I haven't covered it all, for example the rotated subparhelion type raypaths are not simulated.
Well, I have been haphazardly touching some issues here. This stuff is way over my competence. There are tons details that I did not address, tons of open questions. Hopefully more capable guys will step in and explain it all in a coherent manner.
Let's end with some practical tips for those wanting to get their share of these displays. What you are looking for is a mosaic ice surface with fleeting reflections everywhere as you walk on it. The mosaic comes about because the crystal orientations are identical only in small patches.
To see these displays, you need lean really close to the surface: in my videos, the camera lens may be just a few centimeters above the surface and is occasionally even grazing it. From standing height only subparhelia and perhaps weak sub-120 parhelia are created over the patch mosaic.
The backyard versions I made by freezing water in a kind of plastic tray and metallic oven plate. In the metallic plate I never got a good display, so this may be something to avoid. You may want to remove the ice plate from the tray for various reasons, so anything that helps to do this without breaking the ice plate is good.The plastic tray that I used was slightly pliable, bending it detached the ice plate quite handily from it.