|Each frame of animation covers ten minutes|
Tuesday, 21 November 2017
Monday, 30 October 2017
It was a weak odd-radius display which contained not only familiar pyramidal halos with radii of 9, 20, 24 and 35 degrees, but also a mysterious 13° halo! You can notice this diffuse 13° ring between 9° and 20° halos on the image above. You can also notice that the 20° halo is brighter than the 22°. The 35° halo is clearly visible on the image below.
With the naked eye only parhelia were visible during the display. The display was short and lasted about an hour and a half.
Monday, 23 October 2017
Fog turned into diamond dust in an optimal range of -5 to -10° C. I photographed the display in the evening soon after dark, the first photo was taken 16:17. The fog lasted whole night and no doubt the show would have continued whole night too were not the guns shut down soon after 17h, finishing the party before it had even got going. Had there been until morning to play, I am sure wondrous things would have been possible. Actually, there would have been three more nights, as fog continued envelop the city pretty much constantly for three more days and nights.
In the image above — and less clearly in the one below — it looks as if instead of "subanthelic 46° supralateral arc" there is more a "subanthelic cza". If so, that would be just a segment of sub-Kern, but it has an unusual location as we are used for sub-Kerns placing most of their weight at lateral locations with an intensity minimum directly above the subanthelic point. Simulations offer a solution, however: if, instead of plate oriented crystals, Parry oriented crystals of triangularish shape are used, a sub-Kern segment is born that is centered over the subanthelic point and looks like a kind of "subanthelic cza". Allow the crystals to rotate a bit and a halo segment much in the liking of what appears to appear in the photo is formed. As a rudimentary demonstration, below are further simulations with increasing rotation of the column shaped triangularish crystals, showing how the sub-Kern turns into a "subanthelic 46° supralateral arc" (ray numbers have been increased with increasing rotation to keep simulations of roughly the same intensity). Parameter file is given at the bottom.
Wednesday, 18 October 2017
|Every frame of animation is stack which covers 2,5 min. Colored version is here|
-well defined upper and middle Lowitz arcs (1) and possible lower Lowitz arc (2)
-part of helic arc (3)
-supralateral Tape arc (4)
Tuesday, 10 October 2017
This display came into existence suddenly, when in the morning sun came out from behind a clear cut edge of a receding cloud area. Some points:
- Ounasvaara arc in a solar display
- There is a kind of extension to the Ounasvaara arc which makes it drop shaped. The extension is responsible for the narrow end of the drop near the helic arc. It seems to be present also in the first Ounasvaara arc display. It's caused by the same raypaths as Ounasvaara arc, but with an added basal face reflection.
- 120° arcs. Simulations say they are formed in Lowitz oriented crystals. The halo is not centered on 120° parhelia: it lies along a circle of 60 degree radius centered on the subanthelic point. It is made by raypaths that in plate oriented crystals give 120° parhelia and sub-120° parhelia.
- An uppervex Hastings in solar display. All the others – the spotlight ones – are indirect detections, because the lamp has always been at an elevation where Wegener and Hastings overlap.
- Helic arc is brighter than subanthelic arc. I could simulate this by lengthening the Parry crystals, but then the simulation went wrong in other ways too much. If we can't get this right, it kinda tells me we don't understand this display. I was told that I probably regret of not taking a crystal sample. It had not occurred to me, but once I was reminded, it was obvious that I should. In the simulation no column shaped crystals were used. It would have been of interest to see whether the crystal sample concurred.
|This version was worked by Nicolas Lefaudeux|
The display occurred at around -17° C. You don't expect a major display at such temps in Finland. But sometimes they do occur, like was the case with Mikkilä's Kern display in 2007. Low supersaturations were in my mind the key here. They were low because the night was cloudy and thus the diamond dust could not have spawned before the morning when it started clearing up. And at that point, with the sun above horizon at such late time in the season, the air was not getting so much colder as for supersaturations to increase to the point of crapping the display (which is the usual scenario).
This post was modified on 15 Oct 2017 to replace the simulation with a new one. It has labels added to mark some of the features that seem to appear in the photos (sorry for the degree numbers having placed at the end of halo names, there is some glitch in Photoshop which forces this). Also, the parameter file was replaced becase I adjusted the parameters of the column oriented population a bit, increasing crystal h/d from 0.5 to 0.8 and making it a little more triangular. This more burned more fine grained simulation has gained features that are not seen in the images. Possibly with a better camera some of these could have been dug out from the display.
The post was further modified on 21. Oct by adding "originals" of the stacks.
|A singe frame from the very beginning of the series (added 11 Oct. 2017)|
|"Originals" of the stacks.|
Sunday, 1 October 2017
Here is the last post in the series. High sun stuff (only turned upside down). A "subhelic 46° infralateral arc" is visible on both sides of the subsun in the above image. Below are two relevant simulations (for 52 degree elevation), an arrow marks the halo. Crystal parameters, given further below, are identical for both simulations.
Saturday, 30 September 2017
Opposite to the lamp I could see something that thus far has appeared for me only in simulations: diffuse arcs extending all the way from the anthelic point to the subanthelic point. The effect is not that impressive in photos. Neither is the anthelion which really caught my attention: an anthelion formed against the ground in just few meters of air space. In the image above I had tilted the camera sideways so that it is not aligned with the central column of the tripod. This makes the shadow in the middle of the arcs less disturbing. In the image below, taken earlier, I had not yet done this move and there is a more prominent shadow. The image above is a bit spoiled because of spotlight light getting in from the viewfinder. I thought the camera was broken and bought a new one two days later... On one night in the beginning of January Mikkilä called while I was out photographing at around -35° C (-31° F) temps, and he told it was about light leaking. I didn't buy it, having a false memory of the effect appearing also when I shot towards the lamp. In the end it had to dawn that Mikkilä was right and also a feeling (maybe false too) that I must have known this thing in the past but my brain had buried it too deep by now.
So, where was I... yes, of some interest in these photos is the blue edge of the diffuse arc (the 3157 type).
Below are two more shots showing the anomalous Hastgener. These stages of the display are not really that poor (see part II), was I too hasty to make that connection? (Somehow I succeeded in not seeing these photos when writing the part II even if they were ready made in the same folder). Notice the left side subparhelion which seems tilted in the first image which is a single frame. The breeze makes localized, passing disturbances in crystals' orientation and can cause effects like this. At least that's what I seem to think now, but who knows if it is true. Anyway, I think there is a frame from stacking series from one other display where the other subparhelion is completely missing.