Moilanen arc without Parry or tangent arc

Here is an example of Moilanen arc with not even a hint of Parry or tangent arc. However, unlike in the previous post photo, there might be a suggestion of parhelia here. If there occurs a display where Moilanen arc is present with halos from purely random orientation only, one might easily distinguish from the crystal sample the crystals that would orient and make Moilanen arc.

The photo was taken by Marko Mikkilä on 15 January 2009 in Sievi.

Moilanen arc without plate arcs

This recently seen display, although not a bright one, highlights an important issue. There is the Moilanen arc but no plate arcs. "Not the slightest hint for circumzenith arc or sundogs. Absolutely nothing", writes Bertram Radelow, who photographed the display in Davos, Swizerland (air temp. -5°C, sun elevation 9°).

Thus, the crystal wedge angle that makes the Moilanen arc does not seem to occur in plate crystals. Column oriented crystals seem to also be out of question, because in simulations for one thing this orientation would make also lower Moilanen arc, which has not been observed yet. And if we assume that some of the columns or plates take Parry orientation, it makes sense to conclude that Parry crystals are neither the answer.

So, it feels like Moilanen arc crystal makes no other halos at all, and finding the crystals from crystal samples should be easy. But we have looked at many samples already and there has never been anything peculiar occuring in great enought numbers to name as a suspect. It is also interesting that Moilanen arc has not been seen alone yet, which could imply that its crystal after all makes other halos.

It is mysterious, but one day somebody is bound to take those desicive photos. Displays that have common halos only from one crystal orientation (such as here) are of course the best ones to look for the crystal.

Upper Lowitz arc

Glenn Wolford photographed this display on November 9 in Syracuse, N.Y., U.S.A. The noteworthy feature is the upper Lowitz arc from Parry-Lowitz orientation. Click on the photo for simulation. Lowitz crystal tilts in the simulation are 13 degrees and sun elevation 30 degrees. Simulations and crystal figures from Jukka Ruoskanen's software. See also another photo ( 1 ).

4th Elliptical halo!! Yeah baby woot woot woot!!!

While staying with relatives down in Bedford Indiana, one morning before we left to French Lick Casino I saw a large field of AC clouds slowly moving out of the area and I know AC clouds means elliptical halos. I looked up and saw the trailing edge of the clouds nearing the sun and I noticed they were forming virga sheets and as it drew nearer I took the gamble to watch. As the sun came into view I saw a diffuse sunpillar form and it later on got more defined and I watched as a small crescent of light formed in the pillar and it coalesed into an elliptical halo! Throughout the duration I could only see one ellipse and it was quite bright and well defined. I only need two more to tie Mika Sillanpaa's record. Look out Mika I need two more observations to tie your record and who knows I could beat it. I will gamble with halos not at slot machines at least I won't loose money with halos. ( 1 ).

Text: Michael Ellestad

Sub-120° parhelion photographed

Starting from the 1970's we have seen numerous photos of subparhelic circle opposite to the sun and it is a little wonder that sub-120° parhelion has never been observed from an airplane. Even the sub-Liljequist parhelion, of which formation is sensitive to crystal shape deviations from regular hexagon, and which from that point of view should be rarer than sub-120° parhelion, has been photographed a couple of times.

Well, given enough time, things are bound to change. On 31 July this year sub-120° parhelion was finally photographed. The man behind the camera, Tomas Trzicky, was on a return trip from watching a total sun eclipse in China. The halo display appeared on the last stretch of this trip, on its last hour, when the airplane started descending to Prague.

"I was really lucky - actually I was sitting in the isle during most of the flight, one member of our observing group left her window seat for a while, so I more or less routinely checked the white haze outside - and there it was :-)", tells Tomas.

The sub-120° parhelion was captured on two photos, click on the image above to see them. To the left from the halo is a patch of subparhelic circle, which most probably is sub-Liljequist parhelion. Further left, in other photos, subanthelion and faint diffuse anthelic arcs crossing it are also visible ( 1 ). The window was dirty and it was frosty, but it just adds to the magic of discovery.

These photos may explain why sub-120° parhelion has not been captured earlier. It occurs as an isolated white spot, without subparhelic circle crossing it. Unless being exceedingly bright, it must be easily missed. Most certainly sub-120° parhelion has occurred in all of the displays with subparhelic circle, because plates are the major contributor to subparhelic circle intensity. Subparhelic circle made solely by Parry orientation is more of a theoretical consideration, and columns do not make subparhelic circle at all.

Sub-120° parhelion has been photographed once earlier in spotlight beam in diamond dust ( 2 ), but Tomas's "old school" observation is of course the true discovery. See also Les Cowley's report ( 3 ) on the case.

New halo from spotlight beam

It's been before our noses for a year already ( 1 ): the weak colored arc reaching far outside the 46° halo in the display observed on the night of 5/6 November 2008 in Rovaniemi. I have thought of it as some sort of 46° supralateral arc extension below the horizon. But something has not felt quite right with that and I finally decided to run a simulation.

The halo arises in column crystals from 3-5-1 and 3-6-1 raypaths ( 2 ). Thus it is not 46° supralateral arc. Rather, these raypaths make it a reflection of 46° supralateral arc. If circumnadir arc had been visible in the display, this halo would have been tangent to it ( 3 ) similarly as normal 46° supralateral arc is tangent to circumzenith arc.

The simulation above was made with column and random oriented crystals. Crystals towards triangular shape seemed to provide best overall fit with the photo. Light source elevation for the simulation was -11.5 degrees. The simulation on the right is filtered, showing some common halos together with the new halo arc.

What should we call this? Reflected (46°) supralateral arc or sub(-46°) supralateral arc? If we were to choose the former, the "Ounasvaara arc" ( 4 ) which arises from similar raypath (8-4-1) in Parry crystals, could be then called reflected (46°) Parry supralateral arc.

Simulations and crystal raypath figures are from Jukka Ruoskanen's software.

Blue circle and blue spot

These simulations show the relation of blue circle (from random crystals) and blue spot (from oriented crystals). Blue spot on parhelic circle occurs where blue circle crosses it. The blue circle itself has a radius of 64°, as Ágnes Kiricsi has pointed out, and it is centered around the subanthelic point. Sun elevations in the simulations are 10°, 20° and 31°. When sun is higher than 32°, blue spot is no more seen. Simulations are made with Jukka Ruoskanen's software.