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An occurrence of anomalous Hastings/Wegener

45820_e662e364876303651b6b4fbc10d66a83The image above shows what looks like a patch of Wegener or Hastings on top of the 22° halo. But instead of having the usual horizontal curvature, it is bending slightly downwards. Because of the view angle, though, the effect is not as evident as it could be. Anyway, if it were standard Hastings or Wegener, it would curve steeper up in the photo.

We have no idea how it formed, our attempts at simulating have come up empty-handed. The display was seen in Rovaniemi on 23 November, 2015, and the arc appeared at a stage when the display was still progressing to reach its peak.

Nine days later, in the beginning of December, we got another, better sighting, suggesting it is not exceedingly rare. In a similar manner, it did not occur when the display was at its best, but when the display was undergoing a momentary low. We will post about this later.

Jarmo Moilanen, Marko Mikkilä, Marko Riikonen

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Segments of a circular halo from Moilanen crystals observed Nov 27th, 2015, on Mt. Klínovec (CZ)

During last year’s meeting of the German halo observers, we decided to drive on top of Mt. Klínovec (Keilberg) after dinner on Nov 27th, 2015. We used the car headlights as light sources for glittering diamond dust displays from ice crystals within the first few meters above the ground, while facing temperatures in the range of –5 °C to –6 °C at wind speeds of 5 – 6 bft. Simultaneously, there appeared a non-glittering, but slowly changing moon halo display in crystals higher up, including a “traditional” Moilanen arc:

2015_11_27_2003_30s_imgp3912_usm(20:03 CET, unsharp masked, for the original image see here)

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All rare halos are missing in this spotlight display, but why?

The mystery deepens. In two previous posts we wondered why some displays are great in their column orientation halos even though the crystals have well caved ends. Here we show a case that appeared on November 22, 2015 in Rovaniemi, where crystals seem not much different, yet rare halos requiring basal faces are completely absent. Even the 46° supralateral arc gives just a whiff. Poor crystal orientations can’t explain the absence of rare halos as the tanget arc is quite sharp. Had we known only about this display, we would be quite happy to explain with cavities, but knowing about the other displays, it is quite puzzling.

Marko Mikkilä, Jarmo Moilanen, Marko Riikonen

45794_8a0663ee260d24f848f7e4b65dd40b9c45794_9b8acdc9531b9f047262a12e38e0f846

 

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Solar diamond dust display with 87° arc

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A stack of 40 photos. An average stack has been combined with maximum stack to show the crystal glitter of the 87° arc. The photos were taken during ~2 minutes. Sun movement has not been accounted for.

The diamond dust season is soon to arrive in Finland and it is time to wipe the dust off the equipment. In a meanwhile, here is the last winter’s starter for Rovaniemi, on October 30. The temperature during the display was -5° C, a quaranteed number for great stuff.

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AKM’s Circumhorizon Arc Seasons 2015 & 2016

Starting in 2015, inscribed members of AKM’s forum were invited to post photographically documented circumhorizon arcs (CHAs). The reach of this mostly German language website and the geographical limit for CHAs at ca. 55° N, restricted the incoming reports to Germany and its surroundings to latitudes between about 47° N and 52° N, in practice. The possible maximum solar elevation angle for these places varies between 61° and 67°, thus not quite attaining the brightness optimum for CHAs, which comes at a little less than 68°. [1]

On the other hand, it has been found that some of the aesthetically more pleasing CHA apparitions occur at 65° solar elevation or less. This is because the CHA gets wider then, therefore increasing the dispersion of spectral colors. Such CHAs are also situated less high in the sky, where they are more easily seen unintentionally. Also then, an interesting landscape in the foreground may add to the scene’s beauty.

The following table contains a summary for the 2015 and 2016 CHA observations. Observations on the same day have been included, if from different places and reported in the said forum or – in just two cases – directly communicated to this author. Chance findings of related CHAs in other public networks and oral reports solicited by an AKM posts are carried separately. For consistency, three CHAs seen in far-away places by a travelling AKM member were not included in the count. The last column contains the count of AKM’s systematic visual observers.

tabelle

It is clear, that the CHA campaigns for 2015 and 2016 were comparably successful, definitely surpassing the counts for any earlier year. The competitive character of a call for CHAs stipulated an increased time log from skilled observers and made them aware of quite inconspicuous CHAs. Although the meteoros.de forum boasts many hundreds of members, the number of those contributing CHAs, was quite low. The CHA reports for 2015 and 2016, respectively, were delivered by 15 and 19 observers, respectively, who lump together to just 26 different persons for both years. So every CHA reporter on the average had 2.3 specimens. Besides different personal noon-day observing options, the more southerly observers were favored, of course. The most successful six of them recorded 34 CHAs (58% of the grand total).

In concluding, some circumhorizon arc images from 2016 are duplicated from our forum. First place goes to a very nice spectrally pure example, seen June 15th at a solar elevation of 64.1o by Daniel Eggert near Neuburg (Danube).

Photo: Daniel Eggert
Photo: Daniel Eggert

The photo by Isabelle Klein (a) shows a CHA underneath a 22o circumscribed halo, as photographed from the Autobahn A1 near Hermeskeil nine days earlier, on June 6th, at a solar elevation of 63.4o. Unsharp masking of this shot shows an infralateral arc curving upwards from the CHA. Not shown here is the also present complete parhelic circle.

By contrast, Michael Großmann’s photo (b) from Aulendorf, taken June 18th at a solar elevation of 65.3o does not show any hints of a 22o halo.

On July 6th, Elmar Schmidt experienced a long-lasting CHA display in Heidelberg (c). The sky was uniformly covered with cirrus clouds, which washed out the contrast for the halo, which extends for more than 60o of azimuth. To show this better, two portrait oriented wide-angle photos, taken at solar elevation of 63.4o, were stitched together, therefore artificially broadening the circumscribed 22o halo disproportionately w.r. to the CHA.

Karl Kaiser in Schlägl, Austria, took his photo (d) of a delicately colored CHA on July 8th at a solar elevation angle of 63.4o.

[1]        E. Schmidt, A. Haußmann, C. Hinz, P. Zenko: Der Zirkumhorizontalbogen – Teil I: Auftreten und Häufigkeit, VdS-Journal, Nr. 53 (2015), S. 70

Author: Dr. Elmar Schmidt, Bad Schönborn, Germany

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Rare Subhorizontal Halos

I was flying from London back home to Berlin on September the 11th 2016 . The flight was operated by British Airways. The airplane was located above Hankensbüttel / Wittingen (DE, Niedersachsen) when I observed a bright subsun and some bringt subparhelia. The suns altitude was about 40° at this time. For this fact the halos appeared very steep below the horizon, which made it difficult to observe them.

In addition to the subsun and the left subparhelion, the sub parhelic circle was visible for some moments. It appeared in the shape of a bright tail of the subparhelion. But for some moments I could see the sub parhelic circle between them.

The following image was taken with a Samsung smartphone.

2016-09-11_unter-halo

According to the theory, the sub parhelic circle can be produced by horizontal oriented ice crystals. But the sub parhelic circle grows left and right from the subparhelia, so that there is actually a gap between the both subparhelia. During my observation from the airplane, the sub parhelic circle was visible between the both subparhelia. How is it possible?

2016-09-11_simulation2016-09-11_unter-halo_usmThe simulation software called “HaloSim” (L. Cowley & M. Schrieder) leads to a first clue. The sub parhelic circle between the subparhelia could only be simulated with the help of pretty flat Lowitz-oriented crystals. In addition, the simulation shows an “X” which is crossing each of the subparhelia. These are the reflected lowitz arcs or also knows as “Schulthess bows”. The bows are also visible in my picture from September the 11th 2016.

The 1th picture shows a simulation by HaloSim (L. Cowley & M. Schroeder). The 2nd picture was modified with the help of an unsharp mask to highlight some details.

The simulation shows also the 46° tangent arcs (EE52), also knows as 46° lowitz arcs. Especially the lower middle 46° tangent arc (EE52B) is standing out. However, I neither saw these bows nor I found them in my pictures. The reason for that is the fact that my attention was directed to the area near the subsun. Another reason may be the fact, that there were no halo active ice crystals in the higher air layers.

The simulation and the observation do match pretty well and are convincable, so that one can say, Lowitz-oriented crystals are responsible for the presented halo display.

2016-09-11_unter-halo_video-usm

This picture was stacked from a video file. The frames were aligned and modified with photoshop.

I want to thank Michael Großmann and Alexander Haußmann for helping me with the analysis.

Author: Andreas Möller, Berlin, Germany

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Experimental Demonstrations of Column Halos

Experimental Equipment | Photo: Michael Großmann

Did you ever think about showing in a practical way, how ice-crystal halos come to be? An individual halo like, e.g., a sundog is easy to demonstrate, but producing halo phenomena in such a way is more difficult, as a multitude of crystal shapes and orientations are involved.

Raypath sundog | Photo: Michael Großmann

In 2011, I committed myself to the task of generating halos in a darkened room by optomechanical devices, for which the term „halomators“ was coined. Any one of several models can hold an artificial crystal and make it rotate in certain ways. When light impinges on this crystal, different kinds of halos are produced by the possible reflective and refractive raypaths. By means of the so-called sky transform it can be shown that a single crystal produces the same kind of display in a laboratory environment as a multitude of such crystals in nature.

For the experiment shown here, a horizontally rotating column crystal was at first doubly oriented, then only singly.
In the beginning (with a rectangular face of the crystal staying in the horizontal plane of the rotation too) the Parry orientation tape halos very nicely showed, including the corresponding reflection halo like heliac arc, subhelic arc and the parhelic circle. When the crystal was made to rotate about its symmetry axis, the upper tangent arc also appeared.

Natural photographs, however, can show still more halos from oriented columns. This led me to further improve my halomators, for which my profession as an industry mechanic proved helpful. By 2016 I could document numerous other kinds of halos.

“Halomator IV”| Photo: Michael Großmann

The following images are stacks of photographs of halos obtained from singly and doubly oriented columns. They show the following types:

– upper tangent arc
– concave Parry arc
– convex Parry arc
– heliac arc
– subhelic arc
– subanthelic arc
– Tricker’s anthelic arc
– Wegener‘s anthelic arc
– Hasting’s arc
– parhelic circle

Remark: I had to use acrylic (PMMA) as a workable material for my crystals, which does not match the refractive index of ice. Therefore, most deflection angles change. Also, those refraction halos produced in ice by the 90° prism angle do not show at all, because of total internal reflection. (Ways out of this limitation are being investigated by other experimenters and myself, and will then possibly be reported.) Despite of these shortcomings, I found out in many demonstrations, that most people grasp the optics behind a certain halo much better than from a sketch or computer simulation.

Author: Michael Großmann, Bilfingen, Germany

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Presumed Reflection Subsun in Denmark

Bright and defined reflection subsun. Photo: Anders Falk Jensen

On June 5th, 2015, Anders Falk Jensen made a very interesting observation:

“It was very calm, no or very little wind. At 4.20-4.22 local time I observed a red upper pillar around 30 min’s before sunrise in altocumulus virga.

Later on the train at 5.40-5.48 local time, I observed a peculiar looking pillar in front of the altoculumus clouds, while travelling for 12 km from the town of Jelling through Gadbjerg to Give, Denmark. Sunrise had taken place approx. 60 min’s earlier. The solar elevation during the 8 minute observation increased from 5.4 to 6.5 degrees. The azimuth of the Sun changed from 57.1 to 58.6 degrees.

With these data, I later looked on a map and found the lakes Mossø and Skanderborg plus the Bay of Aarhus, located at distances between 44 and 68 km, suitable for providing the reflected sunlight. I then calculated the cloud height for the reflection to be at 2.5 to 3.5 km, appropriate for altocumulus clouds.

So, I believe that sunrays on this morning were reflected off the calm surface of these lakes, then reached ice crystal virga underneath the altocumulus, creating the phenomenon of a reflection subsun/pillar (which actually is like a subsun turned upside down). The sun was hidden by the clouds all the time, which is actually needed for this kind of observation, as a reflection subsun just about coincides with the sun. After years of observing such phenomena, I immediately knew, that this was something extraordinary. The irregularities seen might originate from minor water surface disturbances and the shape of the lake and surroundings. Also of interest are the vertical “pillar slices”. In some of my photos, weak reflection crepuscular rays are also visible.”

It is of note, that for the observation to hold its place as a halo, there must have been ice crystal clouds in about 3 km altitude in June. The ambient ground level temperature was circa 15 degrees centigrade according to the Danish Weather Office. A radiosonde analysis is not available any more from Denmark, but both Norderney in northern Germany and Stavanger in Norway reported rather warm temperatures at the altocumulus cloulds’ height, so this halo came as a surprise in them.

Further examples of reflection subsun: 1 – 2 – 3

Article about reflection subsun