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.

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: 123

Article about reflection subsun

Pyramidalhalo in Calgary, Canada

At about 3:16pm on May 4, 2016, with a sun elevation of 49 degrees, Alan Clark observed pyramidal halos from Calgary, Canada, showing a relatively wide 23deg halo, a distinct 9deg halo, and a hint of an 18.5deg component. A daytime maximum temperature of over 26°C on this day in Calgary broke long-term records. The within which The halo display was formed within cirrus cloud that preceded the arrival of a distinctive cold front.

Alan also produced RGB intensity scans from these halo photos, showing the correct colour separation, with red inner colouring for these halos.

Elliptical halos with small radii observed from Mt. Fichtelberg

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On April 22nd, 2016, I worked on Mt. Fichtelberg (1215 m above sea level) in the German Ore mountains. I noted several interesting phenomena in the sky. An upper air flow from southerly directions had brought in Saharan dust as indicated by a prominent ring of Bishop around the sun, which had already been visible since the day before. On the 22nd, aerosols produced a rather milky sky, with additional thin and high Altocumulus lenticularis clouds due to foehn from the south. These clouds showed a pronounced iridescence when coming close to the sun. This motivated me to investigate the sky in the proximity of the sun in more detail by using dark sunglasses, as it would have been a pity to miss these gorgeous colors.

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The 46° Lowitz arcs and their history

The common halo observer in Central Europe will associate the term “Lowitz arcs” with short segments below the parhelic circle which connect the parhelia and the 22° halo. These so-called “lower Lowitz arcs” were first documented by T. Lowitz in St. Petersburg in 1790. In 1911, A. Wegener pointed out the hypothesis that these arcs might be caused by plate crystals oscillating around their equilibrium position. This statement is recorded in the classical textbook by J.M. Perter and F.M. Exner [1]. In contrast this, R. Greenler postulated that plate crystals might perform full 360° rotations as they fall, referring to a note from R.A.R. Tricker from 1972 [2]. Even today it is still under discussion which kind of crystal motion does occur in nature, since the Lowitz arc simulations for both assumptions coincide in their celestial position and differ only in their intensity distribution [3]. A couple of years after Greenler´s theoretical predictions, the middle and upper Lowitz arcs were observed and photographed in nature, e.g. 1985 in Knau, Thuringia, East Germany [4], 1988 in Dover, Delaware, USA [5] and 1994 in Vaala, Finland [6]. These observations were, however, not inspired by theory, as the arcs were identified only afterwards by comparison with the simulations. In the records of the German “Sektion Halobeobachtungen“ and the later “Arbeitskreis Meteore e.V.“, the upper Lowitz arc was categorized as “unknown halo“ or “abnormal Parry arc“. E. Tränkle presented a simulation of this arc independent from Greenler in 1995 [4].

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November 1, 2014 – Lowitz phenomenon in Miesbach

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On November 1, 2014, Thomas Klein observed in Miesbach/Bavaria a halo phenomenon with multiple appearances. In the morning hours, only the standard halos 22°-ring, both parhelions, upper tangent arc and parry arc were visible. Right after lunch, the first phenomenon was observed in the centre of Miesbach. Beside the halos above, also rare halos were documented, an almost full parhelic arc, both 120° parhelions, left Liljequist parhelion, supralateral arc and cirumzenithal arc. Not be seen but documented on pictures were also helic arc and wegeners arc.

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Ice Fog Halo Phenomenon in Bremerhaven at the North Sea

An impressive ice fog halo phenomenon occurred in Bremerhaven at Northern Germany’s North Sea coast on 21 January 2016. It lasted from the morning into the early afternoon. To observe such a halo display in Germany is quite rare by itself, but to have it in ice fog directly at the relatively mild coast is certainly exceptional.

Visually I was able to document the following types of halos:
• 22° halo
• Both parhelions (extremely bright at times)
• Upper and Lower tangent arc
• Upper and Lower sun pillar
• Circumzenithal arc
• 46° halo
• Parhelic circle (near the sun and up to 90° to the sun’s right)
• Supralateral arc
• Parry arc
• Tricker’s anthelic arc

Image processing revealed the following halos:
• Heliac arc
• Moilanen arc (without snow gun!)

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Webcam Halos in the last winter season I

More and more ski areas install webcams with a very good image quality. They doesn’t show only the current weather situation, but sometimes also halos. Most interesting are the webcams at the mountain peaks, which also show halo types below the horizon.

Such an interesting halophenomenon recorded the webcam Nassfeld-Hermagor in Carinthia, Austria on 3rd January 2016.

This timelapse shows all halos on that day.

Particularly interesting is the image of 2 ‚o clock pm. In addition to the beautiful combination of Infralateral and Supralateral arcs (right) the 120° subparhelion is also recognizable.

1400

1400usmThe lower part of the Wegener anthelic arc is here faint visible. But even better it is seen at the 3 ‚o clock pm image, furthermore heliac arc and subparhelic circle.

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Such a halophenomenon had seen just a few of us in this characteristic.

Authors: Claudia Hinz, Kevin Förster, Andreas Möller

Making divergent subparhelia with spotlight

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Here is divergent light subparhelia flanking the pillar. Spotlight displays are classical displays with little divergenness involved. A way to create truly divergent halos with spotlight is to point it to the ground. The reflection from snow then acts as a divergent light source. Another way that might work is to cover the lamp glass with a layer of snow. That would be a shorter lasting solution, though, as the heat of the lamp will melt the snow.

Most spotlight halos are visibly formed of separate crystal glitter. Not the divergent parhelia. They are solid objects floating majestetically in the air. One feels humbled before their lofty heights, just as a lesser subject might feel in the presence of royalty.

Below is another photo of divergent subparhelia taken some hours later. And also a little lunar display from the same night, which was the 18/19 January night in Rovaniemi.

Jarmo Moilanen / Marko Riikonen

The hiding sub-120° parhelion

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Nothing out of the ordinary here. Just a plate display and its crystals. Visible are the usual folks: subcza, sub-Kern, sub-120° parhelion. The behaviour of the last one in spotlight displays is a little curious, though: while it comes out well in photos, visually it is cryptic. One has to run along the beam to see that ghostly spot of sub-120°. It is not made of big glitter like the sub-Liljequist parhelia – it does not seem to be made of much glitter at all, just faint diffuse spot of light.

Rovaniemi, in the morning hours of 19th January .

Jarmo Moilanen / Marko Riikonen

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