Circular halos of 12°-13° in radius are named “exotic” because they do not fit in the (nowadays) traditional sequence of well-documented halo radii from pyramidal ice crystals (9°, 18°, 20°, 22°, 23°, 24°, 35°, 46°). The first known photographs of such a halo were obtained at the South Pole, December 11th-12th, 1998, by Walter Tape, Jarmo Moilanen and Robert Greenler. Up to now, there are only few more (Michael Theusner, Bremerhaven, October 28th, 2012; Nicolas Lefaudeux, Paris, May 04th, 2014).
A simple diamond dust display that I photographed on the 6th of this month in Rovaniemi, shows above the Moilanen arc another, weaker V-shape. As I uploaded the photo on Taivaanvahti, I was not conscious of the effect, it caught the sharp eye of Panu Lahtinen and Reima Eresmaa who commented on it. Then some photo processing made it stand out more clearly. The version above was worked by Nicolas Lefaudeux. It is a stack of 13 images taken during 125 seconds.
In an earlier post we showed a photo of a weird downward curving patch of Wegener/Hastings. Here is another case that occurred 9 days later on December 2, 2015. This time we also got a nice comparison to normal “Wegstings” by superposing photos taken from the same camera position.
The 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
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:
(20:03 CET, unsharp masked, for the original image see here)
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.
On the night of 6/7 January we had this anticipation that something unusual will occur in the beam because the temperature was forecasted to drop below -30° C. It was clearly a dreamer’s thought, based only on the reason that no one had photographed snow gun originated diamond dust displays below that mark.
When we called it a wraps near the twilight hours, nothing out of the ordinary had happened. But after we woke up and started looking at the photos from the night’s plate displays, there was visible, next to the sub-Kern, an arc that we did not recognize. It was captured at two different locations with three hours passing in between.
Here are those two photos where the arc is seen. In addition, there is an anomalous looking bulge in the sub-Kern arc where the exotic arc is pointing at.
We don’t know how this new halo is formed, nor how to simulate it. It’s a one weird arc.
The lamp was at the usual -5 degree elevation.
Jarmo Moilanen / Marko Mikkilä / Nicolas Lefaudeux / Marko Riikonen
During a sunrise on 2013, May 13th I saw from the Zugspitze (2963m) two pillars with different inclinations. The most remote pillar was diffuse and came from virga below altocumulus; the other one originated from nearby icefog and was narrow and distinct. Unfortunately in most of my photos the two pillars overlap, but at the end they show up separate. The 3-D impression was very fascinating.
Subsuns appear very often during wintertime. It may happen that they appear in two different ice clouds: one of them may be affected by sheer wind causing the crystals to be tilted. Then, two subsuns are visible, one of them being displaced from the solar vertical. A displaced subsun is often a indicator for imminent sheer winds at the observer’s spot.
Author: Claudia Hinz
We look forward to your observations and numerous discussions.