This night conditions were overcast and we were watching halos in spotlight beam. But there was a moment when clouds all turned into ice crystals, allowing moon shine bright and make a passable display. We switched off the spotlight and managed to take some photos before it got cloudy again. Camera lenses were frosted, which caused some blurred areas and bright dots in the images.
Jarmo Moilanen, Marko Mikkilä, Marko Riikonen
Here the spotlight is still on, making its own halos.
On 23 November 2015, we were watching diamond dust halos develop under overcast skies in Rovaniemi. As we stood on a rectangular field a couple of hundred meters across, we followed halos slowly gather momentum in the spotlight beam, reaching climax when clouds were cleared away for a short while – and revealing at the same time also a lunar display. Here is an excerpt from Marko’s observation log written the next day:
“The display just adds gear. We are looking at beautiful subanthelic stuff, subanthelic arc, diffuse arc… It becomes monstrous when the cloud almost disappears. That is when we get also a moon display with full parhelic circle. No one seems to be in a rush to photograph the moon display. The beam display is sheer grotesquerity. The laser scapel sharp, 100% pure glitter of the tangent arc and uppervex Parry.”
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
Crystal samples should be englightening, but all too often they just make you confused. The observation I made on 22 November 2015 in Rovaniemi is a case on point, although an observation recently published by Alexander Haußmann may now provide a solution.
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)
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
The four caleidoscopic arcs carry in their name the location on the celestial sphere where their loops’ cross. For three of these halos – helic arc, Tricker anthelic arc and subanthelic arc – there exists photos showing the crossing.
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.
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.
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).
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
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.
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?
The 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.
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
