Lunar display with Lowitz arcs and an unknown arc

On the night between February 10 and 11 a bright lunar halo display in diamond dust was observed in Tampere, Finland. Bright and well defined Lowitz arcs were the most prominent feature. In addition, an unknown arc can also be seen extending downwards from the parhelion. The display was witnessed by Jari Luomanen and Johanna Järventaus.

More images available at:

https://jari.pic.fi/kuvat/Atmospheric+phenomena+and+sky/Atmospheric+halos/2017_02_10+Outstanding+Lowitz+Arcs/

Subvisual odd radius halos in the UK

In the afternoon of 26 March, 2017, I was spending time outdoors with my family and wasn't too well equipped for serious observing. Of course, I had paid some attention to cirrostratus clouds drifting in the sky, but most of the time I struggled to see any significant halos. There were just occasional patches of 22° halo: or at least that's what I thought they were. But then the upper suncave Parry arc appeared so I had no choice but to start photographing immediately. After all, you don't get Parry every week, and in fact this was my first such encounter in 2017. During the next 20 minutes or so, I took a decent set of photos, but then gave up as it appeared that the display had become insignificant again.

My hope was to find a few more halos in the post-processing, and stacking did a good job indeed. The stack shown above is from the first 50 frames and covers a total of 196 seconds. On the left the unsharp mask is applied on individual frames before stacking. The version in the middle is a gradient-subtracted average stack, which is further processed by using the blue-minus-red subtraction technique on the right. In addition to the usual stuff and the Parry arc, we can identify upper and middle Lowitz arcs as well as a short piece of helic arc to the left from the circumzenith arc. But that's not all - there are also odd radius circular halos.

For comparison, the stack below is from the last set of 30 frames that I took more than 30 minutes after the last signs of the Parry arc had disappeared. This stack covers a total of 174 seconds. I didn't really expect to find anything special at this point, but took the photos anyway out of curiosity. Apparently the odd radius stuff is still in play. My feeling is that it had been there all the time, possibly long before I noticed the Parry for the first time and also long after I had got indoors to celebrate the Mother's day dinner.

What is shown below is an attempt to make the scene as clear as possible by combining photos from two different series into one stack. 100 frames are included, covering 13 minutes in time but missing about six minutes in the middle. My interpretation is that the relatively typical pattern of 9°, 18°, 24°, and 35° halos is complemented by the exotic 13° halo. But I'm not sure and it would be great to hear what readers might think of the case. Whether the 20° halo is missing altogether or masked behind the suspiciously wide 18° halo, I am not sure of that either.

Fine Lowitz arcs in lunar diamond dust display

Vesa Korhonen photographed this lunar display in Hämeenkyrö in the evening of 10 February at 2038 local time. The circular Lowitz arcs are splendid. The upper and lower components are expected to accompany, and seem to be there, but are rather overwhelmed by the intense 22° halo.

Lowitz - the new normal?

In 2017, halo activity in my part of the United Kingdom has so far been very quiet with not much to get excited about apart from the occasional odd radius lunar halo. However, on the 6th February things improved a little with a nice little display which included 22°, both parhelia (sporting parhelic tails), uta, possible Parry, cza, supralateral and all three Lowitz variants. The upper and lower Lowitz were vestigial, but the middle Lowitz illustrated here was quite clearly defined.

This burst of activity got me ruminating about the frequency of certain types of halos and the nature of “rarity”. Compared to many of you 'old hands', I am a comparative newcomer to halo observation. When I first started to observe, many halos were still considered to be extreme rarities or at least exceptionally infrequent. Others, such as the Kern, were so rare that they were considered to be the Holy Grail of halos, so few were their sightings. What I have noticed over the last few years is that many of these rarities are seemingly becoming far more frequent and in my own mind at least, I have downgraded them from ‘rare’ to ‘infrequent’.

Take the Lowitz arc for example. It is only a few short years ago that its very existence was being doubted, controversial to say the least. First, there were a few sightings, then a trickle of photographic images emerged which confirmed it as a reality. Over the past ten years, their frequency has seemingly increased to the point where I will see several per year and look out for them as a matter of course. Whilst not commonplace, they are certainly hovering somewhere in that vague, nebulous no-man’s land between infrequent and relatively frequent. Likewise, the Kern. At first a mythical creature, but now we are seeing the first drips which will eventually become a trickle….

So what has caused this apparent change in frequency, this downgrading of status? I would like to posit two possible causes: the ubiquity of digital imaging and advances in image processing. It is not that these halos are actually becoming more frequent in reality but that the effect of digital imaging and the development of image processing techniques are revealing them to be present in many more displays than were hitherto thought. In the past, one would take a roll of traditional film, but prior to image processing what did one do with them? Answer, nothing in most cases. You either saw the halo on a particular frame or you didn’t. This resulted in some of these rare halos only showing themselves under exceptional conditions. With the advent of inexpensive digital cameras and image processing software we saw far more phenomena being recorded. However, it is only with the introduction of the B-R processing technique pioneered by Nicolas Rossetto and perfected by Nicolas Lefaudeux and to a lesser extent image stacking, do we really notice an apparent increase in all types of rare halos. These techniques alone have been responsible for the massive increase of rare halo frequency and the identification of several new halo species. We have now reached a point where what was new and exciting yesterday, is passé today.

I think this trend is going to continue as more and more observers embrace these new methods of working. We have already seen it occur in the wider field of atmospheric optics where photographic identification of higher order rainbows, especially the third and fourth orders, are now becoming a reality. One might argue where is the hard evidence to prove this is anything but a theory or personal opinion? This evidence is indeed hard to come by, however projects such as Lefaudeux's 'HaloCam' has demonstrated without a shadow of a doubt that certain halos are far more frequent than previously thought. For example, he has very clearly demonstrated that the 46° halo is present almost as often as the 22°, whereas at one time it was considered to be a very infrequent visitor to the skies. So not only will this trend continue, I think it will also accelerate, especially in the field of spotlight displays where new halos are being discovered on a very regular basis. Even in daylight displays, new halos are still being captured from time to time using these techniques.

A few years ago, it seemed like everything that could be seen had been seen. We are now on the cusp of a new era of halo research. Today may indeed be considered passé by some, but tomorrow is definitely going to be tremendously exciting! I want to be a part of that new wave of discovery.

Alec Jones

More results from the latest display in Rovaniemi

Here is some more material from the diamond dust in Rovaniemi three nights ago. After the heaviest Parry-crystal bombarding was over, Moilanen arc appeared, as shown in the photo on the left. Moon gives the beauty spot.

I have crystal photos from this stage, but as usual, they give no clue to Moilanen arc. In the earlier Parry-stage there was no indication of Moilanen arc whatsoever, but I did not manage to get the crystals. This bugs, because comparing the samples might have pushed us forward in solving the mystery.

The upper left image shows parhelia from streetlamp - the stripes that are parallel to the electric lines. Then there are also arcs extending slightly obliquely downwards. While visually parhelia curved towards me, these other arcs curved away and around me. As far as I understand from looking at divergent light simulations by Lars Gislen et. al, this effect is a 120° parhelion. In the photo only the brightest part of 120° parhelia is seen, visually the crystal glitter extented much further. Also a full parhelic circle was seen visually.

The lower left photo shows what was seen around the half moon at its best. For long time there was hardly no moon halo, although in the beam of the halogen torch a great display was present. Some indication of Lowitz arcs is present in the moon photo. The crystal sample may be representative of this stage, but I am not sure. Crystal photos of Lowitz displays are also very welcome

By Marko Riikonen

Rare halos in Czech rep. Oct. 30 and 31

On October 30 in Prague was observed rare halos. Stepanka Kosova had Lowitz arcs and 120 deg. parhelia (title photo). Lukas Shrbeny had nice 120 deg. parhelia too. I observed rare halos in two last days. On October 30 I saw: 9°, 20° halos and Parry suncave arc. On October 31 I seen: Parry suncave arc , upper and lower Lowitz arcs and probably circular Lowitz arc too. M.Popek and R.Manak seen 9° halos in Lunar displays.

 

by Patrik Trncak

 

Originally in Halo reports

Parry and Lowitz arcs in Czech Republic

On October 20 and 21 I and Roman Manak saw an upper suncave Parry arc. On October 21 I also observed Lowitz arcs too. On photo is nice Parry arc by Roman. My Parry arc and my Lowitz arcs.

Unidentified halo display in Romania

Attila Kosa-Kiss from Salonta, Romania observed on 29th September 2006 a very interesting halo display at a sun elevation of 12°. Unfortunately, there were no photos but there is a sketch. The most probable explanation is the existence of suncave [H] and sunvex [G] Parry arcs, as shown by the simulation from Les Cowley. Other possibilities would be an circular Lowitz arc [F], as seen on the simulation with HALOET (random: 0.5, plates: 0.5, columns: 0.5, parry: 0.5, Lowitz: 4.0, number of rays=150000). On the same day was observed several time in Germany and Czech the upper part of Lowitz arcs. But Romania was influenced by another weather front (with another cirrus clouds) like the middle European area. Further comments and ideas are very welcome!

 

by Claudia Hinz

 

Originally in Halo reports

Czechoslovakia Lowitz arcs

This photo show nice circular Lowitz arc. Photo was taken by Michal Nagy from Slovakia at September 29 2006. My photo possible all components of Lowitz arcs was taken in Holesov (Czech rep.) at October 12 2006.

Circular Lowitz arc in Germany

At the end of September weather fronts from an ex-hurricane reached Germany. In the leading cirrus, Lowitz arcs were observed over two days. Hartmut Bretschneider in Schneeberg (Saxony) made the first sighting on 28th September. He first saw a parhelion with a Lowitz arc emanating from the parhelion when the sun was at an elevation of 14 deg. Later when the sun was higher there was a very bright Parry arc and an upper Lowitz arc (right photo). On evening of the following day Werner Krell saw a solitary upper Lowitz arc at Wersau (Hessen). His photo was taken at a sun elevation of 11 deg. [2, 3]

 

by Claudia Hinz

Originally in Halo reports

More rare halos in Czechoslovakia

Today was day of halos for all observers. I was seen: Parry arc, Infralateral arc. Martin Jankovic: Parry arc, 120 parhelia. Milan Cerny: Parry arc. Stepanka Kosova: Parry arc, 120 parhelia. Roman Manak: Parry arc and Martin Popek: 120 parhelia. For discussion: Lukas Shrbeny from Ondrejov had maybe Lowitz arc. You see his link.

Full moon display in Finland

As month earlier, good moon halos visited the skies also this time. The display in the night of 12-13. April was seen over large areas in Finland. Halo developement was best in Hyvinkää, where Jukka Ruoskanen documented the display.

The photo here, taken by Ruoskanen, shows many features of interest. First there is Parry arc above the 22° tangent arc. Second, there are Lowitz arcs. They are best revealed by the gap (shown with an arrow) in the 22° halo at parhelia level. Also, curving of 22° halo towards parhelia is evident. 

Third feature of interest is the 9° halo and the dark area inside it. Sometimes 9° halo is not seen in individual photos, but the conspicious darkening inside the halo location tells about it's existence. Stacking several photos then brings out the halo. The image here was stacked from 18 photos, but 9° halo was visible also in individual photos. 

Finallly, there seems to be also suggestion of 9° upper plate arc, seen as an enhancement on top of 9° halo.

Simulation of reflected Lowitz arcs

Here is an attempt simulate the Jari Luomanen display of 22. January 2006. Reflected Lowitz arcs arise in the simulation from thin plate crystals tilting 10° about the Lowitz axis. Same crystal population also makes the crossing arcs below circumzenith arc - the 46° contact arcs. These are not seen in the photo, but it was not possible to make simulation without them appearing (46° contact arcs are still theoretical, no reliable observations are known). Some other, less serious problems are also evident in the simulation. Reflected Lowitz arcs, however, are well in accordance with the photograph.

Two more crystal populations were used. Oriented plates made parhelia and circumzenith arc and poorly oriented plates the 22° halo. Sun elevation was 7°. More details on the simulation are here. Simulation is made with HaloSim by Les Cowley and Michael Schroeder. Simulation files are here.