Kern arc photographed in Finland

On the 17th November I drove 250 kilometers to the town of Sotkamo to check if there were any diamond dust halos. Two weeks earlier I had made the same trip, but the snowguns hadn't produced any halos. This time, however, the ski resort was surrounded by a thick fog cloud in which diffuse halos were visible.

I started searching for a better spot and after a while of driving the cloud started thinning. 22º halo, parhelia and M-arc were present and I took ice crystal samples before continuing the search. Several kilometers later it started looking really good and I stopped the car by a field where the view was unobstructed.

The parhelia were extremely strong, and I made my first observation of 44º parhelia. Other halos were 22º halo, sunpillar, subsun, subparhelia, upper tangent arc, circumzenith arc, 120º parhelia, 46º halo, parhelic circle and M-arc. The 120º parhelia looked like fuzzy pillars.

I took several hundred photos and ran out of memorycard. Luckily I had an old camera with slide film, but as it also ended pretty fast, the only solution was to get a new memorycard from the local town over 10 kilometers away. When I was back, the display was still going on, but the new card also got filled up in half an hour. So it was time to get home.

Next day, as I was having a closer look at the photos I couldn't believe my eyes what appeared on the screen. The circumzenith arc had a faint extension going all around the zenith: the Kern arc. See this photo, which also shows reflected Lowitz arcs. In some of the photos the 46º halo has an angular appearance revealing the 46º contact arcs , which were first photographed in Muonio a year ago ( 1 - 2 ).

Although readily appears in simulations, the Kern arc has been controversial because of the lack of photos. It was first reported by H.F.A Kern in 1895 in the Netherlands and at least six subsequent reports are known. As an explanation for Kern arc formation, raypath 1-3-5 in plate crystals as well as multiple scattering has been suggested. In the Sotkamo display there were 44º parhelia indicative of the latter, but it is not certain whether this mechanism is applicable higher up in the sky where the crystal cloud is optically much thinner.

Single scattering raypath 1-3-5 produces Kern arc easily, especially when the crystals are towards triangular shape and the sun is low. Both of these circumstances were realized in the Sotkamo display where the sun elevation was six degrees and a considerable number of crystals were semitriangular. As for crystal aspect ratio, it is thick plates that are favourable for Kern arc formation. The crystals in the photos seem to be below optimum thickness, but it should be noted that the crystal samples were collected before the peak of the display when Kern arc was not yet occurring and thus the sample may not fully representative.

The simulation of the display was made with populations of plate, Lowitz and column crystals. Fixed multiple scattering probability (0.15) was applied for all populations. Plates were semitriangular and the Kern arc in the simulation is primarily from single scattering 1-3-5 raypaths. Multiple scattering makes the 44º parhelia. Poorly oriented spinning Lowitz crystals made the 46º contact arcs and Lowitz arcs. It is noteworthy that the apparent 22º halo in the simulation is actually made of Lowitz arcs, which may also have been the case in the display. Columns made the weak 22º upper tangent arc. The simulation was made with a program by Jukka Ruoskanen

During recent years we have seen photographs of numerous displays with very bright parhelia. It is probable that at least some of them involved the Kern arc. This might be worth keeping in mind when the next bright plate crystal display comes along.

Halo and northern lights

Some ten years ago or so my friends and I went though Finnish Meteorological Institute automatic northern light camera films in search for moon halos. At that time I considered the northern lights as unnecessary noise that disturbed the distinction of halos on those low resolution 8 mm films.

Last Thursday I was photographing a moon halo display in Kilpisjärvi biological station, when suddenly green northern lights moved fast across the halos. It was a rather nice treat and above is one photo of those moments.

Also a 9° halo was in the sky on that night, as shown by this photo. Two nights later the 9° halo reappeared, but the display was much poorer.

Moilanen arc and diffuse anthelic arcs in Prichovice

A superb halo complex was observed by Petr Kousal on December 25, 2007 in community of Prichovice. He observed 22° halo, parhelia, pillar and also bright upper tangent arc with sunvex Parry arc. Except for these quite frequent phenomena he observed also Moilanen arc, which tips almost touched the 22° halo ( 1 - 2 - 3 - 4 ).

The best event came when he looked towards anthelion point, where diffuse arcs were clearly visible. This observation of diffuse arcs is the first in the Czech Republic ( 1 - 2 - 3 ).

This display was also captured by Martina Pistorova during her afternoon walk to the outlook-tower Stepanka in Prichovice ( 1 ). Analogous halo complex with Moilanen arc was also observed and photographed by Frantisek Kovarik in community Prichovice ( 1 ).

Also Hana Koukalova observed halo complex in the same community. Faint heliac arc is maybe displayed in one of her pictures ( 1 - 2 ). And finally, also Julia Vachkova observed a few halos together with infralateral arc ( 1 - 2 )

Text: Martin Popek, Lukas Shrbeny

Moilanen arc in Paprsek

In Czech mountains Ivo Bartos observed diamond dust halos on December 23, 2007 near ski area of Paprsek, which is situated in the highest Moravian mountains.

From 2 to 5 pm he most of the time observed sun pillar and parhelia with fragments of 22° halo. Culmination of the phenomenon occured at 4 pm when Moilanen arc appeared. This is the fourth observation of this arc in the Czech Republic.

The first Moilanen arc in the Czech Republic was observed by Ivo Brezina in January 2003 in Horni Misecky along with other bright halos ( 1 - 2 ).

The second case was by Milan Martinek in Bozi Dar in February 2004, who, besides Moilanen arc, observed also upper sunvex Parry arc heliac arc and maybe Lowitz reflected arcs. The photos of the heliac arc were the first in Czech Republic. The third Moilanen arc was observed together with bright upper tangent arc by Emil Brezina on January 1, 2006 in Vsetin.

Also Moilanen arc observed by Jan Bim on December 20, 2006 in Austrian Alps is noteworthy ( 1 - 2 - 3 ).

Text: Martin Popek, Lukas Shrbeny

Two Parry arcs in Ohio

While at work prior to leaving I was outside and happened to look up and saw nice wide tangent arc spreading out. Inside it was a convex Parry, the first decent one since 2000. As I watched and shot photos I could see the more common concave arc and there was also faint supralateral arc and circumzenith arc.

I also visually could see Lowitz arc curving down from upper concave Parry arc and circular lowitz arc near the sunvex arc touching the 22° halo. What a way to start the new year for halos. It was nice to see both Parrys at once. Photos were unsharp masked to enhance the halos.

Text: Michael Ellestad

The arms of parhelia and subparhelia on the Pansky Vrch hill

On December 23, 2007 (1:40 – 3:50 pm) Ladislav Nyc observed during his afternoon walk bright halos in diamont dust. When he went up from inversion cloudiness to see sunrays, on the hill of Pansky Vrch a great spectacle came along. Except for frequent halos like pillar, 22° halo, parhelia and upper and lower tangent arcs also subhalos were visible: bright subsun and subparhelia with arms of parhelia. These arms of parhelia, which join subparhelia and parhelia of 22° halo, are the first ones observed in the Czech Republic. More photos ( 1 - 2 - 3 ).

Also Stanislav Bernard in Sedlonov saw halos during his walk around Orlicke hory, mountains in the north part of the Czech Republic ( 1 - 2 ).

Text: Martin Popek, Lukas Shrbeny

Moon halos in Pec pod Snezkou

On December 23, 2007 from 6 to 7 p.m. local time Lubos Brat observed bright Moon halo complex. 22° halo, complete paraselenic circle, upper and lower tangent arcs and circumzenital arc dominated the display (see a composite image). In addition to these quite frequent halos also upper suncave Parry arc, 46° Parry arc and helic arc were present, as shown by the photo above.

Lower component of the Lowitz arcs may be present as a vague brightening on the 22° halo (right side), see this photo. Lubos Brat observed also halo phenomena in the artificial light and he was the first person in the Czech Republic to take a photo of superparhelia.

More photos of halo phenomena observed in Pec pod Snezkou between December 22, 2007 and January 5, 2008 are available on the Lubos Brat web site Altan Observatory.

Daytime halos were also seen on the 23 December. In the Orlické mountains Hana Tesarova photographed a display with bright circumzenital arc ( 1 – 2 ).

Beautiful circumzenital arc was observed also on December 16, in Western Tatras mountains by Boris (Slovakia), see photo here.

Text: Martin Popek, Lukas Shrbeny