Moilanen arc in Mátraszentimre, Hungary

This photo shows the diamond dust display near Mátraszentimre skiing resort in Hungary on 30th December and was taken by photographer Zsuzsanna Tóth. The snow guns were on, and the halo appeared in the early afternoon and lasted about an hour. The display was the best at around 2 p.m. Then the 22° halo, parhelia and upper tangent arc were accompanied by a Moilanen arc. As indicated by the bright parhelia and a less conspicuous upper tangent arc, the display must have been dominated by plate crystals. Unfortunatelly, however, there was no one around who would have collected samples, so the mystery remains unsolved.

Natural diamond dust is very rare in Hungary, due to our temperate continental climate. But this winter has so far been much colder than the average ones, and it has resulted in a pretty diamond dust display without the assistance of any snow guns on 3rd January in Mogyoród. Alexandra Farkas took this picture of UTA, CZA, and supralateral arc. The halos don't show anything extraordinary, still it was a unique sight in Hungarian winter.

Circumhorizon arc in Vítkovice

When I first saw photos by Vaclav Fego captured on December 22, 2007 in Vitkovice in Krkonose mountains I told myself just one thing – wow, that is amazing, I haven’t seen anything similar for a long time! On the images of this Moon halo display is visible bright and colorful circumhorizon arc together with short projections of infralateral arc low above the southern horizon. Also 22° halo with Parry arc and full paraselenic circle are seen. Here is one photo pointed at higher up in the sky and here is a composite image.

The situation captured on the photos is similar to this simulation, made with Halosim by Les Cowley and Michael Schroeder

Circumhorizon arc appears when elevation of the Moon (or Sun) is 58° or more above the horizon. In this case the elevation of the Moon was 66°, which is several degrees more than that of the Sun at noon at summer solstice in the Czech Republic (the inclination of the Moon’s orbit to the ecliptic can position the Moon 5° higher)!

In the same day there was also nice complex display around the Sun:

From Bedřichov u Kralovky, photo by Vladimir Wasserbauer and from Paseky nad Jizerou, photo by Čenda Jirak.

Text: Martin Popek, Lukas Shrbeny

( addition on 10 Jan: more images by Vaclav Fego: 1 - 2 - 3 )

Diffuse arcs with anthelion on Humlnet webcam

A strange white faint arc appeared on December 17, 2007 on webcam in Pec pod Snezkou, Czech Republic, operated by Humlnet network. Because the webcam is oriented northward, there was a suspicion that at least anthelion could be captured on the photographs. Fortunately, there is an image archive available, so we were able to create stacked image. I used 10 images with apparent anthelion for processing in Registax. The result revealed together with anthelion also quite bright diffuse arcs.

There are another 2 examples of webcam images with halos: Parhelion captured by Hydronet webcam in the Jizera Mountains on December 13, 2007.

Infralateral and supralateral arcs on Humlnet webcam in Zacler (December 25, 2007).

Text: Martin Popek, Tomas Trzicky

22° halo on snow surface with horizontal color segments

This 22° halo was seen on a thin snow layer which formed on a freshly frozen river from power plant induced precipitation and freezing mist. The dark area inside the 22° halo is prominent, indicating well developed solid crystals that scatter light only at halo angles.

The photo shows also broad horizontal segments of cyan and magenta in the outer areas of 22° halo. These segments seem to be very sensitive to the variations in the camera positioning, changing their position relative to the 22° halo and ground features, as shown by other photos taken by Peter Vancoillie.

I have no explanation to offer. The display was seen in Ghent, Belgium on 21 December 2007.

A diversity of surface halos in Juva

It is not unusual to see a 22° halo glittering in separate crystals on snow surface. The display that Jari Piikki observed on 22 December on a frozen lake surface is of a better quality. Towards the sun there were the parhelia and perhaps segments of a 22° halo, as shown in the photo above. Two close-ups are also provided: image 1 and image 2. In image 1 the close-up area of image 2 is marked with two white lines.

Piikki took photos of the responsible ice crystals. They seem to be frost crystals, which top ends has plates grown horizontally. See here and here. Crystals are large; the photos were taken with a standard lens. Some crystals show possible cavities.

The halo display on the ice surface was changing as one moved on the ice. This image shows faint extensions from the parhelia towards the observer. The display does not seem symmetrical, but slightly distorted towards right. This could be caused by uniform atsimuthal orientation of the crystals prisms. At least the crystal photos give an impression of all crystals having similar orientation. This is clear evidence that crystals are frost crystals, not fallen from the sky. Locally inclined surface may also be affecting the halo features. The image with parhelia extensions was taken with camera lens touching the ice, features close to the camera are thus formed in small surface area. Preferential atsimuthal orientation of crystals may be more likely in small than large surface area.

Opposite to the sun a white glow was seen at the subanthelic point (photo taken with camera on tripod). Airborne plates do not produce such effect, at least in simulations. Reflecting complex ice surface or/with frost crystals here must be chancing the rules so that the glow can be formed. Could this be called just a heiligenschein?

At around 120° from the sun on both sides white brightenings (arrow) were observed, indications of 120° parhelia. In airborne crystals the usual 1-3-4-2 and 1-3-4-2-1 raypaths for 120° parhelia and subparhelia are not effective at very low sun elevations, but in frost crystals external reflection from ice surface may allow these raypaths. In airborne crystals other raypaths can make 120° parhelia at low sun, but crystals deviating from regular hexagonal shape are required. Here the frost crystals seem to be pretty regular in shape.

Halos were also observed at the nadir region. These are possibly patches of a circumzenith arc caused by light reflection from ice surface. The colors, on the other hand, seem similar to the halos from 60° refracting angle. According to the observer, sun is most likely towards the upper left corner in the photo.

A question remains whether these halos should be called with sub -prefix or not. This has some significance, because sub-120° parhelia and sub-circumzenith arc (or circumnadir arc) has not been observed yet. Subhalos from airborne plate crystals are characterized by a reflection from bottom basal face. Here the bottom basal face needed for the subhalos formation may be missing or is only partially developed as crystals are at attached on the ice.

Most likely the formation of the halos is to greater amount contributed by a reflection from ice surface before or after the rays enter or exit the crystal. If we take it that a subhalo must arise from ray path fully inside one crystal, then these are not subhalos.

Marko Riikonen, Jarmo Moilanen

Parry Arcs Over Central Europe

December 22nd was a day of complex displays over Central-Europe. While Hungary was covered with thick fog, mountain peaks above 900m witnessed sunshine and favourable conditions for halo-formation. Attila Kovács took the photo of the suncave Parry arc on Bálvány in the Bükk Mountains 956m above sea level. The display started with bright parhelia that appeared at 12:05 UT and lasted about half an hour. At around 12:30-12:40 the complex display began to emerge. First the 22° halo with the upper tangent arc. Altogether, a 22° halo, parhelia, UTA, a long section of the parhelic circle, CZA, supralateral arc and the sharp suncave Parry arc were visible. The Parry arc lasted about 5-10 minutes. There is unfortunatelly no report about the anthelic side.

Although the Czech Republic is two countries away towards the northwest, the distance is not that great for crystals forming a display in high clouds, especially that the Hungarian Parry observation was made in the north of the country. On the very same day Martin Popek photographed an attractive sunvex Parry in Nýdek.

Diamond dust display with a possible new halo

On the evening of 22th December weather conditions finally changed to better. Humidity was up with temperature around -8°C. At the Louekallio ski-resort snow guns produced a crystal cloud and action lasted few hours until crystals suddenly vanished.

Singly oriented columns dominated the swarm. With HID-modded Cyclops Thor Platinum X-15 lamp the display looks quite the same what we have seen already in haloreports, except that there is weird spots on both sides of the upper tanget arc (photo above, see also enhanced image). They seem to extend through the 22° halo towards the lamp, but this may be due to divergent light. In simulations arcs that bear some resemblance to these spots can be produced with slightly tilted Parry crystals, but we certainly need more photos to say what is going on.

Also Moilanen arc appears in the photo. At first glance it may seem to be
connected with the new effect, but closer look reveals they are two separate halos. Diffuse arcs were observed opposite to the lamp.

In the moon light, circumscribed halo, infralateral arcs, 46° halo and full parhelic circle were seen. The long Wegener arc, which continues close to infralateral arcs, was not seen visually. See also another photo of this stage. Later on ice crystals turned to be more randomly oriented. Moon elevation was 52°.

Similar column dominated display was also noticed by Arto Oksanen in Muurame. See his photos here. When 0ksanen first noticed the display, there was Wegener arc above the parhelic circle and he hurried for the camera. Unfortunately, the best moment was gone when he was back. "By the time I got camera from inside, halos had weakened and of parhelic circle only a trace was visible", Oksanen tells.