2007. február 28., szerda

Bright 9° halo around the moon in Germany

On the 23rd of February Harald Wochner took his obligatory view out of the dormer window towards the night sky. Immediately, he realized an unusual circle which later turned out to be a 9° halo around the moon. Right at this moment he took his Camera and tripod and went a couple of hundred meters away from his village in order to have a darker sky. He could also recognize a feeble 22° halo in larger distance from the moon. There one could see the structures a little bit more. The 9° halo maintained itself in a good shape and could partially better be seen than the 22° halo which acted really diffusedly. Which the descending of the moon, the intensity of the circles decreased steadily.

The picture shows the village Wahlwies with its church on the western Lake of Constance. The picture with unsharp mask shows in addition the faint left part of 18° halo.

2007. február 17., szombat

Moilanen arc behaviour

We have now enough photographs of Moilanen arc to make some suppositions of the responsible crystal. As lower component of Moilanen arc does not seem to exist, the crystal must be well oriented. Straight upwards pointing wedge with ~ 34° angle seems to produce an arc that fits well with photographed cases both in shape and location.

In the image above are given simulations of Moilanen arc and 22° halo for solar elevation range of 0-35°. Also the Moilanen arc raypath through the wedge is shown. At 35° light source elevation the Moilanen arc is already disappearing and shows weakly above the 22° halo.

In free fall the depicted simple prism would hardly orient as shown. What kind of crystal causes Moilanen arc is still a mystery. Although Finnish observers have managed to sample crystals from a couple of Moilanen arc displays this winter, the crystal photos have not resulted in a breakthrough.

These images are no news to those who have an inclination to fiddle with halo simulation programs. But as nobody has given them anywhere, I thought they might be of some help for the halo community in knowing what to expect when the next diamond dust swarms in. Simulations are made with software by Mika Sillanpää and Jarmo Moilanen.

Diamond dust display in the Spanish Pyrenees

On January 26, 2007, Claudio Martinez watched and photographed a complex diamond dust halo display at the Baqueira Ski Station in the Spanish Pyrenees. Baqueira is situated at an altitude of 1850m. At about 5.30 pm CET the display showed the 22°-halo with sundogs, anextremely bright upper tangent arc, upper and lower sun pillar and the parhelic circle. Part of these was also visible in front of a mountain ridge. In the upper sun pillar there also appeared the Moilanen arc. Nearby floating ice crystals are also visible as bright sparks in the pictures.

There is also a video existing. You can see it here.

2007. február 9., péntek

Pyramidal heliac arc in Finland


In 8 Feb 2007 an odd radius display was produced by local heating plant plumes in -28°C temperature in Vaala, northern Finland. I photographed this display on a road about 1.5 km away from the heating plant.

Odd radius halos in display were 18° halo, 23° upper plate arc, very faint 35° halo and rare pyramidal heliac arc. See arrows in a stacked and strongly unsharp masked photo shown.

Pyramidal heliac arc is formed by reflection from pyramidal side faces of horizontally oriented pyramidal ice crystal. It is usually visible near the sun only. It is usually very faint but this time I was able to see it also visually.

Same odd radius halos except 35° halo were also present in similar but much fainter display in Vaala couple of days earlier in 6 Feb 2007. More photos from both displays can be seen in Jarmo Moilanen's halo photo gallery or directly 8 Feb. 2007 here and 6. Feb 2007 here.

2007. február 2., péntek

Reflected Lowitz arcs in Finland

On 30th January 2007 I found that local district heating plant was causing a nice diamond dust display. Temperature was -22 C and the steam crystallized immediately. Only a few hundreds meters from the plant was already a plenty of crystals, but the best was about 2 km from the plant.

There I drove to a small road and got out and saw a display like never before. Parhelia were very bright, like fireballs. Also circumzenith arc was bright, but 22 halo was quite weak. Almost full parhelic circle was present with faint 120 parhelia, that looked more like pillars than fuzzy balls.

I had a film camera and eventually run out of film. The only choice was to drive home to get digital camera and fisheye lenses. On returning back the display had lost intensity and the 120 parhelia were completely gone. Anyway, I took about 80 photos with digital and later stacking of those photos revealed faint reflected Lowitz arcs rising up from the parhelia (marked in the photos with arrows). More photos of display is here. The looks of the display is quite similar to the one that was observed by Jari Luomanen a year ago. See photo here.

2007. február 1., csütörtök

First odd radius halos observed 31st January 2007

While at work on break I saw some cirrus clouds gather in the sky and I later saw a halo appear so I got my camera out of the car and my sunglasses. As the minutes passed I notice that there were three halos: 9 degree halo 18 degree halo and possible 23 degree halo. The left side of the 9 degree halo looks strange because it is brighter on one side and has a somewhat vertical look to it.

When I later downloaded the pictures I went through them with adobe photoshop and I applied the USM and I noticed possible 20 degree halo and even a 35 degree halo! You can see at least 4 halos in the enhanced photo. The possible 9 degree column arc and 35 degree halo have been pointed out with black arrows.

Combination of high level cloud and diamond dust activity

On the evening of 30th January cirrostratus clouds filled the sky and odd radius halos (9, 20 and 35) were seen in the Moonlight in Hyvinkää, Finland. The 20 and 35 halos were very weak, and couldn't be seen with naked eye. In addition to the high clouds there were good but fast moving diamond dust areas on the ground level. At times the halo display was a combination of cirrostratus and diamond dust halos. In the photo on the left the parhelic circle was caused solely by diamond dust, whereas the other halos were mainly originated in high clouds. A collection of photographs taken by Jukka Ruoskanen is here. 9 degree halo was also seen in Espoo by Timo Kuhmonen, in Helsinki by Marko Riikonen, in Turku by Ismo Luukkonen and in Tampere by Jari Luomanen.

Exciting divergent light halos were photographed as well in Hyvinkää. A more detailed description of the divergent light halos is here.