Late diamond dust display in Finland

Cold spring has kept diamond dust popping up late. On 28 April a display with sharp Moilanen arc was seen in Järvenpää of southern Finland and could be the latest one on our records. For certain, nothing nearly this good has been seen this far into the spring. Two people sent photos to Taivaanvahti site. The image above was taken by Jarkko Lakso at 6:14 local time and another image was snapped at 6:55 by Emmi Mäkinen.

The cold air mass seems to be in no hurry going anywhere and is forecasted to even tighten its grip at the end of the week. So who knows we are in for more diamond dust surprises at the summer's door.

A colored patch under Moilanen arc

By Marko Riikonen and Jarmo Moilanen

These photos show a colored patch at the bottom of Moilanen arc. We don't quite know what it is. Nicolas Lefaudeux has suggested it could be a segment of circular "Moilanen halo". Such a halo has been photographed by Alexander Haußmann on 27. November, 2015, in Mt. Klínovec of the Czech Republic. Our display occurred in Rovaniemi on 16. December, 2015.

Or then it is the arc which has been observed under Moilanen arc a couple of times in relatively high light source elevation lunar displays. See for example the observation by Jari Luomanen. If so, then the explanation of this arc from rotating Moilanen arc crystals can't be right because the shape is wrong (the lamp is about 7 degrees below horizon). 

There is also 9 and 35° halos - a pretty headache inducing combination were you to try a simulation. A crystal photo is provided. Looks like a lot of pyramids in it, but most are not really textbook pyramids. More crystal photos in the original report in Taivaanvahti.

A possible new halo above Moilanen arc

By Marko Riikonen

A simple diamond dust display that I photographed on the 6th of this month in Rovaniemi, shows above the Moilanen arc another, weaker V-shape. As I uploaded the photo on Taivaanvahti, I was not conscious of the effect, it caught the sharp eye of Panu Lahtinen and Reima Eresmaa who commented on it. Then some photo processing made it stand out more clearly. The version above was worked by Nicolas Lefaudeux. It is a stack of 13 images taken during 125 seconds.

If the effect is indeed real, it can not be accounted for by any known halos. At 10:26-10:27 am when the photos were taken, sun was too high (5.6-5.7 degrees) for reflected Parry to explain it and there is no normal Parry arc or tangent arc in any case.

Soon after I posted the photo on Taivaanvahti, it turned out this has been recognized already years earlier. Marko Mikkilä and Jari Luomanen photographed displays with a brightening above the Moilanen arc, respectively in 2007 and 2014. Both had informed other enthusiasts about the effect in their images, but these failed to create excitement at the time. Now, with the latest display’s somewhat better defined V-shaped arc, these older observations certainly deserve a new look.

One more case of interest is that by Timo Martola in the township of Janakkala last winter. His display contains a V-shaped arc above Moilanen arc, however, because the sun elevation is just right for reflected Parry (4 degrees) and there is also normal Parry and tangent arc, everyone has been content with reflected Parry explanation. Probably that’s what it really is, the display looks much like an earlier one that has a definitive reflected Parry. But with the new observation, we can now entertain the possibility of another explanation for the arc in Martola’s images.

A search of all Moilanen arc photos would be in place to see if more candidates turn up.

The original version from which Lahtinen and Eresmaa noticed the effect.

Torch shaped Moilanen arc

The two images above, which are versions of one stacked image, show a torch shaped Moilanen arc. This is the shape that the halo takes when light source is about 9 degrees below horizon. Below is a simulation for that elevation.  Also shown is another photo in which the places of lamp and camera were switched, giving a more familiar looking Moilanen arc with the lamp about five degrees above the horizon. The display was photographed on the night of 5/6 January in Rovaniemi.

Marko Riikonen / Nicolas Lefaudeux

Two diamond dust displays near Moscow

By Vladimir Galynsky 

On 21 February ice crystals filled the air in Rumyancevo, a suburb of Moscow, and a halo display with relatively strong Moilanen arc was photographed by Alexandr Yakovlev. One of the photos, with unsharp mask enhancement, is shown above. Another photo is also given ( 1 ).

A year earlier, on 1 February 2007 Yakovlev photographed a diamond dust display with subsun and subparhelia from the 7th floor of a building ( 2 - 3 ). In the photos Moilanen arc is also present faintly. An unsharp masked image shows it better ( 4 ).

The original images of both displays are available on my blog ( 5 ).

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

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.

Moilanen arc display with cell phone camera

Jaakko Tähti photographed this moderate display with Moilanen arc on 12. January 2007 in Viitasaari. "The halo display lasted for about four hours and changed constantly. It was a pity I was working inside. At times however I went to take some pics", says Tähti who used his cell phone camera for photographing. The vague double structure in the upper tangent arc seems to indicate that the display contains also an upper sunvex Parry arc.

The following night diamond dust was drifting also in Tampere and Hyvinkää. See the divergent light halos by Jari Luomanen and Jukka Ruoskanen.

Lunar Diamond Dust Display in Pälkäne, Finland

In the evening of 4 November this lunar display graced the sky soon after sunset. Among the halo forms observed are the rare heliac arc, Tape arcs and Moilanen arc. The Moon elevation is ca. 16°.

In the image the entire length of the heliac arc is visible as a beautiful loop encircling the zenith. The Moilanen arc is very intensive and appears to extend beyond the 22 degree halo. Tape arcs can be seen as diffuse brightenings on the supralateral arc.

In the beams of the passing cars a bright pillar, parhelia, upper tangent arc and Moilanen arc were clearly visible. These proved difficult to photograph though. At the local ski resort the snow guns were operating during the display and the crystal swarm was a by-product of this activity. The temperature was below -15 °C.

 

by Jari Luomanen

 

Originally in Halo reports

Diamond Dust Halo in Austria

This picture was taken on December 10, 2005 by Wolfgang Gurgiser at the summit of the Hohe Salve (1829 m, Kitzbühler Alps, Austria) at a temperature of about -7°C. Contrary to what is usual, this halo was not caused by cirrus clouds, but by diamond dust which had direct contact to the ground. This diamond dust consisted of needle-shaped ice crystals smaller than 1 cm.

Besides the 22°-halo, the picture also shows a V-shaped upper tangent arc and Parry arc, the arc of Moilanen which is also V-shaped and situated at 11° above the sun, and – emanating from the sun – the heliac arc.

 

by Claudia Hinz

 

Original post in Halo reports

Winter's best displays from Marko Mikkilä

Marko Mikkilä has opened a gallery for his halo photos. Shown are the best diamond dust displays from the nearby Louekallio ski resort snow machines. The gallery is still under construction, so keep checking.

The image here is from one of the Mikkilä's displays. It's caused by headlights of nearing car. This is actually stacked image from nine individual unsharp masked photos. The stacking program, Registax, was told to align the photos using the right parhelion. 

Above the car lights, there are two V-shaped arcs. The upper one is the common 22° upper tangent arc (perhaps with upper sunvex Parry arc), the lower one is Moilanen arc.

Bright Moilanen arc in Finland

This display was photographed by Pertti Havia on 21. December 2005 in Huhko, Southern Finland. The V-shaped Moilanen arc above the tree line is well developed. Nesting in the glow of the 22° upper tangent arcs, there is also upper sunvex Parry arc. (Shows better in unsharp masked photo which is not shown here).