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.

Another halogen lamp display from Rovaniemi

A bright halogen spotlight and diamond dust is a magic combination.

Spot yourself exactly in the middle of the beam and breathtaking halo views may rewards you. An outsider will see just somebody bathing in the light and may wonder what is going on. There might be a Moon in the sky at the same time - like in the case shown here - but it shows hardly no halos at all. The lamp creates its own universe of halos.

The Ounasvaara snow guns created this display last night in Rovaniemi in the beam of a Cyclops Thor Platinum X-15 halogen lamp. Because of the lack of 46° lateral arcs, this display must have been dominated by Parry crystals. Indeed, in the lower right image there are both upper and lower Tape arcs as an indication of Parry orientation.

An interesting feature is seen in the images on left (the lower image is an unsharp masked from the upper). There seems to be a loop inside the helic arc. Much like the loop formed by the subanthelic arc.

On the upper right is a simulation that shows a quite similar loop (arrow). The crystals in simulation are Parry oriented and they are semitriangular, a half way between a triangle and regular hexagon. The thing in the photo looks to me like a halo and it might be the one shown in the simulation. I have not raytraced it, so I don't know what it might be called. There are some differences in the loop sizes between the simulation and the photos, but then again the projections are not exatly the same.

A bit more could be said about the results of the last night, but this must do for now. The simulation was made with a program by Jukka Ruoskanen.

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 is giving the beauty spot.

I have crystal photos from this stage, but as usual, they give no glue 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 the 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 longer. Also a full parhelic circle was seen visually.

The lower left photo shows is 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.

First diamond dust in Finland

The winter in Lapland was two weeks late but when it finally arrived last weekend, along came the diamond dust. Decent displays were seen here in Rovaniemi on two nights and one day. In the night time I used a bright lamp to create the halos. The photo here is from the second night showing the anthelic region with diffuse arcs. More photos, including all sky views, will follow some time later when I am done with them.

46° contact arcs

About a year ago in Muonio, Finland, a diamond dust display produced a new halo, the 46° contact arcs. The display was shortly reported in the blog, but no simulation was shown. So here is a simulation, together with a composite of the photos that were taken by Päivi Linnansaari. The 46° contact arcs, which arise from Lowitz-oriented crystals, appear as three arcs below the circumzenith arc.

The Lowitz crystals used in the simulation are regular plate-like hexagons, with aspect ratio of 0.4, tilt about the Lowitz axis 28° and Lowitz axis rotation 1°. Sun elevation is 9°. The Lowitz arcs themselves are faintly visible at 10 and 2 o'clock positions, separating from the 22° halo and reaching towards the upper sunvex Parry arc. This is the circular component of the Lowitz arcs, also known as the c-component (after Greenler).

Occasionally, in high cloud displays there is seen a short patch of 46° halo under the circumzenith arc, as shown here in the photo by Stepanka Kosova, taken on 20 August in Prague. It has been sometimes suspected that these might be indications of 46° contact arcs. Whether that's the case, it may be confirmed if a series of photos are taken for stacking.

The simulation is made with HaloSim by Les Cowley and Michael Schroeder.

Odd radius halos in diamond dust in Finland

On 23 February an another diamond dust display with odd radius halos occured in Vaala, Finland. Temperature was dropping from -29°C to -24° during my observation.

A parhelic circle and circumzenithal arc were present with nice parhelia. A subsun and subparhelia were also seen as sparkling ice crystals in front of the ground.

Odd radius halos labelled in this enhanced photo are A) a pyramidal heliac arc, B1) upper 24° plate arc, B2) lower 24° plate arc and C) upper 23° plate arc.

The most brightest odd radius halo was 18° halo and in some photos there probably are also 9° upper plate arc and 20° halo. The ice crystal cloud was produced by a local heating plant about 2 km away. More photos can be found here.

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.

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.

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.

Diamond dust halos over open sea

It is not so often to see diamond dust halos over the open sea, like here in the photograph of Pasi Snellman, taken on 5 November in Porvoo, Southern Finland. The display occurred only above the sea indicating that the open water was the moisture source for ice crystal growth. A couple of of kilometers upwind from the bridge is a small ski center, and according to Snellman snow making was under way there.

This may have provided the nuclei for the ice crystal formation. Snellman also tells that the air temperature was -7° C and sea +5° C.

On 5 November good diamond dust was seen also in Jämsä and Lahti, the latter of which is not reported here in Haloreports.

Diamond dust display in Jämsä

To fill the weekend of diamond dust halos in Finland, Simo Romo sent photographs of a display that was seen on sunday 5. November in Jämsä. The location is not far from Himos ski center where previous night and day Mika Aho photographed good displays, so it's probable that this one also originated from snow machines.

In addition to photographed halos there was also something else to be seen: "I was heading east and in the north-easten sky there was as if a brighter column of fog. Probably it was part of the phenomenon", writes Simo. Most likely he was looking at a diffuse anthelic arc.

The upper photograph is a panorama made of several individual images. The process has not been completely successful and that's why on the left side of upper tangent arc is an artefact.

Diamond dust from Riihivuori snow guns

Towards the last weekend tension was rising among Finnish halo observers. It was going to be clear skies with sinking temperatures and full moon. Most of the ski centers had their snow guns running, so anticipation for diamond dust was high.

On Saturday, 4 November, Arto Oksanen drove to check the sitation at Riihivuori ski center. There was indeed a column crystal dominated display with upper sunvex Parry, as shown in the photo on the left.

Next night Arto did not have to go anywhere, since wind carried the ice clouds straight to his doorsteps, to Muurame town. It was Parry-time again, and now in addition to normal upper suncave there was also the much less commonly seen lower sunvex Parry (photo on the right). Untill the last winter the latter has been considered as an extreme rarity, but now reports have increased, thanks mainly to ski centers' snow guns and active observers around them. The display contained also other halos of interest, like Wegener anthelic arc and anthelion. See also Juha Oksa photos from Muurame the same night.

Low sun Parry in Helsinki

October is probably the worst halo month in Finland. The last chances for good high cloud displays are gone with September and diamond dust is not swarming in until November. So it was nice to see today a low sun Parry starting to develop in the sky upon returning from grocery store. Grabbed pocket camera and tripod from my room and rushed to nearby parking lot.

The two images are stacked from series of 15 and 16 shots. The time span is two minutes in both stacks.

Earlier I had seen low sun Parry's only on two occasions. These were in high arctic Canada during diamond dust conditions. It took 22 years of observing to get one in high clouds.