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Light refraction in a sunshine recorder

Only at very rare occasions, light refraction can be seen as impressive as in this example. The photo was taken by Hermann Scheer at the Meteorological Observatory on Mt. Hoher Sonnblick (3105m) in the Hohe Tauern mountains in Austria. A layer of ice and rime had formed on the glass sphere of the Campbell Stokes sunshine recorder. This layer split the sunlight up into its spectral colours. That is how impressive physics can be.

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Sodalite interference colours

Sodalite – sodium aluminium silicate chloride – is a mineral of volcanic origin (chemical formula: Na8Al6Si6O24Cl2) and it comes from hydrothermal fluids in a volcanic rock’s cavity. The sodalite containing rock itself is not homogenous but consists of many different, small minerals beside the blue sodalite.

The mineral itself is very nice deep royal blue in general, the piece illustrating this article was mined at Mt. Vesuvius and bought in a mineral shop in Italy. The sodalite pieces are full of other crystals, usually well visible whitish veins which mostly consist of calcite.

When looking at the mineral with the help of some magnifying device we can see small parts of it having thin and colourful layers! These coloured parts are concentrated at the edges of the calcite veins or patches and only visible in a magnified form. Here, the translucent calcite was built on the blue sodalite mineral in a later process different from the forming of the blue crystals from the original hydrothermal solution. These places must also contain a very thin layer of air which is responsible for the colours with its interference.

What is unknown: the forming of the air layers. Are they originally there or are they created when the stone is cut from the rocks? I think the later is more possible as the sodalite rocks can more easily break where the white veins run, so the chopping of the rock might create the gaps, resulting interference patterns. The process might be the same as the ice pieces with fissures showing interference colouration too.

The pictures (123) were taken with a cheap digital microscope, the magnificiation which shows the interference colours is 200X. Smaller magnification also shows it but only in tiny coloured spots.

Author: Mónika Landy-Gyebnár, Hungary

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Ice particle iridescence?

Normally, iridescence shows rather faint colours which can only be seen by covering the sun. On December 6, 2010, however, iridescence was visible in such a brightness and colourfulness in high level clouds that at first sight it rather looked like halo fragments than like iridescence. (123)

Manfred Nehonsky also observed extremely bright iridescence on high level foehn clouds over Upper Austria the same day. This iridescence looked like bright mother-of-pearl-clouds.

Another observation made the same day, but by mistake entitled as a halo, can be found here.

I think this is iridescence on globular ice particles as Paul J. Neiman and Joseph A. Shaw suggested in their article “Coronas and Iridescence in Mountain Wave Clouds Over Northeastern Colorado“.

Author: Claudia Hinz, Germany

Hair Ice

Hair ice (in German Haareis) is formed at dead wood by conditions of high humidity and temperatures near freezing point. Water in the pores expands below 4°C and freezes on the surface. In this way fine ice needles were created. (123)

I found it in the Black Forest (Schwarzwald) in southern Germany.

Author: Helga Schöps, Germany

Halo Meeting of the “Arbeitskreis Meteore e.V. / FG Atmosphärische Erscheinungen der VdS e.V.“ at the Sudelfeld (Upper Bavaria), January 08 – 10, 2010

Winter halos in nearby ice crystals are quite a rare sighting in most parts of Germany. However, there are few special places where the chances for such displays are much higher, such as the Alps mountains. To benefit from this, 14 halo enthusiasts met at the Sudelfeld Youth hostel near Bayrischzell in the vicinity of the Wendelstein (1838 m) during the second weekend of January. Already on Thursday (January 07) a very impressive halo phenomenon at the sun could be observed by Reinhard Nitze. Unfortunately, throughout the meeting a complete cover of low-level clouds blocked the sun so that halo observations were restricted to artificial light sources during night time. The highest halo activity was noticed at late Friday evening, involving light pillars (or superlamps), upper and lower 22° tangent arcs (“champagne glasses”), parhelic circles (visible for only few seconds), and superparhelia (not photographed due to fleeting appearance). The phenomena showed remarkable dynamics, lasting for about 10 minutes and being followed by intervals of 30-60 minutes without halos. The influence of snow blowers was discussed as well, since there were some of them running the whole night, approximately 500 m apart from the observation place.

During the second evening only weak light pillars were seen for short times, eventually being replaced by fog bows due to rising temperatures and the transition from ice crystal to water droplet fog. Great fun were the shadow plays using a floodlight in the back of the people what finally led to photos of the “Sudelfeld monster”.Apart from the actual observations, the participants joined a workshop program containing slideshows from Michael Großmann, Claudia Hinz, Reinhard Nitze, and Andreas Zeiske as well as talks dedicated to special topics such as halo image stacking by Georg Dittié, high dynamic range image processing by Claudia Hinz, high precision measurements of the moon’s opposition effect by Elmar Schmidt, microphotography of snow and ice crystals by Reinhard Nitze, and artificial dew bows as well as stereo photography by Alexander Haußmann. The following experimental demonstration of glass bead bows in divergent light was received with great interest and triggered a high amount of photographic activity. Furthermore, an excursion to the nearby Tatzlwurm waterfall (named after some kind of dragon) was organized at Saturday afternoon and revealed a great winter landscape containing a large number of worthwhile photo subjects.

More pictures are here.

Author: Alexander Haußmann, Hörlitz, Germany

Colours inside a cracked piece of ice

After some very cold days in Heréd (Northern Hungary) Karoly Viczian went out to the garden to break the ice in a rainwater collecting barrel. On a small piece of ice he cut out from the barrel he could see some very vivid colours – it reminds me to the diffraction colours of an opal gemstone. So maybe the coloures were produced by some microscopic bubbles inside the ice just the same way as they form in the gemstone that has small spherical structure . But Károly said he had noticed the colours after breaking up the ice, so it seems that the small cracks inside might have produced them with the help of birefringence.

As Károly told me the ice was the outcome of multiple freezing and melting periods, so it might also have separate layers inside. He has more pictures of the same piece of ice. The water was simple rainwater, only some fallen walnut leaves were at the bottom of the barrel, nothing was put in it willingly.
What is the correct explanation of this phenomena?

Posted by Noli

Frost Optics

2008/02/10 Taken in Green Bay, Wisconsin, USA at temperature of -10 F. I looked out to see the sunrise refracting through frost crystals on our back window. The entire pane sparkled with these delicate, miniature creations, but only a few of them were postitioned so that I could see the entire color spectrum at once.

Author:  Peg Zenko, Wisconsin, USA

Diamond-dust Sundog

This very bright “localized” sundog was formed in ice fog among trees along the Bow River in Calgary on a very cold winter day recently. The remarkable feature of this sundog is that trees are profiled against it. The equivalent sundog on the opposite side of the Sun was almost as bright. These sundogs varied in brightness as ice-fog density varied. Individual ice crystals show up as transient bright points.

Author: Alan Clark, Canada

Icy window corona

At the beginning of this winter season at a cold morning – dark outside – with a thin layer of hoarfrost on the inner side of the bus windows I’ve noticed that the light of the street lamps’ light was not simply scattered on the windows, but having colorful corona around them. At that time I had no camera with me… All along the winter I was waiting for the same display each morning when some ice was on the bus windows, but for long weeks I haven’t met with such spectacular phenomena again.This day was my day on 24th January. Very thin layer of frost was on the inner part of the windows, (with some frost ferns too by the corner of the window frame), mainly this layer was made of small uniform ice crystals made of frozen vapor droplets, we might call it an ice film, it was about 0,1 mm thin.All the lamps outside had a corona, no matter how far the lamp was.The street lamps with white light had the most beautiful color range, the orange colored light of sodium vapor lamps had a less distinct colors and they were a bit moved towards the reds. Not only the street lamps’ corona was seen on the ice layer, but a much less spectacular corona around the reflection of the inner lamps of the bus too! At the part of the frost ferns pattern the corona became irregular in shape. When the lamp was near the window I could also see the bigger outer rings of the corona. Almost the same phenomena appears when simple water vapour is on the windows, but that one is really less poor in colors compared to the ice film corona.This was the first time when I could take photos of a corona produced by ice crystals. It’s a pity, I could not take close-up photo of the ice layer itself (the bus was driving me to work so it was permanently moving).

Photos are collected here: The only afterwork was some noise reduction and size reduction. It was totally dark outside, so the pics were taken with ISO200 – ISO400; aperture F4 – F5,6; exp. 1/15 – 1/25 sec. auto white balance; without tripod or any kind of help to avoid moving.I wonder if the same phenomena would appear if the outer side of the windows would have a layer of hoarfrost on it. It’s only weather’s turn to show it up!

Author: Monika Landy-Gyebnar, Veszprem, Hungary

“Subsun” upon ice crystal

While taking the photographs of the iridescent fissures in the ice, I noticed some beautiful ice crystal structures on one of the puddles. When I looked at them more closely, I saw intensive reflections of the sun in them. Animated by the hoar-frost halo I discovered before, I got the idea to photograph the reflection of the sun as a kind of “subsun”. To get the reflection completely into the picture, it was necessary to make a macro of the ice crystal. However, the crystal turned out ot be a lot more complex than I thought.

The reflection of the sun, however, was not a homogenuous surface, but appeared to be a slightly oval shaped, speckled white spot with a broad golden and also speckled rim. It is exactly this reddish-golden rim that gives me quite a headache, reminding me a lot of the reddish coloured fringes which sometimes can be seen at other haloes like parhelic circle or 120°-sundogs. The sequence of colours and the outward manifestation is that of a common aureole. However, in this picture it looks as if the colour came out of the inside of the ice crystals. Especially take a close look at the crystals marked with arrows.

About one week later at another frozen puddle, the reflection of the sun again had a reddish rim. But here the situation is quite different. This time it is a fragment of the frozen water surface. The wind has carried dust upon the ice which with the help of the sun had smolten innumerable tiny holes into the surface which originally had been smooth. Low temperatures then had made it freeze again. All in all, these processes have caused a rather permeable surface structure to develop, so the reflection of the sun is more like a diffraction. Especially in its upper part, there is an indication of iridescence. Who knows, on day somebody might succeed in taking photographs of “ice surface coronae”!

Last but not least: Of course you can also try to take a fragment of ice off a puddle and make some experiments with it. Maybe there will be confirmations of these sightings pointing also out to the possibility of a (additional) light refraction in the red rim.

Author: Reinhard Nitze, Barsinghausen, Germany