Friday, February 26, 2010

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. (1-2-3)

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

Author: Helga Schöps, Germany

Sunday, February 21, 2010

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.

Photo: Claudia Hinz

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.

Photo: Udo Hennig

More pictures are here.

Author: Alexander Haußmann, Hörlitz, Germany

Monday, February 01, 2010

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?