A re-visited 13° halo observation from 2013, and some thoughts about the responsible crystal faces

Circular halos of 12°-13° in radius are named “exotic” because they do not fit in the (nowadays) traditional sequence of well-documented halo radii from pyramidal ice crystals (9°, 18°, 20°, 22°, 23°, 24°, 35°, 46°). The first known photographs of such a halo were obtained at the South Pole, December 11th-12th, 1998, by Walter Tape, Jarmo Moilanen and Robert Greenler. Up to now, there are only few more (Michael Theusner, Bremerhaven, October 28th, 2012; Nicolas Lefaudeux, Paris, May 04th, 2014).

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Pyramidalhalo in Calgary, Canada

At about 3:16pm on May 4, 2016, with a sun elevation of 49 degrees, Alan Clark observed pyramidal halos from Calgary, Canada, showing a relatively wide 23deg halo, a distinct 9deg halo, and a hint of an 18.5deg component. A daytime maximum temperature of over 26°C on this day in Calgary broke long-term records. The within which The halo display was formed within cirrus cloud that preceded the arrival of a distinctive cold front.

Alan also produced RGB intensity scans from these halo photos, showing the correct colour separation, with red inner colouring for these halos.

Odd radius display and its crystals


This odd radius display appeared on the night of 17/18 January in Rovaniemi at -29° C. Visible is the usual duo of 9° and 35° halos, and also what seems like 18° halo.

Crystals were collected. It is hard to make sense of most of the crystals. Many seem to have pyramid faces, but obvious pyramids were very few in the sample.

Jarmo Moilanen / Marko Riikonen

9° and 35° – not your expected combination of odd radius halos


This display is far from being impressive. But it has an interesting combination of odd radius halos: 9° and 35°. Not something that would be expected from your textbook pyramid crystals. We had several displays in such a style this winter.

The display was seen on the night of 7/8 January in Rovaniemi in diamond dust that was being displaced by an increasing snowfall. The temperature at the official measuring site 7 km away was -27° C.

Marko Riikonen / Nicolas Lefaudeux

Odd radius display in California

At around 2 p.m. on February 23, 2016 I was  filming superior mirage of a distant land and superior mirage of a  sea surface. From San Francisco the superior mirages are observed  on warm days, and February 23 was not an exception. The air temperature was higher than 70 degree Fahrenheit. At some point I took my eyes from the horizon and looked up. The sight amazed me. I was looking at bright, circular halos that I have never seen before. Later I found out that the halos I observed were  9 °, 18 °, 20 °, 24 ° and 35 ° radii, and 24 ° upper tangent arc. and that the display has a name: odd radius halos.

Pictures with a different methods of encroachment

From the pictures posted on the NET by other people I found out that a similar display was seen at Ballico, California, which is 50 miles (80 kilometers)  east  of San Francisco. Another observer was located in Sunnyvale 20 miles (32 kilometers) south of San Francisco. It often happens that odd radius halos are observed over vast distances. As a matter of fact on April 14, 1974  the odd radius halos display in England was overdosed at the locations that were 460 kilometers apart.  From Claudia Hinz I’ve learned that odd halos display in Middle Europe are associated with prominent cold fronts that slowly move from north to south, but no cold front arrived in San Francisco on the next day. February 24, 2016 was only slighter cooler than February 23.

halo map-4k

Author: Mila Zinkova, San Francisco

Lunar odd radius display in diamond dust


On four out of last five winters Tapio Koski has photographed lunar diamond dust odd radius halos in the Rovaniemi area. These one-per-winter occurrences are almost solely responsible for lunar diamond dust odd radius displays photographed in Finland during those years. This winter we wanted take part in the tradition. Yet despite numerous odd radius displays we had harvested in the beam, those by the moon – or sun for that matter – were simply not coming.

Except on the night of 20/21 January, which was the month’s last diamond dust night in Rovaniemi. During the day, when driving in the city, we paid attention to Fairbanksian amber, a beautiful yellow glow in the sun direction that can be seen in cold weather and with which we became familiar on the successful halo expedition to Fairbanks in January 1996. This gave us an omen of foreboding that a night of big odd radii diamond dust was finally on the cards for Rovaniemi. Weather forecast was with us too, as the temperature was expected to drop to -33° C – the magic number that Walt Tape has given as being in the center of the temperature range favorable for odd radii.

The display appeared as some thin water cloud that had momentarily overtaken the sky cleared away. The first halo visible was upper 23° plate arc, many others soon followed the suit. In the beam only a crappy plate dominated display was visible – the pyramid stuff was higher up.

Jarmo Moilanen / Marko Riikonen

Halos from oriented pyramids in the spotlight beam

untitled-1On the night of 20/21 January we got photographed oriented pyramid crystal halos in the spotlight beam on two occasions. The first occasion, shown above, got us completely unawares and the odd radii stuff was all gone in the next shot which would have had the exposure right. Colored and solid upper and lower 9° plate arcs were seen, but if they were still present when the camera was placed in the beam, they are nevertheless washed out by the overexposure. In the photo one still sees the 35° halo and lower 20° plate arc. The lower 9° plate arc was of the 23-6 type as the lamp was about 5 degrees below below horizon.

We drove around and switched on the lamp here and there, stubbornly trying to get a rerun, but to no avail. Diamond dust was already on the retreat, the air was drying up even though it was around -33° C. Yet we managed to get something just before it all evaporated, as shown by the image here:

indust_3_ave-and-max_valmis2-ONG24 indust_READY-OMG24

A little simulation study as was necessary to see whether it was column (left) or plate (middle and right) pyramid stuff, but that did not give definitive answer. The plate scenario simulations are identical except that in one is 22° halo and in the other 23°. The 35° and 18/20° stuff above the lamp were initially noticed visually which prompted us take the photo series for this stack.

These last photos were taken at 3:30 am. The two photos below are the first photos of the night at 6 pm. We photographed these lunar and beam displays simultaneously. No odd radii yet at this early hour.

Marko Riikonen / Jarmo Moilanen

Pyramid crystals and odd radius halos, part II


More halo and crystal photos from the 20/21 January night. While this second crystal sampling and photographing session was under way, the display in the beam was photographed constantly, but again odd radius halos are not visible in the photos, expect perhaps for a suggestion of 35° halo at one stage (not shown). Yet again the sample was littered with classical pyramids as shown by the images in the gallery.

The picture above is an appearance of odd radius halos after the crystal business was over with. It is a “blue minus red” (br) of stack with total of 9m30s exposure and contains 9°, 18° and 35° halos. Three more halo images are in the gallery, first a single frame from the stack above, then two that are versions of another stack, the br displaying full 46° halo.

Jarmo Moilanen / Marko Riikonen

Pyramid crystals and odd radius halos, part I


The night of January 20/21 in Rovaniemi was a night of odd radius halos. Here are shown mostly crystals collected during a half hour period. At the same time photos were taken continuously in the spotlight beam, below is one of those stacks. The sample contained plenty of traditional type pyramids – something we have not yet seen this winter. So it is curious that odd radius halos are not conspicuous in the beam photos and at times even completely absent. Maybe the abundant cavities in the crystals caused too much disturbance.

The stack is from a stage where the odd radius stuff was at its best, taken towards the end of the crystal collecting period. Visible are 9°, 18° and 35° halos. The temperature during the night was around -33° C.

Jarmo Moilanen / Marko Riikonen