Diamond dust halos on the night of 12/13 January – part III

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Has anyone seen subparhelic circle inside subparhelia? Neither have I. Not before stacking the photos from the latter part of the 12/13 January night. In one of the stacks this missing segment is seen faintly inside subparhelia. The version of the image above, made by Nicolas Lefaudeux, was done with emphasis on getting the segment stand out as clearly as possible.

Below is a more conventional looking version of the image and simulation. The plate oriented crystals in the simulation were fully triangular. Regular hexagons do not make the missing segment, except at very high light source elevations.

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What else? The arcs that in Finland these days are called the Schulthess arcs are quite well defined, especially in the last photo set of the night (below). One sees both concave and convex components extending from subparhelia to parhelia, though the latter component seems to have a gap around the horizon, not reproduced by the simulation. I have never seen in sun display photos the concave component between parhelia and horizon. It is always just the convex component that is visible.

Marko Riikonen

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Diamond dust halos on the night of 12/13 January – part II

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More photos from the 12/13 January night. The image above is a view opposite to the spotlight. Seen is blue circle, diffuse, Wegener and subhelic arcs. Below are two more images, the blue-minus-red image shows the “column 351/361”, which is the Kern arc equivalent of 46° supralateral arc. The lamp is about 5 degrees below the camera.

Marko Riikonen

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Diamond dust halos on the night of 12/13 January – part I

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With this post starts the presentation of January 12/13 night results in Rovaniemi. All photos are in spotlight beam. The image above is a singe frame with 30s exposure. Just basic halos there. In the rest of the images emphasis is on the crystal glitter formation that makes an intensity threshold at the zenith. The raypath for this effect, which is quite common in spotligth displays, is 3-5-7 and here it is from column oriented crystals. What’s peculiar is the psychedelic colors of individual crystals, as shown by the left side image below that is a maximum stack of four frames. In the 20 frame average stack next to it the colors are washed away. The lamp is the usual 5 degrees below horizon. Below in the smaller thumbnails are two single frames which display the colored glitter even more clearly and another maximum stack of 14 frames. Individual frames are all 30s exposures.

Marko Riikonen

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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:

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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

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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

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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