2011. március 31., csütörtök

South Pole odd radius halo display 6 February 1999

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This was a long lasting display with faint odd radius halos. The scanned slides here only show 9° stuff, but there was more, also the 20° and 24° halos. The crystal orientatation is poorly column oriented as the 9° halo is slightly brighter on the sides. And indeed, in the crystal photos we took with Jarmo Moilanen there were columnar pyramids.

2011. március 27., vasárnap

South Pole halos 5 February 1999

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Basic display at South Pole. The third image is taken by Jarmo Moilanen. The last two images show a contrail display.

2011. március 24., csütörtök

Halo display at South Pole on 4 February 1999

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Just scanned this one from my slides. It is basic South Pole summer season display. In the third and fouth image there is something at the horizon outside the 22° halo. Reflected Lowitz arcs or lower 24° parhelia? Hard to say which one, the clouds mask for example the possible lower 9° parhelia. Maybe there are both. The last heavily usmed image shows faint anthelion / diffuse arcs.

2011. március 22., kedd

Polar stratospheric clouds

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Some photos of polar stratospheric clouds from Lappland. In Finland the PSCs' usually come without irisdescent colours. They occur in winter when there is a deep low pressure over Scandinavia. Thus forecasting their appearance is rather easy. These clouds also are called as mother-of-pearl and nacreous clouds, both names refererring to the irisdescent color in molluscs shells.

The photos above were taken on two occasions, the ones with purple glow on 30 December 1999 and the one with white clouds on 28 November 1999.

2011. március 7., hétfő

C.W.Hissink's ellipse - 9° column arc or an elliptical halo?

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The halo observation by C. W. Hissink 28 June 1901 in Netherland's Zutfen is generally regarded as containing an elliptical halo, and would be thus the second historical record of these rare phomena (the observation is in 1901 Onweders). But could there be a possibility that Hissink did not actually see an elliptical halo, but rather a pyramidal crystal formed 9° column arc, which is an equally rare sight? Hissink measured the halo with an octant and gives 10.5 degree vertical and 7.5 degree horizontal measure for the halo, but it does not say whether these are diameter or radius values. If the former was true, then it would be definitely an ellipse, which are rather small, but in the latter case it would more likely be a 9° column arc.

In the account of the obseravation it is mentioned that the ellipse formed in a lower Ci cloud than the rest of the display (as far as I can understand the text). Elliptical halos never form in high clouds, but rather in middle or low level clouds, typically in the Altocumulus virga. This piece of information would be thus consistent with elliptical halo explanation if we assume there were both high clouds and Ac formed middle level cirrus clouds simultaneously in the sky. Such occurrences of elliptical halos with normal halos have been already photographed at least by Jukka Ruoskanen (the simulations and crystal figures above are made with his HaloPoint software). But then again we have a photographed case by Konstantin Bespalov, where sharply cut segments of odd radius halos with 9° column arc are seen, thus formed in a separate crystal material from the rest of the display (although not separate cloud is really visible). Also the observation of 9° column arc by Martti Perälä in Lapua, Finland, on 27 April 1988 (third image), has a strong resemblance with Hissink's observation. It is identified as "Hissink's halo" in the report, but the estimated 10 and 8 degrees vertical and horizontal sun distances clearly class it as 9° column arc. The sun is at 35-38 degrees elevation, which makes the 9° column arc more elliptical than in Hissink's observation, where the sun was at 47.5 degrees.

Conclusions on the Hissink's observation? Can not really come to any, there is not enough information. Knowing whether it was the diameter or sun distance would give straight answer. Also any piece of additional information about the cloud situation might prove useful, for example if there was a mention of Altocumulus clouds in the sky. If Hissink's halo was indeed a 9° column arc, it would rank again as the second historical record if this halo. There is an earlier display from 5 September 1899, which possibly had a 9° column arc on the other side of the sun, as shown by the fourth image above. But as the display is one sided, one could equally argue that it is just a segment of 9° halo. If, however, it was 9° column arc, Hissink would still get the glory, as he made also this observation.

Afterthought 24 February. The innermost halo lasted 20 minutes. That is long time for an elliptical halo and even longer when we consider that there were simultaneouslyl also halos from normal prismatic crystals. Yeah, if I had to bet, I would definitely go for the 9° column arc now.

2011. március 5., szombat

23° plate arcs from summer 2010

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Some odd radius displays from last summer in Tampere. In most of them there was only 23° plate arc visible. Although the displays were not that impressive, there were plenty of them. In July-August a record breaking heat wave produced many 23° plate arcs, I saw them on 14 days. Stacked images usually revealed more pyramid halos, mostly the 9° halo or 18° plate arcs. 23° plate arc is very easy to identify mistakenly as 22° upper tangent arc.

As a rule, when it is hot weather period, 23° plate arc is more common than 22° upper tangent arc. I am pretty sure they are not limited to Finland and Estonia only (in the latter Marko Krusel has a lot of observations). Hopefully we start getting observations of them coming summer from elsewhere.

The gallery above does not include every odd radius display from last summer. I could not find all them from the hides of my disorganized computer. I'll add them as they come around. Many displays were also not photographed. The dates are given in the file names. In some cases stacking has really made wonders in squeezing out the halos invisible in single frames. In the 15 August display, where there was only solitary 23° plate arc visible to the eye (and nothing more even through a convex "blind spot" mirror), stacking photos taken during about 2 hours unveiled a complex display with 35° halo as shown by the 8 and 9 images in the gallery. The two upper and lower images are single frames, the two in the middle are the same stacked image with different level of unsharp masking. Also the display of 19 August improved markedly by stacking photos taken during only 3 and 13 minutes, the last two images in the gallery. Again comparison with single frames is given.

2011. március 3., csütörtök

Odd radius display in Resolute Bay

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This one occured on 3 April 1998. The spots near the horizon are lower 24° plate arcs. Sometimes is not easy - or even possible - to distinquish them from reflected Lowitz arcs. But this case is obvious, there is also a good lower 9° plate arc. Much fainter are 18°, 23° and upper 24° plate arcs.  The display lasted for several hours, temperature was around -27° C. The source for this display is not known. Maybe it was natural.

2011. március 1., kedd

Diamond dust halo display initiated by a snow blower

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This diamond dust display occurred on 1 April 1998 in Resolute Bay, Canada. The images have been scanned from slides which is why the display has lost its brilliance. But it was not the most brilliant display anyway. What's more interesting here is how it formed. In two photos there is an ice cloud erupting from the Resolute Bay airport. It was caused by a snow blower attached to a tractor that was operating for two hours or so. Most of the snow it blew in the air fell immediately back to the ground, but there also came a cloud of invisible tiny ice particles that started drifting with the wind. These particles acted as a template around which the ice crystals that caused the halo display grew. This happens when air water vapor content exceeds ice saturation, only then can water vapor deposit on these ice nuclei. If the air moisture was below ice saturation, then there would not have been any ice crystal cloud that we see in the photos - and no halos either.

In some of the photos there is rudimentary Moilanen arc, which is not a surprise, since this was a man made display. The photos are in chronological order. As I was running away from the airport the display got constantly better because the crystals had time to grow bigger. After some time Resolute weather station caretaker Wayne Davidson drove by and took me further away from the airport where the display was better defined, though not any brighter, as is seen in the last image.