Another appearance of the mysterious Sub-Kern companion

The image above shows an arc that points towards the bulge in sub-Kern. Its formation is unknown. We captured the arc first time on two occasions on the night of 6/7 January 2016 in Rovaniemi. The current case was photographed in Rovaniemi too, on the night of 28/29 November 2016.

Judging from the crossing of helic arc and (what appears to be) Hastings over the 46° halo, the lamp must be around 3.5 degrees below horizon. I made some quick simulations. The upper one has plates, randoms, and Parry. Plate shaped Parry crystals were used to get the relative intensity of the helic arc and Hastings somewhat comparable to the actual arcs. Simulation has also subanthelic arc, and it seems to be present in the photo, although it is quite broad and diffuse. The lack of Parry arc in the actual display is rather curious.

To make sure that the mystery arc is not some kind of anomalous singularly occurring Tricker, the lower simulation was made with added column oriented crystals. Sure enough, location of the Tricker does not match.

The bulge in sub-Kern seems itself also anomalous and appears to be associated with the mystery arc. The bulge has not been photographed in the numerous displays without this arc.

On some aspects of a display observed in Rovaniemi on the night of 9/10November 2016

By Marko Riikonen

This was a good no-hassle night of diamond dust hunt. The swarm was stationary and I didn’t have to pack up every 20 minutes to follow its whims. During the 6 hours of observing it was necessary to move only once. Also, both two locations were quite good concerning the light pollution. Especially the second place, where I wrapped it up in the morning ours, had a really dark segment which I used to light up the anthelic region.

As for the halos, the start of the night at around midnight was not so inspiring. As I arrived to the snow deposit area near the river, a sneak peek in beam revealed a run-of-the-mill plate display and I though it will just get worse because the temperatures were in the bad range, around -15 C. So I decided I might as well give some minutes for the half-moon display that had a smudge of Moilanen arc. In photographs it was transformed into a nice V-shape.

Then I switched on the sacred light, and to my delight, things improved soon. First to be noticed, when standing a little outside the beam, was an odd intensity threshold which materialized into a helic arc. “Hastgener” followed the suit, it was a beautiful colored arc of crystal glitter. And as I turned facing opposite to the lamp, higher up in the sky were glittering the two vertical parts of the subanthelic arc loop. Nothing much suggestive of column stuff was evident, neither visually nor from the camera display, so I was pretty sure the “Hastgener” must be a Hastings arc.

But was it? This post is about the two photos that I took towards the end of the night in the second location (which is another snow deposit site), where I moved after it got crappy at the first location. I have attempted to make a simulations of those two photos to test the issue, as shown below. While working on them, I also realized from the br image something of moderate interest: there are blue spots on both Liljequist and sub-Liljequist parhelia.

                            It was -20° C at the location where these photos were taken.

I got the best match for the display using two Parry populations in the HaloPoint software: one with strictly oriented crystals and other with 4 degree rotation. The contribution of these two populations are dissected in the image below, as well as of the other two populations used in the simulation. The 4 degree rotational population has an orientation that makes halos look like an intermediate between Parry and column. These two populations were necessary to make the subanthelic arc look right. It is actually quite typical that you have use about 4-5 degree rotating Parry crystals to simulate diamond dust displays. Earlier I have analysed one case from 2010 in Tampere.

Because of the need for rotating population, I would play is safe and say we don’t have a pure uppervex Hastings here, even though the display clearly has Parry domination over columns. The photos taken earlier in the night at the first location may have a cleaner Hastings, but I need to take a closer look at them.

Then to the colors of Liljequist parhelia. In the br version above of the image that points opposite to the camera there are visible blue spots of both Liljequist and sub-Liljequist parhelia. The flashing image below shows that the br image brightenings do not overlap with brightest parts of the Liljequist parhelia in visual image, but are a little further out towards the 120 parhelia. This is the location where the blue spots are seen also in the simulation.

The simulation shows also a narrow slice of reddish color further out from the anthelic point, at the very edge of Liljequist parhelia. The red is there because the fainter outer half of Liljequist parhelia away from anthelic point is made by parhelia which is rotated by 120 degrees (raypath 3567). In br the red color would make a dark spot, but it is not seen in the photos.

Everything said in the two paragraphs above applies also to the sub-stuff. The raypaths are the same, except for and added basal reflection.

So this observation of Liljequist parhelia blue spots adds to the growing list of various blue effects. The sub-Lilje blue spot we seem to have photographed already last winter on the night of 5/6 January, but normal Lilje blue spot is a new catch as far as I know. Other blue effects that have been photographed, in addition to the traditional parhelic circle blue spot, are blue circle, blue subsun and subanthelic arc blue spot. The latter has not been talked about, it is visible in my photo of a spotlight display from the night of 7/8 December 2008.

Correction: the subanthelic arc blue spot has been talked about in the comments section of the link above.

A pure breed uppervex Hastings

In snow gun diamond dust displays Parry orientation is often strongly emphasized in relation to column orientation. There may be no signs of column orientation at all, except for perhaps a slight tanget arc brightening on top of 22° halo.

Such displays have made observers to ask themselves whether the uppervex Hastings arc – the Hastings arc component that is touching the uppervex Parry arc – could be sometimes be obseved in addition to the usual Wegener, or even without it. So far displays where light source elevation allows separation of uppervex Hastings and Wegener have not resulted in any candidates.

However, in spotlight displays where lamp is at or below the horizon, we have managed to photograph during the last and this winter a several of cases that are suggestive of an uppervex Hastings. And not even suggestive, but outright assertive.

The uppervex Hastings intensifies with lowering light source elevation, only complication is that it then starts to overlap with Wegener and identification must be done on the basis of other halos in the display. If Parry orientation halos are prominent and column orientation halos such as 46° lateral arcs, diffuse arcs and subhelic and Tricker arc are very weak or absent, then we might say that the “Hastgener” in the display is indeed Hastings arc.

As an example of a display that leaves little doubt of its Hastings nature, here is shown a one that Marko Mikkilä observed this year, on the 2nd January in Sievi. The lamp was resting on the ground on a rather level field and is according to Mikkilä about 3 degrees below the camera.

We see no evidence of column orientation – no 46° lateral arcs, no Tricker, no subhelic arc. Instead, in the image there is an overwhelming helic arc and Tape arcs, which both are solely Parry orientation born. Thus the faint “Hastgener” must be an uppervex Hastings arc, rather than Wegener.

Above is a attempt at simulating with HaloPoint. It supports the Parry scenario untarnished by columns, even though the details may not be quite right. Perhaps the most striking mismatch is with the subanthelic arc, which is bright in simulation but seems to be missing from the photo. However, there is a darker area which looks as if shaped by subanthelic arc. This seems to be a real effect, we have seen similar looking dark voids inside anthelic arcs before and in an upcoming post I will be showing a good example of such darkness associated with this halo. Perhaps the more intense parts of subanthelic arc are outside left outside of Mikkilä’s photo, although in that case it should have been possible to make a matching simulation. I actually did find an option which was better in that respect, but other parts got too wrong to take it seriously.

An earlier display in the same location by Mikkilä seems to also contain a pure uppervex Hastings.

A distinct Wegener but other reflection halos from column orientation lacking

By Marko Riikonen

Spotlight displays are great in that almost every time you photograph them, you realize you understand halos less and less. This time the puzzle is: Why Wegener in the image above is so strong in comparison to other reflection halos? No subhelic arc is visible and neither there seems to be diffuse arc – I think the spikes at the subanthelic point are lamp artefacts. Of course I can’t not say that for sure, but around the subanthelic point even weak stuff shows up easily to the eye, so had there been diffuse arcs, I should have noticed it. If we accept this, then, in addition to the Wegener, the only suggestion of column reflection halos is what looks like a short patch of Tricker arc cutting across the sub-Kern arc (see the simulation below for comparison).

As for the posed question, I don’t have an answer. In simulations, using plate like column oriented crystals weakens subhelic and diffuse arcs in relation to Wegener, but they are still well visible, as shown by the simulation in the image below, which was done, I think, with h/d 0.3 plates.

Of the other stuff worth a mention in the image – which is a total of 27 min 20 sec exposure – is the sub-120° parhelion. It is quite common in spotlight displays, but to see it one typically has to run alonside the beam. This time it was clearly visible while standing still. There is also a blue spot. At 9 degree elevation it shares exactly the same location with 120° parhelion, which may be there too.

Another photo taken a bit later and at another location, shows a dark circular void at the zenith (or nadir, if you look from the point of view of halos), as shown below. A much more striking instance of this effect was captured by Jari Luomanen in 2013.

This night of halo hunt started on 8 November at 10 pm and lasted until 5 am. The development of the diamond dust quality was a slow and hopeless decline, which happens quite often when temperatures drop towards -15 °C. That is considered by halo hunters the worst temperature, giving crappy displays. Unfortunately the temperature notes were lost as my halo hunting diary got corrupted and shows now page after page ####s instead of letters. But I think it was between -11 and -14 °C through the night.

Diamond dust season opened in Finland

By Marko Riikonen

On the fifth of November the diamond dust season opened in earnest, when Esa Palmi photographed a major display at the Kittilä airport. While the sun side is always the attention gatherer, the main attraction of the display is really on the opposite part of the sky, where a strong subanthelic arc dominates the scene.

Of its loop visible are the segments on the sides, and we are used of having seen this kind of subanthelic arc more commonly in spotlight displays. Simulations tell such intensity distribution results from triangular crystals. Triangulars are regularly needed to model snow gun displays and here the source was the Levi ski resort some 10 km to the north. The triangle interpretation is also in accordance with the missing of uppercave Parry arc: the crystals are falling with their wedge pointed straight up, so only uppervex Parry can form.

Palmi is familiar with halos and did a good job of documenting the display. If something more could have been done, that would have been covering also the area around zenith, where a faint and rare halo called the Ounasvaara arc might have lurked. It forms in triangular Parry crystals and the few known observations are from spotlight displays. Granted, solar displays don’t have as good contrast as spotlight displays, and so if the halo was there, it might have been impossible to see with the eye. But camera would have still recorded it. Actually, no one has seen Ounasvaara arc in spotlight displays either, all finds have been made from photos.

All Palmi’s photos of the display

A major spotlight display with possible 4th Tape arc component

By Jarmo Moilanen, Marko Mikkilä and Marko Riikonen

On 23 November 2015, we were watching diamond dust halos develop under overcast skies in Rovaniemi. As we stood on a rectangular field a couple of hundred meters across, we followed halos slowly gather momentum in the spotlight beam, reaching climax when clouds were cleared away for a short while – and revealing at the same time also a lunar display. Here is an excerpt from Marko’s observation log written the next day:

“The display just adds gear. We are looking at beautiful subanthelic stuff, subanthelic arc, diffuse arc… It becomes monstrous when the cloud almost disappears. That is when we get also a moon display with full parhelic circle. No one seems to be in a rush to photograph the moon display. The beam display is sheer grotesquery. The laser scapel sharp, 100% pure glitter of the tangent arc and uppervex Parry.”

In the photos the lamp is 5-6 degrees below the horizon. In the image above, the most noteworthy feature perhaps is the slight intensity enhancement in the 46° infralateral arc, marked with arrows in the simulation below. These could be sings of the fourth, as of yet unobserved Tape arc component (raypath 14), which is highly unlikely to be ever seen in solar displays as it appears in simulations only when light is several degrees below the horizon. Although it is probably here, we would still hope for a better example from lower light elevations that would make it easier to identify.

Another feature of interest is the “Ounasvaara arc”, which in the photos looks like an odd continuation of circumnadir arc. This Parry orientation halo is visible particularly well in the two photos below, that, unlike the photo above, were taken off-beam, from underneath. Although off-beam images are not visually as appealing for their non-uniform lighting, the halos in the brightest part of the beam are enhanced in them.

We regret of not getting a visual of the Ounasvaara arc – judging from its intensity, it should have been easily visible to the eye. Well, something for the next time.

As usual, we also had a gasoline filled petri dish out to collect the crystals. No serious end cavities this time, which is in accordance with the observation log’s note of “100% pure glitter”.

At last we switched off the lamp to give the moon display the stage. However, by the time we got to it, the lunar halos were already starting to decline. In our next post we will show nevertheless the few photos that were taken.

More photos from three weeks ago in Rovaniemi

It seems putting the photos of the recent displays to my web page will delay. So, in a meanwhile here are two more photos of the display three weeks back.

When light source is at 0° elevation, some difficulties arises in identifying certain halos. Tricker arc and subanthelic arc merge together, as do helic and subhelic arcs. However, the subanthelic arc is formed by Parry-oriented crystals, while Tricker arc is from singly oriented columns. Because in this display the 46° supralateral arc is rather strong, and there are only weak indications of 46° Parry or Tape arcs, probably singly oriented columns were in command. The even brightness of the Tricker/subanthelic loop is also typical for Tricker arc. Subanthelic arc has strong brightenings on the sides - at least in the simulations - and that is actually what seems to be present in the the display of last weekend.

The reason why halos are seen so strongly in the halogen light is probably the relatively dark background sky as compared to sun or moon situation. Yet all the halogen lamp displays that I have photographed so far have been hampered by city lights. Once the crystal cloud drifts to the dark outskirts of the city, more intense appearances should be expected.

By Marko Riikonen

Another halogen lamp display from Rovaniemi

A bright halogen spotlight and diamond dust is a magic combination.

Spot yourself exactly in the middle of the beam and breathtaking halo views may rewards you. An outsider will see just somebody bathing in the light and may wonder what is going on. There might be a Moon in the sky at the same time - like in the case shown here - but it shows hardly no halos at all. The lamp creates its own universe of halos.

The Ounasvaara snow guns created this display last night in Rovaniemi in the beam of a Cyclops Thor Platinum X-15 halogen lamp. Because of the lack of 46° lateral arcs, this display must have been dominated by Parry crystals. Indeed, in the lower right image there are both upper and lower Tape arcs as an indication of Parry orientation.

An interesting feature is seen in the images on left (the lower image is an unsharp masked from the upper). There seems to be a loop inside the helic arc. Much like the loop formed by the subanthelic arc.

On the upper right is a simulation that shows a quite similar loop (arrow). The crystals in simulation are Parry oriented and they are semitriangular, a half way between a triangle and regular hexagon. The thing in the photo looks to me like a halo and it might be the one shown in the simulation. I have not raytraced it, so I don't know what it might be called. There are some differences in the loop sizes between the simulation and the photos, but then again the projections are not exatly the same.

A bit more could be said about the results of the last night, but this must do for now. The simulation was made with a program by Jukka Ruoskanen.

By Marko Riikonen

Diamond dust from Himos snow guns

Mika Aho was also on the halo move on Saturday 4. November. He headed for the Himos ski centre, where some 30 snow guns were operational. The trip was worthwhile. From skiing flanks spread an ice crystal cloud that, even though a bit unclean in appearance, presented some of the rarest halos.

These rare halos are best shown in the photo on the left where several white arcs are seen crossing the sky. Wegener, helic, subhelic, subanthelic and Tricker arcs are all present. Outside Antarctica subanthelic arc has been observed reliably only twice before, both times in Finland. Now Aho's photos add the third observation.

More of the display is to be found here. Like Oksanen, also Aho got halos in moonlight the following night. These photos are under the same link.

 

by Marko Riikonen

 

Originally in Halo reports