Halos on the night of 15/16 December 2016 in Rovaniemi

Fog turned into diamond dust in an optimal range of -5 to -10° C. I photographed the display in the evening soon after dark, the first photo was taken 16:17. The fog lasted whole night and no doubt the show would have continued whole night too were not the guns shut down soon after 17h, finishing the party before it had even got going. Had there been until morning to play, I am sure wondrous things would have been possible. Actually, there would have been three more nights, as fog continued envelop the city pretty much constantly for three more days and nights. 

 

In the image above — and less clearly in the one below — it looks as if instead of "subanthelic 46° supralateral arc" there is more a "subanthelic cza". If so, that would be just a segment of sub-Kern, but it has an unusual location as we are used for sub-Kerns placing most of their weight at lateral locations with an intensity minimum directly above the subanthelic point. Simulations offer a solution, however: if, instead of plate oriented crystals, Parry oriented crystals of triangularish shape are used, a sub-Kern segment is born that is centered over the subanthelic point and looks like a kind of "subanthelic cza". Allow the crystals to rotate a bit and a halo segment much in the liking of what appears to appear in the photo is formed. As a rudimentary demonstration, below are further simulations with increasing rotation of the column shaped triangularish crystals, showing how the sub-Kern turns into a "subanthelic 46° supralateral arc" (ray numbers have been increased with increasing rotation to keep simulations of roughly the same intensity). Parameter file is given at the bottom.  

Halos on the night of 14/15 December 2016 in Rovaniemi, part IV

Here is the last post in the series. High sun stuff (only turned upside down). A "subhelic 46° infralateral arc" is visible on both sides of the subsun in the above image. Below are two relevant simulations (for 52 degree elevation), an arrow marks the halo. Crystal parameters, given further below, are identical for both simulations.

Below is one more photo for a higher light source elevation angle. Judging by the location of the blue circle segment, I would say the elevation is about 57 degrees. The display was already at decline at this point and before midnight the halos were gone because the fog disappeared. 

Halos on the night of 14/15 December 2016 in Rovaniemi, part III

Opposite to the lamp I could see something that thus far has appeared for me only in simulations: diffuse arcs extending all the way from the anthelic point to the subanthelic point. The effect is not that impressive in photos. Neither is the anthelion which really caught my attention: an anthelion formed against the ground in just few meters of air space. In the image above I had tilted the camera sideways so that it is not aligned with the central column of the tripod. This makes the shadow in the middle of the arcs less disturbing. In the image below, taken earlier, I had not yet done this move and there is a more prominent shadow. The image above is a bit spoiled because of spotlight light getting in from the viewfinder. I thought the camera was broken and bought a new one two days later... On one night in the beginning of January Mikkilä called while I was out photographing at around -35° C (-31° F) temps, and he told it was about light leaking. I didn't buy it, having a false memory of the effect appearing also when I shot towards the lamp. In the end it had to dawn that Mikkilä was right and also a feeling (maybe false too) that I must have known this thing in the past but my brain had buried it too deep by now.

So, where was I... yes, of some interest in these photos is the blue edge of the diffuse arc (the 3157 type).

Below are two more shots showing the anomalous Hastgener. These stages of the display are not really that poor (see part II), was I too hasty to make that connection? (Somehow I succeeded in not seeing these photos when writing the part II even if they were ready made in the same folder). Notice the left side subparhelion which seems tilted in the first image which is a single frame. The breeze makes localized, passing disturbances in crystals' orientation and can cause effects like this. At least that's what I seem to think now, but who knows if it is true. Anyway, I think there is a frame from stacking series from one other display where the other subparhelion is completely missing.

Halos on the night of 14/15 December 2016 in Rovaniemi, part II

Here is a collection of images showing an arc that looks like a downwards curving Hastings or Wegener. It's nothing new: the arc was first observed in Rovaniemi on 23 November 2015 and again nine days later in the evening of 2 December. I don't know how it is made, but it seems to occur when the display is suboptimal as compared to its best development. A halo that thrives on (relatively) crappy crystals?

In the display on the evening of 14 December 2016 this anomalous Hastgener was captured on several stacks, one of which is shown above and which also has normal Hastgener. Below are two more photos of which at least the left side one shows the effect. It was true to form, as these stages did not represent the peak of the display.

There was an additional oddity: the Hastgener / anomalous Hastgener has a kind of parhelia near the tangent arc. The feature occurred intermittently and was well visible to the eye. Below are two images showing this "parhelia", the one on the left is a single frame. The brightening seems to be also present in the main image above.

Halos on the night of 14/15 December 2016 in Rovaniemi, part I

Last mid-December, Rovaniemi was shrouded in fog for five days in a row. With temperatures hovering in -5 to -10 C range, the conditions were as good as one can hope for. Just add icy nuclei from snow guns in the air and fog is guaranteed to freeze into a violent display.

The five day diamond dust feast did not materialize. The guns were shut down after a couple of hours after the dark of the second night, and then it was just fog. But I was there on those two first nights to take photos, a selection of which I am going to show in this and coming posts.

I start by two photos from the first night of 14/15 December. Both have, inside the Tricker arc, a faint colored arc, best visible in the blue-minus-red versions. Upon first becoming aware of this feature, I thought, with some excitement, that it might be an exotic halo. This state of mind did not last long, however, because soon the arc turned up in a simulation.

The halo is born from raypaths 3162 and 3152 in column oriented crystals. By its appearance it is a vertically mirrored copy of the more commonly photographed 361/351 arc, which is also seen in the photo (and which has been treated in an article by Walt Tape). At the upper right of the above image is simulation where these arcs are marked, respectively, by left and right pointing arrows. Two column oriented populations were used. The 3152/3162 arc is made by the population that rotates 20 degrees, not by the fully rotating population (see parameter table below). At the lower right of the above image is another simulation, where the the 3152/3162 arc from the limited rotation population is shown without other halos.

Blue subsun finally about right

closeup of the photo below

The year is gearing towards winter, the first glitter in northern Finland expected in less than two months. While waiting for that, I think I should continue clearing the backlog of last winter's results from Rovaniemi before new stuff starts piling up on top and risking buried-in-drawer fate. There is still plenty to show – even what might be called as major displays.

To not inflate it right away, lets start with a more moderate, but nevertheless interesting display. On the night of 16/17 January 2017 a display with full set of kaleidoscopic arcs appeared, and towards the end of the action, when it turned plate dominated, I tried to get the blue subsun photographed.

Earlier past winter and the one before, on a couple of attempts at blue subsun that I had myself or with friends, the aim was to get the lamp elevation right so that the blue would be exactly at the center of the subsun (otherwise you might feel a tinge of uncomfort calling it a blue subsun). It is a precision job: the optimum is at right about 58.5 degree light source elevation, with the tolerance of around half a degree, after which you may not be able to sell it to a demanding customer.

We did't get it quite right then, or the display was otherwise uninspiring, but this time there is a clear blue color passing pretty much through a middle of a well defined subsun. Connoisseurs might still see manoeuvre for one or two tenth of degree improvement, but I am good enough with this to not pay effort to go after it no more. However, there is some other stuff that warrants visiting the extremely low lamp haloversum (like sub-cha and its extension), so blue subsuns are certainly going to come along with the ride.

Odd radius plate arcs in diamond dust display

The lamp in the photo is a couple of degrees below the horizon and there are 18, 20, 24 and 35° plate arcs. Plus a bit of a helic arc that in this kind of display could be of the odd radius type or at least contributed by it. This stage lasted only a few minutes after which lesser halos were visible for the rest of night. Under the outdoor light shining in the photo an upper 23° continued its presence longer. The display appeared on the night of 5/6 January 2017. Temperature was -27° C.

The photo below shows the location. The camera-lamp configuration is not the same as for the photo above, where the lamp and the camera were more level.

Some diamond dust odd radii in Rovaniemi

These photos were taken on the night of 9/10 February. In the image above we see odd radius stuff in the beam: circular halos and some bulges on them indicative of poorly plate oriented pyramids. The arc straight above the lamp on the broad 22° halo should be Parry / upper tangent arc rather than upper 20° plate arc. Visually I could not see the odd radii stuff but the appearance of the glitter made me think for its possibility.

One additional reason to suspect odd radii was the lunar display, which did not seem like your basic 22° halo stuff. The shot below was taken soon after I turned off the spotlight and it indeed has some not so clear odd radii, partly because of the artefacts. I photographed lunar also before the spotlight, and then the stuff was even poorer (this photo is not shown). So the spotlight in between gave the best display, which is of course what one expects

The enhanced version of this photo really brings out the artefacts. Br fouled it so completely that I am not showing it. Up until now I had had this nuisance entering the scene only in raw sun shine, but now it is has expanded its range to moon lit nights.

        

On the brighter side the artefacts became less disturbing when the milky background started clearing as shown by the photo below. Yet even then the br gives a rather ugly result.

Some spotlight stuff from a bridge

My previous post was about one photo from the night of 10/11 February 2017 in Rovaniemi. Here are the rest. Bridges are good places for spotlight stuff. You can get pretty much any elevation and have a view from zenith to nadir as shown above. I should have used this nadir-zenith configuration more, its benefits didn't really sink in until late season. It has a potential to give answers to questions on crystal orientations and shapes that higher up pointing view wouldn't give.

A Rovaniemi display and simulation

This display shows the very common arcs that according to simulations seem to arise from 3b5 type raypaths in Lowitz oriented crystals (where b signifies basal face). I avoid using any names, first because I am uncomfortable with current nomenclature and second, because the situation with these kind of arcs has become confusing. I am getting to have a feeling that there may be two or even three different halos that look quite similar but have different formation.

The match between photo and full simulation on the left is poor. Neither the curvature nor intensity of the simulated 3b5 arcs match with those seen in the photo. The inner arc is curving less steeply in the photo as compared to simulation. And it is most intense near 22° halo while in simulation the arcs barely reach to touch it. I found not possible to make the arcs extend all the way to parhelia in simulation. The filtered simulation on the right shows the maximum extent of the arcs.

Concerning the shape mismatch, it is also noteworthy that the arcs in the photo are separate from 22° halo while the simulated arcs reach to touch it. Added to the right side filtered simulation is circular Lowitz arc to see if that together with the 3b5 arcs could explain what is seen in the photo. The shapes don't quite align. It seems to me there are no Lowitz arcs in this display.

The simulation light source elevation is -32.3 degrees. Concerning the crystal parameters, the parameter table below is not the version that was used to make the simulation on the right, I didn't happen to save the last permutation. But it is close enough. There is a plenty of leeway for 3b5 arcs parameters so exact numbers are not important.

One other thing worth noting in the photo is the subparhelic circle inside subparhelia. Simulations tell it can be formed by Lowitz oriented crystals as German observers demonstrated recently. Or it can be formed by highly triangular crystals. The effect was visible to the eye and its glitter gave an impression of broadness apparent in the photo.

The image is an average of fourteen successive 30s exposures, stacking done with Halostack. The night was 10/11 February. I was a bit late from the show because I was keeping an eye too long at the lowering of the cloud base from my apartment, suddenly realizing when the chimney of the distant power plant disappeared that I have to be going and quick. It was full fog when I curved to the scene on the ski slopes side of Ounasvaara and streetlamp parhelia were awesome solid beams. Obviously, my procrastination at the apartment asks for at least 15 minutes of unremitting self-criticism at the next halo meeting. Typically if it is like that when you arrive, then it is already late when you are ready to photograph. Sure enough, by the time I had it all set up, snow flakes were already falling among the diamond dust just as forecasted. But because the fog was still there the diamond dust was able to hold on to it for enough long to me to secure series of photos at several lamp elevations. Of course the rather ample snowfall (which was actually boosted by the diamond dust to even more) greatly reduced contrast, giving a milky background. Considering these far-from-optimal conditions, the display was surprisingly good.

Pseudo-anthelion

On the evening of 9th February I left my apartment to hunt diamond dust halos, but was also supposed make it to Lappland Chamber Orchestra concert. So with the proper clothing for such an high society occasion underneath the overall and several other layers (it was close to -30° C) I half hoped it would be total crap to allow me to slip to the concert to hear live the Shostakovitch chamber symphony op. 110.

It indeed was quite crappy, or at least I thought so, and after taking some lunar and spotlight shots I was already driving towards the city - only to turn around and come back to do one last check. That settled it: there was an all sky display developing and DSCH was no more on agenda.

Here is highlighted only one set of photos of that display. The three images show an anthelion that moves below the parhelic circle as lunar elevation rises from 30.1 to 30.9 degrees (according to USNO calculator). The images from left to right are stacks of 4, 3 and 4 successive frames with 30s exposures and the values in the upper corner indicate lunar elevation.

In my attempt to simulate the effect with Halopoint there is only one population of column oriented crystals considered with orientations of the crystals restricted to 12 degrees rotation about the c-axis (parameters are shown at end of this post - the last one of the three tables). This, together with plate shape and slightly triangular habit indeed reproduced something that looks like the pseudo-anthelion in the photos.

A look at the raypaths revealed that the effect is an intensified apex of the Tricker arc. This explains the movement as Tricker separates from parhelic circle at light source elevations higher than 30 degrees. To show it in its true form, below left is a filtered simulation that has only the Tricker rays responsible for the effect and for comparison next to it a full simulation with all rays. Further below is depicted the beautiful raypath. This type of variation of Tricker arc raypath which enters and exists through basal face is also drawn in Robert Greenler's "Rainbows, Halos and Glories" on page 85 and Tape's "Atmospheric Halos" on page 26.

The set of simulations below compares two scenarios of traditional diffuse arc anthelion with the Tricker arc pseudo-anthelion. Actually, in the middle simulation both effects seem to be present. Parameters for these simulations are given further below. Left to right order for simulations corresponds to top-bottom order for parameters.

So accepting that this pseudo-anthelion is an anomalously brightened Tricker arc top, I am however less certain about the correctness of the suggested mechanism behind. The simulation does not come out that convincing when you look at the other parts of the display. It seems to me there is going on something that I have no idea of (or then I just didn't simulate enough, like has happened in the past).  

One curious thing is the lack of subhelic arc in the display. Only if I used plates that were h/d 0.2 or thinner could I get rid of the subhelic arc. But that made the simulation in other respects even further from the reality. Such h/d values were also too small for the pseudo-anthelion which seemed to thrive in quite delicate balance around 0.3 value. For reference, see an earlier case where simulation with thin plates in restricted column orientation (or poor Parry orientation) produced a good overall match with spotlight display. I guess next winter I must shape up on crystal sampling to see if displays like this really don't have columns in the dish.

The display itself was rather faint. No hope of seeing, for example, that pseudo-anthelion even though I saw from the camera display that it was there (and thinking it is just a normal anthelion). I'll be posting on some later occasion more photos from this night, including spotlight stuff.

Some photos of a Rovaniemi spotlight display

This was seen on 24 January 2017 in Rovaniemi. The image above is a total of 24 minutes exposure (48 frames). It shows all four kaleidoscopic arcs, which is not really that uncommon combo in the beam reality. Just before the diamond dust disappeared I took also a rare positive elevation lamp shot as shown below left. It's got 5 minutes total exposure. Below right is one of the first sets of the evening with 3 minutes exposure. The br reveals the insides of 46° and 22° halos are somewhat reddish.

It was quite cold, I think temperature was somewhere around -28° C towards the end of hunt. Unfortunately my halo hunt diary is no more because the folder called "halo" recently disappeared from the computer desktop without leaving a trace. It seems the universe don't want those notes to exist. Already earlier this season it got corrupted, all letters turned into #s. But I have a safety copy which has last winter's notes. At least for the time being.

Thanks to Panu Lahtinen, who stacked the image above when my Halostack had some mysterious glitch.

Trying to simulate arcs associated with parhelia in Rovaniemi solar display

Above is a display showing arcs extending outwards from parhelia and an attempt at simulating with Lowitz oriented plates using HaloPoint software. Sun elevation was 14.5 degrees.

In the lower right panel is a simulation with all rays. On the upper right is the same simulation (well, not exactly the same, ray numbers are a bit different) that shows from Lowitz orientation population only rays that experience 3 or 5 hits. This leaves the arcs from 325 and 315 type raypaths (the so called Schulthess arcs) visible while some others, such as Lowitz arcs are filtered out. The Lowitz arcs are seen in the lower left simulation, which has only rays with 2 and 4 hits from Lowitz oriented crystals.

The Lowitz arc scenario is clearly out of question to explain the arcs in the display, there is no match. Then how about the 3 and 5 hit scenario? Comparison is easiest with the flashing image below. The outer arcs fit together quite well but the inner ones don't. The inner arcs are angling too steeply inwards in the simulation.

Did I just do a botched job in matching the simulation to the photo? I admit it is not perfect work, but likely not so bad as to account for the large mismatch of the arcs.

Could it be because of the projection difference between the photo and simulation? I know that my 8 mm Sigma fisheye doesn't align perfectly with HaloPoint fisheye projections. For example, subanthelic arc is always narrower and taller in simulations than in photos. So maybe this too is just down to projection. Some day we might have a simulating tool that allows customization for individual lenses. That would settle the issue.

But even then we would still be long way off explaining these kind of displays. How do you get rid of Lowitz arcs in the simulation? I could not find a way. You have to really burn the Lowitz arcs to get 315 and 325 type arcs. This scorching inevitably gives also 46° contact arcs as is shown by the fuller version of the simulation below. In the fuller version of the photo next to it there are no signs of these arcs. Also, I was not able to simulate the correct length of the outer arcs. Lessening tilts seemed to make them disappear altogether. But I wasn't exhaustive in my attempts, it might have been possible to get them right.

What else? The display has no Kern arc even though cza was quite nice and diamond dust smooth. Clearly Kerns are not to be taken for granted. While observing, I thought there could be a chance here, but at the same time had a feeling that sun is probably too high, the plates too thin (you pretty much can say it without looking at a crystal sample) and tilting too much for the good old H.F.A.

Some words about the hunt itself  - the ryynäys as we say here. I was doing spotlight at the night and things got crappy as supersaturations increased. Diamond dust was everywhere but really poor halos. Expectedly it was no better in the morning. Close to the ski centre, diamond dust was so thick the sun did not shine through. At the edge of the cloud where the sun shone brightly there was quite some crystal glitter in the air, but, as it is with this glitter, it comes at the expense of halos: only pillar and subsun was visible. So I went shopping to a grocery store, hoping that in the meantime warming air brings a positive change.

It got better. However, the display was good only at the receding edge of diamond dust cloud. So I photographed in one place and when it weakened, hopped into car and followed the cloud to a new place to photograph again. I did six such manoeuvres, after which the swarm was soon done away completely by the heating sun. The photo shown here is the best set that I got at the third location.

Some technical info. The display was seen on 7 March 2017 in Rovaniemi. Temperature was probably around -16°C at the time I took the stack. It has 54 photos taken during 5m10s, starting at 10:13. Stacking was done with Registax 5.0. The artefacts seen in the image are a scourge of some series of Nikon cameras, they come in daytime photography and there is nothing you can do about them in post processing. 3000 series is one plagued with this issue (I have 3200 and 3300) and from what I have heard from other people's experiences 5000 series too. Definitely not cameras for halo photography.

Halos and fogbow in the same mix

To photograph a fogbow simultaneously with halos one's best bet may be the foggy autumn mornings with high clouds in the sky. (I leave the possibility of an exhalation fogbow unmentioned).

That should be easy enough. However, connoisseurs might demand the criteria to be that both phenomena must appear in the same cloud. That's making the task a good deal harder. Below freezing temps fogs sometimes have a meager few crystals thrown in the mix and there may be a pillar visible together with fogbow, but anything resembling a proper display is highly uncommon in my experience.

Actually I have never seen one - not until the night of 12/13 December 2016. On that night I was photographing halos at Jokkavaara gravel pits east of Rovaniemi at around -27°C. After the display took a worse turn I went for a little ride to see how things looked a kilometer or so in the city direction. It was the same crap and I returned to the gravel pits.

What a surprise it was to see the place now enshrouded in thick fog. Having just reconnoitered the surroundings I believed diamond dust was right behind the corner, and with the wind being towards the gravel pits, I wondered if the fog might soon start freezing.

True enough, crystals started glittering among the matte fog droplets and it didn't take long to have passable parhelia in the spotlight beam together with fogbow. The more halos intensified the fainter the fogbow became as diamond dust ate away on the water droplets.

It would certainly have been a splendid display if the process had gone all the way. Water cloud born displays tend to be violent. But the fog got an upper hand and situation was reversed to where it started from: only fogbow in the beam and no crystals, no halos. 

So this was a uniform mix of fog droplets and ice crystals. More common are situations where wafts of pure diamond dust and pure fog are alternating in the slight breeze. If you are taking, say, 30 second exposures, an illusion of fogbow being visible at the same time with halos can be created in the image when they in reality occurred at separate times.

Now what if only a display from photons of sun would satisfy the connoisseur? That's really amping up the challenge. There do exist some reports of simultaneous halos and fogbows from polar explorers more than century back, at least from Henryk Arctowki. The only photographs may be those by Ed Stockard in the Greenland Summit Station. But it is not certain if in this case the stuff occurred as one mix or the crystals and fog droplets were as separate layers.

Psychedelic colors in diamond dust

Occasionally diamond dust glints in pink and and cyan colors. Walt Tape, who saw the effect once in Fairbanks, called it as the psychedelic colors. Here are a couple of photos of one psychedelic case this winter. The image above is a maximum stack of 19 frames with 2.5 and 1 second exposures. Below is a single frame with 2.5 second exposure. And below that a maximum stack of 9 frames with 6 s exposures. Colors have been observed so far only in spotlight displays. How they come about, I don't know. A crystal sample could give some answers.