Cult of the Natural?

Occasionally, I get the impression, rightly or wrongly, that some observers consider halos which have been produced by spotlights to be in some way ‘inferior’ or ‘artificial’ when compared to those which have been produced either by the sun or moon. This position is never explicitly stated but is, rather, vaguely hinted at as if there is some unspoken ‘cult of the natural’ operating in the background. The purpose of this post, therefore, is to pose a few questions to our readers and to solicit their thoughts and opinions on the matter. 

For example, do you think that ‘natural’ halos produced by the sun or moon are in any way better than those produced by a lamp? In this context, what do we mean by ‘natural’ and ‘better’? Likewise, are we to consider halos produced by a lamp to be in some way 'inauthentic' or unworthy of our attention? If that is the case, on what do we base our conclusion? Then again, is there really an inherent dichotomy between ‘natural’ and ‘artificial’ in this regard or is the light source completely irrelevant? Finally, are lamp generated halos merely tolerated or deemed acceptable only in the absence of a solar or lunar equivalent?

My own position is that I don't really have a problem with spotlight displays. Whilst I am always pleased to see a good quality solar or lunar display, I consider halos produced by spotlights to be equally valid and at times arguably necessary in the pursuit of the highest level of halo research. Indeed, I would suggest that lamp work has the additional advantage of repeatability (given the presence of the right crystals) and also that an observer can adjust the elevation of the lamp to produce specific effects; such flexibility would simply not be afforded to those who opt for a ‘natural’ only light source approach. Historically, many halos would not have been discovered if it were not for the adoption of this technique, rather they would have remained theoretical possibilities. In this way, I think it is reasonable to suggest that lamp generated halos have demonstrably accelerated halo research.

In closing, I offer above and below two images for your consideration. They were both taken by Marko Riikonen, the world's foremost exponent of the spotlight technique. The display was photographed on 5th/6th November 2008 in Rovaniemi, Finland, one set taken during the night using a lamp, the other set taken the following day. Both images were photographed in roughly the same location and the swarm responsible for the display had remained fairly stable during the intervening period to facilitate this comparison. The images are virtually identical, the only difference being the light source in each case. Are we to conclude then that the daytime images are superior to those taken several hours earlier during the night? Is there really a qualitative difference between the two or is the 'cult of the natural' just a psychological construct? Your comments and opinions as always are greatly appreciated.

© Both images Marko Riikonen

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 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.

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.

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.

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

by Marko Riikonen

In the previous post of this display I discussed two photos taken towards the end of the hunt, just before twilight. Now it is time to look at the photos taken earlier, from midnight onwards at another location. Please mouse over or click the photos to remove the milky veil that the systems adds as default to them.

Of the several stacks that were photographed, I made simulations of two that are shown below. Unlike the morning photos, now only one stricly oriented Parry population was needed to the explain the display’s halos from c-axis horizontally oriented crystals. So here we have a pure case of uppervex Hastings and nothing reminescent of Wegener.

Except that a little detail strikes a dissonant chord. In the lamp side photo above an arc is touching the bottom of the 22° halo whereas the simulation gives an arc that is separated – the lowervex Parry. Thus the lower arc in the photo is suggestive of tangent arc and column orientation. But everything else – the presence of Tape arcs, the bright helic arc, lack of subhelic or 46° lateral arcs – shouts out loud this is pure Parry. So what is going on?

Well, even though spotlight displays have a highly 2D character, there is divergentness involved and halos may extend more towards the lamp than true 2D halos would. Look for example at the upper Tape arcs in the photo. They are deeply embedded into the 46° halo, although in simulation they are separated. In the photo they even seem to extend slightly inside the 46° halo. And in other displays upper tangent arc always pushes through the 22° halo towards the lamp (it may be a different thing with that halo, though, than with Parry). Even in solar displays various arcs can be glued to their circular rings despite simulations telling they should be separated.

So I would not quite yet scrap the pure Parry character of this display because of that little anomaly at the bottom of 22° halo. It is not the first time to be faced with this matter: we were wondering about it last winter in another potential Hastings case.

As for this lamp side view in general, it seemed not possible to get a satisfying match. For example, with all parameters that I tried, a secondary upper Tape arc (if letters are used to denote it, maybe it should be upper Tape arc B, instead of the Tape arc D that I used in an earlier post) was produced outside the primary. As for the Hastings, in the photo it is brightest near the lamp, then has an intensity drop just inside 46° halo before getting again a bit brighter outside. I could not reproduce this variation. I think there is going on something that is beyond the reach of the simulation software. In the simulation shown was used just one Parry population optimized to make a Hastings that is brightest near the lamp and vanishes outwards. The crystals were thin h/d 0.05 plates. Such a solution did not quite produce matching intensity distribution for the helic arc, and I am certainly not proposing this as final solution. The parameter table for the simulation is not given as I happened not to save it. Because in the photo there is Moilanen arc, I added it to the simulation too. Simulation light source elevation is -5 degrees.

Opposite to the lamp the view is very much Parryish, as shown below. In addition to simulation I have provided also a br version of the image because it makes it easier to distinquish the spikes of lamp artefacts from halos. It seems to show that inside the subanthelic arc there is no diffuse arcs, just artefacts. Another image further below also has the hallmarks of pure Parry.

In the sideview image below noteworthy is the very thin core of the sub-120° parhelion. It is as thin as the sun pillar above the Parry arc. In br version this core is better separated from the glow surrounding it. Further below are four other photos from the first part of the night.

 

 

Finally, I make a return to the anthelic region photo from second part of the night. Earlier I had shown only br version of the blue spots in Liljequist parhelia, but they come out also in “visible wavelengths”, as demonstrated by the extremely saturated version below. Noteworthy is also the dark area that seems to be confined by the shape of subanthelic arc even though the top of the subanthelic arc is not seen. This was something I raised up in an earlier post that discussed a display photographed by Marko Mikkilä.

Thin plates in rotating Parry orientation as an explanation for thedisplay on the night of 8/9 November 2016, in Rovaniemi

In an earlier post I told simulation attempts were not successful for this display. Well, I really did not put that much effort into it. Now I have given it a fresh look and managed to get some success.

The problem was the subhelic arc and anthelic arcs that could not be get rid of. In new simulations made with HaloPoint the subhelic arc issue is pretty much resolved and the anthelic arcs also play it low key.

As usual, the simulations do not stand scrutiny of details, but that does not matter regarding main message: that it was necessary to use thin plates in rotating Parry orientation to keep the subhelic arc and anthelic arc stuff in check.

Two simulations are shown above together with the photo. They are identical except that in the other the thin Parry crystals are rotating 15 degrees and in the other 5 degrees. The subhelic arc is actually in there, but it is masked by background noise from the random population. Well, maybe its curve can be detected in the 5 degree simulation, but it is shadowy. It becomes clearer with more burn and finer dot.

The simulation with 5 degree rotation replicates also the diffuse area of light seen above the Wegener arc in the image. It is a spread out helic arc. So maybe we could regard the Wegener rather as an intermediate form between Wegener and Hastings, the “Wegstings”.

If thin plates indeed are the culprit, how can they fall with their basal faces vertical? If we maintain that singular plates can not knife through the air in such orientation, then perhaps there were copious 90 degree crosssed plates in the air, built so that one was glued to the center of the other one’s basal face to provide the right balance for the required orientation. I did not take crystal samples, with one camera it is too much a hassle, particularly as we have again and again come to learn that samples rarely give answers.

Parameters for the other simulation in HaloPoint software. Shown is the thin plate in rotating Parry orientation.

 

 

 

 Finally, a technical factor could have influenced the subhelic arc visibility in the photo. I had placed the camera slightly outside the center of the beam sideways to enhance the sides of the display and this may have had a dampening effect on the visiblity of the higher located subhelic arc. The effect is probably not significant, the camera offset was just a little, but in the future this practise must be dropped in order to get best comparability with simulations (of course, as the spikes at the anthelic region attest, my beam is not regular anyway, so to some extent this issue is there aways). Off the record, I don’t really think that this could have made subhelic arc disappear, rather the opposite, because when the camera is right in the center of the beam, you have more masking bright glitter than when the camera is offset and any threshold intensity halos should be then lost easier. But it is good to let this issue have known.

Another occurrence of an anomalous Hastings/Wegener

By Aleksi Velhola and Marko Riikonen

In an earlier post we showed a photo of a weird downward curving patch of Wegener/Hastings. Here is another case that occurred 9 days later on December 2, 2015. This time we also got a nice comparison to normal “Wegstings” by superposing photos taken from the same camera position.

The anomalous Wegstings appeared on two occasions and was well visible to the eye. At both times the display was less brilliant than at peak stages, during which normal Wegstings was seen. Same was true of the earlier display on 23 November.

A closeup of normal and anomalous Wegstings appearances superposed to one image.

The crystal sample is interesting. Crystals range between plates and equidimensionals, which one would not expect from the strong column orientation halos in the display. It just adds to the ever increasing file of cases where the samples are not what would be expected. The dish was out long time, something like half an hour, so it represents all different stages of the display put together. However, column orientation halos were all the time present.