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 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.

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.