Sharp Lowitz & Parry display, in short time [2023-04-04]

Here are some nice ice halos at the passage of a particular layer of clouds, during a clear sky day (2023-04-04, from near Dole, Jura, France). This clouds layers gave an extraodinary sharp looking display of ice halos, as I rarely saw in 15 years of watching. I was then in the good spot at the right time, for this one. While I was taking care of my lawn, during a clear sky day, I saw some high altitude clouds coming from the north, and decided to take the bet I will have some ice halos, but I did not epected that kind of sharp halos. In all the below images, clouds are coming from the left (North-East).

On this first stack image, you can see the Wegener arc, with almost the part crossing the parhelic circle. There is also the 120° parhelion with reddish edge as well as on the circle.
Process is (as an example of how I do usually, for the image shown above,
named 2023-04-04-[14h57to15h37]-bw-[4-2]-UsM(11)-5s5-notrack-UsM.bmp):
→ B-R ( -bw ) rendering of all the images of the sequence ( -[14h57to15h37] ),
→ 11th stack ( (11) ) of the sequence with 4 images ( -[4 ),
→ then Unsharp mask on this stack ( -UsM ),
→ then a new stack (with Registax, without the track on the sun ( -notrack ))
→ of 5 ( -5s5 ) of last stacks (those ones taken every 2 images ( -2] ))
→ then one more Unsharp filter ( -UsM ) to end it.

Later, like 5-6 minutes later, the layer of clouds enter the 46° FoV from the sun, which gave the most impressive part of the display to me.

Here is one single image, with just B-R rendering (no UsM or what so ever).

Then 2 stack versions witht this image along with some before and after, to see more clearly the Lowitz & Parry display, (on the above one, we can see parts of 46° halo, but not in whiole, because of the hole in the clouds crossing the view... I guess)

and with the images when the clouds are on the side of the sun from my point of view. I even manage to watch clearly the circumscribed halo while i was cutting my lawn.
You can also see the left part of lower Parry arc tangent with the circumscribed halo.

A last part of the display, with clouds on the bottom left of the sun, to see the extension of the lower Lowitz and the extension of the left part of the Lower Parry, tangent to the circumscribed halo.
For this stack, a "min" function is applied during the stacking process, in order to keep the minimum value of each pixel while stacking, and try to make the black forms therefore the colored halos more visible.

A crop on the left sundog, to see the Lowitz crossing and the 2 Parry arcs.

I have not presented any colored versions, because of the heterogeneous form of the clouds mask the halos for this display.

Finally, a time-lapse of the display is available here, which a compilation of differents time-lapses (one for each processing type). From those images are extracted the previous posted here :
www.flickr.com/photos/gaukouphoto/52808574767/in/dateposted/

All images are taken with Canon EoS 6D + 8mm Samyang lens from my roof windows, South-South-East side.
Settings: 1/1000s, ISO100, f/9,4, 1 image every 12s.
Sun mean height is 47° at the time of the sequence.

Google Drive folder shared, with all the images presented here, and the time-lapse.
I still have all the raws of the sequence if needed too.

Possible 46° contact arc in Jena, Germany

46° contact arcs are something of a true rarity. In the display shown above, photographed by Marco Rank yesterday in Jena, underneath the circumzenith arc is a concentration of crystals that could be due to one of the three components of 46° contact arc. 

Or maybe it is just a patch of 46° halo from poorly plate oriented crystals. Below I have made simulations with both scenarios. On the left is simulation with Lowitz crystals that give the 46° contact arc. It makes makes a somewhat better delineated effect than the 46° halo patch of the poorly oriented plate scenario on the right, and is perhaps more in accordance with the photo. 

Yet this is just one photo in a sparse crystal swarm and thus not quite enough to draw firm conclusions. Whether it is 46° contact arc or 46° halo patch (or something intermediate), it is anyway interesting to notice that the Lowitz simulation gives no discernible Lowitz arcs - and that they are not seen in the photo either.

Further below are simulation parameters for the Lowitz simulation. More photos of the display are shown in Marco's post in AKM forum.

46° contact arcs

 

About a year ago in Muonio, Finland, a diamond dust display produced a new halo, the 46° contact arcs. The display was shortly reported in the blog, but no simulation was shown. So here is a simulation, together with a composite of the photos that were taken by Päivi Linnansaari. The 46° contact arcs, which arise from Lowitz-oriented crystals, appear as three arcs below the circumzenith arc.

The Lowitz crystals used in the simulation are regular plate-like hexagons, with aspect ratio of 0.4, tilt about the Lowitz axis 28° and Lowitz axis rotation 1°. Sun elevation is 9°. The Lowitz arcs themselves are faintly visible at 10 and 2 o'clock positions, separating from the 22° halo and reaching towards the upper sunvex Parry arc. This is the circular component of the Lowitz arcs, also known as the c-component (after Greenler).

Occasionally, in high cloud displays there is seen a short patch of 46° halo under the circumzenith arc, as shown here in the photo by Stepanka Kosova, taken on 20 August in Prague. It has been sometimes suspected that these might be indications of 46° contact arcs. Whether that's the case, it may be confirmed if a series of photos are taken for stacking.

The simulation is made with HaloSim by Les Cowley and Michael Schroeder.

 

text: Marko Riikonen 

 

Original post in Halo reports

Diamond dust season opened in Finland

On October 26 the pupils of the Särkijärvi school near the small northern Finland town of Muonio stopped suddenly their indoor activities and rushed out - somebody had noticed a halo wonder in the sky.

At the school were also excursionists from University of Lapland. Among them, Päivi Linnansaari happened to have a camera handy and took several photos of which a selection is presented here.

The display had all the basic flavourings of a great diamond dust display, including the helic arc, circular Lowitz arc and diffuse anthelic arc - the latter of which is seen faintly in the lower left image. But then there is also a new halo: the 46° contact arcs. Theoretically it has been known for quite a while, but no convincing photographs have come up untill now. The halo shows up in the upper right image as three arcs below the circumzenith arc. Probably a comparison with simulation is needed to get a proper grip of it.

The halo display made it also to local newspaper. Couple of kilometres from the location there is a ski center, so the halos may likely have originated from snow guns.