Subparhelia with reflected Lowitz arcs

Bill Burton, USGS, observed nice halo display with very rare reflected Lowitz arcs. Bill: "This photo showing an impressively bright sub-Sun and sub-parhelion was taken from the window of a commercial airliner on a flight from Anchorage to Minneapolis. I was looking down at a thin, cirrus cloud layer over the snow covered farmland of southern Canada when these wonderful halos and arcs appeared. The Sun is above the image, producing this sub-Sun and upward-facing portion of a 22-degree halo. This sub-Sun was brilliant enough to create its own sub-parhelion and 22-degree arc - on the right side of the image. Photo taken on January 11, 2007"

Text was assumed from EPOD

By Patrik Trncak

Reflected Lowitz arcs in Finland

On 30th January 2007 I found that local district heating plant was causing a nice diamond dust display. Temperature was -22 C and the steam crystallized immediately. Only a few hundreds meters from the plant was already a plenty of crystals, but the best was about 2 km from the plant.

There I drove to a small road and got out and saw a display like never before. Parhelia were very bright, like fireballs. Also circumzenith arc was bright, but 22 halo was quite weak. Almost full parhelic circle was present with faint 120 parhelia, that looked more like pillars than fuzzy balls.

I had a film camera and eventually run out of film. The only choice was to drive home to get digital camera and fisheye lenses. On returning back the display had lost intensity and the 120 parhelia were completely gone. Anyway, I took about 80 photos with digital and later stacking of those photos revealed faint reflected Lowitz arcs rising up from the parhelia (marked in the photos with arrows). More photos of display is here. The looks of the display is quite similar to the one that was observed by Jari Luomanen a year ago. See photo here.

Simulation of reflected Lowitz arcs

Here is an attempt simulate the Jari Luomanen display of 22. January 2006. Reflected Lowitz arcs arise in the simulation from thin plate crystals tilting 10° about the Lowitz axis. Same crystal population also makes the crossing arcs below circumzenith arc - the 46° contact arcs. These are not seen in the photo, but it was not possible to make simulation without them appearing (46° contact arcs are still theoretical, no reliable observations are known). Some other, less serious problems are also evident in the simulation. Reflected Lowitz arcs, however, are well in accordance with the photograph.

Two more crystal populations were used. Oriented plates made parhelia and circumzenith arc and poorly oriented plates the 22° halo. Sun elevation was 7°. More details on the simulation are here. Simulation is made with HaloSim by Les Cowley and Michael Schroeder. Simulation files are here.

Another case of reflected Lowitz arcs

 

News about reflected Lowitz arcs prompted another observation. This display was photographed by Juha Oksa on 22. December 2005 in Jyväskylä, Finland. The picture on the left presents arcs (arrow) that seem to match the inward curvature of the inner reflected Lowitz arc component (see Jari Luomanen photo in previous news). Thus we are having displays that have two arcs or either one alone. I would be inclined to believe that all cases are indeed reflected Lowitz arcs. We just have to figure out what kind of crystals make the occurrences with only one component. 

The photo on the right shows reflected Lowitz extending below parhelion (arrow) - the "parhelia leg" effect. But it may also be subparhelia. Effect shows up also in the other image. 

Photo on the left is stacked from three individual unsharp masked images.

Reflected Lowitz arcs in Finland

Over the weekend Siberian high pressure brought cold weather to Finland with diamond dust halos along. The display shown here is the gem of the period. It was photographed by Jari Luomanen on 22. January 2006 at Sahalahti.

It presents two components of reflected Lowitz arcs (arrows). As far as I know, there exists only three earlier observations with two components of these arcs, by Walt Tape and Jarmo Moilanen. Drawings based on photographs of two of the displays can be found here and here (in original slides the arcs are very faint).

Reflected Lowitz arcs were considered already by Hastings in the early 20th century, but it was Swedish meteorologist Göstä Liljequist who gave in depth theoretical treatment in 1956. He named them as "Lateral tangential arcs to the 22° halo". There exists several observations - one by Liljequist himself and others by Tape - that show only the arc that match the curvature of the outer component (lower arrow in the pic). It has turned out difficult to simulate these displays, for one thing because simulations predict also the inner arc.

It possibility that the displays with only the outer arcs are different phenomenon all together. Luomanen photos, however, show genuine refelected Lowitz arcs and so far seem to be the best documentation of the phenomenon. Theoretically reflected Lowitz arcs also extend from parhelion all the way to subparhelion, which can explain observations of "parhelia legs".