Tuesday, 31 January 2006

Twenty years from first observation of Hastings arcs

Hastings arc is rare halo from Parry oriented crystals. It was predicted by C.S Hastings in 1920, but it wasn't until 1986 that it was first time observed, by Walter Tape at South Pole. 

The photo on the left is the latest documentation of Hastings arc. This moon display was seen by Marko Mikkilä at Sievi last December. Like so many of the good diamond dust displays in Finland, it was also made by snow machines. 

The image is stacked from 6 individual unsharp masked images. White arrow marks the Hastings arc, red heliac arc. The display resists succesful simulating. The problem is the oddly short Parry arc. Mikkilä's simulations indicate towards plate shaped Parry crystals - a crystal falling mode that has been thought of as unrealistic.

Hastings arc looks much like the Wegener arc, except that it touches Parry arc instead of 22° upper tangent arc. Simulations series from Parry oriented crystals are here.

A list of known observations:
21. Jan 1986, Walter Tape, South Pole (in Atmospheric halos)
11. Jan 1999, Marko Pekkola, J. Moilanen and M. Riikonen, South Pole.
Dec 2004, Max Emerson, Swizerland (photos and video
17. Dec 2005, Marko Mikkilä, Sievi, Finland.

Monday, 30 January 2006

Nice display at Idaho

Walt Tape sent a note about this display that was photographed by Jim Grossman on 24. January 2006 at Tamarak ski resort in Idaho, USA. Among other more common halos, it shows also Wegener arcs (arrows).

Diamond dust halo displays near the ski resorts are usually generated by snow making. That seems to be also the case now: "There was limited snowmaking occurring at and below the inversion level, but about 1/2 to a mile away from and in the opposite direction from the display", tells Grossman. 

These man made halo displays often get better as ice crystal cloud travels further away from the source. Probably this is due to crystals growing larger as they gather water vapor from the surrounding air. 

A new book about halos

American Geophysical Union (AGU) has published a new halo book:

"Atmospheric Halos and the Search for Angle X"
by Walter Tape and Jarmo Moilanen

You can find description of the book here. You can order it from there too.

Carl Tape has opened a webpage for the book, you can find it here.

Sunday, 29 January 2006

Simulation of 44° parhelion

Here is a simulation of the Jaakko Tähti 44° parhelion display. In order to produce 44° parhelion (left arrow) in the simulation, multiple scattering has been used for plate crystal population. Reflected Lowitz arcs (right arrow) as well as 22° halo are simulated with "normal" single scattering populations.

Photo and simulations are also found here. Simulation is made with program by Mika Sillanpää and Jarmo Moilanen.

Patrik Trncak notified me about another likely case of photographed 44° parhelion. It was documented by Matthew Hyde in Greenland in summer 2002.

Friday, 27 January 2006

44° parhelia, Minnesota

Jaakko Tähti is to be congratulated!

For completeness of the records, part of the Minnesota halos of 3rd January 2004 are shown here. The top image is 'as was' from the camera. Bright left and right hand 44° parhelia were visible in the display.

44° parhelion in Finland

Once thought to be an extremely rare halo, the 44° parhelia is now increasing it's appearances. The display on the right was photographed by Jaakko Tähti on 21. December 2005 at Viitasaari, Finland. To my knowledge, this is the eighth photographed occurrence of 44° parhelion. 

The formation of 44° parhelia differs from other halos in that it's not caused directly from sun rays, but from light rays of another halo - namely the common 22° parhelia. In other words, it is the parhelia of parhelia. Formation of 44° parhelia seem to require diamond dust conditions and very bright 22° parhelia. According to Jarmo Moilanen, also low sun elevation is essential to ensure there are enough ice crystals between the sun and observer. Here the sun elevation is 2°.

List of photographed occurrences of 44° parhelia: 
3 Dec 1970, Saskatoon, Canada, Earle Ripley (photos not shown)
23 Jan 2002, Vaala, Finland, Jarmo Moilanen (drawing shown)
June 2002, Greenland, Matthew Hyde
30 Dec 2002, Juva, Finland, Jari Piikki (drawing shown)
3 Jan 2004, Minnesota, USA 
21 Nov 2004, Teuva, Finland, Heikki Mahlamäki
21 Dec 2005, Viitasaari, Finland, Jaakko Tähti
3 Jan 2006, Stockholm, Sweden, Yvonne Primé

Stockholm Display II

More images of Göte Flodqvist's display are on Mats Mattson's site - this page.

Thursday, 26 January 2006

Wegener Arc - Stockholm

Göte Flodqvist recorded this display at Stockholm on January 3rd. Wegener and subhelic arcs were evident with a bright supralateral arc and a 46° halo. The HaloSim. simulation parameter file can be downloaded here.

Wednesday, 25 January 2006

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.

Tuesday, 24 January 2006

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".

Monday, 23 January 2006

Bright Moilanen arc in Finland

This display was photographed by Pertti Havia on 21. December 2005 in Huhko, Southern Finland. The V-shaped Moilanen arc above the tree line is well developed. Nesting in the glow of the 22° upper tangent arcs, there is also upper sunvex Parry arc. (Shows better in unsharp masked photo which is not shown here).

Saturday, 21 January 2006

US Elliptical halo observations 2005

Here's my elliptical halos I got for 2005 . The first one was Feb 15th 2005 and the second Dec 17th 2005 .

Friday, 20 January 2006

Wegener arcs and heliac observed in Ohio USA

Here's the pics and the Wegener and heliac arcs are annotated with black arrows.

The pics were taken on Jan 15th 2006.

Tuesday, 17 January 2006

Parhelion legs in Italy

9.1.2006 in Colfosco (Italy), HOP member Lukas Kosarek seen some halos on diamond dust. He observed 22 deg halo, 46 deg halo, supralateral arc, circumzenith arc, subsun, subparhelia, 22 parhelia and faint upper tangent arc. About 10:00 UT he seen and take photo of Parhelion legs - interesting phenomena of ice halos. He say: " I seen two orange arcs, join parhelion with subparhelion. It was bright on right side of halo display". Some photos of this display are here: http://www.fotoagrafika.wz.cz

Lower sunvex Parry in Finland

Lower sunvex Parry is a halo of which for long time only one certain report was known: the photograph by Takeshi Ohtake in 1979 in Alaska, shown in Walt Tape's book "Atmospheric Halos". 

Now the sightings of lower sunvex Parry seem to be increasing. Last winter it was photographed twice in Finland and this winter we have two reports as well. Picture above is the latest sighting of lower sunvex Parry (arrow), by Marko Mikkilä at Sievi on the night of 15/16 January 2006. The display was caused by snow machines from nearby ski resort. Moon elevation is 40°. 

Winter's first sunvex Parry was seen on 8. January 2006 at Himos ski resort. Photos of the display by Mika Aho are seen here. Simulations with different crystals are here.

Mikkilä display had also other rare halos. He reports lower Tape arcs, Wegener arcs, helic arc and subhelic arc. Also interesting halos from car headlights were present.

Thursday, 12 January 2006

Lower 23 plate arc observed in Chile

Lower 23 plate arc is a rare halo, that, as far as I am aware, has been observed and photographed only once. This was in Chile on 28. November 1997. Now the lower 23 plate arc seem to have made another appearance - and again in Chile.

The accompanying picture is from halo display seen at Aucanquilcha volcano on 3. Debember 2005 by J. Ruoskanen and I. The image is stacked from 63 individual photos taken during 20 minutes. Unsharp masking has also been used. The simulation is made of populations of random and plate oriented pyramid crystals. Halos are 9°, 18°, 20° and 23° circular halos and lower 23 plate arc (23 lpa). Sun elevation change in the photos was from 71° to 75°, the simulation is for 73°.

Lower 23 plate arc is probably not that rare halo in itself. It's just that resident observers are lacking from the locations where sun regularly rises high enough for it to be seen.

Simulations are made with HaloSim and stacking with Registax.

More stacking technique halo images can be seen here.

Tuesday, 10 January 2006

Halo reports blog opened!

Hi all skywatchers!

This is just opened site to help report halo observations. As this is just opened, we do not have much to report yet. But lets hope that we will have something to tell you about halos. Idea is that there may be several contributors to this blog instead of one. So we probably get more better view what kind of halos are seen around our planet.

Halos are colored or white patch, rings or spots of light formed by sun or moon light refracting or reflecting on ice crystals in atmosphere.

Have a nice skywatching!