Friday, 29 September 2006

Wegener arcs in Czechoslovakia again

Today (9:00 - 11:30 UT) was next nice day. Sky in Holesov showed clear and coloured Wegener arc and other arcs (common halos and upper Parry suncave arc, lower Lowitz arc and infralateral arc).

Display was photographed also by others. Here are the photos by Martin Jankovic from Brno.

[text: Patrik Trncak]

Sunday, 24 September 2006

From archives: odd radius column arcs in 2001

I saw this display in Oulu on 17 September 2001. Because the photos have not been around in the internet, I dare to make posting even though the event is not so recent.

The display has all the odd radius column arcs except the 23° arc. Images are stacked from 3-8 individual images. The one on the lower right is also flipped horizontally to get a bit more definition. For the upper left and lower images, simulations of the pyramid column arcs give crystals as in the figure. Also shown is similarly shaped real crystal, photographed during a weak odd radius column arc display at South Pole in 1999.

From pyramid plate crystals there is the 23° plate arc in all photos, and lower 9° and 24° plate arcs in the upper right photo. The display was discussed in more detail in September 2003 number of journal Weather. It also appears in the book "Atmospheric halos and the search for angle x" by Tape and Moilanen.

By Marko Riikonen

Monday, 18 September 2006

Lowitz arcs in Czech

Martin Popek observed this display with Lowitz acrs on 16. September. Interesting feature is the lower Lowitz component extension above parhelion. In the simulation there is something like that, but it's very, very ghostly. The main body of the lower component below parhelion looks as if it were just a patch of 22° halo - the extension towards parhelion is missing. Same goes with the upper component. This is quite typical way of Lowitz arcs showing up. Circular component is seen only above parhelion.

I was given sun elevation of 39° for this display but somewhat lower elevation gave a bit better simulation results. This is for 33°. The projection in the simulation is clearly not the same as in camera and this may have caused some of the broblems. Simulation is made with Halosim by Les Cowley and Michael Schroeder.

Be the sun elevation 39° or 33°, it does not change much anything fundamentally. Several question could be raised about this display with lenghty discussions. It seems we still have a long way to understanding Lowitz arcs.

By Marko Riikonen

V-shaped Parry and Tape's arc in Germany

On August 31, 2006, clouds moved in destroying all hopes for meteor observations in the night. The halo display in the high clouds close to sunset (1725 UT, Sun elevation approximately 3 deg) observed by Jürgen Rendtel from Marquardt (west of Berlin, 13.0 deg E, 52.5 deg N) included intense V-shaped upper tangent and Parry arcs. Another bright coloured 'spot' of about 3 deg apparent size was found to be part of the supralateral arc and Tape's halo. The image processing by Claudia Hinz using unsharp masking also revealed the convex Parry arc.

By Claudia Hinz

Saturday, 16 September 2006

Circumscribed halo and pyramid halos in Sardinia

This display was captured by Jan Drahokoupil in Sardinia on 6. September. The 22° halo is surrounded by elliptical circumscribed halo. The small halo around the sun is 9° halo or 9° column arc (or both together). Simulations could give better clue. Later on the display changed and there were also 18° plate arcs.

More photos here.

Thursday, 14 September 2006

A fine circumhorizontal arc from Italy

Circumhorizontal arc more than 100° wide above the horizon, very brilliant, for about 25 minutes. The best I have seen from Italy!

Equipment :Canon EOS D30.

A collage of 3 images with a 35mm lens at f/8 and 1/1000 sec. 

31 May 2006 12,20 LT (+2h) Viterbo - Italy

By Paolo Candy

Saturday, 9 September 2006

Odd radii in Czech Republic

During the Czech halo observers meeting in Kuncice, high clouds created some good displays. This odd radius halo complex was seen on 14. August. It shows 9,° 18°, 20°, 22-24° and 35° halos. Judging from the non-uniform intensity distribution of some of the halos (9° and 20° halos being brightest on the sides), this display was caused by poorly oriented columnar pyramid crystals. It's also interesting that 20° halo is brighter than 18° halo. This type of occurrence is uncommon.

This is stacked image processed by Roman Manak and Patrik Trncak. Original photos were taken by Martin Popek.

By Marko Riikonen