Wegener arc on webcam

On Mar/3/2007 I captured a halo display with a remote webcam in Oklahoma/USA. The camera image shows a bright parhelic circle, 120° parhelion and a rare Wegener arc forming a cross on the parhelic circle. A time lapse movie is available here: 

http://www.parhelia.de/storm/2007/flash/wegener.html (Flash)

Mid-elevation halo display with column crystals in control

Throughout my work day there were a number of halos that were coming and going. Around midday there was 22d halo, circumscribed halo, parhelic circle, and parhelia. Later on at break time I got 22 and circumscribed halos and there was a nice infralateral arc on the left and a possible lower suncave parry arc not sure on that need help to identify short piece of arc to the left of 22d halo. Before I left work I imaged an upper suncave parry arc. The final stage had nice upper tangent arc and a complete supralateral arc.

Odd radius halos in diamond dust in Finland

On 23 February an another diamond dust display with odd radius halos occured in Vaala, Finland. Temperature was dropping from -29°C to -24° during my observation.

A parhelic circle and circumzenithal arc were present with nice parhelia. A subsun and subparhelia were also seen as sparkling ice crystals in front of the ground.

Odd radius halos labelled in this enhanced photo are A) a pyramidal heliac arc, B1) upper 24° plate arc, B2) lower 24° plate arc and C) upper 23° plate arc.

The most brightest odd radius halo was 18° halo and in some photos there probably are also 9° upper plate arc and 20° halo. The ice crystal cloud was produced by a local heating plant about 2 km away. More photos can be found here.

Upper Lowitz arc in Germany

On February 21, Wolfgang Hamburg was on holiday in the Erzgebirge, but rather had snow there. Around noon, the cirrus clouds which already had caused an unusual halo activity in Bavaria (see one thread below), arrived at his position in Mulda. So between 1 and 1.30 pm, Wolfgang Hamburg also observed unusually bright sundogs followed by a beautiful display showing Parry arc and upper Lowitz arc. The enhancement of the unsharp mask shows the arc in the "Chinese eye" formed by the halos.

Probable fragment of subheliac arc

On February 20 there were a lot of cirrus shreds in the foehn area of a strong northern low pressure area. Already in the morning there appeared unusually bright sundogs and a circumzenithal arc of the same brightness in these cirrus shreds. Later also a Parry arc appeared together with parts of the parhelic circle and very bright 120°-parhelia which had an accentuated reddish rim. At 11.50 CET, another arc seemed to form above the left 120°-sundog which stayed at its position for about 10 minutes while the cirrus clouds kept moving on. As the simulation for a sun elevation of 24° shows, the position of that arc fragment is identical to the subheliac arc.

Bright 9° halo around the moon in Germany

On the 23rd of February Harald Wochner took his obligatory view out of the dormer window towards the night sky. Immediately, he realized an unusual circle which later turned out to be a 9° halo around the moon. Right at this moment he took his Camera and tripod and went a couple of hundred meters away from his village in order to have a darker sky. He could also recognize a feeble 22° halo in larger distance from the moon. There one could see the structures a little bit more. The 9° halo maintained itself in a good shape and could partially better be seen than the 22° halo which acted really diffusedly. Which the descending of the moon, the intensity of the circles decreased steadily.

The picture shows the village Wahlwies with its church on the western Lake of Constance. The picture with unsharp mask shows in addition the faint left part of 18° halo.

Moilanen arc behaviour

We have now enough photographs of Moilanen arc to make some suppositions of the responsible crystal. As lower component of Moilanen arc does not seem to exist, the crystal must be well oriented. Straight upwards pointing wedge with ~ 34° angle seems to produce an arc that fits well with photographed cases both in shape and location.

In the image above are given simulations of Moilanen arc and 22° halo for solar elevation range of 0-35°. Also the Moilanen arc raypath through the wedge is shown. At 35° light source elevation the Moilanen arc is already disappearing and shows weakly above the 22° halo.

In free fall the depicted simple prism would hardly orient as shown. What kind of crystal causes Moilanen arc is still a mystery. Although Finnish observers have managed to sample crystals from a couple of Moilanen arc displays this winter, the crystal photos have not resulted in a breakthrough.

These images are no news to those who have an inclination to fiddle with halo simulation programs. But as nobody has given them anywhere, I thought they might be of some help for the halo community in knowing what to expect when the next diamond dust swarms in. Simulations are made with software by Mika Sillanpää and Jarmo Moilanen.