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.

Pyramidal heliac arc in Finland

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In 8 Feb 2007 an odd radius display was produced by local heating plant plumes in -28°C temperature in Vaala, northern Finland. I photographed this display on a road about 1.5 km away from the heating plant.

Odd radius halos in display were 18° halo, 23° upper plate arc, very faint 35° halo and rare pyramidal heliac arc. See arrows in a stacked and strongly unsharp masked photo shown.

Pyramidal heliac arc is formed by reflection from pyramidal side faces of horizontally oriented pyramidal ice crystal. It is usually visible near the sun only. It is usually very faint but this time I was able to see it also visually.

Same odd radius halos except 35° halo were also present in similar but much fainter display in Vaala couple of days earlier in 6 Feb 2007. More photos from both displays can be seen in Jarmo Moilanen's halo photo gallery or directly 8 Feb. 2007 here and 6. Feb 2007 here.

Lunar Diamond Dust Display in Pälkäne, Finland

In the evening of 4 November this lunar display graced the sky soon after sunset. Among the halo forms observed are the rare heliac arc, Tape arcs and Moilanen arc. The Moon elevation is ca. 16°.

In the image the entire length of the heliac arc is visible as a beautiful loop encircling the zenith. The Moilanen arc is very intensive and appears to extend beyond the 22 degree halo. Tape arcs can be seen as diffuse brightenings on the supralateral arc.

In the beams of the passing cars a bright pillar, parhelia, upper tangent arc and Moilanen arc were clearly visible. These proved difficult to photograph though. At the local ski resort the snow guns were operating during the display and the crystal swarm was a by-product of this activity. The temperature was below -15 °C.