Night Halos ~ A few of the many images from a night halo session by Jari Luomanen (atmospheric optics) in Finland on 25/26 Nov '13.

"A very challenging night as the conditions kept changing. Temps ranged from minus 6.5 to minus 10. All in all, this was a nearly 14 hour hunt and a very enjoyable one too."

All images ©Jari Luomanen, shown with permission
Upper and lower tangent or Parry arcs - or both!

Finland halo observers carry their own lamps.

Some artificial light generated halos including helic (heliac) arcs.

These are all diamond dust halos downwind of snow guns at the Himos ski center, Jämsä, Finland.

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Notable is the distinct lunar upper Parry arc above the rather diffuse upper tangent arc and 22° halo.

Inside the 22 degree halo and above the moon is the enigmatic Moilanen arc whose crystal origin is as yet not explained.

Stacked images - see below - show Jari's second sighting of a new halo below the Moilanen arc.

There are not many plate crystals as evidenced by the weak paraselenae and no circumzenithal arc.

Halo keys - common, not so common.

Stacked images. Stacking can remove misleading cloud streaks, reveal more detail and show extra halos.

Here the V-shaped Moilanen arc shows up strongly. Below it is possibly the new arc imaged for the first time by Marko Mikkilä (who also first imaged the Kern arc).

Jari Luomanen imaged it in 2006 and his stacked image at right is the third sighting.

Nicolas Lefaudeux has suggested that crystals containing a 34 degree interfacial angle could be responsible. When the prism points upwards a Moilanen arc results. Tumbling about the horizontal prism axis can produce a diffuse arc below the Moilanen arc. However, the nature of the crystals containg the required 34 degree wedge remains a mystery.