Alaska 1999

Aurora photographer Jan Curtis used a 35 mm lens to obtain the image at left. It captures the immensity of the halos better than wide angle and fisheye lenses.

Moving upwards from the weak 22° halo, there is a fine upper tangent arc, a suncave Parry arc, a supralateral arc (or possibly a 46° circular halo) and a circumzenithal arc.

The HaloSim simulation uses randomly oriented columns, plate crystals, singly oriented and Parry oriented columns.

The great Alaska display of 1999 lasted over two and a half hours and was described by Walter Tape as perhaps the best display he had witnessed in the Northern Hemisphere. Cirrostratus clouds produced the display and the crystals were of fine quality and well oriented. Crystal tilts in the simulations had a standard deviation of only half a degree.

The brightly coloured arc A in the HaloSim simulation at right was likely a supralateral arc rather than a 46° halo fragment because, in the display, other arcs from singly oriented columns were strong whereas the 22° halo from poorly oriented crystals was weak.

A subhelic arc, B, Wegener arc, C, and a Tricker oval, D, were visible. These are all very rare halos generated by singly oriented column crystals.

Infralateral arcs (joining the supralateral arcs at the parhelic circle) were not visible: the display was not well developed in that region.

   Finally, two more images from Jan Curtis showing the spectacular circumzenithal and supralateral arcs.