Classic Halos seen by John Adam of Old Dominion University, Virginia during his morning walk to work Thursday Oct 22, '09. ŠJohn Adam.

John's display in an icy cirrus and contrail strewn Virginia sky was made by crystals of four orientations in the cloud layer.

Randomly oriented crystals made the 22° halo. We are still unsure just what the crystals are that produce this the best known of all the halos.

Plates produced the sundogs, contributed to the narrow white parhelic circle and mostly lit the colourful circumzenithal arc high in the sky.

Hexagonal columns drifting with their long axis almost horizontal contributed yet more glints to the parhelic circle but are best revealed by the winged upper tangent arc above the 22° halo. They did more. Light passing through their end faces gave a trace of a supralateral arc curving downwards after touching the circumzenithal arc.

Column crystals with two side faces almost horizontal are said to be 'Parry oriented'. Parry crystals yielded the rare suncave Parry arc above the upper tangent. A bank of contrail turned cirrus hides it in the topmost frame but it is well visible in the image at right. Parry crystals can also generate circumzenithal arcs and might well have contributed a few glints to John's.

There is a fifth crystal orientation - the Lowitz. This display almost had everything but the elusive Lowitz arcs were not to be seen.

The busy contrails? Their shadows cast upon the halo producing cirrus layer show that they were higher up and unconnected with the spectacle.

Atmospheric
Optics

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