Atmospheric
Optics
V shaped Arcs
~ A spectacular ice halo display seen by Pekka L�hteenm�ki (Photography1, 2) at Jalasj�rvi, Finland. Above the low sun are three �V� shaped arcs � sunvex in halo terminology because they are convex to the sun. The lowest is the mysterious Moilanen arc. We are still unsure of what crystals make it but somewhere they must have two icy faces inclined 34 degrees to each other. Above that is the familiar upper tangent arc. Above the tangent arc is a second rarity, a Parry arc. Search the skies regularly and you might see one on average only once a year. Parry first recorded the arc in 1820 while icebound in the Arctic. All images ©Pekka L�hteenm�ki, shown with permission
Helic arcs formed by external reflection from Parry oriented crystals are evident in this shot. The Moilanen arc is particularly sharp and extensive.
Near optically perfect crystals that grew downwind of a nearby ski area likely formed these rare halos.
