Atmospheric
Optics
Jackson Hole Ice Halos
~ A magnificent display of rare halos including Parry infralaterals and Lowitz arcs. Captured by Stephen Lyons while skiing on 3rd December '15. See below for halos labelled on a colour subtraction enhancement and also a comparison with halos at the South Pole where there are skiers but no ski slope snow blowers!
Image ©Stephen Lyons
Colourless arcs like helics and parhelic circle are De-enhanced in colour subtraction enhancements
Compare with a similar South Pole display imaged in 1999 on film by Marko Riikonen.
There are no snow blowers there. However, the crystals are the same - only their nuclei differ.
Go here for a how the rare arcs in both displays formed.
The in-phone panorama maker has distorted the circular 22° halo.
Ice crystals grow on tiny nuclei, airborne sea salt, dust, aerosol etc. In general, the slower the crystal growth the more perfect the eventual crystal. The crystal shape or habit (hexagonal plate, column, pyramidal) depends in a poorly understood way on temperature and humidity amongst probably many other parameters.
Ski-slope snow blowers emit special nuclei to promote snowflake formation. A by-product is near optically perfect halo forming crystals. They grow slowly downwind of the snow formation.
The Jackson Hole display came from them. The helic, 46° Parry arcs are rarities that before snow blowers were only seen in exceptional displays at the South Pole. But the Lowitz arcs are unusual in ski-slope diamond dust.
