Two-State rare pyramidal crystal halos
Two views of rare ice halos from pyramidal crystals in high cirrus cloud. Some crystals were unusually well orientated and made strange ‘parhelia’ or sundogs.
At left: Robert Gorkin's sighting from Delaware on July 2, 2019. Robert captured the earliest known images of complete Lowitz arcs.
At right: Steve Mattan's view 80 miles away in New Jersey. The pyramidal crystal containing cirrus spread over a wide area and encompassed two States. Steve's OPOD contributions range from halos to iridescent sea shells, blue flashes and Death Valley mirages (1,2,3,4,5,6,7,8,9).
Most halos come from small cloud crystals shaped as hexagonal prisms. When short they drift within the cloud as horizontal dinner plates. Longer prisms are called columns. Some cloud conditions generate crystals with extra pyramids on the prism ends. Those have up to 20 faces and make a whole set of new halos.
Most pyramidal halos are circular because the crystals are aerodynamically rather rounded and tumble. They are also far from the ideal shapes pictured at right. Their halos are fuzzy as in the 8, 20 and 23° halos of the display.
The fun starts when less rounded crystals become specially oriented. When tilted like plates they form ‘plate displays’ and their extra arcs are parhelia or pyramidal sundogs. The Delaware - New Jersey halos were a plate display with at least 18° and 23° parhelia.
Less 'spherical' crystals can be partially oriented. these 'plate oriented' crystals made the parhelia or sundogs.
At right: A ten million ray HaloSim simulation. It looks smarter and sharper than nature because it used a very limited set of ideal crystals.
The Delaware - New Jersey display had a faint or missing 9° halo. I suppressed it by using crystals with very narrow central prism sections. The 9° halo rays pass through this central section and in the display it must have been missing or optically impaired.
Notice the simulation's other strange parhelia - these are very rarely seen. Predicted CO2 cloud halos on Mars resemble them.
Tumbling and randomly oriented crystals made the rings