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V-TOPPED
LIGHT PILLARS: Light pillars are
a common sight around cities in winter. Urban lights
bounce off ice crystals in the air, producing tall
luminous columns sometimes mistaken for auroras.
But the light pillars Mike Hollingshead saw on Jan.
26th near a corn mill in Blair, Nebraska, were decidely
uncommon. "They had V-shaped tops,"
he explains, "and some of the Vs were nested."
Here is what he saw:
These light pillars are not just rare, they
are exceptional!" declares atmospheric optics
expert Les Cowley. "Ordinary
pillars are produced by plate-shaped ice crystals
roughly half way between you and the light source.
These are different. Their rarely seen flared
tops show that they were made by column-shaped
crystals drifting slowly downwards and aligned horizontal
by air resistance."
"The flares are a form of the upper
tangent arcs that we sometimes see in daytime
halo displays," he continues. "But even
more exotic, some flares have a second one nested
within them! Some ice crystal columns do not rotate
but instead keep two of their prism faces improbably
horizontal to give us the very uncommon Parry
arcs of solar halo displays. The nested flares
here are amazing and probably the light halo equivalent
of Parry arcs."
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