Wednesday, November 16, 2011

Ice Fog, Light Pillars and Moon Rings

Light pillars over Fairbanks
Moon ring in heavy ice fog
Delivering newspapers at 40 degrees below zero (part 2)

 We got a surprise this week in Fairbanks--temperatures of about 40 below zero (Fahrenheit). It usually doesn’t get that cold until later in winter. Makes me glad I’m not delivering newspapers this winter.
The cold weather doesn’t really bother me. I actually like walking at pretty much any temperature (as long as I’m dressed properly) but getting up every morning at 1:00 am and walking 5 miles got kind of old after a while. While I don’t miss delivering newspapers every night, there are a few things I do miss about those nightly walks. And some of those are directly related to those cold, cold, cold nights.
In Alaska and other frigid climes, we get ice fog, which forms when water vapor and extremely low temperatures try to mix. At 40 degrees below zero, water vapor (from your breath, an open lead on a river, stoves, or from automobile exhausts) cools almost instantly and forms minute ice crystals. Most of those crystals become suspended in the air.
Unfortunately, the geography of Fairbanks traps the cold and ice fog in an inversion layer. Until the local temperatures rise and the ice crystals convert back to water vapor, the ice fog collects—often thickly—and hangs over town. Usually it is thicker along frequently traveled roads.
Ice fog does have a few plusses—at least if you have a warped artistic bent. One is that those thousands of suspended crystals glitter in the light of street lamps, giving a person with the time to enjoy it a fantasy view of the world.
The other plus is that the suspended ice crystals are usually oriented horizontally. The ice fog above you can reflect and refract light back down towards the ground. If the conditions are right you can see pillars or columns of light that seem suspended directly over light sources on the ground.
A similar phenomenon is moon rings, where ice crystals (usually suspended high in the air) can create circular halos around the moon. When the ice crystals are high in the atmosphere, the halo can be well defined. If the ice crystals are lower in the atmosphere (say right in front of you) the halo is more wide-spread.
Ah—I’m growing nostalgic for the good old days. Think I’ll go outside and take a deep breath.

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