Photographer's Note

In an earlier posting, I joked about an 'ethyl-colored' sunset; however, I've noticed here in the high desert, away from any large urban areas, the colors at sunrise and sunset seem particularly colorful.
In trying to understand these observations, I found a discussion by Stephen Corfidi of the NOAA Storm Prediction Center says that typical pollution particles are too large to scatter light well. "As a result, hazy daytime skies, instead of being bright blue, appear grayish or even white. Similarly, the vibrant oranges and reds of "clean" sunsets give way to pale yellows and pinks when dust and haze fill the air...Clean air is, in fact, the main ingredient common to brightly colored sunrises and sunsets."

Because air circulation is more sluggish during the summer, and because the photochemical reactions which result in the formation of smog and haze proceed most rapidly in warmer air. This is why the brilliant sky colors are more common in late fall and winter.

To produce vivid sunset colors, a cloud must be high enough to intercept light which has not suffered color loss by passing through the boundary layer which contains most of the atmosphere's dust and haze. When low clouds do take on vivid hues, it is a clue that the lower atmosphere is very clean and therefore more transparent than usual.

Volcanos produce thin veils of dust at altitudes of 12-18 miles. About 15 minutes after sunset, these high-level clouds come into view. Since their colors achieve greatest intensity after the sun has set at the surface, volcanic twilights are known as "afterglows."

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Additional Photos by Pat Lim (plimrn) Gold Star Critiquer/Gold Star Workshop Editor/Gold Note Writer [C: 3999 W: 226 N: 6734] (21344)
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