Fog Corona near Green Bay

Provided and copyright by: Peg Zenko
Summary authors & editors: Peg Zenko

The foggy sunrise of June 6, 2006, revealed a bit of beauty along a rural roadside near Green Bay, Wisconsin. Fog is basically the same as a cloud, but with its base close enough to the Earth's surface that it restricts visibility to less than 1 kilometer or about 0.6 miles (according to the definition by the U.S. Weather Bureau, Air Force, and Navy). Coronas, whether observed in fog or in mid-altitude clouds, result from the diffraction of sunlight rather than from refraction or reflection. Smaller droplets produce larger diffraction angles and thus a larger corona. The next time a shallow layer of fog accompanies the rising Sun, see if you can observe a corona (looking toward the Sun) or perhaps even a glory (looking away from the Sun) -- such morning magic just may brighten your day.

Related Links:

• Atmospheric Optics
• The Cloud Appreciation Society
• Water in the Atmosphere
• The Atmosphere and the Water Cycle

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