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Arctic Mirage
Tue Feb 01, 2005
Listen in RealAudio 
Weather has profoundly influenced human explorations over the ages. One
atmospheric phenomenon -- the arctic mirage - may even have allowed early
explorers to see the unseeable, what was over the horizon. Hi, I'm Bryan Yeaton for
The Weather Notebook.
The arctic mirage occurs when light is refracted in a downward arc by cold, dense
surface air. Under these conditions, images of objects located below the horizon -
mountains or glaciers -- rise into view, overcoming visual restrictions imposed by
Earth's curvature. While a 3,000-foot mountain normally disappears about 72 miles
away, under arctic mirage conditions, it may remain visible beyond 250 miles.
The arctic mirage possibly aided Eighth-Century Celtic mariners, voyaging into the
open Atlantic from the Faeroe Islands, in discovering Iceland. Under mirage
conditions, Iceland's Vatna Glacier, rising 6,600 feet, becomes visible from the Faeroe
coast 240 miles distant.
Upon his banishment, Viking Erik the Red sailed from Iceland northwestward directly
toward an unknown land rumored to lie beyond the horizon. By sailing this heading,
however, his ships faced contrary winds and currents, to arrive at a coastline protected
by sea ice.
Had Erik initially sailed southwestward, following known favorable winds and currents,
he would have easily reached the accessible Greenland south coast. What, then,
persuaded him to select the northwest route? Under arctic mirage conditions,
Greenland coastal mountains, 186 miles away, become visible from the cliffs of
northeast Iceland.
Having settled Greenland, Viking mariners continued westward into North America's
Arctic, further encouraging exploration.
Subaru of America and The National Science Foundation contribute support for our
show, which is produced by the Mount Washington Observatory.
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