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Arctic Sun
Mon Jul 26, 2004
Listen in RealAudio 
The Arctic summer brings with it the midnight sun. But how warm is that sun within the
Arctic Circle? The simple answer is "not very." Hi, I’m Bryan Yeaton for The Weather
Notebook.
At the Summer Solstice, when the sun is highest in the northern skies, its altitude at
the Arctic Circle only reaches 46 degrees above the horizon, equivalent to the solar
elevation in Boston or Chicago of late March; at the North Pole the elevation is only 23.5
degrees, about the same as those cities in December.
In the High Arctic, the sun’s rays strike the surface at a shallow, grazing angle,
spreading the solar beam over a much larger area and reducing its strength. As a
result, the solar strength in the Arctic Circle at high noon is only about 40 percent of that
at the Equator at the top of the atmosphere. At 80 degrees North, it drops to 17 percent,
and at the true pole, the sunbeams barely graze by in passing.
Because of the sharp angle, solar energy shining down on the Arctic is further depleted
as it passes through roughly six times more atmosphere than in the tropics.
If there is a saving grace, it is the long hours of arctic sunlight, which makes up for the
weak solar beam.
With 24-hours of sunlight at 80 degrees North, the total daily solar input at the top of the
atmosphere is about 35 percent more than at the Equator. With fairly clear skies, this
reduces to about ten percent higher differential at the arctic surface.
The bottom line: even in the long days of an Arctic summer, don’t forget your jacket.
Thanks to our contributing writer, meteorologist Keith Heidorn. The Weather Notebook
receives support from the National Science Foundation and Subaru: Driven By What’s
Inside. We are a program of the Mount Washington Observatory.
Today's Links
Average Solar Energy Maps for the Arctic:
http://arctic.atmos.uiuc.edu/ERA40/solar.html
Picture of the path of the midnight sun:
http://www.ualberta.ca/~aprata/arcticwarming/feedbacks.html
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