Albedo change about to alter
By NED ROZELL
September 23, 2009
You can see it on the mountains-a clean, platinum finish that
wasn't there yesterday. It's in the forecast for here in the
lowlands, too. Snow. Our world is about to change.
We knew it was coming, right? The day I'm writing this, Sept.
21, is the average date at least a trace of snow shows up at
the Fairbanks International Airport. So says my friend, National
Weather Service hydrologist and fan-of-the-cold Ed Plumb.
Sept. 21 is also the date of the earliest measureable snowfall
in Anchorage. The average date that snow endures for the winter
in Anchorage is Oct. 16. Those in Barrow have already seen the
white blanket; their average first date of measureable snowfall
is Aug. 26.
Whatever the day, when snow appears and sticks, warmish temperatures
usually don't make a comeback. A good case study for this was
the abbreviated autumn of 1992 in Interior Alaska. Here in Fairbanks,
about eight inches of snow fell on Sept. 13. You can still see
some birches bent in an arc they assumed that day, when wet snow
weighed down branches still adorned with leaves.
"When we had this early snowcover (in 1992), we had a lot
of calendar days with low temperature records set," said
Ted Fathauer, a forecaster since the 1970s at the Fairbanks Forecast
Office of the National Weather Service.
That month became the September with the lowest average temperature
for Fairbanks, with a low of 3 degrees Fahrenheit on Sept. 30.
More than 24 inches of snow fell in September 1992, and the early
snowfall made things cooler, Fathauer said.
"The incoming (solar) radiation was effectively reflected
by the snowpack," he said. "It's the quality that physicists
have dubbed 'albedo.'"
Albedo, or reflectivity, has its roots in the Latin word albus,
or white. Snow reflects as much as 95 percent of the solar radiation
that strikes it. With that new white coating and a sun angle
that decreases with the day,
winter settles into Alaska for good, with a punch like no other
place in America.
Soon, cold air will ooze into the quiet valleys, rivers will
steam until they freeze, and lowland bogs will solidify, increasing
Alaska's navigable terrain by a wide margin.
And it all starts with snow, which reflects sunlight so well
that climbers on Denali's Kahiltna Glacier can simultaneously
ski and develop sunburn on the roofs of their mouths as they
gasp for air.
That same physical property of extreme reflection is why decreasing
amounts of sea ice floating on the northern oceans are a big
deal. The less ice, the more dark water that absorbs energy from
the sun, and the less ice that forms. On it goes.
Here, a bit farther south than the sea ice zone, the season of
white is once again returning. Celebrate if you're a dog musher,
and ask yourself what you are doing here if you don't like snow.
For up to seven months, and at least portions of the coldest
three months, the entire state can be blanketed from the top
of Denali-which is white on the hottest day of the year-to Annette
on the far south end of the Panhandle, which manages an enduring
snow cover even though it doesn't feature a month with an average
This column is provided
as a public service by the Geophysical Institute, University
of Alaska Fairbanks, in cooperation with the UAF research community.
Ned Rozell is a science writer at the institute.
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