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NASA SATELLITE SAW MORE U. S. SNOW IN
EARLY WINTER; GROUNDHOG MAY SEE MORE COMING
Images
This Groundhog's Day Punxsutawney
Phil may see his shadow which would indicate 6 more weeks of winter
and likely more snow, according to legend in the Pennsylvania town,
but a NASA satellite confirms that it has already been snowier than
usual this winter.
"Composite data from NASA's
Terra satellite show that this winter brought more snowcover in the
early part of the season than average," Dorothy Hall of NASA's
Goddard Space Flight Center said. Results from the Moderate
Resolution Imaging Spectroradiometer (MODIS) aboard NASA's Terra
satellite clearly observed more snowcover in the Midwestern and
western United States in November and December.
Hall noted that results from MODIS
show that, "Snowcover was greater than average in the western
and Midwestern portions of the country for the month of
November." Complementing the snowfall were record cold
temperatures for November and December 2000 throughout the United
States, according to the National Oceanic and Atmospheric
Administration (NOAA).
The continental snowline in November
2000 was considerably farther south than its average position as
determined from NOAA's Environmental Satellite, Data, and
Information Service (NESDIS) records. NOAA/NESDIS' average monthly
snowline is based on satellite-derived snow-cover products that have
been available since the 1960s.
In November the average snowline runs
north of the U.S.-Canadian border except in the Rocky Mountains,
where it dips to the south and extends all the way into northern
Arizona and northern New Mexico. Hall noted, "While the snow
extent in the northeastern part of the country was not particularly
unusual, by mid-November in the Midwest and the western states, the
snow cover was far greater than normal as the snowline extended
through the Dakotas south into Nebraska."
In the west, snow covered large parts
of Colorado, Utah and even parts of Nevada, providing banner
conditions for ski resorts, which had most of their trails open by
Thanksgiving. This winter's increased snowfall was a nice change for
the ski areas that suffered from last year's lesser snowpack.
NOAA/NESDIS has been producing weekly
snow maps of the Northern Hemisphere land surfaces since 1966 using
visible-band satellite imagery. Because snow has such a high
reflectivity compared to other surfaces on Earth, snow covered areas
appear much brighter in satellite imagery than most other surface
types. However, Hall noted that the key difference between the MODIS-produced
snow maps and the images produced by NOAA/NESDIS is that "MODIS
has a higher resolution and an improved ability to discriminate
between snow and clouds."
In the MODIS composite image for the
week of November 16-23, 2000, the black line is the average snow
line for November and the white area is snow cover. Clouds appear
darker than the white snow.
More than 40 percent of the Earth's
land surface in the Northern Hemisphere can be covered with snow
during the winter months. The highly reflective nature of snow
combined with its large surface cover make it an important factor in
the Earth's radiation balance, which includes incoming solar energy
and energy reflected back into space. Because the Earth is in a
steady-state balance of incoming and outgoing energy, its
temperature undergoes small change, but the mean temperature stays
nearly the same. According to the National Snow and Ice Data
Center, snow may reflect up to 80 and 90 percent of incoming solar
energy, whereas a surface without snow would only reflect 10-20
percent. Retained solar energy means increased warmth.
Many areas of the world rely on the
snowmelt for irrigation and drinking water. In the western U.S,
mountain snowpacks contribute up to 75 percent of all year-round
surface water supplies. Therefore, it is necessary to monitor
snowpacks closely throughout the winter and spring for assessment of
water supply and flooding potential, and MODIS data will prove
useful in this capacity.
As an instrument on NASA's Terra
satellite, MODIS continuously observes the Earth's surface in a
sweeping motion, every 1-2 days with a scanning imaging radiometer.
Its wide field of view (over 2,300 kilometers or over 1,429 miles)
provides images of daylight-reflected solar radiation and daytime
and nighttime thermal emissions over the entire globe. Sample MODIS
imagery is available at: http://nsidc.org/NASA/MODIS/
.
Terra was launched on December 18,
1999 and began collecting data on February 24, 2000, part of a
15-year global data set on which to base scientific investigations
about the Earth.
Snow and ice products generated from
MODIS data include daily and 8-day composite snow-cover maps,
including lake ice on large inland lakes, daily and 8-day composite
sea ice-cover maps, and sea ice-surface temperature maps. There will
also be global daily and 8-day composite map products available for
climate modeling. These products are archived at the National Snow
and Ice Data Center (NSIDC) in Boulder, Colorado.
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