NASA
SATELLITE SAW MORE U. S. SNOW IN EARLY WINTER; GROUNDHOG MAY
SEE MORE COMING
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.
This
image shows the snow cover across North America for Days 313-320
(Nov. 16 - Nov. 23) of the year 2000.
This
image shows the snow cover across North America for Days 321-328
(Nov. 24 - Dec. 1) of the year 2000.
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