MODIS data reveal that average winter temperatures in clear-sky
conditions during the 2001-02 winter in the contiguous United States
were more than 3°C (5.4°F) warmer in the daytime and more than 2°C
(3.6°F) warmer at night than the winter of 2000-01.
Daytime temperatures in December 2001 were 4.6°C (8.3°F) warmer than
December 2000. January and February 2002 were also warmer than in 2001,
and unseasonable warmth extended back into the fall, with November
temperatures almost 6°C (10.8°F) warmer in 2001 than 2000. Some of the
biggest temperature differences occurred in the northern Great Plains,
which were much warmer than last year, and northern Utah, which was
colder.
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Average temperatures during December 2001 through
February 2002 for the contiguous United States appear to have been
unseasonably warm from the Rockies eastward. The coldest temperatures
appear black, while dark green, blue, red, yellow, and white indicate
progressively warmer temperatures. MODIS observes both land surface
temperature and emissivity, which indicates how efficiently a surface
absorbs and emits thermal radiation.
Temperature, Continental U.S. (720 by 540)
December-February, 2000–2001
December-February, 2001–2002
November 2001
December 2001
January 2002
February 2002
Temperature, North America (3672 by 1800)
December-February, 2000–2001
December-February, 2001–2002
November 2001
December 2001
January 2002
February 2002
Animations
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large (640 by 480 MPEG)
full size, lossless compressed (720 by 540 Quicktime)
Land Surface Temperature Palette
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Zhengming Wan, a Principal Investigator at the Institute for
Computational Earth System Science, University of California, Santa
Barbara, developed the new technique for using MODIS data to
determine the surface temperature of the Earth. According to Wan, ”The
land surface temperature maps from MODIS provide independent evidence of
previous reports that this past winter was warmer than normal and
confirm our ability to observe from space a characteristic of the Earth
that is important for studying global change.”
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Compared to the winter of 2000-01, temperatures
throughout much of the U.S. were warmer in 2001-02. This map depicts the
differences on a scale from dark blue (colder this year than last) to
red (warmer this year than last). A large region of warm temperatures
dominated the northern Great Plains, while the area around the Great
Salt Lake was a cold spot.
Temperature Difference, Continental U.S. (Winter
2002/2001 - Winter 2000/2001) (720 by 540)
Daytime
Nighttime
Animations
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Temperature Difference Palette
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| His team’s initial evaluation of the MODIS
land surface temperature observations found that most of MODIS’
space-based temperature measurements agreed with comparable ground-based
measurements to within 1°C (1.8°F). Results will be published in a
special issue of the journal Remote Sensing of Environment later
this year. Unlike conventional observations of surface temperature
that are actually measurements of air temperature collected by
thermometers 2 meters (6.6 feet) above the ground, MODIS measures
precisely the thermal radiation emitted from the planet’s
surface—whether that surface is bare ground, lakes, treetops, or
rooftops. This additional detail means farmers could know the
temperature of the air around their crops and the temperature of the
crops themselves, which helps farmers better estimate productivity and
water requirements.
MODIS measures the temperature of nearly every square kilometer (0.4
square miles) of the Earth’s surface roughly twice a day. This regular
coverage enables MODIS to observe snow cover, as well. Monthly MODIS
maps showing snow-covered areas from November 2001 to February 2002
reveal that along with high temperatures, snow was late to arrive and
early to recede in many parts of the United States.
November’s snowline remained well north of its average location near
the border of the United States and Canada, and large areas of the U.S.
Rocky Mountains saw little persistent snow cover that month. In
February, at least 16 states from the Rocky Mountains eastward showed
little to none of their expected snow cover.
Many parts of the U.S. depend on snowmelt for recharging public water
supplies. MODIS’ observations of the extent of snow cover allow
scientists to more accurately estimate water availability in the spring
and summer months.
Launched December 18, 1999, NASA’s Terra satellite is the flagship of
the Earth Observing System series of satellites, part of NASA’s Earth
Science Enterprise, a long-term research program dedicated to
understanding how human-induced and natural changes affect our global
environment. Terra MODIS observations are expected to continue through
at least 2004.
Land surface temperature data are available
free of charge from the EROS Data Center DAAC:
http://edcdaac.usgs.gov/modis/mod11b1.html
Snow cover data are available free of charge from the National
Snow and Ice Data Center:
http://nsidc.org/data/modis/data.html |
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November 2001 snow cover
February 2002 snow cover
MODIS snow cover maps for the United States and
Canada from November 2001 and February 2002 show below average snow
cover for much of the U.S. The solid red line marks the average location
of the monthly snow extent; white areas are snow-covered ground. Snow
was mapped at approximately 5 km pixel resolution on a daily basis, and
then combined, or composited, every eight days. If a pixel was at least
50% snow covered for three out of four 8-day periods in a month (three
out of three for February), it was mapped as snow covered for the whole
month.
Snow Cover, Continental U.S. (720 by 540)
November 2001
December 2001
January 2002
February 2002
Snow Cover, North America (2400 by 1300)
November 2001
December 2001
January 2002
February 2002 |
