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Introduction
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Soil Temperature
Alaska
Russia
Snow Cover
Snow Off Day
Greenness
SINDVI
Nascence
Peak
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Greenness: Nascence
Nascence, or spring greenup, is marked by the day of year (plus or
minus about 5 days) on which NDVI exceeds, for the first time, a threshold
of 0.3. North of 55 deg N, this is usually between late May (DOY = 140)
and the end of June (DOY = 180).
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Average Nascence
Day The average day greenup occurrs (to within about 10 days)
over the period 1982 - 2001. From the Pathfinder data set. |
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Current Nascence
Day Nascence day for the last growing season (to within about
16 days). From the MODIS data set. See Continuing
the time series with MODIS data for discussion of differences
with Pathfinder data. |
Nascence Anomalies (Relative to 1982-2001 Mean)
Nascence Anomaly, First Five Years
Pathfinder Data Minus Mean
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Nascence Anomaly, Last Five Years
Pathfinder Data Minus Mean
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Notes: The anomaly images above show a trend toward
earlier greenup (blue colors) over much of the Arctic in the last five
years of our data record when compared with the first five years. In
contrast to anomalies in SINDVI, however, there is considerable spatial
variation. (The grey areas in the images above are where the threshold
of 0.3 was not exceeded. Shield, bare rock, ice sheets, and areas largely
covered by water have low or zero NDVI.) See Continuing
the time series with MODIS data for discussion of why more recent
MODIS data are not used.
Nascence (Day of Year),
Regional Averages |
Nascence (Day of Year)
Anomaly, Regional Averages |
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Notes: Time series of nascence days (left) and anomalies
(relative to the 1982-2001 mean, right) for regional subsets (red squares
in the images). The nascence time series make evident that unlike SINDVI,
the general advance in the day of spring greenup is not "in sync" everywhere.
The dashed lines are data from MODIS. See Indicator
Processing and Discussion for more information.
Nascence (Day of Year)
Time Series, North Slope Subregions |
Nascence (Day of Year)
Anomaly Time Series, North Slope Subregions |
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Notes: The North Slope, Alaska, region was divided
into subsections based on literature suggesting a different greening
response for coastal versus inland tundra (see Discussion).
Nascence for coastal tundra differs from inland higher elevation
tundra by about 20 days. The anomaly series show that in spite
of different greenness values, the two physiographical provinces
are responding to changes similarly, although there is a suggestion
that coastal tundra may be more sensitive to factors driving nascence
than inland tundra. |
