4.3. Assessment of radar growing season parameters
Radar remote sensing measures of growing season
parameters showed a high degree of spatial and interannual
variability over the 2-year study period that was generally
consistent with site measurements and model simulation
results (See Table 3). The maps in Fig. 6 show the 2000
and 2001 initiation of the growing season as derived from
SeaWinds daily radar backscatter data for all land areas
above 50jN or 1000 m in elevation within the North
American study region. The average date of growing
season onset for both years was approximately May 5th
(F 21 days), though the initiation period ranged over more
than a 40-day period, beginning in southerly latitudes in
early March and advancing northward and to upper elevations
with the progression of spring. Pronounced spatial
variability in the timing of growing season initiation is
particularly evident in the Rocky Mountain region and is
likely due to the effects of sharp elevational gradients on
surface temperature and snow cover seasonal dynamics.
The mean absolute difference in growing season onset
between years 2000 and 2001 for the entire mapped region
was 14.4 (F 20.9) days, indicating substantial interannual
variability in seasonal freeze/thaw and associated ecological
dynamics.