Environmental Engineering Reference
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Fig. 19.14
Spatial distribution of DTR derived from the GOES-8 observations for different
months as averaged from 1996 to 2000 (
a
) January, (
b
) April, (
c
) July, and (
d
) October
make them very attractive for derivation of DTR. Recently, Sun et al. (2007)
applied the split-window algorithm developed by Sun and Pinker in 2003 to
GOES-8 observations. For the first time, a satellite view of continuous spatial
distribution of DTR over the continental United States was shown (Fig.
19.14
).
The 5-year average DTRs for the four mid-seasons show geographical differences,
with western and central USA being systematically higher than those of the eastern
USA or the northwestern coast (Fig.
19.14
). Over the western USA, DTR is larger
in spring and summer than fall and winter. Over the eastern part, DTR is larger in
spring and fall than in summer and winter (dividing line between west and east is
about 100
W). As shown in Fig.
19.15
, which illustrates the 5-year average
meridional mean DTR in July for the following selected LC/LU types: cropland,
forest, grassland, and urban. There exists distinct difference in DTR between the
west and east for each surface type, the DTRs being much larger over the west than
over the east. In general, the DTR of urban area is usually smaller than those of
other surface types.
A remarkable resemblance between high vegetation (Fig.
19.16
) and low DTR
can be seen for all four mid-season months. Evapotranspiration from vegetation
contributes significantly to the decrease in DTR during summer in the eastern
United States (Durre and Wallace
2001
). Moreover, the smaller DTR areas over
the eastern United States are found to have higher sulfate aerosol emissions than the
western USA (Chin et al.
2000
). Sulfate aerosols scatter solar radiation back to
space and tend to cool the surface during daytime and may result in a decreased
DTR (Stone and Weaver
2003
).
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