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(a)
200
z
d
=1mm
z
d
=46mm
150
100
50
0
-50
-100
0
3
6
9
12
15
18
21
24
Time (hour UTC)
(b)
50
z
d
=0mm
z
d
=15mm
z
d
=34mm
z
d
=50mm
z
d
= 100 mm
40
30
20
10
0
3
6
9
12
15
18
21
24
Time (hour UTC)
Figure 2.24
Observations related to soil heat transport in the Negev desert
(September 30, 1997): soil heat lux just below the surface and at 4.6 cm depth (
a
)
and observed soil temperatures at various depths (
b
). Note that local solar time is
more than 2 hours ahead of UTC. (Data from Heusinkveld et al.,
2004
)
as well as the surface temperature show large luctuations (due to clouds) that are
already damped at only a few centimetres below the surface. In the context of sinusoi-
dal temperature variations this can be understood by noting that the damping depth is
smaller for oscillations with a frequency higher than the diurnal cycle (as in the case
of a cloud shadow). Also note the sharp drop to large negative values of
G
at sunset
due to strong longwave cooling of the hot surface.
2.3.5 Force-Restore Method
Although the theory described in the
Section 2.3.2
can be applied directly in operational
hydrological and meteorological models, it appears that a complete numerical solution
of the governing equations requires too much computational time for some applica-
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