Geoscience Reference
In-Depth Information
(a)
600
R
n
400
l
E
200
G
0
H
−
200
00
04
08
12
Time of day (hr)
16
20
24
(b)
600
R
n
400
l
E
H
200
Figure 4.5
Field
measurements of the daily
variation in the surface
energy budget for (a) barley
and (b) Douglas fir forest.
(Redrawn from Arya, 1988,
after Long
et al.
, 1964 and
McNaughton and Black,
1973, published with
permission.)
0
G
+
S
−
200
00
04
08
12
Time of day (hr)
16
20
24
flux dominates over sensible heat. However, forests tend to be more conservative
with respect to transpiring water than annual crops. Perhaps this is because indi-
vidual plants have to survive for many years, which is not necessarily the case for
crops. Consequently, for forests, the proportion of available energy leaving as sen-
sible heat during the day is often greater and often the daytime latent heat and
sensible heat fluxes are roughly equal.
Figure 4.5 shows representative field measurements of the diurnal variation in
the surface energy budget for a well-watered agricultural crop and well-watered
