Geoscience Reference
In-Depth Information
8 0 0
F e b r u a r y 1 9 7 4
6 0 0
4 0 0
2 0 0
0
- 2 0 0
1 5
1 8
2 1
2 4
2 7
1 0 0 0
F e b r u a r y 1 9 7 5
8 0 0
6 0 0
4 0 0
2 0 0
0
1 5
1 8
2 1
2 4
2 7
Fig. 4.14 Comparison of mean daily values of the total turbulent heat flux
H
+
L
e
E
in (W m
−
2
)atthe
sea surface obtained by means of the atmospheric water budget (solid lines) by Nitta (1976) and
by Murty (1976), with the averaged values obtained by a mean-profile method over water
(dashed lines) at several stations in the East China Sea. Because the data were not taken at the
same locations, the areas to which both methods were applied coincided only approximately.
The experiment took place in February of 1974 and 1975, and the area enclosed for the
atmospheric water budget was of the order of 17
10
4
km
2
; its shape was roughly rectangular
×
with center at Okinawa. (After Kondo, 1976.)
and with all flux terms taken as mean values over a sampling period, gives an evaporation
rate
h
so
∂θ
∂
t
dz
+
P
−
q
z
d
1
h
so
E
=−
(4.58)
0
where
θ
is the soil water content as volume fraction,
z
is the vertical coordinate pointing
down from
z
=
0 at the surface,
P
is the rate of precipitation (or irrigation), and
q
z
d
the rate of
downward seepage or drainage through the lower boundary of the soil layer at
z
=
h
so
. Mean
values of the finite difference form of (
∂θ/ ∂
t
) over a sampling period, as a function of
z
, can
be determined by various methods. In the earlier field experiments related to irrigation of
agricultural crops (see Israelsen, 1918; Edlefsen and Bodman, 1941), the method consisted
of soil sampling and gravimetric analysis before and after drying of the samples inanoven.
More recently, the neutron scattering method, TDR and other techniques (see, for example,
Schmugge
et al
., 1980) have become available that allow
in situ
soilmoisture measurements.
