Geoscience Reference
In-Depth Information
Temperature (°F)
36
40
44
48
52
56
60
64
0
0
APR
JUNE
AUG
50
SEPT
20
100
NOV
JAN
40
150
60
200
Warming by surface heating
250
80
Cooling by vertical mixing
300
Cooling by vertical mixing and
surface conduction
100
2
4
6
8
10
Temperature (°C)
12
14
16
18
Figure 3.15
Mean monthly variations of temperature with depth in the surface waters of the eastern
North Pacific. The layer of rapid temperature change is termed the thermocline.
Source: After Tully and Giovando (1963, p. 13, Fig. 4). Reproduced by permission of the Royal Society of Canada.
reducing the temperature response. The relative
depths over which the annual and diurnal temper-
ature variations are effective in wet and dry soils
are roughly as follows:
The different heating qualities of land and water
are also partly accounted for by their different
specific heats
. The specific heat (
c
) of a substance
may be represented by the number of thermal
units required to raise a unit mass of it through
1°C (4184J kg
-1
K
-1
). The specific heat of water is
much greater than for most other common
substances, and water must absorb five times as
much heat energy to raise its temperature by the
same amount as a comparable mass of dry soil.
Thus for dry sand,
c
= 840 J kg
-1
K
-1
.
If unit volumes of water and soil are
considered, the heat capacity, ρ
c
, of the water,
where
Diurnal variation
Annual variation
Wet soil
0.5m
9m
Dry sand
0.2m
3m
However, the
actual
temperature change is greater
in dry soils. For example, the following values of
diurnal temperature range have been observed
during clear summer days at Sapporo, Japan:
10
6
J m
-3
K
-1
),
exceeds that of the sand approximately threefold
(
ρ
= density (
ρ
c
= 4.18
×
Sand
Loam
Peat
Clay
1.6 J m
-3
K
-1
) if the sand is dry and
twofold if it is wet. When this water is cooled the
situation is reversed, for then a large quantity of
heat is released. A meter-thick layer of sea water
ρ
c
= 1.3
×
Surface
40°C
33°C
23°C
21°C
5cm
20
19
14
14
10cm
7
6
2
4
