Geoscience Reference
In-Depth Information
Sub-Antarctic
front
Antarctic
front
110
0.0
Free electrons and
ionized ice particles
be here
7.0
5.0
2.5
100
MESOSPHERE
3.0
4.0
2.0
0.5
2.5
90
mesopause
(-160
º
C at poles
)
Ionization
energy
1.0
80
2.0
1.5
Ozone decreasing
upward
70
1.5
2.0
THERMOSPHERE
60
1.0
2.5
50
stratopause
0.5
3.0
40
STRATOSPHERE
0.25
Ozone heating
by solar radiation
3.5
0.1
30
4.0
20
Subtle T changes define
distinct water bodies
separated by frontal
regions of high gradient
tropopause
4.5
0
10
Greenhouse
effect
TROPOSPHERE
5.0
0
57
º
S
º
S
º
S
º
S61
º
S
º
S
-80
-60
-40
-20
0
20
Temperature (
°
C)
Fig. 2.6
Section across Drake Passage between South America and
Antarctic to show oceanic temperature (
C): depth field.
Fig. 2.5
Mean temperature gradients for atmosphere.
widely by ocean currents. Thermal energy is lost as water is
evaporated (see
latent heat of evaporation
explained in
Section 3.4) by the overlying tropospheric winds but this
is eventually returned as
latent heat of condensation
(Section 3.4) to heat the atmospheres of more frigid
climes. But it is a mistake to assume that the oceans are of
homogenous temperature. Distinct ocean water masses are
present that have small but significant variations in
ambient temperature (Fig. 2.6), which control the density,
and hence buoyancy of one ocean water mass over
another. Those illustrated for the Southern Ocean show
the subtle changes that define fronts of high temperature
gradient.
the equator at 12-18 km altitude. The mean
lapse rate
is
thus some 4
Ckm
1
. The temperature minimum is the
tropopause
. Above this, temperature steadily rises
through the
stratosphere
at about half the tropospheric
lapse rate, to a maximum of about 5
C at 50 km above
the equator. This is because stratospheric temperatures
depend on the radiative heating of ozone molecules by
direct solar shortwave radiation. Another rapid dip in
temperature through the
mesosphere
to the
mesopause
at
about 85 km altitude reflects the decrease in ozone
concentration. Above this the positive 1.6
Ckm
1
lapse
rate in the
thermosphere
(
ionosphere
) to 400 km altitude is
due to the ionization of outer atmosphere gases by
incoming ultra-shortwave radiation in the form of
-rays
and x-rays. Beyond that, in space at 32,000 km, the
temperature is around 750
2.2.6
Temperature in the solid Earth
C.
The gradient of temperature against depth in the Earth is
called a
geotherm
. The simplest estimate would be a linear
one and it is a matter of experience that the downward
gradient is positive. We could either take the geotherm
to be the observed gradient in rock temperature or that
measured in deep boreholes (below
c.
100 m) and extrapo-
late downward, or take the indirect evidence for molten
iron core as the basis for an extrapolation upward. The
mean near-surface temperature gradient on the continents
2.2.5
Temperature in the oceans
Earth's oceans have an important role in governing
climate, since the specific heat capacity of water is very
much greater than that of an equivalent mass of air.
So, ocean water has a very high thermal inertia, or low dif-
fusivity, enabling heat energy produced by high radiation
levels in low-latitude surface waters to be transferred
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