Geoscience Reference
In-Depth Information
3
Heat and energy
SYSTEM
Thermosphere
The sun's energy represents the prime driving source for
our climatic system. In this chapter we will look first at
the nature of the atmosphere through which this energy
has to pass to reach Earth's surface. We will then examine
the internal mechanisms of this energy flow, and consider
the spatial variability of the flows which give rise to
different climates. Perhaps the best way to explain what
is happening with these flows is to follow the path of
sunlight from the top of the atmosphere and describe
what affects it on its journey to Earth's surface. Long-wave
exchanges can then be described.
Pressure
(hPa)
km
80
0.01
0.1
Mesosphere
1
45
Ozone formed by
UV rays
10
Stratosphere
100
12
Troposphere
Surface
1000
-100°C
-50°C
0°C
50°C
100°C
Atmospheric composition
atmosphere below 20 km
Earth's atmosphere is a thin layer of gases extending to
about 80 km above the surface (
Figure 3.1
).
There is no
sudden finish, though, in reality it just gets thinner as it
eventually merges with emissions from the sun and into
space. Despite its thinness, the atmosphere is vital to life
on Earth, providing oxygen for breathing, shielding us
from harmful rays from the sun and interstellar particles
and producing precipitation (in some areas) to sustain life.
Comparison with worlds without an atmosphere, like the
moon, shows its importance.
Table 3.1
lists the main
components of the atmosphere. Nitrogen and oxygen
form the largest proportion, making up about 99 per cent
of the total by volume. Climatologically other gases such
as water vapour, carbon dioxide and ozone play a much
more important part in controlling climate despite their
Gas
Chemical
Volume %
symbol
(dry air)
Nitrogen
N
2
78·08
Oxygen
O
2
20·95
Argon
Ar
0·93
Carbon dioxide
CO
2
0·037
Neon
Ne
0·0018
Krypton
Kr
0·0011
Helium
He
0·0005
Methane
CH
4
0·00017
Ozone
O
3
0·00006
Hydrogen
H
2
0·00005
Xenon
Xe
0·00009
