Environmental Engineering Reference
In-Depth Information
Chapter
3
Heat and energy in the atmosphere
THE ATMOSPHERIC ENERGY SYSTEM
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.
ATMOSPHERIC COMPOSITION
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 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
main 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 much lower concentrations. Their role will be
outlined later in this chapter.
