Environmental Engineering Reference
In-Depth Information
would have less serious results. The reduction in
insolation is accepted, but it is also considered
that there would be a concomitant reduction in
the amount of terrestrial radiation escaping into
space, which would offset the cooling, and
perhaps result in some warming of the lower
atmosphere. The overall effects would depend
very much on the altitude and distribution of the
aerosols (Mitchell 1975).
Contradictory conclusions, such as these—
drawn from the same basic information—are to
be expected in climatological studies. They reflect
the inadequacy of existing knowledge of the
workings of the earth/atmosphere system, and,
although research and technological development
is changing that situation, it remains a major
element in restricting society's response to many
global issues.
temperature and air pressure provide form and
structure in what would otherwise be an
amorphous medium. The commonly accepted
delineation of the atmosphere into a series of
layers, for example, is temperature based (see
Figure 2.4). The lowest layer is the troposphere.
It ranges in thickness from about 8 km at the
poles to 16 km at the equator, mainly as a result
of the difference in energy budgets at the two
locations, and temperatures characteristically
decrease with altitude at a rate of 6.5°C per
kilometre within it—the tropospheric lapse rate.
Temperatures at the upper edge of the
troposphere average between -50 and -60°C, but
in equatorial regions, where it reaches its greatest
altitude, values may be as low as -80°C. The
tropospheric lapse rate is, in fact, quite variable,
particularly close to the surface. Such variations
regularly produce instability in the system, and
help to make the troposphere the most turbulent
of the atmospheric layers.
The troposphere contains as much as 75 per
cent of the gaseous mass of the atmosphere, plus
almost all of the water vapour and other
aerosols (Barry and Chorley 1992). It is also the
THE VERTICAL STRUCTURE OF THE
ATMOSPHERE
Although its gaseous constituents are quite evenly
mixed, the atmosphere is not physically uniform
throughout. Variations in such elements as
Figure 2.4
The vertical
structure of the atmosphere
and its associated temperature
profile
