Environmental Engineering Reference
In-Depth Information
Figure 3.7
Earth's mean annual net radiation budget, from
satellite observations between April 1979 and March 1987.
The figures are W m
-2
.
Source: After Kyle et al. (1993).
and as radiation is absorbed by the surface, so heat is transmitted into the soil and into the
air. This takes place in proportion to the amount of energy originally absorbed. We can
express this mathematically as:
where
Q
* is the net radiation,
Q
H
is the sensible heat transfer into the air and
Q
G
is the
heat flow into or out of the soil. If the surface is damp some of the energy will be used in
evaporation. Therefore:
where
Q
E
is the energy used for evaporation from the soil and transpiration from plants.
This is a simplification, as changes in heat storage can take place and a small amount of
energy is used in plant growth.
The energy transfer into the atmosphere is the final component of the radiation
imbalance between surface and atmosphere. The net radiational loss in the atmosphere is
counteracted by this heat transfer from the surface. So, over a long period, the
atmosphere gains as much energy as it loses.
