Environmental Engineering Reference
In-Depth Information
Figure 3.6
Annual mean absorbed solar radiation, outgoing
long-wave radiation and net radiation averaged around
latitude circles.
Source: After Hartmann (1994).
the tropics (Figure 3.6). In fact, values differ little between equator and poles. For any
particular latitude, we can sum the surface and atmospheric radiation balances to find out
which areas of Earth have a radiation surplus and which areas have a deficit. Using
satellite data, it is now possible to determine the radiation balance of the surface and
atmosphere together, as shown in Figure 3.7. In general there is a surplus of energy
between about 38° N and 38° S and a deficit towards the poles. Naturally the magnitude
of the surplus is identical to that of the deficit, but it does mean that there must be a
steady transfer of energy from the tropics polewards, otherwise the tropics would get
hotter and the polar regions cooler. It is the winds of the world, and to a lesser extent the
ocean currents, which bring about the necessary heat transfer.
HEAT BALANCE
USES OF AVAILABLE ENERGY
In the previous section we showed how Earth's surface normally receives a surplus of
radiation which leads to warming there. This situation cannot last indefinitely, or the
temperature gradient in the air and the soil would become enormous. Energy tends to
flow down a gradient,
