Environmental Engineering Reference
In-Depth Information
maximum between 50° and 60° north and south of the equator, and again at 10° and 30°
north and south (Figure 2.15). This pattern reflects the two types of transfer referred to
earlier; the higher-level transfers are dominant in the subtropical zone, while surface
transfers are most active in middle latitudes.
The transfer of latent heat also shows a complex pattern, related to the distribution of
water vapour in the atmosphere and the dominant, lower-air wind patterns. Thus its main
effects are seen between 20° and 50° north and south of the equator, where winds
blowing outward from the subtropics carry moist air poleward. Nearer the equator the
pattern is reversed. Winds created by equatorial low pressures carry this air into the lower
latitudes. As we shall see in Chapter 6, this pattern is closely related to the global wind
system. Oceanic transfers of energy are most important either side of the equator,
reflecting the outward movement of warm water from the tropical region. As the waters
move polewards they lose heat to the overlying air. As wind patterns move air eastwards
at these higher latitudes, the heat released by the sea eventually warms the western coasts
of the continents such as North America and Europe. Recent satellite evidence would
suggest a higher figure of heat transfer by oceans than is shown in this diagram,
especially about 20° N.
In total, the processes of energy transfer maintain a steady-state equilibrium within the
global system; they replenish energy losses in areas where outputs exceed inputs (the
higher latitudes) and they remove energy from areas where inputs are in excess (the lower
latitudes).
LOCAL AND REGIONAL ENERGY TRANSFERS
While these atmospheric and oceanic processes account for the spatial redistribution of
energy at a global scale, they are not the only means of energy transfer in the global
system. At a more local level, numerous other transfers are taking place.
ATMOSPHERIC TRANSFERS
Within the atmosphere, local and regional winds, convection currents and air masses
carry energy as sensible heat and as latent heat. The uplift of air and the water contained
within it transform some of this energy into potential energy, which is released when the
air sinks or the water condenses. Small, local transfers of energy to Earth's surface occur
owing to friction, while the kinetic energy of the wind is transmitted to soil and rock
particles as these
