ection 2
The weather patterns that we experience in the northern midlatitudes are driven by
the unequal heating of the Earth’s surface. The tropical latitudes (23°S - 23°N) receive
more energy input than the higher latitudes. Because the amount of heat energy rera-
diated by Earth back into space is approximately the same anywhere on the globe, the
energy imbalance is mainly due to two factors (figure 5).
- First, the Sun’s rays are nearly perpendicular to the surface near the equator. As a
result, they travel a shorter distance through the dense lower atmosphere and are
less likely to be reflected or dissipated.
- Second, the tropical regions receive more of the Sun’s energy per unit area due to
the curvature of the Earth.
The presence of waves and weather disturbances in our latitudes is a result of the
Earth-atmosphere system attempting to restore balance to the system by transporting
excess energy from the south to the north.
figure 5.
The general circulation of the atmosphere—the average motion of the winds around
the globe—is also driven by the differential heating of the Earth. In the simplest terms,
excess heating near the equator causes the air to expand or swell over the equatorial
regions. Upward motion associated with this heating is typically concentrated in a
relatively narrow band named theInter-Tropical Convergence Zone(ITCZ). The
WAV E MO T I O N A N D T H E
GE N E R A L CI R C U L AT I O N
S
Z 1
Z 2
differential heating (latitudinal)
A 1
A 2
Earth
Z = the optical path through
Earth’s atmosphere
A = surface area
Z 2 >> Z 1
A 2 >> A 1
Result:
- longer optical path at pole
- more reflection,
absorption, scattering
- larger area per unit of
insolation at pole
