The solid red curves in Figure 1.4(a)(i) and (ii) show the incoming solar radiation reaching the Earth and atmosphere, as a function of latitude, for the northern summer and the southern summer, respectively. The intensity of incoming solar radiation is greatest for mid-latitudes in the hemisphere experiencing summer, while for high latitudes in the winter hemisphere, the oblique angle of the Sun's rays, combined with the long periods of winter darkness, results in amounts of radiation received being low.
However, the Earth not only receives short-wave radiation from the Sun, it also re-emits radiation, of a longer wavelength. Little of this long-wave radiation is radiated directly into space; most of it is absorbed by the
Figure 1.4 (a) The radiation balance at the top of the atmosphere plotted against latitude (scaled according to the Earth's surface area) for (i) the northern summer and (ii) the southern summer. The red solid line is the intensity of incoming solar radiation and the red dashed line is the intensity of radiation lost to space (both determined using satellite-borne radiometer).
(b) The average temperature of surface waters at different latitudes. At a given latitude, there will be surface waters whose annual mean temperatures are higher or lower than shown by the curve; this range is represented by the thickness of the pink envelope.
December-February net deficit
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