Figure 2.4 Simple atmospheric convection system for a hypothetical non-rotating Earth.
Heat is transported to higher latitudes by the atmosphere both directly and indirectly. If you look at Figure 2.2(a) and (b), you will see that motion in the upper troposphere is generally polewards. Air moving equatorwards over the surface of the Earth takes up heat from the oceans and continents. When it later moves polewards, after rising at regions of low atmospheric pressure such as the Equator, heat is also transported polewards. Thus, any mechanism that transfers heat from the surface of the Earth to the atmosphere also contributes to the poleward transport of heat. The most spectacular example of heat transfer from ocean to atmosphere is the generation of tropical cyclones, which will be discussed in Section 2.3.1.
The Hadley cells, of which the Trade Winds are the surface expressions, may be seen as simple convection cells, in the upper limbs of which heat is transported polewards. How heat is carried polewards at higher latitudes is not quite so obvious.
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