Because of the orientation of the Earth with respect to the Sun, there is significantly more solar heat flux at the Equator than at the poles. There exists a temperature gradient between the Equator and the poles; however, the gradient would be much larger if there were no meridional heat transport. In order to reach the temperature gradient observed today, there needs to be a pole-ward flux of about 6 petawatts, which includes both atmospheric and oceanic heat transport (Marshal & Plumb 2008).
Figure 1 reveals the general circulation of the atmosphere. Near the equator there is uprising of hot air that moves to the low-pressure poles. The majority of this air sets at approximately 30°. When the descending air reaches the surface, some goes northward, and some goes southward. Because of the Coriolis force, air in the North Hemisphere is deflected to the right. As a result, pole-ward air starts to move eastward (known as the westeries in meteorological terms, because the air is moving from the west), while the equator-ward air moves westward (easterlies).
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