Rainfall amounts are heavy at low latitudes (Table 10.1), while Antarctica is the driest continent on Earth (Chapter 16). This is explained at least partly by the Clausius— Clapeyron effect (Note 4.C): the troposphere at high, colder latitudes contains less precipitable water than at low, warm latitudes (Figure 6.13).
The poleward decrease of rainfall is not as uniform as the poleward decrease of temperature (Figure 3.4). There is a minimum about the Tropics (i.e. around 23° latitude) and a second maximum around 50° (Figure 10.6), due to the 'general circulation', discussed in Chapter 12. Large-scale convective uplift occurs near the equator, whereas the troposphere slowly subsides about the Tropics, producing clear skies without rain. That explains the dryness of Australia, where 37 per cent of the area receives less than 250 mm/a and 68 per cent below 500 mm/a. The second maximum at midlatitudes is due to large-scale frontal uplift
(Chapter 13). Finally, the air over Antarctica is generally subsiding and therefore free of clouds or rain.
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