Increasing latitude is associated with lower vapour pressures (Figure 6.7), because of lower temperatures. For instance, the average is only 0.07 hPa at Vostok, at 78°S in Antarctica. Figure 6.7 also shows that air is relatively dry over continents, especially in the winter, when particularly low temperatures reduce the saturation vapour pressure. Australia and the Sahara stand out as arid areas, whereas the Amazon basin is notably humid.
Mixing ratios decrease with latitude similarly (Table 6.2), and Figure 6.8 shows how surface dewpoints too vary regularly with latitude at places in South America.
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