- Under zones of high atmospheric pressure associated with the subtropics and centered near 30° latitude. Air descending from the upper atmosphere at these latitudes causes evaporation to exceed precipitation. Much of the Sahara and the Australian desert can be associated with this phenomenon.
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West coasts of continents between 20° and 30° latitude. In these latitudes, prevailing winds are easterly and prevent moist air from coming onto the west coast. Cold ocean currents also occur in these locations and moisture in the sea air condenses as fog along the shore. Some of the world's driest deserts are located right on the coast; they received most of their limited precipitation from fog. Such fog deserts include Baja California in North America, the western Sahara in northern Africa; the Atacama in South America, and the Namib in southern Africa.
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Rainshadows of high mountain ranges. When air masses are forced over mountains and downslope, they warm and their capacity for holding water vapor increases. Evaporation exceeds precipitation and an arid environment or rainshadow is created on the leeward side. Such conditions account for some of the, the Patagonian desert in Argentina; and the Peruvian desert.
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Interiors of continents. Usually in combination with the rainshadow effect, distance from a major source of moist air results in dry climates in the interior of a land mass. The Great Basin desert of the US, the Australian desert, and the Gobi desert of Mongolia can all be explained in large part to their interior positions.