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How does the foehn effect make leeward mountain slopes warmer and drier?
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Asia
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The foehn effect creates warmer and drier conditions on the leeward slopes of mountains through a process of adiabatic temperature changes as air moves across a range.1
The process occurs in two main stages:
- Windward Ascent: As moist air is forced up the windward slope, it expands and cools. As it cools, the moisture condenses into precipitation, a process that releases latent heat into the air mass. By the time the air reaches the mountain peak, it has lost much of its moisture.213
- Leeward Descent: As the now-dry air descends the leeward side, it is compressed and undergoes adiabatic warming. Because the air contains little remaining moisture to evaporate and absorb heat, it warms rapidly as it descends.21
Consequently, the air reaching the foot of the leeward slope is significantly warmer and drier than it was at the start of its ascent on the windward side. In Asia, this phenomenon is observed in various regions, including the Himalayas, the Tien Shan range, and the Elburz Mountains, where it contributes to distinct climatic contrasts.214