Why are there fan winds in Alps and Rocky Mountains?

Brahma wind is a kind of wind blowing from plateau or mountain to lowland, which is easy to occur in mountainous areas. This is a strange weather phenomenon, which forms a dry and hot downward airflow at the leeward foothills of high mountains, causing crops to dry up or die, and even causing forest fires. Meteorology calls this airflow foehn, and this phenomenon is called foehn.

The altitude difference between the Andes and the Rocky Mountains exceeds several kilometers. When the airflow descends at the top of the mountain, the foehn effect often appears in lower areas. The daily average temperature is higher than normal 10℃, sometimes higher than that in areas far away from the foothills (areas without foehn effect). The temperature is getting warmer, dry and hot.