What is the cause of "foehn wind"?

"Foehn wind", as the name suggests, is a fire-like wind, which is a unique weather phenomenon in mountainous areas. Why do foehn winds appear in mountainous areas? This is caused by the downward movement of air flowing over mountains. Meteorologically speaking, when a mass of air rises from the ground to high altitude, the temperature will drop by an average of 6.5°C for every 1,000 meters it rises; conversely, when a mass of air sinks from high altitude to the ground, the temperature will drop by 1,000 meters for every 1,000 meters it rises. The average increase is approximately 6.5°C. This means that when the air drops from a mountain with an altitude of 4,000 to 5,000 meters to the ground, the temperature will rise by more than 20°C, causing the cool climate to suddenly heat up. This is what causes "foehn" winds.

"Foehn" can be seen in many mountainous areas around the world, but the Alps in Europe, the Rocky Mountains in America, and the Caucasus in the former Soviet Union are the most famous. On days when foehn winds blow in the Alps, the daytime temperature can suddenly rise by more than 20°C. The weather in early spring will become like midsummer, which is not only hot, but also very dry, and fires often occur. Strong foehn winds can cause tree leaves to scorch and the ground to crack, causing severe drought.

Foehn can sometimes bring benefits to people. In the Rocky Mountains of North America, the snow is deep in winter. When the foehn wind blows in spring, it will not take long for all the snow to melt. The land is covered with lush green grass, providing pasture for livestock. Therefore, the locals call it "Snow Eater" ". The milder foehn wind can increase local heat and advance the maturity of corn and fruit trees. Therefore, residents of the Caucasus and Tashkent oases in the former Soviet Union simply called it "corn wind".

In our country, Foehn areas can also be seen everywhere, but they are not as obvious as the above-mentioned areas. Traces of it can be seen in the north and south of the Tianshan Mountains, at the foot of the Qinling Mountains, in the hills of southern Sichuan, in the Jinshajiang River Valley, in the Greater and Lesser Hinggan Mountains, at the foot of the Taihang Mountains, and in the mountainous areas of southern Anhui.