What is the cause of the Foehn effect?

The so-called "foehn effect" refers to a kind of hot and dry wind formed when the air continues to sink and the air temperature continues to rise as the altitude continues to decrease.

The foehn effect is mainly measured from the perspective of air temperature and dry humidity. Foehn wind is dry and hot wind. To form foehn winds, two conditions need to be met. The first condition is that the air temperature must be high. This needs to be achieved through the sinking movement of the air. Usually, for every 1,000 meters the air altitude drops, the temperature will increase by about 6.5°C, so when When the air seat sinks more than about 1,000 meters, it will produce a certain Foehn effect. As the altitude difference increases, the Foehn effect becomes more obvious. If the height difference exceeds 3,000 meters, a strong Foehn effect will occur, and it is possible that Change local climate characteristics.

Foehn winds often occur in gusts, blowing downhill from mountains. Foehn wind originally refers to a hot and dry wind formed in the mountain valleys of Germany, Austria and Switzerland after the air flow crosses the Alps. The Rocky Mountains of America and the Caucasus of Russia are both places as famous as the Alps for producing foehn winds. It can also be seen in various parts of our country. For example, the leeward slopes of tall mountains such as the Himalayas, Hengduan Mountains, and Erlang Mountains all have extremely strong foehn effects. Shijiazhuang, located at the eastern foot of the Taihang Mountains, has an average of 19 days of foehn winds per year, with the maximum number of days reaching 49 days.