Lee waves

Schematic representation of leeward waves. The wind that blows in the direction of the mountain forms the first oscillation (A), which is repeated after passing the mountain (B). At the highest points, lenticular (lenticular) clouds form.

Leeward waves in meteorology are a type of standing atmospheric waves. These waves are characterized by periodic changes in atmospheric pressure and air temperature and are caused by its vertical displacement, for example, as a result of an orographic rise when the wind overcomes a mountain range (in this case, leeward waves are called "mountain waves"). Leeward waves can also be caused by wind blowing from an escarp or plateau ^[1] , deviation of the air flow due to thermal upward movement or passage through horizontal convection currents. The leeward waves were first described in 1933 by the German gliders Ganz Deutsch and Wolf Girt over the Krkonoše Mountains ^{[2] [3]} .

The vertical movement of air causes periodic changes in the speed and direction of movement in the stream. Leeward waves always arise in groups on the leeward side of an obstacle or airflow that causes them. On the first descent of such air, a turbulent horizontal vortex arises, the so-called rotor, which leads to oscillations. The leeward waves reach their greatest strength under the condition of a stable horizontal level of the properties of the layers of air above the obstacle and an unstable near-surface layer ^[1] .

A typical leeward wavelength is between 2 and 8 km. If this distance corresponds to the distance between the hills - the waves can amplify, if not - the oscillations quickly damp behind the obstacle. In areas with rough terrain, leeward waves can exist simultaneously in several places. In some cases, they can cause strong winds at low points and form lenticular clouds at high points.