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In meteorology, lee waves are atmospheric stationary waves. The most common form is mountain waves, which are atmospheric internal gravity waves. These were discovered in 1933 by two German glider pilots, Hans Deutschmann and Wolf Hirth, above the Krkonoše.〔On March 10, 1933, German glider pilot Hans Deutschmann (1911–1942) was flying over the Riesen mountains in Silesia when an updraft lifted his plane by a kilometer. The event was observed, and correctly interpreted, by German engineer and glider pilot Wolf Hirth (1900–1959), who wrote about it in: Wolf Hirth, ''Die hohe Schule des Segelfluges'' (advanced school of glider flight ) (Berlin, Germany: Klasing & Co., 1933). The phenomenon was subsequently studied by German glider pilot and atmospheric physicist Joachim P. Küttner (1909 -2011) in: Küttner, J. (1938) "Moazagotl und Föhnwelle" (Lenticular clouds and foehn waves), ''Beiträge zur Physik der Atmosphäre'', 25, 79–114, and Kuettner, J. (1959) "The rotor flow in the lee of mountains." GRD (Research Directorate ) Research Notes No. 6, AFCRC(Force Cambridge Research Center )-TN-58-626, ASTIA (Services Technical Information Agency ) Document No. AD-208862.〕〔(【引用サイトリンク】 Article about wave lift )〕 They are periodic changes of atmospheric pressure, temperature and orthometric height in a current of air caused by vertical displacement, for example orographic lift when the wind blows over a mountain or mountain range. They can also be caused by the surface wind blowing over an escarpment or plateau,〔 or even by upper winds deflected over a thermal updraft or cloud street. The vertical motion forces periodic changes in speed and direction of the air within this air current. They always occur in groups on the lee side of the terrain that triggers them. Usually a turbulent vortex, with its axis of rotation parallel to the mountain range, is generated around the first trough; this is called a rotor. The strongest lee waves are produced when the lapse rate shows a stable layer above the obstruction, with an unstable layer above and below. ==Clouds== Both lee waves and the rotor may be indicated by specific wave cloud formations if there is sufficient moisture in the atmosphere, and sufficient vertical displacement to cool the air to the dew point. Waves may also form in dry air without cloud markers.〔 Wave clouds do not move downwind as clouds usually do, but remain fixed in position relative to the obstruction that forms them. * Around the crest of the wave, adiabatic expansion cooling can form a cloud in shape of a lens (lenticularis). Multiple lenticular clouds can be stacked on top of each other if there are alternating layers of relatively dry and moist air aloft. * The rotor may generate cumulus or cumulus fractus in its upwelling portion, also known as a "roll cloud". The rotor cloud looks like a line of cumulus. It forms on the lee side and parallel to the ridge line. Its base is near the height of the mountain peak, though the top can extend well above the peak and can merge with the lenticular clouds above. Rotor clouds have ragged leeward edges and are dangerously turbulent.〔 * A foehn wall cloud may exist at the lee side of the mountains, however this is not a reliable indication of the presence of lee waves. * A pileus or cap cloud, similar to a lenticular cloud, may form above the mountain or cumulus cloud generating the wave. * Adiabatic compression heating in the trough of each wave oscillation may also evaporate cumulus or stratus clouds in the airmass, creating a "wave window" or "Foehn gap". 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Lee wave」の詳細全文を読む スポンサード リンク
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