The most distinctive characteristic of the mountain wave is the lenticular cloud. These air parcel oscillations occur in concert, parallel to the wave fronts (lines of constant phase). A frequent wintertime weather phenomenon along the Colorado Front Range, the mountain lee wave sets up downwind of the Continental Divide (the snow-capped mountains on the horizon in this video) when winds aloft are westerly and increasing with altitude. {\displaystyle \theta _{0}(z)} The most distinctive are the sharp-edged, lens-, or almond-shaped lenticular clouds, but a variety of stratocumulus , altocumulus , and cirrocumulus forms appear in both the main, vertically propagating waves and in the lee waves. N Although the clouds are over the mountains, these are NOT mountain wave clouds. 'Fluctus' is the Latin word for "billow" or "wave" and this may also be used to describe the cloud formation, though that most often occurs in scientific journals. Mesmerizing wave-like clouds spotted over mountain in Virginia. COMING UP CBSN Denver will air Colorado governor's news conference on … Not an official cloud classification but rather a "supplementary feature", virga form when rain … Roll clouds. b. stratus. is the vertical profile of potential temperature. 5 years ago. The most common form is mountain waves, which are atmospheric internal gravity waves. 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. Some decent mountain wave cloud/sunset time-lapses from a couple different days along the Colorado front range near Boulder, CO. When sufficient moisture is present in the upstream flow, vertically propagating mountain waves produce interesting cloud forms, including altocumulus standing lenticular (ACSL) and other foehn clouds. Unusual wave clouds over the Aral Sea, seen from NASA's Water satellite on March 12, 2009. What are mountain wave clouds and how do they form? Watch Queue Queue The crests of the waves may be identified by the formation of lenticular clouds (lens-shaped), if the air is sufficiently moist. Disk shaped, mountain-wave clouds are known as *a. altocumulus lenticularis. They were discovered by a glider pilot, Wolf Hirth, in 1933. The rising air of the wave, which allows gliders to climb to great heights, can also result in high altitude upset in jet aircraft trying to maintain level cruising flight in lee waves. Special Clouds > Lenticular Clouds (aka Standing Lenticular, Lee-Wave Clouds, or Mountain-Wave Clouds) Learning Goal 1b. Weather fronts mark the boundary or transition zone between two air masses and have an important impact up…, The classification of clouds into types was first proposed by Luke Howard in 1802 and we largely use the s…, Contrails are frequently seen criss-crossing the sky and are created from water vapour coming out of an ai…. Rising, descending or turbulent air in or above the lee waves can cause overspeed or stall, resulting in mach tuck and loss of control, especially when the aircraft is operated near the "coffin corner". These were discovered in 1933 by two German glider pilots, Hans Deutschmann and Wolf Hirth, above the Krkonoše. Mountain wave clouds, a subset of “lee waves” can form in an otherwise stable atmosphere when unsaturated air is forced up by changing terrain beyond the lifting condensation level where the resulting adiabatic expansion causes it to cool below its dew point. Otherwise, when these clouds cannot form in the absence of enough moisture in the air, the presence of a mountain wave is hard to identify, and this can be potentially dangerous to the airplane. θ Provided that there is a steady increase in wind strength with altitude without a significant change in direction, standing waves may be created. The moving air hits the still mountain in the same way the prow of a moving boat hits still water.” As air funneled around the islands in February, its temperature and humidity was just right for the crests of the lee waves to rise and cool the air and form clouds. θ θ {\displaystyle N\cos {\phi }} If there's enough moisture in the air, and the air at the top of the crest of the wave reaches the dew point, a cloud will form. There are a variety of distinctive types of waves which form under different atmospheric conditions. Lee waves are a form of internal gravity waves produced when stably stratified flow is forced over an obstacle. Some decent mountain wave cloud/sunset time-lapses from a couple different days along the Colorado front range near Boulder, CO. The most intense turbulence is usually located at low-levels, leeward of the mountains in or near the rotor cloud, if present; Mountain waves may be denoted by mountain wave clouds - Cirrocumulus Standing Lenticular (CCSL) - Altocumulus Standing Lenticular (ACSL) - Rotor clouds (often associated with the most intense turbulence) 2. At the wave dip, no clouds,” said Wind. Who we are, what we do and organisational news. 22. *e. All of the above are correct. Wave cloud pattern in Tadrart region. When air blows across a mountain range, in certain circumstances, it can set up a train of large standing waves in the air downstream, rather like ripples forming in a river when water flows over an obstruction. 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