{\displaystyle \phi } cos Mountain Wave and Rotor Clouds over the Colorado Front Range. 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. Mountain wave clouds typically contain liquid water drops at temperatures down to approximately 36 °C.14,15However, when the temperature falls below a threshold near this value, the water particles in these wave clouds freeze rapidly, forming small, quasispherical ice particles with diameters that ap- … The most common form is mountain waves, which are atmospheric internal gravity waves. Pilots of powered aircraft tend to avoid flying near lenticular clouds because of the turbulence that accompany them. On the ground, they can result in very strong gusty winds in one place, with still air only a few hundred metres away. 0 b. are usually associated with prominent mountain ranges. θ Cap clouds indicate that there is a strong … Rotors or eddies can also be … Shape: Curved layers, like flying saucers, Latin: Altocumulus lenticularis = “like a lens”. They did this for the first time on August 30, 2006 in Argentina, climbing to an altitude of 15,460 metres (50,720 ft). ) Support your business with world-leading science and technology. there are several terms for mountain wave:- . 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. This video is unavailable. If you look closely you see 2 types of cloud formations. [1][2][3] The vertical motion forces periodic changes in speed and direction of the air within this air current. It can even be a hazard for large aircraft; the phenomenon is believed responsible for many aviation accidents and incidents, including the in-flight breakup of BOAC Flight 911, a Boeing 707, near Mount Fuji, Japan in 1966, and the in-flight separation of an engine on an Evergreen International Airlines Boeing 747 cargo jet near Anchorage, Alaska in 1993.[14]. This is because the presence of the mountain wave results in severe turbulence of the aircraft’s rotor systems. If you look further south you can see cirrus clouds coming off the mountains of Southern North Carolina the upstate of South Carolina into NE Georgia. *e. All of the above are correct. Buoyancy restoring forces therefore act to excite vertical oscillation of the perturbed air parcels at the Brunt-Väisäla frequency, which for the atmosphere is: N And it forms a lenticular cloud, to be specific. b. stratus. These wave fronts represent extrema in the perturbed pressure field (i.e., lines of lowest and highest pressure), while the areas between wave fronts represent extrema in the perturbed buoyancy field (i.e., areas most rapidly gaining or losing buoyancy). In contrast, the phase propagation (or phase speed) of the waves points perpendicular to energy transmission (or group velocity).[6][7]. (CNN) — A rare formation of clouds wowed onlookers at Virginia's Smith Mountain Lake on Tuesday. In this case, the northwesterly winds of the jet stream passed over the Appalachians and made gravity waves on the lee (east) side of the mountains. 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 strange, unnatural looking clouds sometimes form downwind of hills or mountains. The event was observed, and correctly interpreted, by German engineer and glider pilot Wolf Hirth (1900–1959), who wrote about it in: Wolf Hirth, Organisation Scientifique et Technique du Vol à Voile, "An Unexpectedly Heavy and Complex Snowfall Event across the Southern Appalachian Region", Observations of Mountain-Induced Rotors and Related Hypotheses: a Review, Chronological collection of meteorological data, satellite pics and cloud images of mountain waves in Bariloche, Argentina (in Spanish), On High Winds and Foehn Warming associated with Mountain-Wave Events in the Western Foothills of the Southern Appalachian Mountains, An Examination of the Areal Extent of High Winds due to Mountain Waves along the Western Foothills of the Southern Appalachian Mountains, https://en.wikipedia.org/w/index.php?title=Lee_wave&oldid=994069508, Creative Commons Attribution-ShareAlike License, A gradual increase in windspeed with altitude, Wind direction within 30° of perpendicular to the mountain ridgeline, Strong low-altitude winds in a stable atmosphere, This page was last edited on 13 December 2020, at 23:27. By Caitlin O'Kane June 19, 2019 / 8:31 AM / CBS News Seven weird weather phenomenons . 23. The conditions favoring strong lee waves suitable for soaring are: The rotor turbulence may be harmful for other small aircraft such as balloons, hang gliders and paragliders. θ Moisture at high levels & mid-levels along with cold dry surface air make for some cool cloud formations. Skilled (and brave) glider pilots, on the other hand, like them, because they can tell from the shape of the clouds where the air will be rising. Mesmerizing wave-like clouds spotted over mountain in Virginia. {\displaystyle N={\sqrt {{g \over \theta _{0}}{d\theta _{0} \over dz}}}} 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. Energy is transmitted along the wave fronts (parallel to air parcel oscillations), which is the direction of the wave group velocity. At the wave dip, no clouds,” said Wind. The large cloud had mostly dissipated by mid-morning. mountain barriers where wave clouds are generated by flow over these barriers. Verification, impacts and post-processing, Climate information for international development, Science for Impacts, Resilience and Adaptation (SIRA), Atmospheric processes and parametrizations, Regional model evaluation and development, Environmental Hazard and Resilience Services, National Meteorological Library & Archive. Provided that there is a steady increase in wind strength with altitude without a significant change in direction, standing waves may be created. The waves or clouds downwind from the mountain are the mountain are the "standing wave" or "lee wave." 2019-12-01 12:30:13, 117 frames. Lenticular clouds have a lens-shaped or almond-shaped cross section. Sometimes, mountain waves can help to enhance precipitation amounts downwind of mountain ranges. [5] 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. Wave Clouds Cirrus Clouds What is going on here is some chaotic vertical motions caused by the departing low pressure system interacting with the mountains. 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. 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. d. nacreous. Special Clouds > Lenticular Clouds (aka Standing Lenticular, Lee-Wave Clouds, or Mountain-Wave Clouds) Learning Goal 1b. One is a mountain wave pattern over Virginia and West Virginia and also visible in the northern mountains of North Carolina near Boone. Lenticular clouds are a visible sign of mountain waves in the air. mountain-wave cloud A cloud that forms in the rising branches of mountain waves and occupies the crests of the waves. Mountain waves a. are stationary. Watch Queue Queue Although the clouds are over the mountains, these are NOT mountain wave clouds. {\displaystyle N\cos {\phi }} Intense waves can present a significant hazard to aviation by producing severe or even extreme clear air turbulence. '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. The air warms as it drops, and the cloud dissipates. The vertical airflow component of a standing wave may exceed 8,000 ft/min. Unusual wave clouds over the Aral Sea, seen from NASA's Water satellite on March 12, 2009. ( In a way, Lenticular clouds warn pilots of the presence of mountain waves. mountain-wave cloud A cloud that forms in the rising branches of mountain waves and occupies the crests of the waves. Everything you need to know about the forecast, and making the most of the weather. What's really interesting is that even though lenticular clouds appear to stay in a stationary position, the air … Wave clouds typically form when a mountain, island, or even another mass of air forces an air mass to rise. d Mesmerizing wave-like clouds spotted over mountain in Virginia. 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. In fact, a mountain wave action and turbulence can affect aircraft at altitudes into the lower stratosphere, which typically begins around 30,000 to 35,000 feet above sea level! A fairly stable lenticular However, these waves can be present beyond the clouds, and may exist even when no clouds are formed.