Editing Lee wave (section)

{{Short description|Atmospheric stationary oscillations}}
[[File:Vol d'onde.svg|right|thumb|The wind flows towards a mountain and produces a first oscillation (A) followed by more waves. The following waves will have lower amplitude because of the natural damping. [[Lenticular cloud]]s stuck on top of the flow (A) and (B) will appear immobile despite the strong wind.]]
[[File:Lenticular clouds 1.jpg|thumb|Lenticular clouds]]
In [[meteorology]], '''lee waves''' are [[Earth's atmosphere|atmospheric]] stationary waves. The most common form is '''mountain waves''', which are atmospheric internal [[gravity wave]]s.  These were discovered in 1933 by two German [[glider pilot]]s, [[:de:Hans_Deutschmann|Hans Deutschmann]] and [[Wolf Hirth]], above the [[Giant Mountains]].<ref>On 10 March 1933, German glider pilot Hans Deutschmann (1911–1942) was flying over the Giant Mountains in Silesia when an updraft lifted his plane by a kilometre. 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'' [The 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 [Geophysics Research Directorate] Research Notes No. 6, AFCRC[Air Force Cambridge Research Center]-TN-58-626, ASTIA [Armed Services Technical Information Agency] Document No. AD-208862.</ref><ref>{{cite magazine
|title=Modeling and Classification of Mountain Waves
|last=Tokgozlu
|first=A
|author2=Rasulov, M. |author3=Aslan, Z.
 |date=January 2005
|volume=29
|issue=1
|page=22
|magazine=Technical Soaring
|issn=0744-8996
}}</ref><ref>{{cite web
| url = http://www.nateferguson.com/glider.html
| title = Article about wave lift
| access-date = 2006-09-28
}}</ref>
They are [[Frequency|periodic]] changes of [[atmospheric pressure]], [[temperature]] and [[orthometric height]] in a [[Air current|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]],<ref name=Pagen/> or even by upper winds deflected over a [[thermal]] [[updraft]] or [[cloud street]].

The vertical motion forces periodic changes in [[speed]] and [[Boxing the compass|direction]] of the air within this air current. They always occur in groups on the [[Windward and leeward|lee]] side of the [[terrain]] that triggers them. Sometimes, mountain waves can help to enhance precipitation amounts downwind of mountain ranges.<ref>{{cite journal|author1=David M. Gaffin |author2=Stephen S. Parker |author3=Paul D. Kirkwood |title=An Unexpectedly Heavy and Complex Snowfall Event across the Southern Appalachian Region|journal=Weather and Forecasting|date=2003|volume=18|issue=2|pages=224–235|doi=10.1175/1520-0434(2003)018<0224:AUHACS>2.0.CO;2|bibcode=2003WtFor..18..224G|doi-access=free}}</ref> Usually a [[turbulent]] [[vortex]], with its [[rotation|axis of rotation]] parallel to the mountain range, is generated around the first [[Crest (physics)|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.<ref name=Pagen>{{cite book | last = Pagen | first = Dennis | title = Understanding the Sky | publisher = Sport Aviation Pubns | location = City | year = 1992 | isbn = 978-0-936310-10-7 | pages= 169–175 | quote= This is the ideal case, for an unstable layer below and above the stable layer create what can be described as a springboard for the stable layer to bounce on once the mountain begins the oscillation.}}</ref>

Strong winds (with wind gusts over {{convert|100|mph|km/h}}) can be created in the foothills of large mountain ranges by mountain waves.<ref name=WAFarticle>{{cite journal|author=David M. Gaffin|title=On High Winds and Foehn Warming Associated with Mountain-Wave Events in the Western Foothills of the Southern Appalachian Mountains|journal=Weather and Forecasting|date=2009|volume=24|issue=1|pages=53–75|doi=10.1175/2008WAF2007096.1|bibcode=2009WtFor..24...53G|doi-access=free}}</ref><ref>{{cite journal|author=M. N. Raphael|title=The Santa Ana winds of California|journal=Earth Interactions|date=2003|volume=7|issue=8|page=1 |doi=10.1175/1087-3562(2003)007<0001:TSAWOC>2.0.CO;2|bibcode=2003EaInt...7h...1R |doi-access=free}}</ref><ref>{{cite journal|author=Warren Blier|title=The Sundowner Winds of Santa Barbara, California|journal=Weather and Forecasting|date=1998|volume=13|issue=3|pages=702–716|doi=10.1175/1520-0434(1998)013<0702:TSWOSB>2.0.CO;2|bibcode=1978JAtS...35...59L|doi-access=free}}</ref><ref>{{cite journal|author=D. K. Lilly |title=A Severe Downslope Windstorm and Aircraft Turbulence Event Induced by a Mountain Wave|journal=Journal of the Atmospheric Sciences|date=1978|volume=35|issue=1|pages=59–77|doi=10.1175/1520-0469(1978)035<0059:ASDWAA>2.0.CO;2|bibcode=1978JAtS...35...59L |doi-access=free}}</ref> These strong winds can contribute to unexpected wildfire growth and spread (including the [[2016 Great Smoky Mountains wildfires]] when sparks from a wildfire in the Smoky Mountains were blown into the Gatlinburg and Pigeon Forge areas).<ref name=AMSpresentation>{{cite journal|author1=Ryan Shadbolt |author2=Joseph Charney |author3=Hannah Fromm|url=https://ams.confex.com/ams/2019Annual/meetingapp.cgi/Paper/353193|title=A mesoscale simulation of a mountain wave wind event associated with the Chimney Tops 2 fire (2016)|publisher=American Meteorological Society|date=2019|issue=Special Symposium on Mesoscale Meteorological Extremes: Understanding, Prediction, and Projection|pages=5 pp}}</ref>