Academic literature on the topic 'Mountain lee waves'
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Journal articles on the topic "Mountain lee waves"
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Makarenko, N. I., and J. L. Maltseva. "Interference of lee waves over mountain ranges." Natural Hazards and Earth System Sciences 11, no. 1 (January 4, 2011): 27–32. http://dx.doi.org/10.5194/nhess-11-27-2011.
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Abstract. Internal waves in the atmosphere and ocean are generated frequently from the interaction of mean flow with bottom obstacles such as mountains and submarine ridges. Analysis of these environmental phenomena involves theoretical models of non-homogeneous fluid affected by the gravity. In this paper, a semi-analytical model of stratified flow over the mountain range is considered under the assumption of small amplitude of the topography. Attention is focused on stationary wave patterns forced above the rough terrain. Adapted to account for such terrain, model equations involves exact topographic condition settled on the uneven ground surface. Wave solutions corresponding to sinusoidal topography with a finite number of peaks are calculated and examined.
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Vosper, S. B. "Inversion effects on mountain lee waves." Quarterly Journal of the Royal Meteorological Society 130, no. 600 (July 1, 2004): 1723–48. http://dx.doi.org/10.1256/qj.03.63.
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Rhines, P. B. "Jets and Orography: Idealized Experiments with Tip Jets and Lighthill Blocking." Journal of the Atmospheric Sciences 64, no. 10 (October 1, 2007): 3627–39. http://dx.doi.org/10.1175/jas4008.1.
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Abstract This paper describes qualitative features of the generation of jetlike concentrated circulations, wakes, and blocks by simple mountainlike orography, both from idealized laboratory experiments and shallow-water numerical simulations on a sphere. The experiments are unstratified with barotropic lee Rossby waves, and jets induced by mountain orography. A persistent pattern of lee jet formation and lee cyclogenesis owes its origins to arrested topographic Rossby waves above the mountain and potential vorticity (PV) advection through them. The wake jet occurs on the equatorward, eastern flank of the topography. A strong upstream blocking of the westerly flow occurs in a Lighthill mode of long Rossby wave propagation, which depends on βa2/U, the ratio of Rossby wave speed based on the scale of the mountain, to zonal advection speed, U (β is the meridional potential vorticity gradient, f is the Coriolis frequency, and a is the diameter of the mountain). Mountains wider (north–south) than the east–west length scale of stationary Rossby waves will tend to block the oncoming westerly flow. These blocks are essentially β plumes, which are illustrated by their linear Green function. For large βa2/U, upwind blocking is strong; the mountain wake can be unstable, filling the fluid with transient Rossby waves as in the numerical simulations of Polvani et al. For small values, βa2/U ≪ 1 classic lee Rossby waves with large wavelength compared to the mountain diameter are the dominant process. The mountain height, δh, relative to the mean fluid depth, H, affects these transitions as well. Simple lee Rossby waves occur only for such small heights, δh/h ≪ aβ/f, that the f/h contours are not greatly distorted by the mountain. Nongeostrophic dynamics are seen in inertial waves generated by geostrophic shear, and ducted by it, and also in a texture of finescale, inadvertent convection. Weakly damped circulations induced in a shallow-water numerical model on a sphere by a lone mountain in an initially simple westerly wind are also described. Here, with βa2/U ∼1, potential vorticity stirring and transient Rossby waves dominate, and drive zonal flow acceleration. Low-latitude critical layers, when present, exert strong control on the high-latitude waves, and with no restorative damping of the mean zonal flow, they migrate poleward toward the source of waves. While these experiments with homogeneous fluid are very simplified, the baroclinic atmosphere and ocean have many tall or equivalent barotropic eddy structures owing to the barotropization process of geostrophic turbulence.
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Millane, R. P., G. D. Stirling, R. G. Brown, N. Zhang, V. L. Lo, E. Enevoldson, and J. E. Murray. "Estimating Wind Velocities in Mountain Lee Waves Using Sailplane Flight Data*." Journal of Atmospheric and Oceanic Technology 27, no. 1 (January 1, 2010): 147–58. http://dx.doi.org/10.1175/2009jtecha1274.1.
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Abstract Mountain lee waves are a form of atmospheric gravity wave that is generated by flow over mountain topography. Mountain lee waves are of considerable interest, because they can produce drag that affects the general circulation, windstorms, and clear-air turbulence that can be an aviation hazard, and they can affect ozone abundance through mixing and inducing polar stratospheric clouds. There are difficulties, however, in measuring the three-dimensional wind velocities in high-altitude mountain waves. Mountain waves are routinely used by sailplane pilots to gain altitude. Methods are described for estimating three-dimensional wind velocities in mountain waves using data collected during sailplane flights. The data used are the logged sailplane position and airspeed (sailplane speed relative to the local air mass). An algorithm is described to postprocess this data to estimate the three-dimensional wind velocity along the flight path, based on an assumption of a slowly varying horizontal wind velocity. The method can be applied to data from dedicated flights or potentially to existing flight records used as sensors of opportunity. The methods described are applied to data from a sailplane flight in lee waves of the Sierra Nevada in California.
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Draxl, Caroline, Rochelle P. Worsnop, Geng Xia, Yelena Pichugina, Duli Chand, Julie K. Lundquist, Justin Sharp, Garrett Wedam, James M. Wilczak, and Larry K. Berg. "Mountain waves can impact wind power generation." Wind Energy Science 6, no. 1 (January 7, 2021): 45–60. http://dx.doi.org/10.5194/wes-6-45-2021.
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Abstract. Mountains can modify the weather downstream of the terrain. In particular, when stably stratified air ascends a mountain barrier, buoyancy perturbations develop. These perturbations can trigger mountain waves downstream of the mountains that can reach deep into the atmospheric boundary layer where wind turbines operate. Several such cases of mountain waves occurred during the Second Wind Forecast Improvement Project (WFIP2) in the Columbia River basin in the lee of the Cascade Range bounding the states of Washington and Oregon in the Pacific Northwest of the United States. Signals from the mountain waves appear in boundary layer sodar and lidar observations as well as in nacelle wind speeds and power observations from wind plants. Weather Research and Forecasting (WRF) model simulations also produce mountain waves and are compared to satellite, lidar, and sodar observations. Simulated mountain wave wavelengths and wave propagation speeds (group velocities) are analyzed using the fast Fourier transform. We found that not all mountain waves exhibit the same speed and conclude that the speed of propagation, magnitudes of wind speeds, or wavelengths are important parameters for forecasters to recognize the risk for mountain waves and associated large drops or surges in power. When analyzing wind farm power output and nacelle wind speeds, we found that even small oscillations in wind speed caused by mountain waves can induce oscillations between full-rated power of a wind farm and half of the power output, depending on the position of the mountain wave's crests and troughs. For the wind plant analyzed in this paper, mountain-wave-induced fluctuations translate to approximately 11 % of the total wind farm output being influenced by mountain waves. Oscillations in measured wind speeds agree well with WRF simulations in timing and magnitude. We conclude that mountain waves can impact wind turbine and wind farm power output and, therefore, should be considered in complex terrain when designing, building, and forecasting for wind farms.
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TYAGI, AJIT, and OP MADAN. "Mountain waves over Himalayas." MAUSAM 40, no. 2 (April 28, 2022): 79–84. http://dx.doi.org/10.54302/mausam.v40i2.2051.
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This paper documents the observational evidence of mountain waves over western and central Himalayas. The observed wavelength of the cases presented varies from 13 km. The most marked and well-organized mountain waves are observed to the lee of western and central Himalayas over Tibet plateau, which is also the region of highest frequency of wave occurrence. Mean stability profile associated with mountain waves has been developed and it shows high stability in the layer 5-9 km with less stability aloft.
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KUMAR, NARESH, NASEEM AHMAD, S. K. ROY BHOWMIK, and H. R. HATWAR. "Wave drag by two-dimensional mountain lee waves." MAUSAM 57, no. 4 (November 26, 2021): 591–96. http://dx.doi.org/10.54302/mausam.v57i4.498.
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A linear hydrostatic model of a stably stratified air-stream flow over a two-dimensional orographic barrier is considered assuming wind increases linearly with height and stability is constant. Analytical expressions for mountain drags and momentum fluxes are obtained for Assam-Burma hills as well as Western Ghats of India. The general expression for mountain drag also obtained for both the ridges of Assam-Burma hills.
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Röttger, J. "ST radar observations of atmospheric waves over mountainous areas: a review." Annales Geophysicae 18, no. 7 (July 31, 2000): 750–65. http://dx.doi.org/10.1007/s00585-000-0750-2.
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Abstract. Lee and mountain waves are dominant dynamic processes in the atmosphere above mountain areas. ST VHF radars had been intensively used to investigate these wave processes. These studies are summarized in this work. After discussing features of long-period quasi-stationary lee waves, attention is drawn to the frequent occurrence of freely propagating waves of shorter periods, which seem to be more common and characteristic for wave processes generated over mountainous areas. Characteristics of these waves such as their relation to the topography and background winds, the possibility of trapping by and breaking in the tropopause region and their propagation into the stratosphere is investigated. These orographically produced waves transport energy and momentum into the troposphere and stratosphere, which is considered an important contribution to the kinetic energy of the lower atmosphere. The occurrence of inertia-gravity waves in the stratosphere had been confused with lee waves, which is discussed in conclusion. Finally further questions on mountain and lee waves are drawn up, which remain to be solved and where investigations with ST radars could play a fundamental role.Key words: Meteorology and atmospheric dynamics (Middle atmosphere dynamics; Waves and tides; Instruments and techniques)
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Voelger, Peter, and Peter Dalin. "Statistical analysis of observations of polar stratospheric clouds with a lidar in Kiruna, northern Sweden." Atmospheric Chemistry and Physics 23, no. 9 (May 17, 2023): 5551–65. http://dx.doi.org/10.5194/acp-23-5551-2023.
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Abstract. In the present paper, we analyse 11 years of lidar measurements to derive general characteristics of polar stratospheric clouds (PSCs) and to examine how mountain lee waves influence PSC properties. Measurements of PSCs were made with a backscatter lidar located in Kiruna, northern Sweden, in the lee of the Scandinavian mountain range. The statistical analysis demonstrates that nearly half of all observed PSCs consisted of nitric acid trihydrate (NAT) particles, while ice clouds accounted for only a small fraction, and the remainder consisted of supercooled ternary solution (STS) and mixtures of different compositions. Most PSCs were observed around 22 km altitude. Mountain lee waves provide a distinct influence on PSC chemical composition and cloud height distribution. Ice PSCs were about 5 times as frequent, and NAT clouds were about half as frequent under wave conditions. PSCs were on average at 2 km higher altitudes when under the influence of mountain lee waves.
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Broutman, Dave, Jun Ma, Stephen D. Eckermann, and John Lindeman. "Fourier-Ray Modeling of Transient Trapped Lee Waves." Monthly Weather Review 134, no. 10 (October 1, 2006): 2849–56. http://dx.doi.org/10.1175/mwr3232.1.
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Abstract The Fourier-ray method involves ray tracing in a Fourier-transform domain. The ray solutions are then Fourier synthesized to produce a spatial solution. Here previous steady-state developments of the Fourier-ray method are extended to include a transient source of mountain waves. The method is illustrated with an initial value problem in which the background flow is started abruptly from rest and then maintained at steady velocity. The resulting wave transience is modeled in a simple way. All rays that radiate from the mountain, including the initial rays, are assigned the full amplitude of the longtime steady-state solution. Time dependence comes in through the changing position of the initial rays. This is sufficient to account for wave transience in a test case, as demonstrated by comparison with simulations from a mesoscale numerical model.
Dissertations / Theses on the topic "Mountain lee waves"
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Van, Der Mescht Deon. "Mountain wave turbulence in the lee of the Hex River Mountains." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20240.
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Thesis (MSc)--Stellenbosch University, 2012.ENGLISH ABSTRACT: Despite recorded mountain wave related aircraft accidents in South Africa, very little literature exists on South African mountain waves. This study discusses the results of a mountain wave study in the Hex River Mountains in the Western Cape province of South Africa. The aim of this study was to measure mountain wave turbulence on the lee side of the mountains by conducting weather balloon soundings on the upwind and lee sides of the mountains. These soundings were performed over four days in the winter and spring, with each field day representing different synoptic scale weather conditions. Lee wave rotors were detected from several of the lee wave soundings. Significant values of horizontal vorticity around a north-south axis (y-component horizontal vorticity) were detected. The instrumentation was highly sensitive and able to measure even weak up and downdraft velocities associated with the rotors. Strong downdrafts were measured some mountain waves, but no strong downdrafts were detected near rotors which occurred below the mountain waves. The two dimensional positions of balloons were only available after a considerable amount of reanalysis. If this data can be made available onsite shortly after soundings, it can be used to decide where to move launch sites to, in order to obtain optimal results.
AFRIKAANSE OPSOMMING: Ten spyte van gedokumenteerde berggolf-verwante vliegongelukke, bestaan baie min literatuur oor Suid Afrikaanse berggolwe. Hierdie tesis bespreek die resultate van ‘n berggolfstudie in die Hexrivier Berge in the Weskaap Provinsie van Suid- Afrika. Die doel van hierdie studie was om die berggolfturbulensie aan die lykant van die berge te meet deur middel van weerballonopstygings aan beide die winden lykante van die berge. Hierdie opstygings is oor ‘n tydperk van vier winter en lente dae uitgevoer, met elkeen van die dae wat verskillende sinoptiese weersomstandighede verteenwoordig het. Rotors is waargeneem in die data van verskeie ballonopstygings wat aan die lykant uitgevoer is. Beduidende waardes van horisontale vortisiteit rondom ‘n noord-suid as (y-komponent horisontale vortisiteit) is gemeet. Die instrumentasie was hoogs sensitief en kon selfs swak op- en afstrominge meet. Sterk afstrominge is waargeneem in berggolwe, maar nie in die omgewing van rotors wat onmder die berggolwe voorgekom het nie. Die twee-dimensionele posisies van ballonne was slegs na aansienlike heranaliese van die data beskikbaar. Indien hierdie data kort na opstygings beskikbaar is tydens veldwerk, kan dit help met besluite oor alternatiewe posisies waarvandaan ballonopstygings gedoen kan word ten einde optimale resultate te bekom.
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MOZER, JOEL BARNEY. "LEE VORTICITY PRODUCTION BY TROPICAL MOUNTAIN RANGES." Diss., The University of Arizona, 1994. http://hdl.handle.net/10150/186600.
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Numerical simulations using the Penn State University/NCAR MM4 model are performed to examine a stably stratified, zonal easterly flow past large scale three-dimensional mountain ranges in a rotating, initially barotropic, atmosphere. Upstream blocking by the mountain range diverts the flow primarily to the south and around the mountain. Conservation of potential vorticity results in the formation of a horizontal jet at low levels south of the mountain. This jet is barotropically unstable and leads to a continuous production of synoptic scale vorticity maxima which separate from the mountain and propagate downstream. Numerical simulations using topography representative of the Sierra Madre in Mexico imply that this mechanism may be important in providing some of the initial disturbances which grow into tropical cyclones in the eastern North Pacific Ocean. The wave train produced in the simulations corresponds to waves with 3-7 day periods which have been identified observationally in the eastern North Pacific region. The sensitivity of this effect to the stability of the basic state and the upstream wind speed is investigated. Simulations are also performed which show that the Hoggar and Atlas mountains of west-central Africa block the low-level easterlies resulting in a barotropically unstable jet and a train of vorticity maxima which separate from the mountain and propagate downstream. The spacing of these disturbances is roughly 1600 km and they propagate to the east with a period of about 2.5 days. These characteristics correspond to those of observed waves in the Africa/Atlantic region. It will also be shown that the unique topography of north-central Africa results in a mid-tropospheric easterly jet which has a maximum between 0-10°E and 15-20°N. The location and magnitude of this jet correspond to the so-called African easterly jet which is usually attributed to the strong surface temperature gradients over the continent of Africa. The numerical simulations presented in this work suggest that the mechanical effect of the topography may provide a constant source of energy for the maintenance of the African easterly jet.
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Cardoso, Rita Margarida A. P. "Gravity waves, turbulence and rotors in the lee of mountains." Thesis, University of Leeds, 2005. http://etheses.whiterose.ac.uk/13898/.
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This thesis has focussed on analysing the influence of a temperature inversion in the upstream profile of flow over ridges. Under northerly conditions, a temperature inversion is commonly observed in the Falkland islands radiosonde launches and severe turbulence is usually coupled with it. The turbulence is presumed to be linked to gravity wave activity and is associated with high temporal and spatial variability in wind speed and direction. Recirculation zones are commonly found under the crest of the waves and their three dimensional structure pose a significant hazard to air traffic. The data obtained from a field campaign aimed at observing the flow field downwind of a mountain ridge in the vicinity of Mt. Pleasant airport in the Falkland islands is analysed. From the data analysis, a correlation between the temperature inversion and the difference in temperature between the sea surface and air is established. The seasonal distribution of these phenomena is also explained. Due to logistic constraints, there were no radiosonde launches performed upstream during the campaign. To obviate that problem, a one-dimensional boundary layer model with a 1.5-order closure scheme, radiation and cloud parameterisations was developed. The model was then used to simulate the upwind characteristics of some particular case studies during which strong downwind flow was observed. The influence of temperature inversions on the dynamics of trapped lee-waves was simulated through a series of two--dimensional simulations of flow over idealised ridges. The analysis focussed on the effects of topography composed by two ridges and on the effects of an inversion below the ridge summit. These simulations show that the effects of the second ridge can significantly alter the downstream flow and that a temperature inversion below the summit can also induce strong downwind phenomena. A two-dimensional simulation using the one-dimensional vertical profile from the boundary layer model was performed. The results were in reasonable agreement with the observed data for that day.
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Soufflet, Clément. "Étude des interactions des ondes de montagne piégées avec la couche limite." Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS395.
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Ces travaux de thèse, réalisés dans un cadre théorique et validés à l'aide de modèles non linéaires, ont pour objectifs d'approfondir les connaissances théoriques concernant les interactions entre les écoulements forcés par les montagnes et la couche limite. On montre que, dans le cas linéaire, lorsque le vent incident à la surface est faible, les ondes piégées ne sont plus induites par un confinement à bas niveau mais sont analogues à des instabilités de Kelvin-Helmholtz. Elles sont alors conditionnées par la stabilité dynamique de l'écoulement à la surface et favorisées pour des valeurs du nombre de Richardson J<0.25. Pour des reliefs plus élevés, la dynamique non linéaire modifie la stabilité de l'écoulement en aval et les ondes piégées sont inhibées pour des écoulements initialement instables près du sol. A l'inverse pour des écoulements initialement stables à la surface, l'apparition d'effet de Foehn déstabilise l'écoulement en aval, les ondes piégées sont alors dues au développement d'instabilités dans le sillage de la montagne. Les ondes piégées sont liée à la stabilité dynamique de l'écoulement en aval, particulièrement lorsque que le vent incident est faible près de la surface. Ces résultats sont confirmés lorsque la dynamique de la couche limite est représentée de manière simplifiée à l'aide d'un coefficient de viscosité constant, les interactions entre la topographie et l'écoulement moyen sont alors évaluées en estimant les flux de quantité de mouvement. On montre que la transition entre le régime de traînée turbulente dû à la dynamique de la couche limite et le régime de traînée orographique dû aux ondes de gravité se propageant verticalement apparaît pour J ~ 1These thesis works, carried out within a theoretical framework and validated using non-linear models, aim to deepen theoretical knowledge concerning the interactions between the flows forced by mountains and the boundary layer. It is shown that in the linear case, when the incident wind at the surface is low, the trapped lee waves are no longer induced by low-level confinement but are analogous to Kelvin-Helmholtz instabilities. They are conditional to the surface flow stability and favoured for values of the Richardson number J<0.25. For higher mountains the non-linear dynamics modify the downstream flow stability and trapped waves are inhibited for initially unstable flow near the ground. Conversely, for initially stable flow at the surface, the onset of the Foehn effect destabilises the downstream flow and the lee waves are then due to the development of instabilities in the wake of the mountain. Trapped waves are then related to the dynamic stability of the downstream flow, especially when the incident wind is weak near the surface. These results are confirmed when the boundary layer dynamics is represented using a constant viscosity coefficient, the interactions between topography and mean flow are then evaluated by estimating momentum flux. It is shown that the transition between the turbulent drag regime due to boundary layer dynamics and the orographic drag regime due to vertically propagating gravity waves occurs at J ~ 1
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Epifanio, Craig Charles. "High-drag states and lee vortices in stratified flow over topography /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/10072.
Full textBooks on the topic "Mountain lee waves"
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A, Datta, Sharman R. D, and Dryden Flight Research Facility, eds. Lee waves: Benign and malignant. Edwards, Calif: National Aeronautics and Space Administration, Dryden Flight Research Facility, 1993.
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Lee waves: Benign and malignant. Edwards, Calif: National Aeronautics and Space Administration, Dryden Flight Research Facility, 1993.
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Exploring the monster: Mountain lee waves : The aerial elevator. Wind Canyon Books, 2000.
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Zeitlin, Vladimir. Wave Motions in Rotating Shallow Water with Boundaries, Topography, at the Equator, and in Laboratory. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198804338.003.0004.
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The chapter illustrates the influence of lateral boundaries, bottom topography, outcroppings, equatorial tangent plane approximation, and cylindrical channel geometry in laboratory experiments on the wave spectrum, and characteristics of waves in rotating shallow-water model. It is shown that all these effects lead to appearance of wave-guide modes, localised in one spatial direction, and freely propagating in another one. These modes are coastal and equatorial Kelvin waves, topographic and equatorial Rossby waves, shelf and edge waves, equatorial Yanai and inertia–gravity waves, and frontal waves. Their dispersion and polarisation relations are established, and their properties explained. Mountain (lee) waves are also treated.
Book chapters on the topic "Mountain lee waves"
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Golitsyn, G. S., A. N. Gruzdev, N. E. Elansky, N. N. Pertsev, and N. N. Shefov. "Studies of Structure of Orographic Lee Waves." In Proceedings of International Symposium on the Qinghai-Xizang Plateau and Mountain Meteorology, 854–64. Boston, MA: American Meteorological Society, 1986. http://dx.doi.org/10.1007/978-1-935704-19-5_49.
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Xu, Qing, Xiaofeng Li, Shaowu Bao, and Guosheng Zhang. "Tropical Cyclone Eye Morphology and Extratropical-Cyclone-Forced Mountain Lee Waves on SAR Imagery." In Springer Natural Hazards, 373–98. Singapore: Springer Singapore, 2017. http://dx.doi.org/10.1007/978-981-10-2893-9_16.
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Durran, D. R. "LEE WAVES AND MOUNTAIN WAVES." In Encyclopedia of Atmospheric Sciences, 1161–69. Elsevier, 2003. http://dx.doi.org/10.1016/b0-12-227090-8/00202-5.
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Durran, D. R. "MOUNTAIN METEOROLOGY | Lee Waves and Mountain Waves." In Encyclopedia of Atmospheric Sciences, 95–102. Elsevier, 2015. http://dx.doi.org/10.1016/b978-0-12-382225-3.00202-4.
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Adam, John A. "Atmospheric Waves." In Rays, Waves, and Scattering. Princeton University Press, 2017. http://dx.doi.org/10.23943/princeton/9780691148373.003.0014.
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This chapter deals with the underlying mathematics of atmospheric waves. Gravity waves occur between any stable layers of fluids that differ in density. When the fluid boundary is disturbed, buoyancy forces try to restore the equilibrium. The fluid returns to its original shape and overshoots before oscillations finally set in that propagate as waves. Internal gravity or buoyancy waves are often observed in the stable density layering of the upper atmosphere. The chapter first describes the linearized equations governing atmospheric waves before introducing a mathematical model of lee/mountain waves over an isolated mountain ridge, focusing on the basic equations and solutions, trapped lee waves, and billow clouds. It also considers wind shear, Howard's semicircle theorem, and the Taylor–Goldstein equation.
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Searle, Mike. "Continents in Collision: Kashmir, Ladakh, Zanskar." In Colliding Continents. Oxford University Press, 2013. http://dx.doi.org/10.1093/oso/9780199653003.003.0007.
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To understand how the Himalaya were formed it seemed logical to start at the actual zone of plate collision, the Indus suture zone. Most of this collision zone runs across southern Tibet, which in the 1970s was almost impossible to travel through. Following Mao Tse-tung’s Red Army’s invasion and occupation of Tibet in October 1950, that region had remained firmly closed to all foreigners. In the western Himalaya the Indus suture zone runs right across the northernmost province of Ladakh. Ladakh used to be a part of southwestern Tibet before the British annexed it during the Raj. Leh, the ancient capital of Ladakh at 3,500 metres in the Indus Valley, was the final outpost of British India before the great trans-Himalayan barrier of the Karakoram Range. Only the Nubra Valley and the Tangtse Valley north of Leh were beyond the Indus, and these valleys led directly up to the desolate high plateau of Tibet. Leh was a major caravan route and a crossroads of high Asia, with double-humped dromedary camel caravans coming south from the Silk Route towns of Yarkhand and Khotan; Kashmiris and Baltis came from the west and Indian traders from the Hindu regions of Himachal and Chamba to the south. Ladakh, Zanskar, and Zangla were three ancient Himalayan kingdoms ruled by a Giapo, or King, each from a palace that resembled a small version of the Potala Palace in Lhasa. In 1978, when we were climbing in the mountains of Kulu, I had looked from our high summits across to the desert mountains of Lahoul and Zanskar, north of the main Himalayan watershed. Here, in the ancient Buddhist kingdoms of Zanskar and Ladakh lay wave upon wave of unexplored and unclimbed mountains. They lay north of the monsoon limits and in the rain shadow of the main Himalaya, so the vegetation was sparse, and the geology was laid bare. Flying north from Delhi, or east from Kashmir into Leh, the views were simply mesmerizing.
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Paisley, M. F., and I. P. Castro. "Numerical Computations of Stratified Flow Over Three- Dimensional Obstacles." In Numerical Methods for Fluid Dynamics V, 523–31. Oxford University PressOxford, 1996. http://dx.doi.org/10.1093/oso/9780198514800.003.0050.
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Abstract Accurate prediction of the flow dynamics of three-dimensional obstacles (hills and mountains) is fundamental to many environmental considerations, ranging from the dispersion of atmospheric constituents to the prediction of mesoscale meteorology. In the presence of a density gradient the flow is characterised by the Froude number, Fh = U / N h, where U, N and h are the upstream velocity, bouyancy frequency and obstacle height respectively. Interaction with topogaphy can be highly complex, even for relatively simple smooth geometries, and depending on the parameters of the flow (typically obstacle shape and Froude number) a wide range of phenomena can occur. The overall effect of a stable density gradient is to inhibit vertical motion, and this may lead to a significant proportion of the flow passing around an obstacle as well as over it. In general a train of lee waves forms downstream with the wave amplitudes increasing with the spanwise width of the obstacle. For obstacles which are sufficiently wide the amplitudes may be large enough that streamline overturning occurs and the wave breaks, creating a localised region of highly turbulent flow aloft. For obstacles which are sufficiently narrow, on the other hand, the flow mostly passes around the obstacle, leading to the generation of a pair of vertically-oriented wake vortices. In these cases if the Froude number is low enough vortex-shedding may occur, akin to that seen in neutral flow over a cylinder.
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Macmaster, Neil. "The Battle for the douars and the djemâa Elections of 1947." In War in the Mountains, 173–99. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198860211.003.0010.
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The nationalist mobilization of peasants in the Chelif market centres (Chapter 8) went in parallel with the first steps to extend anti-colonial organization directly into the mountainous interior and to form peasant-led cells. Contestation centred, in particular, on the election of the djemâas which allowed delegates to be elected on party lists, a political counter-weight to the caids and commune mixte apparatus. A number of case-studies of such direct penetration into the interior are investigated for the douars north and south of Duperré, to the east of Ténès, and near Cherchell, to track the process of radicalization, and the preparation of rural networks that later became the basis of the early guerrilla movement. The 1947 election marked an important watershed since the unexpected success of the communist and Messalist advance among the peasantry met with a ferocious response from the new governor Naegelin in early 1948, and a wave of police repression, arrests, electoral fraud, and annulling of electoral gains. This ensured the continuation of the moribund commune mixte system, with fatal long-term consequences for the intelligence state, while both communists and nationalists abandoned a peaceful route to independence by preparing for armed insurrection.
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Sueur, Andrew Le, Maurice Sunkin, and Jo Eric Khushal Murkens. "6. Multilevel Governing Within the United Kingdom." In Public Law, 147–78. Oxford University Press, 2023. http://dx.doi.org/10.1093/he/9780192870612.003.0006.
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This chapter examines multilevel governing within the UK. It is organized around three levels of governing: national, regional, and local. For most of the twentieth century, mainland Great Britain (England, Wales, and Scotland) formed a centralized political unit, with policy-making and law-making being led by the UK government and the UK Parliament. There was devolved government in Northern Ireland from 1922, but this was ended by the UK government in 1972 amid mounting civil unrest and paramilitary violence. At the local level, there are 382 principal councils (unitary, upper, and second tier) throughout the United Kingdom. These vary considerably in size, both in terms of their territorial area that they cover and their populations. This chapter discusses how the introduction of devolved government in 1998 has altered the governance arrangements in Scotland, Wales, and Northern Ireland. It also examines how devolution affects the territorial constitution, (see Section 6.4), intergovernmental relations with Westminster (see Section 6.5), and the governance of England (see Section 6.6).
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Le Sueur, Andrew, Maurice Sunkin, and Jo Eric Khushal Murkens. "6. Multilevel Governing Within the United Kingdom." In Public Law, 159–94. Oxford University Press, 2019. http://dx.doi.org/10.1093/he/9780198820284.003.0006.
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This chapter examines multilevel governing within the UK. It is organized around three levels of governing: national, regional, and local. For most of the twentieth century, Great Britain (England, Wales, and Scotland) formed a centralized political unit, with policymaking and law-making being led by the UK government and the UK Parliament. There was devolved government in Northern Ireland from 1922, but this was brought to an end by the UK government in 1972 amid mounting civil unrest and paramilitary violence. At the local level, there are more than 400 local authorities throughout the United Kingdom. These vary considerably in size, both in terms of their territorial area that they cover and their populations.
Conference papers on the topic "Mountain lee waves"
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Tsuchiya, Yosuke, Teppei Matsuzaki, Tetsuo Takeshige, and Tsuyoshi Oguchi. "Development of Cost Advantageous Designs for Headlight System Using Light Emitting Diodes." In JSAE/SAE 2015 Small Engine Technologies Conference & Exhibition. 10-2 Gobancho, Chiyoda-ku, Tokyo, Japan: Society of Automotive Engineers of Japan, 2015. http://dx.doi.org/10.4271/2015-32-0750.
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<div class="section abstract"><div class="htmlview paragraph">So far, the application of LED headlights to the motorcycle has been limited for only high-priced models, because LED light units and the drivers are expensive. In our development, the cost reduction of light source units was examined by implementing multiple medium intensity LEDs. Distributed mounting scheme was created for LEDs placed on the circuit board to meet the heat dissipation requirement without a heat sink, which is usually installed. By new mounting scheme, the requirement of heat dissipation has been successfully fulfilled by only using the copper foil layer. Moreover, by connecting LEDs in series, the driver circuit configuration was made simple while separate circuits are generally required both for a high-beam and a low-beam. By this configuration, the driver cost was reduced. With this circuitry change, some associated issues arose and measures were devised to cope with them. In addition, the method of driver circuitry, established through applications for conventional incandescent light sources, was applied to provide a discrete voltage in half-waves from the ACG apart from the supply from the battery. Using this method, the circuit was made configurable to manage the situation, in which the foreword voltage drop of LED exceeds the output voltage of the battery, without using a booster circuit. With these measures, a significant cost reduction was made feasible. Owing to those achievements, LED headlight system was made applicable to the motorcycle models in low-priced ranges.</div></div>
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Lorenzo, J. P., and R. A. Soref. "Silicon Carrier-Enhanced Electrooptical Guided-Wave Switch." In Photonic Switching. Washington, D.C.: Optica Publishing Group, 1987. http://dx.doi.org/10.1364/phs.1987.thd2.
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Experimental results on an all-silicon 1.3 µm 2 × 2 optical switch are presented in this paper. Waveguiding of 1.3 µm light has been shown to be feasible in silicon with little attenuation expected for doping concentrations below 1017cm−3. (1) This and other state-of-the-art developments(2) has led to the monolithic opto-electronic device under study in this work. A schematic view of the integrated device structure is shown in figure 1. The active region is integrated at the crossing intersection of two raised rib channel waveguides. Each device chip consists of three individual bi directional 2×2 devices with different crossing angles and rib widths. The chip is polished in a special mounting jig to delineate the ridge waveguide ends. Electrooptical interactions are induced by actively altering the refractive index profile under a metallurgical p+/n junction at the waveguide intersection region shown in figure 2. An index decrease in this region is created with injected carriers.(1) Refractive index change near the junction is estimated to be 1.5 × 10−3 for 1018cm−3 free holes.(3)
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Cai, Guanglei, Hui Yang, and Qi Zhao. "Time-Lapse Measurement of P-Wave Velocities Under the Freeze-Thaw Condition in Various Rocks." In 57th U.S. Rock Mechanics/Geomechanics Symposium. ARMA, 2023. http://dx.doi.org/10.56952/arma-2023-0441.
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ABSTRACT Global warming issues have led to pronounced cryospheric changes in mountainous areas and cold regions. Freeze-thaw weathering can alter the properties of rock masses and permafrost soils, drastically changing local environmental and geological conditions. So far, although many in-situ and laboratory tests have investigated the variation of mechanical and hydraulic properties of rock under changing temperatures, the effect of temperature variation on the rock seismic properties (e.g., elastic wave velocity, wave amplitude, wave frequency, and wave attenuation) is still insufficiently studied. In this study, we developed a laboratory setup for time-lapse measurement of ultrasonic wave propagation across rocks under freeze-thaw conditions. The P-wave velocities under changing temperature from −20 °C to 20 °C were continuously recorded for four types of rocks (i.e., granite, marble, sandstone, and gabbro) under both dry and saturated conditions. The results demonstrate that the P-wave velocity of all saturated rocks drops significantly when the temperature is above 0 °C. Particularly, saturated sandstone was observed to have the greatest drop in wave amplitude, probably owing to the relatively high water content due to its high porosity. Also, we observe a hysteresis of wave velocity related to the rocks’ temperature gradient during the freeze-thaw cycles. These findings provide new insights into rock dynamic responses related to temperature changes in the cryosphere and cold regions. INTRODUCTION Global warming has led to extensive and enduring climate anomalies worldwide, including extremely high air temperatures in summer, fierce seasonal floods, devastating rainfalls, and so forth (Goswami, 2009; Masson-Delmotte, 2022; Rovinaru et al., 2022). The temperature rise also causes the melt of the polar glaciers, permafrost, and mountainous ice in cold regions, negatively influencing the slope stability and infrastructure performance for a long term and resulting in rock-mud flow events and uneven settlement of ground surface (Krautblatter et al., 2013; Mamot et al., 2021; Pläsken et al., 2020). Since most polar grounds and alpine mountain areas are underlain by permafrost, which is thermally defined as the lithospheric material (except glaciers) that remains below or equal to 0 °C for at least two consecutive years (Tarnocai, 1989), they are considered particularly sensitive to climate change (Nogués-Bravo et al., 2007; Schiavon & Zecchin, 2007). The degrading permafrost due to increasing temperature can trigger the freeze-thaw weathering effects and therefore affect the thermal, hydraulic, and mechanical properties of the rock masses, soil bodies, and their interfaces resulting in a drastic change in local environmental and geological conditions (Gruber & Haeberli, 2007; Krautblatter et al., 2012). The changes in the cryosphere will consequently increase the occurrence and magnitude of alpine rock hazards such as rock slope landslide, abrupt rockfall activities, and rock-based infrastructure damage resulting from slow and large rock deformation (Haeberli et al., 2017; Stoffel & Huggel, 2012).
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Hackenberg, Daniel, Robert Harper, Robert Ferrara, Jeff Goldhammer, Matthew Rea, Douglas Rogers, James Perry, and Rick Gilbert. "NSWCCD Maneuvering and Seakeeping Basin (MASK) Wavemaker Fabrication and Installation." In SNAME 29th American Towing Tank Conference. SNAME, 2010. http://dx.doi.org/10.5957/attc-2010-020.
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The design, and ongoing development and fabrication of a new segmented flap-type wavemaker array and associated powering, monitoring, control, and safety systems for the Naval Surface Warfare Center, Carderock Division’s (NSWCCD) Maneuvering and Seakeeping Basin (MASK) represents a major technological improvement to the existing wave generation capabilities at the facility. The new wavemaker, comprised of 216 individual wave boards configured as a dry-backed continuous array, incorporates a robust modular electromechanical design, with both position and force-based absorption feedback capabilities, and uses a programmable computer-based wave generation, monitoring, control, and visualization system. An industry technical team comprised of six different companies, in collaboration with NSWCCD facilities and hydrodynamic engineers and scientists have completed detailed design analyses and documentation. This high-visibility program draws on broad technical disciplines including mechanical, electrical, ocean, civil, construction, corrosion, computer, and software engineering expertise, as well as program management and administrative support. The completion of final design documentation, using both 2- and 3-dimensional drawing and modeling techniques, has led to the next phase of system development involving the fabrication, assembly, and design validation of subsystem and component level prototype hardware as well as the fabrication and assembly of long-lead production hardware. Ongoing work includes the off-site fabrication of all mechanical subsystems and components; electric drive, monitoring, communications and control electronics and enclosures; and definition of wavemaker-to-basin mounting structures and the physical interfaces necessary to install the wavemaker system. The size and scope of this project is significant, both in terms of design effort as well as material and fabrication requirements. For example, the finished MASK Basin wavemaker installation will include over 80 tons of stainless and galvanized structural steel, over 65,000 pounds of reinforced fiberglass and over 500 cubic yards (50 truck loads) of poured concrete to support the new wavemaker structures. This paper provides an overview of the wavemaker system design/build process and a current status on the fabrication and assembly of all major system components. Specific topics discussed include: The review and status of overall manufacturing plans and fabrication/ installation schedules. The development of detailed design, manufacturing, and assembly drawings, and fabrication and QA procedures. Materials qualification and selection considerations to meet operational life and maintenance requirements. The lay-up, fabrication, and finishing of large-scale reinforced fiberglass wave paddles. Laser cutting and machining of stainless steel mechanical components. Prototype mechanical hardware fabrication and fitment validation. The assembly of production quantity hardware assemblies and electronic control enclosures