Journal articles on the topic 'Trapped lee waves'
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1
Tutiš, V. "Trapped lee waves: A special analytical solution." Meteorology and Atmospheric Physics 50, no. 4 (December 1992): 189–95. http://dx.doi.org/10.1007/bf01026016.
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Hills, Matthew O. G., and Dale R. Durran. "Nonstationary Trapped Lee Waves Generated by the Passage of an Isolated Jet." Journal of the Atmospheric Sciences 69, no. 10 (May 22, 2012): 3040–59. http://dx.doi.org/10.1175/jas-d-12-047.1.
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Abstract The behavior of nonstationary trapped lee waves in a nonsteady background flow is studied using idealized three-dimensional (3D) numerical simulations. Trapped waves are forced by the passage of an isolated, synoptic-scale barotropic jet over a mountain ridge of finite length. Trapped waves generated within this environment differ significantly in their behavior compared with waves in the more commonly studied two-dimensional (2D) steady flow. After the peak zonal flow has crossed the terrain, two disparate regions form within the mature wave train: 1) upwind of the jet maximum, trapped waves increase their wavelength and tend to untrap and decay, whereas 2) downwind of the jet maximum, wavelengths shorten and waves remain trapped. Waves start to untrap approximately 100 km downwind of the ridge top, and the region of untrapping expands downwind with time as the jet progresses, while waves downstream of the jet maximum persist. Wentzel–Kramers–Brillouin (WKB) ray tracing shows that spatial gradients in the mean flow are the key factor responsible for these behaviors. An example of real-world waves evolving similarly to the modeled waves is presented. As expected, trapped waves forced by steady 2D and horizontally uniform unsteady 3D flows decay downstream because of leakage of wave energy into the stratosphere. Surprisingly, the downstream decay of lee waves is inhibited by the presence of a stratosphere in the isolated-jet simulations. Also unexpected is that the initial trapped wavelength increases quasi-linearly throughout the event, despite the large-scale forcing at the ridge crest being symmetric in time about the midpoint of the isolated-jet simulation.
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Teixeira, Miguel A. C., José Luis Argaín, and Pedro M. A. Miranda. "Orographic Drag Associated with Lee Waves Trapped at an Inversion." Journal of the Atmospheric Sciences 70, no. 9 (September 1, 2013): 2930–47. http://dx.doi.org/10.1175/jas-d-12-0350.1.
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Abstract The drag produced by 2D orographic gravity waves trapped at a temperature inversion and waves propagating in the stably stratified layer existing above are explicitly calculated using linear theory, for a two-layer atmosphere with neutral static stability near the surface, mimicking a well-mixed boundary layer. For realistic values of the flow parameters, trapped-lee-wave drag, which is given by a closed analytical expression, is comparable to propagating-wave drag, especially in moderately to strongly nonhydrostatic conditions. In resonant flow, both drag components substantially exceed the single-layer hydrostatic drag estimate used in most parameterization schemes. Both drag components are optimally amplified for a relatively low-level inversion and Froude numbers Fr ≈ 1. While propagating-wave drag is maximized for approximately hydrostatic flow, trapped-lee-wave drag is maximized for l2a = O(1) (where l2 is the Scorer parameter in the stable layer and a is the mountain width). This roughly happens when the horizontal scale of trapped lee waves matches that of the mountain slope. The drag behavior as a function of Fr for l2H = 0.5 (where H is the inversion height) and different values of l2a shows good agreement with numerical simulations. Regions of parameter space with high trapped-lee-wave drag correlate reasonably well with those where lee-wave rotors were found to occur in previous nonlinear numerical simulations including frictional effects. This suggests that trapped-lee-wave drag, besides giving a relevant contribution to low-level drag exerted on the atmosphere, may also be useful to diagnose lee-rotor formation.
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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.
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Metz, Johnathan J., Dale R. Durran, and Peter N. Blossey. "Unusual Trapped Mountain Lee Waves with Deep Vertical Penetration and Significant Stratospheric Amplitude." Journal of the Atmospheric Sciences 77, no. 2 (January 30, 2020): 633–46. http://dx.doi.org/10.1175/jas-d-19-0093.1.
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Abstract Simulations of the weather over the South Island of New Zealand on 28 July 2014 reveal unusual wave activity in the stratosphere. A series of short-wavelength perturbations resembling trapped lee waves were located downstream of the topography, but these waves were in the stratosphere, and their crests were oriented north–south, in contrast to both the northeast–southwest orientation of the spine of the Southern Alps and the crests of trapped waves present in the lower troposphere. Vertical cross sections through these waves show a nodal structure consistent with that of a higher-order trapped-wave mode. Eigenmode solutions to the vertical structure equation for two-dimensional, linear, Boussinesq waves were obtained for a horizontally homogeneous sounding representative of the 28 July case. These solutions include higher-order modes having large amplitude in the stratosphere that are supported by just the zonal wind component. Two of these higher-order modes correspond to trapped waves that develop in an idealized numerical simulation of the 28 July 2014 case. These higher-order modes are trapped by very strong westerly winds in the midstratosphere and are triggered by north–south-oriented features in the subrange-scale topography. In contrast, the stratospheric cross-mountain wind component is too weak to trap similar high-order modes with crest-parallel orientation.
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Ralph, F. Martin, Paul J. Neiman, Teddie L. Keller, David Levinson, and Len Fedor. "Observations, Simulations, and Analysis of Nonstationary Trapped Lee Waves." Journal of the Atmospheric Sciences 54, no. 10 (May 1997): 1308–33. http://dx.doi.org/10.1175/1520-0469(1997)054<1308:osaaon>2.0.co;2.
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Lott, François. "A New Theory for Downslope Windstorms and Trapped Mountain Waves." Journal of the Atmospheric Sciences 73, no. 9 (August 22, 2016): 3585–97. http://dx.doi.org/10.1175/jas-d-15-0342.1.
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Abstract Linear mountain gravity waves forced by a nonlinear surface boundary condition are derived for a background wind that is null at the surface and increases smoothly to reach a constant value aloft and for a constant buoyancy frequency. In this configuration, the mountain waves have a critical level just below the surface that is dynamically controlled by the surface and minimum Richardson number J. When the flow is very stable , and when the depth over which dissipations act is smaller than the mountain height, this critical-level dynamics easily produces large downslope winds and foehns. The downslope winds are more intense when the stability increases and much less pronounced when it decreases (when J goes below 1). In contrast, the trapped lee waves are very small when the flow is very stable, start to appear when , and can become pure trapped waves (e.g., not decaying downstream) when the flow is unstable (for ). For the trapped waves, these results are explained by the fact that the critical level absorbs the gravity waves downstream of the ridge when , while absorption decreases when J approaches 0.25. Pure trapped lee waves follow that when the absorption can become null in the nondissipative limit. In the background-flow profiles analyzed, the pure trapped lee waves also correspond to neutral modes of Kelvin–Helmholtz instability. The validity of the linear approximation used is tested a posteriori by evaluating the relative amplitude of the neglected nonlinear terms.
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Li, Liye, and Yi-Leng Chen. "Numerical Simulations of Two Trapped Mountain Lee Waves Downstream of Oahu." Journal of Applied Meteorology and Climatology 56, no. 5 (May 2017): 1305–24. http://dx.doi.org/10.1175/jamc-d-15-0341.1.
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AbstractTwo trapped lee-wave events dominated by the transverse mode downstream of the island of Oahu in Hawaii—27 January 2010 and 24 January 2003—are simulated using the Weather Research Forecasting (WRF) Model with a horizontal grid size of 1 km in conjunction with the analyses of soundings, weather maps, and satellite images. The common factors for the occurrences of these transverse trapped mountain-wave events are 1) Froude number [Fr = U/(Nh)] > 1, where U is the upstream speed of the cross-barrier flow, N is stability, and h is the mountain height; 2) insufficient convective available potential energy for the air parcel to become positively buoyant after being lifted to the top of the stable trade wind inversion layer; and 3) increasing cross-barrier wind speed with respect to height through the stable inversion layer, satisfying Scorer’s criteria between the inversion layer and the layer aloft. Within the inversion layer, where the Scorer parameter has a maximum, the wave amplitudes are the greatest. The two trapped mountain waves in winter occurred under strong prefrontal stably stratified southwesterly flow. On the other islands in Hawaii, where the mountaintops are below the base of the inversion, transverse trapped lee waves can occur under similar large-scale settings if the mountain height is lower than U/N. The high-spatial-and-temporal-resolution WRF Model successfully simulates the onset, development, and dissipation of these two events. Sensitivity tests for the 27 January 2010 case are performed with reduced relative humidity (RH). With a lower RH and less-significant latent heating, trapped lee waves have smaller amplitudes and shorter wavelengths.
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Jiang, Qingfang, James D. Doyle, Shouping Wang, and Ronald B. Smith. "On Boundary Layer Separation in the Lee of Mesoscale Topography." Journal of the Atmospheric Sciences 64, no. 2 (February 1, 2007): 401–20. http://dx.doi.org/10.1175/jas3848.1.
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Abstract The onset of boundary layer separation (BLS) forced by gravity waves in the lee of mesoscale topography is investigated based on a series of numerical simulations and analytical formulations. It is demonstrated that BLS forced by trapped waves is governed by a normalized ratio of the vertical velocity maximum to the surface wind speed; other factors such as the mountain height, mountain slope, or the leeside speedup factor are less relevant. The onset of BLS is sensitive to the surface sensible heat flux—a positive heat flux tends to increase the surface wind speed through enhancing the vertical momentum mixing and accordingly inhibits the occurrence of BLS, and a negative heat flux does the opposite. The wave forcing required to cause BLS decreases with an increase of the aerodynamical roughness zo; a larger zo generates larger surface stress and weaker surface winds and therefore promotes BLS. In addition, BLS shows some sensitivity to the terrain geometry, which modulates the wave characteristics. For a wider ridge, a higher mountain is required to generate trapped waves with a wave amplitude comparable to that generated by a lower but narrower ridge. The stronger hydrostatic waves associated with the wider and higher ridge play only a minor role in the onset of BLS. It has been demonstrated that although hydrostatic waves generally do not directly induce BLS, undular bores may form associated with wave breaking in the lower troposphere, which in turn induce BLS. In addition, BLS could occur underneath undular jump heads or associate with trapped waves downstream of a jump head in the presence of a low-level inversion.
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Reeder, Michael J., Neil Adams, and Todd P. Lane. "Radiosonde observations of partially trapped lee waves over Tasmania, Australia." Journal of Geophysical Research: Atmospheres 104, no. D14 (July 1999): 16719–27. http://dx.doi.org/10.1029/1999jd900038.
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Broad, A. S. "Momentum flux due to trapped lee waves forced by mountains." Quarterly Journal of the Royal Meteorological Society 128, no. 584 (July 15, 2002): 2167–73. http://dx.doi.org/10.1256/003590002320603593.
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Chapman, David C., and Dale B. Haidvogel. "Generation of internal lee waves trapped over a tall isolated seamount." Geophysical & Astrophysical Fluid Dynamics 69, no. 1-4 (June 1993): 33–54. http://dx.doi.org/10.1080/03091929308203573.
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Vosper, S. B., P. F. Sheridan, and A. R. Brown. "Flow separation and rotor formation beneath two-dimensional trapped lee waves." Quarterly Journal of the Royal Meteorological Society 132, no. 620 (October 1, 2006): 2415–38. http://dx.doi.org/10.1256/qj.05.174.
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Stiperski, Ivana, and Vanda Grubišić. "Trapped Lee Wave Interference in the Presence of Surface Friction." Journal of the Atmospheric Sciences 68, no. 4 (April 1, 2011): 918–36. http://dx.doi.org/10.1175/2010jas3495.1.
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Abstract Trapped lee wave interference over double bell-shaped obstacles in the presence of surface friction is examined. Idealized high-resolution numerical experiments with the nonhydrostatic Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) are performed to examine the influence of a frictional boundary layer and nonlinearity on wave interference and the impact of interference on wave-induced boundary layer separation and the formation of rotors. The appearance of constructive and destructive interference, controlled by the ratio of the ridge separation distance to the intrinsic horizontal wavelength of lee waves, is found to be predicted well by linear interference theory with orographic adjustment. The friction-induced shortening of intrinsic wavelength displays a strong indirect effect on wave interference. For twin peak orography, the interference-induced variation of wave amplitude is smaller than that predicted by linear theory. The interference is found to affect the formation and strength of rotors most significantly in the lee of the downstream peak; destructive interference suppresses the formation and strength of rotors there, whereas results for constructive interference closely parallel those for a single mountain. Over the valley, under both constructive and destructive interference, rotors are weaker compared to those in the lee of a single ridge while their strength saturates in the finite-amplitude flow regime. Destructive interference is found to be more susceptible to nonlinear effects, with both the orographic adjustment and surface friction displaying a stronger effect on the flow in this state. “Complete” destructive interference, in which waves almost completely cancel out in the lee of the downstream ridge, develops for certain ridge separation distances but only for a downstream ridge smaller than the upstream one.
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Grubišić, Vanda, and Ivana Stiperski. "Lee-Wave Resonances over Double Bell-Shaped Obstacles." Journal of the Atmospheric Sciences 66, no. 5 (May 1, 2009): 1205–28. http://dx.doi.org/10.1175/2008jas2885.1.
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Abstract Lee-wave resonance over double bell-shaped obstacles is investigated through a series of idealized high-resolution numerical simulations with the nonhydrostatic Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) model using a free-slip lower boundary condition. The profiles of wind speed and stability as well as terrain derive from observations of lee-wave events over the Sierra Nevada and Inyo Mountains from the recently completed Terrain-Induced Rotor Experiment (T-REX). Numerical experiments show that double bell-shaped obstacles promote trapped lee waves that are in general shorter than those excited by an isolated ridge. While the permissible trapped lee-wave modes are determined by the upstream atmospheric structure, primarily vertical wind shear, the selected lee-wave wavelengths for two obstacles that are close or equal in height are dictated by the discrete terrain spectrum and correspond to higher harmonics of the primary orographic wavelength, which is equal to the ridge separation distance. The exception is the smallest ridge separation distance examined, one that corresponds to the Owens Valley width and is closest to the wavelength determined by the given upstream atmospheric structure, for which the primary lee-wave and orographic wavelengths were found to nearly coincide. The influence two mountains exert on the overall lee-wave field is found to persist at very large ridge separation distances. For the nonlinear nonhydrostatic waves examined, the ridge separation distance is found to exert a much stronger control over the lee-wave wavelengths than the mountain half-width. Positive and negative interferences of lee waves, which can be detected through their imprint on wave drag and wave amplitudes, were found to produce appreciable differences in the flow structure mainly over the downstream peak, with negative interference characterized by a highly symmetric flow pattern leading to a low drag state.
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Durran, Dale R., Matthew O. G. Hills, and Peter N. Blossey. "The Dissipation of Trapped Lee Waves. Part I: Leakage of Inviscid Waves into the Stratosphere." Journal of the Atmospheric Sciences 72, no. 4 (March 31, 2015): 1569–84. http://dx.doi.org/10.1175/jas-d-14-0238.1.
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Abstract Leaky trapped mountain lee waves are investigated by examining the structure of individual linear modes in multilayer atmospheres. When the static stability and cross-mountain wind speed are constant in the topmost unbounded layer, modes that decay exponentially downstream also grow exponentially with height. This growth with height occurs because packets containing relatively large-amplitude waves follow ray paths through the stratosphere, placing them above packets entering the stratosphere farther downstream that contain relatively low-amplitude waves. Nevertheless, if the trapped wave train is generated by a compact source, all waves disappear above some line parallel to the group velocity that passes just above the source region. The rate of downstream decay due to leakage into the stratosphere is strongly dependent on the atmospheric structure. Downstream dissipation is often significant under realistic atmospheric conditions, which typically include elevated inversions and strong upper-tropospheric winds. On the other hand, idealized profiles with constant Scorer parameters throughout each of two tropospheric layers can exhibit a wide range of behaviors when capped by a third stratospheric layer with typical real-world static stability. Assuming the Scorer parameter in the stratosphere is a little larger than the minimum value necessary to allow a particular mode to propagate vertically, the rate of downstream decay is more sensitive to changes in the height of the tropopause than to further increases in the stability of the stratosphere. Downstream decay is minimized when the tropopause is high and the horizontal wavelength is short.
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Teixeira, M. A. C., J. L. Argaín, and P. M. A. Miranda. "Drag produced by trapped lee waves and propagating mountain waves in a two-layer atmosphere." Quarterly Journal of the Royal Meteorological Society 139, no. 673 (September 11, 2012): 964–81. http://dx.doi.org/10.1002/qj.2008.
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Hills, Matthew O. G., Dale R. Durran, and Peter N. Blossey. "The Dissipation of Trapped Lee Waves. Part II: The Relative Importance of the Boundary Layer and the Stratosphere." Journal of the Atmospheric Sciences 73, no. 3 (February 5, 2016): 943–55. http://dx.doi.org/10.1175/jas-d-15-0175.1.
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Abstract Decaying trapped waves exert a drag on the large-scale flow. The two most studied mechanisms for such decay are boundary layer dissipation and leakage into the stratosphere. If the waves dissipate in the boundary layer, they exert a drag near the surface, whereas, if they leak into the stratosphere, the drag is exerted at the level where the waves dissipate aloft. Although each of these decay mechanisms has been studied in isolation, their relative importance has not been previously assessed. Here, numerical simulations are conducted showing that the relative strength of these two mechanisms depends on the details of the environment supporting the waves. During actual trapped-wave events, the environment often includes elevated inversions and strong winds aloft. Such conditions tend to favor leakage into the stratosphere, although boundary layer dissipation becomes nonnegligible in cases with shorter resonant wavelengths and higher tropopause heights. In contrast, idealized two-layer profiles with constant wind speeds and high static stability beneath a less stable upper troposphere support lee waves that are much more susceptible to boundary dissipation and relatively unaffected by the presence of a stratosphere. One reason that trapped waves in the two-layer case do not leak much energy upward is that the resonant wavelength is greatly reduced in the presence of surface friction. This reduction in wavelength is well predicted by the linear inviscid equations if the basic-state profile is modified a posteriori to include the shallow ground-based shear layer generated by surface friction.
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Nance, Louisa B., and Dale R. Durran. "A Modeling Study of Nonstationary Trapped Mountain Lee Waves. Part II: Nonlinearity." Journal of the Atmospheric Sciences 55, no. 8 (April 1998): 1429–45. http://dx.doi.org/10.1175/1520-0469(1998)055<1429:amsont>2.0.co;2.
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Jiang, Qingfang, James D. Doyle, and Ronald B. Smith. "Interaction between Trapped Waves and Boundary Layers." Journal of the Atmospheric Sciences 63, no. 2 (February 1, 2006): 617–33. http://dx.doi.org/10.1175/jas3640.1.
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Abstract The absorption of trapped lee waves by the atmospheric boundary layer (BL) is investigated based on numerical simulations and theoretical formulations. It is demonstrated that the amplitude of trapped waves decays exponentially with downstream distance due to BL absorption. The decay coefficient, α, defined as the inverse of the e-folding decay distance, is found to be sensitive to both surface momentum and heat fluxes. Specifically, α is larger over a rougher surface, associated with a more turbulent BL. On the other hand, the value of α decreases with increasing surface heating and increases with increasing surface cooling, implying that a stable nocturnal BL is more efficient in absorbing trapped waves than a typically deeper and more turbulent convective BL. A stagnant layer could effectively absorb trapped waves and increase α. Over the range of parameters examined, the absorption coefficient shows little sensitivity to wave amplitude. A relationship is derived to relate the surface reflection factor and the wave decay coefficient. Corresponding to wave absorption, there are positive momentum and negative energy fluxes across the boundary layer top, indicating that an absorbing BL serves as a momentum source and energy sink to trapped waves. Wave reflection by a shallow viscous layer with a linear shear is examined using linear theory, and its implication on BL wave absorption is discussed.
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Zang, Zeng-liang, Ming Zhang, and Hong Huang. "Influence of the Scorer Parameter Profile on the Wavelength of Trapped Lee Waves." Journal of Hydrodynamics 19, no. 2 (April 2007): 165–72. http://dx.doi.org/10.1016/s1001-6058(07)60044-4.
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Udina, Mireia, Maria Rosa Soler, and Ona Sol. "A Modeling Study of a Trapped Lee-Wave Event over the Pyrénées." Monthly Weather Review 145, no. 1 (December 16, 2016): 75–96. http://dx.doi.org/10.1175/mwr-d-16-0031.1.
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Abstract A trapped lee-wave mountain event in the southern part of the Pyrénées area is analyzed using the Weather Research and Forecasting (WRF) Model. Model experiments are designed to address the WRF predictability of such an event and to explore the influence of the model parameters in resolving the mountain waves. The results show that the model is able to capture a trapped lee-wave event using the 1-km horizontal grid model outputs. Different initial conditions, the vertical grid resolution, and the resolved topography lead to changes in the wave field distribution and the wave amplitude meaning that an ensemble of different model settings may be able to quantify the uncertainty of the numerical solutions. However, the model experiments do not significantly change the wavelength of the generated mountain waves, which is shorter in the three-dimensional real simulations than the one derived from satellite imagery. Comparison with observational data from the surface stations and a wind profiler upstream of the mountain range shows that the model underestimates the horizontal wind speed and this can be the reason for the underestimation of the wavelength. In addition, the valley circulations and the formation of a rotor near the surface are explored. The formation of a low-level rotor in the model is intermittent and brief, and it interacts with other flows coming from multiple directions. The first strong wave updraft is located over the valley aligned with the highest mountain peaks and strong vorticity is captured from the surface up to the first wave crest.
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Sauer, Jeremy A., Domingo Muñoz-Esparza, Jesse M. Canfield, Keeley R. Costigan, Rodman R. Linn, and Young-Joon Kim. "A Large-Eddy Simulation Study of Atmospheric Boundary Layer Influence on Stratified Flows over Terrain." Journal of the Atmospheric Sciences 73, no. 7 (June 24, 2016): 2615–32. http://dx.doi.org/10.1175/jas-d-15-0282.1.
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Abstract The impact of atmospheric boundary layer (ABL) interactions with large-scale stably stratified flow over an isolated, two-dimensional hill is investigated using turbulence-resolving large-eddy simulations. The onset of internal gravity wave breaking and leeside flow response regimes of trapped lee waves and nonlinear breakdown (or hydraulic-jump-like state) as they depend on the classical inverse Froude number, Fr−1 = Nh/Ug, is explored in detail. Here, N is the Brunt–Väisälä frequency, h is the hill height, and Ug is the geostrophic wind. The results here demonstrate that the presence of a turbulent ABL influences mountain wave (MW) development in critical aspects, such as dissipation of trapped lee waves and amplified stagnation zone turbulence through Kelvin–Helmholtz instability. It is shown that the nature of interactions between the large-scale flow and the ABL is better characterized by a proposed inverse compensated Froude number, = N(h − zi)/Ug, where zi is the ABL height. In addition, it is found that the onset of the nonlinear-breakdown regime, ≈ 1.0, is initiated when the vertical wavelength becomes comparable to the sufficiently energetic scales of turbulence in the stagnation zone and ABL, yielding an abrupt change in leeside flow response. Finally, energy spectra are presented in the context of MW flows, supporting the existence of a clear transition in leeside flow response, and illustrating two distinct energy distribution states for the trapped-lee-wave and the nonlinear-breakdown regimes.
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Nance, Louisa B., and Dale R. Durran. "A Modeling Study of Nonstationary Trapped Mountain Lee Waves. Part I: Mean-Flow Variability." Journal of the Atmospheric Sciences 54, no. 18 (September 1997): 2275–91. http://dx.doi.org/10.1175/1520-0469(1997)054<2275:amsont>2.0.co;2.
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Colfescu, Ioana, Joseph B. Klemp, Massimo A. Bollasina, Stephen D. Mobbs, and Ralph R. Burton. "The Dynamics of Observed Lee Waves over the Snæfellsnes Peninsula in Iceland." Monthly Weather Review 149, no. 5 (May 2021): 1559–75. http://dx.doi.org/10.1175/mwr-d-20-0288.1.
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AbstractOn 20 October 2016, aircraft observations documented a significant train of lee waves above and downstream of the Snæfellsnes Peninsula on the west coast of Iceland. Simulations of this event with the Weather Research and Forecasting (WRF) Model provide an excellent representation of the observed structure of these mountain waves. The orographic features producing these waves are characterized by the isolated Snæfellsjökull volcano near the tip of the peninsula and a fairly uniform ridge along its spine. Sensitivity simulations with the WRF Model document that the observed wave train consists of a superposition of the waves produced individually by these two dominant orographic features. This behavior is consistent with idealized simulations of a flow over an isolated 3D mountain and over a 2D ridge, which reproduce the essential behavior of the observed waves and those captured in the WRF simulations. Linear analytic analysis confirms the importance of a strong inversion at the top on the boundary layer in promoting significant wave activity extending far downstream of the terrain. However, analysis of the forced and resonant modes for a two-layer atmosphere with a capping inversion suggest that this wave train may not be produced by resonant modes whose energy is trapped beneath the inversion. Rather, these appear to be vertically propagating modes with very small vertical group velocity that can persist far downstream of the mountain. These vertically propagating waves potentially provide a mechanism for producing near-resonant waves farther aloft due to interactions with a stable layer in the midtroposphere.
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Koffi, Ernest N’Dri, Marc Georgelin, Bruno Benech, and Evelyne Richard. "Trapped Lee Waves Observed during PYREX by Constant Volume Balloons: Comparison with Meso-NH Simulations." Journal of the Atmospheric Sciences 57, no. 13 (July 2000): 2007–21. http://dx.doi.org/10.1175/1520-0469(2000)057<2007:tlwodp>2.0.co;2.
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Teixeira, M. A. C., and P. M. A. Miranda. "Drag associated with 3D trapped lee waves over an axisymmetric obstacle in two-layer atmospheres." Quarterly Journal of the Royal Meteorological Society 143, no. 709 (October 2017): 3244–58. http://dx.doi.org/10.1002/qj.3177.
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Hertenstein, Rolf F. "The Influence of Inversions on Rotors." Monthly Weather Review 137, no. 1 (January 1, 2009): 433–46. http://dx.doi.org/10.1175/2008mwr2482.1.
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Abstract Rotors are small-scale circulations about a horizontal or quasi-horizontal axis that usually form in conjunction with high-amplitude mountain waves. The moderate to severe turbulence often found within rotors is a hazard to aviation. Observations and numerical model studies have revealed two types of mountain-wave–rotor systems. The first type is associated with trapped waves, whereas the second, less common, type resembles a hydraulic jump. It has long been known that an upstream, near-mountaintop inversion plays an important role in mountain-wave/rotor formation. In this study, the role of the upstream inversion strength and height in an environment with sheared flow and over a barrier with a steep lee slope is investigated. It is found that the second mountain-wave/rotor type is more likely to form when a strong near-mountaintop inversion is present. Baroclinic generation of horizontal vorticity within the inversion along the lee slope leads to overturning in an upstream direction and spreading of inversion isentropes. The sign and magnitude of vertical shear within the upstream inversion has a modifying influence, with positive shear favoring the formation of trapped-wave systems. Stronger inversions lead to higher-reaching, more turbulent mountain-wave/rotor systems, regardless of type.
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Smith, Ronald B., Qingfang Jiang, and James D. Doyle. "A Theory of Gravity Wave Absorption by a Boundary Layer." Journal of the Atmospheric Sciences 63, no. 2 (February 1, 2006): 774–81. http://dx.doi.org/10.1175/jas3631.1.
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Abstract A one-layer model of the atmospheric boundary layer (BL) is proposed to explain the nature of lee-wave attenuation and gravity wave absorption seen in numerical simulations. Two complex coefficients are defined: the compliance coefficient and the wave reflection coefficient. A real-valued ratio of reflected to incident wave energy is also useful. The key result is that, due to horizontal friction, the wind response in the BL is shifted upstream compared to the phase of disturbances in the free atmosphere. The associated flow divergence modulates the thickness of the BL so that it partially absorbs incident gravity waves. A simple expression is derived relating the reflection coefficient to the attenuation and wavelength shift of trapped lee waves. Results agree qualitatively with the numerical simulations, including the effects of increased surface roughness and heat flux.
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LOTT, FRANCOIS. "Linear mountain drag and averaged pseudo-momentum flux profiles in the presence of trapped lee waves." Tellus A 50, no. 1 (January 1998): 12–25. http://dx.doi.org/10.1034/j.1600-0870.1998.00002.x.
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Georgelin, Marc, and François Lott. "On the Transfer of Momentum by Trapped Lee Waves: Case of the IOP 3 of PYREX." Journal of the Atmospheric Sciences 58, no. 23 (December 2001): 3563–80. http://dx.doi.org/10.1175/1520-0469(2001)058<3563:ottomb>2.0.co;2.
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Lott, François. "Linear mountain drag and averaged pseudo-momentum flux profiles in the presence of trapped lee waves." Tellus A: Dynamic Meteorology and Oceanography 50, no. 1 (January 1998): 12–25. http://dx.doi.org/10.3402/tellusa.v50i1.14509.
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Eckermann, Stephen D., Dave Broutman, Jun Ma, and John Lindeman. "Fourier-Ray Modeling of Short-Wavelength Trapped Lee Waves Observed in Infrared Satellite Imagery near Jan Mayen." Monthly Weather Review 134, no. 10 (October 1, 2006): 2830–48. http://dx.doi.org/10.1175/mwr3218.1.
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Abstract A time-dependent generalization of a Fourier-ray method is presented and tested for fast numerical computation of high-resolution nonhydrostatic mountain-wave fields. The method is used to model mountain waves from Jan Mayen on 25 January 2000, a period when wavelike cloud banding was observed long distances downstream of the island by the Advanced Very High Resolution Radiometer Version 3 (AVHRR-3). Surface weather patterns show intensifying surface geostrophic winds over the island at 1200 UTC caused by rapid eastward passage of a compact low pressure system. The 1200 UTC wind profiles over the island increase with height to a jet maximum of ∼60–70 m s−1, yielding Scorer parameters that indicate vertical trapping of any short wavelength mountain waves. Separate Fourier-ray solutions were computed using high-resolution Jan Mayen orography and 1200 UTC vertical profiles of winds and temperatures over the island from a radiosonde sounding and an analysis system. The radiosonde-based simulations produce a purely diverging trapped wave solution that reproduces the salient features in the AVHRR-3 imagery. Differences in simulated wave patterns governed by the radiosonde and analysis profiles are explained in terms of resonant modes and are corroborated by spatial ray-group trajectories computed for wavenumbers along the resonant mode curves. Output from a nonlinear Lipps–Hemler orographic flow model also compares well with the Fourier-ray solution horizontally. Differences in vertical cross sections are ascribed to the Fourier-ray model’s current omission of tunneling of trapped wave energy through evanescent layers.
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Musgrave, R. C., J. A. MacKinnon, R. Pinkel, A. F. Waterhouse, J. Nash, and S. M. Kelly. "The Influence of Subinertial Internal Tides on Near-Topographic Turbulence at the Mendocino Ridge: Observations and Modeling." Journal of Physical Oceanography 47, no. 8 (August 2017): 2139–54. http://dx.doi.org/10.1175/jpo-d-16-0278.1.
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AbstractShipboard measurements of velocity and density were obtained in the vicinity of a small channel in the Mendocino Ridge, where flows were predominantly tidal. Measured daily inequalities in transport are much greater than those predicted by a barotropic tide model, with the strongest transport associated with full depth flows and the weakest with shallow, surface-confined flows. A regional numerical model of the area finds that the subinertial K1 (diurnal) tidal constituent generates topographically trapped waves that propagate anticyclonically around the ridge and are associated with enhanced near-topographic K1 transports. The interaction of the baroclinic trapped waves with the surface tide produces a tidal flow whose northward transports alternate between being surface confined and full depth. Full depth flows are associated with the generation of a large-amplitude tidal lee wave on the northward face of the ridge, while surface-confined flows are largely nonturbulent. The regional model demonstrates that, consistent with field observations, near-topographic dissipation over the entire ridge is diurnally modulated, despite the semidiurnal tidal constituent having larger barotropic velocities. It is concluded that at this location it is the bottom-trapped subinertial internal tide that governs near-topographic dissipation and mixing. The effect of the trapped wave on regional energetics is to increase the fraction of converted barotropic–baroclinic tidal energy that dissipates locally.
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Réchou, A., V. Barabash, P. Chilson, S. Kirkwood, T. Savitskaya, and K. Stebel. "Mountain wave motions determined by the Esrange MST radar." Annales Geophysicae 17, no. 7 (July 31, 1999): 957–70. http://dx.doi.org/10.1007/s00585-999-0957-9.
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Abstract. A European campaign of ground-based radar, lidar and optical measurements was carried out during the winter of 1996/1997 (28 December-2 February) to study lee waves in the northern part of Scandinavia. The participants operated ozone lidars, backscatter lidars and MST radars at ALOMAR/Andoya and Esrange/Kiruna, and an ALIS imaging system in Kiruna. The Andoya site was generally windward of the Scandinavian mountains, the Kiruna site on the leeward side. The goal of the experiment was to examine the influence of lee waves on the formation of Polar Stratospheric Clouds (PSCs). This paper studies the radar data from MST-radar ESRAD located at Esrange [68.°N, 21.°E], i.e. in the lee of the mountains. We present three cases where strong lee waves were observed: in one case they propagated upwards to the lower stratosphere and in the other two cases they were trapped or absorbed in the troposphere. We examine the local waves and the direction and strength of the local wind using the radar, the synoptic meteorological situation using weather maps (European Meteorological Bulletin) and the synoptic stratospheric temperatures using ECMWF data. We observed that waves propagate up to the stratosphere during frontal passages. When anticyclonic ridges are present, the propagation to the stratosphere is very weak. This is due to trapping of the waves at or below the tropopause. We also show that the radar data alone can be used to characterise the different weather conditions for the three cases studied (through the variation of the height of the tropopause). The synoptic stratospheric temperatures in the three cases were similar, and were above the expected threshold for PSC formation. Lidar and visual observation of PSCs and nacreous clouds, respectively, showed that these were present only in the case when the lee waves propagated up to the lower stratosphere.Key words. Atmospheric composition and structure (aerosols and particles) · Electromagnetic (wave propa- gation) · Meteorology and atmospheric dynamics (mesoscale meteorology)
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Chouza, Fernando, Oliver Reitebuch, Michael Jähn, Stephan Rahm, and Bernadett Weinzierl. "Vertical wind retrieved by airborne lidar and analysis of island induced gravity waves in combination with numerical models and in situ particle measurements." Atmospheric Chemistry and Physics 16, no. 7 (April 14, 2016): 4675–92. http://dx.doi.org/10.5194/acp-16-4675-2016.
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Abstract. This study presents the analysis of island induced gravity waves observed by an airborne Doppler wind lidar (DWL) during SALTRACE. First, the instrumental corrections required for the retrieval of high spatial resolution vertical wind measurements from an airborne DWL are presented and the measurement accuracy estimated by means of two different methods. The estimated systematic error is below −0.05 m s−1 for the selected case of study, while the random error lies between 0.1 and 0.16 m s−1 depending on the estimation method. Then, the presented method is applied to two measurement flights during which the presence of island induced gravity waves was detected. The first case corresponds to a research flight conducted on 17 June 2013 in the Cabo Verde islands region, while the second case corresponds to a measurement flight on 26 June 2013 in the Barbados region. The presence of trapped lee waves predicted by the calculated Scorer parameter profiles was confirmed by the lidar and in situ observations. The DWL measurements are used in combination with in situ wind and particle number density measurements, large-eddy simulations (LES), and wavelet analysis to determine the main characteristics of the observed island induced trapped waves.
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Lott, François. "The Reflection of a Stationary Gravity Wave by a Viscous Boundary Layer." Journal of the Atmospheric Sciences 64, no. 9 (September 1, 2007): 3363–71. http://dx.doi.org/10.1175/jas4020.1.
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Abstract The backward reflection of a stationary gravity wave (GW) propagating toward the ground is examined in the linear viscous case and for large Reynolds numbers (Re). In this case, the stationary GW presents a critical level at the ground because the mean wind is null there. When the mean flow Richardson number at the surface (J) is below 0.25, the GW reflection by the viscous boundary layer is total in the inviscid limit Re → ∞. The GW is a little absorbed when Re is finite, and the reflection decreases when both the dissipation and J increase. When J > 0.25, the GW is absorbed for all values of the Reynolds number, with a general tendency for the GW reflection to decrease when J increases. As a large ground reflection favors the downstream development of a trapped lee wave, the fact that it decreases when J increases explains why the more unstable boundary layers favor the onset of mountain lee waves. It is also shown that the GW reflection when J > 0.25 is substantially larger than that predicted by the conventional inviscid critical level theory and larger than that predicted when the dissipations are represented by Rayleigh friction and Newtonian cooling. The fact that the GW reflection depends strongly on the Richardson number indicates that there is some correspondence between the dynamics of trapped lee waves and the dynamics of Kelvin–Helmholtz instabilities. Accordingly, and in one classical example, it is shown that some among the neutral modes for Kelvin–Helmholtz instabilities that exist in an unbounded flow when J < 0.25 can also be stationary trapped-wave solutions when there is a ground and in the inviscid limit Re → ∞. When Re is finite, these solutions are affected by the dissipation in the boundary layer and decay in the downstream direction. Interestingly, their decay rate increases when both the dissipation and J increase, as does the GW absorption by the viscous boundary layer.
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Grubišić, Vanda, Stefano Serafin, Lukas Strauss, Samuel J. Haimov, Jeffrey R. French, and Larry D. Oolman. "Wave-Induced Boundary Layer Separation in the Lee of the Medicine Bow Mountains. Part II: Numerical Modeling." Journal of the Atmospheric Sciences 72, no. 12 (November 30, 2015): 4865–84. http://dx.doi.org/10.1175/jas-d-14-0381.1.
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Abstract Mountain waves and rotors in the lee of the Medicine Bow Mountains in southeastern Wyoming are investigated in a two-part paper. Part I by French et al. delivers a detailed observational account of two rotor events: one displays characteristics of a hydraulic jump and the other displays characteristics of a classic lee-wave rotor. In Part II, presented here, results of high-resolution numerical simulations are conveyed and physical processes involved in the formation and dynamical evolution of these two rotor events are examined. The simulation results reveal that the origin of the observed rotors lies in boundary layer separation, induced by wave perturbations whose amplitudes reach maxima at or near the mountain top. An undular hydraulic jump that gave rise to a rotor in one of these events was found to be triggered by midtropospheric wave breaking and an ensuing strong downslope windstorm. Lee waves spawning rotors developed under conditions favoring wave energy trapping at low levels in different phases of these two events. The upstream shift of the boundary layer separation zone, documented to occur over a relatively short period of time in both events, is shown to be the manifestation of a transition in flow regimes, from downslope windstorms to trapped lee waves, in response to a rapid change in the upstream environment, related to the passage of a short-wave synoptic disturbance aloft. The model results also suggest that the secondary obstacles surrounding the Medicine Bow Mountains play a role in the dynamics of wave and rotor events by promoting lee-wave resonance in the complex terrain of southeastern Wyoming.
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Yu, C. L., and M. A. C. Teixeira. "Impact of non-hydrostatic effects and trapped lee waves on mountain-wave drag in directionally sheared flow." Quarterly Journal of the Royal Meteorological Society 141, no. 690 (November 7, 2014): 1572–85. http://dx.doi.org/10.1002/qj.2459.
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Grubišić, Vanda, and Brian J. Billings. "Climatology of the Sierra Nevada Mountain-Wave Events." Monthly Weather Review 136, no. 2 (February 1, 2008): 757–68. http://dx.doi.org/10.1175/2007mwr1902.1.
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Abstract This note presents a satellite-based climatology of the Sierra Nevada mountain-wave events. The data presented were obtained by detailed visual inspection of visible satellite imagery to detect mountain lee-wave clouds based on their location, shape, and texture. Consequently, this climatology includes only mountain-wave events during which sufficient moisture was present in the incoming airstream and whose amplitude was large enough to lead to cloud formation atop mountain-wave crests. The climatology is based on data from two mountain-wave seasons in the 1999–2001 period. Mountain-wave events are classified in two types according to cloud type as lee-wave trains and single wave clouds. The frequency of occurrence of these two wave types is examined as a function of the month of occurrence (October–May) and region of formation (north, middle, south, or the entire Sierra Nevada range). Results indicate that the maximum number of mountain-wave events in the lee of the Sierra Nevada occurs in the month of April. For several months, including January and May, frequency of wave events displays substantial interannual variability. Overall, trapped lee waves appear to be more common, in particular in the lee of the northern sierra. A single wave cloud on the lee side of the mountain range was found to be a more common wave form in the southern Sierra Nevada. The average wavelength of the Sierra Nevada lee waves was found to lie between 10 and 15 km, with a minimum at 4 km and a maximum at 32 km.
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Teixeira, Miguel A. C., Alexandre Paci, and Anne Belleudy. "Drag Produced by Waves Trapped at a Density Interface in Nonhydrostatic Flow over an Axisymmetric Hill." Journal of the Atmospheric Sciences 74, no. 6 (May 17, 2017): 1839–57. http://dx.doi.org/10.1175/jas-d-16-0199.1.
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Abstract Linear nonhydrostatic theory is used to evaluate the drag produced by 3D trapped lee waves forced by an axisymmetric hill at a density interface. These waves occur at atmospheric temperature inversions, for example, at the top of the boundary layer, and contribute to low-level drag possibly misrepresented as turbulent form drag in large-scale numerical models. Unlike in 2D waves, the drag has contributions from a continuous range of wavenumbers forced by the topography, because the waves can vary their angle of incidence to match the resonance condition. This leads to nonzero drag for Froude numbers (Fr) both <1 and >1 and a drag maximum typically for Fr slightly below 1, with lower magnitude than in hydrostatic conditions owing to wave dispersion. These features are in good agreement with laboratory experiments using two axisymmetric obstacles, particularly for the lower obstacle, if the effects of a rigid lid above the upper layer and friction are taken into account. Quantitative agreement is less satisfactory for the higher obstacle, as flow nonlinearity increases. However, even in that case the model still largely outperforms both 3D hydrostatic and 2D nonhydrostatic theories, emphasizing the importance of both 3D and nonhydrostatic effects. The associated wave signatures are dominated by transverse waves for Fr lower than at the drag maximum, a dispersive “Kelvin ship-wave” pattern near the maximum, and divergent waves for Fr beyond the maximum. The minimum elevation at the density-interface depression existing immediately downstream of the obstacle is significantly correlated with the drag magnitude.
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Wendoloski, Eric B., David R. Stauffer, and Astrid Suarez. "A Subkilometer-Gridlength Ensemble for Representing Stable Boundary Layer Forecast Uncertainty over Complex Terrain." Monthly Weather Review 144, no. 8 (July 8, 2016): 2769–92. http://dx.doi.org/10.1175/mwr-d-15-0212.1.
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Abstract An ensemble prediction system featuring subkilometer horizontal grid spacing and high vertical resolution is used to quantify forecast uncertainty in the stable boundary layer (SBL). Diversity in initial conditions and/or planetary boundary layer/surface layer physics within the WRF Model provides ensembles with up to 12 members. WRF explicit ensemble data drive trajectory calculations and the Second-Order Closure Integrated Puff (SCIPUFF) model for hazard prediction. Explicit ensemble SCIPUFF forecasts are compared to single-member SCIPUFF forecasts leveraging WRF ensemble wind field uncertainty statistics. The performance of 1.3- and 0.4-km horizontal-gridlength ensemble configurations is evaluated for two case studies of differing flow regimes with respect to the Nittany Valley in central Pennsylvania where uncertainty in atmospheric transport and dispersion (ATD) is dependent on drainage flows and circulations related to trapped lee-wave activity. Results demonstrate that a 12-member ensemble provides reasonable spread in ATD forecasts. Additionally, single-member SCIPUFF surface-dosage probability forecasts using the meteorological ensemble statistics generally reflect the pattern while encompassing the hazard area given by the explicit SCIPUFF ensemble, but at a reduced computational cost. Low-level wind and temperature forecasts given by the 12-member, 0.4-km ensemble are improved significantly over corresponding 1.3-km ensemble forecasts. In general, the 12-member, subkilometer-gridlength ensemble configuration reliably captures temperature and wind fluctuations related to drainage flows and trapped lee-wave activity that directly impact ATD. Localized data assimilation positively impacts overall probabilistic forecast skill when trapped lee waves are present, and drainage flow case results appear more dependent on model physics than initialization strategy.
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Caccia, J.-L., B. Benech, and V. Klaus. "Space–Time Description of Nonstationary Trapped Lee Waves Using ST Radars, Aircraft, and Constant Volume Balloons during the PYREX Experiment." Journal of the Atmospheric Sciences 54, no. 14 (July 1997): 1821–33. http://dx.doi.org/10.1175/1520-0469(1997)054<1821:stdont>2.0.co;2.
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Pattantyus, Andre K., Sen Chiao, and Stanley Czyzyk. "Improving High-Resolution Model Forecasts of Downslope Winds in the Las Vegas Valley." Journal of Applied Meteorology and Climatology 50, no. 6 (June 2011): 1324–40. http://dx.doi.org/10.1175/2011jamc2586.1.
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AbstractNumerical simulations for severe downslope winds as well as trapped lee waves in Nevada’s Las Vegas Valley were performed in this study. The goal of this study was to improve model forecasts of downslope-wind-event intensities. This was measured by assessing different planetary boundary layer (PBL) schemes in the mountain–valley region. The Weather Research and Forecasting Model was adopted for this research. The numerical experiments were constructed using two nested domains, with 4- and 1-km grid resolution. The working hypothesis was that the occurrence of low-level wind shear and surface gustiness in the Las Vegas Valley was guided by the inversion layer in the valley. The choice of boundary layer scheme and model vertical resolution will influence inversion-layer height and consequently result in significant differences in surface wind and temperature forecast error below some near-surface height. Simulations of severe downslope wind events on 15 April 2008 and on 4 October 2009 were conducted. Statistical analyses of model results from three different PBL schemes and different vertical resolutions were performed. The results from the domain with 1-km grid spacing demonstrated remarkable detail of the severe downslope winds associated with low-level wind shear and surface gustiness in the Las Vegas Valley. The simulation results demonstrated that model vertical resolution was primarily responsible for the detail of the lower-level wind and temperature structures. The inverse Froude number and Froude number are two indices that may be included as the forecasting guidance for downslope winds, lee waves, and rotors for the Las Vegas Valley.
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Zhang, Weifeng (Gordon), and Steven J. Lentz. "Wind-Driven Circulation in a Shelf Valley. Part I: Mechanism of the Asymmetrical Response to Along-Shelf Winds in Opposite Directions." Journal of Physical Oceanography 47, no. 12 (December 2017): 2927–47. http://dx.doi.org/10.1175/jpo-d-17-0083.1.
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AbstractMotivated by observations in Hudson shelf valley showing stronger onshore than offshore flows, this study investigates wind-driven flows in idealized shallow shelf valleys. This first part of a two-part sequence focuses on the mechanism of the asymmetrical flow response in a valley to along-shelf winds of opposite directions. Model simulations show that (i) when the wind is in the opposite direction to coastal-trapped wave (CTW) phase propagation, the shelf flow turns onshore in the valley and generates strong up-valley transport and a standing meander on the upstream side (in the sense of CTW phase propagation) of the valley, and (ii) when the wind is in the same direction as CTW phase propagation, the flow forms a symmetric onshore detour pattern over the valley with negligible down-valley transport. Comparison of the modeled upstream meanders in the first scenario with CTW characteristics confirms that the up-valley flow results from CTWs being arrested by the wind-driven shelf flow establishing lee waves. The valley bathymetry generates an initial excessive onshore pressure gradient force that drives the up-valley flow and induces CTW lee waves that sustain the up-valley flow. When the wind-driven shelf flow aligns with CTW phase propagation, the initial disturbance generated in the valley propagates away, allowing the valley flow to adjust to roughly follow isobaths. Because of the similarity in the physical setup, this mechanism of arrested CTWs generating stronger onshore than offshore flow is expected to be applicable to the flow response in slope canyons to along-isobath background flows of opposite directions.
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Igeta, Yosuke, Alexander Yankovsky, Ken-ichi Fukudome, Satoshi Ikeda, Noriyuki Okei, Kota Ayukawa, Atsushi Kaneda, and Tatsuro Watanabe. "Transition of the Tsushima Warm Current Path Observed over Toyama Trough, Japan." Journal of Physical Oceanography 47, no. 11 (November 2017): 2721–39. http://dx.doi.org/10.1175/jpo-d-17-0027.1.
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AbstractMooring, CTD, and ADCP observations were made in 2012 in and around the Toyama Trough (TT) cutting across a continental shelf along the Japanese coast of the Japan Sea between Noto Peninsula (NP) and Sado Island (SI) to investigate spatiotemporal characteristics of path transition of the coastal branch of the Tsushima Warm Current (CBTWC). Around SI, downstream of the TT boundary, a wavelike alongshore current perturbation, accompanied by sea level rise, was observed. This perturbation occurred after the seasonal amplification of the CBTWC around the NP on the upstream boundary of the TT. This process was delineated by the results of numerical experiments performed with a two-layer model using idealized topography. The model showed that a current path of the CBTWC shifted from alongshore mode to offshore mode bridged over the TT in association with the lee eddy development behind the NP toward the SI over the TT. This lee eddy is generated by positive vorticity induced over topographic discontinuity between the continental shelf off the northern coast of the NP and deeper region of the TT. The model indicated the period of eddy formation is 60–90 days if the volume transport is 1 Sv (1 Sv ≡ 106 m3 s−1), whereas the observations showed the formation period was only 47 days at 1.2 Sv of volume transport. To explain this discrepancy, temporal variation of the CBTWC, vortex supply from preexisting eddies, or eddies caused by the scattering of coastal-trapped waves were suggested as new processes that accelerate the growth rate of the lee eddy.
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Mahalov, A., M. Moustaoui, and V. Grubišić. "A numerical study of mountain waves in the upper troposphere and lower stratosphere." Atmospheric Chemistry and Physics Discussions 11, no. 2 (February 8, 2011): 4487–532. http://dx.doi.org/10.5194/acpd-11-4487-2011.
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Abstract. A numerical study of mountain waves in the Upper Troposphere and Lower Stratosphere (UTLS) is presented for two Intensive Observational Periods (IOPs) of the Terrain-induced Rotor Experiment (T-REX). The simulations use the Weather Research and Forecasting (WRF) model and a microscale model that is driven by the finest WRF nest. During IOP8, the simulation results reveal presence of perturbations with short wavelengths in zones of strong vertical wind shear in the UTLS that cause a reversal of momentum fluxes. The spectral properties of these perturbations and the attendant vertical profiles of heat and momentum fluxes show strong divergence near the tropopause indicating that they are generated by shear instability along shear lines locally induced by the primary mountain wave originating from the lower troposphere. This is further confirmed by results of an idealized simulation initialized with the temperature and wind profiles obtained from the microscale model. For IOP6, we analyse distributions of O3 and CO observed in aircraft measurements. These show small scale fluctuations with amplitudes and phases that vary along the path of the flight. Comparison between these fluctuations and the observed vertical velocity show that the behavior of these short fluctuations is due not only to the vertical motion, but also to the local mean vertical gradients where the waves evolve, which are modulated by larger variations. The microscale model simulation results shows favorable agreement with in situ radiosonde and aircraft observations. The high vertical resolution offered by the microscale model is found to be critical for resolution of smaller scale processes such as formation of inversion layer associated with trapped lee waves in the troposphere, and propagating mountain waves in the lower stratosphere.
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Mahalov, A., M. Moustaoui, and V. Grubišić. "A numerical study of mountain waves in the upper troposphere and lower stratosphere." Atmospheric Chemistry and Physics 11, no. 11 (June 1, 2011): 5123–39. http://dx.doi.org/10.5194/acp-11-5123-2011.
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Abstract. A numerical study of mountain waves in the Upper Troposphere and Lower Stratosphere (UTLS) is presented for two Intensive Observational Periods (IOPs) of the Terrain-induced Rotor Experiment (T-REX). The simulations use the Weather Research and Forecasting (WRF) model and a microscale model that is driven by the finest WRF nest. During IOP8, the simulation results reveal presence of perturbations with short wavelengths in zones of strong vertical wind shear in the UTLS that cause a reversal of momentum fluxes. The spectral properties of these perturbations and the attendant vertical profiles of heat and momentum fluxes show strong divergence near the tropopause indicating that they are generated by shear instability along shear lines locally induced by the primary mountain wave originating from the lower troposphere. This is further confirmed by results of an idealized simulation initialized with the temperature and wind profiles obtained from the microscale model. For IOP6, we analyze distributions of O3 and CO observed in aircraft measurements. They show small scale fluctuations with amplitudes and phases that vary along the path of the flight. Detailed comparisons between these fluctuations and the observed vertical velocity show that the behavior of these short fluctuations is due not only to the vertical motion, but also to the local mean vertical gradients where the waves evolve, which are modulated by larger variations. The microscale model simulation results show favorable agreement with in situ radiosonde and aircraft observations. The high vertical resolution offered by the microscale model is found to be critical for resolution of smaller scale processes such as formation of inversion layer associated with trapped lee waves in the troposphere, and propagating mountain waves in the lower stratosphere.
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Koch, Steven E., Cyrille Flamant, James W. Wilson, Bruce M. Gentry, and Brian D. Jamison. "An Atmospheric Soliton Observed with Doppler Radar, Differential Absorption Lidar, and a Molecular Doppler Lidar." Journal of Atmospheric and Oceanic Technology 25, no. 8 (August 1, 2008): 1267–87. http://dx.doi.org/10.1175/2007jtecha951.1.
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Abstract Airborne Leandre II differential absorption lidar (DIAL), S-band dual-polarization Doppler radar (S-Pol), and Goddard Lidar Observatory for Winds (GLOW) Doppler lidar data are used, in conjunction with surface mesonet and special sounding data, to derive the structure and dynamics of a bore and associated solitary wave train (soliton) that were generated in southwestern Kansas during the International H20 Project (IHOP_2002). Vertical cross sections of S-Pol reflectivity, S-Pol radial velocity, and DIAL water vapor mixing ratio show a stunning amplitude-ordered train of trapped solitary waves. DIAL data reveal that the leading wave in the soliton increasingly flattened with time as the soliton dissipated. A method is developed for using the GLOW Doppler winds to obtain the complex two-dimensional vertical circulation accompanying the dissipating soliton. The results show multiple circulations identical in number to the oscillations seen in the S-Pol and DIAL data. The leading updraft occurred precisely at the time that the bore passed over the GLOW facility, as well as when the photon count values suddenly ramped up (suggesting lifting of the low-level inversion by the bore). Additional evidence in support of the validity of the results is provided by the fact that layer displacements computed using the derived vertical motions agree well with those implied by the changes in height of the DIAL mixing ratio surfaces. The depth and speed of propagation of the bore seen in the DIAL and surface mesoanalyses were shown to be consistent with the predictions from bore hydraulic theory. Analysis of National Center for Atmospheric Research (NCAR) Integrated Sounding System (ISS) data shows that a highly pronounced curvature in the profile of bore-relative winds, related to the existence of a very strong low-level jet, effectively trapped the upward leakage of solitary wave energy below 3 km. This finding explains the trapped lee wave–type structures seen in the DIAL, GLOW, and S-Pol data.
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Muñoz-Esparza, Domingo, Jeremy A. Sauer, Rodman R. Linn, and Branko Kosović. "Limitations of One-Dimensional Mesoscale PBL Parameterizations in Reproducing Mountain-Wave Flows." Journal of the Atmospheric Sciences 73, no. 7 (June 24, 2016): 2603–14. http://dx.doi.org/10.1175/jas-d-15-0304.1.
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Abstract Mesoscale models are considered to be the state of the art in modeling mountain-wave flows. Herein, the authors investigate the role and accuracy of planetary boundary layer (PBL) parameterizations in handling the interaction between large-scale mountain waves and the atmospheric boundary layer. To that end, recent large-eddy simulation (LES) results of mountain waves over a symmetric two-dimensional bell-shaped hill are used and compared to four commonly used PBL schemes. It is found that one-dimensional PBL parameterizations produce reasonable agreement with the LES results in terms of vertical wavelength, amplitude of velocity, and turbulent kinetic energy distribution in the downhill shooting-flow region. However, the assumption of horizontal homogeneity in PBL parameterizations does not hold in the context of these complex flow configurations. This inappropriate modeling assumption results in a vertical wavelength shift, producing errors of approximately 10 m s−1 at downstream locations because of the presence of a coherent trapped lee wave that does not mix with the atmospheric boundary layer. In contrast, horizontally integrated momentum flux derived from these PBL schemes displays a realistic pattern. Therefore, results from mesoscale models using ensembles of one-dimensional PBL schemes can still potentially be used to parameterize drag effects in general circulation models. Nonetheless, three-dimensional PBL schemes must be developed in order for mesoscale models to accurately represent complex terrain and other types of flows where one-dimensional PBL assumptions are violated.