Strongly Nonlinear Flow over and around a Three-Dimensional Mountain as a Function of the Horizontal Aspect Ratio

Bauer, Manfred H.; Mayr, Georg J.; Vergeiner, I.; Pichler, Helmut

doi:10.1175/1520-0469(2001)058<3971:snfoaa>2.0.co;2

Cited by 54 publications

(53 citation statements)

References 27 publications

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“…Eckermann et al [152] evaluated the dependence of the momentum fluxes onh for flow over 3D obstacles, essentially confirming the findings of Ólafsson and Bougeault [150] and Bauer et al [56] for the surface drag. They additionally showed that the drag vacillates for flow across an elongated obstacle in the 0.7 ≤h < 3 range, due to cyclical buildup and breakdown of wave activity, with the amplitude of these vacillations decreasing ash increases.…”

Section: Nonlinear Effectssupporting

confidence: 58%

“…Bauer et al [56] and Wells et al [57] studied the interaction of orography anisotropy with flow nonlinearity also assuming elliptical mountains, concluding that flow perpendicular to the major axis of the mountain is substantially more nonlinear than flow parallel to that axis. Wells et al [57], in particular, found that the dependence of the drag on flow direction is quite well captured by linear theory, but its value is typically underestimated for flow across the mountain (and overestimated for flow along it).…”

Section: Orography Anisotropymentioning

confidence: 99%

“…Ólafsson and Bougeault [150] carried out analogous simulations of flow over an elliptical mountain of aspect ratio 5 for 0.500 <h < 6.818, showing that for lowh the linear predictions of flow stagnation aloft (leading to wave breaking) and of stagnation at the surface (leading to flow splitting) [149] are accurate, but for higherh wave breaking occurs mostly at the edges of the mountain, not over its axis of symmetry. Using an essentially similar setup, Bauer et al [56] explored more systematically the dependence of the flow on the horizontal aspect ratio of the mountain, finding that, when γ decreases, theh threshold for the onset of wave breaking, vortex formation and windward stagnation decreases. The interval of h where high-drag states occur, which is centered aroundh ≈ 1, was seen to widen as γ decreases (see Figure 14, right).…”

Section: Nonlinear Effectsmentioning

confidence: 99%

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The physics of orographic gravity wave drag

Teixeira

2014

Front. Phys.

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The drag and momentum fluxes produced by gravity waves generated in flow over orography are reviewed, focusing on adiabatic conditions without phase transitions or radiation effects, and steady mean incoming flow. The orographic gravity wave drag is first introduced in its simplest possible form, for inviscid, linearized, non-rotating flow with the Boussinesq and hydrostatic approximations, and constant wind and static stability. Subsequently, the contributions made by previous authors (primarily using theory and numerical simulations) to elucidate how the drag is affected by additional physical processes are surveyed. These include the effect of orography anisotropy, vertical wind shear, total and partial critical levels, vertical wave reflection and resonance, non-hydrostatic effects and trapped lee waves, rotation and nonlinearity. Frictional and boundary layer effects are also briefly mentioned. A better understanding of all of these aspects is important for guiding the improvement of drag parametrization schemes.

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Section: Nonlinear Effectssupporting

confidence: 58%

Section: Orography Anisotropymentioning

confidence: 99%

Section: Nonlinear Effectsmentioning

confidence: 99%

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The physics of orographic gravity wave drag

Teixeira

2014

Front. Phys.

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“…On a non-rotating plane, for a mountain that is elongated along the flow, stagnation starts at values of Nh/U that are higher than if the mountain is elongated across the flow (Smith, 1989). This has been confirmed by Bauer et al (2000), using 3-D numerical simulations. Neglecting the effects of rotation, westerly flow should in other words be more easily blocked than southerly flow, both impinging on a The Rossby number enters the theory as an additional parameter for flow on a rotating plane.…”

Section: Theorymentioning

confidence: 66%

Multi-scale variability of winds in the complex topography of southwestern Norway

Jonassen¹,

Ólafsson

Reuder³

et al. 2012

Tellus A: Dynamic Meteorology and Oceanography

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A B S T R A C T Multi-scale variability of winds in the complex terrain of southwestern Norway is investigated using up to 20 yr of observations from nine automatic weather stations and reanalysis data. Significant differences between the large-and local-scale winds are found. These differences are mainly governed by the large-scale topography of Southern Norway. Winds from the southeast and statically stable flow from the northwest are found to be significantly reduced at the ground level due to large-scale wake and blocking effects. Southwesterly and northeasterly winds are orographically enhanced. At a local scale, there are differences in the wind speed distributions between the surface stations, both in space and time. These differences can to a large extent be quantified in terms of the Weibull distribution function and associated with the respective geographical locations as discretised in four characteristic surface categories: offshore, inland, coast and mountain. The inland category is found to be associated with relatively low but variable wind speeds, whereas the coastal and offshore locations are dominated by more steady and stronger winds. The mountain wind speed distribution is fundamentally different from the others; it shares the variability with the inland locations but the higher average wind speed with the other categories.

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“…Although most of the literature discusses flows over substantially broader topography than considered here [Schär and Durran, 1997;Bauer et al, 2000], the comparatively low dimensionless mountain height suggests that stratification effects do not play a major role in determining the flow regime. Indeed, as we have used the dry value of the Brunt-Väisälä frequency, and as we have neglected the presence of the boundary layer with vertical mixing and spatially varying height, the stratification effects are likely even smaller than indicated by the dimensionless mountain height (6).…”

Section: Dynamical Considerationsmentioning

confidence: 97%

Fine‐scale modeling of the boundary layer wind field over steep topography

Raderschall

Lehning

Schär

2008

Water Resources Research

105

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[1] This paper describes the adaptation of wind fields to steep and complex terrain using fine-scale numerical modeling. The work is motivated by the need of high-resolution flow fields to predict snow transport and snow cover development for avalanche warning purposes. Applying the nonhydrostatic and compressible atmospheric prediction model Advanced Regional Prediction System (ARPS) to steep alpine topography, the boundary layer flow was simulated and evaluated against measurements. The adaptation of the wind field to steep terrain for specific initial and boundary conditions was simulated. The topography used in our study has a length scale of 500 m, a typical height of 150 m, and maximum slopes of 45°. Numerical experiments with idealized triangular ridges were conducted to find an adequate model configuration. This analysis indicates that a highresolution grid with horizontal spacing of at least 25 m and vertical spacing of 3 m near the surface is necessary to reproduce small-scale flow features such as speed-up, separation, and recirculation. The onset of flow separation is highly sensitive to initial and boundary conditions, slope angle, and surface roughness. The results of the comparison between the model simulations and measurements on our experimental site show that typical wind field characteristics are well reproduced. The simulated wind fields have been used to drive a numerical three-dimensional snow drift model, which is presented in a companion paper by Lehning et al. (2008).

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Strongly Nonlinear Flow over and around a Three-Dimensional Mountain as a Function of the Horizontal Aspect Ratio

Cited by 54 publications

References 27 publications

The physics of orographic gravity wave drag

The physics of orographic gravity wave drag

Multi-scale variability of winds in the complex topography of southwestern Norway

Fine‐scale modeling of the boundary layer wind field over steep topography

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