The accuracy of linear theory for predicting mountain-wave drag: Implications for parametrization schemes

2010 ◽  
Vol 136 (647) ◽  
pp. 429-441 ◽  
Author(s):  
H. Wells ◽  
S. B. Vosper
Keyword(s):  
Linear Theory ◽  
Wave Drag ◽  
Mountain Wave

scholarly journals A Gravity Wave Drag Matrix for Complex Terrain

2018 ◽  
Vol 75 (8) ◽  
pp. 2599-2613 ◽  
Author(s):  
Ronald B. Smith ◽  
Christopher G. Kruse
Keyword(s):  
New Zealand ◽  
Complex Terrain ◽  
Momentum Flux ◽  
Correlation Coefficients ◽  
Wave Drag ◽  
Positive Definite ◽  
Wind Vector ◽  
Mountain Wave ◽  
Wind Speeds ◽  
Aircraft Data

Abstract We propose a simplified scheme to predict mountain wave drag over complex terrain using only the regional-average low-level wind components U and V. The scheme is tuned and tested on data from the South Island of New Zealand, a rough and highly anisotropic terrain. The effect of terrain anisotropy is captured with a hydrostatically computed, 2 × 2 positive-definite wave drag matrix. The wave drag vector is the product of the wind vector and the drag matrix. The nonlinearity in wave generation is captured using a Gaussian terrain smoothing inversely proportional to wind speed. Wind speeds of |U| = 10, 20, and 30 m s−1 give smoothing scales of L = 54, 27, and 18 km, respectively. This smoothing treatment of nonlinearity is consistent with recent aircraft data and high-resolution numerical modeling of waves over New Zealand, indicating that the momentum flux spectra shift to shorter waves during high-drag conditions. The drag matrix model is tested against a 3-month time series of realistic full-physics wave-resolving flow calculations. Correlation coefficients approach 0.9 for both zonal and meridional drag components.

scholarly journals Regional to Global Evolution of Impacts of Parameterized Mountain-Wave Drag in the Lower Stratosphere

2020 ◽  
Vol 33 (8) ◽  
pp. 3093-3106 ◽  
Author(s):  
Christopher G. Kruse
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Climate Model ◽  
Wave Drag ◽  
Mountain Wave ◽  
Global Features ◽  
Mountain Ranges ◽  
The North ◽  
Global Evolution ◽  
And Diffusion

AbstractMountain ranges are regional features on Earth, as are the regions of mountain-wave drag (MWD) exerted by dissipating atmospheric gravity waves generated by flow over them. However, these regional drags have significant global- or zonal-mean impacts on Earth’s atmospheric general circulation (e.g., slowing of the polar night jet). The objective of this work is to understand the regional to global evolution of these impacts. The approach is to track the evolution of MWD-generated potential vorticity (PV) over the winter using the Whole Atmosphere Community Climate Model (WACCM). Within an ensemble of winter-long runs with and without MWD, lower-stratospheric PV is generated over mountains and advected downstream, generating large-scale PV banners. These PV banners are diffused but survive this diffusion and are reinforced over downstream mountain ranges, accumulating into zonal-mean or global features within WACCM. A simple 2D model representing sources, advection, and diffusion of “passive PV” recreates the salient features in the WACCM results, suggesting the winter-long evolution of MWD-generated PV can be crudely understood in terms of horizontal advection and diffusion within a global vortex. In the Northern Hemisphere, cyclonic, equatorward PV banners accumulate zonally into a single zonally symmetric positive PV anomaly. The anticyclonic, poleward PV banners also accumulate into a zonally symmetric feature, but then diffuse over the North Pole into a negative PV polar cap. In the Southern Hemisphere, the same processes are at work, though the different geographic configuration of mountain ranges leads to different patterns of impacts.

Mountain wave drag over double bell-shaped orograghy

1993 ◽  
Vol 119 (509) ◽  
pp. 199-206
Author(s):  
BRANKO GRISOGONO ◽  
SARA C PRYOR ◽  
ROBERT E KEISLAR
Keyword(s):  
Wave Drag ◽  
Mountain Wave

scholarly journals The Midlatitude Lower-Stratospheric Mountain Wave “Valve Layer”

2016 ◽  
Vol 73 (12) ◽  
pp. 5081-5100 ◽  
Author(s):  
Christopher G. Kruse ◽  
Ronald B. Smith ◽  
Stephen D. Eckermann
Keyword(s):  
New Zealand ◽  
Wind Speed ◽  
Gravity Wave ◽  
Momentum Flux ◽  
Climate Models ◽  
Wave Attenuation ◽  
Wave Drag ◽  
Mountain Wave ◽  
Stratospheric Polar Vortex ◽  
Mountain Waves

Abstract The vertical propagation and attenuation of mountain waves launched by New Zealand terrain during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) field campaign are investigated. New Zealand mountain waves were frequently attenuated in a lower-stratospheric weak wind layer between z = 15 and 25 km. This layer is termed a “valve layer,” as conditions within this layer (primarily minimum wind speed) control mountain wave momentum flux through it, analogous to a valve controlling mass flux through a pipe. This valve layer is a climatological feature in the wintertime midlatitude lower stratosphere above the subtropical jet. Mountain wave dynamics within this valve layer are studied using realistic Weather Research and Forecasting (WRF) Model simulations that were extensively validated against research aircraft, radiosonde, and satellite observations. Locally, wave attenuation is horizontally and vertically inhomogeneous, evidenced by numerous regions with wave-induced low Richardson numbers and potential vorticity generation. WRF-simulated gravity wave drag (GWD) is peaked in the valve layer, and momentum flux transmitted through this layer is well approximated by a cubic function of minimum ambient wind speed within it, consistent with linear saturation theory. Valve-layer GWD within the well-validated WRF simulations was 3–6 times larger than that parameterized within MERRA. Previous research suggests increasing parameterized orographic GWD (performed in MERRA2) decreases the stratospheric polar vortex strength by altering planetary wave propagation and drag. The results reported here suggest carefully increasing orographic GWD is warranted, which may help to ameliorate the common cold-pole problem in chemistry–climate models.

An Investigation of a Commercial Aircraft Encounter with Severe Clear-Air Turbulence over Western Greenland

2012 ◽  
Vol 51 (1) ◽  
pp. 42-53 ◽  
Author(s):  
R. D. Sharman ◽  
J. D. Doyle ◽  
M. A. Shapiro
Keyword(s):  
High Resolution ◽  
Prediction Models ◽  
Weather Prediction ◽  
Simulation Models ◽  
Wave Drag ◽  
Commercial Aircraft ◽  
Mountain Wave ◽  
Air Turbulence ◽  
Lee Waves ◽  
Horizontal Grid

AbstractThis study presents digital flight data recorder (DFDR) analyses and high-resolution numerical simulations relevant to a severe clear-air turbulence (CAT) encounter over western Greenland by a Boeing 777 aircraft at 10-km elevation at 1305 UTC 25 May 2010. The environmental flow was dominated by an extratropical cyclone to the southeast of the Greenland tip, resulting in easterly flow at all levels. The results of the analyses indicate that the CAT encounter was related to mountain-wave breaking on the western lee (downslope) of the Greenland plateau. The simulations were not of especially high resolution (5-km horizontal grid spacing) by today’s standards, yet the simulation results do produce large-amplitude lee waves and overturning in good agreement with the encounter location as indicated by the DFDR. The success of this and other simulations in reproducing mountain-wave turbulence (MWT) events suggests that operational implementation of high-resolution nonhydrostatic simulation models, possibly an ensemble of models, over MWT-prone areas could produce more reliable forecasts of MWT than are currently available using gravity-wave-drag or MWT-postprocessing algorithms derived from global weather prediction models of relatively coarse scale.

scholarly journals Mountain Waves in Two-Layer Sheared Flows: Critical-Level Effects, Wave Reflection, and Drag Enhancement

2008 ◽  
Vol 65 (6) ◽  
pp. 1912-1926 ◽  
Author(s):  
Miguel A. C. Teixeira ◽  
Pedro M. A. Miranda ◽  
JoséL. Argaín
Keyword(s):  
Linear Theory ◽  
Shear Flows ◽  
Wave Reflection ◽  
Critical Level ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Critical Levels ◽  
Nonlinear Processes ◽  
Mountain Waves ◽  
The Impact

Abstract Internal gravity waves generated in two-layer stratified shear flows over mountains are investigated here using linear theory and numerical simulations. The impact on the gravity wave drag of wind profiles with constant unidirectional or directional shear up to a certain height and zero shear above, with and without critical levels, is evaluated. This kind of wind profile, which is more realistic than the constant shear extending indefinitely assumed in many analytical studies, leads to important modifications in the drag behavior due to wave reflection at the shear discontinuity and wave filtering by critical levels. In inviscid, nonrotating, and hydrostatic conditions, linear theory predicts that the drag behaves asymmetrically for backward and forward shear flows. These differences primarily depend on the fraction of wavenumbers that pass through their critical level before they are reflected by the shear discontinuity. If this fraction is large, the drag variation is not too different from that predicted for an unbounded shear layer, while if it is small the differences are marked, with the drag being enhanced by a considerable factor at low Richardson numbers (Ri). The drag may be further enhanced by nonlinear processes, but its qualitative variation for relatively low Ri is essentially unchanged. However, nonlinear processes seem to interact constructively with shear, so that the drag for a noninfinite but relatively high Ri is considerably larger than the drag without any shear at all.

scholarly journals An Analytical Model of Mountain Wave Drag for Wind Profiles withShear and Curvature

2004 ◽  
Vol 61 (9) ◽  
pp. 1040-1054 ◽  
Author(s):  
Miguel A. C. Teixeira ◽  
Pedro M. A. Miranda ◽  
Maria Antónia Valente
Keyword(s):  
Analytical Model ◽  
Wave Drag ◽  
Mountain Wave ◽  
Wind Profiles
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