scholarly journals Towards a numerical laboratory for investigations of gravity-wave mean-flow interactions in the atmosphere

2021 ◽  
Author(s):  
Fabienne Schmid ◽  
Elena Gagarina ◽  
Rupert Klein ◽  
Ulrich Achatz
Keyword(s):  
Weather Prediction ◽  
Wave Activity ◽  
Staggered Grid ◽  
Climate Simulation ◽  
Implicit Time ◽  
Small Scale ◽  
Mean Flow ◽  
Flow Interactions ◽  
Flow Effects ◽  
Main Components

AbstractIdealized integral studies of the dynamics of atmospheric inertia-gravity waves (IGWs) from their sources in the troposphere (e.g., by spontaneous emission from jets and fronts) to dissipation and mean-flow effects at higher altitudes could contribute to a better treatment of these processes in IGW parameterizations in numerical weather prediction and climate simulation. It seems important that numerical codes applied for this purpose are efficient and focus on the essentials. Therefore a previously published staggered-grid solver for f-plane soundproof pseudo-incompressible dynamics is extended here by two main components. These are 1) a semi-implicit time stepping scheme for the integration of buoyancy and Coriolis effects, and 2) the incorporation of Newtonian heating consistent with pseudo-incompressible dynamics. This heating function is used to enforce a temperature profile that is baroclinically unstable in the troposphere and it allows the background state to vary in time. Numerical experiments for several benchmarks are compared against a buoyancy/Coriolis-explicit third-order Runge-Kutta scheme, verifying the accuracy and efficiency of the scheme. Preliminary mesoscale simulations with baroclinic-wave activity in the troposphere show intensive small-scale wave activity at high altitudes, and they also indicate there the expected reversal of the zonal-mean-zonal winds.

scholarly journals Eddy-Driven Recirculations from a Localized Transient Forcing

2012 ◽  
Vol 42 (3) ◽  
pp. 430-447 ◽  
Author(s):  
Stephanie Waterman ◽  
Steven R. Jayne
Keyword(s):  
Group Velocity ◽  
Rossby Wave ◽  
Wave Spectrum ◽  
Mean Flow ◽  
Weakly Nonlinear ◽  
Recirculation Gyres ◽  
Flow Interactions ◽  
Flow Effects ◽  
Wave Limit ◽  
Many Sources

Abstract The generation of time-mean recirculation gyres from the nonlinear rectification of an oscillatory, spatially localized vorticity forcing is examined analytically and numerically. Insights into the rectification mechanism are presented and the influence of the variations of forcing parameters, stratification, and mean background flow are explored. This exploration shows that the efficiency of the rectification depends on the properties of the energy radiation from the forcing, which in turn depends on the waves that participate in the rectification process. The particular waves are selected by the relation of the forcing parameters to the available free Rossby wave spectrum. An enhanced response is achieved if the parameters are such to select meridionally propagating waves, and a resonant response results if the forcing selects the Rossby wave with zero zonal group velocity and maximum meridional group velocity, which is optimal for producing rectified flows. Although formulated in a weakly nonlinear wave limit, simulations in a more realistic turbulent system suggest that this understanding of the mechanism remains useful in a strongly nonlinear regime with consideration of mean flow effects and wave–mean flow interaction now needing to be taken into account. The problem presented here is idealized but has general application in the understanding of eddy–eddy and eddy–mean flow interactions as the contrasting limit to that of spatially broad (basinwide) forcing and is relevant given that many sources of oceanic eddies are localized in space.

scholarly journals The Interaction between Atmospheric Gravity Waves and Large-Scale Flows: An Efficient Description beyond the Nonacceleration Paradigm

2016 ◽  
Vol 73 (12) ◽  
pp. 4833-4852 ◽  
Author(s):  
Gergely Bölöni ◽  
Bruno Ribstein ◽  
Jewgenija Muraschko ◽  
Christine Sgoff ◽  
Junhong Wei ◽  
...  
Keyword(s):  
Steady State ◽  
Wave Breaking ◽  
Large Scale ◽  
Climate Models ◽  
Weather Prediction ◽  
Simple Wave ◽  
Mean Flow ◽  
Action Density ◽  
Total Energy Balance ◽  
Flow Interactions

Abstract With the aim of contributing to the improvement of subgrid-scale gravity wave (GW) parameterizations in numerical weather prediction and climate models, the comparative relevance in GW drag of direct GW–mean flow interactions and turbulent wave breakdown are investigated. Of equal interest is how well Wentzel–Kramer–Brillouin (WKB) theory can capture direct wave–mean flow interactions that are excluded by applying the steady-state approximation. WKB is implemented in a very efficient Lagrangian ray-tracing approach that considers wave-action density in phase space, thereby avoiding numerical instabilities due to caustics. It is supplemented by a simple wave-breaking scheme based on a static-instability saturation criterion. Idealized test cases of horizontally homogeneous GW packets are considered where wave-resolving large-eddy simulations (LESs) provide the reference. In all of these cases, the WKB simulations including direct GW–mean flow interactions already reproduce the LES data to a good accuracy without a wave-breaking scheme. The latter scheme provides a next-order correction that is useful for fully capturing the total energy balance between wave and mean flow. Moreover, a steady-state WKB implementation as used in present GW parameterizations where turbulence provides by the noninteraction paradigm, the only possibility to affect the mean flow, is much less able to yield reliable results. The GW energy is damped too strongly and induces an oversimplified mean flow. This argues for WKB approaches to GW parameterization that take wave transience into account.

scholarly journals Progress towards an improved parameterisation of small-scale orographic impacts on the atmospheric boundary layer

2021 ◽  
Author(s):  
Julian Quimbayo-Duarte ◽  
Juerg Schmidli
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Prediction Models ◽  
Weather Prediction ◽  
Vertical Flux ◽  
Initial Time ◽  
Small Scale ◽  
Mean Flow ◽  
Horizontal Momentum ◽  
The Impact

<p>An accurate representation of the momentum budget in numerical models is essential in the quest for reliable weather forecasting, from large scales (climate models) to small scales (numerical weather prediction models, NWP). It is well known that orographic waves play an important role in large-scale circulation. The vertical propagation of such waves is associated with a vertical flux of horizontal momentum, which may be transferred to the mean flow by wave-mean flow interaction and wave-breaking (Sandu et al., 2019). The orography scales inducing such phenomena are often smaller than the model resolution, even for NWP models, leading to the need for parameterisation schemes for orographic drag. Yet, such parameterization in current models is fairly limited (Vosper et al., 2020). The present work aims to contribute to an improved understanding and parameterization of the impact of small-scale orography on the lower atmosphere with a focus on the stable atmospheric boundary layer.</p><p>As a first step, an idealized set of experiments has been designed to explore the capabilities of the Icosahedral Nonhydrostatic model in its large eddy simulation mode (ICON-LES, Dipankar et al., 2015) to represent turbulence processes in the stably-stratified atmosphere. Initial experiments testing the model performance over flat terrain (GABLS experiment, Beare et al., 2006), orographic wave generation (shallow bell-shaped topography, Xue et al., 2000) and moderate complex terrain (U-shaped valley, Burns and Chemel 2014) have been conducted. The results demonstrate that ICON-LES adequately represents the boundary layer processes for the investigated cases in comparison to the literature.</p><p>In a second step, an idealized set of experiments of atmospheric flow over idealized sinusoidal and multiscale terrain has been designed to study the impact of the orographically-induced gravity waves on the total surface drag and the vertical flux of horizontal momentum. The influence of different atmospheric conditions is assessed by varying the background wind speed and the temperature stratification at the initial time.</p>

Generation of inertia-gravity waves in idealized baroclinic-wave life cycles: Explicit vs. semi-implicit time stepping in a finite-volume solver for the pseudo-incompressible equations

2020 ◽  
Author(s):  
Fabienne Schmid ◽  
Elena Gagarina ◽  
Rupert Klein ◽  
Ulrich Achatz
Keyword(s):  
Finite Volume ◽  
Spontaneous Emission ◽  
Gravity Waves ◽  
Prediction Models ◽  
Weather Prediction ◽  
Life Cycles ◽  
Staggered Grid ◽  
Implicit Time ◽  
Baroclinic Wave ◽  
Time Stepping

<div> <div> <div> <p>Inertia–gravity waves (IGWs) emitted from jets and fronts are ubiquitous in the atmosphere and have a significant impact on atmospheric processes (Plougonven and Zhang, 2014). Since the mechanism responsible for the spontaneous emission of IGWs during the evolution of an initially balanced flow remain poorly understood, their representation in numerical weather prediction models is challenging (de la Cámara and Lott, 2015). Better understanding of this IGW source mechanism based on idealized numerical simulations is crucial to improve the accuracy of the forecasts. In this study, idealized baroclinic-wave life cycle experiments on the f-plane are performed to investigate spontaneous emission, using a finite-volume solver for the pseudo-incompressible equations (Rieper et al., 2013). In particular, the implementation of a semi-implicit time stepping scheme, along the lines of Smolarkiewicz and Margolin (1997) and Benaccio and Klein (2019), but adjusted to our staggered grid, permits longer simulation runs with much larger domains. A novelty is the implementation of a simple Newtonian heating function based on Held and Suarez (1994), which is used for forcing a baroclinically unstable temperature profile and allows the background state to vary in time (O’Neill and Klein, 2014). The results of the model with semi-implicit time stepping scheme will be documented and compared to an explicit Runge-Kutta scheme. The analysis may serve as a basis for the development and validation of a parameterization scheme for GWs emitted from jets and fronts.</p> <p>References:</p> <p>Benaccio, T., and R. Klein, 2019: A semi-implicit compressible model for atmospheric flows with seamless access to soundproof and hydrostatic dynamics. Mon. Wea. Rev., 147, 4221-4240.<br>de la Cámara, A., and F. Lott, 2015: A parameterization of gravity waves emitted by fronts and jets. Geophys. Res. Lett., 42, 2071-2078.<br>Held, I.M., and M.J. Suarez, 1994: A Proposal for the Intercomparison of the Dynamical Cores of Atmospheric General Circulation Models. Bull. Amer. Meteor. Soc., 75, 1825-1830.<br>O’Neill, W.P., and R. Klein, 2014: A moist pseudo-incompressible model. Atmos. Res., 142, 133-141. Plougonven R., and F. Zhang, 2014: Internal gravity waves from atmospheric jets and fronts. Rev. Geophys., 52, 33-76.<br>Rieper, F., Hickel, S., and U. Achatz, 2013: A conservative integration of the pseudo-incompressible equations with implicit turbulence parameterization. Mon. Wea. Rev., 141, 861-886. Smolarkiewicz, P.K., and L.G. Margolin, 1997: On forward-in-time differencing for fluids: an Eulerian/semi-Langrangian nonhydrostatic model for stratified flows. Atmosphere-Ocean, 35, 127- 152.</p> </div> </div> </div>

Toward transient subgrid-scale gravity wave representation in atmospheric models. Part I: Propagation model including non-dissipative direct wave-mean-flow interactions

2021 ◽  
Author(s):  
Gergely Bölöni ◽  
Young-Ha Kim ◽  
Sebastian Borchert ◽  
Ulrich Achatz
Keyword(s):  
Steady State ◽  
Gravity Wave ◽  
Climate Model ◽  
Propagation Model ◽  
Small Scale ◽  
Mean Flow ◽  
Direct Wave ◽  
Steady State Assumption ◽  
Flow Interactions ◽  
State Assumption

AbstractCurrent gravity-wave (GW) parameterization (GWP) schemes are using the steady-state assumption, where an instantaneous balance between GWs and mean flow is postulated, thereby neglecting transient, non-dissipative direct interactions between the GW field and the resolved flow. These schemes rely exclusively on wave dissipation, by GW breaking or near critical layers, as a mechanism leading to forcing of the mean flow. In a transient GWP, without steady-state assumption, non-dissipative direct wave-mean-flow interactions are enabled as an additional mechanism. Idealized studies have shown that this is potentially important, so that the transient GWP Multi-Scale Gravity-Wave Model (MS-GWaM) has been implemented into a state-of-the-art weather and climate model. In this implementation, MS-GWaM leads to a zonal-mean circulation well in agreement with observations, and increases GW momentum-flux intermittency as compared to steady-state GWPs, bringing it into better agreement with super-pressure balloon observations. Transient effects taken into account by MS-GWaM are shown to make a difference even on monthly time-scales: in comparison with steady-state GWPs momentum fluxes in the lower stratosphere are increased and the amount of the missing drag at Southern Hemispheric high latitudes is decreased to a modest but non-negligible extent. An analysis of the contribution of different wavelengths to the GW signal in MS-GWaM suggests that small scale GWs play an important role down to horizontal and vertical wavelengths of 50km (or even smaller) and 200m respectively.

scholarly journals Revisiting the Quasi Biennial Oscillation as Seen in ERA5. Part I: Description and Momentum Budget

2020 ◽  
Author(s):  
Hamid A. Pahlavan ◽  
Qiang Fu ◽  
John M. Wallace ◽  
George N. Kiladis
Keyword(s):  
Shear Zones ◽  
Small Scale ◽  
Mean Flow ◽  
Quasi Biennial Oscillation ◽  
Wave Forcing ◽  
Momentum Budget ◽  
Flow Interactions ◽  
Mean Fields ◽  
Mean Meridional Circulation ◽  
Biennial Oscillation

AbstractThe dynamics and momentum budget of the quasi-biennial oscillation (QBO) are examined in the ERA5 reanalysis. Because of ERA5’s higher spatial resolution compared to its predecessors, it is capable of resolving a broader spectrum of atmospheric waves and allows for a better representation of the wave-mean flow interactions, both of which are of crucial importance for QBO studies. It is shown that the QBO-induced mean meridional circulation, which is mainly confined to the winter hemisphere, is strong enough to interrupt the tropical upwelling during the descent of the westerly shear zones. Since the momentum advection tends to damp the QBO, the wave forcing is responsible for both the downward propagation and for the maintenance of the QBO. It is shown that half the required wave forcing is provided by resolved waves during the descent of both westerly and easterly regimes. Planetary-scale waves account for most of the resolved wave forcing of the descent of westerly shear zones and small-scale gravity (SSG) waves with wavelengths shorter than 2000 km account for the remainder. SSG waves account for most of the resolved forcing of the descent of the easterly shear zones. The representation of the mean fields in the QBO is very similar in ERA5 and ERA-I but the resolved wave forcing is substantially stronger in ERA5. The contributions of the various equatorially-trapped wave modes to the QBO forcing are documented in Part II.

Towards a transient gravity wave parametrization in atmospheric models

2021 ◽  
Author(s):  
Georg Sebastian Voelker ◽  
Gergely Bölöni ◽  
Young-Ha Kim ◽  
Ulrich Achatz
Keyword(s):  
Gravity Wave ◽  
Prediction Models ◽  
Weather Prediction ◽  
Potential Temperature ◽  
Internal Gravity Waves ◽  
Wave Drag ◽  
Mean Flow ◽  
Direct Wave ◽  
Flow Interactions ◽  
The Mean

<p>Subgrid-scale internal gravity waves (IGWs) are important distributors of energy in a stratified atmosphere. While they are mostly excited at lower altitudes their effects are most important between the upper troposphere to the mesopause (~85km). During propagation–both in the vertical and the horizontal–nonlinear IGWs can exert a wave drag on the mean winds, interact with the mean potential temperature, and mix atmospheric tracers such as aerosols or greenhouse gases.</p> <p>In state-of-the art weather prediction models IGWs are typically parametrized using the single-column and the steady-state assumptions. These parametrizations take into account dissipative effects of IGWs but neglect their horizontal propagation and all of their transient interaction mechanisms such as direct wave-mean-flow interactions. However, the latter have been shown to contribute to IGW dynamics in various idealized studies.</p> <p>Here we present advances of the use of the transient Multi Scale Gravity Wave Model (MS-GWaM) in the upper atmosphere model UA-ICON. Based on Lagrangian ray-tracing the parametrization includes various non-orographic wave sources, transient propagation in both the horizontal and vertical directions, direct wave-mean-flow interactions and wave breaking. The resulting setup satisfactorily reproduces the observed mean-wind and potential temperature climatology and already shows promising insights into the details of the role of IGWs in the atmosphere.</p>

The acoustics of turbulence near sound-absorbent liners

1972 ◽  
Vol 51 (4) ◽  
pp. 737-749 ◽  
Author(s):  
John E. Ffowcs Williams
Keyword(s):  
Acoustic Properties ◽  
Plane Boundary ◽  
Fourth Power ◽  
Small Scale ◽  
Generation Process ◽  
Mean Flow ◽  
Acoustic Liners ◽  
Rigid Plane ◽  
Flow Effects ◽  
Scale Turbulence

Acoustic liners are often perforated screens backed by sound-absorbent material. Turbulence can interact with these screens to generate additional sound. The dynamics of the generation process is examined in this paper, where the liner is modelled as an infinite rigid plane boundary with a homogeneous array of circular orifices or rigid pistons. The acoustic properties of these boundaries are derived in the long wavelength limit. Small-scale turbulence is scattered by individual apertures into sound. Acoustically transparent surfaces support dipole scattering centres while more ‘opaque’ surfaces have monopoles at the apertures which convert turbulence into sound more effectively. It is shown that the process can be described once the response of an individual aperture in an infinite baffle is known. At low Mach numbers the screen can increase the sound radiated by adjacent turbulence by a factor equal to the inverse fourth power of the Mach number. Mean-flow effects are ignored but they are thought to increase the effects deduced in this preliminary study.

scholarly journals Sudden Stratospheric Warmings as Noise-Induced Transitions

2008 ◽  
Vol 65 (10) ◽  
pp. 3337-3343 ◽  
Author(s):  
Thomas Birner ◽  
Paul D. Williams
Keyword(s):  
Gravity Wave ◽  
Stochastic System ◽  
Planetary Wave ◽  
Planck Equation ◽  
Momentum Equation ◽  
Wave Activity ◽  
Small Scale ◽  
Deterministic System ◽  
Mean Flow ◽  
Mass Model

Sudden stratospheric warmings (SSWs) are usually considered to be initiated by planetary wave activity. Here it is asked whether small-scale variability (e.g., related to gravity waves) can lead to SSWs given a certain amount of planetary wave activity that is by itself not sufficient to cause a SSW. A highly vertically truncated version of the Holton–Mass model of stratospheric wave–mean flow interaction, recently proposed by Ruzmaikin et al., is extended to include stochastic forcing. In the deterministic setting, this low-order model exhibits multiple stable equilibria corresponding to the undisturbed vortex and SSW state, respectively. Momentum forcing due to quasi-random gravity wave activity is introduced as an additive noise term in the zonal momentum equation. Two distinct approaches are pursued to study the stochastic system. First, the system, initialized at the undisturbed state, is numerically integrated many times to derive statistics of first passage times of the system undergoing a transition to the SSW state. Second, the Fokker–Planck equation corresponding to the stochastic system is solved numerically to derive the stationary probability density function of the system. Both approaches show that even small to moderate strengths of the stochastic gravity wave forcing can be sufficient to cause a SSW for cases for which the deterministic system would not have predicted a SSW.

Forecasting of Tornadoes and Downbursts

2020 ◽  
Author(s):  
Djordje Romanic
Keyword(s):  
Chaos Theory ◽  
Prediction Models ◽  
Weather Prediction ◽  
Small Scale ◽  
Weather Forecasts ◽  
Wind Speeds ◽  
The Past ◽  
Extreme Wind ◽  
Extreme Wind Speeds ◽  
Numerical Weather Prediction Models

Tornadoes and downbursts cause extreme wind speeds that often present a threat to human safety, structures, and the environment. While the accuracy of weather forecasts has increased manifold over the past several decades, the current numerical weather prediction models are still not capable of explicitly resolving tornadoes and small-scale downbursts in their operational applications. This chapter describes some of the physical (e.g., tornadogenesis and downburst formation), mathematical (e.g., chaos theory), and computational (e.g., grid resolution) challenges that meteorologists currently face in tornado and downburst forecasting.

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