scholarly journals Gravity Wave Instability Dynamics at High Reynolds Numbers. Part II: Turbulence Evolution, Structure, and Anisotropy

2009 ◽  
Vol 66 (5) ◽  
pp. 1149-1171 ◽  
Author(s):  
David C. Fritts ◽  
Ling Wang ◽  
Joe Werne ◽  
Tom Lund ◽  
Kam Wan
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Wave Breaking ◽  
Spatial Scales ◽  
Reynolds Numbers ◽  
Inertial Range ◽  
Stable Phase ◽  
Wave Instability ◽  
Intrinsic Frequency ◽  
High Reynolds

Abstract This paper examines the character, intermittency, and anisotropy of turbulence accompanying wave instability, breaking, and turbulence evolution and decay for gravity waves (GW) having a high intrinsic frequency, amplitudes above and below nominal convective instability, and a high Reynolds number. Wave breaking at both amplitudes leads to an extended inertial range of turbulence, with turbulence energies that maximize within ∼1 wave period of the onset of breaking. Turbulence sources include both shear and buoyancy, with shear being the major contributor. Turbulence displays considerable intermittency both within and across the phase of the breaking gravity wave and exhibits clear anisotropy throughout the evolution. Turbulence anisotropy is found at all spatial scales and all times but is most pronounced in the most statically stable phase of the GW and at late times as the turbulent flow restratifies.

scholarly journals Gravity Wave Instability Dynamics at High Reynolds Numbers. Part I: Wave Field Evolution at Large Amplitudes and High Frequencies

2009 ◽  
Vol 66 (5) ◽  
pp. 1126-1148 ◽  
Author(s):  
David C. Fritts ◽  
Ling Wang ◽  
Joe Werne ◽  
Tom Lund ◽  
Kam Wan
Keyword(s):  
Gravity Wave ◽  
Wave Breaking ◽  
Wave Amplitude ◽  
Potential Temperature ◽  
Primary Wave ◽  
Wave Instability ◽  
Frequency Wave ◽  
Turbulence Structures ◽  
Developed Turbulence ◽  
High Reynolds

Abstract Direct numerical simulations are employed to examine gravity wave instability dynamics at a high intrinsic frequency, wave amplitudes both above and below nominal convective instability, and a Reynolds number sufficiently high to allow a fully developed turbulence spectrum. Assumptions include no mean shear, uniform stratification, and a monochromatic gravity wave to isolate fluxes due to gravity wave and turbulence structures from those arising from environmental shears or varying wave amplitudes. The results reveal strong wave breaking for both wave amplitudes, severe primary wave amplitude reductions within ∼1 or 2 wave periods, an extended turbulence inertial range, significant excitation of additional wave motions exhibiting upward and downward propagation, and a net positive vertical potential temperature flux due to the primary wave motion, with secondary waves and turbulence contributing variable and negative potential temperature fluxes, respectively. Turbulence maximizes within ∼1 buoyancy period of the onset of breaking, arises almost entirely owing to shear production, and decays rapidly following primary wave amplitude decay. Secondary waves are excited by wave–wave interactions and the turbulence dynamics accompanying wave breaking; they typically have lower frequencies and smaller momentum fluxes than the primary wave following breaking.

Gravity wave intermittency derived from HIRDLS and SABER satellite limb soundings

2020 ◽  
Author(s):  
Manfred Ern ◽  
Peter Preusse ◽  
Martin Riese
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Climate Models ◽  
Spatial Scales ◽  
Wave Activity ◽  
Background Flow ◽  
Wave Source ◽  
Gini Coefficients ◽  
Broadband Emission ◽  
Wave Distribution

<p>Sources of atmospheric gravity waves are mostly located in the troposphere and the lower stratosphere. Gravity waves propagate away from their sources, re-distribute energy and momentum in the atmosphere, and exert drag on the atmospheric background flow where they dissipate. Therefore they are important drivers of the atmospheric circulation. In climate models, their effect on the background circulation is usually parameterized because of their relatively short horizontal and vertical wavelengths that are of the order of 10-1000km and 1-100km, respectively. Gravity wave parametrizations are very simplified. For example, they often neglect the fact that gravity wave source processes and gravity wave propagation conditions can vary on short temporal and spatial scales. Therefore the global distribution of gravity wave activity is very intermittent, which has also important consequences where gravity waves dissipate and exert drag on the background flow, and which should be accounted for in parametrizations.<br>For guiding models, global observations of the gravity wave distribution and its intermittency are needed. We derive gravity wave potential energies and absolute momentum fluxes from observations of the High Resolution Dynamics Limb Sounder (HIRDLS) and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instruments. As a measure of intermittency, we calculate global distributions of Gini coefficients. We find that our results are qualitatively in good agreement with previous findings from satellite, and similar in magnitude to intermittency obtained from previous superpressure balloon campaigns. In the stratosphere, strongest intermittency is found over orographic gravity wave sources, followed by gravity wave activity in the polar night jets. Intermittency in the tropical stratosphere is weakest. However, in the tropical upper mesosphere intermittency is increased, which is likely caused by the modulation of the gravity wave distribution by tides.</p>

scholarly journals Seasonal and nightly variations of gravity-wave energy density in the middle atmosphere measured by the Purple Crow Lidar

2007 ◽  
Vol 25 (10) ◽  
pp. 2139-2145 ◽  
Author(s):  
R. J. Sica ◽  
P. S. Argall
Keyword(s):  
Energy Density ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Wave Energy ◽  
Numerical Models ◽  
Spatial Scales ◽  
Density Fluctuations ◽  
Kinetic Energy Density ◽  
Large Power ◽  
Wave Energy Density

Abstract. The Purple Crow Lidar (PCL) is a large power-aperture product monostatic Rayleigh-Raman-Sodium-resonance-fluorescence lidar, which has been in operation at the Delaware Observatory (42.9° N, 81.4° W, 237 m elevation) near the campus of The University of Western Ontario since 1992. Kinetic-energy density has been calculated from the Rayleigh-scatter system measurements of density fluctuations at temporal-spatial scales relevant for gravity waves, e.g. soundings at 288 m height resolution and 9 min temporal resolution in the upper stratosphere and mesosphere. The seasonal averages from 10 years of measurements show in all seasons some loss of gravity-wave energy in the upper stratosphere. During the equinox periods and summer the measurements are consistent with gravity waves growing in height with little saturation, in agreement with the classic picture of the variations in the height at which gravity waves break given by Lindzen (1981). The mean values compare favourably to previous measurements when computed as nightly averages, but the high temporal-spatial resolution measurements show considerable day-to-day variability. The variability over a night is often extremely large, with typical RMS fluctuations of 50 to 100% at all heights and seasons common. These measurements imply that using a daily or nightly-averaged gravity-wave energy density in numerical models may be highly unrealistic.

scholarly journals Dynamics of helicity in homogeneous skew-isotropic turbulence

2017 ◽  
Vol 821 ◽  
pp. 539-581 ◽  
Author(s):  
Antoine Briard ◽  
Thomas Gomez
Keyword(s):  
Kinetic Energy ◽  
Isotropic Turbulence ◽  
Early Stage ◽  
Helical Structure ◽  
Reynolds Numbers ◽  
Inertial Range ◽  
Scalar Flux ◽  
Antisymmetric Part ◽  
Decaying Turbulence ◽  
High Reynolds

The dynamics of helicity in homogeneous skew-isotropic freely decaying turbulence is investigated, at very high Reynolds numbers, thanks to a classical eddy-damped quasi-normal Markovian (EDQNM) closure. In agreement with previous direct numerical simulations, a $k^{-5/3}$ inertial range is obtained for both the kinetic energy and helical spectra. In the early stage of the decay, when kinetic energy, initially only present at large scales cascades towards small scales, it is found that helicity slightly slows down the nonlinear transfers. Then, when the turbulence is fully developed, theoretical decay exponents are derived and assessed numerically for helicity. Furthermore, it is found that the presence of helicity does not modify the decay rate of the kinetic energy with respect to purely isotropic turbulence, except in Batchelor turbulence where the kinetic energy decays slightly more rapidly. In this case, non-local expansions are used to show analytically that the permanence of the large eddies hypothesis is verified for the helical spectrum, unlike the kinetic energy one. Moreover, the $4/3$ law for the two-point helical structure function is assessed numerically at very large Reynolds numbers. Afterwards, the evolution equation of the helicity dissipation rate is investigated analytically, which provides significant simplifications and leads notably to the definition of a helical derivative skewness and of a helical Taylor scale, which is numerically very close to the classical Taylor longitudinal scale at large Reynolds numbers. Finally, when both a mean scalar gradient and helicity are combined, the quadrature spectrum, linked to the antisymmetric part of the scalar flux, appears and scales like $k^{-7/3}$ and then like $k^{-5/3}$ in the inertial range.

scholarly journals Dynamics of Orographic Gravity Waves Observed in the Mesosphere over the Auckland Islands during the Deep Propagating Gravity Wave Experiment (DEEPWAVE)

2016 ◽  
Vol 73 (10) ◽  
pp. 3855-3876 ◽  
Author(s):  
Stephen D. Eckermann ◽  
Dave Broutman ◽  
Jun Ma ◽  
James D. Doyle ◽  
Pierre-Dominique Pautet ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Wave Breaking ◽  
Large Amplitude ◽  
Middle Atmosphere ◽  
Three Dimensional ◽  
Surface Flow ◽  
Heating Rates ◽  
Wave Fields ◽  
Wave Experiment

Abstract On 14 July 2014 during the Deep Propagating Gravity Wave Experiment (DEEPWAVE), aircraft remote sensing instruments detected large-amplitude gravity wave oscillations within mesospheric airglow and sodium layers at altitudes z ~ 78–83 km downstream of the Auckland Islands, located ~1000 km south of Christchurch, New Zealand. A high-altitude reanalysis and a three-dimensional Fourier gravity wave model are used to investigate the dynamics of this event. At 0700 UTC when the first observations were made, surface flow across the islands’ terrain generated linear three-dimensional wave fields that propagated rapidly to z ~ 78 km, where intense breaking occurred in a narrow layer beneath a zero-wind region at z ~ 83 km. In the following hours, the altitude of weak winds descended under the influence of a large-amplitude migrating semidiurnal tide, leading to intense breaking of these wave fields in subsequent observations starting at 1000 UTC. The linear Fourier model constrained by upstream reanalysis reproduces the salient aspects of observed wave fields, including horizontal wavelengths, phase orientations, temperature and vertical displacement amplitudes, heights and locations of incipient wave breaking, and momentum fluxes. Wave breaking has huge effects on local circulations, with inferred layer-averaged westward flow accelerations of ~350 m s−1 h−1 and dynamical heating rates of ~8 K h−1, supporting recent speculation of important impacts of orographic gravity waves from subantarctic islands on the mean circulation and climate of the middle atmosphere during austral winter.

scholarly journals Revisiting Batchelor's theory of two-dimensional turbulence

2007 ◽  
Vol 591 ◽  
pp. 379-391 ◽  
Author(s):  
DAVID G. DRITSCHEL ◽  
CHUONG V. TRAN ◽  
RICHARD K. SCOTT
Keyword(s):  
Reynolds Number ◽  
Mathematical Analysis ◽  
High Reynolds Number ◽  
Reynolds Numbers ◽  
Inertial Range ◽  
Two Dimensional ◽  
Simple Modification ◽  
High Reynolds Numbers ◽  
Decaying Turbulence ◽  
High Reynolds

Recent mathematical results have shown that a central assumption in the theory of two-dimensional turbulence proposed by Batchelor (Phys. Fluids, vol. 12, 1969, p. 233) is false. That theory, which predicts a χ2/3k−1 enstrophy spectrum in the inertial range of freely-decaying turbulence, and which has evidently been successful in describing certain aspects of numerical simulations at high Reynolds numbers Re, assumes that there is a finite, non-zero enstrophy dissipation χ in the limit of infinite Re. This, however, is not true for flows having finite vorticity. The enstrophy dissipation in fact vanishes.We revisit Batchelor's theory and propose a simple modification of it to ensure vanishing χ in the limit Re → ∞. Our proposal is supported by high Reynolds number simulations which confirm that χ decays like 1/ln Re, and which, following the time of peak enstrophy dissipation, exhibit enstrophy spectra containing an increasing proportion of the total enstrophy 〈ω2〉/2 in the inertial range as Re increases. Together with the mathematical analysis of vanishing χ, these observations motivate a straightforward and, indeed, alarmingly simple modification of Batchelor's theory: just replace Batchelor's enstrophy spectrum χ2/3k−1 with 〈ω2〉 k−1 (ln Re)−1).

scholarly journals Gravity wave penetration into the thermosphere: sensitivity to solar cycle variations and mean winds

2008 ◽  
Vol 26 (12) ◽  
pp. 3841-3861 ◽  
Author(s):  
D. C. Fritts ◽  
S. L. Vadas
Keyword(s):  
Solar Cycle ◽  
Gravity Wave ◽  
Gravity Waves ◽  
Spatial Scales ◽  
Phase Speed ◽  
Wave Structure ◽  
Lower Atmosphere ◽  
Viscous Effects ◽  
Wave Source ◽  
Wave Phase

Abstract. We previously considered various aspects of gravity wave penetration and effects at mesospheric and thermospheric altitudes, including propagation, viscous effects on wave structure, characteristics, and damping, local body forcing, responses to solar cycle temperature variations, and filtering by mean winds. Several of these efforts focused on gravity waves arising from deep convection or in situ body forcing accompanying wave dissipation. Here we generalize these results to a broad range of gravity wave phase speeds, spatial scales, and intrinsic frequencies in order to address all of the major gravity wave sources in the lower atmosphere potentially impacting the thermosphere. We show how penetration altitudes depend on gravity wave phase speed, horizontal and vertical wavelengths, and observed frequencies for a range of thermospheric temperatures spanning realistic solar conditions and winds spanning reasonable mean and tidal amplitudes. Our results emphasize that independent of gravity wave source, thermospheric temperature, and filtering conditions, those gravity waves that penetrate to the highest altitudes have increasing vertical wavelengths and decreasing intrinsic frequencies with increasing altitude. The spatial scales at the highest altitudes at which gravity wave perturbations are observed are inevitably horizontal wavelengths of ~150 to 1000 km and vertical wavelengths of ~150 to 500 km or more, with the larger horizontal scales only becoming important for the stronger Doppler-shifting conditions. Observed and intrinsic periods are typically ~10 to 60 min and ~10 to 30 min, respectively, with the intrinsic periods shorter at the highest altitudes because of preferential penetration of GWs that are up-shifted in frequency by thermospheric winds.

scholarly journals Lagrangian Gravity Wave spectra in the lower stratosphere of current (re)analyses

2020 ◽  
Author(s):  
Aurélien Podglajen ◽  
Albert Hertzog ◽  
Riwal Plougonven ◽  
Bernard Legras
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Lower Stratosphere ◽  
Weather Prediction ◽  
Low Frequency ◽  
Vertical Wind ◽  
Temperature Fields ◽  
Intrinsic Frequency ◽  
Telecommunication System ◽  
Global Telecommunication System

Abstract. Due to their increasing spatial resolution, numerical weather prediction (NWP) models and the associated analyses resolve a growing fraction of the gravity wave (GW) spectrum. However, it is unclear how well this resolved part of the spectrum actually compares to the actual atmospheric variability. In particular, the Lagrangian variability, relevant, e.g., to atmospheric dispersion and to microphysical modeling in the Upper Troposphere-Lower Stratosphere (UTLS), has not yet been documented in recent products. To address this shortcoming, this paper presents an assessment of the GW spectrum as a function of the intrinsic (air parcel following) frequency in recent (re)analyses (ERA-interim, ERA5, the ECMWF operational analysis, MERRA-2 and JRA-55). Long-duration, quasi-Lagrangian balloon observations in the equatorial and Antarctic lower stratosphere are used as a reference for the atmospheric spectrum and compared to synthetic balloon observations along trajectories calculated using the wind and temperature fields of the reanalyses. Overall, the reanalyses represent realistic features of the spectrum, notably the spectral gap between planetary and gravity waves and a peak in horizontal kinetic energy associated with inertial waves near f in the polar region. In the tropics, they represent the slope of the spectrum at low frequency. However, the variability is generally underestimated, even in the low-frequency portion of the spectrum. In particular, the near-inertial peak, although present in the reanalyses, has a much reduced magnitude compared to balloon observations. We compare the variability of temperature, momentum flux and vertical wind speed, which are related to low, mid and high frequency waves, respectively. The distributions (PDFs) have similar shapes, but show increasing disagreement with increasing intrinsic frequency. Since at those altitudes they are mainly caused by gravity waves, we also compare the geographic distribution of vertical wind fluctuations in the different products, which emphasizes the increase of both GW variance and intermittency with horizontal resolution. Finally, we quantify the fraction of resolved variability and its dependency on model resolution for the different variables. In all (re)analyses products, a significant part of the variability is still missing and should hence be parameterized, in particular at high intrinsic frequency. Among the two polar balloon datasets used, one was broadcast on the global telecommunication system for assimilation in analyses while the other is made of independent observations (unassimilated in the reanalyses). Comparing the Lagrangian spectra between the two campaigns shows that they are largely influenced by balloon data assimilation, which especially enhances the variance at low frequency.

scholarly journals The MATS satellite mission – gravity wave studies by Mesospheric Airglow/Aerosol Tomography and Spectroscopy

2020 ◽  
Vol 20 (1) ◽  
pp. 431-455 ◽  
Author(s):  
Jörg Gumbel ◽  
Linda Megner ◽  
Ole Martin Christensen ◽  
Nickolay Ivchenko ◽  
Donal P. Murtagh ◽  
...  
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Near Infrared ◽  
Spatial Scales ◽  
Lower Thermosphere ◽  
Three Dimensional ◽  
Mean Flow ◽  
Satellite Mission ◽  
Cloud Properties ◽  
Mesosphere And Lower Thermosphere

Abstract. Global three-dimensional data are a key to understanding gravity waves in the mesosphere and lower thermosphere. MATS (Mesospheric Airglow/Aerosol Tomography and Spectroscopy) is a new Swedish satellite mission that addresses this need. It applies space-borne limb imaging in combination with tomographic and spectroscopic analysis to obtain gravity wave data on relevant spatial scales. Primary measurement targets are O2 atmospheric band dayglow and nightglow in the near infrared, and sunlight scattered from noctilucent clouds in the ultraviolet. While tomography provides horizontally and vertically resolved data, spectroscopy allows analysis in terms of mesospheric temperature, composition, and cloud properties. Based on these dynamical tracers, MATS will produce a climatology on wave spectra during a 2-year mission. Major scientific objectives include a characterization of gravity waves and their interaction with larger-scale waves and mean flow in the mesosphere and lower thermosphere, as well as their relationship to dynamical conditions in the lower and upper atmosphere. MATS is currently being prepared to be ready for a launch in 2020. This paper provides an overview of scientific goals, measurement concepts, instruments, and analysis ideas.

scholarly journals Ozone-Gravity Wave Interaction in the Upper Stratosphere/Lower Mesosphere

2022 ◽  
Author(s):  
Axel Gabriel
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
General Circulation ◽  
Low Frequency ◽  
Wave Interaction ◽  
General Circulation Models ◽  
Intrinsic Frequency ◽  
Night Time ◽  
Ozone Photochemistry ◽  
Middle Stratosphere

Abstract. The increase in amplitudes of upward propagating gravity waves (GWs) with height due to decreasing density is usually described by exponential growth; however, recent measurements detected a much stronger increase in gravity wave potential energy density (GWPED) during daylight than night-time (increase by a factor of about 4 to 8 between middle stratosphere and upper mesosphere), which is not well understood up to now. This paper suggests that ozone-gravity wave interaction in the upper stratosphere/lower mesosphere is largely responsible for this phenomenon. The coupling between ozone-photochemistry and temperature is particularly strong in the upper stratosphere where the time-mean ozone mixing ratio is decreasing with height; therefore, an initial uplift of an air parcel must lead to a local increase in ozone and in the heating rate compared to the environment, and, hence, to an amplification of the initial uplift. Standard solutions of upward propagating GWs with linear ozone-temperature coupling are formulated suggesting local amplitude amplifications during daylight of 5 to 15 % for low-frequency GWs (periods ≥4 hours), as a function of the intrinsic frequency which decreases if ozone-temperature coupling is included. Subsequently, for horizontal wavelengths larger than 500 km and vertical wavelengths smaller than 5 km, the cumulative amplification during the upward level-by-level propagation leads to much stronger amplitudes in the GW perturbations (factor of about 1.5 to 3) and in the GWPED (factor of about 3 to 9) at upper mesospheric altitudes. The results open a new viewpoint for improving general circulation models with resolved or parameterized GWs.

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