Effects Of Internal Gravity Waves Research Articles

Stability of the 2D anisotropic Boussinesq equations with mixed partial dissipation

Stability is an important property of solutions to many fluid flow equations. In this paper, we focus on the stability problem for two-dimensional Boussinesq equations with only vertical viscosity and horizontal thermal diffusion near a stratified, hydrostatic equilibrium in the domain Ω=T×R, where T=[−12,12] is a 1D periodic box. We are mainly concerned with the H2-stability of global solutions when the initial data are closed to an equilibrium state and sufficiently small. Due to the lack of horizontal viscosity in velocity equations and vertical thermal diffusion in temperature equation, this problem seems to be not trivial and becomes particularly difficult. In order to achieve our main goal, we divide the velocity field and temperature into two parts: the horizontal average and the remaining oscillation part. Besides, we fully exploit the Lt2Lx2-norm of ∂xu2 to help us dominate the nonlinear parts. Our result shows that with a small initial perturbation, there exists a unique global solution to the stated Boussinesq equations. In addition, the perturbation remains small for all time. In particular, our result also demonstrates the stabilizing effect of internal gravity waves, which are induced by the stratified background hydrostatic state.

Infrasound generated by meteorological fronts: Observations and modeling

The results of study of the parameters of infrasound waves (amplitudes, coherences, grazing angles, azimuths, and horizontal phase speeds) detected during a passage of warm and cold fronts through the networks of microbarometers in Moscow region are presented. The observed effect of internal gravity waves on the coherence and phase speed of infrasound from meteorological fronts is analyzed. The differences found in the time dependences of the parameters of infrasound from warm and cold fronts that must be taken into account when detecting infrasound precursors of atmospheric storms are discussed. A possible mechanism for the generation of infrasound by the turbulent airstream flowing around the geometric irregularities of the meteorological front is proposed. [This work was supported by the Russian Science Foundation, Grant No. 21-17-00021.]

Physics-informed neural networks for predicting ocean spatio-temporal fields

Simulations of the ocean environment are important for assessing acoustic variability due to large and small scale changes in the propagation medium. By incorporating the Internal Gravity Waves (IGWs) partial differential equation (PDE) in ocean models, such as the HYbrid Coordinate Ocean Model (HYCOM) system, it is possible to model the impact of tides on acoustic propagation. This requires HYCOM simulations of the ocean environment, which are computationally expensive, especially at the high vertical resolutions required to capture IGWs. In this work, we develop a machine-learning approach to predicting the effects of IGWs without incurring the computational cost of high-resolution numerical modeling. We apply a deep-learning approach in the form of a Physics Informed Neural Network (PINN) that incorporates the IGW PDE system to make predictions about oceanographic quantities of interest with internal tides at high vertical resolution. Training data comprise HYCOM 4D fields (time, depth, latitude, and longitude) both with (IGW-HYCOM) and without tides in the Pacific subtropical/equatorial region. The developed framework is able to map a relationship between lower-resolution HYCOM inputs to highly resolved ocean fields that include internal tides.

Infrasound Generation by Meteorological Fronts and Its Propagation in the Atmosphere

AbstractInfrasound parameters (amplitudes, coherences, grazing angles, azimuths, and horizontal phase speeds) derived during the passage of warm and cold fronts through the networks of microbarometers in the cities of Dubna and Moscow are presented. The significant differences observed in the temporal variations of the parameters of infrasound from warm and cold fronts are discussed. Such differences must be taken into account when detecting infrasound precursors of atmospheric storms. A possible mechanism for the generation of infrasound by the turbulent airstream flowing around the geometric irregularities of the meteorological front is proposed. The observed effect of internal gravity waves on the parameters of infrasound and its frequency spectrum is explained.

The effect of internal gravity waves on cloud evolution in sub-stellar atmospheres

Context. Sub-stellar objects exhibit photometric variability, which is believed to be caused by a number of processes, such as magnetically-driven spots or inhomogeneous cloud coverage. Recent sub-stellar models have shown that turbulent flows and waves, including internal gravity waves, may play an important role in cloud evolution. Aims. The aim of this paper is to investigate the effect of internal gravity waves on dust nucleation and dust growth, and whether observations of the resulting cloud structures could be used to recover atmospheric density information. Methods. For a simplified atmosphere in two dimensions, we numerically solved the governing fluid equations to simulate the effect on dust nucleation and mantle growth as a result of the passage of an internal gravity wave. Furthermore, we derived an expression that relates the properties of the wave-induced cloud structures to observable parameters in order to deduce the atmospheric density. Results. Numerical simulations show that the density, pressure, and temperature variations caused by gravity waves lead to an increase of the dust nucleation rate by up to a factor 20, and an increase of the dust mantle growth rate by up to a factor 1.6, compared to their equilibrium values. Through an exploration of the wider sub-stellar parameter space, we show that in absolute terms, the increase in dust nucleation due to internal gravity waves is stronger in cooler (T dwarfs) and TiO2-rich sub-stellar atmospheres. The relative increase, however, is greater in warm (L dwarf) and TiO2-poor atmospheres due to conditions that are less suited for efficient nucleation at equilibrium. These variations lead to banded areas in which dust formation is much more pronounced, similar to the cloud structures observed on Earth. Conclusions. We show that internal gravity waves propagating in the atmosphere of sub-stellar objects can produce banded clouds structures similar to that observed on Earth. We propose a method with which potential observations of banded clouds could be used to estimate the atmospheric density of sub-stellar objects.

Search for Atmospheric Wave Signatures by Simultaneous Collocated Barometer and Gravimeter Measurements

A spatial distribution model for air density perturbations during the propagation of internal gravity waves (IGWs) is used to derive estimates for gravity perturbations generated by these waves. The estimates show that superconducting gravimeters are capable of detecting IGWs generated by any wave source in the lower atmosphere. Series of barometric and gravimetric measurements at Moxa, Germany (50.6° N, 11.6° E), for 2000–2018 are processed using digital filtering to search for pressure and gravity perturbations with time scales of ~10 min to ~10 h. The annual change in the atmospheric pressure variation with variation scales on the order of and less than 1 h shows a summer maximum, which disappears at higher scales. The summer maximum can be attributed to the effect of IGWs with periods on the order of and less than 1 h from convective clouds that occur in the summer half of the year. The annual change in the gravity variation shows maximums in winter and summer for all the variation scales under consideration. They can be explained by modulating the solar semidiurnal gravitational tide by a semiannual change in the perturbation of the Earth’s gravitational potential.

The Effect of Internal Gravity Waves on Fluctuations in Meteorological Parameters of the Atmospheric Boundary Layer

Variations in the intensity of turbulence during wave activity in the stable atmospheric boundary layer over a homogeneous steppe surface have been analyzed. Eight wave activity episodes recorded with a Doppler sodar in August 2015 at the Tsimlyansk Scientific Station of the Obukhov Institute of Atmospheric Physics have been studied. These episodes include seven trains of Kelvin–Helmholtz waves and one train of buoyancy waves. Variations in the rms deviation of the vertical wind-velocity component, the temperature structure parameter, and vertical heat and momentum fluxes have been estimated for each episode of wave activity. It has been found that Kelvin–Helmholtz waves slightly affect the intensity of turbulence, while buoyancy waves cause the temperature structure parameter and the vertical fluxes to increase by more than an order of magnitude.

Can plume-induced internal gravity waves regulate the core rotation of subgiant stars?

Context.The seismic data provided by the space-borne missions CoRoT andKeplerenabled us to probe the internal rotation of thousands of evolved low-mass stars. Subsequently, several studies showed that current stellar evolution codes are unable to reproduce the low core rotation rates observed in these stars. These results indicate that an additional angular momentum transport process is necessary to counteract the spin up due to the core contraction during the post-main sequence evolution. For several candidates, the transport induced by internal gravity waves (IGW) could play a non-negligible role.Aims.We aim to investigate the effect of IGW generated by penetrative convection on the internal rotation of low-mass stars from the subgiant branch to the beginning of the red giant branch.Methods.A semi-analytical excitation model was used to estimate the angular momentum wave flux. The characteristic timescale associated with the angular momentum transport by IGW was computed and compared to the contraction timescale throughout the radiative region of stellar models at different evolutionary stages.Results.We show that IGW can efficiently counteract the contraction-driven spin up of the core of subgiant stars if the amplitude of the radial-differential rotation (between the center of the star and the top of the radiative zone) is higher than a threshold value. This threshold depends on the evolutionary stage and is comparable to the differential rotation rates inferred for a sample of subgiant stars observed by the satelliteKepler. Such an agreement can therefore be interpreted as the consequence of a regulation mechanism driven by IGW. This result is obtained under the assumption of a smooth rotation profile in the radiative region and holds true even if a wide range of values is considered for the parameters of the generation model. In contrast, on the red giant branch, we find that IGW remain insufficient, on their own, to explain the observations because of an excessive radiative damping.Conclusions.IGW generated by penetrative convection are able to efficiently extract angular momentum from the core of stars on the subgiant branch and accordingly have to be taken into account. Moreover, agreements with the observations reinforce the idea that their effect is essential to regulate the amplitude of the radial-differential rotation in subgiant stars. On the red giant branch, another transport mechanism must likely be invoked.

Modeling of the effect of internal gravity waves on upper atmospheric conditions during sudden stratospheric warming

We present results of modeling of the effect of internal gravity waves (IGW), excited in the region of development of a sudden stratospheric warming (SSW), on upper atmospheric conditions. In the numerical experiment, we use a two-dimensional model of propagation of atmospheric waves, taking into account dissipative and nonlinear processes accompanying wave propagation. As a source of disturbances we consider temperature and density disturbances in the stratosphere during SSWs. Amplitude and frequency characteristics of the source of disturbances are estimated from observations and IGW theory. Numerical calculations showed that waves generated at stratospheric heights during SSW can cause temperature changes in the upper atmosphere. Maximum relative disturbances, caused by such waves, with respect to quiet conditions are observed at 100–200 km. Disturbances of the upper atmosphere in turn have an effect on the dynamics of charged component in the ionosphere and can contribute to observable ionospheric effects of SSW.

Моделирование воздействия внутренних гравитационных волн на состояние верхней атмосферы в период внезапного стратосферного потепления

We present results of modeling of the effect of internal gravity waves (IGW), excited in the region of development of a sudden stratospheric warming (SSW), on upper atmospheric conditions. In the numerical experiment, we use a two-dimensional model of propagation of atmospheric waves, taking into account dissipative and nonlinear processes accompanying wave propagation. As a source of disturbances we consider temperature and density disturbances in the stratosphere during SSWs. Amplitude and frequency characteristics of the source of disturbances are estimated from observations and IGW theory. Numerical calculations showed that waves generated at stratospheric heights during SSW can cause temperature changes in the upper atmosphere. Maximum relative disturbances, generated by such waves, with respect to quiet conditions are observed at 100–200 km. Disturbances of the upper atmosphere in turn have an effect on dynamics of a charged component in the ionosphere and can contribute to observable ionospheric effects of SSW.

Vibration of structures containing compressible liquids with surface tension and sloshing effects. Reduced-order model

This paper deals with the development of the linear vibration of a general viscoelastic structure, with a local wall acoustic impedance, containing an inviscid compressible liquid (but with an additional volume dissipative term), with surface tension (capillarity) and sloshing effects, and neglecting the effects of internal gravity waves and the elastogravity operator. The sloshing problems of incompressible liquids with capillarity effects in elastic structures exhibit a major difficulty induced by the boundary contact conditions on the triple line because the capillarity forces are forces per unit length while the elastic forces are forces per unit surface. The proposed framework has the following novel features: (i) introducing a new appropriate boundary condition for the contact angle condition compatible with a deformable structure considered here as viscoelastic, (ii) considering a compressible liquid while incompressibility hypothesis is generally used for FSI problems including capillarity phenomena, and (iii) constructing a reduced-order model for the computational coupled problem.

Thermal effects of internal gravity waves in the Martian upper atmosphere

For the first time, gravity wave‐induced heating and cooling effects were fully and interactively incorporated into a Martian general circulation model (GCM). Simulations with a comprehensive GCM with an implemented spectral nonlinear gravity wave (GW) parameterization revealed significant thermal effects of GWs in the mesosphere and lower thermosphere (MLT) between 100 and 150 km. Wave‐induced heating and cooling rates are comparable with those due to near‐IR CO2 heating and IR CO2cooling, correspondingly. Accounting for thermal effects of GWs results in a colder simulated MLT, with the most of cooling taking place in middle‐ and high‐latitudes. In the winter hemisphere, the temperature decrease can exceed 45 K. The colder simulated MLT is in a good agreement with the SPICAM stellar occultation measurements and Mars Odyssey aerobraking temperature retrievals. Our experiments suggest that thermal effects of GWs are probably a key physical mechanism in the MLT missing in contemporary Martian GCMs.

Dynamical effects of internal gravity waves in the equinoctial thermosphere

Using a recently developed spectral nonlinear gravity wave (GW) parameterization implemented into a 3-D coupled general circulation model, the effects of a broad spectrum of small-scale internal GWs of lower atmospheric origin on the equinoctial thermosphere are studied for the first time. GWs propagate to F region altitudes in both hemispheres, producing appreciable drag on the mean zonal wind. Some modifications of the two-cell equinoctial mean circulation by GWs are simulated, too. The mean zonal GW drag is comparable to the ion drag up to ∼260km in the middle- and high-latitudes. While the mean dynamical effect of GWs is the deceleration of the mean flow, the instantaneous GW body force can have both signs. In the Southern Hemisphere high-latitude, GWs are found to produce large torque of more than 1000ms−1 day−1 the mechanism of which is investigated in detail. GW anisotropy plays a crucial role in offsetting and modulating wave filtering, introducing increased favourable conditions for westerly harmonics in the high-latitudes. This leads to a very large localized eastward GW drag reaching a maximum in the upper thermosphere as a consequence of enhanced molecular viscosity, thermal conduction, and ion drag. Finally, the high-latitude distribution of the GW body force is presented in the upper thermosphere along with the comparison with ion drag. It demonstrates significant interhemispheric differences and large longitudinal variations in GW momentum deposition.

Energy- and Flux-Budget Turbulence Closure Model for Stably Stratified Flows. Part II: The Role of Internal Gravity Waves

We advance our prior energy- and flux-budget (EFB) turbulence closure model for stably stratified atmospheric flow and extend it to account for an additional vertical flux of momentum and additional productions of turbulent kinetic energy (TKE), turbulent potential energy (TPE) and turbulent flux of potential temperature due to large-scale internal gravity waves (IGW). For the stationary, homogeneous regime, the first version of the EFB model disregarding large-scale IGW yielded universal dependencies of the flux Richardson number, turbulent Prandtl number, energy ratios, and normalised vertical fluxes of momentum and heat on the gradient Richardson number, Ri. Due to the large-scale IGW, these dependencies lose their universality. The maximal value of the flux Richardson number (universal constant ≈0.2–0.25 in the no-IGW regime) becomes strongly variable. In the vertically homogeneous stratification, it increases with increasing wave energy and can even exceed 1. For heterogeneous stratification, when internal gravity waves propagate towards stronger stratification, the maximal flux Richardson number decreases with increasing wave energy, reaches zero and then becomes negative. In other words, the vertical flux of potential temperature becomes counter-gradient. Internal gravity waves also reduce the anisotropy of turbulence: in contrast to the mean wind shear, which generates only horizontal TKE, internal gravity waves generate both horizontal and vertical TKE. Internal gravity waves also increase the share of TPE in the turbulent total energy (TTE = TKE + TPE). A well-known effect of internal gravity waves is their direct contribution to the vertical transport of momentum. Depending on the direction (downward or upward), internal gravity waves either strengthen or weaken the total vertical flux of momentum. Predictions from the proposed model are consistent with available data from atmospheric and laboratory experiments, direct numerical simulations and large-eddy simulations.

CNO enrichment by rotating AGB stars in globular clusters

AGB stars have long been held responsible for the important star-to-star variations in light elements observed in Galactic globular clusters. We analyse the main impacts of a first generation of rotating intermediate-mass stars on the chemical properties of second-generation globular cluster stars. The rotating models were computed without magnetic fields and without the effects of internal gravity waves. They account for the transports by meridional currents and turbulence. We computed the evolution of both standard and rotating stellar models with initial masses between 2.5 and 8 Msun within the metallicity range covered by Galactic globular clusters. During central He-burning, rotational mixing transports fresh CO-rich material from the core towards the hydrogen-burning shell, leading to the production of primary 14N. In stars more massive than M > 4 Msun, the convective envelope reaches this reservoir during the second dredge-up episode, resulting in a large increase in the total C+N+O content at the stellar surface and in the stellar wind. The corresponding pollution depends on the initial metallicity. At low- and intermediate-metallicity, it is at odds with the constancy of C+N+O observed among globular cluster low-mass stars. With the given input physics, our models suggest that massive rotating AGB stars have not shaped the abundance patterns observed in low- and intermediate-metallicity globular clusters. Our non-rotating models, on the other hands, do not predict surface C+N+O enhancements, hence are in a better position as sources of the chemical anomalies in globular clusters showing the constancy of the C+N+O. However at the moment, there is no reason to think that intermediate mass stars were not rotating.

Effects of internal gravity waves on acoustic pulse propagation in the atmospheric wave guides

Recently developed theoretical model of a random internal wave field in the atmosphere is used for calculating the statistical characteristics of the parameters of acoustic pulses propagating in the atmospheric wave guides. The variances, frequency spectra and spatial structure functions of the internal wave-associated fluctuations of the acoustic pulse travel times and grazing angles are calculated and compared to those obtained in the experiments on pulse sounding of the atmosphere. The effects analyzed here include: a scattering of acoustic waves from highly anisotropic wind speed and temperature inhomogeneities into the so-called acoustic shadow zones; a discrete character of the observed frequency spectra of the fluctuations of acoustic pulse parameters in the range 1min-1h; an error caused by internal waves in determining of the angle of arrival of the acoustic signal in the waveguide.

Improved nucleosynthetic yields

Theoretical estimates of nucleosynthesis yields are widely used to infer the meaning of abundance trends, and to predict behavior of abundances in the first stars. We show that the standard prescriptions are incomplete, and illustrate some simple improvements. We consider the effects of internal gravity waves (induced in radiative regions by convective zones) on the evolution of slowly rotating (nonrotating) stars. We demonstrate that such modifications to the standard evolutionary algorithms give better agreement with observation. They imply new phenomena: interations between carbon and oxygen burning shells, detached flames in convective layers, and intermittency, for example. We argue that such hydrodynamic behavior must be part of realistic stellar evolution. Some preliminary results for the Sun and Sirius are discussed.

Influence of Internal Gravity Waves on Counter-Gradient Heat Flux in a Thermaly Stratified Flow.

Effects of internal gravity waves on heat and momentum transfer were experimentally investigated in a strongly stably-stratified mixing layer with a temperature gradient of more than 1000 K/m. A high-resolution thermo-anemometer system gave simultaneous values of velocity and temperature fluctuations from which higher order moments were calculated. In the initial linear stage of streamwise development of the internal gravity waves, usual down-gradient mechanism dominated the heat and the momentum transfer across the mixing layer. As the internal gravity waves developed downstream, the time-averaged heat flux decreased apparently and the phase difference between ω and θ approached -π/2. Waveform analysis on the vertical heat flux clearly showed that the constituent frequency of the internal gravity waves and their harmonics contributed to the occurrence of the counter-gradient heat flux when the internal gravity waves began to collapse downstream through their nonlinear interaction. Where the counter-gradient heat flux occurred, the production terms of the temperature and the velocity fluctuations became negative and the amplitude of the temperature fluctuation apparently decreased contrary to the increase in intensity of the vertical velocity fluctuation.

Aircraft observations of the effects of internal gravity waves on ozone over the western North Atlantic

A series of wave‐like patterns in ozone mixing ratio, potential temperature, and dew point were observed during aircraft horizontal sampling at a constant elevation of approximately 1700 m over the Gulf of Maine and the western North Atlantic. Several hypotheses about the cause for such phenomena are examined. Both the observational evidence and a simple theoretical analysis suggest that the most likely explanation is the atmospheric perturbation associated with internal gravity waves trapped in a stable boundary layer.

Ozone as a tracer of turbulence induced by breaking gravity waves on Mars

A link is established between the vertical structure of the eddy diffusion coefficient and the shape of the ozone profile in the middle atmosphere of Mars. By using a 2-D model of the effect of internal gravity waves on the general circulation pattern (Théodore et al., Icarus 105, 512, 1993a), the eddy diffusion coefficient K is calculated as a function of altitude in solstitial conditions for various latitudes covering polar, mid-latitude and equatorial regions. The vertical profile of K is mainly characterized by a steep increase with altitude above a typlcal level of ≈40 km, in the region of the atmosphere where breaking waves are expected to release their energy. By using a 1-D steady state photochemical model (Blamont and Chassefiere, Icarus 104, 324, 1993), which is proven to provide a realistic diurnal profile of ozone, it is shown that the enhanced vertical transport in the breaking region results in the formation of a thin ozone layer whose contrast is well correlated with the altitude of the breaking level. This correlation is quantitatively analyzed and discussed in view of future observations of ozone by solar and stellar occultation from the Mars 94 space-craft (SPICAM experiment).