scholarly journals Spectra of Acoustic-Gravity Waves in the Atmosphere with a Quasi-Isothermal Upper Layer

Atmosphere ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 818
Author(s):  
Sergey P. Kshevetskii ◽  
Yuliya A. Kurdyaeva ◽  
Nikolai M. Gavrilov
Keyword(s):  
Gravity Waves ◽  
Evolution Operator ◽  
Mathematical Problem ◽  
Cutoff Frequency ◽  
Lower Boundary ◽  
Low Frequency ◽  
Acoustic Gravity Waves ◽  
Wide Range ◽  
Different Altitudes ◽  
Wave Modes

In this paper, we study, in theoretical terms, the structure of the spectrum of acoustic-gravity waves (AGWs) in the nonisothermal atmosphere having asymptotically constant temperature at high altitudes. A mathematical problem of wave propagation from arbitrary initial perturbations in the half-infinite nonisothermal atmosphere is formulated and analyzed for a system of linearized hydrodynamic equations for small-amplitude waves. Besides initial and lower boundary conditions at the ground, wave energy conservation requirements are applied. In this paper, we show that this mathematical problem belongs to the class of wave problems having self-adjoint evolution operators, which ensures the correctness and existence of solutions for a wide range of atmospheric temperature stratifications. A general solution of the problem can be built in the form of basic eigenfunction expansions of the evolution operator. The paper shows that wave frequencies considered as eigenvalues of the self-adjoint evolution operator are real and form two global branches corresponding to high- and low-frequency AGW modes. These two branches are separated since the Brunt–Vaisala frequency is smaller than the acoustic cutoff frequency at the upper boundary of the model. Wave modes belonging to the low-frequency global spectral branch have properties of internal gravity waves (IGWs) at all altitudes. Wave modes of the high-frequency spectral branch at different altitudes may have properties of IGWs or acoustic waves depending on local stratification. The results of simulations using a high-resolution nonlinear numerical model confirm possible changes of AGW properties at different altitudes in the nonisothermal atmosphere.

scholarly journals Nonlinear interaction between acoustic gravity waves

1996 ◽  
Vol 14 (3) ◽  
pp. 304-308 ◽  
Author(s):  
P. Axelsson ◽  
J. Larsson ◽  
L. Stenflo
Keyword(s):  
Gravity Waves ◽  
Nonlinear Interaction ◽  
Low Frequency ◽  
Resonant Interaction ◽  
Coupling Coefficients ◽  
Symmetric Form ◽  
Frequency Limit ◽  
Acoustic Gravity Waves

Abstract. The resonant interaction between three acoustic gravity waves is considered. We improve on the results of previous authors and write the new coupling coefficients in a symmetric form. Particular attention is paid to the low-frequency limit.

Numerical Modeling of Nonlinear Interactions of Spectral Components of Acoustic-Gravity Waves in the Middle and Upper Atmosphere

2020 ◽  
Author(s):  
Nikolai M. Gavrilov ◽  
Sergej P. Kshevetskii
Keyword(s):  
Gravity Waves ◽  
Upper Atmosphere ◽  
Jet Flows ◽  
Small Scale ◽  
Nonlinear Interactions ◽  
Mean Flow ◽  
Wave Source ◽  
Acoustic Gravity Waves ◽  
The Mean ◽  
Wave Modes

<p>Acoustic-gravity waves (AGWs) measuring at big heights may be generated in the troposphere and propagate upwards. A high-resolution three-dimensional numerical model was developed for simulating nonlinear AGWs propagating from the ground to the upper atmosphere. The model algorithms are based on the finite-difference analogues of the main conservation laws. This methodology let us obtaining the physically correct generalized wave solutions of the nonlinear equations. Horizontally moving sinusoidal structures of vertical velocity on the ground are used for the AGW excitation in the model. Numerical simulations were made in an atmospheric region having horizontal dimensions up to several thousand kilometers and the height extention up to 500 km. Vertical distributions of the mean temperature, density, molecular viscosity and thermal conductivity are specified using standard models of the atmosphere.</p><p>Simulations were made for different horizontal wavelengths, amplitudes and speeds of the wave sources at the ground. After “switch on” the tropospheric wave source, an initial AGW pulse very quickly (for several minutes) could propagate to heights up to 100 km and above. AGW amplitudes increase with height and waves may break down in the middle and upper atmosphere. Wave instability and dissipation may lead to formations of wave accelerations of the mean flow and to producing wave-induced jet flows in the middle and upper atmosphere. Nonlinear interactions may lead to instabilities of the initial wave and to the creation of smaller-scale perturbations. These perturbations may increase temperature and wind gradients and could enhance the wave energy dissipation.</p><p>In this study, the wave sources contain a superposition of two AGW modes with different periods, wavelengths and phase speeds. Longer-period AGW modes served as the background conditions for the shorter-period wave modes. Thus, the larger-scale AGWs can modulate amplitudes of small-scale waves. In particular, interactions of two wave modes could sharp vertical temperature gradients and make easier the wave breaking and generating  turbulence. On the other hand, small-wave wave modes might increase dissipation and modify the larger-scale modes.This study was partially supported by the Russian Basic Research Foundation (# 17-05-00458).</p>

Impact of Convectively Generated Low-Frequency Gravity Waves on Evolution of Mesoscale Convective Systems

2020 ◽  
Vol 77 (10) ◽  
pp. 3441-3460
Author(s):  
Rebecca D. Adams-Selin
Keyword(s):  
Gravity Waves ◽  
Low Frequency ◽  
Mesoscale Convective Systems ◽  
Cloud Base ◽  
Mature Stage ◽  
First Order ◽  
Convective Systems ◽  
Stratiform Region ◽  
Mesoscale Convective ◽  
Wave Modes

AbstractIdealized numerical simulations of mesoscale convective systems (MCSs) over a range of instabilities and shears were conducted to examine low-frequency gravity waves generated during initial and mature stages of convection. In all simulations, at initial updraft development a first-order wave was generated by heating extending through the depth of the troposphere. Additional first-order wave modes were generated each time the convective updraft reintensified. Each of these waves stabilized the environment in advance of the system. As precipitation descended below cloud base, and as a stratiform precipitation region developed, second-order wave modes were generated by cooling extending from the midlevels to the surface. These waves destabilized the environment ahead of the system but weakened the 0–5 km shear. Third-order wave modes could be generated by midlevel cooling caused by rear inflow intensification; these wave modes cooled the midlevels destabilizing the environment. The developing stage of each MCS was characterized by a cyclical process: developing updraft, generation of n = 1 wave, increase in precipitation, generation of n = 2 wave, and subsequent environmental destabilization reinvigorating the updraft. After rearward expansion of the stratiform region, the MCSs entered their mature stage and the method of updraft reinvigoration shifted to absorbing discrete convective cells produced in advance of each system. Higher-order wave modes destabilized the environment, making it more favorable to development of these cells and maintenance of the MCS. As initial simulation shear or instability increased, the transition from cyclical wave/updraft development to discrete cell/updraft development occurred more quickly.

scholarly journals Propagation to the upper atmosphere of acoustic-gravity waves from atmospheric fronts in the Moscow region

2019 ◽  
Vol 37 (3) ◽  
pp. 447-454 ◽  
Author(s):  
Yuliya Kurdyaeva ◽  
Sergey Kulichkov ◽  
Sergey Kshevetskii ◽  
Olga Borchevkina ◽  
Elena Golikova
Keyword(s):  
Experimental Data ◽  
Gravity Waves ◽  
Pressure Fluctuations ◽  
Lower Boundary ◽  
Lower Troposphere ◽  
Upper Atmosphere ◽  
Moscow Region ◽  
Atmospheric Front ◽  
Lower Boundary Condition ◽  
Acoustic Gravity Waves

Abstract. The paper uses experimental data of pressure variations on the Earth's surface during the passage of an atmospheric front recorded by a network of four microbarographs in the Moscow region. Applying these experimental data, empirical approximations of atmospheric pressure field oscillations are suggested. The obtained approximating surface pressure functions are used as the lower boundary condition for simulating the vertical propagation of acoustic-gravity waves from a source in the lower troposphere. Estimates of the amplitude of temperature disturbances in the upper atmosphere caused by acoustic-gravity waves from a propagating atmospheric front are obtained. For the amplitude of wave temperature disturbances, values of about 200 K are obtained. The amplitude of temperature disturbances in the upper atmosphere caused by background pressure fluctuations on the Earth's surface is estimated at 4–5 K.

Spectral vs. compartmental averaging of VA/Q distributions: confidence limits

1991 ◽  
Vol 70 (3) ◽  
pp. 1290-1299 ◽  
Author(s):  
X. H. Wang ◽  
C. S. Poon
Keyword(s):  
Frequency Band ◽  
Cutoff Frequency ◽  
Low Frequency ◽  
Inert Gases ◽  
Resolving Power ◽  
Recovery Algorithm ◽  
Nonparametric Approach ◽  
Alternative Approach ◽  
Wide Range ◽  
Average Distribution

We have investigated the method of statistical averaging as a nonparametric approach to obtain a representative ventilation-perfusion (VA/Q) distribution that exemplifies the family of compatible solutions for multiple inert gas elimination data. The variability of the compatible solutions was examined by determining the standard deviation of the statistical average. For six inert gases, it can be predicted that a distribution with up to seven contiguous nonzero VA/Q compartments can be uniquely recovered, whereas the compatible family becomes more diverse, the broader the distribution. For a given compatible family consisting of multimodal distributions with various phase relationships, the average distribution was found to display an uncharacteristically unimodal shape as a result of modal smoothing. To avoid this possible artifact, an alternative approach was adopted in which statistical averaging was performed in the frequency domain. For both deterministic and empirical data, the energy spectra of all feasible VA/Q distributions displayed a well-defined low-frequency band that was invariant within the compatible family and with a bandwidth that approximated the predicted sampling cutoff frequency. The nonuniqueness of the result was ascribable to a variable high-frequency band that was due to an aliasing effect. For a wide range of clinical data, the representative distributions resulting from compartmental and spectral averaging were indistinguishable from each other and had little variability both in the VA/Q and frequency domains. For these cases, therefore, the resolving power of the recovery algorithm was not critical. Finally, an efficient method of finding the average distribution was proposed.

scholarly journals Electromagnetic oscillations of the Earth's upper atmosphere (review)

2010 ◽  
Vol 28 (7) ◽  
pp. 1387-1399 ◽  
Author(s):  
A. G. Khantadze ◽  
G. V. Jandieri ◽  
A. Ishimaru ◽  
T. D. Kaladze ◽  
Zh. M. Diasamidze
Keyword(s):  
Gravity Waves ◽  
Geomagnetic Field ◽  
Large Scale ◽  
Low Frequency ◽  
Planetary Waves ◽  
Upper Atmosphere ◽  
Acoustic Gravity Waves ◽  
Weakly Ionized ◽  
General Dispersion ◽  
Electromagnetic Oscillations

Abstract. A complete theory of low-frequency MHD oscillations of the Earth's weakly ionized ionosphere is formulated. Peculiarities of excitation and propagation of electromagnetic acoustic-gravity, MHD and planetary waves are considered in the Earth's ionosphere. The general dispersion equation is derived for the magneto-acoustic, magneto-gravity and electromagnetic planetary waves in the ionospheric E- and F-regions. The action of the geomagnetic field on the propagation of acoustic-gravity waves is elucidated. The nature of the existence of the comparatively new large-scale electromagnetic planetary branches is emphasized.

scholarly journals Correct boundary conditions for DNS models of nonlinear acoustic-gravity waves forced by atmospheric pressure variations

2017 ◽  
Author(s):  
Yuliya Kurdyaeva ◽  
Sergey Kshevetskii ◽  
Nikolay Gavrilov ◽  
Sergey Kulichkov
Keyword(s):  
Boundary Conditions ◽  
Analytical Solutions ◽  
Atmospheric Pressure ◽  
Mathematical Problem ◽  
Lower Boundary ◽  
Energy Functional ◽  
Variable Pressure ◽  
Linearized Equations ◽  
Acoustic Gravity Waves ◽  
Propagation Of Waves

Abstract. Currently, international networks exist for high-resolution microbarograph recording wave pressure variations at the surface of the Earth. This increases interest in simulating propagation of waves caused by variations of atmospheric pressure. Such mathematical problem involves a set of primitive nonlinear hydrodynamic equations with lower boundary conditions in the form of wavelike pressure variations at the Earth's surface. To analyze the correctness of the problem, the linearized equations are used near the ground for small amplitudes of surface wave excitation. The method of wave energy functional shows that in nondissipative approximation the solution of the boundary problem is uniquely determined by the variable pressure field at the Earth's surface. Respective dissipative problem has also unique solution with the appropriate choice of lower boundary conditions for temperature and velocity components. To test the numerical algorithm, analytical solutions of the linearized equations for acoustic and gravity wave modes are used. Reasonable agreements of numerical and analytical solutions are obtained. Analytical studies show possibilities of sharp changes of temperature and density near the ground. Numerical simulations confirm these analytical results. Obtained algorithms and computer codes can be used for simulations of atmospheric wave propagation from the pressure variations at the Earth's surface.

scholarly journals Vertical propagation acoustic-gravity waves from atmospheric fronts into the upper atmosphere

2019 ◽  
Vol 55 (4) ◽  
pp. 3-12
Author(s):  
Y. A. Kurdyaeva ◽  
S. N. Kulichkov ◽  
S. P. Kshevetskii ◽  
O. P. Borchevkina ◽  
E. V. Golikova
Keyword(s):  
Gravity Waves ◽  
Atmospheric Pressure ◽  
Lower Boundary ◽  
Lower Troposphere ◽  
Upper Atmosphere ◽  
Atmospheric Front ◽  
Lower Boundary Condition ◽  
Acoustic Gravity Waves ◽  
Temperature Disturbance ◽  
Atmospheric Fronts

Using experimental observations of atmospheric pressure variations on the Earth’s surface recorded with a network of 4 microbarographs located in the Moscow region during the passage of an atmospheric front, empirical approximations of oscillations of atmospheric pressure field were constructed. The obtained approximating functions were used as the lower boundary condition for the numerical simulation of acoustic-gravity wave propagation to the upper atmosphere from the source in the lower troposphere. Estimates of the amplitude of temperature disturbances in the upper atmosphere caused by iacoustic gravity waves from the atmospheric front are given. The obtained estimates for the temperature disturbance amplitude take values around 170 K. The amplitude of temperature disturbances in the upper atmosphere, caused by background variations of pressure on the Earth's surface, is estimated at 4-5 K.

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