Variations in the radio-wave absorption in the ionosphere due to internal gravity waves

We estimate the influence of internal gravity waves on the radio-wave absorption in the Earth’s atmosphere. It is shown that the internal gravity waves can lead to significant spatio-temporal variations in the absorption. We conclude that riometric measurements can be used for the diagnostics of internal gravity waves in the Earth’s atmosphere. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 3, pp. 194–198, March 2006.     

Characteristics of atmospheric gravity waves observed using the MU (Middle and Upper atmosphere) radar and GPS (Global Positioning System) radio occultation

The wind velocity and temperature profiles observed in the middle atmosphere (altitude: 10–100 km) show perturbations resulting from superposition of various atmospheric waves, including atmospheric gravity waves. Atmospheric gravity waves are known to play an important role in determining the general circulation in the middle atmosphere by dynamical stresses caused by gravity wave breaking. In this paper, we summarize the characteristics of atmospheric gravity waves observed using the middle and upper atmosphere (MU) radar in Japan, as well as novel satellite data obtained from global positioning system radio occultation (GPS RO) measurements. In particular, we focus on the behavior of gravity waves in the mesosphere (50–90 km), where considerable gravity wave attenuation occurs. We also report on the global distribution of gravity wave activity in the stratosphere (10–50 km), highlighting various excitation mechanisms such as orographic effects, convection in the tropics, meteorological disturbances, the subtropical jet and the polar night jet.     

Effect of Acoustic Gravity Waves on Variations in the Lower-Ionosphere Parameters as Observed using Artificial Periodic Inhomogeneities

We study the effect of acoustic gravity waves on variations in the atmospheric parameters of the lower ionosphere. The observations were carried out by the method of radio-wave scattering on artificial periodic inhomogeneities of the ionospheric plasma, induced by powerful radio-wave heating of the ionosphere. Measuring the altitude profile of the relaxation time of the scattered signal allowed us to determine the atmospheric temperature and density at heights 95 to 120 km, while recording the signal phase made it possible to obtain the vertical velocity of the plasma. The joint analysis of variations in the vertical velocity and the atmospheric temperature and density showed the simultaneous existence of oscillations with the same periods ranging from 5–10 min to a few hours. The amplitudes of these oscillations were, respectively, 1.5 to 4 m s^-1 for the vertical velocity and 6–20% for the temperature and density. We simulate the characteristics of acoustic gravity waves using the linear theory of their free propagation in an unbounded isothermal undisturbed atmosphere. Based on the polarization relations for low-frequency waves, we calculate the corresponding relative amplitudes of variations in the atmospheric temperature and density with periods from 15 min to 4 h using the measured amplitudes of the vertical velocity. Comparison of the calculation results with the measured values shows their good agreement for waves with periods 15–30 min.     

Observations of Acoustic Gravity Waves during the Solar Eclipse of March 20, 2015 in Kaliningrad

Results of observations of atmospheric and ionospheric parameters during the solar eclipse of March 20, 2015 have been described. The observations have been conducted by lidar sensing in the lower atmosphere and analysis of the total electron content (TEC) in the ionosphere in Kaliningrad. Observations at the troposphere altitudes have been conducted using an atmospheric lidar. Ionospheric parameter TEC has been determined according to observations of navigation satellite signals. The spectral analysis of the monitored parameters during the solar eclipse has shown that, in the lower atmosphere and the ionosphere in a period range of 2–20 min, internal gravity waves (IGWs) and infrasonic waves are excited. During the main phase of the eclipse, the major contribution to variations in the parameters of the medium comes from infrasonic vibrations. Changes in the variations in the atmospheric and ionospheric parameters with IGW periods are observed only in the initial and final phases of the eclipse.     

Investigation of acoustic gravity waves in the upper atmosphere by the artificial periodic inhomogeneities method at Nizhny Novgorod

We present the results of observation of acoustic gravity waves in the height range 60–120 km. AGW were studied by means of plasma velocity measurements. The observations, based upon use of a newly-developed diagnostic technique, were carried out during September 1990–May 1991. The method uses the artificial periodic inhomogeneities (API) which occur in the ionosphere illuminated by high- power HF radio waves. This method, based upon measurements of phases of waves back scattered from API, has a time resolution sufficient to observe short-term variations in the atmosphere. Seasonal variations of daily averaged vertical velocities were obtained. Above the turbopause height upward vertical motions dominated. Wave-like oscillations in the vertical velocity, which are most probably caused by AGW, occurred.Published from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 3, pp. 329–334, March, 1996.     

Application of higher-order KdV——mKdV model with higher-degree nonlinear terms to gravity waves in atmosphere

Higher-order Korteweg-de Vries (KdV)-modified KdV (mKdV) equations with a higher-degree of nonlinear terms are derived from a simple incompressible non-hydrostatic Boussinesq equation set in atmosphere and are used to investigate gravity waves in atmosphere. By taking advantage of the auxiliary nonlinear ordinary differential equation, periodic wave and solitary wave solutions of the fifth-order KdV--mKdV models with higher-degree nonlinear terms are obtained under some constraint conditions. The analysis shows that the propagation and the periodic structures of gravity waves depend on the properties of the slope of line of constant phase and atmospheric stability. The Jacobi elliptic function wave and solitary wave solutions with slowly varying amplitude are transformed into triangular waves with the abruptly varying amplitude and breaking gravity waves under the effect of atmospheric instability.     

Disturbances of the upper atmosphere and ionosphere caused by acoustic-gravity wave sources in the lower atmosphere

The results of observations of acoustic-gravity waves in the troposphere and the ionosphere at middle latitudes during periods of passage of the solar terminator are presented. Tropospheric observations were performed using a lidar. The frequency characteristics of variations of the tropospheric parameters are determined based on observations of the intensity of the scattered lidar signal. The characteristics of variations of the total electron content (TEC) in the atmosphere are determined from data collected by GPS navigation satellites. An analysis of the observational data showed that the spectrum of variations of the atmospheric and ionospheric parameters is indicative of acoustic-gravity waves (AGW) propagating from the lower atmosphere. Modeling studies of the vertical propagation of AGW from the Earth’s surface showed that such waves quickly (within ~15 min) reach altitudes of the upper atmosphere (~300 km). The refraction and dissipation of waves in the upper atmosphere produces perturbations of the background state of the atmosphere and gives rise to the waveguide propagation of infrasonic wave components. The observed manifestations of TEC disturbances caused by AGW propagating from the lower atmosphere can be explained by the diurnal variation of the altitude of the ionosphere and the waveguide propagation of infrasonic waves.     

On the effect of temperature fluctuations on line intensities

We investigate the effects of temperature fluctuations in a stellar atmosphere on the intensities of the lines emitted by a multilevel atom, by differentiating the coupled set of radiative transfer and statistical equilibrium equations. We propose a numerical method for the fast computation of large sequences of line profiles when the atmospheric temperatures are fluctuating about a mean curve T(z) (oscillations, waves, turbulence, etc…). This method is applied to a three-level atom simulating the formation of Ca(II) lines in the solar atmosphere and the results are compared with those of direct computations. We show how the variations of atomic level populations, line source functions, and emergent intensities may be related to temperature variations by a sum of several terms corresponding to each atomic transition and arising from the variations of collisional excitation rates. Finally, we discuss the possibility of extending the method to compute profile variations when temperatures, densities and velocities are changing simultaneously within the atmosphere.     

Study of small variations of troposphere parameters by the radioacoustic sounding method

We consider a method based on the study of signal amplitude and phase variations in the radioacoustic sounding (RAS) of the atmosphere for the diagnostics of dynamical and wave processes in the troposphere. We give experimental data on phase variations of the RAS signal from scan to scan in daytime and nighttime sessions. Variations of the signal phase with characteristic time greater than 40 min are likely due to the passage of internal gravity waves (IGW) through the sounding region. The experimental data are in good agreement with the results of computer simulation of IGW propagation. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 11, pp. 1355–1364, November, 1997.     

A study of propagation of nonlinear acoustic-gravity waves in the middle and upper atmosphere by means of numerical modeling

numerical model of the vertical propagation and decay of nonlinear acoustic-gravity waves (AGW) from the Earth surface to the upper atmosphere is described. Monochromatic vertical velocity variations at the Earth surface are used as the AGW source in the model. The numerical method for solving three-dimensional hydrodynamic equations is based on finite-difference representation of the fundamental laws of conservation, which makes it possible to calculate not only smooth, but also physically correct generalized solutions of the hydrodynamic equations. The equations are solved in a range of altitudes from the ground up to 500 km. The background temperature, density, molecular viscosity and thermal conductivity coefficient are specified according to standard atmosphere models. The dependence of the characteristics of the waves on the amplitude of the wave source at the lower boundary is examined. The amplitudes of the AGW increase with the altitude, and the waves can break down due to nonlinear effects in the middle and upper atmosphere, depending on the amplitude of the source.     

Model study of the response of the thermosphere to perturbations of mesospheric tides and planetary waves during a sudden stratospheric warming

The results of numerical simulations of the effects of a sudden stratospheric warming (SSW) in January 2009 are examined. The calculations are performed within the framework of the Global Self-Consistent Model of the Thermosphere, Ionosphere, Protonosphere (GSM TIP), which calculates the parameters of the neutral and charged components of the upper atmosphere. An analysis of the numerical simulation results showed that the perturbation of mesospheric tidal and planetary waves significantly affects the structure of variations of the thermosphere at altitudes below 150 km. At higher altitudes, the characteristics of planetary and tidal waves in the thermosphere are practically insensitive to the corresponding mesospheric perturbations. The calculated space–time structure of ionospheric perturbations caused by mesospheric and planetary tidal waves is in qualitative agreement with observation data. The results show that the main reason for the observed ionospheric effects is the perturbation of the electric fields in the dynamo region. However, the calculated magnitudes of the ionospheric effects produced by the SSW are at least two- to threefold weaker than the observed. It is assumed that, in order to achieve a quantitative agreement between simulation and experimental results on the ionospheric effects of the SSW, it is not enough to consider only the dynamics of planetary and tidal waves in the mesosphere. An additional source of the perturbation of the thermosphere and ionosphere during the SSW may be associated with the propagation of internal gravity waves from the lower atmosphere and their dissipation in the thermosphere.     

Variability of planetary-scale waves at mid-latitudes in the course of strat-warmings during DYANA

Summary This work investigates the variability of planetary-scale waves from motion field observations in the middle atmosphere carried out at the Budrio radar station near Bologna (45°N; 12°E) in the 1989–1990 winter during DYANA (DYnamics Adapted Network for the Atmosphere). Meso-thermospheric zonal winds associated with long-period waves give evidence of significant energy input from below mainly in the course of the two strat-warmings recorded at the end of January and in mid February 1990. Amplification of 10-day waves in the upper mesosphere and lower thermosphere just a few days before the temperature peak at the 10hPa stratospheric level, and the effects induced by these waves on tidal and mean fields, are here taken into account to clarify the influence and the evolution of strat-warmings in the middle atmosphere. Nonlinear mixing processes between planetary and tidal oscillations are indicated to be responsible for the short-term variability pointed out in the amplitude variations of tides.     

Vertical Velocities and Temperature of the Neutral Component in the Upper Atmosphere

Results of measurements of the velocity of the vertical plasma motion and the temperature of the neutral component in the upper atmosphere and comparison of variations in these parameters have been described. The measurements have been carried out by the resonance scattering of radio waves by artificial periodic irregularities in the ionospheric plasma. The irregularities arise when the ionosphere is modificated by a powerful high-frequency radio emission from a Sura midlatitude heating facility. Comparison has been conducted using experimental data on altitude- and time-dependent variations in the above parameters obtained in experiments of 2010 and 2014. It has been shown that, above 100 km, wavelike variations in temperature and velocity are commonly observed simultaneously. In the absence of wavelike variations, there is a tendency to an increase in temperature with an increase in the velocity of the vertical plasma motion regardless of direction. This tendency can be attributed to thermal flows directed upward from the turbulent region of the ionosphere.     

Water vapor as an active scalar in tropical atmospheric dynamics

Water vapor is a constituent of the tropical atmosphere which, though to a significant extent locally controlled by vertical advection, precipitation, and surface evaporation, is also affected by horizontal advection. Water vapor affects the flow in turn, because a humid atmosphere supports deep, precipitating convection more readily than a dry atmosphere. Precipitation heats the atmosphere, and this heating drives the flow. Water vapor is thus a dynamically active constituent. Simplifications to the primitive equations of dynamical meteorology, based on the so-called weak temperature gradient approximation, are presented which highlight this behavior. The weak temperature gradient approximation is valid on large scales near the equator. It eliminates gravity waves, leaving only balanced dynamics, though the fundamental balance occurs in the temperature rather than the momentum equation (as is customary in most balance models of geophysical fluid dynamics). The dynamical role of water vapor is examined in a couple of idealized contexts, where either the vertical or horizontal structure of the flow is severely simplified. (c) 2002 American Institute of Physics.     

Reconstruction of the vertical structure of internal waves in the troposphere from multifrequency measurements in the O2 lines

The observed frequencies of internnal gravity waves (IGWs) and their contribution to the variability of the brightness temperatures were determined on the basis of spectral analysis of the temporal dynamics of the thermal radio emission of the atmosphere at the frequencies 53.5, 54.0, 54.5, and 55.0 GHz. Methods for reconstructing from multifrequency measurements in the O₂ lines the altitude distribution of the perturbation of the temperature of IGWs from the spectral amplitudes of their contribution to the brightness temperature were developed.Scientific-Research Radiophysical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 2, pp. 103–110, February, 1991.     

Nonlinear synthesis of infrasound propagation through an inhomogeneous, absorbing atmosphere

An accurate and efficient method to predict infrasound amplitudes from large explosions in the atmosphere is required for diverse source types, including bolides, volcanic eruptions, and nuclear and chemical explosions. A finite-difference, time-domain approach is developed to solve a set of nonlinear fluid dynamic equations for total pressure, temperature, and density fields rather than acoustic perturbations. Three key features for the purpose of synthesizing nonlinear infrasound propagation in realistic media are that it includes gravitational terms, it allows for acoustic absorption, including molecular vibration losses at frequencies well below the molecular vibration frequencies, and the environmental models are constrained to have axial symmetry, allowing a three-dimensional simulation to be reduced to two dimensions. Numerical experiments are performed to assess the algorithm's accuracy and the effect of source amplitudes and atmospheric variability on infrasound waveforms and shock formation. Results show that infrasound waveforms steepen and their associated spectra are shifted to higher frequencies for nonlinear sources, leading to enhanced infrasound attenuation. Results also indicate that nonlinear infrasound amplitudes depend strongly on atmospheric temperature and pressure variations. The solution for total field variables and insertion of gravitational terms also allows for the computation of other disturbances generated by explosions, including gravity waves.     

On the theory of heat transfer in massive bodies

It has been shown that the allowance for the interactions of quasi-static gravity waves with density fluctuations makes thermal conductivity κ independent of temperature T; according to numerical estimates, the mechanism of this interaction is the most effective mechanism of interaction in bulk solids. The κ(T) dependence is calculated in a wide range of variations in the argument.     

Resonant nonlinear interactions between atmospheric waves in the polar summer mesopause region

Data obtained from the mobile SOUSY VHF radar at And(ya/Norway in summer 1987 have been used to study the nonlinear interactions between planetary waves, tides and gravity waves in the polar mesosphere, and the instability of background atmosphere above the mesopause. It is observed that 35-h planetary wave, diurnal, semidiurnal and terdiurnal tides are the prominent perturbations in the Lomb-Scargle spectra of the zonal wind component. By inspecting the frequency combinations, several triads are identified. By bispectral analysis it is shown that most bispectral peaks stand for quadratic coupling between tidal harmonics or between tide and planetary or gravity wave, and the height dependence of bispectral peaks reflects the variation of wave-wave interactions. Above the mesopause, the occurrence heights of the maximum L-S power spectral peaks corresponding to the prominent wave components tend to increase with their frequencies. This may result from the process in which two low frequency waves interact to generate a high frequency wave. Intensities of the planetary wave and tides increase gradually, arrive at their maxima, and then decay quickly in turn with increasing height. This kind of scene correlates with a "chain" of wave-wave resonant interactions that shifts with height from lower frequency segment to higher frequency segment. By instability analysis, it is observed that above the mesopause, the Richardson number becomes smaller and smaller with height, implying that the turbulent motion grows stronger and stronger and accordingly the background atmosphere more and more instable. It is suggested that the wave-wave sum resonant interaction and the wave dissipation due to instability are two dominant dynamical processes that occur in the mesopause region. The former invokes the energy transfer from lower frequency waves to higher frequency waves. The latter results in the heating of the atmosphere and accelerating of the background flow.     

Propagation of Alfvén surface waves along the ionospheric plasma slab with the effect of gravity

Ionospheric regions connecting the neutral gas atmosphere have been considered to be an incompressible plasma slab surrounded by incompressible plasma on one side and neutral gas on the other side. The effect of gravity on Alfvén surface waves in the slab geometry is studied. As a special case, the propagation of ASW along the plasma-neutral gas interface is also discussed. The existence of two modes of surface waves has been identified and their characteristic behaviour affected by the gravity has been discussed.     

Sound generation due to the interaction of surface waves

Two opposite gravity-capillary waves of equal frequency give rise to the formation of a standing wave on the ocean surface and, thus, in the nonlinear approximation, generate a sound wave of twofold frequency with an amplitude proportional to the squared height of the surface wave [1]. This effect, being caused by the nonlinear interaction of opposite surface waves, can give rise to the radiation of sound waves in both ocean and atmosphere [2]. Opposite waves can appear in the ocean as a result of different ocean-atmosphere interactions and, in particular, as a result of the blocking of capillary waves on the slope of a gravity wave.