Parameters Of Internal Gravity Waves Research Articles

Parameters of internal gravity waves based on observations of noctilucent clouds in Yakutsk

Noctilucent clouds (polar mesospheric clouds) are clusters of ice crystals 10–100 µm in size at an altitude of 80–85 km, only a few kilometers thick, illuminated by the sun's rays. A characteristic feature of noctilucent clouds is that they are observed from Earth only in relatively narrow latitudinal belts of the northern and southern hemispheres. They are a visible indicator of wave processes in the upper atmosphere. The use of modern methods of observation and data processing allows us to track their evolution and, based on these parameters, study the main dynamic characteristics of the upper atmosphere - wind speed and direction, atmospheric-gravity waves and try to establish their sources. The article presents the results of a study of the features of the parameters of internal gravity waves based on observations of noctilucent clouds. Photographic observations were carried out using digital cameras and a phone camera. Using synchronous triangulation observations with identical cameras in Yakutsk and Oktemtsy, it was possible to measure the height of noctilucent clouds. Rare cases of propagation of different types of waves and their parameters are analysed: wavelengths, speeds and directions of their propagation. A case of observation of noctilucent clouds associated with the so-called mesospheric bore is also described - a prominent wave front propagating along a waveguide channel and visually separating the glow region already involved in the wave process from the region in which oscillations have not yet arisen. It is assumed that the sources of wave disturbances are atmospheric fronts and air mass flow around mountain ranges.

Fluctuations in Refracted Star Signals Caused by the Stratospheric Internal Gravity Waves

The application of starlight refraction navigation to spacecraft and space weapons is a significant development. However, the irregular stratospheric atmosphere can cause fluctuations in relative light intensity and refraction angles of refracted stars, which need to be analyzed to provide guidance for system design and simulation verification. The internal gravity wave (IGW) is an important component of the irregular atmosphere. Based on the Rytov approximation, closed-form approximations were obtained, which can more intuitively reveal the relationship between the IGW parameters and the star signals’ statistical characteristics. From the GOMOS observations, the influence of the stratosphere from 25 km to 35 km on the fluctuations in relative intensity and refraction angles was analyzed in this study. As the height increased, the fluctuations in starlight signals gradually weakened. Compared with the numerical solution, the error of the closed-form approximations for relative intensity fluctuations was no more than 10%, and the error for refraction angle fluctuations was 1.0%. Compared with the measured data, the error of the closed-form approximations for relative intensity was 6.3%. The proposed approximations better reflect the relationship between IGW parameters and star signal fluctuations compared to the existing approximation. The research in this article can provide a reference for application assessment based on starlight refraction navigation.

The Study of Internal Gravity Waves in the Earth’s Atmosphere by Radio Occultations: A Review

Internal gravity waves (IGWs) in the middle atmosphere are the main source of mesoscale fluctuations of wind and temperature. The parameterization of IGWs and study of their climatology is necessary for the development of global atmospheric circulation models. In this review, we focus on the application of Radio Occultation (RO) observations for the retrieval of IGW parameters. (1) The simplest approach employs the retrieved temperature profiles. It is based on the fact that IGWs are highly anisotropic structures and can be accurately retrieved by RO. The basic assumption is that all the temperature fluctuations are caused by IGWs. The smoothed background temperature profile defines the the Brunt–Väisälä frequency, which, together with the temperature fluctuations, defines the IGW specific potential energy. Many studies have derived the distribution and climatology of potential energy, which is one of the most important characteristics of IGWs. (2) More detailed analysis of the temperature profiles is based on the derivation of the temperature fluctuation spectra. For saturated IGWs, the spectra must obey the power law with an exponent of −3. Such spectra are obtained by using Wave Optical (WO) processing. (3) More advanced analysis employs space–frequency analysis. It is based on phase-sensitive techniques like cross S- or wavelet transforms in order to identify propagating IGWs. (4) Another direction is the IGW parameter estimate from separate temperature profiles applying the stability condition in terms of the Richardson number. In this framework, a necessary condition is formulated that defines whether or not the temperature fluctuations can be related to IGW events. The temperature profile retrieval involves integral transforms and filtering that constitute the observation filter. (5) A simpler filter is implemented by the analysis of the RO amplitude fluctuation spectra, based on the diffraction theory in the framework of the phase screen and weak fluctuation approximations. The two spectral parameters, the external scale and the structural characteristic, define the specific potential energy. This approach allows the derivation of the spacial and seasonal distributions of IGW activity. We conclude that the success of IGW study by RO is stimulated by a large number of RO observations and advanced techniques based on Fourier and space–time analysis, physical equations describing IGWs, and diffraction theory.

The parameters of internal gravity waves in the atmosphere from the amplitude fluctuations of radio occultation signals

We develop a method for the reconstruction of the statistical parameters of internal gravity wave (IGW) in the atmosphere from the amplitude fluctuations of signals acquired in radio occultation observations. We discuss the choice of the model of the IGW spatial spectrum, derive the relationships between the IGW spectra and the amplitude fluctuation spectra, develop the reconstruction algorithm and estimate its uncertainties. The IGW spectrum parameters to be retrieved are the outer (dominant) scale and the structure characteristic, the latter determining the power of saturated IGW. The method was tested on the COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) observations acquired in the winter and summer seasons 2011. The IGW parameters were reconstructed in the height range from the upper boundary of the tropopause to 28 km. We show the altitude-latitudinal distributions of the IGW parameters and two integral characteristics: the variances of the temperature fluctuations and the IGW potential energy. We perform a detailed comparison of our results with those obtained from radiosonde and radio occultation observations. The developed method can be applied for the global monitoring of IGW parameters and activity in the middle atmosphere.

Latitudinal Distribution of the Parameters of Internal Gravity Waves in the Atmosphere Derived from Amplitude Fluctuations of Radio Occultation Signals

The method of reconstructing the global distribution of statistical parameters of internal gravity waves (IGWs) in the atmosphere has been tested using the data of amplitude fluctuation measurements of a radio signal in satellite radio occultation (RO) observations. In our previous work, for the chosen model of the spatial IGW spectrum, its relationship with the spectra of amplitude fluctuations was obtained, an algorithm for reconstructing the model parameters was developed, and the reconstruction errors were estimated. The reconstructed parameters of the vertical IGW spectrum are the external scale, which separates the unsaturated large-scale waves from saturated small-scale waves, and the structural characteristic, which determines the spectral amplitude of saturated waves. These parameters are used to calculate the variance of temperature fluctuations and the potential energy of the waves. This article presents the altitude–latitude distribution of IGW parameters in the stratosphere according to the measurements of the COSMIC experiment in 2011. The characteristic features of these distributions are noted, and the results are compared with the data of other measurements.

Research into the Variability of Characteristics of Cloud Manifestations of Internal Gravity Waves during Their Lifetime Based on Himawari-8 Satellite Data

The results of studying a variability of internal-gravity-wave characteristics and their signatures based on satellite data are presented. Observations of the wave processes under study over the Russian Federation Pacific coast in the period from 2015 to 2017 are considered. High-periodic Himawari-8 satellite images and thematic products of their processing are used. The methods and algorithms for retrieving parameters of internal gravity waves and their cloud manifestations are described. Trends for various characteristics of wave processes under study are constructed. The typical variability of parameters of internal gravity waves and their signatures is revealed on the basis of the longest lasting episodes of their observation. The results of analysis of coefficients of correlation between the various characteristics of the wave processes under study are presented. Similar episodes of observing signatures of internal gravity waves for the time period under study are established. The processes occurring in the “atmosphere–underlying surface” system and their influence on the creation of favorable conditions for the generation and propagation of wave processes under study are discussed.

Variations of the parameters of internal gravity waves in the atmosphere of Central Asia before earthquakes

Based on the data of experimental studies of wave disturbances in the Earth’s atmosphere before and after the earthquakes in Uzbekistan (May 26, 2013) and Kyrgyzstan (January 8, 2007), earlier unknown changes in the parameters of internal gravity waves are revealed. These changes were manifested during the period of five days before the earthquake and in certain cases can be used for short-term prediction of the time when seismic events are to occur.

Variations of the Parameters of Internal Gravity Waves in the Atmosphere of Central Asia before Earthquakes

Based on the data of experimental studies of wave disturbances in the Earth’s atmosphere before and after the earthquakes in Uzbekistan (May 26, 2013) and Kyrgyzstan (January 8, 2007), earlier unknown changes in the parameters of internal gravity waves are revealed. These changes were manifested during the period of five days before the earthquake and in certain cases can be used for short-term prediction of the time when seismic events are to occur.

Analytical Solution of Direct and Inverse Problems in the Internal Gravity Waves Studies by the Doppler Frequency Shift Method

An analytical solution of direct and inverse problems arising in the study of the internal gravity waves (IGWs) dynamic via recording of the Doppler frequency shift, is presented. The direct problem is to determine the response of the Doppler shift to IGWs in the region of the radio wave reflection point; the inverse problem is the determination of IGW parameters from data on the Doppler frequency shift. Solutions were obtained in an approximation of the isothermal ionosphere for the heights of the F-region. They are presented in a form convenient for their practical use and can have a wide range of applications, including the detection of soliton-like wave structures in the F-region of the ionosphere.

Fluctuations of radio occultation signals in sounding the Earth's atmosphere

Abstract. We discuss the relationships that link the observed fluctuation spectra of the amplitude and phase of signals used for the radio occultation sounding of the Earth's atmosphere, with the spectra of atmospheric inhomogeneities. Our analysis employs the approximation of the phase screen and of weak fluctuations. We make our estimates for the following characteristic inhomogeneity types: (1) the isotropic Kolmogorov turbulence and (2) the anisotropic saturated internal gravity waves. We obtain the expressions for the variances of the amplitude and phase fluctuations of radio occultation signals as well as their estimates for the typical parameters of inhomogeneity models. From the GPS/MET observations, we evaluate the spectra of the amplitude and phase fluctuations in the altitude interval from 4 to 25 km in the middle and polar latitudes. As indicated by theoretical and experimental estimates, the main contribution into the radio signal fluctuations comes from the internal gravity waves. The influence of the Kolmogorov turbulence is negligible. We derive simple relationships that link the parameters of internal gravity waves and the statistical characteristics of the radio signal fluctuations. These results may serve as the basis for the global monitoring of the wave activity in the stratosphere and upper troposphere.

Case study of inclined sporadic E layers in the Earth’s ionosphere observed by CHAMP/GPS radio occultations: Coupling between the tilted plasma layers and internal waves

We have used the radio occultation (RO) satellite data CHAMP/GPS (Challenging Minisatellite Payload/Global Positioning System) for studying the ionosphere of the Earth. A method for deriving the parameters of ionospheric structures is based upon an analysis of the RO signal variations in the phase path and intensity. This method allows one to estimate the spatial displacement of a plasma layer with respect to the ray perigee, and to determine the layer inclination and height correction values. In this paper, we focus on the case study of inclined sporadic E (Es) layers in the high-latitude ionosphere based on available CHAMP RO data. Assuming that the internal gravity waves (IGWs) with the phase-fronts parallel to the ionization layer surfaces are responsible for the tilt angles of sporadic plasma layers, we have developed a new technique for determining the parameters of IGWs linked with the inclined Es structures. A small-scale internal wave may be modulating initially horizontal Es layer in height and causing a direction of the plasma density gradient to be rotated and aligned with that of the wave propagation vector k. The results of determination of the intrinsic wave frequency and period, vertical and horizontal wavelengths, intrinsic vertical and horizontal phase speeds, and other characteristics of IGWs under study are presented and discussed.

Studying internal gravity waves generated by atmospheric fronts over the Moscow region

Internal gravity wave (IGW) data obtained during the passage of atmospheric fronts over the Moscow region in June–July 2015 is analyzed. IGWs were recorded using a group of four microbarographs (developed at the Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences) located at distances of 7 to 54 km between them. Regularities of variations in IGW parameters (spatial coherence, characteristic scales, propagation direction, horizontal propagation velocity, and amplitudes) before, during, and after the passage of an atmospheric front over the observation network, when the observation network finds itself inside the cyclone and outside the front, are studied. The results may be useful in studying the relationships between IGW effects in different physical fields at different atmospheric heights. It is shown that, within periods exceeding 30 min, IGWs are coherent between observation points horizontally spaced at distances of about 60 km (coherence coefficient is 0.6–0.9). It is also shown that there is coherence between wave fluctuations in atmospheric pressure and fluctuations in horizontal wind velocity within the height range 60–200 m. A joint analysis of both atmospheric pressure and horizontal wind fluctuations has revealed the presence of characteristic dominant periods, within which cross coherences between fluctuations in atmospheric pressure and wind velocity have local maxima. These periods are within approximate ranges of 20–29, 37–47, 62–72, and 100–110 min. The corresponding (to these dominant periods) phase propagation velocities of IGWs lie within an interval of 15–25 m/s, and the horizontal wavelengths vary from 52 to 99 km within periods of 35 to 110 min, respectively.

Observation of tsunami‐generated ionospheric signatures over Hawaii caused by the 16 September 2015 Illapel earthquake

AbstractTsunamis generate internal gravity waves (IGWs) that propagate vertically into the atmosphere and can create detectable signatures in the ionosphere. These signatures have consistently been observed in the presence of a tsunami for over a decade in the total electron content and for over 5 years in the 630.0 nm airglow. Here we show perturbations appearing in filtered GPS‐derived total electron content (TEC) and 630.0 nm airglow above Hawaii during the passing of the tsunami induced by the 16 September 2015 earthquake in Illapel, Chile. We report measurements of IGW parameters from both observation methodologies using a combination of prior methods and a newly developed method that uses a Gabor filter bank. A previously developed geometric model that takes into account the assumed posture of tsunami‐induced IGWs in the geomagnetic field and the observation geometry is shown to predict fairly well the expected location of the observation in the sky. Results of the Gabor filtering technique are also compared to previously published results for the 11 March 2011 Tohoku event. An overall comparison between all of the tsunami‐induced signatures that have appeared in both the 630.0 nm airglow and TEC above Hawaii to date is provided.

Surface manifestations of internal waves observed using a land-based video system

This paper presents the results of processing sea-surface optical images in the coastal zone of the Sea of Japan with manifestations of internal gravity waves (IGWs) in the region of the Gamov Peninsula and the results of an analysis of IGW field observations in the same region. The following parameters of IGWs have been determined from the results of processing: their lengths and phase velocities. We calculate the IGW parameters in the region of observations using a mathematical model that takes into account the field data on the vertical stratification of coastal waters and the nonlinearity of the wave process. A comparison of the IGW parameters obtained from model calculations with the parameters obtained from the processing of optical images demonstrates a good agreement between them.

Seasonal variation of space–time parameters of internal gravity waves at Kharkiv (49°30′N, 36°51′E)

Internal gravity waves (IGWs) over Kharkiv (49°30′N, 36°51′E) have been studied by using an automatic goniometer of a meteor radar (AG MR), with its antenna directed to the East. The AG MR carries out Doppler measurements of the radial drift velocity and the position of the reflecting area of meteor trails. In order to obtain information about IGW parameters, an algorithm was used that processes the AG MR wind data by dividing the measured volume into several sub-volumes, and by carrying out wavelet analysis of wind variations in these areas. Results of 1 year (1987) of AG MR data show a good qualitative correspondence with literature results. There is an increase of IGW activity during the change of the zonal background wind in spring and autumn. It was found that the mean IGW horizontal phase velocity and predominating horizontal propagation direction change with season. However, the mean period (1.5 h), the dominant amplitude (∼30 m/s) and the vertical phase velocity do not strongly vary in the course of the year. The mean vertical and horizontal wavelengths were found to be 40 and 250 km, respectively.

Observations of short-period waves with an all-sky camera in the infrared airglow above Yakutsk

The parameters of internal gravity waves detected based on the variations in the hydroxyl molecule emission are statistically analyzed. The wave structures were registered with an all-sky infrared camera at Maimaga optical station (ϕ = 63° N, λ = 129.5° E). The data obtained in the winter period of 1998–2002 are analyzed. In total, 162 waves, the majority of which propagated westward, were recorded. The wavelengths vary from 15.4 to 100 km (the average value is ∼31 km); the observed horizontal phase velocities change from 19 to 166 m/s (the average value is ∼60 m/s), and the estimated periods are 9–90 min (the average value is ∼11 min). The statistical characteristics of the waves do not differ from those of similar waves at middle and low latitudes. The azimuthal dependence of the wave propagation direction is consistent with the theory of wave filtration by a background wind in the middle atmosphere. Probable sources of the waves are mountain ranges located at a distance of 200 km east of the observation site. Somewhat greater values of the mean wavelength and wave propagation velocities than those recorded at lower latitudes may be due to the lower loss of energy and velocity of the waves during their propagation from the source to the mesosphere, although other causes are not ruled out. Ripple-type waves have the same direction of propagation as band-type waves.

Parameters of internal gravity waves in the mesosphere-lower thermosphere region derived from meteor radar wind measurements

Abstract. A procedure of revealing parameters of internal gravity waves from meteor radar wind measurements is presented. The method is based on dividing the measuring volume into different parts and, using wavelet analysis, calculating the phase progression of frequency peaks in the vertical and horizontal direction. Thus, the distribution of vertical and horizontal wavelengths and directions of IGW energy propagation, using meteor radar data, has been obtained. The method was applied to a 4-month data set obtained in July and August, 1998 and 1999. As expected, the majority of waves have been found to propagate upwards, although a considerable number seem to propagate downwards as well. High-frequency (intrinsic periods T* of less than 2 h) waves are dominating. The distribution of waves over the course of an average day is only weakly structured, with weak maxima in the morning and evening.

Horizontal parameters of the internal gravity waves registered over Yakutia

Results of the investigation of the horizontal parameters of internal gravity waves with period >3 hours propagating at the mesopause region are presented. Wave disturbance registrations were carried out at station Maimaga (63°N, 129.5°E) by their influence on the intensity of the nightglow emission OH(7,3). Data obtained at bright moonless nights in winter 1982–1988 were used. Analysis of the 66 selected cases showed that the number of westward waves was greater than eastward ones, the mean value of eastward phase velocity exceeded the westward velocity mean value. It is shown that such horizontal phase velocity behavior can be the effect of the background wind filtration. A distribution of the averaged wave periods depends on the direction of propagation. Suggestions which could explain this effect are listed.

Statistical analysis of gravity waves observed with the middle and upper atmosphere radar in the middle atmosphere: 1. Method and general characteristics

A statistical procedure is developed to obtain the parameters of spectral harmonics of internal gravity waves (IGW) with horizontal wavelengths larger than ∼ 60 km using measurements of wind velocity in the middle atmosphere from the middle and upper atmosphere (MU) radar. The method is applied to find sets of IGW parameters for the winter and summer seasons of 1987–1988 for 6‐km‐thick layers centered at 70, 75, and 80 km at Shigaraki, Japan (34.9°N, 139.4°E). The numbers of selected IGW harmonics having periods from 5 min up to 6 hours vary between 360 and 2000 depending on the season and altitude. Mean vertical wave numbers are 0.6–0.9 km−1 in winter and 0.5–1 km−1 in summer, and horizontal wave numbers are (3–4)×10−2 km−1 and (2–4)×10−2 km−1, respectively. Predominant azimuths of wave vectors and momentum fluxes concentrate near 64° in winter and 90° in summer at all altitudes. In general, the difference between the azimuths of the wave vector and momentum flux is close to zero or 180°. Turbulent and instrumental noise can contribute 20–30% of the observed intensity of the wind variations at altitudes of 70–85 km. The IGW momentum fluxes are 0.2–2.7 m2s−2 in winter and 0.2–1.9 m2s−2 in summer. The wave drag of the mean flow is 0.5–45 m2s−1 in winter and 2–25 m2s−1 in summer. In most cases the momentum flux and wave drag are directed oppositely to the mean wind.

Visible continuum emission and gravity waves

Observed oscillations in the visible continuum emission (5000 Å) are studied considering the usual visible emission mechanism, NO + O (both two-body and three-body paths). Characteristic parameters of internal gravity waves are obtained using Hines' linear theory. Values of the kinetic energy density ϵ, and temperature variations Δθ, due to gravity waves are calculated. The results ( ϵ ~ 10 6 cm 2 s −2, Δθ = 4–9 K) are in agreement with those obtained by means of different techniques reported in the literature. A similar analysis of the simultaneous green-line emission data is made and a comparison is drawn between the results obtained for both emissions. An expression relating relative brightness of continuum emission and relative perturbations of atmospheric density is proposed.