Atmospheric Science Data Center
2013-04-19
article title: Gravity Waves Ripple over Marine Stratocumulus Clouds ... Imaging SpectroRadiometer (MISR), a fingerprint-like gravity wave feature occurs over a deck of marine stratocumulus clouds. Similar ... that occur when a pebble is thrown into a still pond, such "gravity waves" sometimes appear when the relatively stable and stratified air ...
NASA Technical Reports Server (NTRS)
Fritts, David
1987-01-01
Gravity waves contributed to the establishment of the thermal structure, small scale (80 to 100 km) fluctuations in velocity (50 to 80 m/sec) and density (20 to 30%, 0 to peak). Dominant gravity wave spectrum in the middle atmosphere: x-scale, less than 100 km; z-scale, greater than 10 km; t-scale, less than 2 hr. Theorists are beginning to understand middle atmosphere motions. There are two classes: Planetary waves and equatorial motions, gravity waves and tidal motions. The former give rise to variability at large scales, which may alter apparent mean structure. Effects include density and velocity fluctuations, induced mean motions, and stratospheric warmings which lead to the breakup of the polar vortex and cooling of the mesosphere. On this scale are also equatorial quasi-biennial and semi-annual oscillations. Gravity wave and tidal motions produce large rms fluctuations in density and velocity. The magnitude of the density fluctuations compared to the mean density is of the order of the vertical wavelength, which grows with height. Relative density fluctuations are less than, or of the order of 30% below the mesopause. Such motions may cause significant and variable convection, and wind shear. There is a strong seasonal variation in gravity wave amplitude. Additional observations are needed to address and quantify mean and fluctuation statistics of both density and mean velocity, variability of the mean and fluctuations, and to identify dominant gravity wave scales and sources as well as causes of variability, both temporal and geographic.
NASA Astrophysics Data System (ADS)
van Oers, Alexander M.; Maas, Leo R. M.; Bokhove, Onno
2017-02-01
The linear equations governing internal gravity waves in a stratified ideal fluid possess a Hamiltonian structure. A discontinuous Galerkin finite element method has been developed in which this Hamiltonian structure is discretized, resulting in conservation of discrete analogs of phase space and energy. This required (i) the discretization of the Hamiltonian structure using alternating flux functions and symplectic time integration, (ii) the discretization of a divergence-free velocity field using Dirac's theory of constraints and (iii) the handling of large-scale computational demands due to the 3-dimensional nature of internal gravity waves and, in confined, symmetry-breaking fluid domains, possibly its narrow zones of attraction.
Gravity Waves and Linear Inflation From Axion Monodromy
McAllister, Liam; Silverstein, Eva; Westphal, Alexander; /SLAC /Stanford U., Phys. Dept.
2010-08-26
Wrapped branes in string compactifications introduce a monodromy that extends the field range of individual closed-string axions to beyond the Planck scale. Furthermore, approximate shift symmetries of the system naturally control corrections to the axion potential. This suggests a general mechanism for chaotic inflation driven by monodromy-extended closed-string axions. We systematically analyze this possibility and show that the mechanism is compatible with moduli stabilization and can be realized in many types of compactifications, including warped Calabi-Yau manifolds and more general Ricci-curved spaces. In this broad class of models, the potential is linear in the canonical inflaton field, predicting a tensor to scalar ratio r {approx} 0.07 accessible to upcoming cosmic microwave background (CMB) observations.
2D instabilities of surface gravity waves on a linear shear current
NASA Astrophysics Data System (ADS)
Francius, Marc; Kharif, Christian
2016-04-01
instabilities due to resonant four-wave interactions, as well as to study the influence of vorticity and nonlinearity on the characteristics of linear instabilities due to resonant five-wave and six-wave interactions. Depending on the dimensionless depth, superharmonic instabilities due to five-wave interactions can become dominant with increasing positive vorticiy. Acknowledgments: This work was supported by the Direction Générale de l'Armement and funded by the ANR project n°. ANR-13-ASTR-0007. References [1] A. Constantin, Two-dimensionality of gravity water flows of constant non-zero vorticity beneath a surface wave train, Eur. J. Mech. B/Fluids, 2011, 30, 12-16. [2] R. S. Johnson, On the modulation of water waves on shear flows, Proc. Royal Soc. Lond. A., 1976, 347, 537-546. [3] M. Oikawa, K. Chow, D. J. Benney, The propagation of nonlinear wave packets in a shear flow with a free surface, Stud. Appl. Math., 1987, 76, 69-92. [4] A. I Baumstein, Modulation of gravity waves with shear in water, Stud. Appl. Math., 1998, 100, 365-90. [5] R. Thomas, C. Kharif, M. Manna, A nonlinear Schrödinger equation for water waves on finite depth with constant vorticity, Phys. Fluids, 2012, 24, 127102. [6] M. M Rienecker, J. D Fenton, A Fourier approximation method for steady water waves , J. Fluid Mech., 1981, 104, 119-137 [7] M. Francius, C. Kharif, Three-dimensional instabilities of periodic gravity waves in shallow water, J. Fluid Mech., 2006, 561, 417-437
NASA Technical Reports Server (NTRS)
Vanzandt, T. E.
1985-01-01
Atmospheric parameters fluctuate on all scales. In the mesoscale these fluctuations are occasionally sinusoidal so that they can be interpreted as gravity waves. Usually, however, the fluctuations are noise like, so that their cause is not immediately evident. Results of mesoscale observations in the 20 to 120 m altitude range that are suitable for incorporation into a model atmosphere are very limited. In the stratosphere and lower mesosphere observations are sparse and very little data has been summarized into appropriate form. There is much more data in the upper mesosphere and lower thermosphere, but again very little of it has been summarized. The available mesoscale spectra of horizontal wind u versus vertical wave number m in the 20 to 120 km altitude range are shown together with a spectrum from the lower atmosphere for comparison. Further information about these spectra is given. In spite of the large range of altitudes and latitudes, the spectra from the lower atmosphere (NASA, 1971 and DEWAN, 1984) are remarkably similar in both shape and amplitude. The mean slopes of -2.38 for the NASA spectrum and -2.7 for the Dewan spectra are supported by the mean slope of -2.75 found by ROSENBERG et al. (1974). The mesospheric spectrum is too short to establish a shape. Its amplitude is about an order of magnitude larger than the NASA spectrum in the same wave number range. The NASA and Dewan spectra suggest that the mesoscale spectra in the lower atmosphere are insensitive to meteorological conditions.
On the linear approximation of gravity wave saturation in the mesosphere
NASA Technical Reports Server (NTRS)
Chao, W. C.; Schoeberl, M. R.
1984-01-01
Lindzen's model of gravity wave breaking is shown to be inconsistent with the process of convective adjustment and associated turbulent outbreak. The K-theory turbulent diffusion model used by Lindzen implies a spatially uniform turbulent field which is not in agreement with the fact that gravity wave saturation and the associated convection produce turbulence only in restricted zones. The Lindzen model may be corrected to some extent by taking the turbulent Prandtl number for a diffusion acting on the wave itself to be very large. The eddy diffusion coefficients computed by Lindzen then become a factor of 2 larger and eddy transports of heat and constituents by wave fields vanish to first order.
NASA Astrophysics Data System (ADS)
Ribstein, B.; Achatz, U.
2016-09-01
Gravity waves (GWs) play an important role in atmospheric dynamics. Due to their short wavelengths, they must be parameterized in current weather and forecast models, which cannot resolve them explicitly. We are here the first to report the possibility and the implication of having an online GW parameterization in a linear but global model that incorporates their horizontal propagation, the effects of transients and of horizontal background gradients on GW dynamics. The GW parameterization is based on a ray-tracer model with a spectral formulation that is safe against numerical instabilities due to caustics. The global model integrates the linearized primitive equations to obtain solar tides (STs), with a seasonally dependent reference climatology, forced by a climatological daily cycle of the tropospheric and stratospheric heating, and the (instantaneous) GW momentum and buoyancy flux convergences resulting from the ray tracer. Under a more conventional "single-column" approximation, where GWs only propagate vertically and do not respond to horizontal gradients of the resolved flow, GW impacts are shown to be significantly changed in comparison with "full" experiments, leading to significant differences in ST amplitudes and phases, pointing at a sensitive issue of GW parameterizations in general. In the full experiment, significant semidiurnal STs arise even if the tidal model is only forced by diurnal heating rates. This indicates that an important part of the tidal signal is forced directly by GWs via their momentum and buoyancy deposition. In general, the effect of horizontal GW propagation and the GW response to horizontal large-scale flow gradients is rather observed in nonmigrating than in migrating tidal components.
2009-10-09
function with modulus ??),()• In fact, it is the well-known cnoidal wave solution of the peri- odic KdV equation [1]. For the hyperelliptic... KdV ) equation , which describes the dynamics of weakly- nonlinear dispersive waves, for the internal-waves problem. Under the assumption that the...for solving the periodic KdV equation by the scattering trans- form can be split into two distinct steps: the direct problem and the inverse problem
NASA Astrophysics Data System (ADS)
Grishchuk, Leonid Petrovich
The article concerns astronomical phenomena , related with discovery of gravitational waves of various nature: 1) primordial (relic) gravitational waves, analogous to MWBR 2) gravitational waves due to giant collisions in the Universe between 2a) Macroscopic black Holes in the centers of Galaxies 2b) Tidal disruption of neutron stars by Black holes 2c) deformations of the space-time by stellar mass Black Holes moving near giant Black Holes in the centers of Galaxies 2d) Supernovae phenomena 2e) accretion phenomena on Black Holes and Neutron stars. The Earth based interferometric technics (LIGO Project) to detect gravitational waves is described as well as the perspectiva for a space Laser Interferometric Antena (LISA)is discussed. The article represents a modified text of the Plenary talk "Gravity-Wave astronomy" given at the XI International gravitational Conference (July 1986, Stockholm, Sweden).
Gravity wave initiated convection
NASA Technical Reports Server (NTRS)
Hung, R. J.
1990-01-01
The vertical velocity of convection initiated by gravity waves was investigated. In one particular case, the convective motion-initiated and supported by the gravity wave-induced activity (excluding contributions made by other mechanisms) reached its maximum value about one hour before the production of the funnel clouds. In another case, both rawinsonde and geosynchronous satellite imagery were used to study the life cycles of severe convective storms. Cloud modelling with input sounding data and rapid-scan imagery from GOES were used to investigate storm cloud formation, development and dissipation in terms of growth and collapse of cloud tops, as well as, the life cycles of the penetration of overshooting turrets above the tropopause. The results based on these two approaches are presented and discussed.
Inherently Unstable Internal Gravity Waves
NASA Astrophysics Data System (ADS)
Alam, Reza
2016-11-01
Here we show that there exist internal gravity waves that are inherently unstable, that is, they cannot exist in nature for a long time. The instability mechanism is a one-way (irreversible) harmonic-generation resonance that permanently transfers the energy of an internal wave to its higher harmonics. We show that, in fact, there are countably infinite number of such unstable waves. For the harmonic-generation resonance to take place, nonlinear terms in the free surface boundary condition play a pivotal role, and the instability does not obtain for a linearly-stratified fluid if a simplified boundary condition such as rigid lid or linear form is employed. Harmonic-generation resonance discussed here also provides a mechanism for the transfer of the energy of the internal waves to the higher-frequency part of the spectrum where internal waves are more prone to breaking, hence losing energy to turbulence and heat and contributing to oceanic mixing. Yong Liang (yong.liang@berkeley.edu).
Gravity Forcing Of Surface Waves
NASA Astrophysics Data System (ADS)
Kenyon, K. E.
2005-12-01
Surface waves in deep water are forced entirely by gravity at the air-sea interface when no other forces act tangent to the surface. Then according to Newton's second law, the fluid acceleration parallel to the surface must equal the component of gravity parallel to the surface. Between crest and trough the fluid accelerates; between trough and crest the fluid decelerates. By replacing Bernoulli's law, gravity forcing becomes the dynamic boundary condition needed to solve the mathematical problem of these waves. Irrotational waves with a sinusoidal profile satisfy the gravity forcing condition, with the usual dispersion relation, provided the slope is small compared to one, as is true also of the Stokes development. However, the exact wave shape can be calculated using the gravity forcing method in a way that is less complex and less time consuming than that of the Stokes perturbation expansion. To the second order the surface elevation is the same as the Stokes result; the third order calculation has not been made yet. Extensions of the gravity forcing method can easily be carried out for multiple wave trains, solitary waves and bores, waves in finite constant mean depths, and internal waves in a two-layer system. For shoaling surface waves gravity forcing provides a physical understanding of the progressive steepening often observed near shore.
Acoustic-gravity waves, theory and application
NASA Astrophysics Data System (ADS)
Kadri, Usama; Farrell, William E.; Munk, Walter
2015-04-01
Acoustic-gravity waves (AGW) propagate in the ocean under the influence of both the compressibility of sea water and the restoring force of gravity. The gravity dependence vanishes if the wave vector is normal to the ocean surface, but becomes increasingly important as the wave vector acquires a horizontal tilt. They are excited by many sources, including non-linear surface wave interactions, disturbances of the ocean bottom (submarine earthquakes and landslides) and underwater explosions. In this introductory lecture on acoustic-gravity waves, we describe their properties, and their relation to organ pipe modes, to microseisms, and to deep ocean signatures by short surface waves. We discuss the generation of AGW by underwater earthquakes; knowledge of their behaviour with water depth can be applied for the early detection of tsunamis. We also discuss their generation by the non-linear interaction of surface gravity waves, which explains the major role they play in transforming energy from the ocean surface to the crust, as part of the microseisms phenomenon. Finally, they contribute to horizontal water transport at depth, which might affect benthic life.
High Latitude Gravity Wave Forcing by the Disturbed Polar Vortex
NASA Astrophysics Data System (ADS)
Mehta, D.; Gerrard, A. J.; Ebihara, Y.; Weatherwax, A. T.
2015-12-01
We present mesopause gravity wave observations from 589-nm Na all-sky data taken by a multiwavelength all-sky imager located at South Pole, Antarctica. Focusing on gravity waves observed during the 2003 and 2004 austral winter seasons, we investigate possible sources of observed waves using linear gravity wave ray-tracing. By comparing wave ray paths with the structure of the polar vortex obtained from the ECMWF operational model, we show that a unique generator of gravity waves that then propagate into the high latitude mesospause is the disturbance of the polar vortex near 40-km altitude due to the formation of baroclinic instabilities.
Elandt, Ryan B; Shakeri, Mostafa; Alam, Mohammad-Reza
2014-02-01
Here we show that a nonlinear resonance between oceanic surface waves caused by small seabed features (the so-called Bragg resonance) can be utilized to create the equivalent of lenses and curved mirrors for surface gravity waves. Such gravity wave lenses, which are merely small changes to the seafloor topography and therefore are surface noninvasive, can focus or defocus the energy of incident waves toward or away from any desired focal point. We further show that for a broadband incident wave spectrum (i.e., a wave group composed of a multitude of different-frequency waves), a polychromatic topography (occupying no more than the area required for a monochromatic lens) can achieve a broadband lensing effect. Gravity wave lenses can be utilized to create localized high-energy wave zones (e.g., for wave energy harvesting or creating artificial surf zones) as well as to disperse waves in order to create protected areas (e.g., harbors or areas near important offshore facilities). In reverse, lensing of oceanic waves may be caused by natural seabed features and may explain the frequent appearance of very high amplitude waves in certain bodies of water.
Random coupling of acoustic-gravity waves in the atmosphere
NASA Astrophysics Data System (ADS)
Millet, Christophe; Lott, Francois; Haynes, Christophe
2016-11-01
In numerical modeling of long-range acoustic propagation in the atmosphere, the effect of gravity waves on low-frequency acoustic waves is often ignored. As the sound speed far exceeds the gravity wave phase speed, these two types of waves present different spatial scales and their linear coupling is weak. It is possible, however, to obtain relatively strong couplings via sound speed profile changes with altitude. In the present study, this scenario is analyzed for realistic gravity wave fields and the incident acoustic wave is modeled as a narrow-banded acoustic pulse. The gravity waves are represented as a random field using a stochastic multiwave parameterization of non-orographic gravity waves. The parameterization provides independent monochromatic gravity waves, and the gravity wave field is obtained as the linear superposition of the waves produced. When the random terms are retained, a more generalized wave equation is obtained that both qualitatively and quantitatively agrees with the observations of several highly dispersed stratospheric wavetrains. Here, we show that the cumulative effect of gravity wave breakings makes the sensitivity of ground-based acoustic signals large, in that small changes in the parameterization can create or destroy an acoustic wavetrain.
NASA Astrophysics Data System (ADS)
Miles, John
2001-09-01
The eigenvalue problem for gravity waves on a shear flow of depth h and non-inflected velocity profile U(y) (typically parabolic) is revisited, following Burns (1953) and Yih (1972). Complementary variational formulations that provide upper and lower bounds to the Froude number F as a function of the wave speed c and wavenumber k are constructed. These formulations are used to improve Burns's long-wave approximation and to determine Yih's critical wavenumber k[low asterisk], for which the wave is stationary (c = 0) and to which k must be inferior for the existence of an upstream running wave.
Local effects of gravity wave propagation and saturation
NASA Technical Reports Server (NTRS)
Fritts, D. C.
1985-01-01
In recent years, gravity waves were recognized to play a major role in the dynamics of the middle atmosphere. Perhaps the major effect of such motions are the reversal of the vertical shear of the mean zonal wind and the occurrence of a large turbulent diffusivity in the mesosphere due to gravity wave saturation. Yet, despite the importance of these gravity wave effects, the processes and the consequences of gravity wave propagation and saturation are only beginning to be understood in detail. The linear saturation theory predicts drag and turbulent diffusion due to saturating wave motion. This theory, however, fails to address a number of issues that are certain to be important for gravity wave propagation and saturation in the middle atmosphere. These issues, including wave transience, wave superposition, local convective adjustment, and nonlinearity, are discussed.
NASA Astrophysics Data System (ADS)
Revenough, Justin
Elastic waves propagating in simple media manifest a surprisingly rich collection of phenomena. Although some can't withstand the complexities of Earth's structure, the majority only grow more interesting and more important as remote sensing probes for seismologists studying the planet's interior. To fully mine the information carried to the surface by seismic waves, seismologists must produce accurate models of the waves. Great strides have been made in this regard. Problems that were entirely intractable a decade ago are now routinely solved on inexpensive workstations. The mathematical representations of waves coded into algorithms have grown vastly more sophisticated and are troubled by many fewer approximations, enforced symmetries, and limitations. They are far from straightforward, and seismologists using them need a firm grasp on wave propagation in simple media. Linear Elastic Waves, by applied mathematician John G. Harris, responds to this need.
Shear waves in inhomogeneous, compressible fluids in a gravity field.
Godin, Oleg A
2014-03-01
While elastic solids support compressional and shear waves, waves in ideal compressible fluids are usually thought of as compressional waves. Here, a class of acoustic-gravity waves is studied in which the dilatation is identically zero, and the pressure and density remain constant in each fluid particle. These shear waves are described by an exact analytic solution of linearized hydrodynamics equations in inhomogeneous, quiescent, inviscid, compressible fluids with piecewise continuous parameters in a uniform gravity field. It is demonstrated that the shear acoustic-gravity waves also can be supported by moving fluids as well as quiescent, viscous fluids with and without thermal conductivity. Excitation of a shear-wave normal mode by a point source and the normal mode distortion in realistic environmental models are considered. The shear acoustic-gravity waves are likely to play a significant role in coupling wave processes in the ocean and atmosphere.
NASA Astrophysics Data System (ADS)
Lin, C. Y. T.; Deng, Y.; Sheng, C.; Drob, D. P.
2015-12-01
Waves of various spatial and temporal scales, including acoustic waves, gravity waves, tides, and planetary waves, modify the dynamics of the terrestrial atmosphere at all altitudes. Perturbations caused by the natural and mankind activities on the ground, such as volcano eruptions, earthquakes, explosions, propagate upward and impact the upper atmosphere. Among these waves, propagation of the atmospheric acoustic waves is particularly sensitive to the fine structure of the background atmosphere. However, the fine-structured gravity waves (smaller than 1° x 1°) are currently poorly measured especially at the altitudes above 100 km and are computationally too expensive for most models to incorporate properly. The Global Ionosphere Thermosphere Model (GITM) allows for non-hydrostatic solutions and has a flexible resolution. Thus, it is ideal for the study of vertical propagating waves. In this study, the ionospheric and thermospheric response to acoustic-gravity waves is first presented with an artificial source of various frequencies, followed by a case study of the 2014 Tohoku tsunami. Additionally a time-varying spectral gravity wavefield propagated from the ground is implemented into GITM to capture the statistical background structures that is crucial to the upper atmospheric models. Our results show the importance of consideration of background small-scale structures to interpretation of the observed ionospheric and thermospheric perturbations, such as traveling ionospheric disturbances (TIDs) and traveling atmospheric disturbances (TADs).
Gravity related waves in plants.
NASA Astrophysics Data System (ADS)
Wagner, Claudia; Wagner, Orvin
2007-04-01
Calculations using sets of plant internodal spacings and actual measurements give wave velocity ratios and actual velocities. Plant shapes seem to derive from these gravity related waves. The velocities of the waves increase in jumps as their direction of travel changes from vertical to horizontal. The calculated ratios of the vertical velocity to the horizontal velocity are ratios of small integers. Short chunky trees like apple have a small velocity ratio (calculated ratio for apple 4/3) while tall spindly trees like ponderosa pine (3/1) have a large ratio. Measured wave velocities for Ponderosa pine are: 1207±60 cm/s for horizontal and 3469±170cm/s for vertical. The plant internal structure seems to determine the velocity ratio. e.g. see Physiol. Chem. Phys. & Med. NMR (1996) 28: 173-196 and later papers by O.E. Wagner. The results might indicate that gravity is a wave phenomenon since plants respond to gravity in a wavelike fashion. Plants waves seem to have a limited set of frequencies and a recent observation is that they are the same in every direction. The latter permits one to write some very enlightening equations.
AdS waves as exact solutions to quadratic gravity
Guellue, Ibrahim; Sisman, Tahsin Cagri; Tekin, Bayram; Guerses, Metin
2011-04-15
We give an exact solution of the quadratic gravity in D dimensions. The solution is a plane-fronted wave metric with a cosmological constant. This metric solves not only the full quadratic gravity field equations but also the linearized ones which include the linearized equations of the recently found critical gravity. A subset of the solutions change the asymptotic structure of the anti-de Sitter space due to their logarithmic behavior.
Nonstationary Gravity Wave Forcing of the Stratospheric Zonal Mean Wind
NASA Technical Reports Server (NTRS)
Alexander, M. J.; Rosenlof, K. H.
1996-01-01
The role of gravity wave forcing in the zonal mean circulation of the stratosphere is discussed. Starting from some very simple assumptions about the momentum flux spectrum of nonstationary (non-zero phase speed) waves at forcing levels in the troposphere, a linear model is used to calculate wave propagation through climatological zonal mean winds at solstice seasons. As the wave amplitudes exceed their stable limits, a saturation criterion is imposed to account for nonlinear wave breakdown effects, and the resulting vertical gradient in the wave momentum flux is then used to estimate the mean flow forcing per unit mass. Evidence from global, assimilated data sets are used to constrain these forcing estimates. The results suggest the gravity-wave-driven force is accelerative (has the same sign as the mean wind) throughout most of the stratosphere above 20 km. The sense of the gravity wave forcing in the stratosphere is thus opposite to that in the mesosphere, where gravity wave drag is widely believed to play a principal role in decelerating the mesospheric jets. The forcing estimates are further compared to existing gravity wave parameterizations for the same climatological zonal mean conditions. Substantial disagreement is evident in the stratosphere, and we discuss the reasons for the disagreement. The results suggest limits on typical gravity wave amplitudes near source levels in the troposphere at solstice seasons. The gravity wave forcing in the stratosphere appears to have a substantial effect on lower stratospheric temperatures during southern hemisphere summer and thus may be relevant to climate.
Resonant triad interactions of acoustc-gravity waves
NASA Astrophysics Data System (ADS)
Kadri, Usama; Akylas, T. R.
2015-11-01
Surface-acoustic wave disturbances in water of constant depth over a rigid bottom, due to the combined action of gravity and compressibility, are studied. In the linear theory, apart from free-surface (gravity) waves, there is also a countable infinity of acoustic (compression) modes. As the sound speed in water, typically, far exceeds the maximum gravity wave phase speed, these two types of modes feature vastly different spatial and/or temporal scales, and their linear coupling is weak. It is possible, however, to realize significant energy exchange between gravity and acoustic waves via nonlinear interactions. This scenario is analyzed for resonant wave triads that comprise two counter-propagating gravity waves and a long-crested acoustic mode. Owing to this disparity in length scales, the interaction time scale as well as the form of the amplitude evolution equations differ from those of a standard resonant triad. In the case of a perfectly tuned triad of uniform monochromatic wave trains, nearly all the energy initially in the gravity waves can be transferred to the acoustic wave. This mechanism, however, is less efficient when the interacting waves are modulated wavepackets.
Ionospheric disturbances and gravity waves
NASA Technical Reports Server (NTRS)
Eun, H.; Gross, S. H.
1976-01-01
The response of ionization to a gravity wave moving through the ionosphere is studied. Hydrodynamic equations are used, and local thermodynamic equilibrium is imposed for simplicity. The treatment involves a perturbation analysis, and the background medium is assumed to be time stationary, horizontally stratified, and known. It is shown that ionization may be locally resonant at each level for certain frequencies and directions, for which condition neutral and ionized particles are considered closely or critically coupled. The phase direction for this critical coupling is always downward in the absence of a magnetic field. A magnetic field results in two resonant directions for the same frequency, and these directions are mostly downward. Observed TID's associated with gravity waves may be indicative of such resonances. It is also noted that strong coupling may occur to neutral acoustic waves at high altitudes. Previous investigations restrict their use of momentum equations to the diffusion equation. The analysis also shows that such restrictions result in the neglect of terms arising from momentum transport due to any background ambipolar diffusion velocity and wave motion. These terms are mostly relevant at higher altitudes.
Asymptotic Linear Stability of Solitary Water Waves
NASA Astrophysics Data System (ADS)
Pego, Robert L.; Sun, Shu-Ming
2016-12-01
We prove an asymptotic stability result for the water wave equations linearized around small solitary waves. The equations we consider govern irrotational flow of a fluid with constant density bounded below by a rigid horizontal bottom and above by a free surface under the influence of gravity neglecting surface tension. For sufficiently small amplitude waves, with waveform well-approximated by the well-known sech-squared shape of the KdV soliton, solutions of the linearized equations decay at an exponential rate in an energy norm with exponential weight translated with the wave profile. This holds for all solutions with no component in (that is, symplectically orthogonal to) the two-dimensional neutral-mode space arising from infinitesimal translational and wave-speed variation of solitary waves. We also obtain spectral stability in an unweighted energy norm.
Gravity wave reflection: Case study based on rocket data
NASA Astrophysics Data System (ADS)
Wüst, Sabine; Bittner, Michael
2008-03-01
Since gravity waves significantly influence the atmosphere by transporting energy and momentum, it is important to study their wave spectrum and their energy dissipation rates. Besides that, knowledge about gravity wave sources and the propagation of the generated waves is essential. Originating in the lower atmosphere, gravity waves can move upwards; when the background wind field is equal to their phase speed a so-called critical layer is reached. Their breakdown and deposition of energy and momentum is possible. Another mechanism which can take place at critical layers is gravity wave reflection. In this paper, gravity waves which were observed by foil chaff measurements during the DYANA (DYnamics Adapted Network for the Atmosphere) campaign in 1990 in Biscarrosse (44°N, 1°W)--as reported by Wüst and Bittner [2006. Non-linear wave-wave interaction: case studies based on rocket data and first application to satellite data. Journal of Atmospheric and Solar-Terrestrial Physics 68, 959-976]--are investigated to look for gravity wave reflection processes. Following nonlinear theory, energy dissipation rates according to Weinstock [1980. Energy dissipation rates of turbulence in the stable free atmosphere. Journal of the Atmospheric Sciences 38, 880-883] are calculated from foil chaff cloud and falling sphere data and compared with the critical layer heights. Enhanced energy dissipation rates are found at those altitudes where the waves' phase speed matches the zonal background wind speeds. Indication of gravity wave trapping is found between two altitudes of around 95 and 86 km.
Gravity wave turbulence revealed by horizontal vibrations of the container.
Issenmann, B; Falcon, E
2013-01-01
We experimentally study the role of forcing on gravity-capillary wave turbulence. Previous laboratory experiments using spatially localized forcing (vibrating blades) have shown that the frequency power-law exponent of the gravity wave spectrum depends on the forcing parameters. By horizontally vibrating the whole container, we observe a spectrum exponent that does not depend on the forcing parameters for both gravity and capillary regimes. This spatially extended forcing leads to a gravity spectrum exponent in better agreement with the theory than by using a spatially localized forcing. The role of the vessel shape has been also studied. Finally, the wave spectrum is found to scale linearly with the injected power for both regimes whatever the forcing type used.
Plants respond to gravity with gravity related waves.
Wagner, Orvin E
2007-07-01
Gravity related waves in plants control plant shapes by their velocity, vertical to horizontal velocity ratios, and the stepwise change in velocity from horizontal to vertical. Velocities are measured directly while velocity ratios can be derived from internodal spacings or measurements of velocities. Plant wave frequencies are the same in every direction. The wave proofs are overwhelming with plant communication and ac field interaction as added proof.
Effect of nonlinear instability on gravity-wave momentum transport
NASA Technical Reports Server (NTRS)
Dunkerton, Timothy J.
1987-01-01
This paper investigates the nonlinear instability of internal gravity waves and the effects of their nonlinear interaction on momentum flux, using simple theoretical and numerical models. From the result of an analysis of parametric instability of a two-dimensional internal gravity wave as discussed by Yeh and Liu (1981) and Klostermeyer (1982), a group trajectory length scale for a gravity wave packet was determined, expressed in terms of the dominant vertical wavelenght and the degree of convective saturation. It is shown that this analysis justifies the Eikonal saturation method for relatively transient packets, that are well below the saturation amplitude, propagating in a slowly varying mean flow. Conversely, linear theory fails for persistent disturbances and trasient wave packets near convective saturation.
Interactions between intermittent gravity waves and infrasounds
NASA Astrophysics Data System (ADS)
Ribstein, Bruno; Millet, Christophe; Lott, Francois; de La Camara, Alvaro
2016-11-01
Even though the accuracy of atmospheric specifications is constantly improving, it is well known that the main part of gravity waves is still yet not resolved in the available data. In most infrasound modeling studies, the unresolved gravity wave field is often represented as a deterministic field that is superimposed on a given average background state. Direct observations in the lower stratosphere show, however, that the gravity wave field is very intermittent, and is often dominated by rather well defined wave packets. In this study we sample the gravity wave spectrum by launching few monochromatic waves and choose their properties stochastically to mimic the intermittency. The statistics of acoustic signals are computed by decomposing the original signal into a sum of modal pulses. Owing to the disparity of the gravity and acoustic lengthscales, the interaction can be described using a multiplescale analysis and the appropriate amplitude evolution equation involves certain random terms that are related to the gravity wave sources. More specifically, it is shown how the unpredictable low level small-scale dynamics triggers multiple random stratospheric waveguides in which high frequency infrasound components can propagate efficiently.
Wavelet analysis of internal gravity waves
NASA Astrophysics Data System (ADS)
Hawkins, J.; Warn-Varnas, A.; Chin-Bing, S.; King, D.; Smolarkiewicsz, P.
2005-05-01
A series of model studies of internal gravity waves (igw) have been conducted for several regions of interest. Dispersion relations from the results have been computed using wavelet analysis as described by Meyers (1993). The wavelet transform is repeatedly applied over time and the components are evaluated with respect to their amplitude and peak position (Torrence and Compo, 1998). In this sense we have been able to compute dispersion relations from model results and from measured data. Qualitative agreement has been obtained in some cases. The results from wavelet analysis must be carefully interpreted because the igw models are fully nonlinear and wavelet analysis is fundamentally a linear technique. Nevertheless, a great deal of information describing igw propagation can be obtained from the wavelet transform. We address the domains over which wavelet analysis techniques can be applied and discuss the limits of their applicability.
Mesosphere Dynamics with Gravity Wave Forcing. 2; Planetary Waves
NASA Technical Reports Server (NTRS)
Mayr, H. G.; Mengel, J. G.; Chan, K. L.; Porter, H. S.; Einaudi, Franco (Technical Monitor)
2000-01-01
We present results from a non-linear, 3D, time dependent numerical spectral model (NSM) which extends from the ground up into the thermosphere and incorporates Hines' Doppler Spread Parameterization for small-scale gravity waves (GW). Our focal point is the mesosphere where wave interactions are playing a dominant role. We discuss planetary waves in the present paper and diurnal and semi-diurnal tides in the companion paper. Without external time dependent energy or momentum sources, planetary waves (PWs) are generated in the model for zonal wavenumbers 1 to 4, which have amplitudes in the mesosphere above 50 km as large as 30 m/s and periods between 2 and 50 days. The waves are generated primarily during solstice conditions, which indicates that the baroclinic instability (associated with the GW driven reversal in the latitudinal temperature gradient) is playing an important role. Results from a numerical experiment show that GWs are also involved directly in generating the PWs. For the zonal wavenumber m = 1, the predominant wave periods in summer are around 4 days and in winter between 6 and 10 days. For m = 2, the periods are in summer and close to 2.5 and 3.5 days respectively For m = 3, 4 the predominant wave periods are in both seasons close to two days. The latter waves have the characteristics of Rossby gravity waves with meridional winds at equatorial latitudes. A common feature of the PWs (m = 1 to 4) generated in summer and winter is that their vertical wavelengths throughout the mesosphere are large which indicates that the waves are not propagating freely but are generated throughout the region. Another common feature is that the PWs propagate preferentially westward in summer and eastward in winter, being launched from the westward and eastward zonal winds that prevail respectively in summer and winter altitudes below 80 km. During spring and fall, for m = 1 and 2 eastward propagating long period PWs are generated that are launched from the smaller
Gravity waves from cosmic bubble collisions
Salem, Michael P.; Saraswat, Prashant; Shaghoulian, Edgar E-mail: ps88@stanford.edu
2013-02-01
Our local Hubble volume might be contained within a bubble that nucleated in a false vacuum with only two large spatial dimensions. We study bubble collisions in this scenario and find that they generate gravity waves, which are made possible in this context by the reduced symmetry of the global geometry. These gravity waves would produce B-mode polarization in the cosmic microwave background, which could in principle dominate over the inflationary background.
Waves in Radial Gravity Using Magnetic Fluid
NASA Technical Reports Server (NTRS)
Ohlsen, Daniel R.; Hart, John E.; Weidman, Patrick D.
1996-01-01
We are beginning laboratory experiments using magnetically active ferrofluids to study surface waves in novel geometries. Terrestrial gravity is eliminated from the dynamics, and the magnetic body force felt by ferrofluid in the presence of a magnetic field gradient is used to create a geopotential field which is a section of or an entire sphere or cylinder. New optical, electromagnetic and ultrasonic diagnostic techniques are under development to initially study capillary-gravity wave propagation and interaction in such geometries.
Gravity Wave Predictability and Dynamics in Deepwave
NASA Astrophysics Data System (ADS)
Doyle, J. D.; Fritts, D. C.; Smith, R. B.; Eckermann, S. D.; Taylor, M. J.; Dörnbrack, A.; Uddstrom, M.; Reynolds, C. A.; Reinecke, A.; Jiang, Q.
2015-12-01
The DEEP propagating gravity WAVE program (DEEPWAVE) is a comprehensive, airborne and ground-based measurement and modeling program centered on New Zealand and focused on providing a new understanding of gravity wave dynamics and impacts from the troposphere through the mesosphere and lower thermosphere (MLT). This program employed the NSF/NCAR GV (NGV) research aircraft from a base in New Zealand in a 6-week field measurement campaign in June-July 2014. During the field phase, the NGV was equipped with new lidar and airglow instruments, as well as dropwindsondes and a full suite of flight level instruments including the microwave temperature profiler (MTP), providing temperatures and vertical winds spanning altitudes from immediately above the NGV flight altitude (~13 km) to ~100 km. The region near New Zealand was chosen since all the relevant GW sources (e.g., mountains, cyclones, jet streams) occur strongly here, and upper-level winds in austral winter permit gravity waves to propagate to very high altitudes. The COAMPS adjoint modeling system provided forecast sensitivity in real time during the six-week DEEPWAVE field phase. Five missions were conducted using the NGV to observe regions of high forecast sensitivity, as diagnosed using the COAMPS adjoint model. In this presentation, we provide a summary of the sensitivity characteristics and explore the implications for predictability of low-level winds crucial for gravity wave launching, as well as predictability of gravity wave characteristics in the stratosphere. In general, the sensitive regions were characterized by localized strong dynamics, often involving intense baroclinic systems with deep convection. The results of the adjoint modeling system suggest that gravity wave launching and the characteristics of the gravity waves can be linked to these sensitive regions near frontal zones within baroclinic systems. The predictability links between the tropospheric fronts, cyclones, jet regions, and gravity
Helicity-rotation-gravity coupling for gravitational waves
Ramos, Jairzinho; Mashhoon, Bahram
2006-04-15
The consequences of spin-rotation-gravity coupling are worked out for linear gravitational waves. The coupling of helicity of the wave with the rotation of a gravitational-wave antenna is investigated and the resulting modifications in the Doppler effect and aberration are pointed out for incident high-frequency gravitational radiation. Extending these results to the case of a gravitomagnetic field via the gravitational Larmor theorem, the rotation of linear polarization of gravitational radiation propagating in the field of a rotating mass is studied. It is shown that in this case the linear polarization state rotates by twice the Skrotskii angle as a consequence of the spin-2 character of linear gravitational waves.
Observation of gravity-capillary wave turbulence.
Falcon, Eric; Laroche, Claude; Fauve, Stéphan
2007-03-02
We report the observation of the crossover between gravity and capillary wave turbulence on the surface of mercury. The probability density functions of the turbulent wave height are found to be asymmetric and thus non-Gaussian. The surface wave height displays power-law spectra in both regimes. In the capillary region, the exponent is in fair agreement with weak turbulence theory. In the gravity region, it depends on the forcing parameters. This can be related to the finite size of the container. In addition, the scaling of those spectra with the mean energy flux is found in disagreement with weak turbulence theory for both regimes.
Inherently unstable internal gravity waves due to resonant harmonic generation
NASA Astrophysics Data System (ADS)
Liang, Yong; Zareei, Ahmad; Alam, Mohammad-Reza
2017-01-01
Here we show that there exist internal gravity waves that are inherently unstable, that is, they cannot exist in nature for a long time. The instability mechanism is a one-way (irreversible) harmonic-generation resonance that permanently transfers the energy of an internal wave to its higher harmonics. We show that, in fact, there are countably infinite number of such unstable waves. For the harmonic-generation resonance to take place, nonlinear terms in the free surface boundary condition play a pivotal role, and the instability does not obtain for a linearly-stratified fluid if a simplified boundary condition such as rigid lid or linear form is employed. Harmonic-generation resonance presented here also provides a mechanism for the transfer of the energy of the internal waves to the higher-frequency part of the spectrum where internal waves are more prone to breaking, hence losing energy to turbulence and heat and contributing to oceanic mixing.
From Topographic Internal Gravity Waves to Turbulence
NASA Astrophysics Data System (ADS)
Sarkar, S.; Scotti, A.
2017-01-01
Internal gravity waves are a key process linking the large-scale mechanical forcing of the oceans to small-scale turbulence and mixing. In this review, we focus on internal waves generated by barotropic tidal flow over topography. We review progress made in the past decade toward understanding the different processes that can lead to turbulence during the generation, propagation, and reflection of internal waves and how these processes affect mixing. We consider different modeling strategies and new tools that have been developed. Simulation results, the wealth of observational material collected during large-scale experiments, and new laboratory data reveal how the cascade of energy from tidal flow to turbulence occurs through a host of nonlinear processes, including intensified boundary flows, wave breaking, wave-wave interactions, and the instability of high-mode internal wave beams. The roles of various nondimensional parameters involving the ocean state, roughness geometry, and tidal forcing are described.
An experimental study of wave coupling in gravity surface wave turbulence
NASA Astrophysics Data System (ADS)
Aubourg, Quentin; Sommeria, Joel; Viboud, Samuel; Mordant, Nicolas
2016-11-01
Weak turbulence is a theoretical framework aimed at describing wave turbulence (in the weakly nonlinear limit) i.e. a statistical state involving a large number of nonlinearly coupled waves. For gravity waves at the surface of water, it provides a phenomenology that may describe the formation of the spectrum of the ocean surface. Analytical predictions of the spectra are made based on the fact that energy transfer occurs through 4-wave coupling. By using an advanced stereoscopic imaging technique, we measure in time the deformation of the water surface. We obtain a state of wave turbulence by using two small wedge wavemakers in a 13-m diameter wavetank. We then use high order correlator (bi- and tri-coherence) in order to get evidence of the active wave coupling present in our system as used successfully for gravity-capillary wave turbulence. At odds with the weak turbulence theory we observe 3-wave interaction involving 2 quasi linear wave and a bound wave whose frequency lies on the first harmonics of the linear dispersion relation. We do not observe 4-wave coupling within the accuracy of our measurement. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant agreement No 647018-WATU).
Inertio Gravity Waves in the Upper Mesosphere
NASA Technical Reports Server (NTRS)
Mayr, H. G.; Mengel, J. G.; Talaat, E. L.; Porter, H. S.; Chan, K. L.
2003-01-01
In the polar region of the upper mesosphere, horizontal wind oscillations have been observed with periods around 10 hours (Hernandez et al., 1992). Such waves are generated in our Numerical Spectral Model (NSM) and appear to be inertio gravity waves (IGW). Like the planetary waves (PW) in the model, the IGWs are generated by instabilities that arise in the mean zonal circulation. In addition to stationary waves for m = 0, eastward and westward propagating waves for m = 1 to 4 appear above 70 km that grow in magnitude up to about 110 km, having periods between 9 and 11 hours. The m = 1 westward propagating IGWs have the largest amplitudes, which can reach at the poles 30 m/s. Like PWs, the IGWs are intermittent but reveal systematic seasonal variations, with the largest amplitudes occurring generally in winter and spring. The IGWs propagate upward with a vertical wavelength of about 20 km.
Mesospheric gravity-wave climatology at Adelaide
NASA Technical Reports Server (NTRS)
Vincent, R. A.
1986-01-01
The MF Adelaide partial-reflection radar has been operating continuously since November 1983. This has enabled a climatology of gravity-wave activity to be constructed for the mesosphere. The data have been analyzed for a medium-period range of 1 to 8 hr. and a longer period range between 8 and 24 hr. covering the inertio-period waves. The tidal motions have been filtered out prior to analysis. For the data analyses so far (Nov. 1983 to Dec. 1984), a number of interesting features emerged. Firstly, the wave activity at heights above 80 km shows a small seimannual variation with season with the activity being strongest in summer and winter. At heights below 80 km however, there is a similar but more marked variation with the weakest amplitudes occurring at the time of the changeovers in the prevailing circulation. If breaking gravity waves are responsible for much of the turbulence in the mesosphere, then the periods March to April and September to October might also be expected to be periods of weak turbulence. The wave field appears to be partially polarized. The meridional amplitudes are larger than the zonal amplitudes, especially in water. It is found that the degree of polarization is about 15% in summer and 30% in winter. The polarized component is found to propagate in the opposite direction to the background flow in the stratosphere, which suggests that the polarization arises through directional filtering of the waves as they propagate up from below.
Surface wave acoustics of granular packing under gravity
Clement, Eric; Andreotti, Bruno; Bonneau, Lenaic
2009-06-18
Due to the non-linearity of Hertzian contacts, the speed of sound in granular matter increases with pressure. For a packing under gravity and in the presence of a free surface, bulk acoustic waves cannot propagate due to the inherent refraction toward the surface (the mirage effect). Thus, only modes corresponding to surface waves (Raleigh-Hertz modes) are able to propagate the acoustic signal. First, based on a non-linear elasticity model, we describe the main features associated to these surface waves. We show that under gravity, a granular packing is from the acoustic propagation point of view an index gradient waveguide that selects modes of two distinct families i.e. the sagittal and transverse waves localized in the vicinity of the free surface. A striking feature of these surface waves is the multi-modal propagation: for both transverse and sagittal waves, we show the existence of a infinite but discrete series of propagating modes. In each case, we determine the mode shape and and the corresponding dispersion relation. In the case of a finite size system, a geometric waveguide is superimposed to the index gradient wave guide. In this later case, the dispersion relations are modified by the appearance of a cut-off frequency that scales with depth. The second part is devoted to an experimental study of surface waves propagating in a granular packing confined in a long channel. This set-up allows to tune a monomodal emission by taking advantage of the geometric waveguide features combined with properly designed emitters. For both sagittal and transverses waves, we were able to isolate a single mode (the fundamental one) and to plot the dispersion relation. This measurements agree well with the Hertzian scaling law as predicted by meanfield models. Furthermore, it allows us to determine quantitatively relations on the elastic moduli. However, we observe that our data yield a shear modulus abnormally weak when compared to several meanfield predictions.
Stability of steep gravity capillary solitary waves in deep water
NASA Astrophysics Data System (ADS)
Calvo, David C.; Akylas, T. R.
2002-02-01
The stability of steep gravity capillary solitary waves in deep water is numerically investigated using the full nonlinear water-wave equations with surface tension. Out of the two solution branches that bifurcate at the minimum gravity capillary phase speed, solitary waves of depression are found to be stable both in the small-amplitude limit when they are in the form of wavepackets and at finite steepness when they consist of a single trough, consistent with observations. The elevation-wave solution branch, on the other hand, is unstable close to the bifurcation point but becomes stable at finite steepness as a limit point is passed and the wave profile features two well-separated troughs. Motivated by the experiments of Longuet-Higgins & Zhang (1997), we also consider the forced problem of a localized pressure distribution applied to the free surface of a stream with speed below the minimum gravity capillary phase speed. We find that the finite-amplitude forced solitary-wave solution branch computed by Vanden-Broeck & Dias (1992) is unstable but the branch corresponding to Rayleigh’s linearized solution is stable, in agreement also with a weakly nonlinear analysis based on a forced nonlinear Schrödinger equation. The significance of viscous effects is assessed using the approach proposed by Longuet-Higgins (1997): while for free elevation waves the instability predicted on the basis of potential-flow theory is relatively weak compared with viscous damping, the opposite turns out to be the case in the forced problem when the forcing is strong. In this régime, which is relevant to the experiments of Longuet-Higgins & Zhang (1997), the effects of instability can easily dominate viscous effects, and the results of the stability analysis are used to propose a theoretical explanation for the persistent unsteadiness of the forced wave profiles observed in the experiments.
Traveling Gravity Water Waves with Critical Layers
NASA Astrophysics Data System (ADS)
Aasen, Ailo; Varholm, Kristoffer
2017-02-01
We establish the existence of small-amplitude uni- and bimodal steady periodic gravity waves with an affine vorticity distribution, using a bifurcation argument that differs slightly from earlier theory. The solutions describe waves with critical layers and an arbitrary number of crests and troughs in each minimal period. An important part of the analysis is a fairly complete description of the local geometry of the so-called kernel equation, and of the small-amplitude solutions. Finally, we investigate the asymptotic behavior of the bifurcating solutions.
Gravity-jitters and excitation of slosh waves
NASA Technical Reports Server (NTRS)
Hung, R. J.; Lee, C. C.; Leslie, F. W.; Wu, J. L.
1990-01-01
The instability of liquid and gas interface can be induced by the pressure of longitudinal and lateral accelerations, vehicle vibration, and rotational fields of spacecraft in a microgravity environment. Characteristics of slosh waves excited by the restoring force field of gravity jitters have been investigated. Results show that lower frequency gravity jitters excite slosh waves with higher ratio of maximum amplitude to wave length than that of the slosh waves generated by the higher frequency gravity jitters.
Gravity Wave Seeding of Equatorial Plasma Bubbles
NASA Technical Reports Server (NTRS)
Singh, Sardul; Johnson, F. S.; Power, R. A.
1997-01-01
Some examples from the Atmosphere Explorer E data showing plasma bubble development from wavy ion density structures in the bottomside F layer are described. The wavy structures mostly had east-west wavelengths of 150-800 km, in one example it was about 3000 km. The ionization troughs in the wavy structures later broke up into either a multiple-bubble patch or a single bubble, depending upon whether, in the precursor wavy structure, shorter wavelengths were superimposed on the larger scale wavelengths. In the multiple bubble patches, intrabubble spacings vaned from 55 km to 140 km. In a fully developed equatorial spread F case, east-west wavelengths from 690 km down to about 0.5 km were present simultaneously. The spacings between bubble patches or between bubbles in a patch appear to be determined by the wavelengths present in the precursor wave structure. In some cases, deeper bubbles developed on the western edge of a bubble patch, suggesting an east-west asymmetry. Simultaneous horizontal neutral wind measurements showed wavelike perturbations that were closely associated with perturbations in the plasma horizontal drift velocity. We argue that the wave structures observed here that served as the initial seed ion density perturbations were caused by gravity waves, strengthening the view that gravity waves seed equatorial spread F irregularities.
Density response of the mesospheric sodium layer to gravity wave perturbations
NASA Technical Reports Server (NTRS)
Shelton, J. D.; Gardner, C. S.; Sechrist, C. F., Jr.
1980-01-01
Lidar observations of the mesospheric sodium layer often reveal wavelike features moving through the layer. It is often assumed that these features are a layer density response to gravity waves. Chiu and Ching (1978) described the approximate form of the linear response of atmospheric layers to gravity waves. In this paper, their results are used to predict the response of the sodium layer to gravity waves. These simulations are compared with experimental observations and a good correlation is found between the two. Because of the thickness of the sodium layer and the density gradients found in it, a linear model of the layer response is not always adequate to describe gravity wave-sodium layer interactions. Inclusion of nonlinearities in the layer response is briefly discussed. Experimental data is seen to contain features consistent with the predicted nonlinearities.
Propagation of gravity waves across the tropopause
NASA Astrophysics Data System (ADS)
Bense, Vera; Spichtinger, Peter
2015-04-01
The tropopause region is characterised by strong gradients in various atmospheric quantities that exhibit different properties in the troposphere compared to the stratosphere. The temperature lapse rate typically changes from negative to near-zero values resulting in a strong increase in stability. Accordingly, the buoyancy frequency often undergoes a jump at the tropopause. Analysis of radiosounding data also shows the existence of a strong inversion layer (tropopause inversion layer, TIL) characterised by a strong maximum in buoyancy frequency just above the tropopause, see e.g. Birner et al. (2002). Additionally, the magnitude of the vertical wind shear of the horizontal wind maximizes at the tropopause and the region also exhibits characteristical gradients of trace gases. Vertically propagating gravity waves can be excited in the troposphere by several mechanisms, e.g. by flow over topography (e.g. Durran, 1990), by jets and fronts (for a recent review: Plougonven and Zhang, 1990) or by convection (e.g. Clark et al., 1986). When these waves enter the tropopause region, their properties can be changed drastically by the changing stratification and strong wind shear. Within this work, the EULAG (Eulerian/semi-Lagrangian fluid solver, see e.g. Smolarkiewicz and Margolin, 1997) model is used to investigate the impact of the tropopause on vertically propagating gravity waves excited by flows over topography. The choice of topography (sine-shaped mountains, bell-shaped mountain) along with horizontal wind speed and tropospheric value of buoyancy frequency determine the spectrum of waves (horizontal and vertical wavelengths) that is excited in the tropsphere. In order to analyse how these spectra change for several topographies when a tropopause is present, we investigate different idealized cases in a two-dimensional domain. By varying the vertical profiles of buoyancy frequency (step-wise vs. continuos change, including TIL) and wind shear, the tropopause
Waves in Radial Gravity Using Magnetic Fluid
NASA Technical Reports Server (NTRS)
Ohlsen, D. R.; Hart, J. E.; Weidman, P. D.
1999-01-01
Terrestrial laboratory experiments studying various fluid dynamical processes are constrained, by being in an Earth laboratory, to have a gravitational body force which is uniform and unidirectional. Therefore fluid free-surfaces are horizontal and flat. Such free surfaces must have a vertical solid boundary to keep the fluid from spreading horizontally along a gravitational potential surface. In atmospheric, oceanic, or stellar fluid flows that have a horizontal scale of about one-tenth the body radius or larger, sphericity is important in the dynamics. Further, fluids in spherical geometry can cover an entire domain without any sidewall effects, i.e. have truly periodic boundary conditions. We describe spherical body-force laboratory experiments using ferrofluid. Ferrofluids are dilute suspensions of magnetic dipoles, for example magnetite particles of order 10 nm diameter, suspended in a carrier fluid. Ferrofluids are subject to an additional body force in the presence of an applied magnetic field gradient. We use this body force to conduct laboratory experiments in spherical geometry. The present study is a laboratory technique improvement. The apparatus is cylindrically axisymmetric. A cylindrical ceramic magnet is embedded in a smooth, solid, spherical PVC ball. The geopotential field and its gradient, the body force, were made nearly spherical by careful choice of magnet height-to-diameter ratio and magnet size relative to the PVC ball size. Terrestrial gravity is eliminated from the dynamics by immersing the "planet" and its ferrofluid "ocean" in an immiscible silicone oil/freon mixture of the same density. Thus the earth gravity is removed from the dynamics of the ferrofluid/oil interface and the only dynamically active force there is the radial magnetic gravity. The entire apparatus can rotate, and waves are forced on the ferrofluid surface by exterior magnets. The biggest improvement in technique is in the wave visualization. Fluorescing dye is added to
Diagnosis of the forcing of inertial-gravity waves in a severe convection system
NASA Astrophysics Data System (ADS)
Ran, Lingkun; Chen, Changsheng
2016-11-01
The non-hydrostatic wave equation set in Cartesian coordinates is rearranged to gain insight into wave generation in a mesoscale severe convection system. The wave equation is characterized by a wave operator on the lhs, and forcing involving three terms—linear and nonlinear terms, and diabatic heating—on the rhs. The equation was applied to a case of severe convection that occurred in East China. The calculation with simulation data showed that the diabatic forcing and linear and nonlinear forcing presented large magnitude at different altitudes in the severe convection region. Further analysis revealed the diabatic forcing due to condensational latent heating had an important influence on the generation of gravity waves in the middle and lower levels. The linear forcing resulting from the Laplacian of potential-temperature linear forcing was dominant in the middle and upper levels. The nonlinear forcing was determined by the Laplacian of potential-temperature nonlinear forcing. Therefore, the forcing of gravity waves was closely associated with the thermodynamic processes in the severe convection case. The reason may be that, besides the vertical component of pressure gradient force, the vertical oscillation of atmospheric particles was dominated by the buoyancy for inertial gravity waves. The latent heating and potential-temperature linear and nonlinear forcing played an important role in the buoyancy tendency. Consequently, these thermodynamic elements influenced the evolution of inertial-gravity waves.
Toward an internal gravity wave spectrum in global ocean models
NASA Astrophysics Data System (ADS)
Müller, Malte; Arbic, Brian K.; Richman, James G.; Shriver, Jay F.; Kunze, Eric L.; Scott, Robert B.; Wallcraft, Alan J.; Zamudio, Luis
2015-05-01
High-resolution global ocean models forced by atmospheric fields and tides are beginning to display realistic internal gravity wave spectra, especially as model resolution increases. This paper examines internal waves in global simulations with 0.08° and 0.04° (~8 and 4 km) horizontal resolutions, respectively. Frequency spectra of internal wave horizontal kinetic energy in the North Pacific lie closer to observations in the 0.04° simulation than in the 0.08° simulation. The horizontal wave number and frequency (K-ω) kinetic energy spectra contain peaks in the semidiurnal tidal band and near-inertial band, along with a broadband frequency continuum aligned along the linear dispersion relations of low-vertical-mode internal waves. Spectral kinetic energy transfers describe the rate at which nonlinear mechanisms remove or supply kinetic energy in specific K-ω ranges. Energy is transferred out of low-mode inertial and semidiurnal internal waves into a broad continuum of higher-frequency and higher-wave number internal waves.
Conversion of internal gravity waves into magnetic waves
NASA Astrophysics Data System (ADS)
Lecoanet, D.; Vasil, G. M.; Fuller, J.; Cantiello, M.; Burns, K. J.
2017-04-01
Asteroseismology probes the interiors of stars by studying oscillation modes at a star's surface. Although pulsation spectra are well understood for solar-like oscillators, a substantial fraction of red giant stars observed by Kepler exhibit abnormally low-amplitude dipole oscillation modes. Fuller et al. (2015) suggest this effect is produced by strong core magnetic fields that scatter dipole internal gravity waves (IGWs) into higher multipole IGWs or magnetic waves. In this paper, we study the interaction of IGWs with a magnetic field to test this mechanism. We consider two background stellar structures: one with a uniform magnetic field, and another with a magnetic field that varies both horizontally and vertically. We derive analytic solutions to the wave propagation problem and validate them with numerical simulations. In both cases, we find perfect conversion from IGWs into magnetic waves when the IGWs propagate into a region exceeding a critical magnetic field strength. Downward propagating IGWs cannot reflect into upward propagating IGWs because their vertical wavenumber never approaches zero. Instead, they are converted into upward propagating slow (Alfvénic) waves, and we show they will likely dissipate as they propagate back into weakly magnetized regions. Therefore, strong internal magnetic fields can produce dipole mode suppression in red giants, and gravity modes will likely be totally absent from the pulsation spectra of sufficiently magnetized stars.
Characteristic of gravity waves resolved in ECMWF
NASA Astrophysics Data System (ADS)
Preusse, Peter; Eckermann, Stephen; Ern, Manfred; Riese, Martin
Gravity waves (GWs) influence the circulation of the atmosphere on global scale. Because of insufficient measurements and the difficulty to involve all relevant scales in a single model run, they are one of the chief uncertainties in climate and weather prediction. More information, in particular on global scale, is required. Can we employ global models such as the ECMWF high-resolution GCM to infer quantities of resolved GWs? Does this give us insight for the characteristics and relative importance of real GW sources? And can we use such data safely for, e.g., planning measurement campaigns on GWs? Also trajectory studies of cloud formation (cirrus in the UTLS, PSCs) and related dehydration and denitrification rely heavily on realistic temperature structures due to GWs. We here apply techniques developed for an ESA study proving the scientifc break-through which could be reached by a novel infrared limb imager. The 3D temperature structure of mesoscale GWs is exploited to determine amplitudes and 3D wave vectors of GWs at different levels (25km, 35km and 45km altitude) in the stratosphere. Similar to real observations, GW momentum flux is largest in the winter polar vortex and exhibits a second maximum in the summer subtropics. Based on the 3D wavevectors backward ray-tracing is employed to characterize specific sources. For instance, we find for the northern winter strong GW momentum flux (GWMF) associated with mountain waves from Norway and Greenland as well as waves emitted in the lower troposphere from a storm approaching Norway. Waves from these sources spread up to several thousand km in the stratosphere. Together these three events form a burst in the total hemispheric GWMF of a factor of 3. Strong mountain wave events are also found e.g. at Tierra del Fuego and the Antarctic Peninsula, regions which are in the focus of observational and modeling studies for a decade. Gravity waves in the tropical region are associated with deep convection in the upper
Ionospheric acoustic and gravity waves associated with midlatitude thunderstorms
Lay, Erin H.; Shao, Xuan -Min; Kendrick, Alexander K.; Carrano, Charles S.
2015-07-30
Acoustic waves with periods of 2–4 min and gravity waves with periods of 6–16 min have been detected at ionospheric heights (25–350 km) using GPS total electron content measurements. The area disturbed by these waves and the wave amplitudes have been associated with underlying thunderstorm activity. A statistical study comparing Next Generation Weather Radar thunderstorm measurements with ionospheric acoustic and gravity waves in the midlatitude U.S. Great Plains region was performed for the time period of May–July 2005. An increase of ionospheric acoustic wave disturbed area and amplitude is primarily associated with large thunderstorms (mesoscale convective systems). Ionospheric gravity wave disturbed area and amplitude scale with thunderstorm activity, with even small storms (i.e., individual storm cells) producing an increase of gravity waves.
Ionospheric acoustic and gravity waves associated with midlatitude thunderstorms
NASA Astrophysics Data System (ADS)
Lay, Erin H.; Shao, Xuan-Min; Kendrick, Alexander K.; Carrano, Charles S.
2015-07-01
Acoustic waves with periods of 2-4 min and gravity waves with periods of 6-16 min have been detected at ionospheric heights (250-350 km) using GPS total electron content measurements. The area disturbed by these waves and the wave amplitudes have been associated with underlying thunderstorm activity. A statistical study comparing Next Generation Weather Radar thunderstorm measurements with ionospheric acoustic and gravity waves in the midlatitude U.S. Great Plains region was performed for the time period of May-July 2005. An increase of ionospheric acoustic wave disturbed area and amplitude is primarily associated with large thunderstorms (mesoscale convective systems). Ionospheric gravity wave disturbed area and amplitude scale with thunderstorm activity, with even small storms (i.e., individual storm cells) producing an increase of gravity waves.
Global Ray Tracing Simulations of the SABER Gravity Wave Climatology
2009-01-01
amplitudes, vertical wave- D08126 PREUSSE ET AL.: GRAVITY WAVES BY SATELLITE AND RAYTRACER 2 of 25 D08126 lengths and phases of the two strongest wave...with the wind ‘‘drift’’ large D08126 PREUSSE ET AL.: GRAVITY WAVES BY SATELLITE AND RAYTRACER 3 of 25 D08126 distances downstream in taking much...factor (IMF) attributed to the single SCEs in generating the composite. D08126 PREUSSE ET AL.: GRAVITY WAVES BY SATELLITE AND RAYTRACER 4 of 25 D08126
Gravity Waves Ripple over Marine Stratocumulus Clouds
NASA Technical Reports Server (NTRS)
2004-01-01
In this natural-color image from the Multi-angle Imaging SpectroRadiometer (MISR), a fingerprint-like gravity wave feature occurs over a deck of marine stratocumulus clouds. Similar to the ripples that occur when a pebble is thrown into a still pond, such 'gravity waves' sometimes appear when the relatively stable and stratified air masses associated with stratocumulus cloud layers are disturbed by a vertical trigger from the underlying terrain, or by a thunderstorm updraft or some other vertical wind shear. The stratocumulus cellular clouds that underlie the wave feature are associated with sinking air that is strongly cooled at the level of the cloud-tops -- such clouds are common over mid-latitude oceans when the air is unperturbed by cyclonic or frontal activity. This image is centered over the Indian Ocean (at about 38.9o South, 80.6o East), and was acquired on October 29, 2003.
The Multi-angle Imaging SpectroRadiometer observes the daylit Earth continuously and every 9 days views the entire globe between 82o north and 82o south latitude. These data products were generated from a portion of the imagery acquired during Terra orbit 20545. The image covers an area of 245 kilometers x 378 kilometers, and uses data from blocks 121 to 122 within World Reference System-2 path 134.
MISR was built and is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Earth Science, Washington, DC. The Terra satellite is managed by NASA's Goddard Space Flight Center, Greenbelt, MD. JPL is a division of the California Institute of Technology.
Linearized gravity in terms of differential forms
NASA Astrophysics Data System (ADS)
Baykal, Ahmet; Dereli, Tekin
2017-01-01
A technique to linearize gravitational field equations is developed in which the perturbation metric coefficients are treated as second rank, symmetric, 1-form fields belonging to the Minkowski background spacetime by using the exterior algebra of differential forms.
Toward an Internal Gravity Wave Spectrum in Global Ocean Models
2015-05-14
14 MAY 2015 2. REPORT TYPE 3. DATES COVERED 00-00-2015 to 00-00-2015 4. TITLE AND SUBTITLE Toward an Internal Gravity Wave Spectrum in Global...resolution global ocean models forced by atmospheric fields and tides are beginning to display realistic internal gravity wave spectra, especially as
New Gravity Wave Treatments for GISS Climate Models
NASA Technical Reports Server (NTRS)
Geller, Marvin A.; Zhou, Tiehan; Ruedy, Reto; Aleinov, Igor; Nazarenko, Larissa; Tausnev, Nikolai L.; Sun, Shan; Kelley, Maxwell; Cheng, Ye
2010-01-01
Previous versions of GISS climate models have either used formulations of Rayleigh drag to represent unresolved gravity wave interactions with the model resolved flow or have included a rather complicated treatment of unresolved gravity waves that, while being climate interactive, involved the specification of a relatively large number of parameters that were not well constrained by observations and also was computationally very expensive. Here, we introduce a relatively simple and computationally efficient specification of unresolved orographic and non-orographic gravity waves and their interaction with the resolved flow. We show comparisons of the GISS model winds and temperatures with no gravity wave parametrization; with only orographic gravity wave parameterization; and with both orographic and non-orographic gravity wave parameterizations to illustrate how the zonal mean winds and temperatures converge toward observations. We also show that the specifications of orographic and nonorographic gravity waves must be different in the Northern and Southern Hemispheres. We then show results where the non-orographic gravity wave sources are specified to represent sources from convection in the Intertropical Convergence Zone and spontaneous emission from jet imbalances. Finally, we suggest a strategy to include these effects in a climate dependent manner.
New Gravity Wave Treatments for GISS Climate Models
NASA Technical Reports Server (NTRS)
Geller, Marvin A.; Zhou, Tiehan; Ruedy, Reto; Aleinov, Igor; Nazarenko, Larissa; Tausnev, Nikolai L.; Sun, Shan; Kelley, Maxwell; Cheng, Ye
2011-01-01
Previous versions of GISS climate models have either used formulations of Rayleigh drag to represent unresolved gravity wave interactions with the model-resolved flow or have included a rather complicated treatment of unresolved gravity waves that, while being climate interactive, involved the specification of a relatively large number of parameters that were not well constrained by observations and also was computationally very expensive. Here, the authors introduce a relatively simple and computationally efficient specification of unresolved orographic and nonorographic gravity waves and their interaction with the resolved flow. Comparisons of the GISS model winds and temperatures with no gravity wave parameterization; with only orographic gravity wave parameterization; and with both orographic and nonorographic gravity wave parameterizations are shown to illustrate how the zonal mean winds and temperatures converge toward observations. The authors also show that the specifications of orographic and nonorographic gravity waves must be different in the Northern and Southern Hemispheres. Then results are presented where the nonorographic gravity wave sources are specified to represent sources from convection in the intertropical convergence zone and spontaneous emission from jet imbalances. Finally, a strategy to include these effects in a climate-dependent manner is suggested.
Ionospheric acoustic and gravity waves associated with midlatitude thunderstorms
Lay, Erin H.; Shao, Xuan -Min; Kendrick, Alexander K.; ...
2015-07-30
Acoustic waves with periods of 2–4 min and gravity waves with periods of 6–16 min have been detected at ionospheric heights (25–350 km) using GPS total electron content measurements. The area disturbed by these waves and the wave amplitudes have been associated with underlying thunderstorm activity. A statistical study comparing Next Generation Weather Radar thunderstorm measurements with ionospheric acoustic and gravity waves in the midlatitude U.S. Great Plains region was performed for the time period of May–July 2005. An increase of ionospheric acoustic wave disturbed area and amplitude is primarily associated with large thunderstorms (mesoscale convective systems). Ionospheric gravity wavemore » disturbed area and amplitude scale with thunderstorm activity, with even small storms (i.e., individual storm cells) producing an increase of gravity waves.« less
Deterministic forward scatter from surface gravity waves.
Deane, Grant B; Preisig, James C; Tindle, Chris T; Lavery, Andone; Stokes, M Dale
2012-12-01
Deterministic structures in sound reflected by gravity waves, such as focused arrivals and Doppler shifts, have implications for underwater acoustics and sonar, and the performance of underwater acoustic communications systems. A stationary phase analysis of the Helmholtz-Kirchhoff scattering integral yields the trajectory of focused arrivals and their relationship to the curvature of the surface wave field. Deterministic effects along paths up to 70 water depths long are observed in shallow water measurements of surface-scattered sound at the Martha's Vineyard Coastal Observatory. The arrival time and amplitude of surface-scattered pulses are reconciled with model calculations using measurements of surface waves made with an upward-looking sonar mounted mid-way along the propagation path. The root mean square difference between the modeled and observed pulse arrival amplitude and delay, respectively, normalized by the maximum range of amplitudes and delays, is found to be 0.2 or less for the observation periods analyzed. Cross-correlation coefficients for modeled and observed pulse arrival delays varied from 0.83 to 0.16 depending on surface conditions. Cross-correlation coefficients for normalized pulse energy for the same conditions were small and varied from 0.16 to 0.06. In contrast, the modeled and observed pulse arrival delay and amplitude statistics were in good agreement.
Gravitational wave memory: A new approach to study modified gravity
NASA Astrophysics Data System (ADS)
Du, Song Ming; Nishizawa, Atsushi
2016-11-01
It is well known that two types of gravitational wave memory exist in general relativity (GR): the linear memory and the nonlinear, or Christodoulou, memory. These effects, especially the latter, depend on the specific form of the Einstein equation. It can then be speculated that, in modified theories of gravity, the memory can differ from the GR prediction and provides novel phenomena to study these theories. We support this speculation by considering scalar-tensor theories, for which we find two new types of memory: the T memory and the S memory, which contribute to the tensor and scalar components of a gravitational wave, respectively. Specifically, the former is caused by the burst of energy carried away by scalar radiation, while the latter is intimately related to the no scalar hair property of black holes in scalar-tensor gravity. We estimate the size of these two types of memory in gravitational collapses and formulate a detection strategy for the S memory, which can be singled out from tensor gravitational waves. We show that (i) the S memory exists even in spherical symmetry and is observable under current model constraints, and (ii) while the T memory is usually much weaker than the S memory, it can become comparable in the case of spontaneous scalarization.
Gravity wave vertical energy flux at 95 km
NASA Technical Reports Server (NTRS)
Jacob, P. G.; Jacka, F.
1985-01-01
A three-field photometer (3FP) located at Mt. Torrens near Adelaide, is capable of monitoring different airglow emissions from three spaced fields in the sky. A wheel containing up to six different narrow bandpass interference filters can be rotated, allowing each of the filters to be sequentially placed into each of the three fields. The airglow emission of interest is the 557.7 nm line which has an intensity maximum at 95 km. Each circular field of view is located at the apexes of an equilateral triangle centered on zenith with diameters of 5 km and field separations of 13 km when projected to the 95-km level. The sampling period was 30 seconds and typical data lengths were between 7 and 8 hours. The analysis and results from the interaction of gravity waves on the 557.7 nm emission layer are derived using an atmospheric model similar to that proposed by Hines (1960) where the atmosphere is assumed isothermal and perturbations caused by gravity waves are small and adiabatic, therefore, resulting in linearized equations of motion. In the absence of waves, the atmosphere is also considered stationary. Thirteen nights of quality data from January 1983 to October 1984, covering all seasons, are used in this analysis.
Gravity Wave Generation by Largescale Bubbles
NASA Astrophysics Data System (ADS)
Brandenburg, A.
The response of an isothermal atmosphere to small disturbances in entropy is studied taking compressible effects fully into account. The method of Green's functions is applied to solve the linearized hydrodynamic equations by Fourier transformation. A bubble may be created by perturbing the entropy within a finite volume. At first Lamb waves will be then emitted radially and the bubble undergoes a series of Brunt-Väisälä oscillations.
Realistic inflation models and primordial gravity waves
NASA Astrophysics Data System (ADS)
Rehman, Mansoor Ur
We investigate both supersymmetric and non-supersymmetric realistic models of inflation. In non-supersymmetric models, inflation is successfully realized by employing both Coleman Weinberg and Higgs potentials in GUTs such as SU(5) and SO(10). The quantum smearing of tree level predictions is discussed in the Higgs inflation. These quantum corrections can arise from the inflaton couplings to other particles such as GUT scalars. As a result of including these corrections, a reduction in the tensor-to-scalar ratio r, a canonical measure of gravity waves produced during inflation, is observed. In a simple phi4 chaotic model, we reconsider a non-minimal (xi > 0) gravitationalcoupling of inflaton φ arising from the interaction xi R phi2, where R is the Ricci scalar. In estimating bounds on various inflationaryparameters we also include quantum corrections. We emphasize that while working with high precision observations such as the current Planck satellite experiment we cannot ignore these radiative and gravitational corrections in analyzing the predictions of various inflationary models. In supersymmetric hybrid inflation with minimal Kahler potential, the soft SUSY breaking terms are shown to play an important role in realizing inflation consistent with the latest WMAP data. The SUSY hybrid models which we consider here predict exceedingly small values of r. However, to obtain observable gravity waves the non-minimal Kahler potential turns out to be a necessary ingredient. A realistic model of flipped SU(5) model, which benefits from the absence of topological defects, is considered in the standard SUSY hybrid inflation. We also present a discussion of shifted hybrid inflation in a realistic model of SUSY SU(5) GUT.
Experimental observation of negative effective gravity in water waves.
Hu, Xinhua; Yang, Jiong; Zi, Jian; Chan, C T; Ho, Kai-Ming
2013-01-01
The gravity of Earth is responsible for the formation of water waves and usually difficult to change. Although negative effective gravity was recently predicted theoretically in water waves, it has not yet been observed in experiments and remains a mathematical curiosity which is difficult to understand. Here we experimentally demonstrate that close to the resonant frequency of purposely-designed resonating units, negative effective gravity can occur for water waves passing through an array of resonators composing of bottom-mounted split tubes, resulting in the prohibition of water wave propagation. It is found that when negative gravity occurs, the averaged displacement of water surface in a unit cell of the array has a phase difference of π to that along the boundary of the unit cell, consistent with theoretical predictions. Our results provide a mechanism to block water waves and may find applications in wave energy conversion and coastal protection.
Experimental Observation of Negative Effective Gravity in Water Waves
Hu, Xinhua; Yang, Jiong; Zi, Jian; Chan, C. T.; Ho, Kai-Ming
2013-01-01
The gravity of Earth is responsible for the formation of water waves and usually difficult to change. Although negative effective gravity was recently predicted theoretically in water waves, it has not yet been observed in experiments and remains a mathematical curiosity which is difficult to understand. Here we experimentally demonstrate that close to the resonant frequency of purposely-designed resonating units, negative effective gravity can occur for water waves passing through an array of resonators composing of bottom-mounted split tubes, resulting in the prohibition of water wave propagation. It is found that when negative gravity occurs, the averaged displacement of water surface in a unit cell of the array has a phase difference of π to that along the boundary of the unit cell, consistent with theoretical predictions. Our results provide a mechanism to block water waves and may find applications in wave energy conversion and coastal protection. PMID:23715132
Investigating gravity waves evidences in the Venus upper atmosphere
NASA Astrophysics Data System (ADS)
Migliorini, Alessandra; Altieri, Francesca; Shakun, Alexey; Zasova, Ludmila; Piccioni, Giuseppe; Bellucci, Giancarlo; Grassi, Davide
2014-05-01
We present a method to investigate gravity waves properties in the upper mesosphere of Venus, through the O2 nightglow observations acquired with the imaging spectrometer VIRTIS on board Venus Express. Gravity waves are important dynamical features that transport energy and momentum. They are related to the buoyancy force, which lifts air particles. Then, the vertical displacement of air particles produces density changes that cause gravity to act as restoring force. Gravity waves can manifest through fluctuations on temperature and density fields, and hence on airglow intensities. We use the O2 nightglow profiles showing double peaked structures to study the influence of gravity waves in shaping the O2 vertical profiles and infer the waves properties. In analogy to the Earth's and Mars cases, we use a well-known theory to model the O2 nightglow emissions affected by gravity waves propagation. Here we propose a statistical discussion of the gravity waves characteristics, namely vertical wavelength and wave amplitude, with respect to local time and latitude. The method is applied to about 30 profiles showing double peaked structures, and acquired with the VIRTIS/Venus Express spectrometer, during the mission period from 2006-07-05 to 2008-08-15.
GRAVITY WAVES ON HOT EXTRASOLAR PLANETS. I. PROPAGATION AND INTERACTION WITH THE BACKGROUND
Watkins, Chris; Cho, J. Y-K. E-mail: J.Cho@qmul.ac.u
2010-05-01
We study the effects of gravity waves, or g-modes, on hot extrasolar planets. These planets are expected to possess stably stratified atmospheres, which support gravity waves. In this paper, we review the derivation of the equation that governs the linear dynamics of gravity waves and describe its application to a hot extrasolar planet, using HD 209458 b as a generic example. We find that gravity waves can exhibit a wide range of behaviors, even for a single atmospheric profile. The waves can significantly accelerate or decelerate the background mean flow, depending on the difference between the wave phase and mean flow speeds. In addition, the waves can provide significant heating ({approx}10{sup 2} to {approx}10{sup 3} K per planetary rotation), especially to the region of the atmosphere above about 10 scale heights from the excitation region. Furthermore, by propagating horizontally, gravity waves provide a mechanism for transporting momentum and heat from the dayside of a tidally locked planet to its nightside. We discuss work that needs to be undertaken to incorporate these effects in current atmosphere models of extrasolar planets.
Characteristics of Kelvin waves and Mixed Rossby-Gravity waves in opposite QBO phases
NASA Astrophysics Data System (ADS)
Zaman Fathullah, Nur; Lubis, Sandro W.; Setiawan, Sonni
2017-01-01
A 35-year ERA-Interim dataset from the European Center for Medium-Range Weather Forecasts (ECMWF) was used to study the characteristics of Kelvin waves and Mixed Rossby-gravity waves based on a Space-Time Spectral Analysis (STSA). The results show that Kelvin wave activity is stronger during easterly QBO phases, while Mixed Rossby-gravity waves are stronger during westerly QBO phases. Analysis on seasonal variations indicates that the Kelvin waves and Mixed Rossby-Gravity wave activities increase in JJA and SON, respectively. This is associated with a variation of basic mean flow in the lower stratosphere. In addition, the variations of Kelvin and Mixed Rossby-Gravity waves in the troposphere are not significantly affected by the QBO phases. In the troposphere, both Kelvin waves and Mixed Rossby-Gravity waves propagate with a lower phase speed compared to those observed in the stratosphere. This behavior is to be likely due to large.
On the energetics of mean-flow interactions with thermally dissipating gravity waves
NASA Astrophysics Data System (ADS)
Akmaev, R. A.
2007-06-01
Previous studies have demonstrated the importance of downgradient transport by dissipating waves and particularly of downward heat fluxes by gravity waves undergoing thermal dissipation. With a few exceptions, however, this effect has not been represented in gravity-wave parameterizations commonly employed in global numerical models. A general expression relating the heat flux to the wave energy deposition rate caused by thermal dissipation is obtained within the standard linear-theory approach. Although the flux is directed down the gradient of potential temperature, it is not proportional to its magnitude, i.e., is not formally diffusive as commonly represented. With necessary assumptions regarding the partitioning of the total wave energy deposition rate between the thermal and frictional channels, the heat flux may be calculated within any suitable parameterization of gravity-wave drag. The general relation may also be used to estimate net heating rates from observations of wave heat transport. In a more general thermodynamical context, it is noted that gravity-wave dissipation results in atmospheric entropy production as expected for a dissipative process. Without friction, entropy is produced under the conservation of the column potential enthalpy. Thermally dissipating waves thus represent an example of an entropy-generating process hypothesized in the literature but not identified before. Although the downward heat transport results in a local cooling of upper levels, the integrated net effect of the wave energy deposition and heat transport combined is always heating of the whole atmospheric layer in which the dissipation occurs.
Stratospheric gravity wave observations of AIRS and HIRDLS
NASA Astrophysics Data System (ADS)
Meyer, Catrin I.; Hoffmann, Lars; Ern, Manfred; Trinh, Thai
2016-04-01
The Atmospheric InfraRed Sounder (AIRS) aboard NASA's Aqua satellite provides stratospheric temperature observations for a variety of scientific analyses. However, the horizontal resolution of the operational temperature retrievals is generally not sufficient for studies of gravity waves. The AIRS high-resolution retrieval discussed here provides stratospheric temperature profiles for each individual satellite footprint and therefore has nine times better horizontal sampling than the operational data. The retrieval configuration is optimized so that the results provide a trade-off between spatial resolution and retrieval noise that is considered optimal for gravity wave analysis. To validate the AIRS data we performed an intercomparison with stratospheric temperature measurements of the High Resolution Dynamics Limb Sounder (HIRDLS). Selected case studies of gravity wave events are analyzed. AIRS and HIRDLS utilize rather different measurement geometries (nadir and limb) and have different sensitivities to gravity wave horizontal and vertical wavelengths, as indicated by their observational filters. Nevertheless, the wave structures found in the stratosphere in AIRS and HIRDLS data are often in remarkably good agreement. The three-dimensional temperature fields from AIRS allow us to derive the horizontal orientation of the phase fronts, which is a limiting factor for gravity wave analyses based on limb measurements today. In addition, a statistical comparison focuses on temperature variances due to stratospheric gravity wave activity at 20-60 km altitude. The analysis covers monthly zonal averages and time series for the HIRDLS measurement time period (January 2005-March 2008). We found good agreement in the seasonal and latitudinal patterns of gravity wave activity. Time series of gravity wave variances show a strong annual cycle at high latitudes with maxima during wintertime and minima during summertime. Largest variability is found at 60°S during austral
A Simple Theory of Capillary-Gravity Wave Turbulence
NASA Technical Reports Server (NTRS)
Glazman, Roman E.
1995-01-01
Employing a recently proposed 'multi-wave interaction' theory, inertial spectra of capillary gravity waves are derived. This case is characterized by a rather high degree of nonlinearity and a complicated dispersion law. The absence of scale invariance makes this and some other problems of wave turbulence (e.g., nonlinear inertia gravity waves) intractable by small-perturbation techniques, even in the weak-turbulence limit. The analytical solution obtained in the present work for an arbitrary degree of nonlinearity is shown to be in reasonable agreement with experimental data. The theory explains the dependence of the wave spectrum on wind input and describes the accelerated roll-off of the spectral density function in the narrow sub-range separating scale-invariant regimes of purely gravity and capillary waves, while the appropriate (long- and short-wave) limits yield power laws corresponding to the Zakharov-Filonenko and Phillips spectra.
Experimental observation of gravity-capillary solitary waves generated by a moving air-suction
NASA Astrophysics Data System (ADS)
Park, Beomchan; Cho, Yeunwoo
2016-11-01
Gravity-capillary solitary waves are generated by a moving "air-suction" forcing instead of a moving "air-blowing" forcing. The air-suction forcing moves horizontally over the surface of deep water with speeds close to the minimum linear phase speed cmin = 23 cm/s. Three different states are observed according to forcing speed below cmin. At relatively low speeds below cmin, small-amplitude linear circular depressions are observed, and they move steadily ahead of and along with the moving forcing. As the forcing speed increases close to cmin, however, nonlinear 3-D gravity-capillary solitary waves are observed, and they move steadily ahead of and along with the moving forcing. Finally, when the forcing speed is very close to cmin, oblique shedding phenomena of 3-D gravity-capillary solitary waves are observed ahead of the moving forcing. We found that all the linear and nonlinear wave patterns generated by the air-suction forcing correspond to those generated by the air-blowing forcing. The main difference is that 3-D gravity-capillary solitary waves are observed "ahead of" the air-suction forcing, whereas the same waves are observed "behind" the air-blowing forcing. This work was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2014R1A1A1002441).
Studies of Gravity Wave Propagation in the Middle Atmosphere.
2014-09-26
34 . . . . . • * * . , . • :’ . . . , ",.,,- -. ’’’ " . ’-- o p - %"""" * " AFOSR.TR. 85-0505 physical dynamics,inc. PD-NW-85-330R L n STUDIES OF GRAVITY WAVE PROPAGATION IN...8217.. , .,- - -. ( %’. , .;: :..............,....... .-... . ~.b .. .. - ..... ,......... ..-. ....-.. PD-NW-85-330R STUDIES OF GRAVITY WAVE PROPAGATION...Include SewftY CsuiclUon STUDIES OF GRAVITY WAVE PROPAGATION IN THE MIDD E 12. PERSONAL AUTHORE) TMOPHU. r Timothy J. Dunkerton a13a. TYPE OF REPORT I3k
Acoustic Gravity Wave Chemistry Model for the RAYTRACE Code.
2014-09-26
AU)-AI56 850 ACOlUSTIC GRAVITY WAVE CHEMISTRY MODEL FOR THE IAYTRACE I/~ CODE(U) MISSION RESEARCH CORP SANTA BARBIARA CA T E OLD Of MAN 84 MC-N-SlS...DNA-TN-S4-127 ONAOOI-BO-C-0022 UNLSSIFIlED F/O 20/14 NL 1-0 2-8 1111 po 312.2 1--I 11111* i •. AD-A 156 850 DNA-TR-84-127 ACOUSTIC GRAVITY WAVE...Hicih Frequency Radio Propaoation Acoustic Gravity Waves 20. ABSTRACT (Continue en reveree mide if tteceeemr and Identify by block number) This
On the existence of convectively produced gravity waves
NASA Technical Reports Server (NTRS)
Palm, Stephen P.; Melfi, S. H.
1992-01-01
The Boundary Layer Lidar System (BLLS), together with the gustprobe system onboard the NASA Electra has acquired a unique data set which, for the first time, clearly depicts a gravity wave above a convectively driven planetary boundary layer (PBL). In addition, we believe that the data show the development of a trapped gravity wave over a period of about an hour. If this is the case, it would certainly be the first time that such a process has been seen in the atmosphere. We also conclude that the gravity wave, while being initiated by the convection in the PBL, ultimately acts to organize and control scales in the PBL.
Colliding plane waves in F(R)=RN gravity
NASA Astrophysics Data System (ADS)
Tahamtan, T.; Halilsoy, M.; Habib Mazharimousavi, S.
2016-10-01
We identify a region of a specific F( R)= R N gravity solution without external sources which is isometric to the spacetime of colliding plane waves (CPW). The analogy renders construction and collision of plane waves in F( R)= R N gravity possible. The geometry of the interaction region is equivalent to the Reissner-Nordström (RN) one, however there is no Einstein-Maxwell (EM) source --this is made possible by using the model of RN gravity and the parameter N>1 creates the source. For N=1, we naturally recover the plane waves (and their collision) in Einstein's theory.
Gravity waves and instabilities in the lower and middle atmosphere
NASA Technical Reports Server (NTRS)
Klostermeyer, Juergen
1989-01-01
Some basic aspects of mesoscale and small-scale gravity waves and instability mechanisms are discussed. Internal gravity waves with wavelengths between ten and less than one kilometer and periods between several hours and several minutes appear to play a central role in atmospheric wavenumber and frequency spectra. Therefore, the author discusses the propagation of gravity waves in simplified atmospheric models. Their interaction with the wind as well as their mutual interaction and stability mechanisms based on these processes are discussed. Mesosphere stratosphere troposphere radar observations showing the relevant hydrodynamic processes are stressed.
Turbulence-particle interactions under surface gravity waves
NASA Astrophysics Data System (ADS)
Paskyabi, Mostafa Bakhoday
2016-11-01
The dispersion and transport of single inertial particles through an oscillatory turbulent aquatic environment are examined numerically by a Lagrangian particle tracking model using a series of idealised test cases. The turbulent mixing is incorporated into the Lagrangian model by the means of a stochastic scheme in which the inhomogeneous turbulent quantities are governed by a one-dimensional k- ɛ turbulence closure scheme. This vertical mixing model is further modified to include the effects of surface gravity waves including Coriolis-Stokes forcing, wave breaking, and Langmuir circulations. To simplify the complex interactions between the deterministic and the stochastic phases of flow, we assume a time-invariant turbulent flow field and exclude the hydrodynamic biases due to the effects of ambient mean current. The numerical results show that the inertial particles acquire perturbed oscillations traced out as time-varying sinking/rising orbits in the vicinity of the sea surface under linear and cnoidal waves and acquire a non-looping single arc superimposed with the high-frequency fluctuations beneath the nonlinear solitary waves. Furthermore, we briefly summarise some recipes through the course of this paper on the implementation of the stochastic particle tracking models to realistically describe the drift and suspension of inertial particles throughout the water column.
Application of linear inverse theory to borehole gravity data
Burkhard, N.R.
1991-09-01
Traditional borehole gravity interpretations are based upon an earth model which assumes horizontal, laterally infinite, uniformly thick, and constant density layers. I apply discrete stabilized linear inverse theory to determine the density distribution directly from borehole gravity observations that have been corrected for drift, tide, and terrain. The stabilization is the result of including a priori data about the free-air gradient and the density structure in the inversion process. The discrete generalized linear inverse approach enables one to solve for a density distribution using all of the borehole gravity data. Moreover, the data need not be free-air corrected. An important feature of the approach is that density estimates are not required to be density averages between adjacent borehole gravity observations as in the traditional method. This approach further permits the explicit incorporation of independent density information from gamma-gamma logging tools or laboratory core measurements. Finally, explicit linear constraints upon the density and/or free-air gradient can also be handled. The non-uniqueness of the density structure determined by the inversion process is represented in a resolution matrix. 12 refs., 11 figs.
Massive gravitational waves in Chern-Simons modified gravity
Myung, Yun Soo; Moon, Taeyoon E-mail: tymoon@inje.ac.kr
2014-10-01
We consider the nondynamical Chern-Simons (nCS) modified gravity, which is regarded as a parity-odd theory of massive gravity in four dimensions. We first find polarization modes of gravitational waves for θ=x/μ in nCS modified gravity by using the Newman-Penrose formalism where the null complex tetrad is necessary to specify gravitational waves. We show that in the Newman–Penrose formalism, the number of polarization modes is one in addition to an unspecified Ψ{sub 4}, implying three degrees of freedom for θ=x/μ. This compares with two for a canonical embedding of θ=t/μ. Also, if one introduces the Ricci tensor formalism to describe a massive graviton arising from the nCS modified gravity, one finds one massive mode after making second-order wave equations, which is compared to five found from the parity-even Einstein–Weyl gravity.
Mesospheric gravity waves and ionospheric plasma bubbles observed during the COPEX campaign
NASA Astrophysics Data System (ADS)
Paulino, I.; Takahashi, H.; Medeiros, A. F.; Wrasse, C. M.; Buriti, R. A.; Sobral, J. H. A.; Gobbi, D.
2011-07-01
During the Conjugate Point Experiment (COPEX) campaign performed at Boa Vista (2.80∘N;60.70∘W, dip angle21.7∘N) from October to December 2002, 15 medium-scale gravity waves in the OHNIR airglow images were observed. Using a Keogram image analysis, we estimate their parameters. Most of the waves propagate to Northwest, indicating that their main sources are Southeast of Boa Vista. Quasi-simultaneous plasma bubble activities in the OI 630 nm images were observed in seven cases. The distances between the bubble depletions have a linear relationship with the wavelengths of the gravity waves observed in the mesosphere, which suggests a direct contribution of the mesospheric medium-scale gravity waves in seeding the equatorial plasma bubbles.
Role of Gravity Waves in Determining Cirrus Cloud Properties
NASA Technical Reports Server (NTRS)
OCStarr, David; Singleton, Tamara; Lin, Ruei-Fong
2008-01-01
Cirrus clouds are important in the Earth's radiation budget. They typically exhibit variable physical properties within a given cloud system and from system to system. Ambient vertical motion is a key factor in determining the cloud properties in most cases. The obvious exception is convectively generated cirrus (anvils), but even in this case, the subsequent cloud evolution is strongly influenced by the ambient vertical motion field. It is well know that gravity waves are ubiquitous in the atmosphere and occur over a wide range of scales and amplitudes. Moreover, researchers have found that inclusion of statistical account of gravity wave effects can markedly improve the realism of simulations of persisting large-scale cirrus cloud features. Here, we use a 1 -dimensional (z) cirrus cloud model, to systematically examine the effects of gravity waves on cirrus cloud properties. The model includes a detailed representation of cloud microphysical processes (bin microphysics and aerosols) and is run at relatively fine vertical resolution so as to adequately resolve nucleation events, and over an extended time span so as to incorporate the passage of multiple gravity waves. The prescribed gravity waves "propagate" at 15 m s (sup -1), with wavelengths from 5 to 100 km, amplitudes range up to 1 m s (sup -1)'. Despite the fact that the net gravity wave vertical motion forcing is zero, it will be shown that the bulk cloud properties, e.g., vertically-integrated ice water path, can differ quite significantly from simulations without gravity waves and that the effects do depend on the wave characteristics. We conclude that account of gravity wave effects is important if large-scale models are to generate realistic cirrus cloud property climatology (statistics).
Gravity wave detection by GPS radio occultations
NASA Astrophysics Data System (ADS)
Schmidt, Torsten; Arras, Christina; De la Torre, Alejandro; Alexander, Peter; Llamedo, Pablo
2016-07-01
Gravity waves (GWs) play an important role for the general atmospheric circulation due to the related transport of energy and momentum between different regions of the atmosphere. The momentum mostly generated in the troposphere is transported to upper atmospheric levels where GWs break or dissipate and transfer their momentum to the background wind (GW drag). The deposit of GW momentum can occur in the complete altitude range from the upper troposphere-stratosphere, the mesosphere, and even in the thermosphere. A global observation of GW parameters (e.g. potential energy and vertical flux of absolute horizontal momentum) is only possible with satellite data. The radio occultation (RO) technique uses GPS signals received aboard low Earth orbiting satellites for atmospheric limb sounding. Atmospheric temperature profiles in the troposphere/stratosphere and ionospheric electron densities are derived with high vertical resolution. The GPS RO technique is sensitive to GWs with small ratios of vertical to horizontal wavelengths. In this presentation we give an overview about the derivation of GW parameters from RO temperature profiles, review some results of GW detection with RO data, and discuss the limitations of the RO technique. The focus of the presented results is (1) global GW activity in the upper troposphere and lower stratosphere for different seasons, (2) influence of the topography on GW activity from the troposphere to the ionosphere in the Andean region of South America, and (3) the variation of ionospheric sporadic E layers.
2015-09-30
being centimeter scale, surface mixed layer processes arising from the combined actions of tides, winds and mesoscale currents. Issues related to...the internal wave field and how it impacts the surface waves. APPROACH We are focusing on the problem of modification of the wind -wave field...does the wind -wave field evolve in the presence of surface currents driven by ISWs? 3) How does the surface gravity wave field above ISWs modify the
Observations of gravity wave scales, fluxes, and saturation during MAP
NASA Technical Reports Server (NTRS)
Reid, I. M.
1989-01-01
During the MAP/MAC period, considerable improvements in instrumentation and experimental technique have occurred, and many hitherto unavailable parameters relating to gravity waves have become available. Studies of individual wave events and simultaneous observations made with a variety of techniques have provided insight into wave saturation mechanisms. In addition, long data sets of upper middle atmosphere winds were collected at a number of widely spaced sites, allowing climatological investigations of gravity wave amplitudes, wave number spectra, polarization, mean flow acceleration, and other saturation effects to be undertaken. Observations of gravity wave scales, momentum fluxes, saturation and saturation effects obtained during MAP/MAC, made on both a statistical and case study basis are reviewed.
Exploring Gravity Wave Predictability and Dynamics in Deepwave
NASA Astrophysics Data System (ADS)
Doyle, J. D.; Fritts, D. C.; Smith, R. B.; Eckermann, S. D.; Taylor, M. J.; Dörnbrack, A.; Uddstrom, M.; Reynolds, C. A.; Reinecke, A.; Jiang, Q.
2014-12-01
The DEEP propagating gravity WAVE program (DEEPWAVE) is a comprehensive, airborne and ground-based measurement and modeling program centered on New Zealand and focused on providing a new understanding of gravity wave dynamics and impacts from the troposphere through the mesosphere and lower thermosphere (MLT). This program employed the NSF/NCAR GV (NGV) research aircraft from a base in New Zealand in a 6-week field measurement campaign in June-July 2014. During the field phase, the NGV was equipped with new lidar and airglow instruments, as well as dropwindsondes and a full suite of flight level instruments including the microwave temperature profiler (MTP), providing temperatures and vertical winds spanning altitudes from immediately above the NGV flight altitude (~13 km) to ~100 km. The region near New Zealand was chosen since all the relevant GW sources (e.g., mountains, cyclones, jet streams) occur strongly here, and upper-level winds in austral winter permit gravity waves to propagate to very high altitudes. The COAMPS adjoint modeling system provided forecast sensitivity in real time during the six-week DEEPWAVE field phase. Five missions were conducted using the NGV to observe regions of high forecast sensitivity, as diagnosed using the COAMPS adjoint model. In this presentation, we provide a summary of the sensitivity characteristics and explore the implications for predictability of low-level winds crucial for gravity wave launching, as well as predictability of gravity wave characteristics in the stratosphere. In general, the sensitive regions were characterized by localized strong dynamics, often involving intense baroclinic systems with deep convection. The results of the adjoint modeling system suggest that gravity wave launching and the characteristics of the gravity waves can be linked to these sensitive regions near frontal zones within baroclinic systems. The predictability links between the tropospheric fronts, cyclones, jet regions, and gravity
Internal gravity waves from atmospheric jets and fronts
NASA Astrophysics Data System (ADS)
Plougonven, Riwal; Zhang, Fuqing
2014-03-01
For several decades, jets and fronts have been known from observations to be significant sources of internal gravity waves in the atmosphere. Motivations to investigate these waves have included their impact on tropospheric convection, their contribution to local mixing and turbulence in the upper troposphere, their vertical propagation into the middle atmosphere, and the forcing of its global circulation. While many different studies have consistently highlighted jet exit regions as a favored locus for intense gravity waves, the mechanisms responsible for their emission had long remained elusive: one reason is the complexity of the environment in which the waves appear; another reason is that the waves constitute small deviations from the balanced dynamics of the flow generating them; i.e., they arise beyond our fundamental understanding of jets and fronts based on approximations that filter out gravity waves. Over the past two decades, the pressing need for improving parameterizations of nonorographic gravity waves in climate models that include a stratosphere has stimulated renewed investigations. The purpose of this review is to present current knowledge and understanding on gravity waves near jets and fronts from observations, theory, and modeling, and to discuss challenges for progress in coming years.
Gravity wave observations using an all-sky imager network
NASA Astrophysics Data System (ADS)
Wrasse, Cristiano Max; Almeida, Lazaro M.; Abalde Guede, Jose Ricardo; Fagundes, Paulo Roberto; Nicoli Candido, Claudia Maria; Alves Bolzan, Maurício José; Guarnieri, Fernando; Messias Almeida, Lazaro
Gravity waves in the mesosphere were observed by airglow all-sky imager network of the UNI- VAP at São José dos Campos (23o S, 45o W), Braśpolis (22o S, 45o W) and Palmas (10o S, 48o W), a e o Brazil. Gravity wave characteristics like morphology, horizontal wavelength, period, phase speed and propagation direction will be analysed and discussed. The results will be compared with other observation sites in Brazil. Wave directionality will also be discussed in terms of wave sources and wind filtering.
Inertio-Gravity Waves in the Middle Atmosphere.
NASA Astrophysics Data System (ADS)
Zhu, Xun
In this dissertation a variety of aspects of inertio -gravity waves in the middle atmosphere is investigated with simple theoretical and/or numerical methods. Using the models derived from theoretical developments, two distinct numerical simulations are performed to study gravity wave -mean flow interactions in the middle atmosphere. Further, the damping effects of radiative and photochemical processes on inertio-gravity waves are refreshed by some simple mechanistic models. Coy's one-dimensional coupled model proposed in 1983 for gravity wave propagation and wave-mean flow interaction is extended theoretically to three dimension for inertio -gravity wave-mean flow interaction using multi-scale analysis. Two sets of equations for global and local mean flow evolutions are proposed. The effect of waves on global mean flow is characterized by the evolution of the meridional gradient of potential vorticity. The change of the local mean flow is described by a geostrophic adjustment process under external local wave forcing. Lindzen's parameterization for the drag and eddy diffusion produced by breaking internal gravity waves in the mesosphere and lower thermosphere is applied to a global mean flow model in which an isotropic source of waves is specified similar to that given in 1982 by Matsuno. The local mean flow model is used to investigate wave generation by geostrophic processes under local forcing. Fels' results in 1982 on scale-dependent radiative damping rate are extended in several aspects by removing extra assumptions used in his theoretical derivations. It is found that Fels' damping rate coefficients can be used for all waves in the middle atmosphere no matter what their periods are. A simple model is developed for the coupled effects of radiative heating and ozone photochemistry on inertio-gravity waves in the region 16-70 km. A model similar to ozone photochemistry is also used to study the amplification of gravity waves by recombination of atomic oxygen in
Tsunami and acoustic-gravity waves in water of constant depth
Hendin, Gali; Stiassnie, Michael
2013-08-15
A study of wave radiation by a rather general bottom displacement, in a compressible ocean of otherwise constant depth, is carried out within the framework of a three-dimensional linear theory. Simple analytic expressions for the flow field, at large distance from the disturbance, are derived. Realistic numerical examples indicate that the Acoustic-Gravity waves, which significantly precede the Tsunami, are expected to leave a measurable signature on bottom-pressure records that should be considered for early detection of Tsunami.
Integrated gravity and gravity gradient 3D inversion using the non-linear conjugate gradient
NASA Astrophysics Data System (ADS)
Qin, Pengbo; Huang, Danian; Yuan, Yuan; Geng, Meixia; Liu, Jie
2016-03-01
Gravity data, which are critical in mineral, oil, and gas exploration, are obtained from the vertical component of the gravity field, while gravity gradient data are measured from changes in the gravity field in three directions. However, few studies have sought to improve exploration techniques by integrating gravity and gravity gradient data using inversion methods. In this study, we developed a new method to integrate gravity and gravity gradient data in a 3D density inversion using the non-linear conjugate gradient (NLCG) method and the minimum gradient support (MGS) functional to regularize the 3D inverse problem and to obtain a clear and accurate image of the anomalous body. The NLCG algorithm, which is suitable for solving large-scale nonlinear optimization problems and requires no memory storage, was compared to the Broyden-Fletcher-Goldfarb-Shanno (BFGS) quasi-Newton algorithm and the results indicated that the convergence rate of NLCG is slower, but that the storage requirement and computation time is lower. To counteract the decay in kernel function, we introduced a depth weighting function for anomalous bodies at the same depth, with information about anomalous body depth obtained from well log and seismic exploration data. For anomalous bodies at different depths, we introduced a spatial gradient weighting function to incorporate additional information obtained in the inversion. We concluded that the spatial gradient weighting function enhanced the spatial resolution of the recovered model. Furthermore, our results showed that including multiple components for inversion increased the resolution of the recovered model. We validated our model by applying our inversion method to survey data from Vinton salt dome, Louisiana, USA. The results showed good agreement with known geologic information; thus confirming the accuracy of this approach.
Intercomparison of stratospheric gravity wave observations with AIRS and IASI
NASA Astrophysics Data System (ADS)
Hoffmann, Lars; Alexander, M. Joan; Clerbaux, Cathy; Grimsdell, Alison W.; Meyer, Catrin I.; Rößler, Thomas; Tournier, Bernard
2015-04-01
Gravity waves are an important driver for the atmospheric circulation and have substantial impact on weather and climate. Satellite instruments offer excellent opportunities to study gravity waves on a global scale. This study focuses on observations from the Atmospheric Infrared Sounder (AIRS) onboard the National Aeronautics and Space Administration's Aqua satellite and the Infrared Atmospheric Sounding Interferometer (IASI) onboard the European MetOp satellites. The main aim of this study is an intercomparison of stratospheric gravity wave observations of both instruments. In particular, we analyzed AIRS and IASI 4.3 μm brightness temperature measurements, which directly relate to stratospheric temperature. Three case studies showed that AIRS and IASI provide a clear and consistent picture of the temporal development of individual gravity wave events. Statistical comparisons based on a five-year period of measurements (2008 - 2012) showed similar spatial and temporal patterns of gravity wave activity. However, the statistical comparisons also revealed systematic differences of variances between AIRS and IASI that we attribute to the different spatial measurement characteristics of both instruments. We also found differences between day- and nighttime data that are partly due to the local time variations of the gravity wave sources. While AIRS has been used successfully in many previous gravity wave studies, IASI data are applied here for the first time for that purpose. Our study shows that gravity wave observations from different hyperspectral infrared sounders such as AIRS and IASI can be directly related to each other, if instrument-specific characteristics such as different noise levels and spatial resolution and sampling are carefully considered. The ability to combine observations from different satellites provides an opportunity to create a long-term record, which is an exciting prospect for future climatological studies of stratospheric gravity wave
NASA Technical Reports Server (NTRS)
Smith, S. A.; Fritts, D. C.; Vanzandt, T. E.
1986-01-01
The results of a comparison of mesospheric wind fluctuation spectra computed from radial wind velocity estimates made by the Poker Flat mesosphere-stratosphere-troposphere (MST) radar are compared with a gravity-wave model developed by VanZandt (1982, 1985). The principal conclusion of this comparison is that gravity waves can account for 80% of the mesospheric power spectral density.
Non-linear structure in modified action theories of gravity
NASA Astrophysics Data System (ADS)
Lima, Marcos V.
We study the effects and carry out a suite of cosmological simulations of modified action f(R) models where cosmic acceleration arises from an alteration of gravity instead of dark energy. These models introduce an extra scalar degree of freedom which enhances the force of gravity below the Compton scale of the scalar. The simulations exhibit the so-called chameleon mechanism, necessary for satisfying local constraints on gravity, where this scale depends on environment, in particular the depth of the local gravitational potential. We find that the chameleon mechanism can substantially suppress the enhancement of power spectrum in the non-linear regime if the background field value is comparable to or smaller than the depth of the gravitational potentials of typical structures. Nonetheless power spectrum enhancements at intermediate scales remain at a measurable level even when the expansion history is indistinguishable from a cosmological constant, cold dark matter model. We also investigate the effects of the modified dynamics on halo properties such as their abundance and clustering. We find that the f(R) effects on the halo mass- function and bias depend mostly on the linear power spectrum modifications, but that the chameleon mechanism suppresses the modifications at high-mass halos with deep potential wells. The f(R) modifications also affect the threshold density for collapse, or similarly the overdensity for virialization and therefore can change halo definitions from those of ACDM. As a result, simple scaling relations that take the linear matter power spectrum into a non-linear spectrum fail to capture the modifications of f(R) due to the change in collapsed structures, the chameleon mechanism, and the time evolution of the modifications. A quantification of these effects, including modifications on halo profiles, is necessary to accurately describe halo properties and potentially construct a halo model of the non-linear power spectrum.
NASA Technical Reports Server (NTRS)
Mayr, Hans G.; Mengel, J. G.; Chan, K. L.; Huang, F. T.
2010-01-01
As Lindzen (1981) had shown, small-scale gravity waves (GW) produce the observed reversals of the zonal-mean circulation and temperature variations in the upper mesosphere. The waves also play a major role in modulating and amplifying the diurnal tides (DT) (e.g., Waltersheid, 1981; Fritts and Vincent, 1987; Fritts, 1995a). We summarize here the modeling studies with the mechanistic numerical spectral model (NSM) with Doppler spread parameterization for GW (Hines, 1997a, b), which describes in the middle atmosphere: (a) migrating and non-migrating DT, (b) planetary waves (PW), and (c) global-scale inertio gravity waves. Numerical experiments are discussed that illuminate the influence of GW filtering and nonlinear interactions between DT, PW, and zonal mean variations. Keywords: Theoretical modeling, Middle atmosphere dynamics, Gravity wave interactions, Migrating and non-migrating tides, Planetary waves, Global-scale inertio gravity waves.
Angular momentum transport via internal gravity waves in evolving stars
Fuller, Jim; Lecoanet, Daniel; Cantiello, Matteo; Brown, Ben
2014-11-20
Recent asteroseismic advances have allowed for direct measurements of the internal rotation rates of many subgiant and red giant stars. Unlike the nearly rigidly rotating Sun, these evolved stars contain radiative cores that spin faster than their overlying convective envelopes, but slower than they would in the absence of internal angular momentum transport. We investigate the role of internal gravity waves in angular momentum transport in evolving low-mass stars. In agreement with previous results, we find that convectively excited gravity waves can prevent the development of strong differential rotation in the radiative cores of Sun-like stars. As stars evolve into subgiants, however, low-frequency gravity waves become strongly attenuated and cannot propagate below the hydrogen-burning shell, allowing the spin of the core to decouple from the convective envelope. This decoupling occurs at the base of the subgiant branch when stars have surface temperatures of T ≈ 5500 K. However, gravity waves can still spin down the upper radiative region, implying that the observed differential rotation is likely confined to the deep core near the hydrogen-burning shell. The torque on the upper radiative region may also prevent the core from accreting high angular momentum material and slow the rate of core spin-up. The observed spin-down of cores on the red giant branch cannot be totally attributed to gravity waves, but the waves may enhance shear within the radiative region and thus increase the efficacy of viscous/magnetic torques.
Observed and Modeled Stratospheric Gravity Waves above Hurricane Humberto
NASA Astrophysics Data System (ADS)
Kuester, M.; Alexander, J.; Ray, E.
2004-05-01
A three-dimensional model can be a very powerful tool to the study of various properties of hurricanes including areas of deep convection as possible sources of internal gravity waves. Data collected by aircraft, although extremely useful, does not give a full picture of the dynamics of the system because only a few slices through the storm can be sampled within the limitations of the campaign. A validated model can help to fill in the gaps where the sampled data cannot. In this study, a three-dimensional MM5 model is used to study the characteristics of Hurricane Humberto, a category 2 hurricane observed in September 2001 during the the fourth field campaign in the Convection and Moisture Experiment series (CAMEX4). Of particular interest to this study are internal gravity waves induced by the convective activity within the rain bands of the hurricane. Further understanding of the sources for these waves and their effects on the large-scale circulation is an ongoing topic of research. Vertical velocity perturbations and potential temperature contours are used to pinpoint vertically propagating gravity waves in the stratosphere. Possible correlations between areas of deep convection as gravity wave sources within the storm and observed vertically propagating gravity waves are presented. Comparison of model results to data collected during the CAMEX4 on board the high-altitude NASA ER-2 aircraft with the ER-2 Doppler Radar (EDOP) and Microwave Temperature Profiler (MTP) will also be presented.
Turbulence and stress owing to gravity wave and tidal breakdown
NASA Technical Reports Server (NTRS)
Lindzen, R. S.
1981-01-01
For some years it has been accepted that tides and gravity waves propagating into the upper mesosphere from below are the major source of turbulence in the upper mesosphere. The considered investigation has the objective to examine the implications of such a situation in some detail. The main propagating diurnal mode seems to be the primary contributor at tropical latitudes. Because of the high phase speed of this mode, it is only slightly affected by the mean zonal flow of the atmosphere. Wavebreaking appears to occur around 85 km, leading to a layer of enhanced eddy diffusion and wave induced acceleration extending between 85 km and about 108 km. Above 108 km molecular transport dominates. Gravity waves appear to be dominant at middle and high latitudes. The flow distribution will effectively determine which gravity waves (depending on phase speed) can reach the mesosphere.
Mapping High Latitude Gravity Wave Amplitudes over Antarctica during Summer
NASA Astrophysics Data System (ADS)
Badenhausen, P.; Millan, R. M.; Gerrard, A. J.
2015-12-01
Appropriate inclusion of gravity wave amplitudes into general circulation models is required to get accurate atmospheric circulation characteristics. However, high latitude gravity wave amplitudes are particularly difficult to obtain due to the challenging experimental and logistical constraints in these regions. In this study, we present gravity wave climatology of high latitudes during austral summer conditions over the Antarctic continent. These data were obtained using high-resolution GPS measurements aboard long duration high altitude balloon flights that were flown as part of the NASA Balloon Array for Radiation-belt Relativistic Electron Losses (BARREL) mission in December 2013-February 2014 and December 2012-February 2013. The results show increased gravity wave activity along the coast of the Antarctic continent, particularly over the Peninsula and Halley Bay, whereas at higher latitudes, particularly over regions near the South Pole, gravity wave amplitudes decrease substantially. Through use of horizontal winds data, we obtained measurements of the vertical transport of horizontal momentum fluxes, which were unusually high for the summer high latitude lower stratosphere. Such unique measurements as these are immediately applicable to understanding of upwelling in the summer middle atmosphere as well as to the formation of overlaying mesospheric clouds formation.
Infrasound monitoring, acoustic-gravity waves and global atmospheric dynamics
NASA Astrophysics Data System (ADS)
Blanc, E.; Le Pichon, A.; Ceranna, L.; Farges, T.
2008-12-01
For the verification of the Comprehensive nuclear Test Ban Treaty, the International Monitoring System has been developed. As part of this system, the infrasound network provides an unique opportunity to monitor continuously pressure waves in the atmosphere. Such infrasonic waves propagate in the channel formed by the temperature and wind gradients of the atmosphere. Long term observations provide information about the evolution of the propagation conditions and then of atmospheric parameters. The monitoring of continuous sources, as ocean swell, gives the characteristics of the stratospheric wave channel submitted to stratospheric warming effects. Large scale gravity waves, which are also observed by the network, produce a forcing of the stratosphere at low and middle latitudes and long-lived changes in the stratospheric circulation towards high latitudes, leading to fluctuations in the strength of the polar vortex. These fluctuations move down to the lower stratosphere with possible effects on the tropospheric temperature. Gravity wave monitoring in Antarctica reveals a gravity wave system probably related to the wind effect over mountains. At mid latitudes an additional main sources of disturbances is the thunderstorm activity. The infrasound monitoring system allows a better knowledge of the atmospheric wave systems and of the dynamics of the atmosphere. In return this better knowledge of the wave systems allow a better identification of the possible explosion signals in the background of the atmospheric waves and then to improve the discrimination methods
Saturated-cascade similitude theory of gravity wave spectra
NASA Astrophysics Data System (ADS)
Dewan, Edmond
1997-12-01
A theory is presented, which is based mainly on dimensional analysis (but also on gravity wave theory), that attempts to explain all the types of gravity wave power spectral densities (PSDs) now being measured. This theory is based on two concepts, namely, wave saturation and wave cascade. The immediate result of the simultaneous presence of these two processes is that there should exist a unique relation between the vertical (or horizontal) wavelength of a gravity wave and its period (provided the Brunt Period and dissipation rate are given and Doppler effects are omitted). This relation provides a way to derive all of the intrinsic spectra from the fundamental one which is the vertical wavenumber PSD of the horizontal winds. The most important suggestion to emerge from this theory is that ɛ, the dissipation rate, is the main controlling independent variable for the amplitude of all but 3 of the 12 spectra predicted. It would also control the wavelength-period relations. Comparisons are made between observations and theory, and important experimental tests are proposed. This model presently appears to be useful in the analysis of gravity wave data obtained by means of lidars, radars, interferometers, and imagers. In addition, it raises a number of new scientific issues for future research.
Characterisitics of Inertial Gravity Waves in the Antarctic Stratosphere
NASA Astrophysics Data System (ADS)
Murphy, D. J.; Klekociuk, A. R.; Alexander, S.; Love, P. T.; Vincent, R. A.
2013-12-01
A decade of radiosonde observations of wind and temperature in the troposphere and lower stratosphere have made it possible to compile a climatology of low-frequency gravity waves above Davis, Antarctica (69S, 78E). Wave characteristics, extracted using wavelet analysis [Zink and Vincent, 2001], show strong seasonal and height variations. In particular, the high prevalence of down-going waves in the winter lower stratosphere previously identified at other Antarctic sites [Moffat-Griffin et al. 2011; Yoshiki and Sato, 2000] has been shown to exist at Davis. The vertical structure and seasonal variation of down-going wave percentages are shown in Figure 1a, and a relationship with the background zonal wind structure (contoured) is suggested. Figures 1b and 1c show that the down-going waves replace up-going waves in the winter lower stratosphere. Statistical distributions of the characteristics of the up and down-going waves show strong similarities suggesting a common source. It is also possible that both classes of waves have characteristics that are more strongly dependent on propagation conditions than their source mechanism. It has been suggested [Sato and Yoshiki, 2008] that imbalance processes in the polar night jet may play a role in their production. This possibility is considered along with the propagation characteristics of the waves to explore their role in the dynamics of the polar stratosphere, and to examine the adequacy of their representation in atmospheric models. References: Moffat-Griffin, T., R. E. Hibbins, M. J. Jarvis and S. R. Colwell, Seasonal variations of gravity wave activity in the lower stratosphere over an Antarctic Peninsula station, J. Geophys. Res., 116, D14111, doi:10.1029/2010JD015349, 2011. Sato, K. And M. Yoshiki, Gravity wave generation around the polar vortex in the stratosphere revealed by 3-hourly radiosonde observations at Syowa station, J. Atmos. Sci., 65, 3719-3735, 2008. Yoshiki, M. And K. Sato, A statistical study of
First tsunami gravity wave detection in ionospheric radio occultation data
Coïsson, Pierdavide; Lognonné, Philippe; Walwer, Damian; ...
2015-05-09
After the 11 March 2011 earthquake and tsunami off the coast of Tohoku, the ionospheric signature of the displacements induced in the overlying atmosphere has been observed by ground stations in various regions of the Pacific Ocean. We analyze here the data of radio occultation satellites, detecting the tsunami-driven gravity wave for the first time using a fully space-based ionospheric observation system. One satellite of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) recorded an occultation in the region above the tsunami 2.5 h after the earthquake. The ionosphere was sounded from top to bottom, thus providing themore » vertical structure of the gravity wave excited by the tsunami propagation, observed as oscillations of the ionospheric Total Electron Content (TEC). The observed vertical wavelength was about 50 km, with maximum amplitude exceeding 1 total electron content unit when the occultation reached 200 km height. We compared the observations with synthetic data obtained by summation of the tsunami-coupled gravity normal modes of the Earth/Ocean/atmosphere system, which models the associated motion of the ionosphere plasma. These results provide experimental constraints on the attenuation of the gravity wave with altitude due to atmosphere viscosity, improving the understanding of the propagation of tsunami-driven gravity waves in the upper atmosphere. They demonstrate that the amplitude of the tsunami can be estimated to within 20% by the recorded ionospheric data.« less
First tsunami gravity wave detection in ionospheric radio occultation data
Coïsson, Pierdavide; Lognonné, Philippe; Walwer, Damian; Rolland, Lucie M.
2015-05-09
After the 11 March 2011 earthquake and tsunami off the coast of Tohoku, the ionospheric signature of the displacements induced in the overlying atmosphere has been observed by ground stations in various regions of the Pacific Ocean. We analyze here the data of radio occultation satellites, detecting the tsunami-driven gravity wave for the first time using a fully space-based ionospheric observation system. One satellite of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) recorded an occultation in the region above the tsunami 2.5 h after the earthquake. The ionosphere was sounded from top to bottom, thus providing the vertical structure of the gravity wave excited by the tsunami propagation, observed as oscillations of the ionospheric Total Electron Content (TEC). The observed vertical wavelength was about 50 km, with maximum amplitude exceeding 1 total electron content unit when the occultation reached 200 km height. We compared the observations with synthetic data obtained by summation of the tsunami-coupled gravity normal modes of the Earth/Ocean/atmosphere system, which models the associated motion of the ionosphere plasma. These results provide experimental constraints on the attenuation of the gravity wave with altitude due to atmosphere viscosity, improving the understanding of the propagation of tsunami-driven gravity waves in the upper atmosphere. They demonstrate that the amplitude of the tsunami can be estimated to within 20% by the recorded ionospheric data.
Properties of QBO and SAO Generated by Gravity Waves
NASA Technical Reports Server (NTRS)
Mayr, H. G.; Mengel, J. G.; Reddy, C. A.; Chan, K. L.; Porter, H. S.
1999-01-01
We present an extension for the 2D (zonal mean) version of our Numerical Spectral Mode (NSM) that incorporates Hines' Doppler spread parameterization (DSP) for small scale gravity waves (GW). This model is applied to describe the seasonal variations and the semi-annual and quasi-biennial oscillations (SAO and QBO). Our earlier model reproduced the salient features of the mean zonal circulation in the middle atmosphere, including the QBO extension into the upper mesosphere inferred from UARS measurements. In the present model we incorporate also tropospheric heating to reproduce the upwelling at equatorial latitudes associated with the Brewer-Dobson circulation that affects significantly the dynamics of the stratosphere as Dunkerton had pointed out. Upward vertical winds increase the period of the QBO observed from the ground. To compensate for that, one needs to increase the eddy diffusivity and the GW momentum flux, bringing the latter closer to values recommended in the DSP. The QBO period in the model is 30 months (mo), which is conducive to synchronize this oscillation with the seasonal cycle of solar forcing. Multi-year interannual oscillations are generated through wave filtering by the solar driven annual oscillation in the zonal circulation. Quadratic non-linearities generate interseasonal variations to produce a complicated pattern of variability associated with the QBO. The computed temperature amplitudes for the SAO and QBO are in substantial agreement with observations at equatorial and extratropical latitudes. At high latitudes, however, the observed QBO amplitudes are significantly larger, which may be a signature of propagating planetary waves not included in the present model. The assumption of hydrostatic equilibrium not being imposed, we find that the effects from the vertical Coriolis force associated with the equatorial oscillations are large for the vertical winds and significant for the temperature variations even outside the tropics but are
Climatology of gravity waves over Poker Flat, Alaska for 1983
NASA Technical Reports Server (NTRS)
Balsley, B. B.; Garello, R.
1986-01-01
An analysis of short-period wind fluctuations over Poker Flat, Alaska, obtained using the Poker Flat mesosphere-stratosphere-troposphere radar is presented. Results are shown for the troposphere and lower stratosphere as well as for the upper mesosphere and lower thermosphere. Contours depict various levels of wind variance (m2s-2). These results pertain only to wind fluctuation periods lying between one and six hours. These particular fluctuations are generally considered to arise primarily from atmospheric gravity waves. Insofar as this is true, the figure thus describes a general climatology of gravity waves at high latitudes.
Simultaneous rocket and MST radar observation of an internal gravity wave breaking in the mesosphere
NASA Technical Reports Server (NTRS)
Smith, S. A.; Fritts, D. C.; Balsley, B. B.; Philbrick, C. R.
1986-01-01
In June, 1983, the Structure and Atmospheric Turbulence Environment (STATE) rocket and Poker Flat Mesophere-Stratosphere-Troposphere radar campaign was conducted to measure the interaction between turbulence, electron density and electron density gradient that has produced unusually strong MST radar echoes from the summer mesosphere over Poker Flat, Alaska. Analysis or radar wind measurements and a concurrent wind and temperature profile obtained from a rocket probe carrying a three-axis accelerometer are given. The two data sets provide a fairly complete (and in some cases, redundant) picture of the breaking (or more correctly, the saturation) of a large-amplitude, low-frequency, long-wavelength internal gravity wave. The data show that small-scale turbulence and small-scale wave intensity is greatest at those altitudes where the large-scale wave-induced temperature lapse rate is most negative or most nearly unstable, but the wind shear due to the large-scale wave is a minimum. A brief review of linear gravity-wave theory is presented as an aid to the identification of the gravity-wave signature in the radar and rocket data. Analysis of the time and height cross sections of wind speed and turbulence intensity observed by the Poker Flat MST radar follows. Then, the vertical profile of temperature and winds measured by a rocket probe examined. Finally, the use of the independent data sets provided by the rocket and the radar are discussed and implications for theories of wave saturation are presented.
Gravity-Wave Dynamics in the Atmosphere
2010-02-01
of wave-induced downslope winds. Journal of the Atmospheric Sciences, 32(2):320–339, 1975. [12] P. K. Kundu and I. M. Cohen. Fluid Mechanics . Elsevier...Wave Beams and Local Generation of Solitary Waves in the Ocean Thermocline”, Journal of Fluid Mechanics , 593, 297-313 (2007) Akylas, T. R. & Druecke...334–348, 1992. [4] T. H. Bell. Lee waves in stratified flows with simple harmonic time-dependence. Journal of Fluid Mechanics , 67(FEB25):705–722
NASA Technical Reports Server (NTRS)
Koch, Steven E.; Dorian, Paul B.
1988-01-01
The multiscale environment of gravity wave events and the probable mechanisms of their origin are examined on the basis of observations taken during the Cooperative Convective Precipitation Experiment in extreme eastern Montana, during the period from 1200 UTC July 11, 1981, to 0500 UTC July 12. During this time, two distinct gravity wave episodes were diagnosed. The results of the analysis of the evolving structures in the subsynoptic-scale and mesoscale environments indicate that the observed mesoscale gravity waves were generated by geostrophic adjustment processes, with additional energy supplied through interaction with the critical level; their coherence was maintained through a ducting mechanism.
Satellite based study of stratospheric gravity waves generated by topography
NASA Astrophysics Data System (ADS)
Kumar, K. N.; Thokuluwa, R.; Musali, K.
2011-12-01
Atmospheric Gravity Waves (AGWs) are oscillations manifested in atmospheric thermodynamic parameters like wind velocities, temperature, air density, pressure etc. at all altitudes in the atmosphere. The important sources of AGWs include wind flows over topography, latent heating of the atmosphere associated with convection, strong wind shears, adjustment of unbalanced flows in the vicinity of jet streams and frontal systems etc. Of these, mountain waves generated by airflow over topography are believed to be one of the dominant sources, particularly in the extra-tropics during winter. The study of mountain waves has been considered valuable by the scientific community for reasons such as, their impact on aviation, formation of rectilinear clouds etc. Moreover, mountain waves can easily transport momentum and energy vertically up through the middle atmosphere and the effect of which is essential to understand the general middle atmospheric circulation and chemistry. In the present study, we describe a mountain wave event observed in three dimensions using Atmospheric Infrared Sounder (AIRS) satellite measured atmospheric radiance and temperatures over the western Himalayan mountain region. As a supplement to the AIRS measurements, we have also used the temperature information obtained from Microwave Limb Sounder (MLS). The mountain wave event is also well represented in the high resolution Modern Era Retrospective-analysis for Research and Applications (MERRA) reanalysis data. It is found also close agreement between the observed and theoretical vertical wavelengths for a stationary gravity wave calculated reanalysis winds. Using three dimensional (3d) wave properties of the wave, we also estimated the wave momentum flux.
Resonant Interactions of Capillary-Gravity Water Waves
NASA Astrophysics Data System (ADS)
Martin, Calin Iulian
2016-11-01
We show here that capillary-gravity wave trains can propagate at the free surface of a rotational water flow of constant non-zero vorticity over a flat bed only if the flow is two-dimensional. Moreover, we also show that the vorticity must have only one non zero component which points in the horizontal direction orthogonal to the direction of wave propagation. This result is of relevance in the study of nonlinear resonances of wave trains. We perform such a study for three- and four wave interactions.
NASA Astrophysics Data System (ADS)
Hostetler, Chris Alan
Gravity wave models for the horizontal wave number spectra of atmospheric velocity and density fluctuations are derived by assuming that both saturated and unsaturated waves obey the polarization and dispersion relations and that the joint (m,w) spectrum is separable. The models show that the joint (k,l,m) and (k,l,w) spectra are not separable. The one-dimensional horizontal wave number spectra models are consistent with existing observations of horizontal wave number spectra in the lower stratosphere and upper mesosphere. The gravity wave models are used to analyze the effects of Doppler shifting caused by the mean wind field on the separability of gravity wave spectra. If the intrinsic joint (m,w) spectrum is separable, Doppler effects associated with even small mean winds will destroy separability of the observed joint (m,w(sub o)) spectrum, particularly at high vertical wave numbers. Vertical and horizontal wave number spectra of density perturbations in the upper stratosphere (25-40 km) and the upper mesosphere (approximately 80-105 km) measured during the ALOHA-90 campaign are presented. The spectra were inferred from approximately 45 h of airborne Na/Rayleigh lidar observations in the vicinity of Hawaii. Density variances, vertical shear variances, Richardson's numbers, characteristic vertical and horizontal wave numbers, and power law slopes of the vertical and horizontal wave number spectra are computed and discussed. The observed m-spectra contradict the predictions of the linear instability theory of Dewan and Good, and the scale-dependent diffusive filtering theory of Gardner, and appear to be compatible with the Doppler spreading theory of Hines, the scale-dependent diffusion theory of Weinstock, the scale-independent diffusive filtering theory of Gardner, and the similitude model of Dewan. In the stratosphere, the m-spectra exhibit significant energy at low wave numbers less than the values expected for m(sub *). The source of this energy is believed
Numerical simulation of the resonantly excited capillary-gravity waves
NASA Astrophysics Data System (ADS)
Hanazaki, Hideshi; Hirata, Motonori; Okino, Shinya
2015-11-01
Capillary gravity waves excited by an obstacle are investigated by a direct numerical simulation. In the flow without capillary effects, it is well known that large-amplitude upstream advancing solitary waves are generated periodically under the resonant condition, i.e., when the phase velocity of the long surface waves and the mean flow velocity agrees. With capillary effects, solutions of the Euler equations show the generation of very short waves further upstream of the solitary waves and also in the depression region downstream of the obstacle. The overall characteristics of these waves agree with the solutions of the forced fifth-order KdV equation, while the weakly nonlinear theory generally overestimates the wavelength of the short waves.
NASA Astrophysics Data System (ADS)
Bičák, Jiří; Schmidt, Josef
2016-01-01
The question of the uniqueness of energy-momentum tensors in the linearized general relativity and in the linear massive gravity is analyzed without using variational techniques. We start from a natural ansatz for the form of the tensor (for example, that it is a linear combination of the terms quadratic in the first derivatives), and require it to be conserved as a consequence of field equations. In the case of the linear gravity in a general gauge we find a four-parametric system of conserved second-rank tensors which contains a unique symmetric tensor. This turns out to be the linearized Landau-Lifshitz pseudotensor employed often in full general relativity. We elucidate the relation of the four-parametric system to the expression proposed recently by Butcher et al. "on physical grounds" in harmonic gauge, and we show that the results coincide in the case of high-frequency waves in vacuum after a suitable averaging. In the massive gravity we show how one can arrive at the expression which coincides with the "generalized linear symmetric Landau-Lifshitz" tensor. However, there exists another uniquely given simpler symmetric tensor which can be obtained by adding the divergence of a suitable superpotential to the canonical energy-momentum tensor following from the Fierz-Pauli action. In contrast to the symmetric tensor derived by the Belinfante procedure which involves the second derivatives of the field variables, this expression contains only the field and its first derivatives. It is simpler than the generalized Landau-Lifshitz tensor but both yield the same total quantities since they differ by the divergence of a superpotential. We also discuss the role of the gauge conditions in the proofs of the uniqueness. In the Appendix, the symbolic tensor manipulation software cadabra is briefly described. It is very effective in obtaining various results which would otherwise require lengthy calculations.
NASA Astrophysics Data System (ADS)
Alexander, M. J.; Sherwood, S.; Mahoney, M. J.; Bui, P.
2003-12-01
Gravity waves are known to affect cloud formation via the temperature perturbations they cause, and these effects can be significant in conditions that are otherwise marginal for cloud formation. Cirrus clouds near the tropopause can form in the cold phases of gravity waves. The ER-2 aircraft observations during the CRYSTAL-FACE campaign provide a unique set for gravity wave analysis. For the first time, data from both the Microwave Temperature Profiler (MTP) and Meteorological Measurement System (MMS) were obtained together from the ER-2 platform, with flight paths near convection. Analyses of MTP and MMS data can be combined to provide the full set of gravity wave parameters needed to model their origin, propagation, and eventual fate. This wave analysis requires long, constant-level flight paths. First a wavelet analysis in horizontal wavenumber is performed along the flight path direction for measurements of temperature and horizontal wind. From this, the strongest wave modes are identified, and the vertical wavenumber estimated from the MTP data for these modes. Linear wave theory is then employed to compute the propagation directions and intrinsic frequencies for these strongest wave modes. The results of this analysis thus provide the full three-dimensional propagation characteristics for the dominant gravity wave modes in the data. We subsequently use these results to examine their role in cirrus cloud formation at lower altitudes, and compare the results to in situ measurements made from the WB-57F aircraft platform.
Advances in understanding the gravity wave spectrum during MAP
NASA Technical Reports Server (NTRS)
Vanzandt, T. E.
1989-01-01
Prior to MAP, virtually nothing was known about gravity wave spectra in the atmosphere. The development of observational techniques has played a major role in these studies. Radar and lidar have been particularly important since they can measure atmospheric parameters continuously over large height ranges. Some advances made are: (1) The observed fluctuations and power spectra in the free atmosphere are mostly if not entirely due to a superposition of gravity waves, which can be modeled by the Garrett Munk (GM) model; (2) There is no evidence that 2-D turbulence makes a significant contribution to the observed fluctuations. In any case, the agreement between observations and the GM model shows that the 2DT contribution must be relatively small; (3) Spectra versus vertical wave number are saturated at large wave number, with theory and observations indicating that t approximately equals 3; and (4) Vertical velocity fluctuations and spectra measured near rough terrain are strongly contaminated by mountain waves. But over very flat terrain the spectra are dominated by gravity waves at periods shorter than about 6 hours and apparently by synoptic scale velocities at periods longer than 6 hours. Thus it may be possible to study synoptic scale vertical velocities using radars located in very flat terrain.
A Plant's Response to Gravity as a Wave Guide Phenomenon
NASA Astrophysics Data System (ADS)
Wagner, Orvin
1997-11-01
Plant experimental data provides a unifying wave theory (W-wave theory) for the growth and development of plants. A plant's response to gravity is an important aspect of this theory. It appears that a plant part is tuned to the angle with which it initially grew with respect to the gravitational field and changes produce correction responses. This is true because the velocity of W-waves (whose standing waves determine plant structure) within plant tissue is found to be different in different directions (angle a) with respect to the gravitational field. I found that there are preferred values of a, namely integral multiples of near 5 degrees for some plants. Conifers apparently are more sensitive to the gravitational field than deciduous trees, in the cases studied, so their structure is determined in more detail by the gravitational field. A plant's response to gravity appears to be a fundamental phenomenon and may provide a new model for gravity that can be experimentally verified in the laboratory. Along these same lines accelerometers placed in plant tissue indicate that plants produce gravity related forces that facilitate sap flow. See the
Educing the emission mechanism of internal gravity waves in the differentially heat rotating annulus
NASA Astrophysics Data System (ADS)
Rolland, Joran; Hien, Steffen; Achatz, Ulrich; Borchert, Sebastian; Fruman, Mark
2016-04-01
geostrophic balance. For the first stage of this investigation, we separated the flow between a balance and an imbalanced part at first order in Rossby number: the balanced pressure field was computed through an inversion of the potential vorticity equation [3]. The balanced horizontal velocity field and buoyancy were then computed using the geostrophic and hydrostatic balance conditions. We first checked that this decomposition gave on the one hand a large scaled balanced flow, comprising mostly of the baroclinic wave, and on the other hand a small scale flow comprising mostly of the gravity wave signal. We then proceeded with the central stage of the validation: we simulated the tangent linear dynamics of the imbalanced part of the flow [4]. The equations are linearised about the balanced part, and any imbalances forces the modeled imbalanced part. The output of this simulation compares very well with the actual imbalanced part, thus confirming that the observed gravity waves are indeed generated through spontaneous imbalance. To our knowledge, this is the first demonstration of emission by this mechanism in a flow which is not idealised: a flow which can be obtained as a result of a numerical simulation of primitive equations or actually observed in a laboratory experiment. References [1] R. Plougonven, F. Zhang, Internal gravity waves from atmospheric jets and fronts, Rev. Geophys. 52, 33-76 (2014). [2] S. Borchert, U. Achatz, M.D. Fruman, Spontaneous Gravity wave emission in the differentially heated annulus, J. Fluid Mech. 758, 287-311 (2014). [3] F. Zhang, S.E . Koch, C. A. Davis, M. L. Kaplan, A Survey of unbalanced flow diagnostics and their application, Adv. Atmo. Sci. 17, 165-183 (2000). [4] S. Wang, F. Zhang, Source of gravity waves within a vortex dipole jet revealed by a linear model, J. Atmo. Sci. 67, 1438-1455 (2010).
NASA Technical Reports Server (NTRS)
Koch, Steven E.; Golus, Robert E.
1988-01-01
This paper presents a statistical analysis of the characteristics of the wavelike activity that occurred over the north-central United States on July 11-12, 1981, using data from the Cooperative Convective Precipitation Experiment in Montana. In particular, two distinct wave episodes of about 8-h duration within a longer (33 h) period of wave activity were studied in detail. It is demonstrated that the observed phenomena display features consistent with those of mesoscale gravity waves. The principles of statistical methods used to detect and track mesoscale gravity waves are discussed together with their limitations.
Energy density of relic gravity waves from inflation
Sahni, V. )
1990-07-15
We evaluate both the spectral energy density and the total energy density for relic gravity waves produced during the transition from an early inflationary phase to a matter-dominated Friedmann-Robertson-Walker-type expansion: {ital a}{similar to}{ital t}{sup {ital c}} ({ital c}{lt}1). We find that for power-law inflation the spectral energy density for gravity waves has more power on larger scales than for purely exponential inflation. Evaluating the energy density of created massless particles (both gravitons and massless scalars) we find that in the case of exponential inflation the ratio of the density of created particles to the total density of matter is a constant, if {ital c}{ge}1/2. This unusual behavior is a consequence of the fact that the equation of state for created particles mimics the equation of state for matter driving the expansion of the Universe. As a result, self-consistent solutions of the Einstein equations can be found, in which the expansion of the Universe is sustained solely by the ongoing production of massless particles, so that {ital G}{sub {mu}{nu}}=8{pi}{ital G}{l angle}{ital T}{sub {mu}{nu}}{r angle}. In the case of power-law and quasiexponential inflation we find that the ratio of the energy density of gravity waves to the background matter density increases with time, as gravity waves with longer wavelengths and larger amplitudes enter the horizon at successively later epochs. This could lead to the energy density of gravity waves becoming comparable to the energy density of matter at late times, if inflation commenced at Planckian energies.
Experimental study of spatiotemporally localized surface gravity water waves.
Chabchoub, A; Akhmediev, N; Hoffmann, N P
2012-07-01
We present experimental results on the study of spatiotemporally localized surface wave events on deep water that can be modeled using the Peregrine breather solution of the nonlinear Schrödinger equation. These are often considered as prototypes of oceanic rogue waves that can focus wave energy into a single wave packet. For small steepness values of the carrier gravity waves the Peregrine breathers are relatively wide, thus providing an excellent agreement between the theory and experimental results. For larger steepnesses the focusing leads to temporally and spatially shorter events. Nevertheless, agreement between measurements and the Peregrine breather theory remains reasonably good, with discrepancies of modulation gradients and spatiotemporal symmetries being tolerable. Lifetimes and travel distances of the spatiotemporally localized wave events determined from the experiment are in good agreement with the theory.
NASA Astrophysics Data System (ADS)
Duncan, J. H.; Diorio, J. D.; Lisiewski, A.; Harris, R.
2009-11-01
The wave pattern generated by a small pressure source moving across a water surface at speeds less than the minimum phase speed for linear gravity-capillary waves (cmin = 23 cm/s) was investigated experimentally. The resulting wave pattern was measured using cinematic shadowgraph and laser-induced fluorescence (LIF) techniques. The results show the existence of several distinct behavioral states. At low speeds, no wave behavior is observed and the pattern resembles the symmetric stationary condition. However, at a critical speed, but still below cmin, the pattern undergoes a sudden transition to an asymmetric state with a stationary, 2D solitary wave that forms behind the pressure source. This solitary wave is elongated in the cross-stream relative to the stream-wise direction and resembles gravity-capillary ``lumps'' observed in previous numerical calculations. As the translation speed approaches cmin, another time-dependent behavior is observed characterized by periodic ``shedding'' from a V-shaped solitary wave pattern. This work will be discussed in conjunction with the recent numerical calculations of T. Akylas and his research group.
Mesospheric Non-Migrating Tides Generated With Planetary Waves: II Influence of Gravity Waves
NASA Technical Reports Server (NTRS)
Mayr, H. G.; Mengel, J. G.; Talaat, E. L.; Porter, H. S.; Chan, K. L.
2003-01-01
We demonstrated that, in our model, non-linear interactions between planetary waves (PW) and migrating tides could generate in the upper mesosphere non-migrating tides with amplitudes comparable to those observed. The Numerical Spectral Model (NSM) we employ incorporates Hines Doppler Spread Parameterization for small-scale gravity waves (GW), which affect in numerous ways the dynamics of the mesosphere. The latitudinal (seasonal) reversals in the temperature and zonal circulation, which are largely caused by GWs (Lindzen, 198l), filter the PWs and contribute to the instabilities that generate the PWs. The PWs in turn are amplified by the momentum deposition of upward propagating GWs, as are the migrating tides. The GWs thus affect significantly the migrating tides and PWs, the building blocks of non-migrating tides. In the present paper, we demonstrate that GW filtering also contributes to the non-linear coupling between PWs and tides. Two computer experiments are presented to make this point. In one, we simply turn off the GW source to show the effect. In the second case, we demonstrate the effect by selectively suppressing the momentum source for the m = 0 non-migrating tides.
Nonlinear reflection of internal gravity wave onto a slope
NASA Astrophysics Data System (ADS)
Raja, Keshav; Sommeria, Joel; Staquet, Chantal; Leclair, Matthieu; Grisouard, Nicolas; Gostiaux, Louis
2016-04-01
reflected wave. We study the momentum and energy budget of the process in order to understand the mechanism of generation of mean flow, its interaction with the wave and account for the loss of wave energy upon reflection. REFERENCES N. Grisouard, M. Leclair, L. Gostiaux and C. Staquet 2013. Large scale energy transfer from an internal gravity wave reflecting on a simple slope IUTAM Symposium Procedia 8 119-128 M. Leclair, K. Raja and C. Staquet 2016. Nonlinear reflection of a two-dimensional finite-width internal gravity wave onto a slope Journal of Fluid Mechanics. in preparation
Investigating seasonal gravity wave activity in the summer polar mesosphere
NASA Astrophysics Data System (ADS)
Zhao, Y.; Taylor, M. J.; Randall, C. E.; Lumpe, J. D.; Siskind, D. E.; Bailey, S. M.; Russell, J. M.
2015-05-01
The NASA Aeronomy of Ice in the Mesosphere (AIM) satellite is the first spaceborne mission dedicated to studying high-altitude (~83 km) Polar Mesospheric Clouds (PMCs). Since its launch in 2007, the Cloud Imaging and Particle Size (CIPS) instrument onboard AIM has obtained large-field, high resolution (25 km2/pixel) images of the PMCs, enabling a unique investigation of mesospheric gravity wave activity in the summer polar mesosphere where previous measurements have been sparse. In this study, we have analyzed 12 consecutive seasons of AIM/CIPS PMC albedo data to determine the statistical properties of medium and large horizontal scale (>100 km) gravity waves present in the PMC data. Over 60,000 wave events with horizontal scale-sizes ranging up to >2000 km have been identified and measured, revealing a wealth of wave events particularly in the ~300-800 km range where our analysis sensitivity is largest. These data are ideal for investigating the intra-seasonal, inter-annual and hemispheric variability of these waves as observed over the whole summer polar cap regions. Throughout this 6 year study, the wave activity in the southern hemisphere was found to be consistently 10-15% higher than in the northern hemisphere and both the northern and southern hemisphere wave activity was determined to decrease systematically (by ~15%) during the course of each summer season. This decrease agrees well with previous seasonal stratospheric studies of variations in the wave energy, suggesting a direct influence of the lower atmospheric sources on polar mesospheric dynamics. Very similar and consistent results were also found from season to season in both hemispheres providing new information for gravity wave modeling and dynamical studies of the high-latitude summer-time mesosphere.
NASA Astrophysics Data System (ADS)
Dugan, J. P.; Piotrowski, C. C.; Williams, J. Z.
2001-08-01
Visible images of nearshore ocean waves obtained from an aircraft have been utilized to estimate the surface currents and water depth below the waves. A digital framing camera was mounted in a motion-stabilized turret and used to obtain temporal sequences of high-quality optical images of shoaling ocean waves. Data on the position and attitude of the camera/turret were used to map the image data to a rectilinear coordinate system at the level of the surface, effectively separating the spatial and temporal modulations due to the waves. The resulting three-dimensional (3-D) space-time data sets were Fourier transformed to obtain frequency-wave number spectra of these modulations. These spectra contain information on the propagation characteristics of the waves, such as their wavelengths and frequencies, and their directions and speeds of propagation. The water depth and current vector have been estimated by choosing these parameters so that a "best" fit is obtained between the theoretical dispersion relation for linear gravity waves and these 3-D wave spectra. Image data sets were acquired during the Shoaling Waves Experiment (SHOWEX) along the quasi-linear coastline in the vicinity of the Army Corps of Engineers' Field Research Facility (FRF) near Duck on the North Carolina Outer Banks. Summary wave parameters and bathymetry and current retrievals are typically within 10% of contemporaneous in situ measurements, though outliers occur.
Correlation between opposite-helicity gravitons: Imprints on gravity-wave and microwave backgrounds
NASA Astrophysics Data System (ADS)
Gubitosi, Giulia; Magueijo, João
2017-01-01
We examine some of the roots of parity violation for gravitons and uncover a closely related new effect: correlations between right- and left-handed gravitons. Such correlators have spin 4 if they involve gravitons moving along the same direction and spin zero for gravitons moving with opposite directions. In the first case, the most immediate implication would be a degree of linear polarization for the tensor vacuum fluctuations, which could be seen by gravity-wave detectors sensitive enough to probe the primordial background, its degree of polarization and anisotropies. Looking at the anisotropy of the gravity waves linear polarization, we identify the parity respecting and violating components of the effect. The imprint on the cosmic microwave background temperature and polarization would be more elusive, since it averages to zero in the two-point functions, appearing only in their cosmic variance or in fourth-order correlators. In contrast, spin-zero correlations would have an effect on the two-point function of the cosmic microwave background temperature and polarization, enhancing the B B component if they were anticorrelations. Such correlations represent an amplitude for the production of standing waves, as first envisaged by Grishchuk, and could also leave an interesting signature for gravity-wave detectors.
NASA Technical Reports Server (NTRS)
Choi, Hyun-Joo; Chun, Hye-Yeong; Gong, Jie; Wu, Dong L.
2012-01-01
The realism of ray-based spectral parameterization of convective gravity wave drag, which considers the updated moving speed of the convective source and multiple wave propagation directions, is tested against the Atmospheric Infrared Sounder (AIRS) onboard the Aqua satellite. Offline parameterization calculations are performed using the global reanalysis data for January and July 2005, and gravity wave temperature variances (GWTVs) are calculated at z = 2.5 hPa (unfiltered GWTV). AIRS-filtered GWTV, which is directly compared with AIRS, is calculated by applying the AIRS visibility function to the unfiltered GWTV. A comparison between the parameterization calculations and AIRS observations shows that the spatial distribution of the AIRS-filtered GWTV agrees well with that of the AIRS GWTV. However, the magnitude of the AIRS-filtered GWTV is smaller than that of the AIRS GWTV. When an additional cloud top gravity wave momentum flux spectrum with longer horizontal wavelength components that were obtained from the mesoscale simulations is included in the parameterization, both the magnitude and spatial distribution of the AIRS-filtered GWTVs from the parameterization are in good agreement with those of the AIRS GWTVs. The AIRS GWTV can be reproduced reasonably well by the parameterization not only with multiple wave propagation directions but also with two wave propagation directions of 45 degrees (northeast-southwest) and 135 degrees (northwest-southeast), which are optimally chosen for computational efficiency.
Dust gravitational drift wave in complex plasma under gravity
Salahshoor, M. Niknam, A. R.
2014-12-15
The dispersion relation of electrostatic waves in a complex plasma under gravity is presented. It is assumed that the waves propagate parallel to the external fields. The effects of weak electric field, neutral drag force, and ion drag force are also taken into account. The dispersion relation is numerically examined in an appropriate parameter space in which the gravity plays the dominant role in the dynamics of microparticles. The numerical results show that, in the low pressure complex plasma under gravity, a low frequency drift wave can be developed in the long wavelength limit. The stability state of this wave is switched at a certain critical wavenumber in such a way that the damped mode is transformed into a growing one. Furthermore, the influence of the external fields on the dispersion properties is analyzed. It is shown that the wave instability is essentially due to the electrostatic streaming of plasma particles. It is also found that by increasing the electric field strength, the stability switching occurs at smaller wavenumbers.
High frequency atmospheric gravity wave damping in the mesosphere
NASA Astrophysics Data System (ADS)
Swenson, G. R.; Liu, A. Z.; Li, F.; Tang, J.
2003-09-01
Correlative measurements of temperature and winds by Na lidar and brightness in OH and O 2 Atmospheric band airglow have been made at Albuquerque, NM and Maui, HI for a study of high frequency (period less than 30 minutes) Atmospheric Gravity Waves. Wave studies from four nights have been made and the correlative information describes the intrinsic wave properties with altitude, their damping characteristics, and resulting accelerations to the large scale circulation in the 85-100 km altitude region. Generally, saturated to super-saturated conditions were observed below 95 km. Above this altitude, they were less saturated to freely propagating.
Soundproof simulations of stratospheric gravity waves on unstructured meshes
NASA Astrophysics Data System (ADS)
Smolarkiewicz, P.; Szmelter, J.
2012-04-01
An edge-based unstructured-mesh semi-implicit model is presented that integrates nonhydrostatic soundproof equations, inclusive of anelastic and pseudo-incompressible systems of partial differential equations. The model numerics employ nonoscillatory forward-in-time MPDATA methods [Smolarkiewicz, 2006, Int. J. Numer. Meth. Fl., 50, 1123-1144] using finite-volume spatial discretization and unstructured meshes with arbitrarily shaped cells. Implicit treatment of gravity waves benefits both accuracy and stability of the model. The unstructured-mesh solutions are compared to equivalent structured-grid results for intricate, multiscale internal-wave phenomenon of a non-Boussinesq amplification and breaking of deep stratospheric gravity waves. The departures of the anelastic and pseudo-incompressible results are quantified in reference to a recent asymptotic theory [Achatz et al., 2010, J. Fluid Mech., 663, 120-147].
Propagation and Breaking at High Altitudes of Gravity Waves Excited by Tropospheric Forcing
NASA Technical Reports Server (NTRS)
Prusa, Joseph M.; Smolarkiewicz, Piotr K.; Garcia, Rolando R.
1996-01-01
An anelastic approximation is used with a time-variable coordinate transformation to formulate a two-dimensional numerical model that describes the evolution of gravity waves. The model is solved using a semi-Lagrangian method with monotone (nonoscillatory) interpolation of all advected fields. The time-variable transformation is used to generate disturbances at the lower boundary that approximate the effect of a traveling line of thunderstorms (a squall line) or of flow over a broad topographic obstacle. The vertical propagation and breaking of the gravity wave field (under conditions typical of summer solstice) is illustrated for each of these cases. It is shown that the wave field at high altitudes is dominated by a single horizontal wavelength; which is not always related simply to the horizontal dimension of the source. The morphology of wave breaking depends on the horizontal wavelength; for sufficiently short waves, breaking involves roughly one half of the wavelength. In common with other studies, it is found that the breaking waves undergo "self-acceleration," such that the zonal-mean intrinsic frequency remains approximately constant in spite of large changes in the background wind. It is also shown that many of the features obtained in the calculations can be understood in terms of linear wave theory. In particular, linear theory provides insights into the wavelength of the waves that break at high altitudes, the onset and evolution of breaking. the horizontal extent of the breaking region and its position relative to the forcing, and the minimum and maximum altitudes where breaking occurs. Wave breaking ceases at the altitude where the background dissipation rate (which in our model is a proxy for molecular diffusion) becomes greater than the rate of dissipation due to wave breaking, This altitude, in effect, the model turbopause, is shown to depend on a relatively small number of parameters that characterize the waves and the background state.
The Binary Pulsar: Gravity Waves Exist.
ERIC Educational Resources Information Center
Will, Clifford
1987-01-01
Reviews the history of pulsars generally and the 1974 discovery of the binary pulsar by Joe Taylor and Russell Hulse specifically. Details the data collection and analysis used by Taylor and Hulse. Uses this discussion as support for Albert Einstein's theory of gravitational waves. (CW)
Primordial gravitational waves in bimetric gravity
Sakakihara, Yuki; Soda, Jiro E-mail: jiro@phys.sci.kobe-u.ac.jp
2015-09-01
We study primordial tensor power-spectra generated during inflation in bimetric gravity. More precisely, we examine a homogeneous expanding spacetime in a minimal bimetric model with an inflaton and calculate tensor perturbations on the homogeneous background under slow-roll approximation. In terms of the mass eigenstates, only the power-spectrum of the massless state remains constant and both the power-spectrum of the massive state and the cross power-spectrum rapidly decay during inflation. The amplitude of the physical power-spectrum is suppressed due to the flavor mixing. All power-spectra in the flavor eigenstates coincide with each other up to the first order of the slow-roll parameter.
Upper atmospheric gravity wave details revealed in nightglow satellite imagery
Miller, Steven D.; Straka, William C.; Yue, Jia; Smith, Steven M.; Alexander, M. Joan; Hoffmann, Lars; Setvák, Martin; Partain, Philip T.
2015-01-01
Gravity waves (disturbances to the density structure of the atmosphere whose restoring forces are gravity and buoyancy) comprise the principal form of energy exchange between the lower and upper atmosphere. Wave breaking drives the mean upper atmospheric circulation, determining boundary conditions to stratospheric processes, which in turn influence tropospheric weather and climate patterns on various spatial and temporal scales. Despite their recognized importance, very little is known about upper-level gravity wave characteristics. The knowledge gap is mainly due to lack of global, high-resolution observations from currently available satellite observing systems. Consequently, representations of wave-related processes in global models are crude, highly parameterized, and poorly constrained, limiting the description of various processes influenced by them. Here we highlight, through a series of examples, the unanticipated ability of the Day/Night Band (DNB) on the NOAA/NASA Suomi National Polar-orbiting Partnership environmental satellite to resolve gravity structures near the mesopause via nightglow emissions at unprecedented subkilometric detail. On moonless nights, the Day/Night Band observations provide all-weather viewing of waves as they modulate the nightglow layer located near the mesopause (∼90 km above mean sea level). These waves are launched by a variety of physical mechanisms, ranging from orography to convection, intensifying fronts, and even seismic and volcanic events. Cross-referencing the Day/Night Band imagery with conventional thermal infrared imagery also available helps to discern nightglow structures and in some cases to attribute their sources. The capability stands to advance our basic understanding of a critical yet poorly constrained driver of the atmospheric circulation. PMID:26630004
Upper atmospheric gravity wave details revealed in nightglow satellite imagery.
Miller, Steven D; Straka, William C; Yue, Jia; Smith, Steven M; Alexander, M Joan; Hoffmann, Lars; Setvák, Martin; Partain, Philip T
2015-12-08
Gravity waves (disturbances to the density structure of the atmosphere whose restoring forces are gravity and buoyancy) comprise the principal form of energy exchange between the lower and upper atmosphere. Wave breaking drives the mean upper atmospheric circulation, determining boundary conditions to stratospheric processes, which in turn influence tropospheric weather and climate patterns on various spatial and temporal scales. Despite their recognized importance, very little is known about upper-level gravity wave characteristics. The knowledge gap is mainly due to lack of global, high-resolution observations from currently available satellite observing systems. Consequently, representations of wave-related processes in global models are crude, highly parameterized, and poorly constrained, limiting the description of various processes influenced by them. Here we highlight, through a series of examples, the unanticipated ability of the Day/Night Band (DNB) on the NOAA/NASA Suomi National Polar-orbiting Partnership environmental satellite to resolve gravity structures near the mesopause via nightglow emissions at unprecedented subkilometric detail. On moonless nights, the Day/Night Band observations provide all-weather viewing of waves as they modulate the nightglow layer located near the mesopause (∼ 90 km above mean sea level). These waves are launched by a variety of physical mechanisms, ranging from orography to convection, intensifying fronts, and even seismic and volcanic events. Cross-referencing the Day/Night Band imagery with conventional thermal infrared imagery also available helps to discern nightglow structures and in some cases to attribute their sources. The capability stands to advance our basic understanding of a critical yet poorly constrained driver of the atmospheric circulation.
Linking Atmospheric Gravity Wave Research to the Undergraduate Curriculum
NASA Astrophysics Data System (ADS)
Gay, J.; Nielsen, K.
2015-12-01
Atmospheric gravity waves are often generated in the lower atmosphere and can, under favorable atmospheric conditions, propagate into the mesosphere and lower thermosphere. As a consequence of this vertical propagation, the waves carry momentum fluxes and energy from the lower atmosphere into the near-space environment, providing a strong coupling across atmospheric layers. While these waves have been observed and studied in details for decades, there are still many questions to be addressed regarding the tropospheric source location and nature of individually observed waves in the mesosphere. In an effort to increase undergraduate student research experiences, we are linking atmospheric gravity wave research and undergraduate curriculum to improve both academic and scholarly experiences by our students. In this particular case, we present a research project addressing the identification of tropospheric source locations of mesospheric waves observed by airglow imagers. The project involves observations, theory, and modeling techniques with a strong emphasis on how each part plays a role in the curriculum. Specifically, a simple ray tracing model is propagating observed waves downwards through the atmosphere until the point of origin is reached. In the process, we apply basic calculus, numerical methods, and simple fluid dynamics related to course taught at the undergraduate level.
Detecting gravity waves from binary black holes
NASA Technical Reports Server (NTRS)
Wahlquist, Hugo D.
1989-01-01
One of the most attractive possible sources of strong gravitational waves would be a binary system comprising massive black holes (BH). The gravitational radiation from a binary is an elliptically polarized, periodic wave which could be observed continuously - or at intervals whenever a detector was available. This continuity of the signal is certainly appealing compared to waiting for individual pulses from infrequent random events. It also has the advantage over pulses that continued observation can increase the signal-to-noise ratio almost indefinitely. Furthermore, this system is dynamically simple; the theory of the generation of the radiation is unambiguous; all characteristics of the signal can be precisely related to the dynamical parameters of the source. The current situation is that while there is no observational evidence as yet for the existence of massive binary BH, their formation is theoretically plausible, and within certain coupled constraints of mass and location, their existence cannot be observationally excluded. Detecting gravitational waves from these objects might be the first observational proof of their existence.
Constraining gravity with hadron physics: neutron stars, modified gravity and gravitational waves
NASA Astrophysics Data System (ADS)
Llanes-Estrada, Felipe J.
2017-03-01
The finding of Gravitational Waves (GW) by the aLIGO scientific and VIRGO collaborations opens opportunities to better test and understand strong interactions, both nuclear-hadronic and gravitational. Assuming General Relativity holds, one can constrain hadron physics at a neutron star. But precise knowledge of the Equation of State and transport properties in hadron matter can also be used to constrain the theory of gravity itself. I review a couple of these opportunities in the context of modified f (R) gravity, the maximum mass of neutron stars, and progress in the Equation of State of neutron matter from the chiral effective field theory of QCD.
Planetary-scale inertio gravity waves in the Mesosphere
NASA Astrophysics Data System (ADS)
Mayr, H. G.; Mengel, J. G.; Talaat, E. R.; Porter, H. S.; Chan, K. L.
2003-12-01
In the polar region of the upper mesosphere, horizontal wind oscillations have been observed with periods around 10 hours. Waves with such periods are generated in our Numerical Spectral Model (NSM), and they are identified as planetary-scale inertio gravity waves (IGW). These waves have periods between 9 and 11 hours and appear above 70 km in the zonal mean (m = 0), as well as in m = 1 to 4 propagating eastward and westward. They grow in magnitude to altitudes near 100 km and have vertical wavelengths of about 25 km. The m = 1 westward IGWs have the largest amplitudes, up to 30 m/s at the poles. The IGWs occur intermittently but reveal systematic seasonal variations. Their amplitudes generally are largest in late winter and spring. Numerical experiments show that the waves also appear without tidal excitation. Like the planetary waves in the model, the IGWs are produced by instabilities that arise in the mean zonal circulation.
Airborne sodium lidar measurements of gravity wave intrinsic parameters
NASA Astrophysics Data System (ADS)
Kwon, Kang H.; Gardner, Chester S.
1990-11-01
A data analysis technique for determining gravity wave intrinsic parameters including wave propagation direction is described. The technique involves measuring the altitude variations of the wave-induced density perturbations of the atmospheric Na layer. This technique can be used with airborne lidars, multiple ground-based lidars, and steerable lidars. In this paper the technique is applied to airborne Na lidar data obtained during a round-trip flight from Denver, Colorado, to the Pacific Coast in November 1986. During the flight, strong wave perturbations were observed in the Na layer near the Pacific coast over a horizontal distance of nearly 700 km. The intrinsic horizontal wavelength of this wave was estimated to be about 85 km, and the vertical wavelength was 4.1 km. The intrinsic period was about 102 min, and the propagation direction was almost due south.
Spectra of Baroclinic Inertia-Gravity Wave Turbulence
NASA Technical Reports Server (NTRS)
Glazman, Roman E.
1996-01-01
Baroclinic inertia-gravity (IG) waves form a persistent background of thermocline depth and sea surface height oscillations. They also contribute to the kinetic energy of horizontal motions in the subsurface layer. Measured by the ratio of water particle velocity to wave phase speed, the wave nonlinearity may be rather high. Given a continuous supply of energy from external sources, nonlinear wave-wave interactions among IG waves would result in inertial cascades of energy, momentum, and wave action. Based on a recently developed theory of wave turbulence in scale-dependent systems, these cascades are investigated and IG wave spectra are derived for an arbitrary degree of wave nonlinearity. Comparisons with satellite-altimetry-based spectra of surface height variations and with energy spectra of horizontal velocity fluctuations show good agreement. The well-known spectral peak at the inertial frequency is thus explained as a result of the inverse cascade. Finally, we discuss a possibility of inferring the internal Rossby radius of deformation and other dynamical properties of the upper thermocline from the spectra of SSH (sea surface height) variations based on altimeter measurements.
Propagation of Love waves in a void medium over a sandy half space under gravity
NASA Astrophysics Data System (ADS)
Patra, Pulak; Gupta, Asit Kumar; Kundu, Santimoy
2017-03-01
The present study investigates the propagation of Love wave in a void layer resting over a sandy half space under the effect of gravitational force. The equations of motion have been gathered separately for different layers, and the boundary conditions have been introduced for two different layers at their interface. The mathematical analysis of the problem has been dealt with the help of Whittaker's function by expanding it asymptotically up to linear terms. The study reveals that in such a situation there exist two different wave fronts for the two above-mentioned layers: one is for the effects of gravity and sandy parameters, whereas other is for the effect of void parameter.
Gravity Waves in the Atmospheres of Mars and Venus
NASA Astrophysics Data System (ADS)
Tellmann, Silvia; Paetzold, Martin; Häusler, Bernd; Bird, Michael K.; Tyler, G. Leonard; Hinson, David P.; Imamura, Takeshi
2016-10-01
Gravity waves are ubiquitous in all stably stratified planetary atmospheres and play a major role in the redistribution of energy and momentum. Gravity waves can be excited by many different mechanisms, e.g. by airflow over orographic obstacles or by convection in an adjacent layer.Gravity waves on Mars were observed in the lower atmosphere [1,2] but are also expected to play a major role in the cooling of the thermosphere [3] and the polar warming [4]. They might be excited by convection in the daytime boundary layer or by strong winter jets in combination with the pronounced topographic diversity on Mars.On Venus, gravity waves play an important role in the mesosphere above the cloud layer [5] and probably below. Convection in the cloud layer is one of the most important source mechanisms but certain correlations with topography were observed by different experiments [6,7,8].Temperature height profiles from the radio science experiments on Mars Express (MaRS) [9] and Venus Express (VeRa) [10] have the exceptionally high vertical resolution necessary to study small-scale vertical gravity waves, their global distribution, and possible source mechanisms.Atmospheric instabilities, which are clearly identified in the data, can be investigated to gain further insight into possible atmospheric processes contributing to the excitation of gravity waves.[1] Creasey, J. E., et al.,(2006), Geophys. Res. Lett., 33, L01803, doi:10.1029/2005GL024037.[2]Tellmann, S., et al.(2013), J. Geophys. Res. Planets, 118, 306-320, doi:10.1002/jgre.20058.[3]Medvedev, A. S., et al.(2015), J. Geophys. Res. Planets, 120, 913-927. doi:10.1002/2015JE004802.[4] Barnes, J. R. (1990), J. Geophys. Res., 95, B2, 1401-1421.[5] Tellmann, S., et al. (2012), Icarus, 221, 471 - 480.[6] Blamont, J.E. et al., (1986) 231, 1422-1425.[7] Bertaux J.-L., et al. (2016), J. Geophys. Res., Planets, in press.[8] Piccialli, A., et al. (2014), Icarus, 227, 94 - 111.[9] Pätzold, M., et al. (2016), Planet. Space Sci
Tropical stratospheric gravity wave activity and relationships to clouds
NASA Astrophysics Data System (ADS)
Alexander, M. Joan; Beres, Jadwiga H.; Pfister, Leonhard
2000-09-01
Wind measurements from NASA's ER-2 aircraft in the stratosphere are used to obtain information on the momentum flux carried by gravity waves with horizontal wavelengths between 5 and 150 km. Tropical data are compared with the cloud brightness temperature below the aircraft as an indicator of deep convective activity. A striking correlation between cold, high clouds and large gravity wave momentum flux is seen in data from the Stratosphere-Troposphere Exchange Project (STEP) tropical campaign during the monsoon season over northern Australia and Indonesia. There is an enhancement in the flux carried by waves propagating against the background wind in these observations. The same analysis was performed with data from more recent ER-2 flights over the tropical Pacific Ocean during the Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/MAESA), Stratospheric Tracers of Atmospheric Transport (STRAT), and Photochemistry of Ozone Loss in the Arctic Region in Summer (POLARIS) campaigns which took place in 1994, 1995-1996, and 1997, respectively. These data also show a correlation between gravity wave momentum flux and deep convective clouds, but the relationship is much weaker, and the magnitudes of the momentum flux over the deepest clouds are about 7 times smaller than those seen in the STEP data. The reasons for these differences remain uncertain, but possibilities include both real geophysical differences and differences associated with the flight paths during the 1987 versus later campaigns.
Gravity Related Standing Waves in Plants
NASA Astrophysics Data System (ADS)
Wagner, Claudia
2005-04-01
Leaf and branch spacing are termed internodal spacings (1/2 wavelengths here) in the literature. There is apparently a unique set of available 1/2λ' s with the choice determined by growing conditions. The ratio of the usually larger vertical velocity to the horizontal wave velocity is apparently determined by the genotype and shapes the plant. The ratio for a particular plant can often be found by measuring several hundred vertical and horizontal spacings and taking reciprocals. Then find the horizontal reciprocal average Ah and do the same for the vertical to get Av Then equating frequencies vvAv=vhAh (also equals similar terms for other 5^o integral^ multiples) gives vv/vh=Ah/Av. Standard deviations for Av and Ah are in the range of 15-50%. The ratios, however, are nearly exactly (usually within 1%) ratios of small integers like 3/1 for Ponderosa pine.In species, where higher frequencies dominate, one can often measure cell lengths as half wavelengths and similarly arrive at the velocity ratio. Velocities are found by disturbing the standing waves and plotting the resultant electrical signal from spaced probes as a function of time. See chatlink.com/˜oedphd
Transition from geostrophic turbulence to inertia–gravity waves in the atmospheric energy spectrum
Callies, Jörn; Ferrari, Raffaele; Bühler, Oliver
2014-01-01
Midlatitude fluctuations of the atmospheric winds on scales of thousands of kilometers, the most energetic of such fluctuations, are strongly constrained by the Earth’s rotation and the atmosphere’s stratification. As a result of these constraints, the flow is quasi-2D and energy is trapped at large scales—nonlinear turbulent interactions transfer energy to larger scales, but not to smaller scales. Aircraft observations of wind and temperature near the tropopause indicate that fluctuations at horizontal scales smaller than about 500 km are more energetic than expected from these quasi-2D dynamics. We present an analysis of the observations that indicates that these smaller-scale motions are due to approximately linear inertia–gravity waves, contrary to recent claims that these scales are strongly turbulent. Specifically, the aircraft velocity and temperature measurements are separated into two components: one due to the quasi-2D dynamics and one due to linear inertia–gravity waves. Quasi-2D dynamics dominate at scales larger than 500 km; inertia–gravity waves dominate at scales smaller than 500 km. PMID:25404349
Evolution of cosmological gravitational waves in f(R) gravity
Ananda, K. N.; Carloni, S.; Dunsby, P. K. S.
2008-01-15
We give a rigorous and mathematically clear presentation of the covariant and gauge-invariant theory of gravitational waves in a perturbed Friedmann-Lemaitre-Robertson-Walker universe for fourth order gravity, where the matter is described by a perfect fluid with a barotropic equation of state. As an example of a consistent analysis of tensor perturbations in fourth order gravity, we apply the formalism to a simple background solution of R{sup n} gravity. We obtain the exact solutions of the perturbation equations for scales much bigger than and smaller than the Hubble radius. It is shown that the evolution of tensor modes is highly sensitive to the choice of n and an interesting new feature arises. During the radiation dominated era, their exists a growing tensor perturbation for nearly all choices of n. This occurs even when the background model is undergoing accelerated expansion as opposed to the case of general relativity. Consequently, cosmological gravitational wave modes can in principle provide a strong constraint on the theory of gravity independent of other cosmological data sets.
Gravity wave momentum flux in the lower stratosphere over convection
NASA Technical Reports Server (NTRS)
Alexander, M. Joan; Pfister, Leonhard
1995-01-01
This work describes a method for estimating vertical fluxes of horizontal momentum carried by short horizontal scale gravity waves (lambda(sub x) = 10-100 km) using aircraft measured winds in the lower stratosphere. We utilize in situ wind vector and pressure altitude measurements provided by the Meteorological Measurement System (MMS) on board the ER-2 aircraft to compute the momentum flux vectors at the flight level above deep convection during the tropical experiment of the Stratosphere Troposphere Exchange Project (STEP-Tropical). Data from Flight 9 are presented here for illustration. The vertical flux of horizontal momentum these observations points in opposite directions on either side of the location of a strong convective updraft in the cloud shield. This property of internal gravity waves propagating from a central source compares favorably with previously described model results.
Gravity-wave induced CO2 clouds on Mars
NASA Astrophysics Data System (ADS)
Yiǧit, Erdal; Medvedev, Alexander S.; Hartogh, Paul
2016-07-01
We present the first general circulation model simulations that quantify and reproduce patches of extremely cold air required for CO2 condensation and cloud formation in the Martian mesosphere. They are created by subgrid-scale gravity waves (GWs) accounted for in the model with the whole atmosphere GW parameterization of Yiǧit et al. (2008)}. Distributions of GW-induced temperature fluctuations and occurrences of supersaturation conditions are in a good agreement with observations of high-altitude CO2 ice clouds. Our study confirms the key role of GWs in facilitating CO2 cloud formation, discusses their tidal modulation, and predicts clouds at altitudes higher than have been observed to date. Reference: Yiǧit, E., A. D. Aylward, and A. S. Medvedev (2008), Parameterization of the effects of vertically propagating gravity waves for thermosphere general circulation models: Sensitivity study, J. Geophys. Res., 113, D19106, doi:10.1029/2008JD010135.
Interactions between small and medium scale gravity waves in the mesosphere and lower thermosphere
NASA Astrophysics Data System (ADS)
Heale, Christopher; Snively, Jonathan
2016-07-01
Gravity waves play a prominent role in the momentum and energy budget of the Earth's upper atmosphere [e.g. Fritts and Alexander ,Rev. Geophys., 41, 1003, 2003]. Small scale waves with large vertical wavelengths are able to propagate into the thermosphere where they will dissipate and deposit their energy and momentum [e.g. Vadas and Fritts, J. Geoph. Res.,110, D15103, 2005; Yiǧit et al., J. Geophys. Res.-Atmospheres, 114, D07101, 14, 2009; Liu et al., Ann. Geophys., 31, 2013; Heale et al., J. Geophys. Res. Space Physics, 119, 2014]. However, small scale waves are also prone to refraction, reflection, filtering, and instabilities by the temperature and wind structure of the atmosphere. One of the primary sources of variability on scales relevant to these small-scale waves is other, larger scale waves. The use of multiple instruments and Airglow keograms has begun to uncover the richness of the spectrum in the atmosphere, but interaction and relatively poorly understood [e.g. Fritts et al., J. Geophys. Res. Atmos., 119, 2014; Bossert et al., J. Geophys. Res. Atmos., 120, 2015; Lu et al., J. Geophys. Res. Atmos., 120, 2015; Yuan et al., J. Geophys. Res. Atmos., 121, 2016]. We use a 2D nonlinear, compressible numerical model to investigate the character of interactions between small-scale and medium-scale gravity waves at varied amplitudes as they approach nonlinearity. We investigate the relative importance of linear and nonlinear interaction processes and their effects on the propagation of multiple wave packets, and the possibility of energy exchanges and the threshold of onset for instability or breaking within the waves. Furthermore, we assess the validity of linear interpretations of observational data where coherent large-amplitude waves are detected at multiple, separated scales.
Tropopause to Mesopause Gravity Waves in August: Measurement and Modeling
2006-01-01
Journal of Atmospheric and Solar - Terrestrial Physics 68 (2006) 1730–1751 Tropopause to mesopause gravity waves in August: Measurement and modeling...descending orbit nodes were treated separately to avoid mixing of different ARTICLE IN PRESS P. Preusse et al. / Journal of Atmospheric and Solar - Terrestrial Physics 68...ranges from 2 to 14 dB at 25 km altitude and increases to 8–24 dB at 60 km altitude. P. Preusse et al. /
Analysis of Gravity Waves Structures Visible in Noctilucent Cloud Images
2010-01-01
author. Tel.: +1 4357978128. E-mail address: dominiquepautet@gmail.com Keywords: Noctilucent clouds ( NLC ); Mesosphere lower thermosphere (MLT...clouds ( NLC ) are high-altitude bright cloud formations visible under certain conditions from high-latitude places during the summer months. Even if the...visible in the NLC images taken every summer night since 2004 from Stockholm, Sweden (59.4ºN). The parameters of 30 short-period gravity wave events
Interseasonal Variations in the Middle Atmosphere Forced by Gravity Waves
NASA Technical Reports Server (NTRS)
Mayr, H. G.; Mengel, J. G.; Drob, D. P.; Porter, H. S.; Chan, K. L.; Bhartia, P. K. (Technical Monitor)
2002-01-01
In our Numerical Spectral Model (NSM), which incorporates Hines' Doppler Spread Parameterization, gravity waves (GW) propagating in the east/west direction can generate the essential features of the observed equatorial oscillations in the zonal circulation and in particular the QBO (quasi-biennial oscillation) extending from the stratosphere into the upper mesosphere. We report here that the NSM also produces inter-seasonal variations in the zonally symmetric (m = 0) meridional circulation. A distinct but variable meridional wind oscillation (MWO) is generated, which appears to be the counterpart to the QBO. With a vertical grid-point resolution of about 0.5 km, the NSM produces the MWO through momentum deposition of GWs propagating in the north/south direction. The resulting momentum source represents a third (generally odd) order non-linear function of the meridional winds, and this enables the oscillation, as in the case of the QBO for the zonal winds. Since the meridional winds are relatively small compared to the zonal winds, however, the vertical wavelength that maintains the MWO is much smaller, i.e., only about 10 km instead of 40 km for the QBO. Consistent with the associated increase of the viscous stress, the period of the MWO is then short compared with that of the QBO, i.e., only about two to four months. Depending on the strength of the GW forcing, the computed amplitudes of the MWO are typically 4 m/s in the upper stratosphere and mesosphere, and the associated temperature amplitudes are between about 2 and 3 K. These amplitudes may be observable with the instruments on the TIMED spacecraft. Extended computer simulations with the NSM in 2D (two-dimensional) and 3D (three-dimensional) reveal that the MWO is modulated by and in turn influences the QBO.
Interseasonal Variations in the Middle Atmosphere Forced by Gravity Waves
NASA Technical Reports Server (NTRS)
Mayr, H. G.; Mengel, J. G.; Drob, D. P.; Porter, H. S.; Bhartia, P. K. (Technical Monitor)
2002-01-01
In our Numerical Spectral Model (NSM), which incorporates Hines' Doppler Spread Parameterization, gravity waves (GW) propagating in the east/west direction can generate the essential features of the observed equatorial oscillations of the zonal circulation and in particular the QBO (quasi-biennial oscillation) extending from the stratosphere into the upper mesosphere. We report here that the NSM also produces inter-seasonal variations in the zonally symmetric meridional circulation. A distinct meridional oscillation (MO) is generated, which appears to be the counterpart to the QBO. With a vertical grid-point resolution of about 0.5 km, the NSM produces the MO through momentum deposition of GW's propagating in the north/south direction. This process is inherently non-linear, of third (odd) order, which enables the oscillation. Since the meridional winds are relatively small compared to the zonal winds, the vertical wavelength required to maintain the MO is also smaller, i.e., only about 10 km instead of the 30 km for the QBO. The corresponding viscous stress is then larger, and the period of the MO is thus short compared with that of the QBO, i.e., only about 3 to 4 months. Depending on the strength of the GW forcing, the computed amplitudes of the meridional wind oscillation are typically 5 m/s in the upper stratosphere and mesosphere, and the associated temperature amplitudes are between about 2 and 3 K. These amplitudes may be observable with the instruments on the TIMED spacecraft. Extended computer simulations with the NSM in 2D and 3D reveal that the MO at low latitudes is modulated by the QBO and in turn can influence it to produce a hemispherically asymmetric component. The annual circulation from the summer to the winter hemisphere is likely to play an important role.
Selection rules for the nonlinear interaction of internal gravity waves.
Jiang, Chung-Hsiang; Marcus, Philip S
2009-03-27
Two intersecting beams of internal gravity waves will generically create two wave packets by nonlinear interaction. The frequency of one packet will be the sum and that of the other packet will be the difference of the frequencies of the intersecting beams. In principle, each packet should form an "X" pattern, or "St. Andrew's cross" consisting of four beams outgoing from the point of intersection. Here we derive selection rules and show that most of the expected nonlinear beams are forbidden. These rules can also be applied to the reflection of a beam from a boundary.
Generation of vortices by gravity waves on a water surface
NASA Astrophysics Data System (ADS)
Filatov, S. V.; Aliev, S. A.; Levchenko, A. A.; Khramov, D. A.
2016-11-01
The generation of a vortex motion on a water surface by gravity waves at frequencies of 3 and 4 Hz and wavelengths of 17 and 9.7 cm, respectively, has been studied experimentally. It has been shown that the results can be described by a model of the formation of a vorticity by nonlinear waves. It has been shown for the first time that the vorticity amplitude on a water surface depends on the phase difference between the waves propagating at an angle of 90° with respect to each other and with a period of 360°. A quadratic dependence of the surface vorticity amplitude on the angular amplitude of the waves has been observed. Transfer of the energy of the vortex motion from the pumping region to a larger scale has been discovered.
Characteristics of acoustic gravity waves obtained from Dynasonde data
NASA Astrophysics Data System (ADS)
Negrea, Cǎtǎlin; Zabotin, Nikolay; Bullett, Terrence; Fuller-Rowell, Tim; Fang, Tzu-Wei; Codrescu, Mihail
2016-04-01
Traveling ionospheric disturbances (TIDs) are ubiquitous in the thermosphere-ionosphere and are often assumed to be caused by acoustic gravity waves (AGWs). This study performs an analysis of the TID and AGW activity above Wallops Island, VA, during October 2013. The variations in electron density and ionospheric tilts obtained with the Dynasonde technique are used as primary indicators of wave activity. The temporal and spectral characteristics of the data are discussed in detail, using also results of the Whole Atmosphere Model (WAM) and the Global Ionosphere Plasmasphere Model (GIP). The full set of propagation parameters (frequency, and the vertical, zonal and meridional wave vector components) of the TIDs is determined over the 160-220 km height range. A test of the self-consistency of these results within the confines of the theoretical AGW dispersion relation is devised. This is applied to a sample data set of 24 October 2013. A remarkable agreement has been achieved for wave periods between 52 and 21 min, for which we can rigorously claim the TIDs are caused by underlying acoustic gravity waves. The Wallops Island Dynasonde can operate for extended periods at a 2 min cadence, allowing determination of the statistical distributions of propagation parameters. A dominant population of TIDs is identified in the frequency band below 1 mHz, and for it, the distributions of the horizontal wavelengths, vertical wavelengths, and horizontal phase speeds are obtained.
Brunt-Doppler ducting of small-period gravity waves
Wang, D.Y.; Tuan, T.F. )
1988-09-01
The variation of the Brunt period with height lends itself to a natural ducting and filtering mechanism for low-altitude short-period gravity waves. The authors investigate this mechanism in combination with Doppler ducting produced by the variation in horizontal winds. Both the frequency dispersion at fixed propagation direction and the direction dispersion at fixed frequency have been examined in a COSPAR background atmosphere with zonal and meridional winds. The results show that not only are the low-altitude short-period gravity waves ducted, but unlike the usual ducting mechanisms due to uneven structure and dissipation which produce only partially guided modes, this mechanism produces primarily guided modes in the absence of winds and a mixture of fully and partially guided modes with winds. The wind effects are very large on the higher modes and less significant on the few lowest modes, including the Lamb mode. Investigation of viscous dissipation, nonlinearity, and instability have shown that viscosity is unimportant for most altitudes of interest and that nonlinearity and instability can play a role for all but the lowest guided modes. They propose that simultaneous continuous observation of airglow at mesospheric and ionospheric altitudes be made to verify not only the low-altitude Brunt-Doppler ducting for short-period gravity waves, but also the vertical energy distribution of the medium- and large-scale TIDs.
NASA Technical Reports Server (NTRS)
Mayr, H. G.; Mengel, J. G.; Chan, K. L.; Trob, D.; Porter, H. C.; Einaudi, Franco (Technical Monitor)
2000-01-01
Special Session: SA03 The mesosphere/lower thermosphere region: Structure, dynamics, composition, and emission. Ground based and satellite observations in the upper mesosphere and lower thermosphere (MLT) reveal large seasonal variations in the horizontal wind fields of the diurnal and semidiurnal tides. To provide an understanding of the observations, we discuss results obtained with our Numerical Spectral Model (NMS) that incorporates the gravity wave Doppler Spread Parameterization (DSP) of Hines. Our model reproduces many of the salient features observed, and we discuss numerical experiments that delineate the important processes involved. Gravity wave momentum deposition and the seasonal variations in the tidal excitation contribute primarily to produce the large equinoctial amplitude maxima in the diurnal tide. Gravity wave induced variations in eddy viscosity, not accounted for in the model, have been shown by Akmaev to be important too. For the semidiurnal tide, with amplitude maximum observed during winter solstice, these processes also contribute, but filtering by the mean zonal circulation is more important. A deficiency of our model is that it cannot reproduce the observed seasonal variations in the phase of the semidiurnal tide, and numerical experiments are being carried out to diagnose the cause and to alleviate this problem. The dynamical components of the upper mesosphere are tightly coupled through non-linear processes and wave filtering, and this may constrain the model and require it to reproduce in detail the observed phenomenology.
Long-Term Global Morphology of Gravity Wave Activity Using UARS Data
NASA Technical Reports Server (NTRS)
Eckermann, Stephen D.; Bacmeister, Julio T.; Wu, Dong L.
1998-01-01
This is the first quarter's report on research to extract global gravity-wave data from satellite data and to model those observations synoptically. Preliminary analysis of global maps of extracted middle atmospheric temperature variance from the CRISTA instrument is presented, which appear to contain gravity-wave information. Corresponding simulations of global gravity-wave and mountain-wave activity during this mission period are described using global ray-tracing and mountain-wave models, and interesting similarities among simulated data and CRISTA data are noted. Climatological simulations of mesospheric gravity-wave activity using the HWM-03 wind-temperature climatology are also reported, for comparison with UARS MLS data. Preparatory work on modeling of gravity wave observations from space-based platforms and subsequent interpretation of the MLS gravity-wave product are also described. Preliminary interpretation and relation to the research objectives are provided, and further action for the next quarter's research is recommended.
Linear and Nonlinear Electrostatic Waves in Unmagnetized Dusty Plasmas
Mamun, A. A.; Shukla, P. K.
2010-12-14
A rigorous and systematic theoretical study has been made of linear and nonlinear electrostatic waves propagating in unmagnetized dusty plasmas. The basic features of linear and nonlinear electrostatic waves (particularly, dust-ion-acoustic and dust-acoustic waves) for different space and laboratory dusty plasma conditions are described. The experimental observations of such linear and nonlinear features of dust-ion-acoustic and dust-acoustic waves are briefly discussed.
NASA Astrophysics Data System (ADS)
Kriske, Richard
2010-10-01
The author has previously proposed that perhaps there needs to be a look at the CMBR as being a measure of curvature. It seems that a valid theory of curved space in a four dimensional space time would allow the Red Shift to occur due to the changing orientation of the time dimension that would slowly point more and more away from any observer at any point until like the Earth's horizon in two curved space dimensions to point away from the observer and give the sharp cut off of the Horizon. A three curved space dimensional cut off would result in the appearace of increasing velocity as the distance from the observer increases and this without the Big-Bang theory. What would one observe for Gravitational waves on this surface? The three space dimensions would wiggle and the time dimension (which is not curved) would move to stay perpendicular to this motion, giving odd accelerations and I predict a different Microwave signal. Perhaps a nonuniformity in the Back Ground radiation that would shift over time.
Understanding airglow signatures of short-period gravity waves
NASA Astrophysics Data System (ADS)
Snively, Jonathan; Taylor, Michael J.; Pendleton, William R., Jr.; Pautet, Pierre-Dominique
Airglow imaging is a primary tool in the study of gravity waves at mesospheric and lower-thermospheric (MLT) altitudes, clearly revealing signatures of small-scale (<100 km) and short-period (<30 min) waves. Short-period waves are in particular able to carry significant momentum into the MLT [e.g., Fritts and Alexander, 2003, Rev. Geophys., 41(1)]. However, quantification of short-period wave fluxes and propagation characteristics is complicated by their susceptibility to refraction by ambient wind and thermal structure at airglow altitudes. These effects lead to vertical wavelengths that vary dramatically with altitude throughout the airglow layers, and reflection and ducting, which can prevent the accurate assessment of ampli-tude and vertical direction of propagation [e.g., Fritts, 2000, JGR, 105(D17), 22,355-22,360]. To investigate airglow signatures of short-period gravity waves, we utilize a two-dimensional nonlinear dynamics model coupled with OH Meinel band and OI 557.7 nm airglow photochem-istry models. Case studies where the ambient atmospheric structure significantly influences wave propagation are presented, for both ducted and reflected waves, and also for waves ap-proaching critical levels. Arising from Doppler shifts to higher and lower intrinsic frequencies, respectively, these effects contribute to significant variation of vertical wavelength throughout the airglow region, and may limit the altitude of propagation. Cancellation effects of vertically-integrated airglow volume emission rate perturbations are discussed, along with observable nonlinear features due to large amplitude [e.g., Huang et al., 2003, JGR, 108(A5), 1173], and effects of partial perturbations to airglow layers by vertically-confined waves [e.g., Snively et al., JGR, In Review, 2010]. In particular, it is demonstrated that high temporal and spatial resolution measurements of airglow intensity and brightness-weighted temperature, combined with detailed descriptions of ambient
Gravity-capillary waves in finite depth on flows of constant vorticity
NASA Astrophysics Data System (ADS)
Hsu, Hung-Chu; Francius, Marc; Montalvo, Pablo; Kharif, Christian
2016-11-01
This paper considers two-dimensional periodic gravity-capillary waves propagating steadily in finite depth on a linear shear current (constant vorticity). A perturbation series solution for steady periodic waves, accurate up to the third order, is derived using a classical Stokes expansion procedure, which allows us to include surface tension effects in the analysis of wave-current interactions in the presence of constant vorticity. The analytical results are then compared with numerical computations with the full equations. The main results are (i) the phase velocity is strongly dependent on the value of the vorticity; (ii) the singularities (Wilton singularities) in the Stokes expansion in powers of wave amplitude that correspond to a Bond number of 1/2 and 1/3, which are the consequences of the non-uniformity in the ordering of the Fourier coefficients, are found to be influenced by vorticity; (iii) different surface profiles of capillary-gravity waves are computed and the effect of vorticity on those profiles is shown to be important, in particular that the solutions exhibit type-2-like wave features, characterized by a secondary maximum on the surface profile with a trough between the two maxima.
Gravity-capillary waves in finite depth on flows of constant vorticity.
Hsu, Hung-Chu; Francius, Marc; Montalvo, Pablo; Kharif, Christian
2016-11-01
This paper considers two-dimensional periodic gravity-capillary waves propagating steadily in finite depth on a linear shear current (constant vorticity). A perturbation series solution for steady periodic waves, accurate up to the third order, is derived using a classical Stokes expansion procedure, which allows us to include surface tension effects in the analysis of wave-current interactions in the presence of constant vorticity. The analytical results are then compared with numerical computations with the full equations. The main results are (i) the phase velocity is strongly dependent on the value of the vorticity; (ii) the singularities (Wilton singularities) in the Stokes expansion in powers of wave amplitude that correspond to a Bond number of 1/2 and 1/3, which are the consequences of the non-uniformity in the ordering of the Fourier coefficients, are found to be influenced by vorticity; (iii) different surface profiles of capillary-gravity waves are computed and the effect of vorticity on those profiles is shown to be important, in particular that the solutions exhibit type-2-like wave features, characterized by a secondary maximum on the surface profile with a trough between the two maxima.
Impact of mountain gravity waves on infrasound propagation
NASA Astrophysics Data System (ADS)
Damiens, Florentin; Lott, François; Millet, Christophe
2016-04-01
Linear theory of acoustic propagation is used to analyze how mountain waves can change the characteristics of infrasound signals. The mountain wave model is based on the integration of the linear inviscid Taylor-Goldstein equation forced by a nonlinear surface boundary condition. For the acoustic propagation we solve the wave equation using the normal mode method together with the effective sound speed approximation. For large-amplitude mountain waves we use direct numerical simulations to compute the interactions between the mountain waves and the infrasound component. It is shown that the mountain waves perturb the low level waveguide, which leads to significant acoustic dispersion. The mountain waves also impact the arrival time and spread of the signals substantially and can produce a strong absorption of the wave signal. To interpret our results we follow each acoustic mode separately and show which mode is impacted and how. We also show that the phase shift between the acoustic modes over the horizontal length of the mountain wave field may yield to destructive interferences in the lee side of the mountain, resulting in a new form of infrasound absorption. The statistical relevance of those results is tested using a stochastic version of the mountain wave model and large enough sample sizes.
Gravity jitter effected slosh waves and the stability of a rotating bubble under microgravity
NASA Technical Reports Server (NTRS)
Hung, R. J.; Lee, C. C.; Leslie, F. W.
1991-01-01
The instability of liquid and gas interface can be induced by the pressure of longitudinal and lateral accelerations, vehicle vibration, and rotational fields of spacecraft in a microgravity environment. Characteristics of slosh waves excited by the restoring force field of gravity jitters have been investigated. Results show that lower frequency gravity jitters excite slosh wave with higher ratio of maximum amplitude to wave length than that of the slosh waves generated by the higher frequency gravity jitters.
Merkel, A; Tournat, V; Gusev, V
2014-08-01
We report the experimental observation of the gravity-induced asymmetry for the nonlinear transformation of acoustic waves in a noncohesive granular phononic crystal. Because of the gravity, the contact precompression increases with depth inducing space variations of not only the linear and nonlinear elastic moduli but also of the acoustic wave dissipation. We show experimentally and explain theoretically that, in contrast to symmetric propagation of linear waves, the amplitude of the nonlinearly self-demodulated wave depends on whether the propagation of the waves is in the direction of the gravity or in the opposite direction. Among the observed nonlinear processes, we report frequency mixing of the two transverse-rotational modes belonging to the optical band of vibrations and propagating with negative phase velocities, which results in the excitation of a longitudinal wave belonging to the acoustic band of vibrations and propagating with positive phase velocity. We show that the measurements of the gravity-induced asymmetry in the nonlinear acoustic phenomena can be used to compare the in-depth distributions of the contact nonlinearity and of acoustic absorption.
NASA Astrophysics Data System (ADS)
Merkel, A.; Tournat, V.; Gusev, V.
2014-08-01
We report the experimental observation of the gravity-induced asymmetry for the nonlinear transformation of acoustic waves in a noncohesive granular phononic crystal. Because of the gravity, the contact precompression increases with depth inducing space variations of not only the linear and nonlinear elastic moduli but also of the acoustic wave dissipation. We show experimentally and explain theoretically that, in contrast to symmetric propagation of linear waves, the amplitude of the nonlinearly self-demodulated wave depends on whether the propagation of the waves is in the direction of the gravity or in the opposite direction. Among the observed nonlinear processes, we report frequency mixing of the two transverse-rotational modes belonging to the optical band of vibrations and propagating with negative phase velocities, which results in the excitation of a longitudinal wave belonging to the acoustic band of vibrations and propagating with positive phase velocity. We show that the measurements of the gravity-induced asymmetry in the nonlinear acoustic phenomena can be used to compare the in-depth distributions of the contact nonlinearity and of acoustic absorption.
Characteristics of mesospheric gravity waves measured by an OH airglow imager at Qujing, China
NASA Astrophysics Data System (ADS)
Li, Qinzeng; Chen, Jinsong; Yuan, Wei; Yue, Jia; Liu, Xiao; Xu, Jiyao; Liu, Mohan
An all-sky imager was installed at Qujing (25.6ºN, 103.7ºE) to investigate the characteristics of mesospheric gravity waves over the Yunnan-Guizhou Plateau. Using OH airglow images from November 2011 to October 2013, we detected 332 events of gravity waves. Along with the collocated meteor radar wind measurements and mean temperature data from SABER instrument onboard the TIMED satellite, the propagation condition (freely propagating, ducted, or evanescent) of these gravity waves was estimated. Most gravity waves exhibited ducted and evanescent behavior. About 20% of the events are freely propagating waves. We analyzed the sources in the lower atmosphere for these freely propagating gravity waves using ray tracing analysis. Statistical analysis shows a clear relation between mesospheric gravity wave activity and jet streams around Yunnan-Guizhou-Tibet Plateau. We also investigate the statistical features of all observed gravity waves. The propagation directions of the gravity waves show a strong northeastward preference in summer, while almost all gravity waves propagate southeastward in winter. The gravity waves propagation directions in winter are significantly different from other observations at northern middle latitudes, such as Xinglong(40.2ºN,117.4ºE), Shigaraki(34.9ºN,136.1 ºE), Urbana IL(40ºN, 80ºW). They all found the gravity waves presented southwestward propagation directions in winter. The horizontal wavelengths of observed gravity waves are typically from 10 to 35 km, the vertical wavelengths from 10 to 30 km, the observed periods from 4 to 8 min and the observed horizontal phase speeds of 30 to 90 m/s. The intrinsic periods are mainly in the range of 4-8 min. The intrinsic phase speeds are mainly in the range of 40-100 m/s. The wind filtering in the middle atmosphere plays a role in controlling the propagation directions of the gravity waves.
Gravitational-wave probe of effective quantum gravity
Alexander, Stephon; Finn, Lee Samuel; Yunes, Nicolas
2008-09-15
All modern routes leading to a quantum theory of gravity - i.e., perturbative quantum gravitational one-loop exact correction to the global chiral current in the standard model, string theory, and loop quantum gravity - require modification of the classical Einstein-Hilbert action for the spacetime metric by the addition of a parity-violating Chern-Simons term. The introduction of such a term leads to spacetimes that manifest an amplitude birefringence in the propagation of gravitational waves. While the degree of birefringence may be intrinsically small, its effects on a gravitational wave accumulate as the wave propagates. Observation of gravitational waves that have propagated over cosmological distances may allow the measurement of even a small birefringence, providing evidence of quantum gravitational effects. The proposed Laser Interferometer Space Antenna (LISA) will be sensitive enough to observe the gravitational waves from sources at cosmological distances great enough that interesting bounds on the Chern-Simons coupling may be found. Here we evaluate the effect of a Chern-Simons induced spacetime birefringence to the propagation of gravitational waves from such systems. Focusing attention on the gravitational waves from coalescing binary black holes systems, which LISA will be capable of observing at redshifts approaching 30, we find that the signature of Chern-Simons gravity is a time-dependent change in the apparent orientation of the binary's orbital angular momentum with respect to the observer line-of-sight, with the magnitude of change reflecting the integrated history of the Chern-Simons coupling over the worldline of the radiation wave front. While spin-orbit coupling in the binary system will also lead to an evolution of the system's orbital angular momentum, the time dependence and other details of this real effect are different than the apparent effect produced by Chern-Simons birefringence, allowing the two effects to be separately identified
Surface gravity waves over a two-dimensional random seabed.
Pihl, Jørgen H; Mei, Chiang C; Hancock, Matthew J
2002-07-01
We extend homogenization theory to study the two-dimensional evolution of weakly nonlinear waves in a sea where the bathymetry is random over a large area. A deterministic nonlinear Schrödinger equation is derived for the envelope of a nearly sinusoidal progressive wave train. Randomness is shown to yield a linear term with a complex coefficient depending on a certain statistical average of the bathymetry. Numerical solutions are discussed for the diffraction of a Stokes wave in head-sea incidence towards a bathymetry of given plan form. Effects of the height and plan form of the randomness, as well as wave nonlinearity are examined analytically and numerically.
Stratospheric Gravity Wave Scales And Fluxes During Deepwave
NASA Astrophysics Data System (ADS)
Smith, R. B.
2015-12-01
The Gulfstream V research aircraft flights for the Deepwave project in June and July 2014 included 97 legs over the Southern Alps of New Zealand and 150 legs over the Tasman Sea and Southern Ocean, mostly in the low stratosphere at 12.1 km altitude. Improved instrument calibration, redundant sensors, longer flight legs, energy flux estimation and wavelet and filter analysis revealed new gravity wave properties. Over the sea, flight level wave amplitudes mostly fall below our detection threshold. Over terrain, disturbances show characteristic mountain wave attributes of positive vertical energy flux (EFz), negative momentum flux and upwind horizontal energy flux. In some cases, the fluxes change rapidly within an eight hour flight, even though environmental conditions are unchanged, suggesting high sensitivity or auto-oscillation. The extreme EFz=22W/m2.Most intriguing is the variety of disturbance scales found over New Zealand. In many cases, the dominant wavelength of the flux carrying mountain waves is long; between 60 and 150km. In the strong cases however, with EFz>4W/m2, the wave "downshifts" to an intermediate wavelength between 20 to 60 km. Two other disturbance scales are seen. In all cases, the vertical wind variance at flight level is dominated by short "fluxless" waves with wavelengths in the 8 to 15km range. These waves propagate upwind but they carry no vertical momentum or energy fluxes. These fluxless waves may be secondary ducted waves riding on the tropopause inversion. In four cases, mountain waves stagnate the wind and turbulent wave breaking is found with a dominant wavelength of 500m.
Peralta, J.; López-Valverde, M. A.; Imamura, T.; Read, P. L.; Luz, D.; Piccialli, A.
2014-07-01
This paper is the first of a two-part study devoted to developing tools for a systematic classification of the wide variety of atmospheric waves expected on slowly rotating planets with atmospheric superrotation. Starting with the primitive equations for a cyclostrophic regime, we have deduced the analytical solution for the possible waves, simultaneously including the effect of the metric terms for the centrifugal force and the meridional shear of the background wind. In those cases when the conditions for the method of the multiple scales in height are met, these wave solutions are also valid when vertical shear of the background wind is present. A total of six types of waves have been found and their properties were characterized in terms of the corresponding dispersion relations and wave structures. In this first part, only waves that are direct solutions of the generic dispersion relation are studied—acoustic and inertia-gravity waves. Concerning inertia-gravity waves, we found that in the cases of short horizontal wavelengths, null background wind, or propagation in the equatorial region, only pure gravity waves are possible, while for the limit of large horizontal wavelengths and/or null static stability, the waves are inertial. The correspondence between classical atmospheric approximations and wave filtering has been examined too, and we carried out a classification of the mesoscale waves found in the clouds of Venus at different vertical levels of its atmosphere. Finally, the classification of waves in exoplanets is discussed and we provide a list of possible candidates with cyclostrophic regimes.
Statistics and Physics of Stratospheric Gravity Wave Attenuation over New Zealand
NASA Astrophysics Data System (ADS)
Kruse, C. G.; Smith, R. B.
2015-12-01
The DEEPWAVE field project took place over the New Zealand region during June and July of 2014 and was focused on observing orographic and non-orographic gravity waves from their source regions in the troposphere to attenuation regions in the stratosphere, mesosphere, and thermosphere. An important preliminary finding of this project is that many mountain wave events are attenuated in a 15-20km "valve layer" in the lower stratosphere, characterized by weak winds and non-linearity. This valve layer strongly attenuates about half of New Zealand mountain wave events, reducing wave momentum fluxes by as much as 90% and producing a maximum in momentum flux divergence. This work further characterizes this lower-stratospheric mountain wave attenuation and seeks to understand the physics of actual wave attenuation events "reproduced" within 6- and 2-km resolution realistic WRF simulations. Local attenuation diagnostics, such as Richardson Number, stratification, and the non-linearity ratio, are used to characterize the size and 3-D distribution of attenuation regions and to diagnose dissipation mechanisms. Potential vorticity (PV) is also used as a diagnostic to identify attenuation regions and also to trace the influences of these regions downstream. Preliminary work has revealed that mountain wave attenuation over New Zealand is spatially inhomogeneous, generates PV in dipoles, and that lateral shear instabilities cause lateral mixing 1000s of kilometers downstream of the attenuation regions.
Comparison of simulated and observed convective gravity waves
NASA Astrophysics Data System (ADS)
Kalisch, S.; Chun, H.-Y.; Ern, M.; Preusse, P.; Trinh, Q. T.; Eckermann, S. D.; Riese, M.
2016-11-01
Gravity waves (GWs) from convection have horizontal wavelengths typically shorter than 100 km. Resolving these waves in state-of-the-art atmospheric models still remains challenging. Also, their time-dependent excitation process cannot be represented by a common GW drag parametrization with static launch distribution. Thus, the aim of this paper is to investigate the excitation and three-dimensional propagation of GWs forced by deep convection in the troposphere and estimate their influence on the middle atmosphere. For that purpose, the GW ray tracer Gravity-wave Regional Or Global Ray Tracer (GROGRAT) has been coupled to the Yonsei convective GW source model. The remaining free model parameters have been constrained by measurements. This work led to a coupled convective GW model representing convective GWs forced from small cells of deep convection up to large-scale convective clusters. In order to compare our simulation results with observed global distributions of momentum flux, limitations of satellite instruments were taken into account: The observational filter of a limb-viewing satellite instrument restricts measurements of GWs to waves with horizontal wavelengths longer than 100 km. Convective GWs, however, often have shorter wavelengths. This effect is taken into account when comparing simulated and observable GW spectra. We find good overall agreement between simulated and observed GW global distributions, if superimposed with a nonorographic background spectrum for higher-latitude coverage. Our findings indicate that parts of the convective GW spectrum can indeed be observed by limb-sounding satellites.
NASA Astrophysics Data System (ADS)
Matsuda, Takashi S.; Nakamura, Takuji; Murphy, Damian; Tsutsumi, Masaki; Moffat-Griffin, Tracy; Zhao, Yucheng; Pautet, Pierre-Dominique; Ejiri, Mitsumu K.; Taylor, Michael
2016-07-01
ANGWIN (Antarctic Gravity Wave Imaging/Instrument Network) is an international airglow imager/instrument network in the Antarctic, which commenced observations in 2011. It seeks to reveal characteristics of mesospheric gravity waves, and to study sources, propagation, breaking of the gravity waves over the Antarctic and the effects on general circulation and upper atmosphere. In this study, we compared distributions of horizontal phase velocity of the gravity waves at around 90 km altitude observed in the mesospheric airglow imaging over different locations using our new statistical analysis method of 3-D Fourier transform, developed by Matsuda et al. (2014). Results from the airglow imagers at four stations at Syowa (69S, 40E), Halley (76S, 27W), Davis (69S, 78E) and McMurdo (78S, 156E) out of the ANGWIN imagers have been compared, for the observation period between April 6 and May 21 in 2013. In addition to the horizontal distribution of propagation and phase speed, gravity wave energies have been quantitatively compared, indicating a smaller GW activity in higher latitude stations. We further investigated frequency dependence of gravity wave propagation direction, as well as nightly variation of the gravity wave direction and correlation with the background wind variations. We found that variation of propagation direction is partly due to the effect of background wind in the middle atmosphere, but variation of wave sources could play important role as well. Secondary wave generation is also needed to explain the observed results.
Role of gravity waves in vertical coupling during sudden stratospheric warmings
NASA Astrophysics Data System (ADS)
Yiğit, Erdal; Medvedev, Alexander S.
2016-12-01
Gravity waves are primarily generated in the lower atmosphere, and can reach thermospheric heights in the course of their propagation. This paper reviews the recent progress in understanding the role of gravity waves in vertical coupling during sudden stratospheric warmings. Modeling of gravity wave effects is briefly reviewed, and the recent developments in the field are presented. Then, the impact of these waves on the general circulation of the upper atmosphere is outlined. Finally, the role of gravity waves in vertical coupling between the lower and the upper atmosphere is discussed in the context of sudden stratospheric warmings.
Gravity Waves and Convection in Colorado during July 1983.
NASA Astrophysics Data System (ADS)
Einaudi, F.; Clark, W. L.; Green, J. L.; Vanzandt, T. E.; Fua, D.
1987-06-01
In order to gain insight into the complex dynamics of a convective system interacting with a gravity wave train, we have carried out an experiment in northeast Colorado during July and August, 1983, utilizing data from several program areas in NOAA. Pressure data from the PROFS mesonetwork of microbarograph stations were combined with velocity profiles from the Wave Propagation Laboratory UHF wind profiler (ST) radar at Stapleton Airport in Denver and convective cell location data from the NWS Limon weather radar. Several events were clearly visible in the microbarograph data, from which four (called Events A, B, C and D) in late July were selected for further study. These events differed from each other in fundamental ways.In each event the waves represent oscillations of a substantial depth of the troposphere and seem to appear and disappear together with the convective cells. In Events A and B the waves have a critical level and are probably unstable modes generated by wind shear in the jet stream, from which they extract energy. We suggest that the convective cells cause the selection of some modes over others in a system that is initially dynamically unstable. In Event A the wave appears to be locked together with the convective cells, which move at the same velocity as the phase velocity of the wave. The wave and the cells seem to grow and evolve synergetically. In Event B the wave and convective cells commence at about the same time, but the cell velocities are quite different from the wave phase velocity. The cell velocities vary substantially over the time of the event and appear to be controlled by the local winds.In the Events C and D, the waves move faster than the maximum wind in the jet and at least twice as fast as the convective cells. It is suggested that these are nonsingular neutral modes whose excitation depends on a number of mechanisms, such as vertical convective motions and acceleration in the jet flow.
Sheen, D.R.; Liu, C.H.
1988-12-01
Two types of disturbances observed in the ionization density and the line-of-sight ion velocity data from the Worldwide Atmospheric Gravity Wave Study are analyzed and compared with theoretical studies. The study concentrates on the source-response relationship between auroral activities and gravity waves observed in the F-region. In the first section, the measured and derived wave parameters for a semiperiodic TID observed on October 18, 1985 during a moderately magnetically active period are shown to be consistent with predictions from wave theory. In the second section, the background wave spectra observed during several magnetically quiet days are analyzed. It is shown that the neutral vertical velocity spectrum can be modeled as a power law type spectrum. The overall kinetic energy of this spectrum is calculated and compared with the TID. 32 references.
INTERNAL GRAVITY WAVES IN MASSIVE STARS: ANGULAR MOMENTUM TRANSPORT
Rogers, T. M.; Lin, D. N. C.; McElwaine, J. N.; Lau, H. H. B. E-mail: lin@ucolick.org E-mail: hblau@astro.uni-bonn.de
2013-07-20
We present numerical simulations of internal gravity waves (IGW) in a star with a convective core and extended radiative envelope. We report on amplitudes, spectra, dissipation, and consequent angular momentum transport by such waves. We find that these waves are generated efficiently and transport angular momentum on short timescales over large distances. We show that, as in Earth's atmosphere, IGW drive equatorial flows which change magnitude and direction on short timescales. These results have profound consequences for the observational inferences of massive stars, as well as their long term angular momentum evolution. We suggest IGW angular momentum transport may explain many observational mysteries, such as: the misalignment of hot Jupiters around hot stars, the Be class of stars, Ni enrichment anomalies in massive stars, and the non-synchronous orbits of interacting binaries.
Experimental study of three-wave interactions among capillary-gravity surface waves
NASA Astrophysics Data System (ADS)
Haudin, Florence; Cazaubiel, Annette; Deike, Luc; Jamin, Timothée; Falcon, Eric; Berhanu, Michael
2016-04-01
In propagating wave systems, three- or four-wave resonant interactions constitute a classical nonlinear mechanism exchanging energy between the different scales. Here we investigate three-wave interactions for gravity-capillary surface waves in a closed laboratory tank. We generate two crossing wave trains and we study their interaction. Using two optical methods, a local one (laser doppler vibrometry) and a spatiotemporal one (diffusive light photography), a third wave of smaller amplitude is detected, verifying the three-wave resonance conditions in frequency and in wave number. Furthermore, by focusing on the stationary regime and by taking into account viscous dissipation, we directly estimate the growth rate of the resonant mode. The latter is then compared to the predictions of the weakly nonlinear triadic resonance interaction theory. The obtained results confirm qualitatively and extend previous experimental results obtained only for collinear wave trains. Finally, we discuss the relevance of three-wave interaction mechanisms in recent experiments studying gravity-capillary turbulence.
NASA Astrophysics Data System (ADS)
Imamura, Takeshi; Watanabe, Ayuka; Maejima, Yasumitsu
2016-03-01
Generation of gravity waves by convection was studied using a nonlinear two-dimensional model. A boundary-layer convection forced by a horizontally-uniform heating and a plume forced by a localized heating representing a local dust storm were tested. The results suggest that vigorous convection occurs due to the low density of the martian atmosphere and that short-period waves having frequencies near the buoyancy frequency can be preferentially generated. The propagation of those gravity waves to thermospheric heights was studied using a linearized one-dimensional model. Because of the fast vertical propagation the waves attain large amplitudes in the lower thermosphere, being consistent with Mars Global Surveyor and Mars Odyssey's accelerometer measurements and MAVEN's neutral and ion measurements. The heating and cooling caused by the waves are expected to be significant in the energy budget of the thermosphere, and the vertical mixing induced by those gravity waves should influence the homopause height. Since the thermospheric densities of light, minor species increase with the lowering of the homopause, a lower homopause may have enhanced the escape of such species to space for early Mars, where slower, weaker gravity waves should dominate.
Projected constraints on Lorentz-violating gravity with gravitational waves
NASA Astrophysics Data System (ADS)
Hansen, Devin; Yunes, Nicolás; Yagi, Kent
2015-04-01
Gravitational waves are excellent tools to probe the foundations of general relativity in the strongly dynamical and nonlinear regime. One such foundation is Lorentz symmetry, which can be broken in the gravitational sector by the existence of a preferred time direction and, thus, a preferred frame at each spacetime point. This leads to a modification in the orbital decay rate of binary systems, and also in the generation and chirping of their associated gravitational waves. Here we study whether waves emitted in the late, quasicircular inspiral of nonspinning, neutron star binaries can place competitive constraints on two proxies of gravitational Lorentz violation: Einstein-Æther theory and khronometric gravity. We model the waves in the small-coupling (or decoupling) limit and in the post-Newtonian approximation, by perturbatively solving the field equations in small deformations from general relativity and in the small-velocity or weak-gravity approximation. We assume that a gravitational wave consistent with general relativity has been detected with second- and third-generation, ground-based detectors, and with the proposed space-based mission DECIGO, with and without coincident electromagnetic counterparts. Without a counterpart, a detection consistent with general relativity can only place competitive constraints on gravitational Lorentz violation when using future, third-generation or space-based instruments. On the other hand, a single counterpart is enough to place constraints that are 10 orders of magnitude more stringent than current binary pulsar bounds, even when using second-generation detectors. This is because Lorentz violation forces the group velocity of gravitational waves to be different from that of light, and this difference can be very accurately constrained with coincident observations.
Dynamics and Predictability of Deep Propagating Atmospheric Gravity Waves
NASA Astrophysics Data System (ADS)
Doyle, J.; Fritts, D. C.; Smith, R.; Eckermann, S. D.
2012-12-01
An overview will be provided of the first field campaign that attempts to follow deeply propagating gravity waves (GWs) from their tropospheric sources to their mesospheric breakdown. The DEEP propagating gravity WAVE experiment over New Zealand (DEEPWAVE-NZ) is a comprehensive, airborne and ground-based measurement and modeling program focused on providing a new understanding of GW dynamics and impacts from the troposphere through the mesosphere and lower thermosphere (MLT). This program will employ the new NSF/NCAR GV (NGV) research aircraft from a base in New Zealand in a 6-week field measurement campaign in June-July 2014. The NGV will be equipped with new lidar and airglow instruments for the DEEPWAVE measurement program, providing temperatures and vertical winds spanning altitudes from immediately above the NGV flight altitude (~13 km) to ~100 km. The region near New Zealand is chosen since all the relevant GW sources occur strongly here, and upper-level winds in austral winter permit GWs to propagate to very high altitudes. Given large-amplitude GWs that propagate routinely into the MLT, the New Zealand region offers an ideal natural laboratory for studying these important GW dynamics and effects impacting weather and climate over a much deeper atmospheric layer than previous campaigns have attempted (0-100 km altitude). The logistics of making measurements in the vicinity of New Zealand are potentially easier than from the Andes and Drake Passage region. A suite of GW-focused modeling and predictability tools will be used to guide NGV flight planning to GW events of greatest scientific significance. These models will also drive scientific interpretation of the GW measurements, together providing answers to the key science questions posed by DEEPWAVE about GW dynamics, morphology, predictability and impacts from 0-100 km. Preliminary results will be presented from high-resolution and adjoint models applied over areas featuring deep wave propagation. The high
Turbulent dynamics of breaking internal gravity waves on slopes
NASA Astrophysics Data System (ADS)
Arthur, Robert; Fringer, Oliver
2014-11-01
The turbulent dynamics of breaking internal gravity waves on slopes are investigated using a high-resolution numerical model. A Navier-Stokes code is employed in an idealized, three-dimensional domain where an internal solitary wave of depression impinges upon a sloping bottom. A bottom-following curvilinear grid is used to capture the bathymetry accurately, and the vertical grid spacing Δz+ = O(1) near the bottom in the breaking region to resolve the near-wall flow. In order to understand the transition to turbulence as a result of wave breaking, flow variability is analyzed in the cross-stream dimension. In particular, streamwise vorticity, or secondary streamwise rolls that lead to the turbulent breakdown of the wave, is found to develop in regions of unstable stratification. Dissipation and irreversible mixing of the density field are analyzed as a function of time, and related to breaking dynamics; irreversible mixing is quantified in terms of the change in background potential energy inside the domain. The mixing efficiency is also calculated for various wave and slope conditions. These results have application to the nearshore coastal ocean, where breaking internal waves affect the distributions of ecologically important scalars such as temperature, oxygen, and nutrients.
Monitoring gravity waves detected by I33MG
NASA Astrophysics Data System (ADS)
Randrianarinosy, Fanomezana; Andrianaivoarisora, Jean Bernardo; Tahina Rakotoariza, Andriniaina; Rambolamanana, Gérard; Harifidy Ramanantsoa, Andry
2013-04-01
Since September 2001, I33MG has recorded and stored data in the National Data Centre which belongs to the Laboratory of Seismology and Infrasound at the Institute and Observatory of Geophysics in Antananarivo (IOGA). The recorded data allowed us to monitor different sources of infrasound such as microbaroms, lightning, volcanoes, cyclones, mountain associated waves, explosions, etc which can be distinguished as acoustic waves. Besides, in the framework of the ARISE project, atmospheric waves having frequency below the acoustic cut-off frequency, known as gravity waves, are considered. Buoyancy oscillations are observed that fill the atmosphere and ocean and propagate long distances horizontally and vertically, have length scales from meters to thousands of kilometers, time scales from seconds to weeks, and release energy into turbulence by wave breaking. WinPMCC based on the Progressive Multi-Channel Correlation (PMCC) is used to detect and to get the wave parameters. Azimuth variation versus time is observed but events are mostly found from 200° to 360°, 0° to 100° and a few from 100° to 200°.
Planetary and Gravity Waves in the Mesosphere and Lower Thermosphere
NASA Technical Reports Server (NTRS)
Vincent, R. A.
1985-01-01
Rocket and ground based studies of the mesosphere and lower thermosphere show that waves play an important role in the dynamics of their region. The waves manifest themselves in wind, temperature, density, pressure, ionization and airglow fluctuations in the 80-120 km height range. Rockets have enabled the density and temperature structure to be measured with excellent height resolution, while long term studies of wind motions using MST, partial reflection and meteor radars and, more recently, lidar investigations of temperature and density, have enabled the temporal behaviour of the waves to be better understood. A composite of power spectra is shown of wind motions measured near the mesopause at widely separated locations and illustrates how wave energy is distributed as a function of frequency. The spectra show three distinct parts; (1) a long period section corresponding to periods longer than 24 h; (2) a section between 12 and 24 h priod where the spectra are dominated by narrow; peaks associated with the semidiurnal and diurnal tides and (3) a section at periods less than 12 h where the spectral density decreases montonically (except for the 8 h tidal peak). The long period section is associated with transient planetary scale waves while the short period motions are caused by gravity waves.
Time and space analysis of turbulence of gravity surface waves
NASA Astrophysics Data System (ADS)
Mordant, Nicolas; Aubourg, Quentin; Viboud, Samuel; Sommeria, Joel
2016-11-01
Wave turbulence is a statistical state made of a very large number of nonlinearly interacting waves. The Weak Turbulence Theory was developed to describe such a situation in the weakly nonlinear regime. Although, oceanic data tend to be compatible with the theory, laboratory data fail to fulfill the theoretical predictions. A space-time resolved measurement of the waves have proven to be especially fruitful to identify the mechanism at play in turbulence of gravity-capillary waves. We developed an image processing algorithm to measure the motion of the surface of water with both space and time resolution. We first seed the surface with slightly buoyant polystyrene particles and use 3 cameras to reconstruct the surface. Our stereoscopic algorithm is coupled to PIV so that to obtain both the surface deformation and the velocity of the water surface. Such a coupling is shown to improve the sensitivity of the measurement by one order of magnitude. We use this technique to probe the existence of weakly nonlinear turbulence excited by two small wedge wavemakers in a 13-m diameter wave flume. We observe a truly weakly nonlinear regime of isotropic wave turbulence. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Grant Agreement No 647018-WATU).
Large stationary gravity wave in the atmosphere of Venus
NASA Astrophysics Data System (ADS)
Fukuhara, Tetsuya; Futaguchi, Masahiko; Hashimoto, George L.; Horinouchi, Takeshi; Imamura, Takeshi; Iwagaimi, Naomoto; Kouyama, Toru; Murakami, Shin-Ya; Nakamura, Masato; Ogohara, Kazunori; Sato, Mitsuteru; Sato, Takao M.; Suzuki, Makoto; Taguchi, Makoto; Takagi, Seiko; Ueno, Munetaka; Watanabe, Shigeto; Yamada, Manabu; Yamazaki, Atsushi
2017-01-01
The planet Venus is covered by thick clouds of sulfuric acid that move westwards because the entire upper atmosphere rotates much faster than the planet itself. At the cloud tops, about 65 km in altitude, small-scale features are predominantly carried by the background wind at speeds of approximately 100 m s-1. In contrast, planetary-scale atmospheric features have been observed to move slightly faster or slower than the background wind, a phenomenon that has been interpreted to reflect the propagation of planetary-scale waves. Here we report the detection of an interhemispheric bow-shaped structure stretching 10,000 km across at the cloud-top level of Venus in middle infrared and ultraviolet images from the Japanese orbiter Akatsuki. Over several days of observation, the bow-shaped structure remained relatively fixed in position above the highland on the slowly rotating surface, despite the background atmospheric super rotation. We suggest that the bow-shaped structure is the result of an atmospheric gravity wave generated in the lower atmosphere by mountain topography that then propagated upwards. Numerical simulations provide preliminary support for this interpretation, but the formation and propagation of a mountain gravity wave remain difficult to reconcile with assumed near-surface conditions on Venus. We suggest that winds in the deep atmosphere may be spatially or temporally more variable than previously thought.
Wave drag due to generation of capillary-gravity surface waves
NASA Astrophysics Data System (ADS)
Burghelea, Teodor; Steinberg, Victor
2002-11-01
The onset of the wave resistance via the generation of capillary-gravity waves by a small object moving with a velocity V is investigated experimentally. Due to the existence of a minimum phase velocity Vc for surface waves, the problem is similar to the generation of rotons in superfluid helium near their minimum. In both cases, waves or rotons are produced at V>Vc due to Cherenkov radiation. We find that the transition to the wave drag state is continuous: in the vicinity of the bifurcation the wave resistance force is proportional to (V-Vc) for various fluids. This observation contradicts the theory of Raphaël and de Gennes. We also find that the reduced wave drag force for different fluids and different ball size may be scaled in such a way that all the data collapse on a single curve. The capillary-gravity wave pattern and the shape of the wave-generating region are investigated both experimentally and theoretically. Good agreement between the theory and the experimental data is found in this case.
Model-data comparisons of moments of nonbreaking shoaling surface gravity waves
NASA Technical Reports Server (NTRS)
Elgar, Steve; Freilich, M. H.; Guza, R. T.
1990-01-01
The predictions of linear and nonlinear (Boussinesq) shoaling wave models for nonbreaking unidirectional surface gravity waves are compared to field observations, with particular emphasis on quantities that may be important for cross-shore sediment transport. The extensive data sets were obtained on two natural beaches, span water depths between 1 and 10 m, and include incident wave power spectra with narrow, broad, and bimodal shapes. Significant wave heights varied between approximately 30 and 100 cm, and peak periods between approximately 8 and 18 s. The evolution of total variances of sea surface elevation, cross-shore velocity, and horizontal acceleration is modeled at least qualitatively well by both linear and nonlinear theories. Only the nonlinear theory predicts the increasingly asymmetric sea surface elevations and horizontal velocities (pitched-forward wave shapes) and the weaker variation of skewness (difference between crest and trough profiles) which are observed to occur during shoaling. The nonlinear theory also models qualitatively well the large skewed accelerations which occur during the passage of asymmetric waves.
Ralph, F.M.; Venkateswaran, S.V. ); Mazaudier, C. ); Crochet, M. )
1993-02-01
Observations from two Doppler sodars and a radar wind profiler have been used in conjunction with data from a rawinsonde station and a mesoscale surface observation network to conduct a case study of a gravity current entering into an environment containing a nocturnal inversion and an elevated neutral layer. On the basis of synoptic and mesoscale analyses, it is concluded that the gravity current might have originated either as a scale-contracted cold front or as a gust front resulting from thunderstorm outflows observed very near the leading edge of a cold front. Despite this ambiguity, the detailed vertical structure of the gravity current itself is well resolved from the data. Moreover, the vertical velocity measurements provided by the sodars and the radar wind profiler at high time resolution have given unique information about the height structure of gravity waves excited by the gravity current. Although only wave periods, and not phase speeds or wavelengths, are directly measured, it is possible to make reasonable inferences about wave excitation mechanisms and about the influence and control of ambient stratification on wave-field characteristics. Both Kelvin-Helmholtz waves generated in the regions of high wind shear found in association with the gravity current and lee-type waves forced by the gravity current acting as an obstacle to opposing prefrontal flow are identified. It is also found that the propagation speed of the gravity current and the relative depths of the prefrontal inversion and the postfrontal cold air were not favorable for the formation of either internal bores or solitary waves at the time of day at which the gravity current was being observed. 42 refs., 18 figs., 1 tab.
NASA Astrophysics Data System (ADS)
Nicolls, M. J.; Vadas, S.; Sulzer, M. P.; Aponte, N.
2013-12-01
We report on experimental techniques and results for extracting horizontal and vertical wave parameters of thermospheric gravity waves using incoherent scatter radar (ISR) measurements of the three-dimensional properties of traveling ionospheric disturbances (TIDs). We use results from the Poker Flat Incoherent Scatter Radar (PFISR) and the Arecibo Observatory (AO) to extract the three-dimensional properties of waves, including horizontal and vertical wavelengths, phase speeds, and propagation directions. Comparison to theoretical ray tracing results sheds light on the dissipative and wind filtering mechanisms that drive the measurements. High-resolution vertical wavelength measurements reveal maxima at the altitudes near where the TID amplitude is maximum, consistent with gravity wave packet theory. Simultaneous measurements of lower thermospheric neutral winds reveal the effects of strong winds (often greater that 150 m/s) on determining the wave spectra at higher altitudes. We discuss how these measurements can shed light on the lower atmospheric sources that contribute to thermospheric gravity waves and drive ionospheric variability.
Surface gravity waves at equilibrium with a steady wind
NASA Technical Reports Server (NTRS)
Glazman, Roman E.
1994-01-01
Observations of wave fields' spatial evolution and of gravity wave spectra S(sub omega) are analyzed on the basis of the data reported by several research groups as well as on a 2-year data set of wind and wave measurements by stationary National Oceanic and Atmospheric Administration buoys near the Hawaiian Islands. We seek to clarify the role of the wave energy advection (with the wave group velocity) in the overall energy balance. This advective transfer appears to be no less important than the local (breaking wave induced) dissipation as a factor of wind-wave equilibrium. The advection is found to manifest itself in the shape of wave spectra by reducing the rate at which the spectra density of the wave energy, S(sub omega approximately omega (exp -p), falls off as the frequency increases away from the spectra peak. This and other conclusions are derived by comparing the field observations with theoretical predictions of the weak turbulence theory for a spatially inhomogeneous, statistically stationary, wave field. The observations also indicate that the typical wave age xi = C(sub 0)/U in the open ocean is much greater than the limiting value 1.2 attributed to the 'fully developed sea.' Although the observed spectra can be approximated by a power law with a single 'effective' exponent, this apparent exponent, p, is found to depend on the wave age. At high xi and at frequencies below the generation range, -p tends to -3 rather than the value of -11/3 predicted by the Zakharov-Zaslavskii theory. This deviation is interpreted as pointing to a nonconservative nature of the inverse cascade, the latter including a leakage of energy to low-wavenumber modes. Dependence of the overall effective exponent on xi is shown to be responsible for variation in the coefficients b, B, c, C appearing in empirical fetch laws, such as xi = C bar-x (exp c) and e = B bar-x (exp B), where bar-x and e are the dimensionless fetch and wave energy, respectively.
Nonlinear gravity waves in the water flow with inhomogeneous vorticity
NASA Astrophysics Data System (ADS)
Abrashkin, Anatoly; Pelinovsky, Efim
2016-04-01
Nonlinear Schrodinger equation is derived for weakly modulated nonlinear wave packets in the infinite-depth water flow with inhomogeneous vorticity. Governing 2-D equations are written in Lagrangian variables. Nonlinear Schrodinger equation is obtained in the third order of perturbation theory taking into account weak non-uniform vortex current. Two limiting cases are analyzed. The first one corresponds to the uniform surface flow and is described by the classic nonlinear Schrodinger equation allowed the modulational instability. The second one is the Gerstner's wave packet. In this limiting case the nonlinear term is absent confirming known fact that nonlinear Gerstner's wave has the linear dispersion relation.
Long-Term Global Morphology of Gravity Wave Activity Using UARS Data
NASA Technical Reports Server (NTRS)
Eckermann, Stephen D.; Bacmeister, Julio T.; Wu, Dong L.
1998-01-01
Progress in research into the global morphology of gravity wave activity using UARS data is described for the period March-June, 1998. Highlights this quarter include further progress in the analysis and interpretation of CRISTA temperature variances; model-generated climatologies of mesospheric gravity wave activity using the HWM-93 wind and temperature model; and modeling of gravity wave detection from space-based platforms. Preliminary interpretations and recommended avenues for further analysis are also described.
Observation and Modeling of Tsunami-Generated Gravity Waves in the Earth’s Upper Atmosphere
2014-10-15
Observation and modeling of tsunami -generated gravity waves in the earth’s upper atmosphere 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR...ABSTRACT Build a compatible set of models which 1) calculate the atmospheric gravity waves (GWs) excited by a tsunami , 2) propagate these GWs into...modeling of tsunami -generated gravity waves in the earth’s upper atmosphere Sharon L. Vadas NWRA/CoRA 3380 S. Mitchell Lane Boulder, CO 80301, USA phone
Quantum Gravity Explanation of the Wave-Particle Duality
NASA Astrophysics Data System (ADS)
Winterberg, Friedwardt
2016-03-01
A quantum gravity explanation of the quantum-mechanical wave-particle duality is given by the watt-less emission of gravitational waves from a particle described by the Dirac equation. This explanation is possible through the existence of negative energy, and hence negative mass solutions of Einstein's gravitational field equations. They permit to understand the Dirac equation as the equation for a gravitationally bound positive-negative mass (pole-dipole particle) two-body configuration, with the mass of the Dirac particle equal to the positive mass of the gravitational field binding the positive with the negative mass particle, and with the positive and negative mass particles making a luminal ``Zitterbewegung'' (quivering motion), emitting a watt-less oscillating positive-negative space curvature wave. Is it shown that this thusly produced ``Zitterbewegung'' reproduces the quantum potential of the Madelung-transformed Schrödinger equation. The watt-less gravitational wave emitted by the quivering particles is conjectured to be the de Broglie pilot wave.
Internal Gravity Waves: Generation and Breaking Mechanisms by Laboratory Experiments
NASA Astrophysics Data System (ADS)
la Forgia, Giovanni; Adduce, Claudia; Falcini, Federico
2016-04-01
Internal gravity waves (IGWs), occurring within estuaries and the coastal oceans, are manifest as large amplitude undulations of the pycnocline. IGWs propagating horizontally in a two layer stratified fluid are studied. The breaking of an IGW of depression shoaling upon a uniformly sloping boundary is investigated experimentally. Breaking dynamics beneath the shoaling waves causes both mixing and wave-induced near-bottom vortices suspending and redistributing the bed material. Laboratory experiments are conducted in a Perspex tank through the standard lock-release method, following the technique described in Sutherland et al. (2013). Each experiment is analysed and the instantaneous pycnocline position is measured, in order to obtain both geometric and kinematic features of the IGW: amplitude, wavelength and celerity. IGWs main features depend on the geometrical parameters that define the initial experimental setting: the density difference between the layers, the total depth, the layers depth ratio, the aspect ratio, and the displacement between the pycnoclines. Relations between IGWs geometric and kinematic features and the initial setting parameters are analysed. The approach of the IGWs toward a uniform slope is investigated in the present experiments. Depending on wave and slope characteristics, different breaking and mixing processes are observed. Sediments are sprinkled on the slope to visualize boundary layer separation in order to analyze the suspension e redistribution mechanisms due to the wave breaking.
NASA Astrophysics Data System (ADS)
Fetzer, Eric J.; Gille, John C.
1996-02-01
Zonal-mean gravity wave variance in the Limb Infrared Monitor of the Stratosphere (LIMS) temperature data is seen to correlate strongly with the residual term in the LIMS zonal-mean momentum budget throughout much of the observed mesosphere. This momentum residual is attributed to gravity wave momentum transport at scales that cannot be directly sampled by the LIMS instrument Correlation is highest in the vicinity of the fall and winter mesospheric jets, where both gravity wave variance and momentum residual reach their largest values. Correlation is also high in the Southern Hemisphere subtropical mesophere, where gravity wave variance and the momentum residual have broad temporal maxima during the easterly acceleration of the stratopause semi-annual oscillation (SAO). This subtropical correlation has important implications for the SAO eastward acceleration, which several studies suggest is forced by gravity wave momentum flux divergence. Correlation between gravity wave variance and inferred gravity wave momentum flux divergence is unexpected because variance is dominated by large scales and long periods (inertio-gravity waves), while both theoretical arguments and ground-based observations indicate that momentum transport is dominated by periods under 1 h. The results of this study suggest a broadband gravity wave field experiencing forcing and loss processes, which are largely independent of frequency.
Do waves carrying orbital angular momentum possess azimuthal linear momentum?
Speirits, Fiona C; Barnett, Stephen M
2013-09-06
All beams are a superposition of plane waves, which carry linear momentum in the direction of propagation with no net azimuthal component. However, plane waves incident on a hologram can produce a vortex beam carrying orbital angular momentum that seems to require an azimuthal linear momentum, which presents a paradox. We resolve this by showing that the azimuthal momentum is not a true linear momentum but the azimuthal momentum density is a true component of the linear momentum density.
Characteristic of gravity waves resolved in ECMWF anaylses
NASA Astrophysics Data System (ADS)
Preusse, Peter; Ern, Manfred; Riese, Martin
2014-05-01
Gravity waves (GWs) influence the circulation of the atmosphere on global scale. Can we employ global models such as the ECMWF high-resolution GCM to infer quantities of resolved GWs? Does this give us insight for the characteristics and relative importance of real GW sources? And can we use such data savely for, e.g., campaign planing? We here apply techniques developed for an ESA study proving the scientifc break-through which could be reached by a novel infrared limb imager. The 3D wave structure of mesoscale GWs is exploited to determine amplitudes and 3D wave vectors of GWs at different levels (25km, 35km and 45km altitude) in the stratosphere. Similar to real observations, GW momentum flux is largest in the winter polar vortex and exhibits a second maximum in the summer subtropics. Based on the 3D wavevectors backward ray-tracing is employed to characterize specific sources. For instance, we find for the northern winter strong GWMF associated with mountain waves from Norway and Greenland as well as waves emitted in the lower troposphere from a storm approaching Norway. Waves from these sources spread up to several thousand km in the stratosphere. Together these three events form a burst in the total hemispheric GWMF of a factor of 3. Strong mountain wave events are also found e.g. at Tierre del Fuego and the Antarctic Peninsula, regions which are in the focus of observational and modeling studies for a decade. Gravity waves in the tropical region are likely generated above deep convection in the upper troposphere. They have significantly larger horizontal wavelengths but shorter vertical wavelengths than indicated by observations. They also exhibit lower phase speeds than waves simulated by mesoscale modeling of deep convection events. This difference is not due to the model resolution. Rather, GWs in ECMWF are excited aloft of the convection in the altitudes of largest wind-shear and least dynamical stability. GWs which are excited by resonant forcing
Impact of ENSO on seasonal variations of Kelvin Waves and mixed Rossby-Gravity Waves
NASA Astrophysics Data System (ADS)
Rakhman, Saeful; Lubis, Sandro W.; Setiawan, Sonni
2017-01-01
Characteristics of atmospheric equatorial Kelvin waves and mixed Rossby-Gravity (MRG) waves as well as their relationship with tropical convective activity associated with El Niño-Southern Oscillation (ENSO) were analyzed. Kelvin waves and MRG waves were identified by using a Space-Time Spectral Analysis (STSA) technique, where the differences in the strength of both waves were quantified by taking the wave spectrum differences for each ENSO phase. Our result showed that Kelvin wave activity is stronger during an El Nino years, whereas the MRG wave activity is stronger during the La Nina years. Seasonal variations of Kelvin wave activity occurs predominantly in MAM over the central to the east Pacific in the El Nino years, while the strongest seasonal variation of MRG wave activity occus in MAM and SON over the northern and southern Pacific during La Nina years. The local variation of Kelvin wave and MRG wave activities are found to be controlled by variation in lower level atmospheric convection induced by sea surface temperature in the tropical Pacific Ocean.
Holographic p-wave superconductors from Gauss-Bonnet gravity
Cai Ronggen; Nie Zhangyu; Zhang Haiqing
2010-09-15
We study the holographic p-wave superconductors in a five-dimensional Gauss-Bonnet gravity with an SU(2) Yang-Mills gauge field. In the probe approximation, we find that when the Gauss-Bonnet coefficient grows, the condensation of the vector field becomes harder, both the perpendicular and parallel components, with respect to the direction of the condensation, of the anisotropic conductivity decrease. We also study the mass of the quasiparticle excitations, the gap frequency and the DC conductivities of the p-wave superconductor. All of them depend on the Gauss-Bonnet coefficient. In addition, we observe a strange behavior for the condensation and the relation between the gap frequency and the mass of quasiparticles when the Gauss-Bonnet coefficient is larger than 9/100, which is the upper bound for the Gauss-Bonnet coefficient from the causality of the dual field theory.
Transport of inertial anisotropic particles under surface gravity waves
NASA Astrophysics Data System (ADS)
Dibenedetto, Michelle; Koseff, Jeffrey; Ouellette, Nicholas
2016-11-01
The motion of neutrally and almost-neutrally buoyant particles under surface gravity waves is relevant to the transport of microplastic debris and other small particulates in the ocean. Consequently, a number of studies have looked at the transport of spherical particles or mobile plankton in these conditions. However, the effects of particle-shape anisotropy on the trajectories and behavior of irregularly shaped particles in this type of oscillatory flow are still relatively unknown. To better understand these issues, we created an idealized numerical model which simulates the three-dimensional behavior of anisotropic spheroids in flow described by Airy wave theory. The particle's response is calculated using a simplified Maxey-Riley equation coupled with Jeffery's equation for particle rotation. We show that the particle dynamics are strongly dependent on their initial conditions and shape, with some some additional dependence on Stokes number.
Effect of surface gravity waves on atmospheric circulation
Janssen, P.A.E.M. |
1994-12-31
During the last decade there has been considerable interest in the problem of the interaction of wind and waves with emphasis on the sea state dependence of the momentum transfer across the air-sea interface. Simulations with the WAM model show that, depending on the sea state, the drag coefficient may vary by a factor of two. Therefore, one may wonder whether two-way interaction has impact on e.g. the evolution of a depression and the atmospheric circulation. In order to study systematic effects on the atmospheric circulation, climate runs have to be performed. Performing Monte Carlo Forecasting with the coupled WAM-ECMWF model for the winter season 1990, it is concluded that surface gravity waves have a significant impact on the atmospheric circulation.
Modulational development of nonlinear gravity-wave groups
NASA Technical Reports Server (NTRS)
Chereskin, T. K.; Mollo-Christensen, E.
1985-01-01
Observations of the development of nonlinear surface gravity-wave groups are presented, and the amplitude and phase modulations are calculated using Hilbert-transform techniques. With increasing propagation distance and wave steepness, the phase modulation develops local phase reversals whose locations correspond to amplitude minima or nodes. The concomitant frequency modulation develops jumps or discontinuities. The observations are compared with recent similar results for wavetrains. The observations are modelled numerically using the cubic nonlinear Schroedinger equation. The motivation is twofold: to examine quantitatively the evolution of phase as well as amplitude modulation, and to test the inviscid predictions for the asymptotic behavior of groups versus long-time observations. Although dissipation rules out the recurrence, there is a long-time coherence of the groups. The phase modulation is found to distinguish between dispersive and soliton behavior.
Analytical and numerical investigation on nonlinear internal gravity waves
NASA Astrophysics Data System (ADS)
Kshevetskii, S. P.
The propagation of long, weakly nonlinear internal waves in a stratified gas is studied. Hydrodynamic equations for an ideal fluid with the perfect gas law describe the atmospheric gas behaviour. If we neglect the term Ͽ dw/dt (product of the density and vertical acceleration), we come to a so-called quasistatic model, while we name the full hydro-dynamic model as a nonquasistatic one. Both quasistatic and nonquasistatic models are used for wave simulation and the models are compared among themselves. It is shown that a smooth classical solution of a nonlinear quasistatic problem does not exist for all t because a gradient catastrophe of non-linear internal waves occurs. To overcome this difficulty, we search for the solution of the quasistatic problem in terms of a generalised function theory as a limit of special regularised equations containing some additional dissipation term when the dissipation factor vanishes. It is shown that such solutions of the quasistatic problem qualitatively differ from solutions of a nonquasistatic nature. It is explained by the fact that in a nonquasistatic model the vertical acceleration term plays the role of a regularizator with respect to a quasistatic model, while the solution qualitatively depends on the regularizator used. The numerical models are compared with some analytical results. Within the framework of the analytical model, any internal wave is described as a system of wave modes; each wave mode interacts with others due to equation non-linearity. In the principal order of a perturbation theory, each wave mode is described by some equation of a KdV type. The analytical model reveals that, in a nonquasistatic model, an internal wave should disintegrate into solitons. The time of wave disintegration into solitons, the scales and amount of solitons generated are important characteristics of the non-linear process; they are found with the help of analytical and numerical investigations. Satisfactory coincidence of
Linear coupling of acoustic and cyclotron waves in plasma flows
Rogava, Andria; Gogoberidze, Grigol
2005-05-15
It is found that in magnetized electrostatic plasma flows the velocity shear couples ion-acoustic waves with ion-cyclotron waves and leads, under favorable conditions, to their efficient reciprocal transformations. It is shown that in a two-dimensional setup this coupling has a remarkable feature: it is governed by equations that are mathematically equal to the ones describing coupling of sound waves with internal gravity waves [Rogava and Mahajan, Phys. Rev. E 55, 1185 (1997)] in neutral fluids. For flows with low shearing rates a fully analytic, quantitative description of the coupling efficiency, based on a noteworthy quantum-mechanical analogy, is given and transformation coefficients are calculated.
Chaotic particle motion under linear surface waves.
Bohr, Tomas; Hansen, Jonas Lundbek
1996-12-01
We investigate the motion of infinitesimal particles in the flow field inside the fluid under a traveling surface wave. It is shown that, even for two-dimensional waves, a superposition of two or more traveling harmonic waves is enough to generate chaotic particle motion, i.e., Lagrangian chaos. (c) 1996 American Institute of Physics.
Generalized analytical model for benthic water flux forced by surface gravity waves
King, J.N.; Mehta, A.J.; Dean, R.G.
2009-01-01
A generalized analytical model for benthic water flux forced by linear surface gravity waves over a series of layered hydrogeologic units is developed by adapting a previous solution for a hydrogeologic unit with an infinite thickness (Case I) to a unit with a finite thickness (Case II) and to a dual-unit system (Case III). The model compares favorably with laboratory observations. The amplitude of wave-forced benthic water flux is shown to be directly proportional to the amplitude of the wave, the permeability of the hydrogeologic unit, and the wave number and inversely proportional to the kinematic viscosity of water. A dimensionless amplitude parameter is introduced and shown to reach a maximum where the product of water depth and the wave number is 1.2. Submarine groundwater discharge (SGD) is a benthic water discharge flux to a marine water body. The Case I model estimates an 11.5-cm/d SGD forced by a wave with a 1 s period and 5-cm amplitude in water that is 0.5-m deep. As this wave propagates into a region with a 0.3-m-thick hydrogeologic unit, with a no-flow bottom boundary, the Case II model estimates a 9.7-cm/d wave-forced SGD. As this wave propagates into a region with a 0.2-m-thick hydrogeologic unit over an infinitely thick, more permeable unit, the Case III quasi-confined model estimates a 15.7-cm/d wave-forced SGD. The quasi-confined model has benthic constituent flux implications in coral reef, karst, and clastic regions. Waves may undermine tracer and seepage meter estimates of SGD at some locations. Copyright 2009 by the American Geophysical Union.
Stabilization of linear higher derivative gravity with constraints
Chen, Tai-jun; Lim, Eugene A. E-mail: eugene.a.lim@gmail.com
2014-05-01
We show that the instabilities of higher derivative gravity models with quadratic curvature invariant αR{sup 2}+βR{sub μν}R{sup μν} can be removed by judicious addition of constraints at the quadratic level of metric fluctuations around Minkowski/de Sitter background. With a suitable parameter choice, we find that the instabilities of helicity-0, 1, 2 modes can be removed while reducing the dimensionality of the original phase space. To retain the renormalization properties of higher derivative gravity, Lorentz symmetry in the constrained theory is explicitly broken.
Stabilization of linear higher derivative gravity with constraints
NASA Astrophysics Data System (ADS)
Chen, Tai-jun; Lim, Eugene A.
2014-05-01
We show that the instabilities of higher derivative gravity models with quadratic curvature invariant αR2+βRμνRμν can be removed by judicious addition of constraints at the quadratic level of metric fluctuations around Minkowski/de Sitter background. With a suitable parameter choice, we find that the instabilities of helicity-0, 1, 2 modes can be removed while reducing the dimensionality of the original phase space. To retain the renormalization properties of higher derivative gravity, Lorentz symmetry in the constrained theory is explicitly broken.
Characteristics of Kelvin waves and gravity waves observed with radiosondes over Indonesia
NASA Astrophysics Data System (ADS)
Shimizu, Atsushi; Tsuda, Toshitaka
1997-11-01
Profiles of wind velocity and temperature at 0-35 km were observed by means of radiosondes in west Java, Indonesia, during November 1992 and April 1993 and used to study the behavior of various atmospheric waves in the equatorial atmosphere. An oscillation, of zonal winds with a period of about 27 days was found in the troposphere, which was associated with variations in humidity and cloud top height. Kelvin waves showed phase progression beginning at cloud top height (13-16 km) and were particularly enhanced near the tropopause. The Kelvin waves strongly modulated the tropopause structure including the tropopause height, minimum temperature, and atmospheric stability. A hodograph analysis was applied to determine the propagation characteristics of inertial gravity waves. Height variation of the vertical group velocity suggests that the gravity waves were generated in the troposphere, while the horizontal phase velocity distribution suggests that they were interacting with the background mean zonal winds. These wave activities were enhanced when tall, convective clouds passed over the site, suggesting that cumulus convection seems to play a key role in generating these waves in the equatorial region.
Gravity Waves Near 300 km Over the Polar Caps
NASA Technical Reports Server (NTRS)
Johnson, F. S.; Hanson, W. B.; Hodges, R. R.; Coley, W. R.; Carignan, G. R.; Spencer, N. W.
1995-01-01
Distinctive wave forms in the distributions of vertical velocity and temperature of both neutral particles and ions are frequently observed from Dynamics Explorer 2 at altitudes above 250 km over the polar caps. These are interpreted as being due to internal gravity waves propagating in the neutral atmosphere. The disturbances characterized by vertical velocity perturbations of the order of 100 m/s and horizontal wave lengths along the satellite path of about 500 km. They often extend across the entire polar cap. The associated temperature perturbations indicate that the horizontal phase progression is from the nightside to the dayside. Vertical displacements are inferred to be of the order of 10 km and the periods to be of the order of 10(exp 3) s. The waves must propagate in the neutral atmosphere, but they usually are most clearly recognizable in the observations of ion vertical velocity and ion temperature. By combining the neutral pressure calculated from the observed neutral concentration and temperature with the vertical component of the neutral velocity, an upward energy flux of the order of 0.04 erg/sq cm-s at 250 km has been calculated, which is about equal to the maximum total solar ultraviolet heat input above that altitude. Upward energy fluxes calculated from observations on orbital passes at altitudes from 250 to 560 km indicate relatively little attenuation with altitude.
The response of superpressure balloons to gravity wave motions
NASA Astrophysics Data System (ADS)
Vincent, R. A.; Hertzog, A.
2014-04-01
Superpressure balloons (SPB), which float on constant density (isopycnic) surfaces, provide a unique way of measuring the properties of atmospheric gravity waves (GW) as a function of wave intrinsic frequency. Here we devise a quasi-analytic method of investigating the SPB response to GW motions. It is shown that the results agree well with more rigorous numerical simulations of balloon motions and provide a better understanding of the response of SPB to GW, especially at high frequencies. The methodology is applied to ascertain the accuracy of GW studies using 12 m diameter SPB deployed in the 2010 Concordiasi campaign in the Antarctic. In comparison with the situation in earlier campaigns, the vertical displacements of the SPB were measured directly using GPS. It is shown using a large number of Monte Carlo-type simulations with realistic instrumental noise that important wave parameters, such as momentum flux, phase speed and wavelengths, can be retrieved with good accuracy from SPB observations for intrinsic wave periods greater than ca. 10 min. The noise floor for momentum flux is estimated to be ca. 10-4 mPa.
Frontal instability and the radiation of inertia gravity waves
NASA Astrophysics Data System (ADS)
Flór, J.-B.; Scolan, H.
2009-04-01
In this experimental study we consider the instability of a density front in a differentially rotating two-layer fluid. Within the rotating frame the upper layer is accelerated by the differential rotation of a lid at the surface. In contrast to former comparable experiments of this type, we consider miscible fluids in a relatively wide annular tank. Velocity and dye measurements (PIV and LIF) allow for the measurements of the velocity and density fields. In the parameter space set by rotational Froude number and dissipation (i.e. ratio of spin-down time to disk rotation time), different flow regimes are observed, ranging from axisymmetric to irregular baroclinic instable flows. The different regimes more or less adjoin those found for immiscible fluids by Williams et al. (J. Fluid Mech. 2005). In the present experiments, we find a new type of instability that is due to the resonant interaction between Kelvin and Rossby waves (first studied Sakai, J. Fluid Mech 1989) and compare our experimental results with the analytical results obtained on an annular domain by Gula, Zeitlin and Plougonven (2009). Further, observations in the unstable flow regimes suggest 'spontaneous emission' of inertia gravity waves. The origin of these waves is discussed in the light of Kelvin-Helmholtz instability Hölmböe instability, and geostrophic adjustment waves.
NASA Astrophysics Data System (ADS)
Lombriser, Lucas; Lima, Nelson A.
2017-02-01
With the advent of gravitational-wave astronomy marked by the aLIGO GW150914 and GW151226 observations, a measurement of the cosmological speed of gravity will likely soon be realised. We show that a confirmation of equality to the speed of light as indicated by indirect Galactic observations will have important consequences for a very large class of alternative explanations of the late-time accelerated expansion of our Universe. It will break the dark degeneracy of self-accelerated Horndeski scalar-tensor theories in the large-scale structure that currently limits a rigorous discrimination between acceleration from modified gravity and from a cosmological constant or dark energy. Signatures of a self-acceleration must then manifest in the linear, unscreened cosmological structure. We describe the minimal modification required for self-acceleration with standard gravitational-wave speed and show that its maximum likelihood yields a 3σ poorer fit to cosmological observations compared to a cosmological constant. Hence, equality between the speeds challenges the concept of cosmic acceleration from a genuine scalar-tensor modification of gravity.
Simultaneous observations of storm-generated sprite and gravity wave over Bangladesh
NASA Astrophysics Data System (ADS)
Chou, Chien-Chung; Dai, Jeff; Kuo, Cheng-Ling; Huang, Tai-Yin
2016-09-01
We report simultaneous observations of sprite and gravity wave generated by a storm over Bangladesh. The origin of a concentric gravity wave can be traced to the storm region on 27 April 2014 over Bangladesh with a low cloud top surface temperature (175 K). After data analysis, the time period of the concentric gravity wave is found to be 8.8-8.9 min. The horizontal wavelength is found to be 50 km for red emissions ( 55 km for green emissions), and the horizontal phase velocity is 94.4 ± 31.7 m s-1 for red emissions (102.6 ± 29.4 m s-1 for green emissions). Using the dispersion relation of gravity wave, the elevation angle of wave propagation direction is found to be 53.3°. The sprite associated with the gravity wave was also recorded at 1534 UT on 27 April 2014. The initiation time of storm-generated gravity wave is estimated to be 1454 UT at which lightning activity was relatively low using lightning data. At time 1534 UT of the recorded sprite, the lightning rate was close to its maximum value. The storm-generated gravity wave could be thought as a precursor phenomenon for lightning and sprites since one of the necessary conditions for gravity wave, lightning, and sprites is strong convection inside storms.
Multi-wave interaction theory for wind-generated surface gravity waves
NASA Technical Reports Server (NTRS)
Glazman, Roman E.
1992-01-01
Consistently employing the assumption of localness of wave-wave interactions in the wavenumber space, the Kolmogorov treatment of the energy cascade is applied to the case of wind-generated surface gravity waves. The effective number v of resonantly interacting wave harmonics is not limited to four but is found as a solution of a coupled system of equations expressing: (i) the dependence of the spectrum shape on the degree of the wave nonlinearity, and (ii) the continuity of the wave action flux through the spectrum given a continuous positive input from wind. The latter is specified in a Miles-type fashion, and a simple scaling relationship based on the concept of the turnover time is derived in place of the kinetic equation. The mathematical problem is reduced to an ordinary differential equation of first order. The exponent in the 'power law' for the spectral density of the wave potential energy and the effective number of resonantly interacting wave harmonics are found as functions of the wave frequency and of external factors of wind-wave interaction. The solution is close to the Zakharov-Filonenko spectrum at low frequencies and low wind input while approaching the Phillips spectrum at high frequencies and sufficiently high wind.
NASA Astrophysics Data System (ADS)
Schmidt, Carsten; Wüst, Sabine; Hannawald, Patrick; Bittner, Michael
2016-04-01
The upper mesosphere lower thermosphere region is well known for enhanced gravity wave breaking. Airglow emissions originating in this height region provide a good possibility for detailed studies of gravity wave behavior in this altitude. Therefore, rotational temperatures and intensities of the OH(3-1), OH(4-2), OH(6-2) and O2b(0-1)-transitions recorded at the NDMC (Network for the Detection of Mesospheric Change) site Oberpfaffenhofen (48.1°N, 10.3°E), Germany are examined. First results indicate, that both significant amplitude growth from the lower (~87km) OH airglow emissions to the higher (~95km) O2 airglow emissions of more than 100% as well as strong damping can be observed. On several occasions OH- and O2-emissions show completely independent behavior - probably related to the complete breakup of a gravity wave. These amplitude changes are set into relation to emission layer height, vertical wavelength, absolute temperature and potential seasonal dependence. Observations from further NDMC sites in France, Germany and Austria are used to discuss the evolution of these waves on horizontal scales from 100km to 1000km.
Stratification and Dissipation Effects in Running 2D Surface and Internal Gravity Waves
NASA Astrophysics Data System (ADS)
Kistovich, A. V.; Chashechkin, Yu. D.
2012-04-01
Problem of 2D gravity wave propagation inside and along a free surface of a deep viscous stratified fluid is analyzed analytically basing on set of fundamental governing equations that are continuity and Navier-Stokes neglecting by compressibility effects. Conventional boundary conditions taking into account solid films on the free surface where used. In a limit of clean fluid surface the set is transformed into partial differential equation of the fourth order for a stream function. The sense of applied approximations is discussed. In infinitesimal limit the equation is split on independent sub-equations with characteristic dispersion relations describing propagating independent surface and internal waves. Waves are supplemented by fine flow components. Relations between amplitude of regular waves and singular perturbed components corresponding of a fine structure are derived and discussed. Expressions for vorticity and rate of baroclinic generation of vorticity are presented. Waves of finite amplitudes are investigated in the limit of non-viscous fluid. Two kinds of the running surface wave forms for different values of the wave steepness were calculated and discussed. New approximate non-linear equations was solved and a set of solutions for stratified and homogeneous fluids describing running waves of small finite and large steepness of the waves are constructed. Received expressions for drift velocity are transferred into well-known Stokes solutions in limit of small steepness. Calculations of running periodic internal waves are compared with data of laboratory experiments performed on USU "HPC IPMech RAS" under support of Ministry of Education and Science of the Russian Federation (Goscontract No. 16.518.11.7059. Extrapolation results of calculations on the environmental conditions are speculated.
NASA Astrophysics Data System (ADS)
Sivakandan, Mani; Patra, Amit; Sripathi, Samireddipelle; Thokuluwa, Ramkumar; Paulino, Igo; Taori, Alok; Kandula, Niranjan
2016-07-01
Equatorial plasma bubble (EPB) occurs in the equatorial ionosphere in pre-mid night (most of the time) as well as post-midnight (rarely) hours. The generation of EPBs by Rayleigh-Taylor Instability (RTI) due to seeding of gravity wave perturbation (polarization electric field) have well been explained theoretically by several authors but experimental evidence supporting this hypothesis is very limited. Using co-located observations from Gadanki (13.5oN, 79.2o E) using an all sky airglow imager and Gadanki Ionospheric Radar Interferometer (GIRI) and Ionosonde observations from Tirunelveli (8.7o N, 77.8o E), we investigate the role of gravity waves in the generation EPB during geomagnetic quiet conditions. To avoid any changes occurring in the background ionosphere owing to the large scale features (e.g., seasonal variation), we use four consecutive nights (03-06, February, 2014). Out of these four nights on two nights we have noted very strong plasma depletions in the OI 630 nm airglow emission and radar plumes. We analyse data to identify cases where, 1) EPBs occurred with large amplitudes of mesospheric gravity waves, 2) Occurrence of EPBs without large amplitudes of mesospheric gravity waves, and 3) identifiable mesospheric gravity waves without occurrence of EPBs. In order to calculate the mesospheric gravity wave parameter we used mesospheric OH airglow emission imager data, to identify their propagation to the E-region, we used E-region observations made using the MST radar which resembled the gravity wave signatures. Together with these, by using ray tracing techniques, we have identified the source region of the noted gravity wave events also. These results are discussed in detail in the present study.
The role of gravity waves in solar-terrestrial atmosphere coupling and severe storm detection
NASA Technical Reports Server (NTRS)
Hung, R. J.; Smith, R. E.
1979-01-01
The role that gravity waves play in the coupling of the solar wind and the ionosphere, the coupling of high and low latitude ionospheres, and the coupling of the ionosphere and the neutral atmosphere are discussed. Examples are given of the detection of tornado touchdowns from locating the sources of the gravity waves.
Effect of gravity wave temperature variations on homogeneous ice nucleation
NASA Astrophysics Data System (ADS)
Dinh, Tra; Podglajen, Aurélien; Hertzog, Albert; Legras, Bernard; Plougonven, Riwal
2015-04-01
Observations of cirrus clouds in the tropical tropopause layer (TTL) have shown various ice number concentrations (INC) (e.g., Jensen et al. 2013), which has lead to a puzzle regarding their formation. In particular, the frequently observed low numbers of ice crystals seemed hard to reconcile with homogeneous nucleation knowing the ubuquity of gravity waves with vertical velocity of the order of 0.1 m/s. Using artificial time series, Spichtinger and Krämer (2013) have illustrated that the variation of vertical velocity during a nucleation event could terminate it and limit the INC. However, their study was limited to constructed temperature time series. Here, we carry out numerical simulations of homogeneous ice nucleation forced by temperature time series data collected by isopycnic balloon flights near the tropical tropopause. The balloons collected data at high frequency (30 s), so gravity wave signals are well resolved in the temperature time series. With the observed temperature time series, the numerical simulations with homogeneous freezing show a full range of ice number concentrations (INC) as previously observed in the tropical upper troposphere. The simulations confirm that the dynamical time scale of temperature variations (as seen from observations) can be shorter than the nucleation time scale. They show the existence of two regimes for homogeneous ice nucleation : one limited by the depletion of water vapor by the nucleated ice crystals (those we name vapor events) and one limited by the reincrease of temperature after its initial decrease (temperature events). Low INC may thus be obtained for temperature events when the gravity wave perturbations produce a non-persistent cooling rate (even with large magnitude) such that the absolute change in temperature remains small during nucleation. This result for temperature events is explained analytically by a dependence of the INC on the absolute drop in temperature (and not on the cooling rate). This
Modeling the QBO and SAO Driven by Gravity Waves
NASA Technical Reports Server (NTRS)
Mayr, H. G.; Mengel, J. G.; Chan, K. L.; Porter, H. S.
1999-01-01
Hines' Doppler spread parameterization (DSP) for small scale gravity waves (GW) is applied in a global scale numerical spectral model (NSM) to describe the semi-annual and quasi-biennial oscillations (SAO and QBO) as well as the long term interannual variations that are driven by wave mean flow interactions. This model has been successful in simulating the salient features observed near the equator at altitudes above 20 km, including the QBO extension into the upper mesosphere inferred from UARS measurements. The model has now been extended to describe also the mean zonal and meridional circulations of the upper troposphere and lower stratosphere that affect the equatorial QBO and its global scale extension. This is accomplished in part through tuning of the GW parameterization, and preliminary results lead to the following conclusions: (1) To reproduce the upwelling at equatorial latitudes associated with the Brewer/Dobson circulation that in part is modulated in the model by the vertical component of the Coriolis force, the eddy diffusivity in the lower stratosphere had to be enhanced and the related GW spectrum modified to bring it in closer agreement with the form recommended for the DSP. (2) To compensate for the required increase in the diffusivity, the observed QBO requires a larger GW source that is closer to the middle of the range recommended for the DSP. (3) Through global scale momentum redistribution, the above developments are conducive to extending the QBO and SAO oscillations to higher latitudes. Multi-year interannual oscillations are generated through wave filtering by the solar driven annual oscillation in the zonal circulation. (4) In a 3D version of the model, wave momentum is absorbed and dissipated by tides and planetary waves. Thus, a somewhat larger GW source is required to generate realistic amplitudes for the QBO and SAO.
Ray Tracing Modeling of Gravity Wave Propagation and Dissipation
NASA Astrophysics Data System (ADS)
Vadas, Sharon; Crowley, Geoff
In this paper, we describe a ray trace model which calculates the wavevector, location and phase of a gravity wave (GW) as it propagates in the lower atmosphere and thermosphere. If used for a discreet transient source (such as a deep convective plume), we describe how this model can calculate the body forcing and the heat/cooling that are created when the GWs within a wave packet dissipate in the thermosphere from kinematic viscosity and thermal diffusivity. Although the body force calculation requires only the divergence of the momentum flux, the heat/cooling calculation requires the reconstructed GW field (e.g., density, velocity perturbations), which in turn requires the GW dissipative polarization relations. We describe these relations. We then describe the results of a recent study involving GWs identified from TIDDBIT HF Doppler sounder data taken at Wallops Island, VI, USA. Using this ray trace model, we determine if the unusual neutral wind profile measured by a rocket experiment at high altitudes (~290-370 km) could have been caused by the propagation and dissipation of several waves observed by TIDDBIT at lower altitudes.
Study of internal gravity waves in the meteor zone
NASA Technical Reports Server (NTRS)
Gavrilov, N. M.
1987-01-01
An important component of the dynamical regime of the atmosphere at heights near 100 km are internal gravity waves (IGW) with periods from about 5 min to about 17.5 hrs which propagate from the lower atmospheric layers and are generated in the uppermost region of the atmosphere. As IGW propagate upwards, their amplitudes increase and they have a considerable effect on upper atmospheric processes: (1) they provide heat flux divergences comparable with solar heating; (2) they influence the gaseous composition and produce wave variations of the concentrations of gaseous components and emissions of the upper atmosphere; and (3) they cause considerable acceleration of the mean stream. It was concluded that the periods, wavelengths, amplitudes and velocities of IGW propagation in the meteor zone are now measured quite reliably. However, for estimating the influence of IGW on the thermal regime and the circulation of the upper atmosphere these parameters are not as important as the values of wave fluxes of energy, heat, moment and mass.
Smoothed-particle-hydrodynamics modeling of dissipation mechanisms in gravity waves.
Colagrossi, Andrea; Souto-Iglesias, Antonio; Antuono, Matteo; Marrone, Salvatore
2013-02-01
The smoothed-particle-hydrodynamics (SPH) method has been used to study the evolution of free-surface Newtonian viscous flows specifically focusing on dissipation mechanisms in gravity waves. The numerical results have been compared with an analytical solution of the linearized Navier-Stokes equations for Reynolds numbers in the range 50-5000. We found that a correct choice of the number of neighboring particles is of fundamental importance in order to obtain convergence towards the analytical solution. This number has to increase with higher Reynolds numbers in order to prevent the onset of spurious vorticity inside the bulk of the fluid, leading to an unphysical overdamping of the wave amplitude. This generation of spurious vorticity strongly depends on the specific kernel function used in the SPH model.
FFT and Wavelet analysis for the study of gravity wave activity over a modeled hurricane environment
NASA Astrophysics Data System (ADS)
Kuester, M. A.; Alexander, J.; Ray, E.
2005-12-01
Understanding of gravity waves and their sources are important for driving global circulations in climate and weather forecasting models. Temperature fluctuations associated with gravity waves near the tropopause also affect cirrus cloud formation, which is important to the study of radiative forcing in the atmosphere. Deep convection is believed to be a major source for these waves and hurricanes may be particularly long-lived and intense sources. Simulations of Hurricane Humberto have been studied using the Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) fifth-generation Mesoscale Model (MM5). Humberto is simulated at both tropical storm and hurricane stages. Information about gravity waves and their sources can be inferred from horizontal wind and temperature variances in the troposphere and lower stratosphere. Both Fast Fourier Transform (FFT) and Wavelet analyses are employed to investigate wave properties and behavior in the lower stratosphere. FFT analysis gives an overall view of storm affects while Wavelet analysis gives a local picture of gravity wave activity. It is found that a hurricane can be a significant source of deep heating which actively triggers gravity waves from the hot tower region of the storm eye wall. Convectively generated gravity waves are observed in the lower stratosphere of this model with horizontal scales of 10-250 km, vertical scales around 5 km and with intrinsic periods of approximately 20 minutes. Some specific characteristics of gravity waves found above the storm will be presented along with further discussion from the wave activity observed with the model. Deep convection over the oceans is thought to play a key role in atmospheric forcing via the creation of vertically propagating gravity waves and hurricane induced gravity waves may play a role in stratospheric forcing during the hurricane season.
Evidence of a saturated gravity-wave spectrum throughout the atmosphere
NASA Technical Reports Server (NTRS)
Fritts, D. C.; Smith, S. A.
1986-01-01
The view adapted here is that the dominant mesoscale motions are due to internal gravity waves and show that previous and new vertical wave number spectra of horizontal winds are consistent with the notion of a saturation limit on wave amplitudes. It is also proposed that, at any height, only those vertical wave numbers m less than m sub asterisk are at saturation amplitudes, where m sub asterisk is the vertical wave number of the dominant energy-containing scale. Wave numbers m less than m sub asterisk are unsaturated, but experience growth with height due to the decrease of atmospheric density. The result is a saturated spectrum of gravity waves with both m sub asterisk decreasing and wave energy increasing with height. This saturation theory is consistent with a variety of atmospheric spectral observations and provides a basis for the notion of a universal spectrum of atmospheric gravity waves.
Gravity wave-induced variability of the middle thermosphere
NASA Astrophysics Data System (ADS)
Forbes, Jeffrey M.; Bruinsma, Sean L.; Doornbos, Eelco; Zhang, Xiaoli
2016-07-01
Contemporary theory, modeling, and first-principles simulations indicate that dissipation of gravity waves (GW) plays an important role in modifying the mean circulation, thermal structure, and composition of the thermosphere. GW can propagate into the thermosphere from various sources in the lower atmosphere, deposit energy, and momentum into the thermosphere, and thereby modify its mean circulation, thermal structure and composition. However, measurements that verify or constrain predictions of GW propagation well into the thermosphere, especially on a global basis, are extremely limited. In this paper total mass densities and cross-track winds between 230 and 280 km derived from accelerometer measurements on the Gravity Field and Ocean Circulation Earth Explorer (GOCE) satellite between November 2009 and October 2013 are used to reveal the global morphology of horizontal structures between 128 km and 640 km, which are assumed to mainly reflect the presence of GW. The zonal-mean RMS variability at these scales is quantified in terms of seasonal-latitudinal dependences and dawn-dusk differences, which are interpreted in terms of current theoretical and modeling results. Little evidence is found for any longitude variability that can be attributed to specific source regions, except at high latitudes where polar/auroral sources and magnetic control dominate and near the Andes and the Antarctic Peninsula during local winter.
Holographic p-wave superfluid in Gauss-Bonnet gravity
NASA Astrophysics Data System (ADS)
Liu, Shancheng; Pan, Qiyuan; Jing, Jiliang
2017-02-01
We construct the holographic p-wave superfluid in Gauss-Bonnet gravity via a Maxwell complex vector field model and investigate the effect of the curvature correction on the superfluid phase transition in the probe limit. We obtain the rich phase structure and find that the higher curvature correction hinders the condensate of the vector field but makes it easier for the appearance of translating point from the second-order transition to the first-order one or for the emergence of the Cave of Winds. Moreover, for the supercurrents versus the superfluid velocity, we observe that our results near the critical temperature are independent of the Gauss-Bonnet parameter and agree well with the Ginzburg-Landau prediction.
Precession resonance mechanism in deep-water gravity surface waves
NASA Astrophysics Data System (ADS)
Bustamante, Miguel; Lucas, Dan
2016-11-01
Discovered by Bustamante et al. in 2014 and published in Phys. Rev. Lett. in the same year, precession resonance is a mechanism whereby strong nonlinear energy transfers occur between modes of oscillations whose frequencies are detuned: the amplitude-dependent precession frequencies of the phases help restore the resonance, hence the name "precession resonance". After explaining how this mechanism works and how robust it is, we will discuss new applications of this effect in systems of technological interest, focusing on deep-water gravity surface waves. We report transfer efficiencies of up to 40%, depending on the numerical-experimental setup. All evidence gathered so far points to the conclusion that, to leading order, this effect is dominated by triad interactions at small (but finite) amplitudes. Joint work with Dan Lucas (DAMTP, Cambridge). Financially supported by Science Foundation Ireland (SFI) under research Grant No. 12/IP/1491.
NASA Astrophysics Data System (ADS)
McKenzie, J. F.; Doyle, T. B.
2010-01-01
This letter reports on the important features of an analysis of the combined theory of gravity - inertial - Rossby waves on a β-plane in the Boussinesq approximation. In particular, it is shown that the coupling between higher frequency gravity - inertial waves and lower frequency Rossby waves, arising from the accumulated influences of the β effect, stratification characterized by the Väisäla - Brunt frequency N, the Coriolis frequency f, and the component of vertical propagation wave number kz , may lead to an unstable coupling between buoyancy - inertial modes with westward propagating Rossby waves. “Supersonic” fast rotators (such as Jupiter) are predicted to be unstable in a fairly narrow band of latitudes around their equators. The Earth is moderately supersonic and exhibits instability within about 34° of its equator. Slow “subsonic” rotators (e.g. Mercury, Venus, and the Sun's corona) are unstable at all latitudes except those very close to the poles where the β effect vanishes.
NASA Technical Reports Server (NTRS)
Fritts, David C.
2004-01-01
The specific objectives of this research effort included the following: 1) Quantification of gravity wave propagation throughout the lower and middle atmosphere in order to define the roles of topographic and convective sources and filtering by mean and low-frequency winds in defining the wave field and wave fluxes at greater altitudes; 2) The influences of wave instability processes in constraining wave amplitudes and fluxes and generating turbulence and transport; 3) Gravity wave forcing of the mean circulation and thermal structure in the presence of variable motion fields and wave-wave interactions, since the mean forcing may be a small residual when wave interactions, anisotropy, and momentum and heat fluxes are large; 4) The statistical forcing and variability imposed on the thermosphere at greater altitudes by the strong wave forcing and interactions occurring in the MLTI.
Gravity wave motions and momentum fluxes in the middle atmosphere at Adelaide, Australia
NASA Technical Reports Server (NTRS)
Vincent, R. A.; Fritts, D. C.
1985-01-01
A study was made of gravity wave momentum fluxes in the middle atmosphere using data collected during June 1984 at Adelaide, Australia (35 deg S). The primary objectives were to identify that portion of the gravity wave spectrum that contributes most of the momentum transport and flux divergence and to examine the temporal variability of wave energies and momentum fluxes. The data were obtained with an HF (2 MHz) radar operated in a Doppler configuration with two coplanar off-vertical beams. This technique provides a direct measure of the vertical flux of horizontal momentum due to an arbitrary spectrum of gravity wave and other motions in the plane of the radar beams.
NASA Technical Reports Server (NTRS)
Pfister, Leonhard; Chan, Kwoklong R.; Gary, Bruce; Singh, Hanwant B. (Technical Monitor)
1995-01-01
The advent of high altitude aircraft measurements in the stratosphere over tropical convective systems has made it possible to observe the mesoscale disturbances in the temperature field that these systems excite. Such measurements show that these disturbances have horizontal scales comparable to those of the underlying anvils (about 50-100 km) with peak to peak theta surface variations of about 300-400 meters. Moreover, correlative wind measurements from the tropical phase of the Stratosphere-Troposphere Exchange Project (STEP) clearly show that these disturbances are gravity waves. We present two case studies of anvil-scale gravity waves over convective systems. Using steady and time-dependent linear models of gravity wave propagation in the stratosphere, we show: (1) that the underlying convective systems are indeed the source of the observed phenomena; and (2) that their generating mechanism can be crudely represented as flow over a time-dependent mountain. We will then discuss the effects gravity waves of the observed amplitudes have on the circulation of the middle atmosphere, particularly the quasi-biennial, and semiannual oscillations.
NASA Astrophysics Data System (ADS)
Brissaud, Quentin; Garcia, Raphael; Martin, Roland; Komatitsch, Dimitri; Sladen, Anthony
2016-04-01
Acoustic and gravity waves propagating in planetary atmospheres have been studied intensively as markers of specific phenomena (tectonic events, explosions) or as contributors to atmosphere dynamics. To get a better understanding of the physics behind these dynamic processes, both acoustic and gravity waves propagation should be modeled in an attenuating and windy 3D atmosphere from the ground all the way to the upper thermosphere. Thus, in order to provide an efficient numerical tool at the regional or global scale we introduce a high-order finite- difference time domain (FDTD) approach that relies on the linearized compressible Navier-Stokes equations with non constant physical parameters (density, viscosities and speed of sound) and background velocities (wind). We present applications of these simulations to the propagation of gravity waves generated by tsunamis for realistic cases for which atmospheric models are extracted from empirical models including 3D variations of atmospheric parameters, and tsunami forcing at the ocean surface is extracted from finite-fault dislocation simulations. We describe the specific difficulties induced by the size of the simulation, the boundary conditions and the spherical geometry and compare the simulation outputs to data gathered by gravimetric satellites crossing gravity waves generated by tsunamis.
Gravity Wave Disturbances in the F-Region Ionosphere Above Large Earthquakes
NASA Astrophysics Data System (ADS)
Bruff, Margie
The direction of propagation, duration and wavelength of gravity waves in the ionosphere above large earthquakes were studied using data from the Super Dual Auroral Radar Network. Ground scatter data were plotted versus range and time to identify gravity waves as alternating focused and de-focused regions of radar power in wave-like patterns. The wave patterns before and after earthquakes were analyzed to determine the directions of propagation and wavelengths. Conditions were considered 48 hours before and after each identified disturbances to exclude waves from geomagnetic activity. Gravity waves were found travelling away from the epicenter before all six earthquakes for which data were available and after four of the six earthquakes. Gravity waves travelled in at least two directions away from the epicenter in all cases, and even stronger patterns were found for two earthquakes. Waves appeared, on average, 4 days before, persisting 2-3 hours, and 1-2 days after earthquakes, persisting 4-6 hours. Most wavelengths were between 200-300 km. We show a possible correlation between magnitude and depth of earthquakes and gravity wave patterns, but study of more earthquakes is required. This study provides a better understanding of the causes of ionospheric gravity wave disturbances and has potential applications for predicting earthquakes.
Wave Driven Non-linear Flow Oscillator for the 22-Year Solar Cycle
NASA Technical Reports Server (NTRS)
Mayr, Hans G.; Wolff, Charles L.; Hartle, Richard E.; Einaudi, Franco (Technical Monitor)
2000-01-01
In the Earth's atmosphere, a zonal flow oscillation is observed with periods between 20 and 32 months, the Quasi Biennial Oscillation. This oscillation does not require external time dependent forcing but is maintained by non-linear wave momentum deposition. It is proposed that such a mechanism also drives long-period oscillations in planetary and stellar interiors. We apply this mechanism to generate a flow oscillation for the 22-year solar cycle. The oscillation would occur just below the convective envelope where waves can propagate. Using scale analysis, we present results from a simplified model that incorporates Hines' gravity wave parameterization. Wave amplitudes less than 10 m/s can produce reversing zonal flows of 25 m/s that should be sufficient to generate a corresponding oscillation in the poloidal magnetic field. Low buoyancy frequency and the associated increase in turbulence help to produce the desired oscillation period of the flow.
NASA Technical Reports Server (NTRS)
Shelton, J. D.; Gardner, C. S.
1981-01-01
The density response of atmospheric layers to gravity waves is developed in two forms, an exact solution and a perturbation series solution. The degree of nonlinearity in the layer density response is described by the series solution whereas the exact solution gives insight into the nature of the responses. Density perturbation in an atmospheric layer are shown to be substantially greater than the atmospheric density perturbation associated with the propagation of a gravity wave. Because of the density gradients present in atmospheric layers, interesting effects were observed such as a phase reversal in the linear layer response which occurs near the layer peak. Once the layer response is understood, the sodium layer can be used as a tracer of atmospheric wave motions. A two dimensional digital signal processing technique was developed. Both spatial and temporal filtering are utilized to enhance the resolution by decreasing shot noise by more han 10 dB. Many of the features associated with a layer density response to gravity waves were observed in high resolution density profiles of the mesospheric sodium layer. These include nonlinearities as well as the phase reversal in the linear layer response.
Linearized f(R) gravity: Gravitational radiation and Solar System tests
Berry, Christopher P. L.; Gair, Jonathan R.
2011-05-15
We investigate the linearized form of metric f(R)-gravity, assuming that f(R) is analytic about R=0 so it may be expanded as f(R)=R+a{sub 2}R{sup 2}/2+.... Gravitational radiation is modified, admitting an extra mode of oscillation, that of the Ricci scalar. We derive an effective energy-momentum tensor for the radiation. We also present weak-field metrics for simple sources. These are distinct from the equivalent Kerr (or Schwarzschild) forms. We apply the metrics to tests that could constrain f(R). We show that light deflection experiments cannot distinguish f(R)-gravity from general relativity as both have an effective post-Newtonian parameter {gamma}=1. We find that planetary precession rates are enhanced relative to general relativity; from the orbit of Mercury we derive the bound |a{sub 2}| < or approx. 1.2x10{sup 18} m{sup 2}. Gravitational-wave astronomy may be more useful: considering the phase of a gravitational waveform we estimate deviations from general relativity could be measurable for an extreme-mass-ratio inspiral about a 10{sup 6}M{sub {center_dot}} black hole if |a{sub 2}| > or approx. 10{sup 17}m{sup 2}, assuming that the weak-field metric of the black hole coincides with that of a point mass. However Eoet-Wash experiments provide the strictest bound |a{sub 2}| < or approx. 2x10{sup -9} m{sup 2}. Although the astronomical bounds are weaker, they are still of interest in the case that the effective form of f(R) is modified in different regions, perhaps through the chameleon mechanism. Assuming the laboratory bound is universal, we conclude that the propagating Ricci scalar mode cannot be excited by astrophysical sources.
Horizontal propagation of Gravity Waves in the ionosphere
NASA Astrophysics Data System (ADS)
Chum, J.; Base, J.; Hruska, F.; Buresova, D.; McKinnell, L. A.; Athieno, R.
2010-12-01
Using a multi-point Continuous Doppler sounding system we investigate propagation directions and velocities of Gravity Waves (GWs) in the ionosphere at altitudes from ~150 km to ~250 km. The velocities and directions are computed from the time delays between the observations of corresponding GWs at different reflection points that correspond to various sounding paths. We focused on the GWs that produce an S-shaped trace in Doppler shift spectrograms since it is know that these patterns are formed if the disturbances (waves) mainly propagate in the horizontal plane. The S-shaped signatures also make it possible to estimate the errors of measurements. The system that we used was developed in the Institute of Atmospheric Physics, Czech Republic and has been operated in the western part of the Czech Republic. A statistical study based on the analysis of about 100 events during the last solar minimum show that the analyzed GWs propagate with typical horizontal velocities from ~100 to ~200 m/s. The north-south component of GW velocities depends on the season and/or daytime. At the same time, it has an opposite sign than the north-south component of neutral winds calculated by the HWM07 model. A similar system was also installed in the South Africa, close to Cape Town at the end of May 2010. The first results of the observation of GW propagation in the ionosphere over the South Africa will also be presented.
Mass Distribution in Plumes: constraints from gravity waves
NASA Astrophysics Data System (ADS)
Sacks, S. I.; Baines, P. G.
2012-12-01
The Soufriere Hills volcano on Montserrat Island in the Caribbean has been active for more than 15 years. A small network, consisting of 4 sites, 5 - 10 km distant from the Soufriere Hills Volcano, was installed early in 2003. Each site has borehole strainmeters as well as micro-barographs and gave clear data from all volcanic events. A number of vulcanian explosions followed the major dome collapse on 13th July, 2003 and have continued until at least January 2008.. The plumes from these fragmentation events gave rise to an ~800 second period atmospheric pressure signal of 20 - 50 pascal amplitude propagating at about 30 m/sec. The onset is rarefaction. The data are consistent with a gravity wave confined to the troposphere. Note that plumes penetrating the stratosphere have a very different air pressure character. Initial modeling indicated that the coda of these waves was sensitive to the mass distribution in the plume. Since only the data beyond about 1000 seconds are found to yield information about mass distribution, we can use a simple impulsive source. The data, and particularly the coda, are best satisfied if most of the effective mass is at mid-plume, with reduced amounts near the surface and high in the troposphere. This suggests that the heavier ash particles fall as the plume rises. Since particle size impacts the event's hazard, this type of observation may have predictive capability.
Long-term Global Morphology of Gravity Wave Activity Using UARS Data
NASA Technical Reports Server (NTRS)
Eckermann, Stephen D.; Jackman, C. (Technical Monitor)
2000-01-01
An extensive body of research this quarter is documented. Further methodical analysis of temperature residuals in Cryogenic Limb Array Etalon Spectrometer (CLAES) Version 8 level 3AT data show signatures during December 1992 at middle and high northern latitudes that, when compared to Naval Research Laboratory/Mountain Wave Forecast Model (NRL)/(MWFM) mountain wave hindcasts, reveal evidence of long mountain waves in these data over Eurasia, Greenland, Scandinavia and North America. The explicit detection of gravity waves in limb-scanned Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) temperatures is modeled at length, to derive visibility functions. These insights are used to convert CRISTA gravity wave temperature residuals into data that more closely resemble gravity wave fluctuations detected in data from other satellite instruments, such as Microwave Limb Sounder (MLS), Limb Infrared Monitor of the Stratosphere (LIMS) and Global Positioning System/Meteorology (GPS)/(MET). Finally, newly issued mesospheric temperatures from inversion of CRISTA 15gin emissions are analyzed using a new method that uses separate Kalman fits to the ascending and descending node data. This allows us to study global gravity wave amplitudes at two local times, 12 hours apart. In the equatorial mesosphere, where a large diurnal tidal temperature signal exists, we see modulations of gravity wave activity that are consistent with gravity wave-tidal interactions produced by tidal temperature variability.
NASA Astrophysics Data System (ADS)
Borchert, Sebastian; Achatz, Ulrich; Rieper, Felix; Fruman, Mark
2013-04-01
We use a numerical model of the classic differentially heated rotating annulus experiment to study the spontaneous emission of gravity waves (GWs) from jet stream imbalances, which is a major source of these waves in the atmosphere for which no satisfactory parameterization exists. Atmospheric observations are the main tool for the testing and verification of theoretical concepts but have their limitations. Given their specific potential for yielding reproducible data and for studying process dependence on external system parameters, laboratory experiments are an invaluable complementary tool. Experiments with a rotating annulus exhibiting a jet modulated by large-scale waves due to baroclinic instability have already been used to study GWs: Williams et al (2008) observed spontaneously emitted interfacial GWs in a two-layer flow, and Jacoby et al (2011) detected GWs emitted from boundary-layer instabilities in a differentially heated rotating annulus. Employing a finite-volume code for the numerical simulation of a continuously stratified liquid in a differentially heated rotating annulus, we here investigate the GWs in a wide and shallow annulus with relatively large temperature difference between inner and outer cylinder walls. In this atmosphere-like regime where the Brunt-Vaisala frequency is larger than the inertial frequency, various analyses suggest a distinct gravity wave activity. To identify regions of GW emission we decompose the flow into the geostrophic and ageostrophic part through the inversion of the quasi-geostrophic potential vorticity (e.g. Verkley, 2009). The analysis of the geostrophic sources of the ageostrophic flow indicates that, in addition to boundary layer instabilities, spontaneous imbalance in the jet region acts as an important source mechanism. Jacoby, T. N. L., Read, P. L., Williams, P. D. and Young, R. M. B., 2011: Generation of inertia-gravity waves in the rotating thermal annulus by a localised boundary layer instability. Geophys
Linear connections with a propagating spin-3 field in gravity
Baekler, Peter; Boulanger, Nicolas; Hehl, Friedrich W.
2006-12-15
We show that Fronsdal's Lagrangian for a free massless spin-3 gauge field in Minkowski spacetime is contained in a general Yang-Mills-like Lagrangian of metric-affine gravity (MAG), the gauge theory of the general affine group in the presence of a metric. Because of the geometric character of MAG, this can best be seen by using Vasiliev's frame formalism for higher-spin gauge fields in which the spin-3 frame is identified with the tracefree nonmetricity one-form associated with the shear generators of GL(n,R). Furthermore, for specific gravitational gauge models in the framework of full nonlinear MAG, exact solutions are constructed, featuring propagating massless and massive spin-3 fields.
Using a new algorithm to track mixed-Rossby gravity waves (MRG) waves in reanalysis data
NASA Astrophysics Data System (ADS)
Au-Yeung, A. Y. M.; Tam, C. Y.
2015-12-01
A new algorithm has been developed to track westward travelling mixed-Rossby gravity waves (MRG) waves in the western Pacific based on the theoretical meridional wind structure stated in the shallow water equation (SWE) solutions. Applied to space-time filtered (period=3 to 8 days and wavenumber =-20 to 0), asymmetric meridional wind data at the 850hPa level from the NCEP CFS reanalysis, the algorithm finds locations with Gaussian-shaped meridional wind structure stated in SWE solutions through space and time. Two groups of MRG waves were found: one with higher wavenumber (11) and another one with lower-wavenumber (6). Moreover, the MRG waves show very different dispersive properties and occurrence behavior in the western and eastern equatorial Pacific. While both groups appear in the western Pacific, mainly 6 waves were found in the eastern Pacific. The fact that both 6 and 11 waves appear in the western Pacific agrees with past discussions on the co-existence of MRG waves and tropical-disturbance type (TD-type) waves. Also, the high wavenumber wave activities mainly appear west of the dateline, meaning that some triggering process may have taken place there. Northwestward wave train movement was found west of 140E in the low-level wind composites. On the other hand, negative correlation between meridional wind and temperature (negative) found in the vertical composites indicates downward vertical wave activity flux prior to the occurrences of MRG waves. Finally, in the western Pacific, kinetic energy energetics suggests that energy source of transient eddies is from the confluent background flow and also the zonal wind shear terms in the western Pacific. Overall, our method provides a way to identify the MRG waves instantaneously; in contrast, most of the methods employed in the past (e.g., spectral analysis or lag correlation/regression) are based on aggregates of data and they can only examine wave properties averaged over a certain period of time. Since MRG
Analysis of non linear partially standing waves from 3D velocity measurements
NASA Astrophysics Data System (ADS)
Drevard, D.; Rey, V.; Svendsen, Ib; Fraunie, P.
2003-04-01
Surface gravity waves in the ocean exhibit an energy spectrum distributed in both frequency and direction of propagation. Wave data collection is of great importance in coastal zones for engineering and scientific studies. In particular, partially standing waves measurements near coastal structures and steep or barred beaches may be a requirement, for instance for morphodynamic studies. The aim of the present study is the analysis of partially standing surface waves icluding non-linear effects. According to 1st order Stokes theory, synchronous measurements of horizontal and vertical velocity components allow calculation of rate of standing waves (Drevard et al, 2003). In the present study, it is demonstrated that for deep water conditions, partially standing 2nd order Stokes waves induced velocity field is still represented by the 1st order solution for the velocity potential contrary to the surface elevation which exhibits harmonic components. For intermediate water depth, harmonic components appear not only in the surface elevation but also in the velocity fields, but their weight remains much smaller, because of the vertical decreasing wave induced motion. For irregular waves, the influence of the spectrum width on the non-linear effects in the analysis is discussed. Keywords: Wave measurements ; reflection ; non-linear effects Acknowledgements: This work was initiated during the stay of Prof. Ib Svendsen, as invited Professor, at LSEET in autumn 2002. This study is carried out in the framework of the Scientific French National Programmes PNEC ART7 and PATOM. Their financial supports are acknowledged References: Drevard, D., Meuret, A., Rey, V. Piazzola, J. And Dolle, A.. (2002). "Partially reflected waves measurements using Acoustic Doppler Velocimeter (ADV)", Submitted to ISOPE 03, Honolulu, Hawaii, May 2003.
Satellite radio occultation investigations of internal gravity waves in the planetary atmospheres
NASA Astrophysics Data System (ADS)
Kirillovich, Ivan; Gubenko, Vladimir; Pavelyev, Alexander
Internal gravity waves (IGWs) modulate the structure and circulation of the Earth’s atmosphere, producing quasi-periodic variations in the wind velocity, temperature and density. Similar effects are anticipated for the Venus and Mars since IGWs are a characteristic of stably stratified atmosphere. In this context, an original method for the determination of IGW parameters from a vertical temperature profile measurement in a planetary atmosphere has been developed [Gubenko et al., 2008, 2011, 2012]. This method does not require any additional information not contained in the profile and may be used for the analysis of profiles measured by various techniques. The criterion for the IGW identification has been formulated and argued. In the case when this criterion is satisfied, the analyzed temperature fluctuations can be considered as wave-induced. The method is based on the analysis of relative amplitudes of the wave field and on the linear IGW saturation theory in which these amplitudes are restricted by dynamical (shear) instability processes in the atmosphere. When the amplitude of an internal wave reaches the shear instability threshold, energy is assumed to be dissipated in such a way that the IGW amplitude is maintained at the instability threshold level as the wave propagates upwards. We have extended the developed technique [Gubenko et al., 2008] in order to reconstruct the complete set of wave characteristics including such important parameters as the wave kinetic and potential energy per unit mass and IGW fluxes of the energy and horizontal momentum [Gubenko et al., 2011]. We propose also an alternative method to estimate the relative amplitudes and to extract IGW parameters from an analysis of perturbations of the Brunt-Vaislala frequency squared [Gubenko et al., 2011]. An application of the developed method to the radio occultation (RO) temperature data has given the possibility to identify the IGWs in the Earth's, Martian and Venusian atmospheres and
NASA Astrophysics Data System (ADS)
Preusse, Peter; Eckermann, Stephen D.; Offermann, Dirk
2000-12-01
Gravity wave temperature fluctuations acquired by the CRISTA instrument are compared to previous estimates of zonal-mean gravity wave temperature variance inferred from the LIMS, MLS and GPS/MET satellite instruments during northern winter. Careful attention is paid to the range of vertical wavelengths resolved by each instrument. Good agreement between CRISTA data and previously published results from LIMS, MLS and GPS/MET are found. Key latitudinal features in these variances are consistent with previous findings from ground-based measurements and some simple models. We conclude that all four satellite instruments provide reliable global data on zonal-mean gravity wave temperature fluctuations throughout the middle atmosphere.
An Investigation of a Gravity Wave during GALE: 6 February 1986
1990-01-01
1967: The critical layer for internal gravity waves in a shear flow. J. Fluid Mech., 27, 513-559. Bosart, L . F. and A. Seimon , 1988: A case study of...gravity waves in a shear flow. J. Fluid Mech., 27, 513-559. Bosart, L . F. and A. Seimon , 1988: A case study of an unusually intense gravity wave. Mon...108, 804-816. Barnes, S. L ., 1964: A Technique for maximizing details in numerical weather map analysis. J. Appl. Meteor., 3, 396-409. -,1973
Gravity waves as a probe of the Hubble expansion rate during an electroweak scale phase transition
Chung, Daniel J. H.; Zhou Peng
2010-07-15
Just as big bang nucleosynthesis allows us to probe the expansion rate when the temperature of the Universe was around 1 MeV, the measurement of gravity waves from electroweak scale first order phase transitions may allow us to probe the expansion rate when the temperature of the Universe was at the electroweak scale. We compute the simple transformation rule for the gravity wave spectrum under the scaling transformation of the Hubble expansion rate. We then apply this directly to the scenario of quintessence kination domination and show how gravity wave spectra would shift relative to Laser Interferometer Space Antenna and Big Bang Observer projected sensitivities.
Internal Gravity Waves in the Magnetized Solar Atmosphere. I. Magnetic Field Effects
NASA Astrophysics Data System (ADS)
Vigeesh, G.; Jackiewicz, J.; Steiner, O.
2017-02-01
Observations of the solar atmosphere show that internal gravity waves are generated by overshooting convection, but are suppressed at locations of magnetic flux, which is thought to be the result of mode conversion into magnetoacoustic waves. Here, we present a study of the acoustic-gravity wave spectrum emerging from a realistic, self-consistent simulation of solar (magneto)convection. A magnetic field free, hydrodynamic simulation and a magnetohydrodynamic (MHD) simulation with an initial, vertical, homogeneous field of 50 G flux density were carried out and compared with each other to highlight the effect of magnetic fields on the internal gravity wave propagation in the Sun’s atmosphere. We find that the internal gravity waves are absent or partially reflected back into the lower layers in the presence of magnetic fields and argue that the suppression is due to the coupling of internal gravity waves to slow magnetoacoustic waves still within the high-β region of the upper photosphere. The conversion to Alfvén waves is highly unlikely in our model because there is no strongly inclined magnetic field present. We argue that the suppression of internal waves observed within magnetic flux concentrations may also be due to nonlinear breaking of internal waves due to vortex flows that are ubiquitously present in the upper photosphere and the chromosphere.
NASA Astrophysics Data System (ADS)
Savina, Olga; Bespalov, Peter; Misonova, Vera; Petrov, Kiril
2014-05-01
We examine two mutually complementing tasks related to the theoretical analysis of acoustic-gravity disturbances in the Earth's atmosphere and its influence on magnetosphere processes. Our research is based on modern atmospherical models. We study waves propagation, absorption, and filtration. The atmospheric nonisothermicity is taken into account, for example, by introduction of a two-layered atmosphere temperature model. For a study of more delicate effects, a piecewise-linear model, for which the analytical solution is written by the hypergeometric functions, is employed. Also we consider an influence of acoustic-gravity waves on VLF electromagnetic wave excitation in the magnetosphere. This influence occurs as a result of the following processes: a modulation of the plasma density by acoustic-gravity waves in the ionosphere, a modulation of reflection from the ionosphere for VLF waves, and a modification of the magnetospheric resonator Q-factor for VLF waves. Variation of the magnetospheric resonator Q-factor has an influence on the operation of the plasma magnetospheric maser, where the active substances are radiation belts particles and the working modes are electromagnetic VLF waves (whistler-type waves). The plasma magnetospheric maser can be responsible for an excitation of self-oscillations. These self-oscillations are frequently characterized by alternating stages of accumulation and precipitation of energetic particles into the ionosphere during a pulse of whistler emissions. Numerical and analytical investigations of the response of self-oscillations to harmonic oscillations of the whistler reflection coefficient shows that even a small modulation rate can significantly changes the magnetospheric VLF emissions. Our results can explain the causes of the modulation of energetic electron fluxes and whistler wave intensity with a time scale from 10 to 150 seconds in the day-side magnetosphere. Such quasi-periodic VLF emissions are often observed in the sub
Magnetoelastic shear wave propagation in pre-stressed anisotropic media under gravity
NASA Astrophysics Data System (ADS)
Kumari, Nirmala; Chattopadhyay, Amares; Singh, Abhishek K.; Sahu, Sanjeev A.
2017-02-01
The present study investigates the propagation of shear wave (horizontally polarized) in two initially stressed heterogeneous anisotropic (magnetoelastic transversely isotropic) layers in the crust overlying a transversely isotropic gravitating semi-infinite medium. Heterogeneities in both the anisotropic layers are caused due to exponential variation (case-I) and linear variation (case-II) in the elastic constants with respect to the space variable pointing positively downwards. The dispersion relations have been established in closed form using Whittaker's asymptotic expansion and were found to be in the well-agreement to the classical Love wave equations. The substantial effects of magnetoelastic coupling parameters, heterogeneity parameters, horizontal compressive initial stresses, Biot's gravity parameter, and wave number on the phase velocity of shear waves have been computed and depicted by means of a graph. As a special case, dispersion equations have been deduced when the two layers and half-space are isotropic and homogeneous. The comparative study for both cases of heterogeneity of the layers has been performed and also depicted by means of graphical illustrations.
Perturbations of the Richardson number field by gravity waves
NASA Technical Reports Server (NTRS)
Wurtele, M. G.; Sharman, R. D.
1985-01-01
An analytic solution is presented for a stratified fluid of arbitrary constant Richardson number. By computer aided analysis the perturbation fields, including that of the Richardson number can be calculated. The results of the linear analytic model were compared with nonlinear simulations, leading to the following conclusions: (1) the perturbations in the Richardson number field, when small, are produced primarily by the perturbations of the shear; (2) perturbations of in the Richardson number field, even when small, are not symmetric, the increase being significantly larger than the decrease (the linear analytic solution and the nonlinear simulations both confirm this result); (3) as the perturbations grow, this asymmetry increases, but more so in the nonlinear simulations than in the linear analysis; (4) for large perturbations of the shear flow, the static stability, as represented by N2, is the dominating mechanism, becoming zero or negative, and producing convective overturning; and (5) the convectional measure of linearity in lee wave theory, NH/U, is no longer the critical parameter (it is suggested that (H/u sub 0) (du sub 0/dz) takes on this role in a shearing flow).
NASA Technical Reports Server (NTRS)
Li, Tao; She, C. -Y.; Liu, Han-Li; Leblanc, Thierry; McDermid, I. Stuart
2007-01-01
In December 2004, the Colorado State University sodium lidar system at Fort Collins, Colorado (41 deg N, 105 deg W), conducted an approximately 80-hour continuous campaign for the simultaneous observations of mesopause region sodium density, temperature, and zonal and meridional winds. This data set reveals the significant inertia-gravity wave activities with a period of approximately 18 hours, which are strong in both wind components since UT day 338 (second day of the campaign), and weak in temperature and sodium density. The considerable variability of wave activities was observed with both wind amplitudes growing up to approximately 40 m/s at 95-100 km in day 339 and then decreasing dramatically in day 340. We also found that the sodium density wave perturbation is correlated in phase with temperature perturbation below 90 km, and approximately 180 deg out of phase above. Applying the linear wave theory, we estimated the wave horizontal propagation direction, horizontal wavelength, and apparent horizontal phase speed to be approximately 25 deg south of west, approximately 1800 +/- 150 km, and approximately 28 +/- 2 m/s, respectively of wave intrinsic period, intrinsic phase speed, and vertical wavelength were also estimated. While the onset of enhanced inertia-gravity wave amplitude in the night of 338 was observed to be in coincidence with short-period gravity wave breaking via convective instability, the decrease of inertia-gravity wave amplitude after noon of day 339 was also observed to coincide with the development of atmospheric dynamical instability layers with downward phase progression clearly correlated with the 18-hour inertia-gravity wave, suggesting likely breaking of this inertia-gravity wave via dynamical (shear) instability.
Could linear hysteresis contribute to shear wave losses in tissues?
Parker, Kevin J
2015-04-01
For nearly 100 y in the study of cyclical motion in materials, a particular phenomenon called "linear hysteresis" or "ideal hysteretic damping" has been widely observed. More recently in the field of shear wave elastography, the basic mechanisms underlying shear wave losses in soft tissues are in question. Could linear hysteresis play a role? An underlying theoretical question must be answered: Is there a real and causal physical model that is capable of producing linear hysteresis over a band of shear wave frequencies used in diagnostic imaging schemes? One model that can approximately produce classic linear hysteresis behavior, by examining a generalized Maxwell model with a specific power law relaxation spectrum, is described here. This provides a theoretical plausibility for the phenomenon as a candidate for models of tissue behavior.
Gravity Wave Variances and Propagation Derived from AIRS Radiances
NASA Technical Reports Server (NTRS)
Gong, Jie; Wu, Dong L.; Eckermann, S. D.
2012-01-01
As the first gravity wave (GW) climatology study using nadir-viewing infrared sounders, 50 Atmospheric Infrared Sounder (AIRS) radiance channels are selected to estimate GW variances at pressure levels between 2-100 hPa. The GW variance for each scan in the cross-track direction is derived from radiance perturbations in the scan, independently of adjacent scans along the orbit. Since the scanning swaths are perpendicular to the satellite orbits, which are inclined meridionally at most latitudes, the zonal component of GW propagation can be inferred by differencing the variances derived between the westmost and the eastmost viewing angles. Consistent with previous GW studies using various satellite instruments, monthly mean AIRS variance shows large enhancements over meridionally oriented mountain ranges as well as some islands at winter hemisphere high latitudes. Enhanced wave activities are also found above tropical deep convective regions. GWs prefer to propagate westward above mountain ranges, and eastward above deep convection. AIRS 90 field-of-views (FOVs), ranging from +48 deg. to -48 deg. off nadir, can detect large-amplitude GWs with a phase velocity propagating preferentially at steep angles (e.g., those from orographic and convective sources). The annual cycle dominates the GW variances and the preferred propagation directions for all latitudes. Indication of a weak two-year variation in the tropics is found, which is presumably related to the Quasi-biennial oscillation (QBO). AIRS geometry makes its out-tracks capable of detecting GWs with vertical wavelengths substantially shorter than the thickness of instrument weighting functions. The novel discovery of AIRS capability of observing shallow inertia GWs will expand the potential of satellite GW remote sensing and provide further constraints on the GW drag parameterization schemes in the general circulation models (GCMs).
Precision Pulsar Timing and Gravity Waves: Recent Advances in Instrumentation
NASA Astrophysics Data System (ADS)
Demorest, P.; Ramachandran, R.; Backer, D.; Ferdman, R.; Stairs, I.; Nice, D.
2004-12-01
High-precision pulsar timing is a unique and useful tool for many different scientific applications, including studies of the interstellar medium, relativistic binary systems, and long period gravitational wave studies. Our group has designed and installed a new generation of pulsar instrumentation at several radio observatories over the past year: The Arecibo Signal Processor (ASP), the Green Bank Astronomical Signal Processor (GASP), and the Berkeley-Orleans-Nancay processor (BON). These machines perform real time coherent dedispersion of the pulsar signal on up to 64 MHz of bandwidth, and quasi-real time up to 128 MHz. They use high dynamic range voltage sampling (8 bits), which significantly reduces digitization artifacts. The processing is done in an array of personal computers, which makes the machines extremely flexible for future development. We present preliminary results from several different studies using this new instrumentation. At Green Bank, we have initiated a program of long-term precision timing of 15 pulsars using the 100m Green Bank Telescope. The data from this project will be used to study binary systems, and contribute to the ongoing multi-observatory effort to create a Pulsar Timing Array - a group of many pulsars distributed about the sky which can be used to detect gravitational radiation with a period of 1-10 years. We also have continuous use of a 85ft telescope at Green Bank which we have used to study dispersion measure fluctuations of PSR B1937+21 on timescales of 1 day to several years. These fluctuations are a potential systematic effect for the gravity wave study, and also help us learn more about the nature of interstellar weather.
NASA Astrophysics Data System (ADS)
Borchert, S.; Achatz, U.; Rieper, F.; Fruman, M. D.
2012-04-01
We use a numerical model of the classic differentially heated rotating annulus experiment to study the spontaneous emission of gravity waves (GWs) from jet stream imbalances, which is a major source of these waves in the atmosphere for which no satisfactory parameterization exists. Atmospheric observations are the main tool for the testing and verification of theoretical concepts but have their limitations. Given their specific potential for yielding reproducible data and for studying process dependence on external system parameters, laboratory experiments are an invaluable complementary tool. Experiments with a rotating annulus exhibiting a jet modulated by large-scale waves due to baroclinic instability have already been used to study GWs: Williams et al (2008) observed spontaneously emitted interfacial GWs in a two-layer flow, and Jacoby et al (2011) detected GWs emitted from boundary-layer instabilities in a differentially heated rotating annulus. Employing a new finite-volume code for the numerical simulation of a continuously stratified liquid in a differentially heated rotating annulus, we here investigate whether such an experiment might be useful for studies of spontaneous imbalance. A major problem was the identification of experimental parameters yielding an atmosphere-like regime where the Brunt-Vaisala frequency is larger than the inertial frequency, so that energy transport by the lowest-frequency waves is predominantly horizontal while high-frequency GWs transport energy vertically. We show that this is indeed the case for a wide and shallow annulus with relatively large temperature difference between the inner and outer cylinder walls. We also show that this set-up yields a conspicuous signal in the horizontal divergence field close to the meandering jet. Various analyses support the notion that this signal is predominantly due to GWs superposed on a geostrophic flow. Jacoby, T. N. L., Read, P. L., Williams, P. D. and Young, R. M. B., 2011
NASA Astrophysics Data System (ADS)
Venkat Ratnam, Madineni; Karanam, Kishore Kumar; Sunkara, Eswaraiah; Vijaya Bhaskara Rao, S.; Subrahmanyam, K. V.; Ramanjaneyulu, L.
2016-07-01
Mesosphere and Lower Thermosphere (MLT) mean winds, gravity waves, tidal and planetary wave characteristics are investigated using two years (2013-2015) of advanced meteor radar installed at Tirupathi (13.63oN, 79.4oE), India. The observations reveal the presence of high frequency gravity waves (30-120 minutes), atmospheric tides (diurnal, semi-diurnal and terr-diurnal) along with long period oscillations in both zonal and meridional winds. Background mean zonal winds show clear semi-annual oscillation in the mesosphere, whereas meridional winds are characterized by annual oscillation as expected. Diurnal tide amplitudes are significantly larger (60-80 m/s) than semi-diurnal (10-20 m/s) and terr-diurnal (5-8 m/s) tides and larger in meridional than zonal winds. The measured meridional components are in good agreement with Global Scale Wave Model (GSWM-09) predictions than zonal up to ~90 km in all the seasons, except fall equinox. Diurnal tidal phase matches well than the amplitudes between observations and model predictions. However, no similarity is being found in the semi-diurnal tides between observations and model. The measurements are further compared with nearby Thumba meteor radar (8.5oN, 77oE) observations. Some differences do exist between the measurements from Tirupati and Thumba meteor radar and model outputs at greater heights and the possible reasons are discussed. SVU meteor radar observations clearly showed the dominance of well-known ultra-fast kelvin waves (3.5 days), 5-8 day, 16 day, 27 day, and 30-40 day oscillations. Due to higher meteor count extending up to 110 km, we could investigate the variability of these PWs and oscillations covering wider range (70-110 km) for the first time. Significant change above 100 km is noticed in all the above mentioned PW activity and oscillations. We also used ERA-Interim reanalysis data sets available at 0.125x0.125 degree grids for investigating the characteristics of these PW right from surface to 1 h
NASA Technical Reports Server (NTRS)
Bassiri, Sassan; Hajj, George A.
1993-01-01
Natural and man-made events like earthquakes and nuclear explosions launch atmospheric gravity waves (AGW) into the atmosphere. Since the particle density decreases exponentially with height, the gravity waves increase exponentially in amplitude as they propagate toward the upper atmosphere and ionosphere. As atmospheric gravity waves approach the ionospheric heights, the neutral particles carried by gravity waves collide with electrons and ions, setting these particles in motion. This motion of charged particles manifests itself by wave-like fluctuations and disturbances that are known as traveling ionospheric disturbances (TID). The perturbation in the total electron content due to TID's is derived analytically from first principles. Using the tilted dipole magnetic field approximation and a Chapman layer distribution for the electron density, the variations of the total electron content versus the line-of-sight direction are numerically analyzed. The temporal variation associated with the total electron content measurements due to AGW's can be used as a means of detecting characteristics of the gravity waves. As an example, detection of tsunami generated earthquakes from their associated atmospheric gravity waves using the Global Positioning System is simulated.
Seasonal and interannual variability of mesospheric gravity wave activity at high and mid-latitudes
NASA Astrophysics Data System (ADS)
Hoffmann, Peter; Singer, Werner; Becker, Erich; Latteck, Ralph; Keuer, Dieter
The seasonal variation and interannual variability of the gravity wave activity in the mesosphere/lower thermosphere (MLT) region at high and mid-latitudes is investigated. Variations of the gravity wave activity are examined in relation to the filtering processes due to the changes of the background winds, tides and planetary waves. Our studies are basing on wind measurements from meteor and MF radars at Andenes (69° N, 16° E) and Juliusruh (55° N, 13° E). These measurements are supplemented by mesospheric temperatures derived from meteor decay times. Additionally, turbulent energy dissipation rates have been estimated from spectral width measurements using a 3 MHz Doppler radar near Andenes. Particular attention is directed to the influence of the solar activity on the gravity wave activity during the summer months when the mesospheric winds show the strongest correlation with the solar activity. Possible dependencies between the occurrence rates of polar mesospheric summer echoes (PMSE) and the gravity wave activity are discussed. Furthermore, the activity of gravity waves and their dissipation are investigated in winter in relation with wind changes during sudden stratospheric warming (SSW) events. The summer/ winter behavior of the gravity wave activity will be compared to simulations with the simple general circulation model KMCM (K¨hlungsborn Mechanistic u Circulation Model) that extends up to 100 km. In all cases, the percentage rates of the kinetic energy of defined period ranges in relation to the total variances of the horizontal wind fluctuations are estimated.
On the generation and evolution of internal gravity waves
NASA Technical Reports Server (NTRS)
Lansing, F. S.; Maxworthy, T.
1984-01-01
The tidal generation and evolution of internal gravity waves is investigated experimentally and theoretically using a two-dimensional two-layer model. Time-dependent flow is created by moving a profile of maximum submerged depth 7.7 cm through a total stroke of 29 cm in water above a freon-kerosene mixture in an 8.6-m-long 30-cm-deep 20-cm-wide transparent channel, and the deformation of the fluid interface is recorded photographically. A theoretical model of the interface as a set of discrete vortices is constructed numerically; the rigid structures are represented by a source distribution; governing equations in Lagrangian form are obtained; and two integrodifferential equations relating baroclinic vorticity generation and source-density generation are derived. The experimental and computed results are shown in photographs and graphs, respectively, and found to be in good agreement at small Froude numbers. The reasons for small discrepancies in the position of the maximum interface displacement at large Froude numbers are examined.
Quantum Cause of Gravity Waves and Dark Matter
NASA Astrophysics Data System (ADS)
Goradia, Shantilal; Goradia Team
2016-09-01
Per Einstein's theory mass tells space how to curve and space tells mass how to move. How do they tell''? The question boils down to information created by quantum particles blinking ON and OFF analogous to `Ying and Yang' or some more complex ways that may include dark matter. If not, what creates curvature of space-time? Consciousness, dark matter, quantum physics, uncertainty principle, constants of nature like strong coupling, fine structure constant, cosmological constant introduced by Einstein, information, gravitation etc. are fundamentally consequences of that ONE TOE. Vedic philosophers, who impressed Schrodinger so much, called it ATMA split in the categories of AnuAtma (particle soul), JivAtma (life soul) and ParamAtma (Omnipresent soul) which we relate to quantum physics, biology and cosmology. There is no separate TOE for any one thing. The long range relativistic propagations of the strong and weak couplings of the microscopic black holes in are just gravity waves. What else could they be?
Structured elves: Modulation by convectively generated gravity waves
NASA Astrophysics Data System (ADS)
Yue, Jia; Lyons, Walter A.
2015-02-01
We report on a markedly striated elve (Emissions of Light and Very Low Frequency Perturbations due to Electromagnetic Pulse Source) (a "tiger elve") observed using an intensified high-speed Phantom camera system at the Yucca Ridge Field Station near Fort Collins, Colorado, on the night of 12 June 2013. This elve was induced by a 204 kA positive cloud-to-ground lightning flash within a mesoscale convective system in western South Dakota. A halo and a sprite followed the elve. The banded structure in the elve was aligned with convectively generated gravity waves (CGGWs) independently observed by a collocated color near-infrared camera. Assuming the height of the OH layer and elve both to be 85 km, photogrammetry allowed projection of the elve and the CGGWs onto the same geographic map. The tiger elve stripes approximately overlay on the troughs (dark bands) of CGGWs. This is consistent with model predictions that the ionization rate in the D region ionosphere is inversely proportional to the air density, which is modulated by the CGGWs.
Tropical Gravity Wave Momentum Fluxes and Latent Heating Distributions
NASA Technical Reports Server (NTRS)
Geller, Marvin A.; Zhou, Tiehan; Love, Peter T.
2015-01-01
Recent satellite determinations of global distributions of absolute gravity wave (GW) momentum fluxes in the lower stratosphere show maxima over the summer subtropical continents and little evidence of GW momentum fluxes associated with the intertropical convergence zone (ITCZ). This seems to be at odds with parameterizations forGWmomentum fluxes, where the source is a function of latent heating rates, which are largest in the region of the ITCZ in terms of monthly averages. The authors have examined global distributions of atmospheric latent heating, cloud-top-pressure altitudes, and lower-stratosphere absolute GW momentum fluxes and have found that monthly averages of the lower-stratosphere GW momentum fluxes more closely resemble the monthly mean cloud-top altitudes rather than the monthly mean rates of latent heating. These regions of highest cloud-top altitudes occur when rates of latent heating are largest on the time scale of cloud growth. This, plus previously published studies, suggests that convective sources for stratospheric GW momentum fluxes, being a function of the rate of latent heating, will require either a climate model to correctly model this rate of latent heating or some ad hoc adjustments to account for shortcomings in a climate model's land-sea differences in convective latent heating.
Formation of ionospheric sporadic E by atmospheric gravity waves
NASA Astrophysics Data System (ADS)
Didebulidze, Goderdzi; Dalakishvili, Giorgi; Matiashvili, Giorgi
2016-07-01
The atmospheric gravity waves (AGWs) significantly influence the behavior of the thermosphere ions/electrons. It is shown, that in the lower thermosphere when the background wind present, the AGWs evolving in this wind affect the heavy metallic ions vertical motions and can lead to their convergence into horizontal thin layers and consequently form ionosphere sporadic E (Es). For certain values of the velocity of horizontal back-ground wind, occurring in this region, the declined propagation of the AGWs in the mid-latitude lower thermosphere can cause formation multilayered sporadic E. The distances between such Es layers i.e. distance between locations of maximal ions/electrons densities occur is about one AGWs vertical wavelength. The observed phenomena like of sporadic E multilayered structures and Es layers downward motions are demonstrated by using 3-D numerical simulations describing Es formation by AGWs. The formation of quasi-periodic echoes like structures by AGWs evolving in the horizontal inhomogeneous wind and possibility of its ions/electrons density oscillations by smaller periods (smaller than Bunt-Väisälä period), which also is observed phenomena, is shown. Acknowledgements: This work has been supported by Shota Rustaveli National Science Foundation grant No 31/81.
Ionospheric gravity wave measurements with the USU dynasonde
NASA Technical Reports Server (NTRS)
Berkey, Frank T.; Deng, Jun Yuan
1992-01-01
A method for the measurement of ionospheric Gravity Wave (GW) using the USU Dynasonde is outlined. This method consists of a series of individual procedures, which includes functions for data acquisition, adaptive scaling, polarization discrimination, interpolation and extrapolation, digital filtering, windowing, spectrum analysis, GW detection, and graphics display. Concepts of system theory are applied to treat the ionosphere as a system. An adaptive ionogram scaling method was developed for automatically extracting ionogram echo traces from noisy raw sounding data. The method uses the well known Least Mean Square (LMS) algorithm to form a stochastic optimal estimate of the echo trace which is then used to control a moving window. The window tracks the echo trace, simultaneously eliminating the noise and interference. Experimental results show that the proposed method functions as designed. Case studies which extract GW from ionosonde measurements were carried out using the techniques described. Geophysically significant events were detected and the resultant processed results are illustrated graphically. This method was also developed for real time implementation in mind.
Constraints on gravity wave induced diffusion in the middle atmosphere
NASA Technical Reports Server (NTRS)
Strobel, Darrell F.
1988-01-01
A review of the important constraints on gravity wave induced diffusion of chemical tracers, heat and momentum is given. Ground-based microwave spectroscopy measurements of H2O and CO and rocket-based mass spectrometer measurements of Ar constrain the eddy diffusion coefficient for constituent transport (K sub zz) to be (1-3) x 10 to the 5th sq cm/sec in the upper mesosphere. Atomic oxygen data also limits K sub zz to a comparable value in the mesopause. From the energy balance of the upper mesosphere the eddy diffusion coefficient for heat transport (D sub H) is, at most, 6 x 10 to the 5th sq cm/sec at the mesopause and decreasing substantially with decreasing altitude. The available evidence for mean wind deceleration and the corresponding eddy diffusion coefficient for momentum stresses (D sub M) suggests that it is at least 1 x 10 to the 6th sq cm/sec in the upper mesosphere. Consequently the eddy Prandtl number for macroscopic scale lengths is greater than 3.
NASA Astrophysics Data System (ADS)
Diorio, J. D.; Watkins, N.; Zuech, J.; Duncan, J. H.
2008-11-01
There have been several recent numerical investigations that have shown the existence of three-dimensional nonlinear solitary surface wave patterns that propagate with speeds less than the minimum wave phase speed prescribed by linear theory (23 cm/s for clean water). In the present study, wave patterns were generated by translating a small-diameter region of high pressure across a water surface. The high-pressure region was created by forcing air through a small-diameter vertically oriented tube attached to a carriage that propelled it horizontally at speeds near 23 cm/s. The wave pattern was measured with a cinematic LIF technique. It was found that a steady solitary wave pattern can exist at speeds below the linear-theory minimum phase speed, while for speeds above the minimum, a pattern of gravity-capillary waves was produced. The solitary wave pattern, which only appeared when the pressure forcing was large, dissipated rapidly when the forcing was turned off. The streamwise dimension of the solitary wave was much smaller than the transverse dimension.
Some classes of gravitational shock waves from higher order theories of gravity
NASA Astrophysics Data System (ADS)
Oikonomou, V. K.
2017-02-01
We study the gravitational shock wave generated by a massless high energy particle in the context of higher order gravities of the form F(R,R_{μν}R^{μν},R_{μναβ}R^{μν αβ}). In the case of F(R) gravity, we investigate the gravitational shock wave solutions corresponding to various cosmologically viable gravities, and as we demonstrate the solutions are rescaled versions of the Einstein-Hilbert gravity solution. Interestingly enough, other higher order gravities result to the general relativistic solution, except for some specific gravities of the form F(R_{μν}R^{μν}) and F(R,R_{μν}R^{μν}), which we study in detail. In addition, when realistic Gauss-Bonnet gravities of the form R+F(G) are considered, the gravitational shock wave solutions are identical to the general relativistic solution. Finally, the singularity structure of the gravitational shock waves solutions is studied, and it is shown that the effect of higher order gravities makes the singularities milder in comparison to the general relativistic solutions, and in some particular cases the singularities seem to be absent.
Gravity wave vertical coupling on Earth and Mars: similarities and peculiarities
NASA Astrophysics Data System (ADS)
Medvedev, Alexander S.; Kuroda, Takeshi; Yiǧit, Erdal
2016-07-01
Gravity waves play a major role in the dynamical coupling between the lower and upper atmosphere both on Earth and Mars. A significant progress with understanding gravity wave phenomena in the Martian atmosphere has been achieved over the last decade. We present some of these findings focusing on comparison with the terrestrial atmosphere. Gravity waves are stronger on Mars, thanks to more violent meteorology and rougher topography. They transport energy and momentum upon propagation to the mesosphere and thermosphere, and affect the circulation there. Gravity waves facilitate a formation of mesospheric CO2 ice clouds, and cause a strong thermospheric response to dust storms in the troposphere. This talk promotes a view of coupling processes not only as an Earth phenomenon, but as a universal mechanism in planetary atmospheres.
On the covariant gauge {alpha} of the linearized gravity in de Sitter spacetime
Cheong, Lee Yen
2012-09-26
In previous work, we studied the linearized gravity with covariant gauge {beta}= 2/3 and {alpha}= 5/3. It was found that the sum of the source and initial contributions reproduces the correct field configuration over the whole de Sitter spacetime. In this paper, we extend this work to generalizing the linearized gravitational field in an arbitrary value of the gauge parameter {alpha} but the gauge parameter {beta} remains the same.
NASA Technical Reports Server (NTRS)
Alexander, M. Joan
1996-01-01
This work evaluates the interaction of a simulated spectrum of convectively generated gravity waves with realistic middle atmosphere mean winds. The wave spectrum is derived from the nonlinear convection model described by Alexander et al. [1995] that simulated a two-dimensional midlatitude squall line. This spectrum becomes input to a linear ray tracing model for evaluation of wave propagation as a function of height through climatological background wind and buoyancy frequency profiles. The energy defined by the spectrum as a function of wavenumber and frequency is distributed spatially and temporally into wave packets for the purpose of estimating wave amplitudes at the lower boundary of the ray tracing model. A wavelet analysis provides an estimate of these wave packet widths in space and time. Without this redistribution of energies into wave packets the Fourier analysis alone inaccurately assumes the energy is evenly distributed throughout the storm model domain. The growth with height of wave amplitudes is derived from wave action flux conservation coupled to a convective instability saturation condition. Mean flow accelerations and wave energy dissipation profiles are derived from this analysis and compared to parameterized estimates of gravity wave forcing, providing a measure of the importance of the storm source to global gravity wave forcing. The results suggest that a single large convective storm system like the simulated squall line could provide a significant fraction of the zonal mean gravity wave forcing at some levels, particularly in the mesosphere. The vertical distributions of mean flow acceleration and energy dissipation do not much resemble the parameterized profiles in form because of the peculiarities of the spectral properties of the waves from the storm source. The ray tracing model developed herein provides a tool for examining the role of convectively generated waves in middle atmosphere physics.
NASA Technical Reports Server (NTRS)
Alexander, Joan
1996-01-01
This work evaluates the interaction of a simulated spectrum of convectively generated gravity waves with realistic middle atmosphere mean winds. The wave spectrum is derived from the nonlinear convection model described by Alexander et al. that simulated a two-dimensional midlatitude squall line. This spectrum becomes input to a linear ray tracing model for evaluation of wave propagation as a function of height through climatological background wind and buoyancy frequency profiles. The energy defined by the spectrum as a function of wavenumber and frequency is distributed spatially and temporally into wave packets for the purpose of estimating wave amplitudes at the lower boundary of the ray tracing model. A wavelet analysis provides an estimate of these wave packet widths in space and time. Without this redistribution of energies into wave packets the Fourier analysis alone inaccurately assumes the energy is evenly distributed throughout the storm model domain. The growth with height of wave amplitudes is derived from wave action flux conservation coupled to a convective instability saturation condition. Mean flow accelerations and wave energy dissipation profiles are derived from this analysis and compared to parameterized estimates of gravity wave forcing, providing a measure of the importance of the storm source to global gravity wave forcing. The results suggest that a single large convective storm system like the simulated squall line could provide a significant fraction of the zonal mean gravity wave forcing at some levels, particularly in the mesosphere. The vertical distributions of mean flow acceleration and energy dissipation do not much resemble the parameterized profiles in form because of the peculiarities of the spectral properties of the waves from the storm source. The ray tracing model developed herein provides a tool for examining the role of convectively generated waves in middle atmosphere physics.
Activity maps of gravity waves and triads derived from CHAMP and SABER data
NASA Astrophysics Data System (ADS)
Wernicke, Jeannette; Wüst, Sabine; Bittner, Michael
Gravity waves have significant influence on the circulation and thermal structure of the atmo-sphere by transporting energy and momentum. One mechanism of coupling multiple altitudinal levels is the nonlinear wave-wave interaction called triad: two gravity waves can form a third one with different physical properties that can transport energy and momentum to areas far away from its origin. Due to the coarse spatial resolution most global circulation models are unable to resolve gravity waves. So, the effects have to be parameterised. In order to obtain a realistic representation it is important to expand the knowledge about the physical properties of gravity waves. Activity maps of gravity waves and triads are retrieved using satellite measurements from CHAMP (CHAllenging Minisatellite Payload) and SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) in an area (50° N, 10° W) to (43° N, 20° E) during the years 2001 to 2008. To retrieve these maps temperature profiles are analysed using the innovative detrending algo-rithm ECUS-D (Ensemble of CUbic Splines for Detrending) to separate background temper-ature and wave signatures. For gravity waves an activity index is calculated. The dominant wavelengths are estimated and searched for nonlinearities. To analyse different observational filters the measurements are compared to each other and to the results of campaign SIGMA-1 (Satellite Validation Impact of Gravity Waves in the Middle Atmosphere). SIGMA-1 is based mainly on radiosonde measurements with high temporal reso-lution at the observatory Hohenpeißenberg and additional synoptic measurements of radiosonde stations in the surrounding region.
Four years of gravity waves monitoring in Antarctica : Impact for global atmospheric studies
NASA Astrophysics Data System (ADS)
Blanc, E.; Le Pichon, A.; Ceranna, L.
2007-12-01
The development of the Infrasound International Monitoring System, used for the verification of the Comprehensive Test Ban Treaty, offers a powerful way to measure, permanently and at a global scale, the atmospheric waves at different latitudes. Infrasound stations using several microbarometers are very sensitive acoustic antennas, measuring the main characteristics of infrasound waves including velocity and direction of the wave front. Associated with new data processing methods, a global analysis of the atmospheric disturbances is now possible in a large frequency range. The networks if mostly sensitive to infrasound in the range 0.01 to 10 Hz, but most of gravity waves, which are characterized by very large amplitudes, are also detected by the network. The Antarctic stations are especially interesting for the study of gravity waves, because they are controlled by the polar vortex, and because they are rarely disturbed by the low latitude mountain gravity waves activity which is less important than in the Northern hemisphere. The monitoring of the gravity wave activity in the Antarctica station I27DE from 2003 up to 2007 reveals two active gravity wave systems. The first one, characterized by an azimuth from East, is produced in the troposphere by the wind blowing over mountains. The second system, characterized by an azimuth from West, is correlated with the wind and the temperature gradients in the lower stratosphere and is related with the polar stratospheric vortex. During magnetic storms infrasound waves are generally observed with a North azimuth at frequencies from 0.5 Hz to few Hz, however, gravity waves are generally not observed. A strong wave system has been observed coming from North only once in January 2005 several days after a major magnetic storm. The origin of this wave system in terms of magnetic storm or other processes related with the global dynamics of the stratosphere is discussed.
Linear and nonlinear propagation of water wave groups
NASA Technical Reports Server (NTRS)
Pierson, W. J., Jr.; Donelan, M. A.; Hui, W. H.
1992-01-01
Results are presented from a study of the evolution of waveforms with known analytical group shapes, in the form of both transient wave groups and the cloidal (cn) and dnoidal (dn) wave trains as derived from the nonlinear Schroedinger equation. The waveforms were generated in a long wind-wave tank of the Canada Centre for Inland Waters. It was found that the low-amplitude transients behaved as predicted by the linear theory and that the cn and dn wave trains of moderate steepness behaved almost as predicted by the nonlinear Schroedinger equation. Some of the results did not fit into any of the available theories for waves on water, but they provide important insight on how actual groups of waves propagate and on higher-order effects for a transient waveform.
Wave Dissipation and Balance - NOPP Wave Project
2014-09-30
processes that affect wind-generated ocean gravity waves. The various dissipative processes that contribute to the spectral wave evolution are isolated...over mature ocean surface wave spectra. J. Phys. Oceanogr., 34:3345–2358, 2004. K. Hasselmann. On the non-linear energy transfer in a gravity wave...P. Giovanangeli. Air flow structure over short- gravity breaking water waves. Boundary-Layer Meteorol., 126:477–705, 2008. doi: 10.1007/s10546-007
A Comparison Between Gravity Wave Momentum Fluxes in Observations and Climate Models
NASA Technical Reports Server (NTRS)
Geller, Marvin A.; Alexadner, M. Joan; Love, Peter T.; Bacmeister, Julio; Ern, Manfred; Hertzog, Albert; Manzini, Elisa; Preusse, Peter; Sato, Kaoru; Scaife, Adam A.; Zhou, Tiehan
2013-01-01
For the first time, a formal comparison is made between gravity wave momentum fluxes in models and those derived from observations. Although gravity waves occur over a wide range of spatial and temporal scales, the focus of this paper is on scales that are being parameterized in present climate models, sub-1000-km scales. Only observational methods that permit derivation of gravity wave momentum fluxes over large geographical areas are discussed, and these are from satellite temperature measurements, constant-density long-duration balloons, and high-vertical-resolution radiosonde data. The models discussed include two high-resolution models in which gravity waves are explicitly modeled, Kanto and the Community Atmosphere Model, version 5 (CAM5), and three climate models containing gravity wave parameterizations,MAECHAM5, Hadley Centre Global Environmental Model 3 (HadGEM3), and the Goddard Institute for Space Studies (GISS) model. Measurements generally show similar flux magnitudes as in models, except that the fluxes derived from satellite measurements fall off more rapidly with height. This is likely due to limitations on the observable range of wavelengths, although other factors may contribute. When one accounts for this more rapid fall off, the geographical distribution of the fluxes from observations and models compare reasonably well, except for certain features that depend on the specification of the nonorographic gravity wave source functions in the climate models. For instance, both the observed fluxes and those in the high-resolution models are very small at summer high latitudes, but this is not the case for some of the climate models. This comparison between gravity wave fluxes from climate models, high-resolution models, and fluxes derived from observations indicates that such efforts offer a promising path toward improving specifications of gravity wave sources in climate models.
Incorporation of a Gravity Wave Momentum Deposition Parameterization into the VTGCM
NASA Astrophysics Data System (ADS)
Brecht, A. S.; Zalucha, A. M.; Bougher, S. W.; Rafkin, S. C.; Alexander, M.
2011-12-01
The National Center for Atmospheric Research (NCAR) thermospheric general circulation model for Venus (VTGCM) is a three dimensional model that can calculate temperatures, zonal winds, meridional winds, vertical winds, and concentration of specific species. The calculated nightside warm region (near ~100 km) and the O2-IR and NO-UV nightglow intensity distributions have been produced to represent mean conditions observed by Venus Express data and ground-based observations with the use of Rayleigh friction (Brecht et al. JGR, 2011). Rayleigh friction is implemented to parameterize gravity wave momentum drag effects on the global mean zonal wind flow. The purpose is to obtain a first order approximation of the necessary drag to reproduce observations. In addition, Rayleigh friction provides guidelines for the implementation and adjustment of a gravity wave momentum deposition scheme. Most recently, the Alexander and Dunkerton (AMS, 1999) gravity wave momentum parameterization has been incorporated into the VTGCM. The parameterization is designed to deposit momentum fluxes locally and totally at the altitude of wave breaking. Further, it allows waves to continue to propagate above the breaking altitude. Specific fields will be shown to illustrate the impacts the parameterization has on the global circulation (i.e. temperatures, zonal winds, and night airglow distributions (O2 IR and NO UV)). In addition, the chosen values for parameters will be discussed and their importance for depositing the gravity wave momentum. The gravity wave momentum parameterization launches waves from the cloud region within the VTGCM and provides a strong source for asymmetrical global winds.
NASA Astrophysics Data System (ADS)
Cho, Yeunwoo
2014-11-01
The shedding phenomena of 3-D viscous gravity-capillary solitary waves generated by a moving air-forcing on the surface of deep water are investigated. Near the resonance where the forcing speed is close to 23 cm/s, two kinds of shedding modes are possible; Anti-symmetric and symmetric modes. A relevant theoretical model equation is numerically solved for the identification of shedding of solitary waves, and is analytically studied in terms of their linear stability to transverse perturbations. Furthermore, by tracing trajectories of shed solitary waves, the decay rate of a 3-D solitary wave due to viscous dissipation is estimated. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF-2014R1A1A1002441).
McLandress, C. ); McFarlane, N.A. )
1993-07-01
A quasigeostrophic model is used to study the combined interaction among orographically generated gravity wave drag, forced planetary waves, and zonal mean flows in the Northern Hemisphere winter stratosphere and mesosphere. The localized gravity wave drag is shown to generate planetary waves in the mesosphere that, in turn, exert a substantial drag on the zonal mean flow via the Eliassen-Palm flux divergence. The amount of planetary wave drag is found to depend not only on the presence of the localized source of orographic gravity wave drag but also on the presence of upward-propagating planetary waves in the lower stratosphere. The zonal mean wind field exhibits a split jet structure with the larger jet maximum situated in the upper stratosphere at 30[degrees]N. This feature is shown to arise from the presence of weak winds above the subtropical tropospheric jet maximum, which results in a region of low-level gravity wave breaking and reduced drag and larger winds above. 33 refs., 18 figs.
Generation of internal gravity waves by tidal flow over random oceanic topography
NASA Astrophysics Data System (ADS)
Zhao, Jiajun; Zhang, Likun; Swinney, Harry
2015-03-01
Internal waves (IWs) are gravity waves that propagate within density-stratified fluids such as the ocean, atmosphere, and protoplanetary disks. IWs generated by tidal flow over oceanic topography provide much of the energy needed to sustain vertical mixing, which plays a critical role in ocean circulation and global climate. Therefore, it is important to determine the amount of energy that is extracted from tidal flow over topography and radiated into IWs. We conduct 2D numerical simulations to determine the IW power generated by tidal flow over random topographies that have the seafloor spectrum. The power is found to saturate with increasing topographic roughness, and to scale linearly with the characteristic height of the topography. The linear dependence on the topographic height is, surprisingly, nearly independent of the value of the exponent characterizing the topographic spectrum. Our results should lead to improved predictions of the IW power generated by tidal flow over global ocean topography. Research supported by the Office of Naval Research and the Texas Advanced Computing Center. JZ is supported also by the President's Graduate Fellowship from the National University of Singapore.
An Object Oriented, Finite Element Framework for Linear Wave Equations
Koning, Joseph M.
2004-03-01
This dissertation documents an object oriented framework which can be used to solve any linear wave equation. The linear wave equations are expressed in the differential forms language. This differential forms expression allows a strict discrete interpretation of the system. The framework is implemented using the Galerkin Finite Element Method to define the discrete differential forms and operators. Finite element basis functions including standard scalar Nodal and vector Nedelec basis functions are used to implement the discrete differential forms resulting in a mixed finite element system. Discretizations of scalar and vector wave equations in the time and frequency domains will be demonstrated in both differential forms and vector calculi. This framework conserves energy, maintains physical continuity, is valid on unstructured grids, conditionally stable and second order accurate. Examples including linear electrodynamics, acoustics, elasticity and magnetohydrodynamics are demonstrated.
Local energy decay for linear wave equations with variable coefficients
NASA Astrophysics Data System (ADS)
Ikehata, Ryo
2005-06-01
A uniform local energy decay result is derived to the linear wave equation with spatial variable coefficients. We deal with this equation in an exterior domain with a star-shaped complement. Our advantage is that we do not assume any compactness of the support on the initial data, and its proof is quite simple. This generalizes a previous famous result due to Morawetz [The decay of solutions of the exterior initial-boundary value problem for the wave equation, Comm. Pure Appl. Math. 14 (1961) 561-568]. In order to prove local energy decay, we mainly apply two types of ideas due to Ikehata-Matsuyama [L2-behaviour of solutions to the linear heat and wave equations in exterior domains, Sci. Math. Japon. 55 (2002) 33-42] and Todorova-Yordanov [Critical exponent for a nonlinear wave equation with damping, J. Differential Equations 174 (2001) 464-489].
On asymmetric generalized solitary gravity-capillary waves in finite depth.
Gao, T; Wang, Z; Vanden-Broeck, J-M
2016-10-01
Generalized solitary waves propagating at the surface of a fluid of finite depth are considered. The fluid is assumed to be inviscid and incompressible and the flow to be irrotational. Both the effects of gravity and surface tension are included. It is shown that in addition to the classical symmetric waves, there are new asymmetric solutions. These new branches of solutions bifurcate from the branches of symmetric waves. The detailed bifurcation diagrams as well as typical wave profiles are presented.
Thermospheric Gravity Wave Characteristics Obtained Using the Poker Flat Incoherent Scatter Radar
NASA Astrophysics Data System (ADS)
Negale, M.; Nielsen, K.; Taylor, M. J.; Nicolls, M. J.
2014-12-01
Atmospheric gravity waves are known to play an important role in atmospheric circulation through momentum deposition in the mesosphere and lower thermosphere (MLT) region (~80 - 110 km). Over the past decade, modeling and observational studies have shown that these waves can penetrate to high altitudes and play similar roles in the thermospheric region (~110 - 400 km). Several case studies have revealed their presence in the thermosphere, but the distributions and variability of thermospheric gravity wave parameters are currently unknown. Using methods developed by Nicolls and Heinselman (2007), we present new high-latitude thermospheric wave characteristic distributions obtained using the Poker Flat Incoherent Scatter Radar (PFISR) during a one year period from August 2010 - July 2011. Their winter season distributions (January 2010 - April 2011) are compared to recent results obtained using a co-located all sky airglow imager measuring the MLT gravity wave field.
Suomi NPP VIIRS/DNB imagery of nightglow gravity waves from various sources over China
NASA Astrophysics Data System (ADS)
Lai, Chang; Yue, Jia; Xu, Jiyao; Straka, William C.; Miller, Steven D.; Liu, Xiao
2017-04-01
Observation of atmospheric gravity waves provides critical insight to weather and climate researches. Some gravity waves survive middle-atmospheric filtering as they propagate upward to the mesopause region and disturb the nightglow emission layer near 90 km AMSL, making the waves visible to both ground and space sensors. Based on the high-resolution images obtained by Day/Night Band on NOAA/NASA Suomi National Polar-orbiting Partnership environmental satellite, four representative gravity wave events over China are analyzed. With the help of VIIRS thermal infrared brightness temperature and MERRA wind data, we surmise that these waves originated from orography, thunderstorm, typhoon and baroclinic, respectively. Nadir viewing satellite observations cover a wide area and unlike the surface-based perspective, do not suffer from cloud obscuration. These new observations over remote areas provide important guidance for future deployment of ground based camera systems in China.
Exploring Gravity Wave Dynamics and Predictability in DeepWave (Invited)
NASA Astrophysics Data System (ADS)
Doyle, J. D.; Fritts, D. C.; Smith, R. B.; Eckermann, S. D.; Taylor, M. J.
2013-12-01
An overview is provided of the first research program that attempts to follow deeply propagating gravity waves (GWs) from their tropospheric sources to their mesospheric breakdown. The DEEP propagating gravity WAVE program (DEEPWAVE) is a comprehensive, airborne and ground-based measurement and modeling program centered on New Zealand and focused on providing a new understanding of GW dynamics and impacts from the troposphere through the mesosphere and lower thermosphere (MLT). This program will employ the NSF/NCAR GV (NGV) research aircraft from a base in New Zealand in a 6-week field measurement campaign in June-July 2014. The NGV will be equipped with new lidar and airglow instruments for the DEEPWAVE measurement program, providing temperatures and vertical winds spanning altitudes from immediately above the NGV flight altitude (~13 km) to ~100 km. Observations from these instruments obtained during a recent NGV test flight will be shown. The region near New Zealand is chosen since all the relevant GW sources (e.g., mountains, cyclones, jet streams) occur strongly here, and upper-level winds in austral winter permit GWs to propagate to very high altitudes. Given large-amplitude GWs that propagate routinely into the MLT, the New Zealand region offers an ideal natural laboratory for studying these important GW dynamics and effects impacting weather and climate over a much deeper atmospheric layer than previous campaigns have attempted (0-100 km altitude). In this presentation, we provide examples from a suite of GW-focused modeling and predictability tools that will be used to guide NGV flight planning to GW events of greatest scientific significance. These models will also drive scientific interpretation of the GW measurements, together providing answers to the key science questions posed by DEEPWAVE about GW dynamics, morphology, predictability and impacts from 0-100 km. Preliminary results will be presented from high-resolution and adjoint models with deep
Spherically symmetric analysis on open FLRW solution in non-linear massive gravity
Chiang, Chien-I; Izumi, Keisuke; Chen, Pisin E-mail: izumi@phys.ntu.edu.tw
2012-12-01
We study non-linear massive gravity in the spherically symmetric context. Our main motivation is to investigate the effect of helicity-0 mode which remains elusive after analysis of cosmological perturbation around an open Friedmann-Lemaitre-Robertson-Walker (FLRW) universe. The non-linear form of the effective energy-momentum tensor stemming from the mass term is derived for the spherically symmetric case. Only in the special case where the area of the two sphere is not deviated away from the FLRW universe, the effective energy momentum tensor becomes completely the same as that of cosmological constant. This opens a window for discriminating the non-linear massive gravity from general relativity (GR). Indeed, by further solving these spherically symmetric gravitational equations of motion in vacuum to the linear order, we obtain a solution which has an arbitrary time-dependent parameter. In GR, this parameter is a constant and corresponds to the mass of a star. Our result means that Birkhoff's theorem no longer holds in the non-linear massive gravity and suggests that energy can probably be emitted superluminously (with infinite speed) on the self-accelerating background by the helicity-0 mode, which could be a potential plague of this theory.
Global Gravity Wave Variances from Aura MLS: Characteristics and Interpretation
NASA Technical Reports Server (NTRS)
Wu, Dong L.; Eckermann, Stephen D.
2008-01-01
The gravity wave (GW)-resolving capabilities of 118-GHz saturated thermal radiances acquired throughout the stratosphere by the Microwave Limb Sounder (MLS) on the Aura satellite are investigated and initial results presented. Because the saturated (optically thick) radiances resolve GW perturbations from a given altitude at different horizontal locations, variances are evaluated at 12 pressure altitudes between 21 and 51 km using the 40 saturated radiances found at the bottom of each limb scan. Forward modeling simulations show that these variances are controlled mostly by GWs with vertical wavelengths z 5 km and horizontal along-track wavelengths of y 100-200 km. The tilted cigar-shaped three-dimensional weighting functions yield highly selective responses to GWs of high intrinsic frequency that propagate toward the instrument. The latter property is used to infer the net meridional component of GW propagation by differencing the variances acquired from ascending (A) and descending (D) orbits. Because of improved vertical resolution and sensitivity, Aura MLS GW variances are 5?8 times larger than those from the Upper Atmosphere Research Satellite (UARS) MLS. Like UARS MLS variances, monthly-mean Aura MLS variances in January and July 2005 are enhanced when local background wind speeds are large, due largely to GW visibility effects. Zonal asymmetries in variance maps reveal enhanced GW activity at high latitudes due to forcing by flow over major mountain ranges and at tropical and subtropical latitudes due to enhanced deep convective generation as inferred from contemporaneous MLS cloud-ice data. At 21-28-km altitude (heights not measured by the UARS MLS), GW variance in the tropics is systematically enhanced and shows clear variations with the phase of the quasi-biennial oscillation, in general agreement with GW temperature variances derived from radiosonde, rocketsonde, and limb-scan vertical profiles.
Standing wave bi-directional linearly moving ultrasonic motor.
He, S; Chen, W; Tao, X; Chen, Z
1998-01-01
A standing wave bi-directional linearly moving ultrasonic motor has been studied for the purpose of implementing a practical linear ultrasonic motor with simple structure, simple driving and high resolution. The fundamental principle of this linear motor is projections on the right sides of a standing wave crests generating thrust force right-diagonally on the slider pressed against the projections. Correspondingly, projections on the left sides of the wave crests make the slider move toward the left. In order to realize bi-directional actuating, vibration mode B3 or B4 is excited in a rectangular plate-type vibrator to make the projections on the right sides or the left sides of the wave crests. In this paper, the operation principle of the linear motor is demonstrated. Furthermore, a prototype linear ultrasonic motor of 40 mm in length, 10 mm in width is fabricated and investigated. The following performances have been achieved: maximum speed 200 mm/s, maximum force output 150 gf, and resolution less than 0.1 microm.
Spectrograms of ship wakes: identifying linear and nonlinear wave signals
NASA Astrophysics Data System (ADS)
Pethiyagoda, Ravindra; McCue, Scott W.; Moroney, Timothy J.
2017-01-01
A spectrogram is a useful way of using short-time discrete Fourier transforms to visualise surface height measurements taken of ship wakes in real world conditions. For a steadily moving ship that leaves behind small-amplitude waves, the spectrogram is known to have two clear linear components, a sliding-frequency mode caused by the divergent waves and a constant-frequency mode for the transverse waves. However, recent observations of high speed ferry data have identified additional components of the spectrograms that are not yet explained. We use computer simulations of linear and nonlinear ship wave patterns and apply time-frequency analysis to generate spectrograms for an idealised ship. We clarify the role of the linear dispersion relation and ship speed on the two linear components. We use a simple weakly nonlinear theory to identify higher order effects in a spectrogram and, while the high speed ferry data is very noisy, we propose that certain additional features in the experimental data are caused by nonlinearity. Finally, we provide a possible explanation for a further discrepancy between the high speed ferry spectrograms and linear theory by accounting for ship acceleration.
Multifractal energy exchange between gravity waves and turbulence in an upper tropospheric front
NASA Astrophysics Data System (ADS)
Koch, Steven
2014-05-01
Intermittent generation of strong turbulence measured by reconnaissance aircraft occurred in association with a wide spectrum of upward propagating gravity waves above the core of an upper level jet stream. The turbulence generation process could be described as an energy cascade process, initiated as gravity-inertia waves were produced in a region of diagnosed unbalanced upper-level frontogenesis near a tropopause fold. High resolution numerical weather prediction model forecasts produced bimodal waves with dominant wavelengths of 120-216 km and 1-20 km, the latter of which perturbed the atmosphere to create conditions conducive to turbulence generation. Cross spectral, wavelet transformation, and polarization analysis of the in situ aircraft data allowed unambiguous determination of the presence of the spectrum of gravity waves, reconstruction of the waves' evolving character, and identification of intermittent wave packets. Introduction of wavelet cross spectrum into the Stokes parameter theory shed light on how turbulence production was intimately related to increasing levels of polarization, only to be followed by sudden reduction of polarization as turbulence arose. Wavelet and structure function analysis indicated that episodes of high turbulent kinetic energy were the result of upscale feedback effects ("inverse energy cascade" processes linked to wave breaking). The bi-fractal nature of the gravity waves and turbulence suggest new approaches for parameterizing sub grid-scale effects caused by the interaction of waves and turbulence in numerical models.
Characteristics and sources of gravity waves observed in noctilucent cloud over Norway
NASA Astrophysics Data System (ADS)
Demissie, T. D.; Espy, P. J.; Kleinknecht, N. H.; Hatlen, M.; Kaifler, N.; Baumgarten, G.
2014-11-01
Four years of noctilucent cloud (NLC) images from an automated digital camera in Trondheim and results from a ray-tracing model are used to extend the climatology of gravity waves to higher latitudes and to identify their sources during summertime. The climatology of the summertime gravity waves detected in NLC between 64 and 74° N is similar to that observed between 60 and 64° N by Pautet et al. (2011). The direction of propagation of gravity waves observed in the NLC north of 64° N is a continuation of the north and northeast propagation as observed in south of 64° N. However, a unique population of fast, short wavelength waves propagating towards the SW is observed in the NLC, which is consistent with transverse instabilities generated in situ by breaking gravity waves (Fritts and Alexander, 2003). The relative amplitude of the waves observed in the NLC Mie scatter have been combined with ray-tracing results to show that waves propagating from near the tropopause, rather than those resulting from secondary generation in the stratosphere or mesosphere, are more likely to be the sources of the prominent wave structures observed in the NLC. The coastal region of Norway along the latitude of 70° N is identified as the primary source region of the waves generated near the tropopause.
Wavemaker theories for acoustic-gravity waves over a finite depth
NASA Astrophysics Data System (ADS)
Tian, Miao; Kadri, Usama
2016-04-01
Acoustic-gravity waves (hereafter AGWs) in ocean have received much interest recently, mainly with respect to early detection of tsunamis as they travel at near the speed of sound in water which makes them ideal candidates for early detection of tsunamis. While the generation mechanisms of AGWs have been studied from the perspective of vertical oscillations of seafloor (Yamamoto, 1982; Stiassnie, 2010) and triad wave-wave interaction (Longuet-Higgins 1950; Kadri and Stiassnie 2013; Kadri and Akylas 2016), in the current study we are interested in their generation by wave-structure interaction with possible application to the energy sector. Here, we develop two wavemaker theories to analyze different wave modes generated by impermeable (the classic Havelock's theory) and porous (porous wavemaker theory) plates in weakly compressible fluids. Slight modification has been made to the porous theory so that, unlike the previous theory (Chwang, 1983), the new solution depends on the geometry of the plate. The expressions for three different types of plates (piston, flap, delta-function) are introduced. Analytical solutions are also derived for the potential amplitude of the gravity, evanescent, and acoustic-gravity waves, as well as the surface elevation, velocity distribution, and pressure for AGWs. Both theories reduce to previous results for incompressible flow when the compressibility is negligible. We also show numerical examples for AGW generated in a wave flume as well as in deep ocean. Our current study sets the theoretical background towards remote sensing by AGWs, for optimized deep ocean wave-power harnessing, among others. References Chwang, A.T. 1983 A porous-wavemaker theory. Journal of Fluid Mechanics, 132, 395- 406. Kadri, U., Stiassnie, M. 2013 Generation of an acoustic-gravity wave by two gravity waves, and their subsequent mutual interaction. J. Fluid Mech. 735, R6. Kadri U., Akylas T.R. 2016 On resonant triad interactions of acoustic-gravity waves. J
Optimum contact conditions for miniaturized surface acoustic wave linear motor
Takasaki; Kurosawa; Higuchi
2000-03-01
This paper reports the successful operation of a 70 MHz driving surface acoustic wave (SAW) linear motor with a miniaturized stator transducer. This paper also deals with an investigation into an optimized slider design for the miniaturized SAW linear motor. The performance of three silicon type sliders, with different projection size, was compared. Output forces of the three sliders were measured with change of pre-load. It was found that the slider with smaller projection tended to produce greater output force.
Asymmetric transmission of linearly polarized waves in terahertz chiral metamaterials
NASA Astrophysics Data System (ADS)
Fang, Shenying; Luan, Kang; Ma, Hui Feng; Lv, Wenjin; Li, Yuxiang; Zhu, Zheng; Guan, Chunying; Shi, Jinhui; Cui, Tie Jun
2017-01-01
We experimentally demonstrate the asymmetric transmission of linearly polarized waves in a multilayer chiral metamaterial in the terahertz (THz) regime. The chiral metamaterial is constructed by two stacked orthogonal metallic layers embedded in polyimide dielectric layers. Simulated and measured results show that the proposed multilayer chiral metamaterial can achieve dual-band direction-dependent cross-polarization conversions for both x- and y-polarized THz waves. The polarized wave passing through the metamaterial will be converted into its orthogonal polarization state, while the same polarized wave is blocked along the reversed propagation direction. In addition, the asymmetric transmission band may be effectively engineered to other frequencies by slightly adjusting the gap width. We believe that our findings are beneficial in manipulating the polarization state of THz waves and exploring polarization-sensitive THz devices.
Gravity waves from non-minimal quadratic inflation
Pallis, Constantinos; Shafi, Qaisar
2015-03-12
We discuss non-minimal quadratic inflation in supersymmetric (SUSY) and non-SUSY models which entails a linear coupling of the inflaton to gravity. Imposing a lower bound on the parameter c{sub R}, involved in the coupling between the inflaton and the Ricci scalar curvature, inflation can be attained even for subplanckian values of the inflaton while the corresponding effective theory respects the perturbative unitarity up to the Planck scale. Working in the non-SUSY context we also consider radiative corrections to the inflationary potential due to a possible coupling of the inflaton to bosons or fermions. We find ranges of the parameters, depending mildly on the renormalization scale, with adjustable values of the spectral index n{sub s}, tensor-to-scalar ratio r≃(2−4)⋅10{sup −3}, and an inflaton mass close to 3⋅10{sup 13} GeV. In the SUSY framework we employ two gauge singlet chiral superfields, a logarithmic Kähler potential including all the allowed terms up to fourth order in powers of the various fields, and determine uniquely the superpotential by applying a continuous R and a global U(1) symmetry. When the Kähler manifold exhibits a no-scale-type symmetry, the model predicts n{sub s}≃0.963 and r≃0.004. Beyond no-scale SUGRA, n{sub s} and r depend crucially on the coefficient involved in the fourth order term, which mixes the inflaton with the accompanying non-inflaton field in the Kähler potential, and the prefactor encountered in it. Increasing slightly the latter above (−3), an efficient enhancement of the resulting r can be achieved putting it in the observable range. The inflaton mass in the last case is confined in the range (5−9)⋅10{sup 13} GeV.
NASA Astrophysics Data System (ADS)
Uieda, Leonardo; Barbosa, Valéria C. F.
2016-10-01
Estimating the relief of the Moho from gravity data is a computationally intensive non-linear inverse problem. What is more, the modeling must take the Earths curvature into account when the study area is of regional scale or greater. We present a regularized non-linear gravity inversion method that has a low computational footprint and employs a spherical Earth approximation. To achieve this, we combine the highly efficient Bott's method with smoothness regularization and a discretization of the anomalous Moho into tesseroids (spherical prisms). The computational efficiency of our method is attained by harnessing the fact that all matrices involved are sparse. The inversion results are controlled by three hyper-parameters: the regularization parameter, the anomalous Moho density-contrast, and the reference Moho depth. We estimate the regularization parameter using the method of hold-out cross-validation. Additionally, we estimate the density-contrast and the reference depth using knowledge of the Moho depth at certain points. We apply the proposed method to estimate the Moho depth for the South American continent using satellite gravity data and seismological data. The final Moho model is in accordance with previous gravity-derived models and seismological data. The misfit to the gravity and seismological data is worse in the Andes and best in oceanic areas, central Brazil and Patagonia, and along the Atlantic coast. Similarly to previous results, the model suggests a thinner crust of 30-35 km under the Andean foreland basins. Discrepancies with the seismological data are greatest in the Guyana Shield, the central Solimões and Amazonas Basins, the Paraná Basins, and the Borborema province. These differences suggest the existence of crustal or mantle density anomalies that were unaccounted for during gravity data processing.
Observations of gravity waves from satellite and implications for the wave driving of the SAO
NASA Astrophysics Data System (ADS)
Ern, Manfred; Preusse, Peter; Riese, Martin
2015-04-01
The dynamics at low latitudes in the stratosphere and lower mesosphere is governed by an interplay of the quasi-biennial oscillation (QBO) and the semiannual oscillation (SAO) of the zonal wind. It is known that tropical dynamics has significant influence on the atmosphere over a large range of altitudes and latitudes. For example, QBO and SAO effects are seen in the MLT region, and there is a significant influence of the QBO on surface weather and climate in the Northern Hemisphere during winter. Still, global models have large difficulties in simulating a realistic QBO and SAO. One main uncertainty is the wave driving of these oscillations, in particular the driving by gravity waves (GWs). We derive GW temperature variances, GW momentum fluxes and potential GW drag from over three years of High Resolution Dynamics Limb Sounder (HIRDLS) satellite data in the stratopause region. These observations are compared with the SAO driving due to planetary waves, as well as the zonal wind tendencies, both determined from the ECMWF ERA-Interim (ERAI) reanalysis. HIRDLS satellite observations and ERAI support the general assumption that, due to selective filtering of the GW spectrum by the QBO in the stratosphere, GWs mainly contribute to the SAO momentum budget during SAO eastward wind shear. However, during SAO westward wind shear the GW contribution is usually smaller, and the wave driving is dominated by planetary waves, probably of extratropical origin. Still, we find indications in both satellite observations and ERAI that sometimes GW drag is important also during SAO westward wind shear.
NASA Astrophysics Data System (ADS)
Snively, J. B.; Zettergren, M. D.
2013-12-01
The existence of acoustic waves (periods ~1-5 minutes) and gravity waves (periods >4 minutes) in the ionosphere above active tropospheric convection has been appreciated for more than forty years [e.g., Georges, Rev. Geophys. and Space Phys., 11(3), 1973]. Likewise, gravity waves exhibiting cylindrical symmetry and curvature of phase fronts have been observed via imaging of the mesospheric airglow layers [e.g., Yue et al., JGR, 118(8), 2013], clearly associated with tropospheric convection; gravity wave signatures have also recently been detected above convection in ionospheric total electron content (TEC) measurements [Lay et al., GRL, 40, 2013]. We here investigate the observable features of acoustic waves, and their relationship to upward-propagating gravity waves generated by the same sources, as they arrive in the mesosphere, lower-thermosphere, and ionosphere (MLTI). Numerical simulations using a nonlinear, cylindrically-axisymmetric, compressible atmospheric dynamics model confirm that acoustic waves generated by transient tropospheric sources may produce "concentric ring" signatures in the mesospheric hydroxyl airglow layer that precede the arrival of gravity waves. As amplitudes increase with altitude and decreasing neutral density, the modeled acoustic waves achieve temperature and vertical wind perturbations on the order of ~10s of Kelvin and m/s throughout the E- and F-region. Using a coupled multi-fluid ionospheric model [Zettergren and Semeter, JGR, 117(A6), 2012], extended for low-latitudes using a 2D dipole magnetic field coordinate system, we investigate acoustic wave perturbations to the ionosphere in the meridional direction. Resulting perturbations are predicted to be detectable by ground-based radar and GPS TEC measurements, or via in situ instrumentation. Although transient and short-lived, the acoustic waves' airglow and ionospheric signatures are likely to in some cases be observable, and may provide important insight into the regional
NASA Astrophysics Data System (ADS)
Watanabe, Shingo; Miyahara, Saburo
2009-04-01
The interaction of gravity waves (GWs) and the migrating diurnal tide are studied in a GW-resolving general circulation model (GCM) by calculating the tidal components of zonal wind accelerations and equivalent Rayleigh friction due to tidal induced GW dissipation. Two 15-day periods for perpetual equinoctial and solstice simulations are analyzed, which are performed with the Japanese Atmospheric General circulation model for Upper Atmosphere Research (JAGUAR) high-resolution GCM. The model can directly simulate GWs with horizontal wavelengths greater than about 190 km, and, thus reproduce the general features of the mean winds and temperatures from the surface to the mesosphere and lower thermosphere (MLT). The amplitudes of the migrating diurnal tide are successfully simulated during both seasons, and the tidal winds affect the altitudes of GW dissipation in the low-latitude MLT. The tidal component of GW forcing has maximal values of about 15 m s-1 d-1 near the maximal vertical shears of the tidal winds and generally works to shorten the vertical wavelength of the migrating diurnal tide. The phase relationship between the tidal winds and the tidal induced GW forcing is not exactly 90° out of phase, causing amplification/suppression of the tide. The GW forcing amplifies the migrating diurnal tide during the equinox, while during the solstice, it suppresses the tidal winds in the upper mesosphere of both hemispheres. This difference in behavior can be attributed to a seasonal variation of the mean zonal winds, because combination of the mean and tidal winds affects the altitudes of GW dissipation.
Modeling study of the impacts of inertial gravity wave forcing in middle atmosphere polar region
NASA Astrophysics Data System (ADS)
Tan, B.; Liu, H.; Chu, X.
2012-12-01
The 'cold pole' problem refers to the cold bias of polar stratosphere temperature in the Southern Hemisphere in most general circulation models (GCMs) and chemistry climate models (CCMs) during the winter and spring. Accompanying the 'cold pole' is the excessively strong jet in the stratosphere and late vortex breaking. It is a long-standing problem in most models, implying the lack of wave forcing in the southern stratosphere. In current study we investigate the feasibility of using parameterized inertial gravity wave forcing to reduce the cold bias. The NCAR Whole Atmosphere Community Climate Model (WACCM 4.0) is used for this study. A new scheme that parameterizes inertial gravity waves is included in the WACCM. Although the inertial gravity waves are likely to break in the stratosphere and impact the middle atmosphere circulation, they are not well resolved by the model nor properly parameterized. Using the new gravity wave scheme, the simulated wintertime temperature is ~20 K warmer in the southern polar region while the simulated wintertime zonal wind jet is about 10 to 30 m/s slower than the originals. Also, the polar vortex in the Southern Hemisphere breaks earlier and the wind reversal level during spring is lower. All these changes make the WACCM simulations closer to ERA-40, suggesting that additional gravity waves are able to reduce the 'cold pole' bias.
Mesoscale Gravity Waves Generated by Tropical Convection: An Examination of the Results
NASA Technical Reports Server (NTRS)
Pfister, Leonhard; Bui, P.; Chan, K. Roland (Technical Monitor)
1997-01-01
Convection represents the predominant source of gravity wave energy from the tropical troposphere. These gravity waves are of clear importance to stratospheric dynamics through their momentum flux, and the distribution of that momentum flux in phase speed. This momentum flux drives large scale mean circulations, such as the quasi-biennial oscillation, which are important in the transport of trace constituents and pollutants from stratospheric aircraft. Unlike topographically generated waves, whose momentum flux is strongly peaked at one phase speed (stationary), the momentum flux distribution of highly transient convective sources is broadly distributed in phase speed. The nature of that distribution as well as the overall magnitude of the momentum flux associated with convectively generated gravity waves is important. This is because in the tropical stratosphere gravity waves break, deposit their momentum, and exert a drag at the level where their phase speed is comparable to the mean flow. In the tropics, the stratospheric mean flow varies strongly with altitude, season, and interannually. In fact, gravity waves play a critical role in driving these variations. Additional information is contained in the original extended abstract.
On the detection and attribution of gravity waves generated by the 20 March 2015 solar eclipse.
Marlton, G J; Williams, P D; Nicoll, K A
2016-09-28
Internal gravity waves are generated as adjustment radiation whenever a sudden change in forcing causes the atmosphere to depart from its large-scale balanced state. Such a forcing anomaly occurs during a solar eclipse, when the Moon's shadow cools part of the Earth's surface. The resulting atmospheric gravity waves are associated with pressure and temperature perturbations, which in principle are detectable both at the surface and aloft. In this study, surface pressure and temperature data from two UK sites at Reading and Lerwick are examined for eclipse-driven gravity wave perturbations during the 20 March 2015 solar eclipse over northwest Europe. Radiosonde wind data from the same two sites are also analysed using a moving parcel analysis method, to determine the periodicities of the waves aloft. On this occasion, the perturbations both at the surface and aloft are found not to be confidently attributable to eclipse-driven gravity waves. We conclude that the complex synoptic weather conditions over the UK at the time of this particular eclipse helped to mask any eclipse-driven gravity waves.This article is part of the themed issue 'Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse'.
On the detection and attribution of gravity waves generated by the 20 March 2015 solar eclipse
2016-01-01
Internal gravity waves are generated as adjustment radiation whenever a sudden change in forcing causes the atmosphere to depart from its large-scale balanced state. Such a forcing anomaly occurs during a solar eclipse, when the Moon’s shadow cools part of the Earth’s surface. The resulting atmospheric gravity waves are associated with pressure and temperature perturbations, which in principle are detectable both at the surface and aloft. In this study, surface pressure and temperature data from two UK sites at Reading and Lerwick are examined for eclipse-driven gravity wave perturbations during the 20 March 2015 solar eclipse over northwest Europe. Radiosonde wind data from the same two sites are also analysed using a moving parcel analysis method, to determine the periodicities of the waves aloft. On this occasion, the perturbations both at the surface and aloft are found not to be confidently attributable to eclipse-driven gravity waves. We conclude that the complex synoptic weather conditions over the UK at the time of this particular eclipse helped to mask any eclipse-driven gravity waves. This article is part of the themed issue ‘Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse’. PMID:27550763
Non-linear Langmuir waves in a warm quantum plasma
Dubinov, Alexander E. Kitaev, Ilya N.
2014-10-15
A non-linear differential equation describing the Langmuir waves in a warm quantum electron-ion plasma has been derived. Its numerical solutions of the equation show that ordinary electronic oscillations, similar to the classical oscillations, occur along with small-scale quantum Langmuir oscillations induced by the Bohm quantum force.
Mathematical Methods in Wave Propagation: Part 2--Non-Linear Wave Front Analysis
ERIC Educational Resources Information Center
Jeffrey, Alan
1971-01-01
The paper presents applications and methods of analysis for non-linear hyperbolic partial differential equations. The paper is concluded by an account of wave front analysis as applied to the piston problem of gas dynamics. (JG)
The Transfer Function Model (TFM) as a Tool for Simulating Gravity Wave Phenomena in the Mesosphere
NASA Astrophysics Data System (ADS)
Porter, H.; Mayr, H.; Moore, J.; Wilson, S.; Armaly, A.
2008-12-01
The Transfer Function Model (TFM) is semi-analytical and linear, and it is designed to describe the acoustic gravity waves (GW) propagating over the globe and from the ground to 600 km under the influence of vertical temperature variations. Wave interactions with the flow are not accounted for. With an expansion in terms of frequency-dependent spherical harmonics, the time consuming vertical integration of the conservation equations is reduced to computing the transfer function (TF). (The applied lower and upper boundary conditions assure that spurious wave reflections will not occur.) The TF describes the dynamical properties of the medium divorced from the complexities of the temporal and horizontal variations of the excitation source. Given the TF, the atmospheric response to a chosen source is then obtained in short order to simulate the GW propagating through the atmosphere over the globe. In the past, this model has been applied to study auroral processes, which produce distinct wave phenomena such as: (1) standing lamb modes that propagate horizontally in the viscous medium of the thermosphere, (2) waves generated in the auroral oval that experience geometric amplification propagating to the pole where constructive interference generates secondary waves that propagate equatorward, (3) ducted modes propagating through the middle atmosphere that leak back into the thermosphere, and (4) GWs reflected from the Earth's surface that reach the thermosphere in a narrow propagation cone. Well-defined spectral features characterize these wave modes in the TF to provide analytical understanding. We propose the TFM as a tool for simulating GW in the mesosphere and in particular the features observed in Polar Mesospheric Clouds (PMC). With present-day computers, it takes less than one hour to compute the TF, so that there is virtually no practical limitation on the source configurations that can be applied and tested in the lower atmosphere. And there is no limitation on
Auroral origin of medium scale gravity waves in neutral composition and temperature
NASA Technical Reports Server (NTRS)
Chandra, S.; Spencer, N. W.; Krankowsky, D.; Laemmerzahl, P.
1979-01-01
The kinetic temperature and neutral composition data obtained from the Aeros B neutral atmosphere temperature experiment and the neutral and ion mass spectrometer show spatial structures characteristic of medium scale gravity waves with a wavelength in the range of several hundred kilometers. These waves are associated with auroral activity, and their spatial structure reflects the time history of the auroral electrojet. The medium scale gravity waves tend to propagate to mid-latitudes on the nightside. On the dayside their range is limited to high latitudes. Gravity waves are carriers of auroral energy to middle and low latitudes where they may cause irreversible changes in temperature via viscous dissipation. Since auroral activity occurs frequently, it is suggested that this energy reaches the mid-latitude region of the thermosphere much more frequently than is indicated by planetary magnetic indices.
Vertical temperature and density patterns in the Arctic mesosphere analyzed as gravity waves
NASA Technical Reports Server (NTRS)
Eberstein, I. J.; Theon, J. S.
1975-01-01
Rocket soundings conducted from high latitude sites in the Arctic mesosphere are described. Temperature and wind profiles and one density profile were observed independently to obtain the thermodynamic structure, the wind structure, and their interdependence in the mesosphere. Temperature profiles from all soundings were averaged, and a smooth curve (or series of smooth curves) drawn through the points. A hydrostatic atmosphere based on the average, measured temperature profile was computed, and deviations from the mean atmosphere were analyzed in terms of gravity wave theory. The vertical wavelengths of the deviations were 10-20 km, and the wave amplitudes slowly increased with height. The experimental data were matched by calculated gravity waves having a period of 15-20 minutes and a horizontal wavelength of 60-80 km. The wind measurements are consistent with the thermodynamic measurements. The results also suggest that gravity waves travel from East to West with a horizontal phase velocity of approximately 60 m sec-1.
NASA Astrophysics Data System (ADS)
England, S. L.; Dobbin, A.; Harris, M. J.; Arnold, N. F.; Aylward, A. D.
2006-02-01
Momentum deposition by gravity wave breaking is known to affect the amplitude and phase of the diurnal tide. Modelling studies of this interaction have produced some conflicting results and as yet, the exact nature of this interaction is not fully understood. In this study, the effects of parameterised gravity wave momentum deposition on the diurnal tide and subsequently on green line airglow from atomic oxygen during equinox are investigated using the Coupled Middle Atmosphere and Thermosphere (CMAT) general circulation model. The effects of gravity wave drag calculated by two different parameterisations, Meyer [1999. Gravity wave interactions with the diurnal propagating tide. Journal of Geophysical Research 104, 4223 4239] and Medvedev and Klaassen [2000. Parameterisation of gravity wave momentum deposition based on non-linear wave interactions: basic formulation and sensitivity tests. Journal of Atmospheric and Terrestrial Physics 62, 1015 1033], are compared in the low latitude MLT region between 70 and 120 km, where the amplitude of the diurnal tide and green line volume emission rates maximise. Results indicate that momentum sources from both gravity wave parameterisations act to reduce the mid-latitude zonal jets and advance the phase of the diurnal tide, such that the peak amplitude at a given height occurs at an earlier time of day. Gravity wave momentum deposition as parameterised by Meyer [1999. Gravity wave interactions with the diurnal propagating tide. Journal of Geophysical Research 104, 4223 4239] results in a reduction of the amplitude of the diurnal tide in the MLT region, whereas the tidal amplitude is increased when the Medvedev and Klaassen [2000. Parameterisation of gravity wave momentum deposition based on non-linear wave interactions: basic formulation and sensitivity tests. Journal of Atmospheric and Terrestrial Physics 62, 1015 1033] parameterisation is used. Both parameterisations affect the local time variability of the simulated
Convectively Generated Meso-Scale Gravity Waves in ER-2 Observations During CRYSTAL-FACE
NASA Astrophysics Data System (ADS)
Wang, L.; Alexander, M. J.
2004-12-01
The MMS and MTP data from ER-2 observations during the CRYSTAL-FACE campaign are analyzed to retrieve meso-scale gravity wave information at the aircraft flight level. For a given flight segment, the S-transform is used to locate small-scale (10-25 km) gravity wave events. The Stokes method and the MTP method are then used to determine the horizontal propagation directions, and the vertical scales of the wave events, respectively. Other wave parameters, such as horizontal scales, group velocities, can also be derived. From the estimated propagation directions, group velocities, and the ground-based radar reflectivity observations, some wave events are traced back to convectively active regions, suggesting convection as the source of the waves.
Investigation of the role of gravity waves in the generation of equatorial bubbles
NASA Technical Reports Server (NTRS)
Johnson, Francis S.; Coley, William R.
1995-01-01
The following areas of interest in this progress report are: (1) the continuation of software development in the examination of F-region gravity-wave power using in-situ data from the Atmosphere Explorer (AE-E); (2) the inquiry into the use of the San Marco data for the study of the initiation and growth of bubbles, particularly when the satellite passes through the early evening hours at relatively high altitudes, and the development of bubbles using not only the San Marco data but includes the use of airglow observations made in Hawaii; and (3) the promising development in the observation of distinct well formed waves at about 400 km altitude in the equatorial region. These waves look very much like waves seen over the polar cap that are attributed to internal gravity waves in the neutral atmosphere driving ionization up and down the magnetic field lines. These equatorial waves show no modulation of the total ion concentration.
Observation of gravity waves during the extreme tornado outbreak of 3 April 1974
NASA Technical Reports Server (NTRS)
Hung, R. J.; Phan, T.; Smith, R. E.
1978-01-01
A continuous wave-spectrum high-frequency radiowave Doppler sounder array was used to observe upper-atmospheric disturbances during an extreme tornado outbreak. The observations indicated that gravity waves with two harmonic wave periods were detected at the F-region ionospheric height. Using a group ray path computational technique, the observed gravity waves were traced in order to locate potential sources. The signals were apparently excited 1-3 hours before tornado touchdown. Reverse ray tracing indicated that the wave source was located at the aurora zone with a Kp index of 6 at the time of wave excitation. The summation of the 24-hour Kp index for the day was 36. The results agree with existing theories (Testud, 1970; Titheridge, 1971; Kato, 1976) for the excitation of large-scale traveling ionospheric disturbances associated with geomagnetic activity in the aurora zone.
Observation of Wood's anomalies on surface gravity waves propagating on a channel.
Schmessane, Andrea
2016-09-01
I report on experiments demonstrating the appearance of Wood's anomalies in surface gravity waves propagating along a channel with a submerged obstacle. Space-time measurements of surface gravity waves allow one to compute the stationary complex field of the wave and the amplitude growth of localized and propagative modes over all the entire channel, including the scattering region. This allows one to access the near and far field dynamics, which constitute a new and complementary way of observation of mode resonances of the incoming wave displaying Wood's anomalies. Transmission coefficient, dispersion relations and normalized wave energy of the incoming wave and the excited mode are measured and found to be in good agreement with theoretical predictions.
Density Waves in Saturn's Rings: Non-linear Dispersion and Moon Libration Effects
NASA Astrophysics Data System (ADS)
Sremcevic, Miodrag; Stewart, G. R.; Albers, N.; Colwell, J. E.; Esposito, L. W.
2008-05-01
We analyze strong spiral density waves in stellar occultations by Saturn's A ring observed with the Cassini Ultraviolet Imaging Spectrograph (UVIS) and find that waves dispersion relation exhibits a clear deviation from the linear trend. All waves examined here reveal an intrinsic quadratic radial dependence on the wavenumber. We provide evidence that the deviation from the linear trend is caused by the ring's pressure term acting against the self-gravity of the ring particles. From the observed dispersion relation and using the theory of Goldreich and Tremaine (1978, 1979, ApJ) where the pressure is parameterized as p=σ c2, we measure the velocity dispersion c=2-5 mm/s in the A ring. Additionally, in all first order Pandora waves the dispersion relation exhibits a wiggly structure. Comparing 60 stellar UVIS occultations between 2004 and 2008 we infer that this wavenumber oscillation propagates away from the resonance location with a period of about 600 days. This inferred period is consistent with the 3:2 near corotation resonance between Pandora and Mimas (French et al., 2003, Icarus). The observed libration in wavenumber allows us to accurately measure the group velocity in the rings and obtain independent estimates of both surface density and velocity dispersion of the rings.
NASA Technical Reports Server (NTRS)
Koch, Steven E.; Golus, Robert E.; Dorian, Paul B.
1988-01-01
The interactions between preexisting gravity waves and convective systems were investigated using data obtained by the Cooperative Convection Precipitation Experiment observational network in Montana on July 11-12, 1981. The results indicate that strong convection substantially affects gravity waves locally by augmenting the wave amplitude, reducing its wavelength, distorting the wave shape, altering the wave phase velocity, and greatly weakening the in-phase covariance between the perturbation wind and pressure fields. These convective effects upon gravity waves are explained in terms of hydrostatic and nonhydrostatic pressure forces and gust front processes associated with thunderstorms.
Quantum Linear Gravity in de Sitter Universe on Gupta-Bleuler Vacuum State
NASA Astrophysics Data System (ADS)
Enayati, M.; Takook, M. V.; Rouhani, S.
2017-04-01
Application of Krein space quantization to the linear gravity in de Sitter space-time have constructed on Gupta-Bleuler vacuum state, resulting in removal of infrared divergence and preserving de Sitter covariant. By pursuing this path, the non uniqueness of vacuum expectation value of the product of field operators in curved space-time disappears as well. Then the vacuum expectation value of the product of field operators can be defined properly and uniquely.
On the spectrum of thermospheric gravity waves observed by the Super Dual Auroral Radar Network
NASA Astrophysics Data System (ADS)
Bristow, W. A.; Greenwald, R. A.
1997-06-01
The spectrum of acoustic gravity waves in the thermosphere observed using the Super Dual Auroral Radar Network HF radar network is presented and various features are discussed. HF radars are sensitive to medium-scale gravity waves in the thermosphere that interact with the F-region ionization. The interaction of waves in the neutral atmosphere with the ionization is discussed to determine the relationship of the observed spectrum to the gravity wave spectrum. The observations showed that (1) the observed spectrum shows peaks at frequencies that correspond to quasi-monochromatic wave packets observed in the time series; (2) the spectrum often shows multiple peaks at harmonic frequencies; and (3) the spectrum nearly always shows a background level with a power law decrease having a slope of -5/3. It was also found that the overall level of the spectrum was elevated when gravity waves were present, possibly indicating an energy cascade process from the quasi-monochromatic wave to the power law background.
NASA Astrophysics Data System (ADS)
Ličer, Matjaž; Mourre, Baptiste; Troupin, Charles; Krietemeyer, Andreas; Jansá, Agusti; Tintoré, Joaquín
2017-03-01
We use a high resolution nested ocean modelling system forced by synthetic atmospheric gravity waves to investigate Balearic meteotsunami generation, amplification and propagation properties. We determine how meteotsunami amplitude outside and inside of the Balearic port of Ciutadella depends on forcing gravity wave direction, speed and trajectory. We quantify the contributions of Mallorca shelves and Menorca Channel for different gravity wave forcing angles and speeds. The Channel is demonstrated to be the key build-up region determining meteotsunami amplitude in Ciutadella while northern and southern Mallorca shelves serve mostly as barotropic wave guides but do not significantly contribute to seiche amplitude in Ciutadella. This fact seriously reduces early-warning alert times in cases of locally generated pressure perturbations. We track meteotsunami propagation paths in the Menorca Channel for several forcing velocities and show that the Channel bathymetry serves as a focusing lens for meteotsunami waves whose paths are constrained by the forcing direction. We show that faster meteotsunamis propagate over deeper ocean regions, as required by Proudman resonance. We estimate meteotsunami speed under sub- and supercritical forcing and derive a first order estimate of its magnitude. We show that meteotsunamis, generated by supercritical gravity waves, propagate with a velocity which is equal to an arithmetic mean of the forcing velocity and local barotropic ocean wave speed.
Gravity waves observation of wind field in stratosphere based on a Rayleigh Doppler lidar.
Zhao, Ruocan; Dou, Xiankang; Sun, Dongsong; Xue, Xianghui; Zheng, Jun; Han, Yuli; Chen, Tingdi; Wang, Guocheng; Zhou, Yingjie
2016-03-21
Simultaneous wind and temperature measurements in stratosphere with high time-spatial resolution for gravity waves study are scarce. In this paper we perform wind field gravity waves cases in the stratosphere observed by a mobile Rayleigh Doppler lidar. This lidar system with both wind and temperature measurements were implemented for atmosphere gravity waves research in the altitude region 15-60 km. Observations were carried out for two periods of time: 3 months started from November 4, 2014 in Xinzhou, China (38.425°N,112.729°E) and 2 months started from October 7, 2015 in Jiuquan, China (39.741°N, 98.495°E) . The mesoscale fluctuations of the horizontal wind velocity and the two dimensional spectra analysis of these fluctuations show the presence of dominant oscillatory modes with wavelength of 4-14 km and period of around 10 hours in several cases. The simultaneous temperature observations make it possible to identify gravity wave cases from the relationships between different variables: temperature and horizontal wind. The observed cases demonstrate the Rayleigh Doppler Lidar's capacity to study gravity waves.
NASA Astrophysics Data System (ADS)
Fritts, David C.; Janches, Diego
2008-03-01
A previous study by Zhou and Morton (2006) employed dual-beam incoherent scatter radar measurements of radial velocities at the Arecibo Observatory to study the structure, dynamics, and momentum fluxes of gravity waves in the mesosphere and lower thermosphere for ˜8 h on 28 July 2001. Because of erroneous assumptions about wave character and inferences of the relationship between radial velocities, however, the advertised results of this previous study are largely in error. The purposes of the present study are both to point out these errors to help avoid such pitfalls in the future and to provide a new interpretation of these data, which represent a very interesting case study of gravity wave dynamics at these altitudes. Specific findings of the present study (largely in contradiction to the previous analysis) include (1) the ˜15-min oscillation was apparently a large-amplitude Doppler-ducted gravity wave structure propagating at one or two maxima of the westward large-scale wind present during the event; (2) the gravity wave exhibited a deep and coherent vertical phase structure, except between the two westward wind maxima at later times, entirely inconsistent with proximity to a critical level; (3) the dominant motions within the gravity wavefield were vertical velocities up to ˜10 m s-1, except for inferred horizontal motions where the vertical motions changed phase and above and below the vertical velocity maxima, as dictated by the continuity equation; (4) there were likely no regions of dynamical instability accompanying these ducted wave motions; and (5) momentum fluxes due to this wave motion were small, despite its very large amplitude.
A linear phase retrieval wave-front sensor
NASA Astrophysics Data System (ADS)
Li, Min; Li, Xin-Yang; Jiang, Wen-Han
2008-12-01
A method to retrieve small phase aberration from a single far-field image is proposed. It only needs to calibrate the inherent aberration of the imaging system once, and then the difference between a single measured image with aberration and the calibrated image with inherent aberration is got to retrieve the disturbed phase aberration by an approximate linear relationship. Computer simulations are employed to analyze the performance of this linear phase retrieval (LPR) wave-front sensor. The dynamic range of this method is discussed without noise to judge how small it is needed to satisfy the method. The results show that the proposed small phase retrieval method works well when the RMS phase error is less than 1.6 rad. The Linear Phase Retrieval wave-front sensor and the Hartmann-Shack wave-front sensor are compared on the same stochastic wave-front aberration. The influence of different calculation condition on the retrieval results is compared and analyzed. After analyzing the target resolution, it is thought that a reasonable target size is advantageous to the retrieval precision. At the same time, the LPR sensor can realize the alike precision measurement by using less detect cell, such as 8 pixelx8 pixel in our experiment. From the retrieval results of different orders, the error rate are less than 0.25 and it is comparatively accurate to retrieve pre-35 order aberrations.
Characteristics of Mesospheric Gravity Waves Observed in the Central Region of Brazil
NASA Astrophysics Data System (ADS)
Wrasse, Cristiano Max; Messias Almeida, Lazaro; Abalde Guede, Jose Ricardo; Valentin Bageston, José; Pillat, Valdir G.; Lima, Washington L. C.
Gravity waves observations were carried out at Palmas (10.16o S, 48.26o W) Brazil, between September 2007 and December 2008, using an all-sky airglow imager to measure the OH emis-sion. The gravity waves were divided in two groups following they morphology as band and ripples type waves. The main characteristics of the band type waves are: horizontal wavelength between 10-35 km; observed period raging from 5 to 25 minutes; observed phase speed between 5-60 m/s. Preferential propagation directions of the bands are northward and southward, show-ing a clear anisotropy. For the ripples the main wave parameters are: horizontal wavelength ranging between 5 and 15 km; observed period mainly distributed between 5 and 15 minutes and horizontal phase velocity from 5 to 30 m/s. The ripples showed the same anisotropy as in the preferential propagation direction as the band type waves. The gravity wave characteristics observed at Palmas were compared with other observations carried out in Brazil, showing simi-lar features. In order to explain the seasonal variation of the wave propagation direction, maps of Outgoing Longwave Radiation (ORL) were used to locate regions with intense deep con-vection (OLR < 220 W.m-2 ) in the lower atmosphere. During summer and autumn the wave sources regions are well correlated with deep convection areas located at west and northwest of Palmas.
Improving GOMOS High Resolution Temperature validation by discriminating atmospheric gravity waves
NASA Astrophysics Data System (ADS)
Quirino Iannone, Rosario; Casadio, Stefano; Saavedra de Miguel, Lidia; De Laurentis, Marta; Brizzi, Gabriele; Dehn, Angelika
2013-04-01
Atmospheric gravity waves play an important role in the thermodynamic processes of the atmosphere. The gravity waves, once generated in the upper troposphere and lower stratosphere, propagate upward and deposit their energy and momentum when dissipating. These atmospheric waves can cause strong fluctuations in the thermal structure of the middle and upper atmosphere. The satellite temperature retrievals, together with innovative analysis methods, are often used to provide constraints for model parameterization, which can improve the treatment of these phenomena in climate-prediction models, as the temperature profiles are expected to present wave-like structures due to the global distribution of the gravity-wave momentum flux. The analysis of temperature variability as a function of spatial and temporal separation indicates that gravity wave activity has impacts also on validation study site selection. The aim of this study is to analyse the characteristics of the atmospheric gravity waves detectable in the GOMOS (Global Ozone Monitoring by Occultation of Stars) High Resolution Temperature Profiles (HRTP). These are collected over altitudes ranging from 18 to 35 km, in the 2002 to 2012 time period. The GOMOS instrument is a medium-resolution star-occultation spectrometer operating in the ultraviolet-visible-near-infrared (UV-VIS-NIR) spectral range, onboard of the ESA/ENVISAT platform. The HRTP products are the result of the analysis of the two fast photometer measurements, and the retrieval is based on a GPS-like inversion scheme (Kyrola et al., 2010). Following our new approach, based on the use of the "Morlet" wavelet transform (Torrence and Compo, 1998), it is possible to capture the vertical amplitude and phase of waves of very different size along the temperature profile. The wavy signal is estimated and subtracted to the original profile, thus providing a "wave-free" profile. Comparison of wave-free temperature profiles and gravity wave structures with those
Interaction of acoustic-gravity waves with an elastic shelf-break
NASA Astrophysics Data System (ADS)
Tian, Miao; Kadri, Usama
2016-04-01
In contrast to surface gravity waves that induce flow field which decays exponentially with depth, acoustic-gravity waves oscillate throughout the water column. Their oscillatory profile exerts stresses to the ground which provides a natural explanation for the earth's microseism (Longuet-Higgins, 1950). This work is an extension of the shelf-break problem by Kadri and Stiassnie (2012) who considered the sea floor and the shelf-break to be rigid, and the elastic problem by Eyov et al. (2013) who illustrated the importance of the sea-floor elasticity. In this study we formulate and solve the two-dimensional problem of an incident acoustic-gravity wave mode propagating over an elastic wall and interacting with a shelf-break in a weakly compressible fluid. As the modes approach the shelf-break, part of the energy is reflected whereas the other part is transmitted. A mathematical model is formulated by matching particular solutions for each subregion of constant depth along vertical boundaries; the resulting matrix equation is then solved numerically. The physical properties of these waves are studied, and compared with those for waves over a rigid bottom. The present work broadens our knowledge of acoustic-gravity-waves propagation in realistic environment and can potentially benefit the early detection of tsunami, generated from landslides or submarine earthquakes. References Eyov E., Klar A., Kadri U. , Stiassnie M. 2013 Progressive waves in a compressible-ocean with an elastic bottom. Wave Motion 50, 929-939. Kadri, U., and M. Stiassnie, 2012 Acoustic-Gravity waves interacting with the shelf break. J. Geophys. Res. 117, C03035. Longuet-Higgins, M.S. 1950 A theory of the origin of microseisms. Philos. Trans. R. Soc. Lond. A 243, 1-35.
Linear and Nonlinear MHD Wave Processes in Plasmas. Final Report
Tataronis, J. A.
2004-06-01
This program treats theoretically low frequency linear and nonlinear wave processes in magnetized plasmas. A primary objective has been to evaluate the effectiveness of MHD waves to heat plasma and drive current in toroidal configurations. The research covers the following topics: (1) the existence and properties of the MHD continua in plasma equilibria without spatial symmetry; (2) low frequency nonresonant current drive and nonlinear Alfven wave effects; and (3) nonlinear electron acceleration by rf and random plasma waves. Results have contributed to the fundamental knowledge base of MHD activity in symmetric and asymmetric toroidal plasmas. Among the accomplishments of this research effort, the following are highlighted: Identification of the MHD continuum mode singularities in toroidal geometry. Derivation of a third order ordinary differential equation that governs nonlinear current drive in the singular layers of the Alfvkn continuum modes in axisymmetric toroidal geometry. Bounded solutions of this ODE implies a net average current parallel to the toroidal equilibrium magnetic field. Discovery of a new unstable continuum of the linearized MHD equation in axially periodic circular plasma cylinders with shear and incompressibility. This continuum, which we named “accumulation continuum” and which is related to ballooning modes, arises as discrete unstable eigenfrequency accumulate on the imaginary frequency axis in the limit of large mode numbers. Development of techniques to control nonlinear electron acceleration through the action of multiple coherent and random plasmas waves. Two important elements of this program aye student participation and student training in plasma theory.
Startup performance of the traveling wave versus standing wave linear accelerator.
Buchgeister, M; Nüsslin, F
1998-04-01
The startup performance of medical linear accelerators is of increasing importance for modern radiotherapy techniques. The traveling wave-type linear accelerator of the SL series of Philips (now Elekta Oncology Systems) has been modified in its flight tube design to meet this goal of a fast rise time of the radiation field. The new slitless flight tube combined with a redesigned gun servo electronic now achieves start up times of the radiation comparable with those of a standing wave linear accelerator (Siemens Mevatron) according to our measurements.
The Role of Gravity Waves in the Formation and Organization of Clouds during TWPICE
Reeder, Michael J.; Lane, Todd P.; Hankinson, Mai Chi Nguyen
2013-09-27
All convective clouds emit gravity waves. While it is certain that convectively-generated waves play important parts in determining the climate, their precise roles remain uncertain and their effects are not (generally) represented in climate models. The work described here focuses mostly on observations and modeling of convectively-generated gravity waves, using the intensive observations from the DoE-sponsored Tropical Warm Pool International Cloud Experiment (TWP-ICE), which took place in Darwin, from 17 January to 13 February 2006. Among other things, the research has implications the part played by convectively-generated gravity waves in the formation of cirrus, in the initiation and organization of further convection, and in the subgrid-scale momentum transport and associated large-scale stresses imposed on the troposphere and stratosphere. The analysis shows two groups of inertia-gravity waves are detected: group L in the middle stratosphere during the suppressed monsoon period, and group S in the lower stratosphere during the monsoon break period. Waves belonging to group L propagate to the south-east with a mean intrinsic period of 35 h, and have vertical and horizontal wavelengths of about 5-6 km and 3000-6000 km, respectively. Ray tracing calculations indicate that these waves originate from a deep convective region near Indonesia. Waves belonging to group S propagate to the south-south-east with an intrinsic period, vertical wavelength and horizontal wavelength of about 45 h, 2 km and 2000-4000 km, respectively. These waves are shown to be associated with shallow convection in the oceanic area within about 1000 km of Darwin. The intrinsic periods of high-frequency waves are estimated to be between 20-40 minutes. The high-frequency wave activity in the stratosphere, defined by mass-weighted variance of the vertical motion of the sonde, has a maximum following the afternoon local convection indicating that these waves are generated by local convection
NASA Astrophysics Data System (ADS)
Kim, E. H.; Valeo, E. J.; Johnson, J.; Kim, H.; Lee, D. H.; Phillips, C.
2014-12-01
We have developed a two-dimensional, finite element code that solves the electromagnetic full wave equations in global magnetospheric geometry. The code produces the three-dimensional wave structure, including mode conversion effects, for plasma waves launched in a two-dimensional axisymmetric background plasma with general magnetic field topology. Using this code, we have examined how EMIC waves are generated and propagated along the magnetic field line. While left-handed polarized EMIC waves are known to be excited by the cyclotron instability associated with hot and anisotropic ion distributions in the equatorial region of the magnetosphere, the generation mechanism of linear and right-handed polarized EMIC waves, which are often observed near the magnetic equator, remains as one of the unsolved scientific questions. In this presentation, we show the linear polarization of the EMIC waves can be explained by mode conversion at the ion-ion hybrid (IIH) resonance (an analogue of the field-line resonance when the resonance frequency is on the order of the heavy ion cyclotron frequency) when externally driven compressional waves propagate into an increasing/decreasing heavy ion concentration or inhomogeneous magnetic field. Since these mode-converted waves depend sensitively on the heavy ion concentration, it possible to estimate the heavy ion concentration ratio from the wave propagation characteristics. We also evaluated the absorption coefficients at the IIH resonance at Earth's geosynchronous orbit for variable concentrations of He+ and wave frequencies and have found that the resonance only occurs for a limited range of wave frequencies, defined such that the IIH resonance frequency is close to, but not exactly the same as the crossover frequency. Using the wave absorption and observed EMIC waves from the GOES-12 satellite, we demonstrate how this technique can be used to estimate that the He+ concentration is around 4% near L = 6.6.
Gravitational-wave observations as a tool for testing relativistic gravity
NASA Technical Reports Server (NTRS)
Eardley, D. M.; Lee, D. L.; Lightman, A. P.
1973-01-01
Gravitational radiation in the far field was examined using a formalism that encompassed all metric theories of gravity. There are six possible modes of polarization, which can be completely resolved by feasible experiments. A theoretical framework is set forth for classification of waves and theories, based on the Lorentz transformation properties of the six modes. Also shown in detail is how the six modes may be experimentally identified and to what extent such information limits the correct theory of gravity.
Compound gravity receptor polarization vectors evidenced by linear vestibular evoked potentials
NASA Technical Reports Server (NTRS)
Jones, S. M.; Jones, T. A.; Bell, P. L.; Taylor, M. J.
2001-01-01
The utricle and saccule are gravity receptor organs of the vestibular system. These receptors rely on a high-density otoconial membrane to detect linear acceleration and the position of the cranium relative to Earth's gravitational vector. The linear vestibular evoked potential (VsEP) has been shown to be an effective non-invasive functional test specifically for otoconial gravity receptors (Jones et al., 1999). Moreover, there is some evidence that the VsEP can be used to independently test utricular and saccular function (Taylor et al., 1997; Jones et al., 1998). Here we characterize compound macular polarization vectors for the utricle and saccule in hatchling chickens. Pulsed linear acceleration stimuli were presented in two axes, the dorsoventral (DV, +/- Z axis) to isolate the saccule, and the interaural (IA, +/- Y axis) to isolate the utricle. Traditional signal averaging was used to resolve responses recorded from the surface of the skull. Latency and amplitude of eighth nerve components of the linear VsEP were measured. Gravity receptor responses exhibited clear preferences for one stimulus direction in each axis. With respect to each utricular macula, lateral translation in the IA axis produced maximum ipsilateral response amplitudes with substantially greater amplitude intensity (AI) slopes than medially directed movement. Downward caudal motions in the DV axis produced substantially larger response amplitudes and AI slopes. The results show that the macula lagena does not contribute to the VsEP compound polarization vectors of the sacculus and utricle. The findings suggest further that preferred compound vectors for the utricle depend on the pars externa (i.e. lateral hair cell field) whereas for the saccule they depend on pars interna (i.e. superior hair cell fields). These data provide evidence that maculae saccule and utricle can be selectively evaluated using the linear VsEP.
Optical and near-infrared linear polarization of low and intermediate-gravity ultracool dwarfs
NASA Astrophysics Data System (ADS)
Miles-Páez, P. A.; Zapatero Osorio, M. R.; Pallé, E.; Peña Ramírez, K.
2017-04-01
We aim to study the optical and near-infrared linear polarimetric properties of a sample of young M7-L7 dwarfs (≈ 1-500 Myr) with spectroscopic signatures of low- and intermediate-gravity atmospheres. We collected optical (RIZ) and near-infrared (YJHKs) linear polarimetry images on various time-scales from ∼0.2 h to months. Linear polarization degrees in the interval 0-1.5 per cent (I and J bands) were measured with accuracies ranging from ±0.1 to ±0.9 per cent depending on the observing filter and the target brightness. We found that the young field dwarfs in our sample show similar polarimetric degrees at both I and J bands, and that there is no obvious trend with the spectral type. The two Taurus sources in our sample show intense levels of J-band linear polarization probably due to surrounding discs. By compiling data from the literature for high-gravity M7-L7 dwarfs with likely ages ≥500 Myr, we did not observe any apparent difference in the linear polarimetry intensity between the young and old samples that could be ascribed to differing atmospheric gravities. Polarimetric variability with peak to peak amplitudes up to 1.5 per cent is detected on scales of about a rotation in two out of four targets that were monitored over several hours. Long-term polarimetric variability is also detected in nearly all dwarfs of the sample with data spanning months to years.
Long-Term Global Morphology of Gravity Wave Activity Using UARS Data
NASA Technical Reports Server (NTRS)
Eckermann, Stephen D.; Jackman, Charles H. (Technical Monitor)
2000-01-01
This report provides a broad outline of the total body of research conducted during the past three years. We report on detailed model studies of the precise way in which infrared limb scanning satellites explicitly detect gravity waves, and use these insights to resolve earlier discrepant zonal mean estimates of gravity wave variances from satellite limb scanners. Detailed analysis of CRISTA temperature fluctuations are outlined, which provide new global information on long-wavelength stratospheric gravity waves generated by mountains, tropical convection and the mid-latitude jet stream- vortex system, as well as interactions higher in the mesosphere with the diurnal tide. The detailed insights gained from analyzing CRISTA data are applied to provide a multi- year analysis of stratospheric mountain waves over the Andes evident in MLS limb-track data. We also demonstrate for the first time that stratospheric temperature data from the CLAES instrument on UARS resolved gravity waves, and we highlight mountain wave information in a subset of these data. Final conclusions and recommendations are set forth, and the present findings are directly related to the original goals of the research contract. A full list of publications that resulted from this research is provided.
Long-Term Global Morphology of Gravity Wave Activity Using UARS Data
NASA Technical Reports Server (NTRS)
Eckermann, Stephen D.
2000-01-01
This report provides a broad outline of the total body of research conducted during the past three years. We report on detailed model studies of the precise way in which infrared limb scanning satellites explicitly detect gravity waves, and use these insights to resolve earlier discrepant zonal mean estimates of gravity wave variances from satellite limb scanners. Detailed analysis of CRISTA temperature fluctuations are outlined, which provide new global information on long-wavelength stratospheric gravity waves generated by mountains, tropical convection and the mid-latitude jet stream-vortex system, as well as interactions higher in the mesosphere with the diurnal tide. The detailed insights gained from analyzing CRISTA data are applied to provide a multiyear analysis of stratospheric mountain waves over the Andes evident in MLS limb-track data. We also demonstrate for the first time that stratospheric temperature data from the CLAES instrument on UARS resolved gravity waves, and we highlight mountain wave information in a subset of these data. Final conclusions and recommendations are set forth, and the present findings are directly related to the original goals of the research contract. A full list of publications that resulted from this research is provided.
On Sub-linear Convergence for Linearly Degenerate Waves in Capturing Schemes
Banks, J W; Aslam, T; Rider, W J
2008-03-17
A common attribute of capturing schemes used to find approximate solutions to the Euler equations is a sub-linear rate of convergence with respect to mesh resolution. Purely nonlinear jumps, such as shock waves produce a first-order convergence rate, but linearly degenerate discontinuous waves, where present, produce sub-linear convergence rates which eventually dominate the global rate of convergence. The classical explanation for this phenomenon investigates the behavior of the exact solution to the numerical method in combination with the finite error terms, often referred to as the modified equation. For a first-order method, the modified equation produces the hyperbolic evolution equation with second-order diffusive terms. In the frame of reference of the traveling wave, the solution of a discontinuous wave consists of a diffusive layer that grows with a rate of t{sup 1/2}, yielding a convergence rate of 1/2. Self-similar heuristics for higher order discretizations produce a growth rate for the layer thickness of {Delta}t{sup 1/(p+1)} which yields an estimate for the convergence rate as p/(p+1) where p is the order of the discretization. In this paper we show that this estimated convergence rate can be derived with greater rigor for both dissipative and dispersive forms of the discrete error. In particular, the form of the analytical solution for linear modified equations can be solved exactly. These estimates and forms for the error are confirmed in a variety of demonstrations ranging from simple linear waves to multidimensional solutions of the Euler equations.
Observations indicating parametric instabilities in internal gravity waves at thermospheric heights
NASA Astrophysics Data System (ADS)
Klostermeyer, J.
1984-06-01
The frequency spectrum of atmospheric waves produced by the Mount St. Helens eruption is examined. Data were taken in the form of ground level pressure variations, the ionospheric electron content variations, and the Doppler shift of HF radio waves reflected from the ionospheric F layer. Attention is focused on the Doppler data and the electron content. The eruption was found to have caused a strong Lamb wave whose horizontal proportions could not be measured with the available ground stations. The Doppler characteristics did, however, match those of a simulated unstable gravity wave in resonance conditions. It is suggested that observed acoustic double peaks are signs of parametric instabilities of gravity waves produced by penetrative cumulus convection.
NASA Technical Reports Server (NTRS)
Mayr, H. G.; Mengel, J. G.; Chan, K. L.; Porter, H. S.; Einaudi, Franco (Technical Monitor)
2000-01-01
Our Numerical Spectral Model (NSM), which extends from the ground up into the thermosphere, is non-linear, time-dependent and has been employed for 2D and 3D applications. The standard version of the NSM incorporates Hines' Doppler Spread Parameterization for small scale gravity waves (GW), but planetary waves generated in the troposphere have also been incorporated. The NSM has been applied to describe: (1) the anomalous seasonal variations of the zonal circulation and temperature in the upper mesosphere, (2) the equatorial oscillations (quasi-biennial and semi-annual oscillations (QBO and SAO)) extending from the stratosphere into the upper mesosphere, (3) the diurnal and semi-diurnal tides, and (4) the planetary waves that are excited in the mesosphere. With the emphasis to provide understanding, we present here results from numerical experiments with the NSM that shed light on the GW processes that are of central importance in the mesosphere and lower thermosphere. These are our conclusions: (1) The large semiannual variations in the diurnal tide (DT), with peak amplitudes observed around equinox, are produced primarily by GW interactions that involve, in part, planetary waves. The DT, like planetary waves, tends to be amplified by GW momentum deposition, which reduces also the vertical wavelength, but variations in eddy viscosity associated with GW interactions are also important. (2) The semidiurnal tide (SDT) and its phase in particular, is strongly influenced by the mean zonal circulation. The SDT, individually, is also amplified by GW. But the DT filters out GW such that the GW interaction effectively reduces the amplitude of the SDT, producing a strong nonlinear interaction between the DT and SDT. (3) Without external time dependent energy or momentum sources, planetary waves (PW) are generated in the model for zonal wavenumbers 1 to 4, which have amplitudes in the mesosphere above 50 km as large as 40 m/s and periods between 50 and 2 days. The waves are
Steady flow over an arbitrary obstruction based on the gravity wave equations
NASA Astrophysics Data System (ADS)
Mungkasi, S.; Supriyadi, B.; Wiryanto, L. H.
2016-11-01
We derive an analytical solution to a steady state problem of the gravity wave equations. An arbitrary bottom topography is considered. The problem is assumed to be one dimensional. The depth, discharge and topography elevation at the left-end of the space domain are assumed to have the same values as those at the right-end. We obtain that the fluid surface on the whole interior space domain remains horizontal and is not influenced by the topography shape when we use the gravity wave equations. Furthermore, the analytical solution that we derive is used to test the performance of a finite volume method. We find that the gravity wave equations give some advantages in comparison to the shallow water equations.
Short-period mesospheric gravity waves and their sources at the South Pole
NASA Astrophysics Data System (ADS)
Mehta, Dhvanit; Gerrard, Andrew J.; Ebihara, Yusuke; Weatherwax, Allan T.; Lanzerotti, Louis J.
2017-01-01
The sourcing locations and mechanisms for short-period, upward-propagating gravity waves at high polar latitudes remain largely unknown. Using all-sky imager data from the Amundsen-Scott South Pole Station, we determine the spatial and temporal characteristics of 94 observed small-scale waves in 3 austral winter months in 2003 and 2004. These data, together with background atmospheres from synoptic and/or climatological empirical models, are used to model gravity wave propagation from the polar mesosphere to each wave's source using a ray-tracing model. Our results provide a compelling case that a significant proportion of the observed waves are launched in several discrete layers in the tropopause and/or stratosphere. Analyses of synoptic geopotentials and temperatures indicate that wave formation is a result of baroclinic instability processes in the stratosphere and the interaction of planetary waves with the background wind fields in the tropopause. These results are significant for defining the influences of the polar vortex on the production of these small-scale, upward-propagating gravity waves at the highest polar latitudes.
Investigating Mesospheric Gravity Wave Dynamics Over McMurdo Station, Antarctica (77° S)
NASA Astrophysics Data System (ADS)
Pugmire, J. R.; Taylor, M. J.; Pautet, P. D.; Zhao, Y.
2014-12-01
The ANtarctic Gravity Wave Instrument Network (ANGWIN) is an NSF sponsored international program designed to develop and utilize a network of gravity wave observatories using existing and new instrumentation operated at several established research stations around the continent. The primary goal is to better understand and quantify large-scale gravity wave climatology and their effects on the upper atmosphere over Antarctica. ANGWIN currently comprises research measurements from five nations (U.S., U.K., Australia, Japan, and Brazil) at seven international stations. Utah State University's Atmospheric Imaging Lab operates an all-sky CCD, all-sky infrared imagers and an Advanced Mesospheric Temperature Mapper (AMTM) imager at several research stations (Davis, Halley, Rothera, McMurdo, and South Pole). In this poster we present new measurements, mainly focusing on short-period (< 1 hour) mesospheric gravity waves, imaged from McMurdo Station (77°S, 166°E) on Ross Island, Antarctica. The infrared camera has operated successfully from the NSF Arrival Heights Facility alongside the University of Colorado Fe Lidar during the past three winter seasons (March-September 2012-2014). Image data were recorded every ~10 seconds enabling detailed measurements of individual gravity wave events in the infrared OH emission layer (peak altitude ~87 km). Here we present example data illustrating the broad range of wave activity observed at this site and summarize novel measurements of the wave characteristics observed during the first two winter seasons. The results are contrasted with other emerging ANGWIN wave measurements from around the continent.
Role of acoustic-gravity waves in generating equatorial ionospheric irregularities
Argo, P.E.
1980-01-01
Irregularities in the equatorial ionospheric plasma (F-layer) have been observed and studied for many years. Even so, the creation mechanisms have successfully remained a source of controversy for equally many years. This is mainly due to the difficulty in observing the irregularities, because in situ measurements give a spatial trace at a near single time, while radio observations have tended to give a series of height profiles with changing time. One mechanism is the spatial resonance amplification of traveling ionospheric disturbance (TIDs) generated by acoustic gravity waves. As the wave profile in the plasma steepens, the stored energy begins to release through the Rayleigh-Taylor instability, which then creates a spectrum of smaller scale irregularities. In this dissertation the interaction of the acoustic gravity wave and the ionospheric plasma are examined, and it is found that the above mechanism is indeed feasible. In Chapter 3, the interaction between a neutral wave and the plasma is quantified, and the condiions for growth of resonant plasma waves is established. These conditions are met during the post-sunset period near the geomagnetic equator, which is exactly when and where the irregularities are encountered. For irregularity generation the Rayleigh-Taylor mechanism requires a steep positive gradient of density - a fact that previously has seemed to be impossible on the topside of the F-layer. However, in this thesis it is shown that acoustic gravity waves can generate positive slopes even on the topsideF-layer. Consequently, acoustic gravity waves constitute a single mechanism that can be used to explain both bottomside and topside irregularities. Experimental evidence for the creation of equatorial ionospheric irregularities by acoustic gravity waves has been sparse, although wavelike structures appear to permeate the irregularity profiles.
Surface wave and linear operating mode of a plasma antenna
Bogachev, N. N. Bogdankevich, I. L.; Gusein-zade, N. G.; Rukhadze, A. A.
2015-10-15
The relation between the propagation conditions of a surface electromagnetic wave along a finiteradius plasma cylinder and the linear operating mode of a plasma antenna is investigated. The solution to the dispersion relation for a surface wave propagating along a finite-radius plasma cylinder is analyzed for weakly and strongly collisional plasmas. Computer simulations of an asymmetrical plasma dipole antenna are performed using the KARAT code, wherein the dielectric properties of plasma are described in terms of the Drude model. The plasma parameters corresponding to the linear operating mode of a plasma antenna are determined. It is demonstrated that the characteristics of the plasma antenna in this mode are close to those of an analogous metal antenna.
NASA Astrophysics Data System (ADS)
Sofieva, V. F.; Gurvich, A. S.; Dalaudier, F.
2008-12-01
Stellar scintillations observed through the Earth atmosphere are caused by air density irregularities generated mainly by internal gravity waves (GW) and turbulence. The strength of scintillation measurements is that they cover the transition between the saturated part of the gravity wave spectrum and isotropic turbulence. This allows visualization of gravity wave breaking and of resulting turbulence. In this presentation, we show global distributions and seasonal variations of the GW and turbulence spectra parameters retrieved from GOMOS data in 2003, for altitudes 30-50 km. In addition, we show global distributions of GW potential energy per unit mass and of turbulent structure characteristic CT2 . Since other measurements at such small scales are very scarce in this altitude range, the obtained global distributions provide unique and complementary information about small-scale air density irregularities. At altitudes and locations overlapping with other measurements, the GW and turbulence parameters retrieved from scintillations are in a good qualitative and quantitative agreement with that obtains from other measurements. Our main findings and observations are: (i) Strong enhancement of gravity wave activity at high latitudes in winter, accompanying with a strong turbulence appearing at altitudes above 40-45 km; indication on breaking of gravity waves in the polar night jet; (ii) The turbulent structure characteristic CT2 can reach values of 0.003 K2 m-2/3 in high- latitude winter stratosphere; these values are comparable with that in the boundary layer; (iii) Moderate turbulence enhancements in the tropics, located mainly over continents and related probably to tropical deep convection; (iv) Increase of GW outer scale in the equatorial region; (v) Exceptional gravity wave spectra and a very strong turbulence during sudden stratospheric warmings.
NASA Astrophysics Data System (ADS)
Hoffmann, Lars; Grimsdell, Alison W.; Alexander, M. Joan
2016-07-01
Stratospheric gravity waves from small-scale orographic sources are currently not well-represented in general circulation models. This may be a reason why many simulations have difficulty reproducing the dynamical behavior of the Southern Hemisphere polar vortex in a realistic manner. Here we discuss a 12-year record (2003-2014) of stratospheric gravity wave activity at Southern Hemisphere orographic hotspots as observed by the Atmospheric InfraRed Sounder (AIRS) aboard the National Aeronautics and Space Administration's (NASA) Aqua satellite. We introduce a simple and effective approach, referred to as the "two-box method", to detect gravity wave activity from infrared nadir sounder measurements and to discriminate between gravity waves from orographic and other sources. From austral mid-fall to mid-spring (April-October) the contributions of orographic sources to the observed gravity wave occurrence frequencies were found to be largest for the Andes (90 %), followed by the Antarctic Peninsula (76 %), Kerguelen Islands (73 %), Tasmania (70 %), New Zealand (67 %), Heard Island (60 %), and other hotspots (24-54 %). Mountain wave activity was found to be closely correlated with peak terrain altitudes, and with zonal winds in the lower troposphere and mid-stratosphere. We propose a simple model to predict the occurrence of mountain wave events in the AIRS observations using zonal wind thresholds at 3 and 750 hPa. The model has significant predictive skill for hotspots where gravity wave activity is primarily due to orographic sources. It typically reproduces seasonal variations of the mountain wave occurrence frequencies at the Antarctic Peninsula and Kerguelen Islands from near zero to over 60 % with mean absolute errors of 4-5 percentage points. The prediction model can be used to disentangle upper level wind effects on observed occurrence frequencies from low-level source and other influences. The data and methods presented here can help to identify interesting
Development of a new standing wave type ultrasonic linear motor
NASA Astrophysics Data System (ADS)
Roh, Yongrae R.; Kwon, Jaewha; Lee, Soosun
2002-07-01
This paper presents a new standing wave type linear motor that can move bi-directionally with identical performance in both the forward and backward directions. The motor consists of a metallic stator and two piezoceramic plates bonded to the stator with the spatial phase difference of a half wavelength. With two electric driving signals either in-phase or out-of-phase for the two piezoceramic plates, the piezoceramic plates excite two ultrasonic standing waves with a certain phase difference. They generate a new standing wave when combined. The operation principle of the motor is verified through finite element analyses. For an experimental illustration of the theoretical and numerical results, a sample motor is fabricated and characterized following the numerical design. The experimental results confirm the validity and practical applicability of the new motor structure.
The effect of a gravity wave drag parameterization scheme on GLA fourth order GCM forecasts
NASA Technical Reports Server (NTRS)
Helfand, H. M.; Jusem, J. C.; Pfaendtner, J.; Tenenbaum, J.; Kalnay, E.
1987-01-01
Ten-day forecast experiments have been performed to determined whether the introduction of a simple orographic gravity wave drag scheme into a fourth-order GCM would reduce the climate drift of the fine resolution model and improve the model's medium range predictive skill. Error reduction due to the gravity waves is found in stratospheric predictions, where the improvement is confined mainly to the zonal mean component. Improvements are noted in the Northern Hemisphere climatology, where low level westerlies are weakened and shifted poleward, and in the Southern Hemisphere, where the roaring forties and fifties are better simulated.
On Modifications of the Zakharov Equation for Surface Gravity Waves.
1983-07-01
finite water depth (in section 2) and show its relations to the cubic Schr - dinger equation and to Hasselmann’s nonlinear interaction model (in section 3...on a modification of the nonlinear Schr { dinger equation for waves moving over an uneven bottom. Progress Report, Department of Civil Eng. Technion...7th Conf. of Coastal Engineering, Vol. 1, 184-196. Stiassnie, M. 1983 Note on the modified nonlinear Schr ~ dinger equation for deep water waves. Wave
Freely decaying weak turbulence for sea surface gravity waves.
Onorato, M; Osborne, A R; Serio, M; Resio, D; Pushkarev, A; Zakharov, V E; Brandini, C
2002-09-30
We study the long-time evolution of deep-water ocean surface waves in order to better understand the behavior of the nonlinear interaction processes that need to be accurately predicted in numerical models of wind-generated ocean surface waves. Of particular interest are those nonlinear interactions which are predicted by weak turbulence theory to result in a wave energy spectrum of the form of [k](-2.5). We numerically implement the primitive Euler equations for surface waves and demonstrate agreement between weak turbulence theory and the numerical results.
Full linear perturbations and localization of gravity on f( R, T) brane
NASA Astrophysics Data System (ADS)
Gu, Bao-Min; Zhang, Yu-Peng; Yu, Hao; Liu, Yu-Xiao
2017-02-01
We study the thick brane world system constructed in the recently proposed f( R, T) theories of gravity, with R the Ricci scalar and T the trace of the energy-momentum tensor. We try to get the analytic background solutions and discuss the full linear perturbations, especially the scalar perturbations. We compare how the brane world model is modified with that of general relativity coupled to a canonical scalar field. It is found that some more interesting background solutions are allowed, and only the scalar perturbation mode is modified. There is no tachyon state existing in this model and only the massless tensor mode can be localized on the brane, which recovers the effective four-dimensional gravity. These conclusions hold provided that two constraints on the original formalism of the action are satisfied.
Rayleigh lidar observations of gravity wave activity in the upper stratosphere at Urbana, Ill.
NASA Technical Reports Server (NTRS)
Gardner, C. S.; Miller, M. S.; Liu, C. H.
1988-01-01
During 13 nights of Rayleigh lidar measurements at Urbana, Ill. in 1984 to 1986, thirty-six quasi-monochromatic gravity waves were observed in the 35 to 50 km altitude region of the stratosphere. The characteristics of the waves are compared with other lidar and radar measurements of gravity waves and the theoretical models of wave saturation and dissipation phenomena. The measured vertical wavelengths ranged from 2 to 11.5 km and the measured vertical phase velocities ranged from 10 to 85 cm/s. The vertical wavelengths and vertical phase velocities were used to infer observed wave periods which ranged from 100 to 1000 min and horizontal wavelengths which ranged from 70 to 2000 km. Dominant wave activity was found at vertical wavelengths between 2 to 4 km and 7 to 10 km. No significant seasonal variations were evident in the observed parameters. Vertical and horizontal wavelengths showed a clear tendency to increase with wave periods, which is consistent with recent sodium lidar studies of quasi-monochromatic waves near the mesopause. An average amplitude growth length of 20.9 km for the rms wind perturbations was estimated from the data. Kinetic energy density associated with the waves decreased with height, suggesting that waves in this altitude region were subject to dissipation or saturation effects.
Onorato, M; Osborne, A R; Serio, M; Cavaleri, L; Brandini, C; Stansberg, C T
2004-12-01
We study random surface gravity wave fields and address the formation of large-amplitude waves in a laboratory environment. Experiments are performed in one of the largest wave tank facilities in the world. We present experimental evidence that the tail of the probability density function for wave height strongly depends on the Benjamin-Feir index (BFI)-i.e., the ratio between wave steepness and spectral bandwidth. While for a small BFI the probability density functions obtained experimentally are consistent with the Rayleigh distribution, for a large BFI the Rayleigh distribution clearly underestimates the probability of large events. These results confirm experimentally the fact that large-amplitude waves in random spectra may result from the modulational instability.
High-Resolution Infra-Red Imaging Studies of Mesospheric Gravity Waves (Invited)
NASA Astrophysics Data System (ADS)
Taylor, M. J.; Pautet, P.; Zhao, Y.; Pendleton, W. R.; Yuan, T.; Esplin, R.; McLain, D.; Fritts, D. C.; Stober, G.
2013-12-01
This presentation highlights new research capabilities and recent results focusing on polar latitudes using two new infra-red imaging systems operating at the ALOMAR Arctic Observatory, Norway and at the Amundsen-Scott Base, South Pole, Antarctica. The Advanced Mesospheric Temperature Mapper (AMTM) is a novel infrared digital imaging system that measures selected emission lines in the mesospheric OH (3,1) band (at ~1.5μm) to create high-quality intensity and temperature maps of a broad spectrum of mesospheric gravity waves (with periods ranging from several minutes to many hours). The data are obtained with an unprecedented spatial (~0.5 km) and temporal (typically 30 sec) resolution over a large 120° field of view enabling detailed measurements of wave propagation and dissipation at the ~87 km level, even in the presence of strong aurora. Several new results will be presented and discussed, including high-resolution imaging studies of gravity wave breaking, first evidence of gravity wave 'self-acceleration' and new coordinated lidar, radar and AMTM measurements of gravity wave propagation and ducting at mid-latitudes.
Vertical temperature and density patterns in the Arctic mesosphere analyzed as gravity waves
NASA Technical Reports Server (NTRS)
Eberstein, I. J.; Theon, J. S.
1978-01-01
Three series of rocket soundings including pitot soundings, grenade soundings, and paired pitot-grenade soundings, were conducted from high latitude sites during winter. Temperature and wind profiles and one density profile were observed independently to obtain the thermodynamic structure, the wind structure, and thus their interdependence in the mesosphere. Temperature profiles from all soundings in each series were averaged, and a smooth curve (or series of smooth curves) drawn through the points. A hydrostatic atmosphere based on the average, measured temperature profile was computed, and deviations from the mean atmosphere were analyzed in terms of gravity wave theory. The vertical wavelengths of the deviations were 10-20 km, and the wave amplitudes slowly increased with height. The experimental data were matched by calculated gravity waves having a period ranging between 15 and 80 minutes and horizontal wavelengths of 60 to 280 km. The interpretation is generally consistent with the results of others who have studied gravity-acoustic waves in the atmosphere. The wind measurements are consistent with the thermodynamic measurements. The results also suggest that gravity waves traveled from east to west with a horizontal phase velocity of approximately 60 m/sec.
NASA Astrophysics Data System (ADS)
Fetzer, Eric J.; Gille, John C.
1994-09-01
Small-scale features in temperature data from the Limb Infrared Monitor of the Stratosphere satellite experiment are isolated by subtracting profiles of globally mapped temperatures (containing zonal waves 0-6) from inverted temperature profiles. These features are interpreted as internal gravity waves. The preponderance of the variance is associated with the longest wavelengths, corresponding to the lowest frequencies (inertio-gravity waves). The data include approximately 2000 daily soundings between late October 1978 and late May 1979, all longitudes, latitudes from about 65°S to 85°N, and altitudes from the tropopause to the middle mesosphere (pressures from 100 to 0.1 mb). Zonal-mean gravity wave variance is compared with background winds, and variance maps are presented for five one-week periods: early November, early January, early February, late March, and early May. Time-height plots of zonal mean wave variance and background winds in the latitude bands 45°-55°S, 5°S-5°N, and 45°-55°N are also presented. Variance ranges from about 2.0 K2 in the northern late spring lower stratosphere to about 315 K2 in the northern late fall mesosphere. The Northern Hemisphere gravity wave variance field undergoes an approximate twofold increase between fall and early winter, but the maximum remains quasi-stationary; during the same period the mesospheric jet moves by several thousand kilometers. The Northern Hemisphere gravity wave field is strongly distorted by the late January minor warming, and decreases gradually between early March and late May. The tropical gravity wave variance is approximately constant with time below 40 km, but shows an increasingly strong semiannual signal above 40 km. The tropical maximum extends through January and February but is confined in altitude near 60 km. Southern Hemisphere variance decreases toward a broad minimum in January and February, but climbs rapidly after the autumnal equinox. The gravity wave variance fields during
Gravity wave characteristics retrieved from radiosonde observations during DEEPWAVE-NZ
NASA Astrophysics Data System (ADS)
Gisinger, Sonja; Dörnbrack, Andreas; Ehard, Benedikt; Kaifler, Bernd; Kaifler, Natalie; Rapp, Markus; Garhammer, Markus; Bramberger, Martina; Portele, Tanja; Siller, Maria
2015-04-01
The field phase of DEEPWAVE-NZ (DEEP propagating gravity WAVE experiment over New Zealand) took place in June and July 2014 on the southern island of New Zealand. One goal of DEEPWAVE-NZ was to explore the propagation of gravity waves excited by the flow across the southern island into the middle atmosphere. Airborne measurements with the NSF/NCAR GV and the DLR Falcon research aircraft were complemented with ground-based measurements at various stations on the southern island. At Lauder (45 S 169 E), long-lasting upper stratospheric and mesospheric observations were taken by the DLR Rayleigh lidar and the University of Utah Advanced Mesospheric Temperature Mapper and Airglow Imager. To provide data in the lower atmosphere up to 30 km altitude, radiosonde measurements were conducted in periods of mountain wave activity. The 98 radiosondes launched in Lauder reached a mean height of 31.2 km and a maximum ceiling of 36.6 km. We present a comprehensive wave analysis of the radiosoundings using wavelets. This analysis, inter alia, isolates single wave packages and wave properties like intrinsic frequency, horizontal direction of propagation and vertical propagation direction (upward or downward) by means of Stokes parameters. The results will be presented for different cases of mountain induced gravity waves which occurred during DEEPWAVE-NZ.
Surface gravity waves and their acoustic signatures, 1-30 Hz, on the mid-Pacific sea floor.
Farrell, W E; Munk, Walter
2013-10-01
In 1999, Duennebier et al. deployed a hydrophone and geophone below the conjugate depth in the abyssal Pacific, midway between Hawaii and California. Real time data were transmitted for 3 yr over an abandoned ATT cable. These data have been analyzed in the frequency band 1 to 30 Hz. Between 1 and 6 Hz, the bottom data are interpreted as acoustic radiation from surface gravity waves, an extension to higher frequencies of a non-linear mechanism proposed by Longuet-Higgins in 1950 to explain microseisms. The inferred surface wave spectrum for wave lengths between 6 m and 17 cm is saturated (wind-independent) and roughly consistent with the traditional Phillips κ(-4) wave number spectrum. Shorter ocean waves have a strong wind dependence and a less steep wave number dependence. Similar features are found in the bottom record between 6 and 30 Hz. But this leads to an enigma: The derived surface spectrum inferred from the Longuet-Higgins mechanism with conventional assumptions for the dispersion relation is associated with mean square slopes that greatly exceed those derived from glitter. Regardless of the generation mechanism, the measured bottom intensities between 10 and 30 Hz are well below minimum noise standards reported in the literature.
Dual piezoelecttic actuators for the traveling wave ultrasonic linear motor
NASA Astrophysics Data System (ADS)
Suybangdum, P.; Smithmaitrie, P.; Laoratanakul, P.
2009-12-01
The effect of a dual piezoelectric actuators ultrasonic linear motor is studied in this research. The two piezoelectric actuators are bonded with a linear elastic stator. The stator generates the traveling wave when the actuators are subjected to the harmonic excitations. Vibration characteristics of the linear stator are determined by using the finite element analysis, i.e., modal, harmonic and transient responses. In the experiment, the motor characteristics are tested, i.e., the maximum velocity, operating frequency and applied voltage. In addition, the relationship between the pre-load and velocity of the motor is reported. The result shows that the maximum velocity of the motor occurs at a specific per-load. The comparison of the operating frequency and harmonic response shows well agreement between the finite element and experimental results.
Dual piezoelecttic actuators for the traveling wave ultrasonic linear motor
NASA Astrophysics Data System (ADS)
Suybangdum, P.; Smithmaitrie, P.; Laoratanakul, P.
2010-03-01
The effect of a dual piezoelectric actuators ultrasonic linear motor is studied in this research. The two piezoelectric actuators are bonded with a linear elastic stator. The stator generates the traveling wave when the actuators are subjected to the harmonic excitations. Vibration characteristics of the linear stator are determined by using the finite element analysis, i.e., modal, harmonic and transient responses. In the experiment, the motor characteristics are tested, i.e., the maximum velocity, operating frequency and applied voltage. In addition, the relationship between the pre-load and velocity of the motor is reported. The result shows that the maximum velocity of the motor occurs at a specific per-load. The comparison of the operating frequency and harmonic response shows well agreement between the finite element and experimental results.
Surface Gravity Waves: Resonance in a Fish Tank
ERIC Educational Resources Information Center
Sinick, Scott J.; Lynch, John J.
2010-01-01
In this work, an inexpensive 10-gallon glass aquarium was used to study wave motion in water. The waves travel at speeds comparable to a person walking ([approximately]1 m/s). The scale of the motion allows for distances to be measured with a meterstick and for times to be measured with a stopwatch. For a wide range of water depths, standing waves…
NASA Astrophysics Data System (ADS)
Kinoshita, T.; Sato, K.
2012-12-01
The Transformed Eulerian-Mean (TEM) equations formulated by Andrews and McIntyre (1976, 1978) has been widely used to examine wave-mean flow interaction in the meridional cross section. Although a lot of efforts have been made to generalize the TEM equations to three dimensions so far, formulae derived by previous studies are applicable to particular waves, mainly Rossby waves on the quasi-geostrophic (QG) equations or inertia-gravity waves on the primitive equations. This study has newly formulated three-dimensional (3D) TEM equations which are applicable to both Rossby waves and gravity waves. The formulae can be used to examine the 3D material transport driven by these waves. Moreover, two kinds of 3D wave activity flux have been derived respectively for describing the wave force to the mean flow and for the wave propagation. The residual mean flow is expressed with the sum of the Eulerian-mean flow and the Stokes drift in the 2D TEM equations. Thus, a formulation is made for the 3D Stokes drift on the primitive equation (PRSD) from its original definition using a small amplitude theory for a slowly-varying mean flow. The PRSD is equivalent to the 3D Stokes drift derived by Kinoshita et al. (2010) for gravity waves for the constant Coriolis parameter and to the 3D QG Stokes drift which is also derived in this study for the small Rossby number limit. The 3D wave activity flux (3D-flux-M), whose divergence corresponds to the wave force, is derived by using PRSD. The 3D residual mean flow associated with synoptic-scale wave disturbances in the upper troposphere in April is investigated by applying the new formulae to ERA-Interim data. It is found that the sum of time-mean unbalanced flow and PRSD is southward in the east end of the storm track although it is northward in the west as is consistent with the 2D residual flow. A case study is also made for dominant gravity waves around the Southern Andes by applying the PRSD and 3D-flux-M to the simulation data of a
NASA Astrophysics Data System (ADS)
Maeda, Takuto; Tsushima, Hiroaki; Furumura, Takashi
2016-04-01
We numerically simulated the propagation of tsunami waves with finite difference methods by using perfectly matched layer (PML) boundary conditions to effectively eliminate artificial reflections from model boundaries. The PML method damps the tsunami height and velocity of seawater only in directions perpendicular to the boundary. Although the additional terms required to implement the PML conditions make the use of the PML technique difficult for linear dispersive tsunami waves, we have proposed an empirical extension of the PML method for modeling dispersive tsunami waves. Even for heterogeneous, realistic bathymetries, numerical tests demonstrated that the PML boundary condition dramatically decreased artificial reflections from model boundaries compared to the use of traditional boundary conditions. The use of PML boundary conditions for numerical modeling of tsunamis is especially useful because it facilitates use of the later phases of tsunamis that would otherwise be compromised by artifacts caused by reflections from model boundaries.
Similarity rules in gravity jitter-related spacecraft liquid propellant slosh waves excitation
NASA Technical Reports Server (NTRS)
Hung, R. J.; Lee, C. C.; Leslie, F. W.
1992-01-01
The dynamical behavior of fluids, in particular the effect of surface tension on partially filled rotating fluids in a full-scale prototype Gravity Probe-B Spacecraft propellant tank and various 10 percent subscale containers with identical values of similarity parameters such as Bond number, dynamical capillary number, rotational Reynolds number, and Weber number, as well as imposed gravity jitters have been investigated. It is shown that the Bond number can be used to simulate the wave characteristics of slosh wave excitation, whereas the Weber number can be used to simulate the wave amplitude of slosh-mode excitation. It is shown that a dynamical capillary number can be used to simulate the induced perturbation of the fluid stress distribution exerted on the wall. This distribution is governed by the interaction between surface tension (slosh-wave excitation along the liquid-vapor interface) and viscous (fluid stress exerted on the wall) forces.
Gravity wave and tidal structures between 60 and 140 km inferred from space shuttle reentry data
NASA Technical Reports Server (NTRS)
Fritts, David C.; Wang, Ding-Yi; Blanchard, Robert C.
1993-01-01
This study presents an analysis of density measurements made using high-resolution accelerometers aboard several space shuttles at altitudes from 60 to 140 km during reentry into the earth's atmosphere. The observed density fluctuations are interpreted in terms of gravity waves and tides and provide evidence of the importance of such motions well into the thermosphere. Height profiles of fractional density variance reveal that wave amplitudes increase at a rate consistent with observations at lower levels up to about 90 km. The rate of amplitude growth decreases at greater heights, however, and appears to cease above about 110 km. Wave amplitudes are nevertheless large at these heights and suggest that gravity waves may play an important role in forcing of the lower thermosphere.
Gravity wave and tidal structures between 60 and 140 km inferred from space shuttle reentry data
Fritts, D.C. ); Dingyi Wang ); Blanchard, R.C. )
1993-03-15
This study presents an analysis of density measurements made using high-resolution accelerometers aboard several space shuttles at altitudes from 60 to 140 km during reentry into the earth's atmosphere. The observed density fluctuations are interpreted in terms of gravity waves and tides and provide evidence of the importance of such motions well into the thermosphere. Height profiles of fractional density variance reveal that wave amplitudes increase at a rate consistent with observations at lower levels up to [approximately]90 km. The rate of amplitude growth decreases at greater heights, however, and appears to cease above [approximately]110 km. Wave amplitudes are nevertheless large at these heights and suggest that gravity waves may play an important role in forcing of the lower thermosphere.
Natorf, L.; Schlegel, K.; Wernik, A.W. Space Research Centre, Warsaw )
1992-12-01
Large-scale wavelike fluctuations of ion velocity, as measured by the European incoherent scatter radar along the geomagnetic field line, have been attributed to gravity wave effects. The height-dependent parameters of the causative gravity waves are calculated, taking into account the neutral horizontal wind and the electric field. The results are compared with the solutions of a dissipative dispersion relation. Much better agreement is achieved for the imaginary part of the vertical wave vector than for its real part. The calculated wave damping is greater than that given by theory. The possible reasons for this are discussed. It is suggested that E x B drift of the ions and vertical neutral winds, which are characteristic features of the auroral zone ionosphere, may contribute to the observed discrepancies. 40 refs.
Trapping and instability of directional gravity waves in localized water currents
NASA Astrophysics Data System (ADS)
Eliasson, B.; Haas, F.
2014-06-01
The influence of localized water currents on the nonlinear dynamics and stability of large amplitude, statistically distributed gravity waves is investigated theoretically and numerically by means of an evolution equation for a Wigner function governing the spectrum of waves. It is shown that water waves propagating in the opposite direction of a localized current channel can be trapped in the channel, which can lead to the amplification of the wave intensity. Under certain conditions the wave intensity can be further localized due to a self-focusing (Benjamin-Feir) instability. The localized amplification of the wave intensity may increase the probability of extreme events in the form of freak waves, which have been observed in connection with ocean currents.
Numerical simulation of the capillary-gravity waves excited by an obstacle
NASA Astrophysics Data System (ADS)
Hanazaki, Hideshi; Inomata, Ryosuke
2016-11-01
Capillary gravity waves excited by an obstacle are investigated by the unsteady numerical solution of the Euler equations. It is well known that the large-amplitude upstream advancing solitary waves are generated periodically under the resonant condition of Fr =1 (Fr: Froude number), i.e., when the phase velocity of the long surface waves agrees with the mean flow speed. With capillary effects (Bo>0), short waves are newly generated by the upstream solitary waves of large amplitude. In this study it is investigated how the characteristics of the solitary waves and the short waves, especially their amplitudes, change due to the variation of the obstacle height and the Froude number. The results will be compared also with the solutions of the forced KdV-type equations.
Estimating gravity wave parameters from oblique high-frequency backscatter: Modeling and analysis
Bristow, W.A.; Greenwald, R.A.
1995-03-01
A new technique for estimating electron density perturbation amplitudes of traveling ionospheric disturbances (TIDs), using HF radar data, is presented. TIDs are observed in HF radar data as enhancements of the ground-scattered power which propagate through the radar`s field of view. These TIDs are the ionospheric manifestation of atmospheric acoustic-gravity waves. TID electron density perturbation amplitudes were estimated by simulating the radar returns, using HF ray tracing through a model ionosphere perturbed by a model gravity wave. The simulation determined the return power in the ground-scattered portion of the signal as a function of range, and this was compared to HF radar data from the Goose Bay HF radar at a time when evidence of gravity waves was present in the data. By varying the amplitude of the electron density perturbation in the model it was possible to estimate the perturbation of the actual wave. It was found that the perturbations that are observed by the Goose Bay HF radar are of the order of 20% to 35%. It was also found that the number of observable power enhancements, and the relative amplitudes of these enhancements, depended on the vertical thickness of the gravity wave`s source region. From the simulations and observations it was estimated that the source region for the case presented here was approximately 20 km thick. In addition, the energy in the wave packet was calculated and compared to an estimate of the available energy in the source region. It was found that the wave energy was about 0.2% of the estimated available source region energy. 20 refs., 12 figs.
Deepwave2014; Observing Gravity Waves from the Troposphere to the Mesosphere
NASA Astrophysics Data System (ADS)
Smith, R. B.; Fritts, D. C.; Doyle, J. D.; Eckermann, S. D.; Taylor, M. J.; Dörnbrack, A.; Uddstrom, M.; Nugent, A. D.; Kruse, C.
2014-12-01
The recent Deepwave field project in New Zealand ran from May 25 to July 28, 2014. Its objectives were to observe, understand and predict the deep propagation of gravity waves from the Troposphere into the Stratosphere, Mesosphere and Thermosphere. In addition to surface and satellite-borne sensors, the project used two research aircraft with airborne sensors; the NSF/NCAR Gulfstream V (GV) and the German DLR Falcon. The GV was uniquely instrumented to observe wave launching (dropsondes), waves properties in the low stratosphere (flight level winds, pressure and temperature), waves in the middle stratosphere (MTP and Rayleigh Lidar) and waves near the mesopause (Sodium Lidar and OH IR mapper). In this report, we describe GV flight level wave energy flux statistics from the 97 aircraft legs (49.1 hours) over the terrain of New Zealand and the 157 aircraft legs (84.3 hours) over the Southern Ocean. For example, the vertical energy flux at Z=12km for the terrain flights varied from zero to 27 W/m2 with an average value of about 4W/m2. Wavelet co-spectral analysis of flight level data is used to determine the dominant location and wavelength of the flux-carrying gravity waves. Dominant horizontal wavelengths for the flux-carrying waves over terrain varied from 30 to 200km. Using a high resolution WRF simulation, the various mechanisms for the decrease of energy flux with height are examined including dissipation, dispersion, refraction, reflection and secondary wave generation.
Observations of height-dependent pressure-perturbation structure of a strong mesoscale gravity wave
NASA Technical Reports Server (NTRS)
Starr, David O'C.; Korb, C. L.; Schwemmer, Geary K.; Weng, Chi Y.
1992-01-01
Airborne observations using a downward-looking, dual-frequency, near-infrared, differential absorption lidar system provide the first measurements of the height-dependent pressure-perturbation field associated with a strong mesoscale gravity wave. A pressure-perturbation amplitude of 3.5 mb was measured within the lowest 1.6 km of the atmosphere over a 52-km flight line. Corresponding vertical displacements of 250-500 m were inferred from lidar-observed displacement of aerosol layers. Accounting for probable wave orientation, a horizontal wavelength of about 40 km was estimated. Satellite observations reveal wave structure of a comparable scale in concurrent cirrus cloud fields over an extended area. Smaller-scale waves were also observed. Local meteorological soundings are analyzed to confirm the existence of a suitable wave duct. Potential wave-generation mechanisms are examined and discussed. The large pressure-perturbation wave is attributed to rapid amplification or possible wave breaking of a gravity wave as it propagated offshore and interacted with a very stable marine boundary layer capped by a strong shear layer.
Studies of gravity wave propagation in the mesosphere observed by MU radar
NASA Astrophysics Data System (ADS)
Lue, H. Y.; Kuo, F. S.; Fukao, S.; Nakamura, T.
2013-05-01
Mesospheric data were analyzed by a composite method combining phase and group velocity tracing technique and the spectra method of Stokes parameter analysis to obtain the propagation parameters of atmospheric gravity waves (AGW) in the height ranges between 63.6 and 99.3 km, observed using the MU radar at Shigaraki in Japan in the months of November and July in the years 1986, 1988 and 1989. The data of waves with downward phase velocity and the data of waves with upward phase velocity were independently treated. First, the vertical phase velocity and vertical group velocity as well as the characteristic wave period for each wave packet were obtained by phase and group velocity tracing technique. Then its horizontal wavelength, intrinsic wave period and horizontal group velocity were obtained by the dispersion relation. The intrinsic frequency and azimuth of wave vector of each wave packet were checked by Stokes parameters analysis. The results showed that the waves with intrinsic periods in the range 30 min-4.5 h had horizontal wavelength ranging from 25 to 240 km, vertical wavelength from 2.5 to 12 km, and horizontal group velocities from 15 to 60 m s-1. Both upward moving wave packets and downward moving wave packets had horizontal group velocities mostly directed in the sector between directions NNE (north-north-east) and SEE in the month of November, and mostly in the sector between directions NW and SWS in the month of July. Comparing with mean wind directions, the gravity waves appeared to be more likely to propagate along with mean wind than against it. This apparent prevalence for downstream wave packets was found to be caused by a systematic filtering effect existing in the process of phase and group velocity tracing analysis: A significant portion of upstream wave packets might have been Doppler shifted out of the vertical range in phase and group velocity tracing analysis.
On the physical mechanism of front-back asymmetry of nonlinear gravity-capillary waves
NASA Astrophysics Data System (ADS)
Dosaev, Alexander; Troitskaya, Yulia; Shrira, Victor
2016-04-01
In nature wind waves of all scales are asymmetric both with respect to the horizontal and vertical axes. The front-back (or fore-aft asymmetry), i.e. the asymmetry with respect to the vertical axis, manifests itself in steeper front slopes. Although it can be important for remote sensing of sea surface and wave field interaction with wind, especially for the waves of gravity-capillary range, at present the understanding of physical mechanisms causing the gravity-capillary waves asymmetry and its dependence on parameters is very poor; there has been no study dedicated to this problem. Here we address this gap. The decimetre-range water waves in many respects essentially differ from the waves of other ranges: wind forcing is stronger, steep waves develop a characteristic pattern of capillary ripples on their forward slopes. These 'parasitic capillaries', generated by a narrow pressure distribution associated with an underlying longer wave' crest, remain quasi-stationary with regard to the longer wave. The train of capillaries is localised on the front slope and decays towards the trough. We investigate the nature of the asymmetry of such waves by extensive numerical simulations of the Euler equations employing the method of conformal mapping for two-dimensional potential flow and taking into account wave generation by wind and dissipation due to molecular viscosity. We examine the role of various factors contributing to the wave profile asymmetry: wind pumping, viscous stresses, the Reynolds stresses caused by ripples and found the latter to be by far the most important. It is the lop-sided ripple distribution which leads to noticeable fore-aft asymmetry of the mean wave profile. We also found how the asymmetry depends on wavelength, steepness, wind and viscosity, which enables us to parametrize these dependencies for applications in microwave remote sensing and wave generation.
High-Resolution Temperature Mapping of Mesospheric Gravity Waves and Breaking Events
NASA Astrophysics Data System (ADS)
Taylor, Michael J.; Pautet, Pierre-Dominique; Zhao, Yucheng; Yuan, Tao; Pendleon, William R.; Fritts, David; Esplin, Roy; McLain, David; Stober, Gunter
2016-04-01
This presentation highlights new research capabilities and recent results using a novel infra-red imaging system operating at high-latitudes at the ALOMAR Arctic Observatory, Norway (69°N), and at Amundsen-Scott South Pole Station, Antarctica (90°S). The Advanced Mesospheric Temperature Mapper (AMTM) is a high-performance digital imaging system that measures selected emission lines in the mesospheric OH (3,1) band (at ~1.55 μm) to create high-quality intensity and temperature maps of a broad spectrum of gravity waves at the ~87 km level (with periods ranging from several minutes to many hours). The temperature data are obtained with an unprecedented spatial (~0.5 km) and temporal (typically 30 sec) resolution over a large 120° field of view enabling detailed studies of gravity wave propagation and breaking events in the Mesosphere and Lower Thermosphere (MLT) region, even in the presence of strong aurora and moonlight. New results include high-resolution wintertime studies of continuous (24-hr) gravity wave activity and spectral evolution, and first evidence of gravity wave "self-acceleration" in the MLT region using coordinated lidar and radar measurements. These results are complemented by very high resolution (~4 sec) gravity wave observations using a third AMTM developed for airborne measurements on the National Science Foundation (NSF) Gulfstream V aircraft as part of the DEEPWAVE program. This mission was successfully conducted from New Zealand during the Austral winter, June-July 2014, and obtained spectacular new data on mesospheric mountain waves, including large amplitude breaking events associated with variable orographic forcing over the Southern Alps.
Coupling of Surface and Internal Gravity Waves: A Hamiltonian Model
1974-04-01
which w^ shall use is the somewhat unrealistic, but convenient, thin thermocline model: N(z) = 0, except near z = -D, -D+6 f N2(z)dz = g 5p/po...L) = C, -L ~*1 ~ (51) we satisfy the resonance condition between the internal wave and adjacent pairs of surface waves. In this case , a...modes as listed in Column II of Table II to represent the ocean environment. In this case , in addition to the surface waves having the equilibrium
Mixed Symmetry-Tipe (k,1) Massless Tensor Fields. Consistent Interactions Of Dual Linearized Gravity
NASA Astrophysics Data System (ADS)
Bizdadea, C.; Saliu, S. O.; Toma, M.
2012-12-01
A particular case of interactions of a single massless tensor field with the mixed symmetry corresponding to a two-column Young diagram (k,1) with k=4, dual to linearized gravity in D=7, is considered in the context of: self-couplings, cross-interactions with a Pauli-Fierz field, cross-couplings to purely matter theories, and interactions with an Abelian 1-form. The general approach relies on the deformation of the solution to the master equation from the antifield-BRST formalism by means of the local cohomology of the BRST differential.
An ultrasonic linear motor using ridge-mode traveling waves.
Tominaga, Masahiko; Kaminaga, Ryuta; Friend, James R; Nakamura, Kentaro; Ueha, Sadayuki
2005-10-01
A new type of ultrasonic linear motor is presented using traveling waves excited along a ridge atop a substrate. The ridge cross section was designed to permit only the fundamental mode to be excited during operation of the motor, with a Langevin transducer used as the source of vibration in this study. The ridge waveguide was first made of lossy media to avoid reflecting vibration energy back toward the vibration source, forming a traveling wave. A 5-mm-wide, 15-mm-tall rectangular acrylic ridge was used to move a slider placed upon it toward the vibration source, in opposition to the direction of the traveling wave transmitted along the waveguide ridge. Using a low-loss 3 x 6-mm aluminum rectangular ridge combined with a damper clamped onto the far end of the waveguide, similar results were obtained. To obtain bidirectional operation, the damper was replaced with a second Langevin transducer, giving a pair of transducers located perpendicularly to the ends of the ridge and driven with an appropriate phase difference. The moving direction of the slider was reversed by shifting this phase difference by about 180 degrees. With this simple configuration, it may soon be possible to fabricate a linear micromotor system on a silicon substrate or other semiconductor wafer adjacent to other electronic and optoelectronic devices.
Stability of Steep Gravity--Capillary Solitary Waves in Deep Water
NASA Astrophysics Data System (ADS)
Akylas, T. R.; Calvo, D. C.
2000-11-01
The stability of steep gravity--capillary solitary waves in deep water is numerically investigated using the full nonlinear water-wave equations with surface tension. As was found in prior work based on model equations for small-amplitude solitary waves in shallow water, out of the two solution branches that bifurcate at the minimum gravity--capillary phase speed, solitary waves of depression again turn out to be stable while those of elevation are unstable to small disturbances. Motivated by the experiments of Longuet-Higgins & Zhang (Phys. Fluids 9:1963--1968, 1997), we also consider the forced problem of a localised pressure distribution applied to the free surface of a stream with speed below the minimum gravity--capillary phase speed. We find that the finite-amplitude forced solitary-wave solution branch computed by Vanden-Broeck & Dias (J. Fluid Mech. 240:549--557, 1992) is unstable but the branch corresponding to Rayleigh's linearised solution is stable. The significance of viscous effects is assessed; the effects of instability in steep waves generally are comparable to, and in some cases greater than, those of dissipation. These findings are discussed in connection with the experimental observations of Longuet-Higgins & Zhang.
A Model Study of Zonal Forcing in the Equatorial Stratosphere by Convectively Induced Gravity Waves
NASA Technical Reports Server (NTRS)
Alexander, M. J.; Holton, James R.
1997-01-01
A two-dimensional cloud-resolving model is used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation (QBO) of the zonal winds in the equatorial stratosphere. A simulation with constant background stratospheric winds is compared to simulations with background winds characteristic of the westerly and easterly QBO phases, respectively. In all three cases a broad spectrum of both eastward and westward propagating gravity waves is excited. In the constant background wind case the vertical momentum flux is nearly constant with height in the stratosphere, after correction for waves leaving the model domain. In the easterly and westerly shear cases, however, westward and eastward propagating waves, respectively, are strongly damped as they approach their critical levels, owing to the strongly scale-dependent vertical diffusion in the model. The profiles of zonal forcing induced by this wave damping are similar to profiles given by critical level absorption, but displaced slightly downward. The magnitude of the zonal forcing is of order 5 m/s/day. It is estimated that if 2% of the area of the Tropics were occupied by storms of similar magnitude, mesoscale gravity waves could provide nearly 1/4 of the zonal forcing required for the QBO.
Gravity wave forcing in the middle atmosphere due to reduced ozone heating during a solar eclipse
NASA Technical Reports Server (NTRS)
Fritts, David C.; Luo, Zhangai
1993-01-01
We present an analysis of the gravity wave structure and the associated forcing of the middle atmosphere induced by the screening of the ozone layer from solar heating during a solar eclipse. Fourier integral techniques and numerical evaluation of the integral solutions were used to assess the wave field structure and to compute the gravity wave forcing of the atmosphere at greater heights. Our solutions reveal dominant periods of a few hours, characteristic horizontal and vertical scales of about 5000 to 10,000 km and 200 km, respectively, and an integrated momentum flux in the direction of eclipse motion of about 5.6 x 10 exp 8 N at each height above the forcing level. These results suggest that responses to solar eclipses may be difficult to detect above background gravity wave and tidal fluctuations until well into the thermosphere. Conversely, the induced body forces may penetrate to considerable heights because of the large wave scales and will have significant effects at levels where the wave field is dissipated.
NASA Astrophysics Data System (ADS)
Wachter, Paul; Schmidt, Carsten; Wüst, Sabine; Bittner, Michael
2014-05-01
GRIPS (Ground based Infrared P-branch Spectrometer) airglow measurements allow the derivation of kinetic temperature in the mesopause region averaged over a field of view of some 10km x 10km. In 2011, three identical GRIPS instruments were setup at Oberpfaffenhofen (11.28°E, 48.09°N), Germany, in a way that their fields of view form an equilateral triangle shape in the mesopause with a horizontal dimension of approximately 70km. Using this setup, GRIPS time series cannot only be analyzed with respect to gravity wave periods, but also spatial wave parameters can be derived. Based on the results of the harmonic analysis the horizontal wavelength, phase speed and the direction of propagation were determined for gravity wave events from February to July 2011. We present distinct relationships between periods, amplitudes, phase speeds and wavelengths, which were identified in this dataset. Further data analysis of the derived wave parameters show preferred directions of propagation and suggest seasonal variations of the wave characteristics. The presentation will be concluded by the introduction of a measurement setup relying on one GRIPS instrument which is equipped with a variably adjustable mirror optic. The capability to scan multiple fields of view during nightly measurements will offer longer-term investigations of mesopause gravity waves.
Cosmic Tsunamis in Modified Gravity: Disruption of Screening Mechanisms from Scalar Waves
NASA Astrophysics Data System (ADS)
Hagala, R.; Llinares, C.; Mota, D. F.
2017-03-01
Extending general relativity by adding extra degrees of freedom is a popular approach for explaining the accelerated expansion of the Universe and to build high energy completions of the theory of gravity. The presence of such new degrees of freedom is, however, tightly constrained from several observations and experiments that aim to test general relativity in a wide range of scales. The viability of a given modified theory of gravity, therefore, strongly depends on the existence of a screening mechanism that suppresses the extra degrees of freedom. We perform simulations, and find that waves propagating in the new degrees of freedom can significantly impact the efficiency of some screening mechanisms, thereby threatening the viability of these modified gravity theories. Specifically, we show that the waves produced in the symmetron model can increase the amplitude of the fifth force and the parametrized post Newtonian parameters by several orders of magnitude.
Fermi and LIGO Hone in on Gravity Wave Source
Fermi's GBM saw a fading X-ray source at nearly the same moment LIGO detected gravitational waves from a black hole merger in 2015. This movie shows how scientists can narrow down the location of t...
Linear and non-linear numerical simulations of poloidal Alfven waves
NASA Astrophysics Data System (ADS)
Ribeiro, A.
2013-05-01
Among the many of numerical simulations of MHD turbulence, few studies had been made of Alfven waves interacting with realistic boundaries. Thus, we have developed a novel hybrid spectral/finite element code, which is capable of simulate properly realistic boundaries properties. Our model is based on a Fourier decompositions of all variables in the azimuthal direction and on a finite element projection in the meridian plan. In order to simulate realistic boundary conditions for the magnetic field we solve the induction equation enforcing continuity of the magnetic field H at the interface with the external insulating medium through a Interior Penalty Galerkin method (IPG) [1]. I will present the results of our investigation of Alfven waves propagating in a cylinder filled of liquid metal submitted to an axial magnetic field. Poloidal Alfven waves are excited magnetically by imposing an azimuthal current pulse at the bottom of the cylinder. In the linear axisymmetric model we find a good agreement with previous experiments in liquid metals by Lundquist and by Lenhert and more recently by Alboussiere et al [2]. This axisymmetric study is extended to the non linear regime, where the amplitudes of the perturbations are comparable to the external applied magnetic field,in this conditions a complex response is found due to waves waves interactions. [1] J. L. Guermond, J.L Leorat, F. Luddens, C. Nore, A. Ribeiro. Effects of discontinuous magnetic permeability on magnetodynamic problems, Journal of Computational Physics Volume 230, Issue 16, 10 July 2011, Pages 6299 -- 6319. [2] T. Alboussiere, P. Cardin, F. Debray, H. C. Nataf, F. Plunian, A. Ribeiro, D. Schmitt, Experimental evidence of Alfven wave propagation in a Gallium alloy, Physics of fluids, 2011, vol. 23, nb 9.
A case study of gravity waves-convective storms interaction 9 May 1979
NASA Technical Reports Server (NTRS)
Stobie, J. G.; Einaudi, F.; Uccellini, L. W.
1983-01-01
An analysis is presented of a series of severe storms which occurred in the north central United States on 9 May 1979 and whose spatial distribution and movement correlate well with observed gravity waves. Two gravity wave trains of 2.1-3 mb amplitude, 2.5-3.3 h period and 240-265 km horizontal wavelength were isolated through power spectra analysis and cross-correlation techniques applied to National Weather Service barograph traces. The wave trains propagated in the 200 deg direction, which coincided with the jet axis, with a phase velocity of 20-30 m/s and within a 300 km wide band. The storms were identified on enhanced infrared GOES satellite pictures with the help of radar summaries. These convective systems initially developed in Nebraska and propagated north-northeast at 25 m/s, revealing wave-like characteristics with a separation of 300-400 km. The convective systems were closely linked to the observed wave trains with cell intensity, height and associated rainfall maximized at the wave ridge. One of the two wave trains developed in regions of weak or no convection and appeared to initiate more intense convective clusters downstream from the point of origin. It is shown that the characteristics of the wave trains are consistent with those of gravity waves generated in a region of strong vertical shear associated with the jet. It is suggested that the wave trains continue to extract energy from the basic state all along their track through critical level interaction.
NASA Astrophysics Data System (ADS)
Snively, J. B.; Zettergren, M. D.
2014-12-01
Strong acoustic waves with periods ~1-4 minutes have been confirmed to perturb the ionosphere following their generation by earthquakes [e.g., Garcia et al., GRL, 40(5), 2013] and volcanic eruption events [e.g., Heki, GRL, 33, L14303, 2006]. Clear acoustic and gravity wave signatures have also been reported in ionospheric data above strong tropospheric convection [Nishioka, GRL, 40(21), 2013], and prior modeling results suggest that convectively-generated acoustic waves with ~3-4 minute periods are readily detectable above their sources in TEC [Zettergren and Snively, GRL, 40(20), 2013]. These observations have provided quantitative insight into the coupling of processes occurring near Earth's surface with the upper atmosphere and ionosphere over short time-scales. Here, we investigate acoustic waves and short-period gravity waves generated by sources near ground level, and the observable responses of the mesosphere, lower-thermosphere, and ionosphere (MLTI) systems. Numerical simulations are performed using a nonlinear, compressible, atmospheric dynamics model, in cylindrically-axisymmetric coordinates, to investigate wave generation, upward propagation, steepening, and dissipation. Acoustic waves may produce observable signatures in the mesospheric hydroxyl airglow layer [e.g., Snively, GRL, 40(17), 2013], and can strongly perturb the lower-thermosphere and E- and F-region ionosphere, prior to the arrival of simultaneously-generated gravity waves. Using a coupled multi-fluid ionospheric model [Zettergren and Semeter, JGR, 117(A6), 2012], extended for mid and low latitudes using a 2D dipole magnetic field coordinate system [Zettergren and Snively, GRL, 40(20), 2013], we investigate its response to realistic acoustic wave perturbations. In particular, we demonstrate that the MLT and ionospheric responses are significantly and nonlinearly determined by the acoustic wave source geometry, spectrum, and amplitude, in addition to the local ambient state of the
A statistical study of variations of internal gravity wave energy characteristics in meteor zone
NASA Technical Reports Server (NTRS)
Gavrilov, N. M.; Kalov, E. D.
1987-01-01
Internal gravity wave (IGW) parameters obtained by the radiometer method have been considered by many other researchers. The results of the processing of regular radiometeor measurements taken during 1979 to 1980 in Obninsk (55.1 deg N, 36.6 deg E) are presented.
Tropospheric gravity waves observed by three closely-spaced ST radars
NASA Technical Reports Server (NTRS)
Carter, D. A.; Eriddle, A. C. AFGARELLO, R.ly stable thro; Eriddle, A. C. AFGARELLO, R.ly stable thro
1985-01-01
During a 6 week period in 1982, 3 ST (Stratosphere-Troposphere) radars measured horizontal and vertical wavelengths of small scale tropospheric gravity waves. These 50 MHz, vertically-directed radars were located in a trianglar network with approximately 5 km spacing on the southern coast of France at the mouth of the Rhone River during the ALPEX (Alpine Experiment) program.
Wright, J.W.; Pitteway, M.L.V.
1982-03-01
A sequence of digital ionograms is processed by dopplionogram and gonionogram methods. Together, these disclose a disturbance in the F region which descends in altitude with time. Two wavelike periods of the disturbance are evident. The Doppler and angle-of-arrival behavior are consistent with a semiquantitative model of the plasma perturbations caused by an internal atmospheric gravity wave.
Capillary Gravity Waves over an Obstruction - Forced Generalized KdV equation
NASA Astrophysics Data System (ADS)
Choi, Jeongwhan; Whang, S. I.; Sun, Shu-Ming
2013-11-01
Capillary gravity surface waves of an ideal fluid flow over an obstruction is considered. When the Bond number is near the critical value 1/3, a forced generalized KdV equation of fifth order is derived. We study the equation analytically and numerically. Existence and stability of solutions are studied and new types of numerical solutions are found.
Wind effects on the modulational instability of surface gravity waves
NASA Astrophysics Data System (ADS)
Brunetti, Maura; Kasparian, Jérôme
2015-04-01
The modulational instability is a fundamental mechanism for nonlinear exchanges of energy between carrier and sideband waves. It is one of the processes at the origin of rogue-wave formation in deep-water. Since the wind is the energy source in surface wave propagation, accurate modelling of the wind is critical for understanding rogue-wave phenomenon. We describe how different forcing terms, due to different modelling of the wind action, affect the band of positive gain of the modulational instability. In particular, we consider the wind-forced nonlinear Schrödinger equation obtained in the potential flow framework when the Miles growth rate is of the order of the wave steepness [1]. In this case, the form of the wind-forcing terms gives rise to the enhancement of the modulational instability and to a band of positive gain with infinite width [2]. This regime is characterised by the fact that the ratio between wave momentum and norm is not a constant of motion [2], in contrast to what happens in the standard case where the Miles growth rate is of the order of the steepness squared. References [1] M. Brunetti, N. Marchiando, N. Berti, J. Kasparian, 2014, Phys. Lett. A, 378, 1025-1030 [2] M. Brunetti, J. Kasparian, 2014, Phys. Lett. A, 378, 3626-3630
Effect of background rotation on the evolution of 3D internal gravity wave beams
NASA Astrophysics Data System (ADS)
Fan, Boyu; Akylas, T. R.
2016-11-01
The effect of background rotation on the 3D propagation of internal gravity wave beams (IGWB) is studied, assuming that variations in the along-beam and transverse directions are of long length scale relative to the beam width. The present study generalizes the asymptotic model of KA (Kataoka & Akylas 2015) who considered the analogous problem in the absence of rotation. It is shown that the role of mean vertical vorticity in the earlier analysis is now taken by the flow mean potential vorticity (MPV). Specifically, 3D variations enable resonant transfer of energy to the flow MPV, resulting in strong nonlinear coupling between a 3D IGWB and its induced mean flow. This coupling mechanism is governed by a system of two nonlinear equations of the same form as those derived in KA. Accordingly, the induced mean flow features a purely inviscid modulational component, as well as a viscous one akin to acoustic streaming; the latter grows linearly with time for a quasi-steady IGWB. On the other hand, owing to background rotation, the induced mean flow in the vicinity of the IGWB is no longer purely horizontal and develops an asymmetric behavior. Supported by NSF.
Modeling Wave Driven Non-linear Flow Oscillations: The Terrestrial QBO and a Solar Analog
NASA Technical Reports Server (NTRS)
Mayr, Hans G.; Bhartia, P. K. (Technical Monitor)
2001-01-01
The Quasi Biennial Oscillation (QBO) of the zonal circulation observed in the terrestrial atmosphere at low latitudes is driven by wave mean flow interaction as was demonstrated first by Lindzen and Holton (1968), shown in a laboratory experiment by Plumb and McEwan (1978), and modeled by others (e.g., Plumb, Dunkerton). Although influenced by the seasonal cycle of solar forcing, the QBO, in principle, represents a nonlinear flow oscillation that can be maintained by a steady source of upward propagating waves. The wave driven non-linearity is of third or odd order in the flow velocity, which regenerates the fundamental harmonic itself to keep the oscillation going - the fluid dynamical analog of the displacement mechanism in the mechanical clock. Applying Hines' Doppler Spread Parameterization (DSP) for gravity waves (GW), we discuss with a global-scale spectral model numerical experiments that elucidate some properties of the QBO and its possible effects on the climatology of the atmosphere. Depending on the period of the QBO, wave filtering can cause interaction with the seasonal variations to produce pronounced oscillations with beat periods around 10 years. Since the seasonal cycle and its variability influence the period of the QBO, it may also be a potent conduit of solar activity variations to lower altitudes. Analogous to the terrestrial QBO, we propose that a flow oscillation may account for the 22-year periodicity of the solar magnetic cycle, potentially answering Dicke (1978) who asked, "Is there a chronometer hidden deep inside the Sun?" The oscillation would occur below the convection region, where gravity waves can propagate. Employing a simplified, analytic model, Hines' DSP is applied to estimate the flow oscillation. Depending on the adopted horizontal wavelengths of GW's, wave amplitudes less than 10 m/s can be made to produce oscillating zonal flows of about 20 m/s that should be large enough to generate a significant oscillation in the magnetic
NASA Astrophysics Data System (ADS)
Charland, J.; Rey, V.; Touboul, J.
2012-04-01
Part of evanescent modes in the normally incident gravity surface wave's energy layout around a submerged obstacle Jenna Charland *1, Vincent Rey *2, Julien Touboul *2 *1 Mediterraneen Institute of Oceanography. Institut des Sciences de l'Ingénieur Toulon-Var. Avenue Georges Pompidou, BP 56, 83162 La Valette du Var Cedex, France. Centre National de la Recherche Scientifique, Délégation Normandie. Projet soutenu financièrement par la Délégation Générale de l'Armement. *2 Mediterraneen Institute of Oceanography. Institut des Sciences de l'Ingénieur Toulon-Var. Avenue Georges Pompidou, BP 56, 83162 La Valette du Var Cedex, France. During the last decades various studies have been performed to understand the wave propagation over varying bathymetries. Few answers related to this non linear problem were given by the Patarapanich's studies which described the reflection coefficient of a submerged plate as a function of the wavelength. Later Le-Thi-Minh [2] demonstrated the necessity of taking into account the evanescent modes to better describe the propagation of waves over a varying bathymetry. However, all these studies stare at pseudo-stationary state that allows neither the comprehension of the transient behaviour of propagative modes nor the role of the evanescent modes in this unstationnary process. Our study deals with the wave establishment over a submerged plate or step and focuses on the evanescent modes establishment. Rey [3] described the propagation of a normally incident surface gravity wave over a varying topography on the behaviour of the fluid using a linearized potential theory solved by a numerical model using an integral method. This model has a large field of application and has been adapted to our case. This code still solves a stationary problem but allows us to calculate the contribution of the evanescent modes in the energy layout around a submerged plate or a submerged step. The results will show the importance of the trapped energy
Estimating gravity wave parameters from oblique high-frequency backscatter: Modeling and analysis
NASA Technical Reports Server (NTRS)
Bristow, W. A.; Greenwald, R. A.
1995-01-01
A new technique for estimating electron density perturbation amplitudes of traveling ionospheric disturbances (TIDs), using HF radar data, is presented. TIDs are observed in HF radar data as enhancements of the ground-scattered power which propagate through the radar's field of view. These TIDs are the ionospheric manifestation of atmospheric acoustic-gravity waves. TID electron density perturbation amplitudes were estimated by simulating the radar returns, using HF ray tracing through a model ionosphere perturbed by a model gravity wave. The simulation determined the return power in the ground-scattered portion of the signal as a function of range, and this was compared to HF radar data from the Goose Bay HF radar at a time when evidence of gravity waves was present in the data. By varying the amplitude of the electron density perturbation in the model it was possible to estimate the perturbation of the actual wave. It was found that the perturbations that are observed by the Goose Bay HF radar are of the order of 20% to 35%. It was also found that the number of observable power enhancements, and the relative amplitudes of these enhancements, depended on the vertical thickness of the gravity wave's source region. From the simulations and observations it was estimated that the source region for the case presented here was approximately 20 km thick. In addition, the energy in the wave packet was calculated and compared to an estimate of the available energy in the source region. It was found that the wave energy was about 0.2% of the estimated available source region energy.
Mesosphere Dynamics with Gravity Wave Forcing. 1; Diurnal and Semi-Diurnal Tides
NASA Technical Reports Server (NTRS)
Mayr, H. G.; Mengel, J. G.; Chan, K. L.; Porter, H. S.; Einaudi, Franco (Technical Monitor)
2000-01-01
We present results from a nonlinear, 3D, time dependent numerical spectral model (NSM), which extends from the ground up into the thermosphere and incorporates Hines' Doppler Spread Parameterization for small-scale gravity waves (GW). Our focal point is the mesosphere that is dominated by wave interactions. We discuss diurnal and semi-diurnal tides ill the present paper (Part 1) and planetary waves in the companion paper (Part 2). To provide an understanding of the seasonal variations of tides, in particular with regard to gravity wave processes, numerical experiments are performed that lead to the following conclusions: 1. The large semiannual variations in tile diurnal tide (DT), with peak amplitudes observed around equinox, are produced primarily by GW interactions that involve, in part, planetary waves. 2. The DT, like planetary waves, tends to be amplified by GW momentum deposition, which reduces also the vertical wavelength. 3.Variations in eddy viscosity associated with GW interactions tend to peak in late spring and early fall and call also influence the DT. 4. The semidiurnal semidiurnal tide (SDT), and its phase in particular, is strongly influenced by the mean zonal circulation. 5. The SDT, individually, is amplified by GW's. But the DT filters out GW's such that the wave interaction effectively reduces the amplitude of the SDT, effectively producing a strong nonlinear interaction between the DT and SDT. 6.) Planetary waves generated internally by baroclinic instability and GW interaction produce large amplitude modulations of the DT and SDT.
Ray tracing of gravity waves as a possible warning system for tornadic storms and hurricanes
NASA Technical Reports Server (NTRS)
Hung, R. J.; Smith, R. E.
1978-01-01
Gravity waves with wave periods of 13 to 15 min and horizontal phase velocities of 90 to 220 m/sec were present in ground-based observations of the upper atmosphere during time periods when tornadoes were occurring and gravity waves with wave periods of 20 to 25 min and horizontal phase velocities of 100 to 200 m/sec were detected when a hurricane was present. Combinations of available neutral atmosphere data and model parameter values were used with a group ray tracing technique in an attempt to locate the sources of these waves. Computed sources of the waves with periods of 13 to 15 min were located within 50 km of the locations where tornadoes touched down from 2 to 4 h later. In the case of the waves with periods of 20 to 25 min it was found that the computed location of the source was roughly where the hurricane would be located 3 h after the waves were excited. The applicability of the present study to a tornado and hurricane warning system is noted.
NASA Technical Reports Server (NTRS)
Jacobson, Raymond A.; Larsen, M. F.
1993-01-01
Low frequency, large amplitude waves are often observed at mesospheric heights in radar and lidar wind measurements. A series of individual profiles of 1-hr averages of velocity data that were taken in October 1981 using the MST radar at Poker Flat, Alaska are presented. The vertical wavelength of this wave-like event is about 15 km and has a period close to 10 hours. A clear downward phase propagation can be seen, and so these oscillations are usually, and probably correctly, interpreted as being gravity wave flow perturbations. We investigate an alternative explanation that may also be possible; specifically, we investigate the possibility that the perturbed flow is a pseudo-wave structure produced by mean flow acceleration due to gravity waves propagating upward from below and breaking in the mesosphere. The question is whether effects similar to those that produce the much longer period Quasi-Biennial Oscillation (QBO) in the equatorial stratosphere can produce mesospheric pseudo-waves (MPW) at much shorter periods.
NASA Astrophysics Data System (ADS)
Brissaud, Q.; Garcia, R.; Martin, R.; Komatitsch, D.
2014-12-01
Low-frequency events such as tsunamis generate acoustic and gravity waves which quickly propagate in the atmosphere. Since the atmospheric density decreases exponentially as the altitude increases and from the conservation of the kinetic energy, those waves see their amplitude raise (to the order of 105 at 200km of altitude), allowing their detection in the upper atmosphere. Various tools have been developed through years to model this propagation, such as normal modes modeling or to a greater extent time-reversal techniques, but none offer a low-frequency multi-dimensional atmospheric wave modelling.A modeling tool is worthy interest since there are many different phenomena, from quakes to atmospheric explosions, able to propagate acoustic and gravity waves. In order to provide a fine modeling of the precise observations of these waves by GOCE satellite data, we developed a new numerical modeling tool.Starting from the SPECFEM program that already propagate waves in solid, porous or fluid media using a spectral element method, this work offers a tool with the ability to model acoustic and gravity waves propagation in a stratified attenuating atmosphere with a bottom forcing or an atmospheric source.Atmospheric attenuation is required in a proper modeling framework since it has a crucial impact on acoustic wave propagation. Indeed, it plays the role of a frequency filter that damps high-frequency signals. The bottom forcing feature has been implemented due to its ability to easily model the coupling with the Earth's or ocean's surface (that vibrates when a surface wave go through it) but also huge atmospheric events.
Near-Inertial Internal Gravity Waves in the Ocean.
Alford, Matthew H; MacKinnon, Jennifer A; Simmons, Harper L; Nash, Jonathan D
2016-01-01
We review the physics of near-inertial waves (NIWs) in the ocean and the observations, theory, and models that have provided our present knowledge. NIWs appear nearly everywhere in the ocean as a spectral peak at and just above the local inertial period f, and the longest vertical wavelengths can propagate at least hundreds of kilometers toward the equator from their source regions; shorter vertical wavelengths do not travel as far and do not contain as much energy, but lead to turbulent mixing owing to their high shear. NIWs are generated by a variety of mechanisms, including the wind, nonlinear interactions with waves of other frequencies, lee waves over bottom topography, and geostrophic adjustment; the partition among these is not known, although the wind is likely the most important. NIWs likely interact strongly with mesoscale and submesoscale motions, in ways that are just beginning to be understood.
Near-Inertial Internal Gravity Waves in the Ocean
NASA Astrophysics Data System (ADS)
Alford, Matthew H.; MacKinnon, Jennifer A.; Simmons, Harper L.; Nash, Jonathan D.
2016-01-01
We review the physics of near-inertial waves (NIWs) in the ocean and the observations, theory, and models that have provided our present knowledge. NIWs appear nearly everywhere in the ocean as a spectral peak at and just above the local inertial period f, and the longest vertical wavelengths can propagate at least hundreds of kilometers toward the equator from their source regions; shorter vertical wavelengths do not travel as far and do not contain as much energy, but lead to turbulent mixing owing to their high shear. NIWs are generated by a variety of mechanisms, including the wind, nonlinear interactions with waves of other frequencies, lee waves over bottom topography, and geostrophic adjustment; the partition among these is not known, although the wind is likely the most important. NIWs likely interact strongly with mesoscale and submesoscale motions, in ways that are just beginning to be understood.
Benini, Marco Dappiaggi, Claudio; Murro, Simone
2014-08-01
We discuss the quantization of linearized gravity on globally hyperbolic, asymptotically flat, vacuum spacetimes, and the construction of distinguished states which are both of Hadamard form and invariant under the action of all bulk isometries. The procedure, we follow, consists of looking for a realization of the observables of the theory as a sub-algebra of an auxiliary, non-dynamical algebra constructed on future null infinity ℱ⁺. The applicability of this scheme is tantamount to proving that a solution of the equations of motion for linearized gravity can be extended smoothly to ℱ⁺. This has been claimed to be possible provided that a suitable gauge fixing condition, first written by Geroch and Xanthopoulos [“Asymptotic simplicity is stable,” J. Math. Phys. 19, 714 (1978)], is imposed. We review its definition critically, showing that there exists a previously unnoticed obstruction in its implementation leading us to introducing the concept of radiative observables. These constitute an algebra for which a Hadamard state induced from null infinity and invariant under the action of all spacetime isometries exists and it is explicitly constructed.
NASA Astrophysics Data System (ADS)
Masnadi, Naeem; Cho, Yeunwoo; Duncan, James H.; Akylas, Triantaphyllos
2015-11-01
The non-linear response of a water free surface to a pressure source moving at speeds near the minimum speed of linear gravity-capillary waves (Cmin ~ 23 cm/s) is investigated with experiments and theory. In the experiments, waves are generated by a vertically oriented air-jet that moves at a constant speed over the water surface in a long tank. The 3-D surface shape behind the air-jet is measured using a cinematic refraction-based technique combined with an LIF technique. At towing speeds just below Cmin, an unsteady pattern is formed where localized depressions periodically appear in pairs and move away from the source along the arms of a downstream V-shaped pattern. This behavior is analogous to the periodic shedding of solitary waves upstream of a source moving at the maximum wave speed in shallow water. The gravity-capillary depressions are rapidly damped by viscosity and their speed-amplitude characteristics closely match those from inviscid calculations of gravity-capillary lumps. The shedding frequency of the lumps in the present experiments increases with both increasing towing speed and air-flow rate. Predictions of this behavior using a model equation that incorporates damping and a quadratic nonlinearity are in good agreement with the experiments. The partial support of the National Science Foundation under grant OCE0751853 is gratefully acknowledged.
Observations and a model of gravity-wave variability in the middle atmosphere
NASA Technical Reports Server (NTRS)
Fritts, D. C.; Vincent, R. A.
1986-01-01
A major goal was to determine what portion of the gravity-wave frequency spectrum accounted for the majority of the momentum flux and divergence, as this has important implications for the middle atmosphere response. It was found that approx. 70% of the total flux and divergence was due to wave motions with observed periods less than 1 hour, consistent with expectations based on the shape of the observed gravity-wave spectrum (FrItts, 1984). This dominance of the momentum flux and divergence by high-frequency motions implies a potential for the modulation of those quantities by large-amplitude motions at lower frequencies. A second, striking aspect of the velocity and momentum flux data is its dramatic diurnal variability, particularly at certain levels. This variability is illustrated with the momentum flux, computed in 8-hr blocks. The dominant contributions here are due to waves with periods less than 1 hr. The variability with height and size of the mean square velocity in the west beam and the momentum flux, energed over the 3-day period. A detailed analysis of the various tidal motions present during this data interval was performed, and it was determined that variations in the zontal wind profile imposed by the diurnal tidal motion are probably responsible for the modulation of the gravity-wave amplitudes and momentum fluxes.
NASA Astrophysics Data System (ADS)
Yuan, T.; Cai, X.; Pautet, P. D.; Fish, C. S.; Zhao, Y.; Taylor, M. J.; Pendleton, W. R., Jr.
2014-12-01
Gravity waves have been known to deposit energy and momentum through dissipation during their upward propagation, which changes the dynamic flow and thermal structure in the lower thermosphere. For an upward propagating gravity wave packet with rich spectrum, various theoretical works and model simulations have indicated that the wave components with high frequency and larger vertical wavelength experience dissipation at higher altitude and dominate earlier stage, while the low frequency components, with short vertical wavelength, dominate during the latter part of the propagation. However, the evidences of such critical dissipation mechanism in the gravity wave packet propagation process have yet been comprehensively studied and discussed in the experimental observations. In this paper, utilizing the observations from the Na lidar, the Meteor Wind Radar (MWR) and the Advanced Mesospheric Temperature Mapper (AMTM) at Utah State University, we investigate several cases of this dynamic scenario over Logan, Utah (41.7°N, 111.8°W), to study the waves' evolution as they are propagating upward.
Observations of Atmospheric Gravity Wave damping in the Mesosphere with lidar and airglow
NASA Astrophysics Data System (ADS)
Swenson, G. R.; Li, F.; Liu, A.; Thakker, P.
2002-12-01
Correlative measurements of temperature and winds by Na lidar and brightness in OH and O2 Atmospheric band airglow have been made at Albuquerque, NM and Maui, HI for a study of high frequency (Period less than 30 minutes) Atmospheric Gravity Waves (AGWs). Waves studies from four nights have been made and the correlative information describes the intrinsic wave properties with altitude, their damping characteristics, and resulting accelerations to the large scale dynamics in the 85-100 km altidude region. Generally, saturated to super-saturated conditions were observed below 95 km. Above this altitude, they became freely propagating.
A nonreflecting upper boundary condition for anelastic nonhydrostatic mesoscale gravity-wave models
NASA Technical Reports Server (NTRS)
Kim, Young-Joon; Kar, Sajal K.; Arakawa, Akio
1993-01-01
A sponge layer is formulated to prevent spurious reflection of vertically propagating quasi-stationary gravity waves at the upper boundary of a two-dimensional numerical anelastic nonhydrostatic model. The sponge layer includes damping of both Newtonian-cooling type and Rayleigh-friction type, whose coefficients are determined in such a way that the reflectivity of wave energy at the bottom of the layer is zero. Unlike the formulations in earlier studies, our formulation includes the effects of vertical discretization, vertical mean density variation, and nonhydrostaticity. This sponge formulation is found effective in suppressing false downward reflection of waves for various types of quasi-stationary forcing.
A model for gravity-wave spectra observed by Doppler sounding systems
NASA Technical Reports Server (NTRS)
Vanzandt, T. E.
1986-01-01
A model for Mesosphere - Stratosphere - Troposphere (MST) radar spectra is developed following the formalism presented by Pinkel (1981). Expressions for the one-dimensional spectra of radial velocity versus frequency and versus radial wave number are presented. Their dependence on the parameters of the gravity-wave spectrum and on the experimental parameters, radar zenith angle and averaging time are described and the conditions for critical tests of the gravity-wave hypothesis are discussed. The model spectra is compared with spectra observed in the Arctic summer mesosphere by the Poker Flat radar. This model applies to any monostatic Doppler sounding system, including MST radar, Doppler lidar and Doppler sonar in the atmosphere, and Doppler sonar in the ocean.
A nonhydrostatic unstructured-mesh soundproof model for simulation of internal gravity waves
NASA Astrophysics Data System (ADS)
Smolarkiewicz, Piotr; Szmelter, Joanna
2011-12-01
A semi-implicit edge-based unstructured-mesh model is developed that integrates nonhydrostatic soundproof equations, inclusive of anelastic and pseudo-incompressible systems of partial differential equations. The model builds on nonoscillatory forward-in-time MPDATA approach using finite-volume discretization and unstructured meshes with arbitrarily shaped cells. Implicit treatment of gravity waves benefits both accuracy and stability of the model. The unstructured-mesh solutions are compared to equivalent structured-grid results for intricate, multiscale internal-wave phenomenon of a non-Boussinesq amplification and breaking of deep stratospheric gravity waves. The departures of the anelastic and pseudoincompressible results are quantified in reference to a recent asymptotic theory [Achatz et al. 2010, J. Fluid Mech., 663, 120-147)].
The response of plasma density to breaking inertial gravity wave in the lower regions of ionosphere
Tang, Wenbo Mahalov, Alex
2014-04-15
We present a three-dimensional numerical study for the E and lower F region ionosphere coupled with the neutral atmosphere dynamics. This model is developed based on a previous ionospheric model that examines the transport patterns of plasma density given a prescribed neutral atmospheric flow. Inclusion of neutral dynamics in the model allows us to examine the charge-neutral interactions over the full evolution cycle of an inertial gravity wave when the background flow spins up from rest, saturates and eventually breaks. Using Lagrangian analyses, we show the mixing patterns of the ionospheric responses and the formation of ionospheric layers. The corresponding plasma density in this flow develops complex wave structures and small-scale patches during the gravity wave breaking event.
Gravity waves in the thermosphere observed by the AE satellites
NASA Technical Reports Server (NTRS)
Gross, S. H.; Reber, C. A.; Huang, F. T.
1983-01-01
Atmospheric Explorer (AE) satellite data were used to investigate the spectra characteristics of wave-like structure observed in the neutral and ionized components of the thermosphere. Power spectral analysis derived by the maximum entropy method indicate the existence of a broad spectrum of scale sizes for the fluctuations ranging from tens to thousands of kilometers.
NASA Astrophysics Data System (ADS)
Hedlin, Michael; de Groot-Hedlin, Catherine; Hoffmann, Lars; Alexander, M. Joan; Stephan, Claudia
2016-04-01
The upgrade of the USArray Transportable Array (TA) with microbarometers and infrasound microphones has created an opportunity for a broad range of new studies of atmospheric sources and the large- and small-scale atmospheric structure through which signals from these events propagate. These studies are akin to early studies of seismic events and the Earth's interior structure that were made possible by the first seismic networks. In one early study with the new dataset we use the method of de Groot-Hedlin and Hedlin (2015) to recast the TA as a massive collection of 3-element arrays to detect and locate large infrasonic events. Over 2,000 events have been detected in 2013. The events cluster in highly active regions on land and offshore. Stratospherically ducted signals from some of these events have been recorded more than 2,000 km from the source and clearly show dispersion due to propagation through atmospheric gravity waves. Modeling of these signals has been used to test statistical models of atmospheric gravity waves. The network is also useful for making direct observations of gravity waves. We are currently studying TA and satellite observations of gravity waves from singular events to better understand how the waves near ground level relate to those observed aloft. We are also studying the long-term statistics of these waves from the beginning of 2010 through 2014. Early work using data bandpass filtered from 1-6 hr shows that both the TA and satellite data reveal highly active source regions, such as near the Great Lakes. de Groot-Hedlin and Hedlin, 2015, A method for detecting and locating geophysical events using clusters of arrays, Geophysical Journal International, v203, p960-971, doi: 10.1093/gji/ggv345.
Thermal Effect of Gravity Waves in the Upper Atmosphere and its Parameterization
NASA Astrophysics Data System (ADS)
Akmaev, R. A.
2005-12-01
Previous work has demonstrated the importance of the vertical heat transport by dissipating gravity waves in addition to the momentum deposition commonly represented in gravity-wave parameterizations. This work has been initiated by the need to incorporate the heat transfer into the widely used Doppler-spread Parameterization (DSP) by C. O. Hines. The exact description of the effect, otherwise known as ``dynamical cooling," depends on partitioning of the total wave energy deposition rate between the thermal and frictional dissipation channels. Since the DSP does not explicitly distinguish between the two types of dissipation, certain assumptions have to be made. The resulting general expression relating the heat flux with the total wave energy deposition rate is then in general agreement with other studies using similar assumptions, and may be implemented within any suitable parameterization. It is noted that, as waves enter the thermosphere and become primarily dissipated by molecular viscosity and thermal conductivity, the partitioning ratio may actually change compared to that commonly assumed for the middle atmosphere. More generally, it is observed that the wave dissipation results in an increase of both the energy and entropy of the background stratification as is expected for a dissipative process. On balance, energy is deposited into the mean stratification and the familiar term ``dynamical cooling" may be somewhat misleading. The general relation may also be recommended for estimates of the net heating from available observations of wave heat fluxes in the upper atmosphere.
Linear mode conversion and the operator theory of wave mechanics
NASA Astrophysics Data System (ADS)
Dendy, R. O.
1988-02-01
The linear mode conversion regime for the approximate dispersion relation [ω-ω1(x,k)][ω-ω2(x,k)]=η occurs near x=xc, k=kc such that ω1(xc,kc)=ω2(xc, kc). Cairns and Lashmore-Davies [Phys. Fluids 25, 1605 (1982); 26, 1268 (1983)] have recently expressed the associated energy flow in terms of a single parameter that involves η and the partial derivatives of ω1 and ω2. In this paper, a different, wave-mechanical approach is used to obtain the same result. The process of linear mode conversion is discussed using the system L̂Ψ=i ∂Ψ/∂t, where L̂ is a Hermitian operator. The degeneracy of plasma modes, and their coupling by warm plasma corrections in an inhomogeneous plasma, is dealt with using first-order perturbation theory. Simple coupled first-order differential equations for the wave amplitudes follow, which can be integrated directly. The calculated energy flow reproduces the expression that is obtained from the theory of Cairns and Lashmore-Davies.
NASA Astrophysics Data System (ADS)
Martin, Roland; Brissaud, Quentin; Garcia, Raphael; Komatitsch, Dimitri
2015-04-01
During low-frequency events such as tsunamis, acoustic and gravity waves are generated and quickly propagate in the atmosphere. Due to the exponential decrease of the atmospheric density with the altitude, the conservation of the kinetic energy imposes that the amplitude of those waves increases (to the order of 105 at 200km of altitude), which allows their detection in the upper atmosphere. This propagation bas been modelled for years with different tools, such as normal modes modeling or to a greater extent time-reversal techniques, but a low-frequency multi-dimensional atmospheric wave modelling is still crucially needed. A modeling tool is worth of interest since there are many different sources, as earthquakes or atmospheric explosions, able to propagate acoustic and gravity waves. In order to provide a fine modeling of the precise observations of these waves by GOCE satellite data, we developed a new numerical modeling tool. By adding some developments to the SPECFEM package that already models wave propagation in solid, porous or fluid media using a spectral element method, we show here that acoustic and gravity waves propagation can now be modelled in a stratified attenuating atmosphere with a bottom forcing or an atmospheric source. The bottom forcing feature has been implemented to easily model the coupling with the Earth's or ocean's vibrating surfaces but also huge atmospheric events. Atmospheric attenuation is also introduced since it has a crucial impact on acoustic wave propagation. Indeed, it plays the role of a frequency filter that damps high-frequency signals.
Interactions between gravity waves and cold air outflows in a stably stratified uniform flow
NASA Technical Reports Server (NTRS)
Lin, Yuh-Lang; Wang, Ting-An; Weglarz, Ronald P.
1993-01-01
Interactions between gravity waves and cold air outflows in a stably stratified uniform flow forced by various combinations of prescribed heat sinks and sources are studied using a hydrostatic two-dimensional nonlinear numerical model. The formation time for the development of a stagnation point or reversed flow at the surface is not always directly proportional to the Froude number when wave reflections exist from upper levels. A density current is able to form by the wave-otuflow interaction, even though the Froude number is greater than a critical value. This is the result of the wave-outflow interaction shifting the flow response to a different location in the characteristic parameter space. A density current is able to form or be destroyed due to the wave-outflow interaction between a traveling gravity wave and cold air outflow. This is proved by performing experiments with a steady-state heat sink and an additional transient heat source. In a quiescent fluid, a region of cold air, convergence, and upward motion is formed after the collision between two outflows produced by two prescribed heat sinks. After the collision, the individual cold air outflows lose their own identity and merge into a single, stationary, cold air outflow region. Gravity waves tend to suppress this new stationary cold air outflow after the collision. The region of upward motion associated with the collision is confined to a very shallow layer. In a moving airstream, a density current produced by a heat sink may be suppressed or enhanced nonlinearly by an adjacent heat sink due to the wave-outflow interaction.
Linear waves on a surface of vertical rivulet
NASA Astrophysics Data System (ADS)
Aktershev, S. P.; Alekseenko, S. V.; Arkhipov, D. G.
2016-10-01
The type of film flow whereby the fluid flows in the form of many streamlets is typically called a rivulet flow. Whereas an individual streamlet bounded by two contact lines is called a rivulet. Special attention has been paid to rivulet flows because of their practical value for a variety of devices in power engineering and chemical technology, such as absorbers, distillation columns, evaporators, and heat exchangers for the liquefaction of natural gas. In the present paper the waves in vertical rivulet are investigated analytically. The Kapitza-Shkadov model is used to describe the wavy rivulet flow since it was well proven in the study of nonlinear waves in falling liquid films over a wide range of Reynolds numbers. The equations of the wavy rivulet flow are derived on the basis of the weighed residual method. These equations turn out to be the projections of the Shkadov's model equations on system of basis functions, constructed in special way. Linearizing these equations results in the dispersion relations for plane waves. The stability criterion for rivulet flows is deduced, and the analysis of dispersion relations depending on dimensionless parameters is carried out.
Gravity waves and turbulence from troposphere to mesosphere over the Indian MST radar station
NASA Astrophysics Data System (ADS)
Chakravarty, Subhas
The Indian MST radar facility at Gadanki (13.5° N, 79.2° E) has been utilised to study the backscattered signals received near simultaneously from troposphere, stratosphere and meso-sphere. The main objective is to identify the signatures of gravity waves in the troposphere/stratosphere and their upward propagation to produce mesospheric turbulence. The observations were car-ried out during different months of 2001-2003 using five beam positions for E-W, N-S at 10° beam angle and the Zenith direction, variable pulse widths (range bins between 150 m to 2.4 km) and minimum time resolution of 80 s (for one radar scan) covering the height range of 4-85 km. While results shown on the intermittent, inhomogeneous and anisotropic nature of mesospheric scattering regions are explained by the neutral turbulence driven perturbations in the radio refractive index corresponding to the Bragg scale of about 3 m for the radar frequency of 53 MHz, the seasonal variation in the occurrence of scattering layer heights between 70-80 km (including stratification and multiple layers) and signal strengths are dependent on (but may not be limited to) the severe weather related tropical convective sources generating grav-ity waves in the troposphere, their propagation through the stratosphere and breaking in the mesosphere. The spectrum of gravity waves of a convective event with different phase velocities would go through various interaction regimes with the mean flows acting as filters as well as producing turbulence in all the three regions of interest. On a typical day (e.g. 25 June 2002) of well developed mesospheric scattering layer, the height profile of SNR (related to different turbulence patches) shows an average maximum value of 15 dB below 18 km with 3-4 prominent and continuous tropospheric scatter layers of 3 km thickness and 5 dB in the mesosphere with 2 km thick intermittent layer around 74 km. Wind velocity contours show a reversal in mean wind direction around 8-10 km
Tsuda, Toshitaka
2014-01-01
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.
TSUDA, Toshitaka
2014-01-01
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. PMID:24492645
NASA Astrophysics Data System (ADS)
Yu, C.; Xue, X.; Dou, X.; Wu, J.
2015-12-01
The adjustment of gravity wave parameterization associated with model convection has made possible the spontaneous generation of the quasi-biennial oscillation (QBO) in the Whole Atmosphere Community Climate Model (WACCM 4.0), although there are some mismatching when compared with the observation. The parameterization is based on Lindzen's linear saturation theory which can better describe inertia-gravity waves (IGW) by taking the Coriolis effects into consideration. In this work we improve the parameterization by importing a more realistic double Gaussian distribution IGW spectrum, which is calculated from tropical radiosonde observations. A series of WACCM simulations are performed to determine the relationship between the period and amplitude of equatorial zonal wind oscillations and the feature of parameterized IGW. All of these simulations are capable of generating equatorial wind oscillations in the stratosphere using the standard spatial resolution settings. The period of the oscillation is associate inversely with the strength of the IGW forcing, but the central values of double Gaussian distribution IGW have influence both on the magnitude and period of the oscillation. In fact, the eastward and westward IGWs affect the amplitude of the QBO wind, respectively, and the strength of IGWs forcing determines the accelerating rate of the QBO wind. Furthermore, stronger forcing of IGWs can lead to a deeper propagate of the QBO phase, which can extend the lowest altitude of the constant zonal wind amplitudes to about 100 hPa.
NASA Astrophysics Data System (ADS)
Alexander, M. Joan
2015-08-01
Satellite limb-sounding methods provide the best global temperature data available for simultaneous measurement of gravity wave horizontal and vertical structures needed to estimate momentum flux and constrain wave effects on general circulation. Gravity waves vary in the three spatial dimensions and time, so the ideal measurement observes all three dimensions at high resolution nearly simultaneously. High Resolution Dynamics Limb Sounder (HIRDLS) measurements give near-simultaneous profiles in close proximity and at high vertical resolution, but these coincident profiles lie only along the plane of the measurement track. Here we combine HIRDLS and radio occultation data sets to obtain three-dimensional properties of gravity waves on a global scale as well as seasonal variations. The results show dramatic changes from previous estimates using either data set alone. Changes include much larger momentum fluxes and latitudinal variations in propagation direction that support an enhanced role for gravity wave forcing of middle atmosphere circulation.
NASA Astrophysics Data System (ADS)
Vasilyev, Pavel; Karpov, Ivan; Kshevetskiy, Sergey
2016-09-01
We present results of modeling of the effect of internal gravity waves (IGW), excited in the region of the 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.
Effect of small floating disks on the propagation of gravity waves
NASA Astrophysics Data System (ADS)
De Santi, F.; Olla, P.
2017-04-01
A dispersion relation for gravity waves in water covered by disk-like impurities embedded in a viscous matrix is derived. The macroscopic equations are obtained by ensemble-averaging the fluid equations at the disk scale in the asymptotic limit of long waves and low disk surface fraction. Various regimes are identified depending on the disk radii and the thickness and viscosity of the top layer. Semi-quantitative analysis in the close-packing regime suggests dramatic modification of the dynamics, with orders of magnitude increase in wave damping and wave dispersion. A simplified model working in this regime is proposed. Possible applications to wave propagation in an ice-covered ocean are discussed and comparison with field data is provided.
Observations of Planetary Mixed Rossby-Gravity Waves in the Upper Stratosphere.
NASA Astrophysics Data System (ADS)
Randel, William J.; Boville, Byron A.; Gille, John C.
1990-12-01
Observational evidence is presented for planetary scale (zonal wave number 1-2) mixed Rossby-gravity (MRG) waves in the equatorial upper stratosphere (35-50 km). These waves are detected in Limb Infrared Monitor of the Stratosphere (LIMS) measurements as coherently propagating temperature maxima of amplitude 0.1-0.3 K, which are antisymmetric (out of phase) about the equator, centered near 10°-15° north and south latitude. These features have vertical wavelengths of order 10-15 km, periods near 2-3 days, and zonal phase velocities close to 200 m s1. Both eastward and westward propagating waves are found, and the observed vertical wavelengths and meridional structures are in good agreement with the MRG dispersion relation. Theoretical estimates of the zonal accelerations attributable to these waves suggest they do not contribute substantially to the zonal momentum balance in the middle atmosphere.
NASA Astrophysics Data System (ADS)
Ern, Manfred; Trinh, Quang Thai; Kaufmann, Martin; Krisch, Isabell; Preusse, Peter; Ungermann, Jörn; Zhu, Yajun; Gille, John C.; Mlynczak, Martin G.; Russell, James M., III; Schwartz, Michael J.; Riese, Martin
2016-08-01
Sudden stratospheric warmings (SSWs) are circulation anomalies in the polar region during winter. They mostly occur in the Northern Hemisphere and affect also surface weather and climate. Both planetary waves and gravity waves contribute to the onset and evolution of SSWs. While the role of planetary waves for SSW evolution has been recognized, the effect of gravity waves is still not fully understood, and has not been comprehensively analyzed based on global observations. In particular, information on the gravity wave driving of the background winds during SSWs is still missing.We investigate the boreal winters from 2001/2002 until 2013/2014. Absolute gravity wave momentum fluxes and gravity wave dissipation (potential drag) are estimated from temperature observations of the satellite instruments HIRDLS and SABER. In agreement with previous work, we find that sometimes gravity wave activity is enhanced before or around the central date of major SSWs, particularly during vortex-split events. Often, SSWs are associated with polar-night jet oscillation (PJO) events. For these events, we find that gravity wave activity is strongly suppressed when the wind has reversed from eastward to westward (usually after the central date of a major SSW). In addition, gravity wave potential drag at the bottom of the newly forming eastward-directed jet is remarkably weak, while considerable potential drag at the top of the jet likely contributes to the downward propagation of both the jet and the new elevated stratopause. During PJO events, we also find some indication for poleward propagation of gravity waves. Another striking finding is that obviously localized gravity wave sources, likely mountain waves and jet-generated gravity waves, play an important role during the evolution of SSWs and potentially contribute to the triggering of SSWs by preconditioning the shape of the polar vortex. The distribution of these hot spots is highly variable and strongly depends on the zonal and
NASA Astrophysics Data System (ADS)
Lefevre, Maxence; Spiga, Aymeric; Lebonnois, Sebastien
2016-10-01
One of the main questions that remains unclear about the dynamics of the atmosphere of Venus and its interaction with the photochemistry is the characterization of the cloud convective layer which mixes momentum, heat, chemical species and generates gravity waves observed by Venus Express. This dynamical forcing induced by the cloud layer has been proposed as a significant contribution to the maintenance of the super-rotation. However these waves develop from regional to local scales and can not be resolved by global circulation models (GCM) developed insofar. Therefore we developed an unprecedented 3D Venusian mesoscale model based on the Martian mesoscale model using the Weather Research and Forecast terrestrial model. We report the first application of this model : simulating convection in the Venusian cloud layer and associated gravity waves by 3D turbulent-resolving simulations (Large-Eddy Simulations). The model employs an offline radiative forcing based on heating rates extracted from the LMD Venus GCM consisting of three distinct kind of rates. Two radiative ones for short wave (solar) and long wave (IR) and one for the adiabatic cooling/warming due to the global dynamics of the atmosphere (mainly the Hadley cell) with 2 different cloud models. Therefore we are able to characterize the convection and associated gravity waves in function of latitude and local time. To assess the impact of the general circulation on the convection we ran simulations with forcing from a 1D radiative model.The resolved convective layer takes place between 1.0 105 and 3.8 104 Pa with vertical wind between ± 3 m/s, is organized as polygonal closed cells of about 8x8km2, and emits gravity waves on either side with temperature perturbations of about 0.5 K with vertical wavelength of 1 km and horizontal wavelength from 1 to almost 20 km. The order of magnitude of the resolved plumes is consistent with observations though underestimated.We are working on coupling the model with a
Higher order dispersion in the propagation of a gravity wave packet
NASA Technical Reports Server (NTRS)
Yeh, K. C.; Dong, B.
1989-01-01
To the first order of approximation, the complex amplitude of a wave packet in an anisotropic and dispersive medium is convected with the group of velocity. However, a gravity wave is a vector wave. Its wave packet must be formed by superposition of various wave numbers with corresponding frequencies, as is the case for scalar waves, and additionally by superposing many eigenmodes which also depend on the wave number. To represent the vector wave packet self-consistently, it is found that a gradient term must be included in the expansion. For a Guassian wave packet, this gradient term is shown to have important implications on the velocity vector as represented by its hodograph. Numerical results show that the hodograph is influenced by the location of the relative position of interest from the center of a Gaussian pulse. Higher order expansion shows that an initial Gaussian wave packet will retain its Gaussian shape as it propagates, but the pulse will spread in all directions with its major axis undergoing a rotation. Numerical results indicate that these higher order dispersive effects may be marginally observable in the atmosphere.
Non-linear Oscillations of Compact Stars and Gravitational Waves
NASA Astrophysics Data System (ADS)
Passamonti, Andrea
2006-07-01
This thesis investigates in the time domain a particular class of second order perturbations of a perfect fluid non-rotating compact star: those arising from the coupling between first order radial and non-radial perturbations. This problem has been treated by developing a gauge invariant formalism based on the 2-parameter perturbation theory (Sopuerta, Bruni and Gualtieri, 2004) where the radial and non-radial perturbations have been separately parameterized. The non-linear perturbations obey inhomogeneous partial differential equations, where the structure of the differential operator is given by the previous perturbative orders and the source terms are quadratic in the first order perturbations. In the exterior spacetime the sources vanish, thus the gravitational wave properties are completely described by the second order Zerilli and Regge-Wheeler functions. As main initial configuration we have considered a first order differentially rotating and radially pulsating star. Although at first perturbative order this configuration does not exhibit any gravitational radiation, we have found a new interesting gravitational signal at non-linear order, in which the radial normal modes are precisely mirrored. In addition, a resonance effect is present when the frequencies of the radial pulsations are close to the first axial w-mode. Finally, we have roughly estimated the damping times of the radial pulsations due to the non-linear gravitational emission. The coupling near the resonance results to be a very effective mechanism for extracting energy from the radial oscillations.
Sheen, D.R.
1987-01-01
In the Worldwide Atmospheric Gravity Wave Study (WAGS) campaign, the source-response relationship between the auroral activities and the gravity waves observed in the ionosphere was studied. Ionospheric parameters observed with the incoherent scatter radars at Sondrestrom and Millstone Hill were compared with predicted results based on gravity-wave theory. In the observed data, usually two types of disturbances can be identified. One is the distinct, semiperiodic traveling ionospheric disturbance. The other is the ever-present, semirandom perturbations. The first type is classified as the special event, and one which was observed on October 18, 1985 during a moderately magnetic-active period is analyzed. The second type is classified as the background wave spectra, and these spectra under various levels of magnetic activity are analyzed. The observed parameters used in this study are the ionization density and the line-of-sight ion velocity. This provides more information than in most of the previous investigations of traveling ionospheric disturbances, in which only electron-density perturbations were used.
Ruohoniemi, J.M.; Greenwald, R.A.; Baker, K.B.; Samson, J.C.
1990-05-03
An HF backscatter radar at Goose Bay, Labrador made it possible to observe irregularities in the distribution of ionospheric ionization at E and F region altitudes (100 - 600 km) in the high-latitude (65 - 85 deg Lambda) ionosphere. Recently it has been established that the passage of atmospheric gravity waves perturbs the ionosphere in ways that are readily detected in returns that reflect off the ionospheric layers. The particular strength of the technique lies in the nearly instantaneous measurement of gravity wave effects over large areas ( 1 million sq. km). With this information the propagation of gravity waves can be accurately modelled. Generally gravity waves are observed during daylight hours propagating away from the auroral electrojets. The propagation mode involves penetration of wave energy through the lower atmosphere and subsequent reflection by the earth's surface. The frequencies associated with the waves lie in the 0.4 - 0.6 mHz range and the wavelengths vary from 300 to 500 km. The excitation sources appear to lie in the vicinity of the high-latitude electrojets. In this paper we outline the analysis of gravity wave effects on HF propagation and present an example of a modelled gravity wave event.
Rayleigh lidar observations of gravity wave activity in the stratosphere and lower mesosphere
NASA Technical Reports Server (NTRS)
Miller, M. S.; Gardner, C. S.; Liu, C. H.
1987-01-01
Forty-two monochromatic gravity wave events were observed in the 25 to 55 km altitude region during 16 nights of Rayleigh lidar measurements at Poker Flat, Alaska and Urbana, Illinois. The measured wave parameters were compared to previous radar and lidar measurements of gravity wave activity. Vertical wavelengths, lambda(z), between 2 and 11.5 km with vertical phase velocities, c(z), between 0.1 and 1 m/s were observed. Measured values of lambda(z) and c(z) were used to infer observed wave periods, T(ob), between 50 and 1000 minutes and horizontal wavelengths, lambda(x), from 25 to 2000 km. Dominant wave activity was found at vertical wavelengths between 2 to 4 km and 7 to 10 km. No seasonal variations were evident in the observed wave parameters. Vertical and horizontal wavelengths showed a clear tendency to increase with T(ob), which is consistent with recent sodium lidar studies of monochromatic wave events near the mesopause. Measured power law relationships between the wave parameters were lambda(z) varies as T(ob) sup 0.96, lambda(x) varies as T(ob) sup 1.8, and c(z) varies as T(ob) sup -0.85. The kinetic energy calculated for the monochromatic wave events varied as k(z) sup -2, k(x) sup -1, and f(ob) sup -1.7. The atmospheric scale heights calculated for each observation date range from 6.5 to 7.6 km with a mean value of 7 km. The increase of rms wind perturbations with altitude indicated an amplitude growth length of 20.9 km. The altitude profile of kinetic energy density decreased with height, suggesting that waves in this altitude region were subject to dissipation or saturation effects.
Polar mesosphere and lower thermosphere dynamics: 1. Mean wind and gravity wave climatologies
NASA Astrophysics Data System (ADS)
Dowdy, Andrew J.; Vincent, Robert A.; Tsutsumi, Masaki; Igarashi, Kiyoshi; Murayama, Yasuhiro; Singer, Werner; Murphy, Damian J.
2007-09-01
Mean wind and gravity wave climatologies are presented for the polar mesosphere and lower thermosphere (MLT). The data were derived using MF radars at Davis (69°S, 78°E) and Syowa (69°S, 40°E) in the Antarctic and Poker Flat (65°N, 147°W) and Andenes (69°N, 16°E) in the Arctic. The dynamics of the Antarctic MLT are found to be significantly different from the Arctic MLT. Summer maxima in both the westward and equatorward winds occur closer to the solstice in the Antarctic than in the Arctic. The greater symmetry around the solstice suggests radiative effects may play a greater role in controlling the state of the Antarctic MLT than in the Arctic, where dynamical effects appear to be more important. Gravity wave observations also suggest that wave drag may be greater in the Arctic than in the Antarctic. The equatorward flow near the mesopause persists later in summer in the Arctic than in the Antarctic, as do observations of polar mesospheric clouds and polar mesospheric summer echoes. All three phenomena begin at about the same time in each hemisphere, but end later in the Arctic than in the Antarctic. It is proposed that the magnitude of the meridional winds can be used as a proxy for gravity wave driving and the consequent adiabatic cooling in the MLT. Seasonal variations in gravity wave activity are predominately combinations of annual and semiannual components. Significant hemispheric differences are observed for both the timing and magnitude of these seasonal variations.
NASA Astrophysics Data System (ADS)
Kinoshita, Takenari; Murayama, Yasuhiro; Kawamura, Seiji
2015-07-01
The interactions between gravity waves and atmospheric tidal waves have been observationally studied, although the phase relation between them has not been fully understood. In this study, the long-term wind velocity data observed with the Poker Flat MF radar (65°N, 147°W) were analyzed for the period of 1999-2008 to show local time dependence and seasonal climatologies of the 12 h and 24 h components in the mesospheric winds and their modulations of gravity wave kinetic energy. We made climatological 1 day composite plots of the kinetic energy of gravity waves for wave periods of 1-4 h and harmonic components of horizontal wind for each month. The results show that the kinetic energy of gravity waves peaks twice at 3-6 LT and 18-21 LT, which tend to coincide with the transition of the 12 h component of zonal wind from westward to eastward flow. On the other hand, a 2 month case study revealed that the gravity wave kinetic energy and the 12 h components of zonal wind appear to keep their phase difference constant (like a "phase locked") for more than 10 days. Events of this kind are also found in other years. To examine whether this relation can be explained by interaction between the 12 h component of zonal wind and gravity waves, we applied a gravity wave drag model to the background state defined as the sum of observed monthly mean and harmonic components of zonal wind. It is suggested that the orographic gravity wave drag has a 12 h periodicity and that the time of the drag enhancement changes in time following change in the phase of harmonic components of winds.
Concentric gravity waves over northern China observed by an airglow imager network and satellites
NASA Astrophysics Data System (ADS)
Xu, Jiyao; Li, Qinzeng; Yue, Jia; Hoffmann, Lars; Straka, William C.; Wang, Cuimei; Liu, Mohan; Yuan, Wei; Han, Sai; Miller, Steven D.; Sun, Longchang; Liu, Xiao; Liu, Weijun; Yang, Jing; Ning, Baiqi
2015-11-01
The first no-gap OH airglow all-sky imager network was established in northern China in February 2012. The network is composed of six all-sky airglow imagers that make observations of OH airglow gravity waves and cover an area of about 2000 km east and west and about 1400 km south and north. An unusual outbreak of Concentric Gravity Wave (CGW) events were observed by the network nearly every night during the first half of August 2013. These events were coincidentally observed by satellite sensors from Fengyun-2 (FY-2), Atmospheric Infrared Sounder (AIRS)/Aqua, and Visible Infrared Imaging Radiometer Suite (VIIRS)/Suomi National Polar-orbiting Partnership (NPP). Combination of the ground imager network with satellites provides multilevel observations of the CGWs from the stratosphere to the mesopause region. In this paper, two representative CGW events in August 2013 are studied in detail: first is the CGW on the night of 13 August 2013, likely launched by a single thunderstorm. The temporal and spatial analyses indicate that the CGW horizontal wavelengths follow freely propagating waves based on a GW dispersion relation within 300 km from the storm center. In contrast, the more distant observed gravity wave field exhibits a smaller horizontal wavelength of ~20 km, and our analysis strongly suggest this wave field represents a ducted wave. A second event, exhibiting multiple CGWs, was induced by two very strong thunderstorms on 9 August 2013. Multiscale waves with horizontal wavelengths ranging from less than 10 km to 200 km were observed.
Finite amplitude gravity waves in the Venus atmosphere generated by surface topography
NASA Technical Reports Server (NTRS)
Young, R. E.; Houben, H.; Walterscheid, R. L.; Schubert, G.
1992-01-01
A two-dimensional, fully nonlinear, nonhydrostatic, gravity wave model is used to study the evolution of gravity waves generated near the surface of Venus. The model extends from near the surface to well above the cloud layers. Waves are forced by applying a vertical wind at the bottom boundary. The boundary vertical wind is determined by the product of the horizontal wind and the gradient of the surface height. When wave amplitudes are small, the near-surface horizontal wind is the zonally averaged basic-state zonal wind, and the length scales of the forcing that results are characteristic of the surface height variation. When the forcing becomes larger and wave amplitudes affect the near-surface horizontal wind field, the forcing spectrum becomes more complicated, and a spectrum of waves is generated that is not a direct reflection of the spectrum of the surface height variation. Model spatial resolution required depends on the amplitude of forcing; for very nonlinear cases considered, vertical resolution was 250 m, and horizontal resolution was slightly greater than 1 km. For smaller forcing amplitudes, spatial resolution was much coarser, being 1 km in the vertical and about 10 km in the horizontal. Background static stability and mean wind are typical of those observed in the Venus atmosphere.
Impacts of climate changes on ocean surface gravity waves over the eastern Canadian shelf
NASA Astrophysics Data System (ADS)
Guo, Lanli; Sheng, Jinyu
2017-03-01
A numerical study is conducted to investigate the impact of climate changes on ocean surface gravity waves over the eastern Canadian shelf (ECS). The "business-as-usual" climate scenario known as Representative Concentration Pathway RCP8.5 is considered in this study. Changes in the ocean surface gravity waves over the study region for the period 1979-2100 are examined based on 3 hourly ocean waves simulated by the third-generation ocean wave model known as WAVEWATCHIII. The wave model is driven by surface winds and ice conditions produced by the Canadian Regional Climate Model (CanRCM4). The whole study period is divided into the present (1979-2008), near future (2021-2050) and far future (2071-2100) periods to quantify possible future changes of ocean waves over the ECS. In comparison with the present ocean wave conditions, the time-mean significant wave heights (H s ) are expected to increase over most of the ECS in the near future and decrease over this region in the far future period. The time-means of the annual 5% largest H s are projected to increase over the ECS in both near and far future periods due mainly to the changes in surface winds. The future changes in the time-means of the annual 5% largest H s and 10-m wind speeds are projected to be twice as strong as the changes in annual means. An analysis of inverse wave ages suggests that the occurrence of wind seas is projected to increase over the southern Labrador and central Newfoundland Shelves in the near future period, and occurrence of swells is projected to increase over other areas of the ECS in both the near and far future periods.
Long-Term Observation of Small and Medium-Scale Gravity Waves over the Brazilian Equatorial Region
NASA Astrophysics Data System (ADS)
Essien, Patrick; Buriti, Ricardo; Wrasse, Cristiano M.; Medeiros, Amauri; Paulino, Igo; Takahashi, Hisao; Campos, Jose Andre
2016-07-01
This paper reports the long term observations of small and medium-scale gravity waves over Brazilian equatorial region. Coordinated optical and radio measurements were made from OLAP at Sao Joao do Cariri (7.400S, 36.500W) to investigate the occurrences and properties and to characterize the regional mesospheric gravity wave field. All-sky imager measurements were made from the site. for almost 11 consecutive years (September 2000 to November 2010). Most of the waves propagated were characterized as small-scale gravity. The characteristics of the two waves events agreed well with previous gravity wave studies from Brazil and other sites. However, significant differences in the wave propagation headings indicate dissimilar source regions. The observed medium-scale gravity wave events constitute an important new dataset to study their mesospheric properties at equatorial latitudes. These data exhibited similar propagation headings to the short period events, suggesting they originated from the same source regions. It was also observed that some of the medium-scale were capable of propagating into the lower thermosphere where they may have acted directly as seeds for the Rayleigh-Taylor instability development. The wave events were primarily generated by meteorological processes since there was no correlation between the evolution of the wave events and solar cycle F10.7.
NASA Astrophysics Data System (ADS)
Ern, M.; Hoffmann, L.; Preusse, P.
2017-01-01
In order to reduce uncertainties in modeling the stratospheric circulation, global observations of gravity wave momentum flux (GWMF) vectors are required for comparison with distributions of resolved and parametrized GWMF in global models. For the first time, we derive GWMF vectors globally from data of a nadir-viewing satellite instrument: we apply a 3-D method to an Atmospheric Infrared Sounder (AIRS) temperature data set that was optimized for gravity wave (GW) analysis. For January 2009, the resulting distributions of GW amplitudes and of net GWMF highlight the importance of GWs in the polar vortex and the summertime subtropics. Net GWMF is preferentially directed opposite to the background wind, and, interestingly, it is dominated by large-amplitude GWs of relatively long horizontal wavelength. For convective GW sources, these large horizontal scales are in contradiction with traditional thoughts. However, the observational filter effect needs to be kept in mind when interpreting the results.
Evidence of gravity wave-tidal interaction observed near the summer mesopause at Poker Flat, Alaska
NASA Technical Reports Server (NTRS)
Wang, Ding-Yi; Fritts, David C.
1991-01-01
An analysis of gravity wave-tidal interaction observed near the mesopause by the MST radar at Poker Flat in July of 1986 is presented. The observations revealed daily mean wind maxima of about 60 m/sec westward and 20 m/sec southward with daily mean momentum fluxes, contributed by gravity waves with periods less than 1 hour of 4-5 sq m/sec sq eastward and 1-2 sq m/sec sq northward. Considerable hourly height variability was found to exist for both winds and momentum fluxes. A significant modulation of the fluxes by tidal winds was observed, characterized by out-of-phase correlations over a number of heights.
NASA Astrophysics Data System (ADS)
Suvorov, Arthur George; Melatos, Andrew
2016-08-01
The Ernst formulation of the Einstein equations is generalized to accommodate f (R ) theories of gravity. It is shown that, as in general relativity, the axisymmetric f (R ) field equations for a vacuum spacetime that is either stationary or cylindrically symmetric reduce to a single, nonlinear differential equation for a complex-valued scalar function. As a worked example, we apply the generalized Ernst equations to derive a f (R ) generalization of the Zipoy-Voorhees metric, which may be used to describe the gravitational field outside of an ellipsoidal neutron star. We also apply the theory to investigate the phase speed of large-amplitude gravitational waves in f (R ) gravity in the context of solitonlike solutions that display shock-wave behavior across the causal boundary.
Observation of atmospheric gravity wave cause and effect during October 1985 WAGS campaign
Rice, D.D.; Hunsucker, R.D.; Lanzerotti, L.J.; Crowley, G.; Williams, P.J.S.
1988-12-01
Moderate geomagnetic activity followed by a large scale TID was observed in Europe and eastern North America near 1200 UT on October 18, 1985 during the Worldwide Atmospheric Gravity Wave Study. The speed and direction of the TID are estimated, suggesting that it was caused by an atmospheric gravity wave expanding from a localized source over the Arctic Ocean. Auroral imaging shows that the source region was located near the westward edge of an expanding auroral bulge and may have been associated with a westward traveling surge. The TID periods increased with distance from the source region and the largest TID amplitudes were seen along a line perpendicular to the orientation of the auroral oval. 19 references.
Water Surface Currents, Short Gravity-Capillary Waves and Radar Backscatter
NASA Technical Reports Server (NTRS)
Atakturk, Serhad S.; Katsaros, Kristina B.
1993-01-01
Despite their importance for air-sea interaction and microwave remote sensing of the ocean surface, intrinsic properties of short gravity-capillary waves are not well established. This is largely due to water surface currents and their effects on the direct measurements of wave parameters conducted at a fixed point. Frequencies of small scale waves propagating on a surface which itself is in motion, are subject to Doppler shifts. Hence, the high frequency tail of the wave spectra obtained from such temporal observations is smeared. Conversion of this smeared measured-frequency spectra to intrinsic-frequency (or wavenumber) spectra requires corrections for the Doppler shifts. Such attempts in the past have not been very successful in particular when field data were used. This becomes evident if the amplitude modulation of short waves by underlying long waves is considered. Microwave radar studies show that the amplitude of a short wave component attains its maximum value near the crests and its minimum in the troughs of the long waves. Doppler-shifted wave data yield similar results but much larger in modulation magnitude, as expected. In general, Doppler shift corrections reduce the modulation magnitude. Overcorrection may result in a negligible modulation or even in a strong modulation with the maximum amplitude in the wave troughs. The latter situation is clearly contradictory to our visual observations as well as the radar results and imply that the advection by currents is overestimated. In this study, a differential-advection approach is used in which small scale waves are advected by the currents evaluated not at the free surface, but at a depth proportional to their wavelengths. Applicability of this approach is verified by the excellent agreement in phase and magnitude of short-wave modulation between results based on radar and on wave-gauge measurements conducted on a lake.
Spatial gravity wave characteristics obtained from multiple OH(3-1) airglow temperature time series
NASA Astrophysics Data System (ADS)
Wachter, Paul; Schmidt, Carsten; Wüst, Sabine; Bittner, Michael
2015-12-01
We present a new approach for the detection of gravity waves in OH-airglow observations at the measurement site Oberpfaffenhofen (11.27°E, 48.08°N), Germany. The measurements were performed at the German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR) during the period from February 4th, 2011 to July 6th, 2011. In this case study the observations were carried out by three identical Ground-based Infrared P-branch Spectrometers (GRIPS). These instruments provide OH(3-1) rotational temperature time series, which enable spatio-temporal investigations of gravity wave characteristics in the mesopause region. The instruments were aligned in such a way that their fields of view (FOV) formed an equilateral triangle in the OH-emission layer at a height of 87 km. The Harmonic Analysis is applied in order to identify joint temperature oscillations in the three individual datasets. Dependent on the specific gravity wave activity in a single night, it is possible to detect up to four different wave patterns with this method. The values obtained for the waves' periods and phases are then used to derive further parameters, such as horizontal wavelength, phase velocity and the direction of propagation. We identify systematic relationships between periods and amplitudes as well as between periods and horizontal wavelengths. A predominant propagation direction towards the East and North-North-East characterizes the waves during the observation period. There are also indications of seasonal effects in the temporal development of the horizontal wavelength and the phase velocity. During late winter and early spring the derived horizontal wavelengths and the phase velocities are smaller than in the subsequent period from early April to July 2011.
NASA Technical Reports Server (NTRS)
Shemdin, O. H.
1978-01-01
Results are presented from laboratory and field experiments on the modulation of short waves by long waves. The field study employed a wave follower capable of tracking ocean waves with frequencies less than 1.0 Hz and heights less than 2.0 m. A high-response laser-optical system was used to detect upwind-downwind and cross-wind slopes of short waves. The laboratory study was conducted with wind over periodic long waves. The laboratory findings are discussed and compared with laboratory radar measurements and also short wave measurements obtained in the field. It is found that long waves significantly modulate the short wave dispersion by their orbital velocity, and that demodulation is necessary if the data collected by remote sensors are to be compared to surface penetrating devices. The modulation level is weak for wavelengths in the range 2.76-3.30 cm. Other relevant results are also presented.
Linear Electrostatic Waves in Unmagnetized Arbitrarily Degenerate Quantum Plasmas
NASA Astrophysics Data System (ADS)
Rightley, Shane; Uzdensky, Dmitri
2012-10-01
Plasmas in which the inter-particle spacing approaches the thermal de Broglie wavelength are subject to quantum statistical effects due to Pauli exclusion, and many familiar plasma phenomena are modified on such length scales because of the Heisenberg uncertainty principle. The question of how to model these quantum plasmas is a naturally interesting one, as it pushes the envelope of our knowledge of plasma physics and applies the well-established principles of quantum mechanics in a novel context. Such models are important for microelectronic systems, dense laser-produced plasmas, and some extreme astrophysical environments. For completely degenerate plasmas, both kinetic and fluid theories have already been developed. In this presentation, unmagnetized Fermi-Dirac equilibrium plasmas with finite temperature and arbitrary degree of degeneracy are considered. Linear dispersion relations for electrostatic waves and oscillations, including Landau damping, are derived and analyzed. The analysis is carried out using a self-consistent mean-field quantum kinetic model (the Wigner-Poisson system). Growth of waves due to kinetic instabilities, such as the Buneman and bump-on-tail instabilities, is also considered.
LIGA-fabricated compact mm-wave linear accelerator cavities.
Song, J.J.; Bajikar, S.S.; DeCarlo, F.; Kang, Y.W.; Kustom, R.L.; Mancini, D.C.; Nassiri, A.; Lai, B.; Feinerman, A.D.; White, V.
1998-03-23
Millimeter-wave rf cavities for use in linear accelerators, free-electron lasers, and mm-wave undulatory are under development at Argonne National Laboratory. Typical cavity dimensions are in the 1000 mm range, and the overall length of the accelerator structure, which consists of 30-100 cavities, is about 50-100 mm. An accuracy of 0.2% in the cavity dimensions is necessary in order to achieve a high Q-factor of the cavity. To achieve this these structures are being fabricated using deep X-ray lithography, electroforming, and assembly (LIGA). The first prototype cavity structures are designed for 108 GHz and 2p/3-mode operation. Input and output couplers are integrated with the cavity structures. The cavities are fabricated on copper substrates by electroforming copper into 1-mm-thick PMMA resists patterned by deep x-ray lithography and polishing the copper down to the desired thickness. These are fabricated separately and subsequently assembled with precision spacing and alignment using microspheres, optical fibers, or microfabricated spacers/alignment pieces. Details of the fabrication process, alignment, and assembly work are presented in here.
NASA Technical Reports Server (NTRS)
Li, Shuhua; Chern, Jiundar; Joiner, Joanna; Lin, Shian-Jiann; Pawson, Steven; daSilva, Arlindo; Atlas, Robert (Technical Monitor)
2002-01-01
The damping of mesoscale gravity waves has important effects on the global circulation, structure, and composition of the atmosphere. A number of assimilation and forecast experiments have been conducted to examine the sensitivity of meteorological analyses and forecasts to the representation of gravity wave impacts in a data assimilation system (DAS). The experiments were conducted with the Finite-Volume (FV) DAS developed at NASA's Data Assimilation Office (DAO), The main purpose of this research is to determine the optimal combination of wave number, phase speed, wavelength, etc. for representing gravity-wave drag (GWD) in FVDAS. The GWD included in FVDAS includes a spectrum of waves, as would be forced by topography and transient motions (e.g., convection) in the troposphere. The sensitivity experiments are performed by modifying several parameters, such as the number of waves allowed, their wavelength, the background stress amplitude, etc. The results show that the assimilated fields are very sensitive to the number of gravity waves represented in the system, especially at high latitudes of the middle and upper stratosphere and mesosphere in winter. The analyzed stratopause temperature varies by up to 10K when the GWD scheme is modified from a multiple-wave scheme (using a stationary wave and waves with phase speeds of 10, 20, 30 and 40 m/s in each direction) to a single, stationary wave. Insight into the reality of the various versions of the GWD can be obtained by examining the "Observation minus Forecast" residuals from the FVDAS.
Acoustic and gravity waves in the neutral atmosphere and the ionosphere, generated by severe storms
NASA Technical Reports Server (NTRS)
Balachandran, N. K.
1983-01-01
Gravity waves in the neutral atmosphere and their propagation in the ionosphere and the study of infrasonic signals from thunder were investigated. Doppler shifts of the order of 0.1 Hz are determined and they provide high-resolution measurements of the movements in the ionosphere. By using an array of transmitters with different frequencies and at different locations, the horizontal and vertical propagation vectors of disturbances propagating through the ionosphere are determined.
Internal gravity wave-atmospheric wind interaction - A cause of clear air turbulence.
NASA Technical Reports Server (NTRS)
Bekofske, K.; Liu, V. C.
1972-01-01
The interaction between an internal gravity wave (IGW) and a vertical wind shear is discussed as a possible cause in the production of clear air turbulence in the free atmosphere. It is shown that under certain typical condition the interaction of an IGW with a background wind shear near a critical level provides a mechanism for depositing sufficient momentum in certain regions of the atmosphere to significantly increase the local mean wind shear and to lead to the production of turbulence.
The COBE cosmic 3 K anisotropy experiment: A gravity wave and cosmic string probe
NASA Technical Reports Server (NTRS)
Bennett, Charles L.; Smoot, George F.
1989-01-01
Among the experiments to be carried into orbit next year, by the COBE satellite, are differential microwave radiometers. They will make sensitive all-sky maps of the temperature of the cosmic microwave background radiation at three frequencies, giving dipole, quadrupole, and higher order multipole measurements of the background radiation. The experiment will either detect, or place significant constraints on, the existence of cosmic strings and long wavelength gravity waves.
NASA Astrophysics Data System (ADS)
Costantino, Lorenzo; Heinrich, Philippe; Mzé, Nahoudha; Hauchecorne, Alain
2016-04-01
In this work we perform numerical simulations of convective gravity waves (GWs), using the WRF (Weather Research and Forecasting) model. We first run an idealized, simplified and highly resolved simulation with model top at 80 km. Below 60 km of altitude, a vertical grid spacing smaller than 1 km is supposed to reliably resolve the effects of GW breaking. An eastward linear wind shear interacts with the GW field generated by a single convective thunderstorm. After 70 min of integration time, averaging within a radius of 300 km from the storm centre, results show that wave breaking in the upper stratosphere is largely dominated by saturation effects, driving an average drag force up to -41 m s -1 day -1. In the lower stratosphere, mean wave drag is positive and equal to 4.4 m s -1 day -1. In a second step, realistic WRF simulations are compared with lidar measurements from the NDACC network (Network for the Detection of Atmospheric Composition Changes) of gravity wave potential energy (E p) over OHP (Haute-Provence Observatory, southern France). Using a vertical grid spacing smaller than 1 km below 50 km of altitude, WRF seems to reliably reproduce the effect of GW dynamics and capture qualitative aspects of wave momentum and energy propagation and transfer to background mean flow. Averaging within a radius of 120 km from the storm centre, the resulting drag force for the study case (2 h storm) is negative in the higher (-1 m s -1 day -1) and positive in the lower stratosphere (0.23 m s -1 day -1). Vertical structures of simulated potential energy profiles are found to be in good agreement with those measured by lidar. E p is mostly conserved with altitude in August while, in October, E p decreases in the upper stratosphere to grow again in the lower mesosphere. On the other hand, the magnitude of simulated wave energy is clearly underestimated with respect to lidar data by about 3-4 times. Keywords: Meteorology and atmospheric dynamics (mesoscale meteorology middle
A longitudinal component in massive gravitational waves arising from a bimetric theory of gravity
NASA Astrophysics Data System (ADS)
Corda, Christian
2007-10-01
After a brief review of the work of de Paula, Miranda and Marinho on massive gravitational waves arising from a bimetric theory of gravity, in this paper it is shown that the presence of the mass generates a longitudinal component in a particular polarization of the wave. The effect of this polarization on test masses is performed using the geodesic deviation. At the end of this paper the detectability of this particular polarization is also discussed, showing that its angular dependence could, in principle, discriminate such polarization with respect to the ones of general relativity, will present or future detectors achieve a high sensitivity.
Traveling neutral disturbances. [acoustic-gravity wave coupling to minor species in atmosphere
NASA Technical Reports Server (NTRS)
Gross, S. H.; Eun, H.
1976-01-01
The coupling of acoustic-gravity waves in the main atmosphere to acoustic waves characteristic of individual minor species in the atmosphere is postulated. Such coupling would exist as a result of resonances in the response of the minor species, and its likelihood depends on the mass of the atmospheric particle relative to the major species mass, the diffusion of the minor species, and the direction of propagation of the main disturbance. These minor-species disturbances may explain some AE-C measurements in the thermosphere and could possibly play a role in the distribution of minor species and their chemistry in the mesosphere.
Dissipation Mechanisms for Ducted Gravity Waves in the Mesosphere and Lower Thermosphere
NASA Astrophysics Data System (ADS)
Snively, J. B.; Taylor, M. J.
2008-12-01
Gravity waves of short period (4-12 minute) and small scale (15-40 km horizontal wavelength) are frequently observed in mesopause airglow imaging experiments. The propagation of small-scale gravity waves, however, is strongly affected by local background structure and dynamics associated with large-scale waves and tides, and existing background conditions [Fritts et al., JASTP, 68, 247, 2006]. Vertical variations of temperature or wind can also produce ducts, in which trapped waves are frequently observed to propagate [e.g., Isler et al., JGR, 102(D22), 26301, 1997; Walterscheid et al., JASTP, 61, 461, 1999]; spatially- periodic structure of large-scale waves and tides may lead to formation of alternating layers of evanescence and ducted propagation [e.g., Snively et al., JGR, 112, A03304, 2007; Fritts and Janches, JGR, 113, D05112, 2008]. At higher altitudes, and for larger wave magnitudes, interactions between the small and large scales become increasingly nonlinear. Small-scale perturbations to large-scale wave fields may contribute to the formation of dynamic or convective instabilities [e.g., Fritts and Alexander, RG, 41(1), 1003, 2003, and references cited therein]; strong wind flows may also provide critical layers to some portion of the wave spectrum that would otherwise be propagating or ducted. Ducted or evanescent waves can produce strong airglow signatures, due to long vertical wavelengths and strong induced vertical fluid perturbations [Hines and Tarasick, GRL, 21(24), 2729, 1994], and form a significant fraction of observed waves in airglow data. Although commonly assumed to be horizontally- propagating, waves that appear locally trapped may still be subject to vertical tunneling [e.g., Sutherland and Yewchuk, JFM, 511, 125, 2004, and references cited therein]. Stable ducted waves may therefore tunnel into adjacent ducts, or into regions that may include critical layers, or alternatively facilitate instability or breaking, leading to turbulence and