Linking Atmospheric Gravity Wave Research to the Undergraduate Curriculum
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.
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
2015-12-01
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
Gravity Waves in the Atmospheres of Mars and Venus
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
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.
Atmospheric gravity waves due to the Tohoku-Oki tsunami observed in the thermosphere by GOCE
Garcia, R.F.; Doornbos, E.N.; Bruinsma, S.; Hebert, H.
2014-01-01
Oceanic tsunami waves couple with atmospheric gravity waves, as previously observed through ionospheric and airglow perturbations. Aerodynamic velocities and density variations are computed from Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) accelerometer and thruster data during T
Atmospheric gravity waves in the Red Sea: a new hotspot
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J. M. Magalhaes
2011-02-01
Full Text Available The region of the Middle East around the Red Sea (between 32° E and 44° E longitude and 12° N and 28° N latitude is a currently undocumented hotspot for atmospheric gravity waves (AGWs. Satellite imagery shows evidence that this region is prone to relatively high occurrence of AGWs compared to other areas in the world, and reveals the spatial characteristics of these waves. The favorable conditions for wave propagation in this region are illustrated with three typical cases of AGWs propagating in the lower troposphere over the sea. Using weakly nonlinear long wave theory and the observed characteristic wavelengths we obtain phase speeds which are consistent with those observed and typical for AGWs, with the Korteweg-de Vries theory performing slightly better than Benjamin-Davis-Acrivos-Ono theory as far as phase speeds are concerned. ERS-SAR and Envisat-ASAR satellite data analysis between 1993 and 2008 reveals signatures consistent with horizontally propagating large-scale internal waves. These signatures cover the entire Red Sea and are more frequently observed between April and September, although they also occur during the rest of the year. The region's (seasonal propagation conditions for AGWs, based upon average vertical atmospheric stratification profiles suggest that many of the signatures identified in the satellite images are atmospheric internal waves.
Atmospheric gravity waves in the Red Sea: a new hotspot
Magalhaes, J. M.
2011-02-03
The region of the Middle East around the Red Sea (between 32° E and 44° E longitude and 12° N and 28° N latitude) is a currently undocumented hotspot for atmospheric gravity waves (AGWs). Satellite imagery shows evidence that this region is prone to relatively high occurrence of AGWs compared to other areas in the world, and reveals the spatial characteristics of these waves. The favorable conditions for wave propagation in this region are illustrated with three typical cases of AGWs propagating in the lower troposphere over the sea. Using weakly nonlinear long wave theory and the observed characteristic wavelengths we obtain phase speeds which are consistent with those observed and typical for AGWs, with the Korteweg-de Vries theory performing slightly better than Benjamin-Davis-Acrivos-Ono theory as far as phase speeds are concerned. ERS-SAR and Envisat-ASAR satellite data analysis between 1993 and 2008 reveals signatures consistent with horizontally propagating large-scale internal waves. These signatures cover the entire Red Sea and are more frequently observed between April and September, although they also occur during the rest of the year. The region\\'s (seasonal) propagation conditions for AGWs, based upon average vertical atmospheric stratification profiles suggest that many of the signatures identified in the satellite images are atmospheric internal waves. © Author(s) 2011.
Grazing Occultation reveals Gravity Wave Breaking in Pluto's High Atmosphere
Kern, Susan D.; McCarthy, D. W.; Kulesa, C. A.; Hubbard, W. B.; Person, M. J.; Elliot, J. L.; Gulbis, A. A.
2007-10-01
Occultation observations of the star P445.3 (2UCAC 25823784; McDonald & Elliot 2000, AJ 120, 1599) by (134340) Pluto on 2007 March 18.453 UT were simultaneously collected in visible and H-band wavelengths from the 6.5-m MMT (Mt. Hopkins) in Arizona. The event was grazing and slow (6.77 km/s), lasting 4 minutes. These conditions facilitated the detection of large-scale, nearly limb-aligned features in Pluto's atmosphere over a pressure range of 0.1-0.7 μbar (0.01-0.07 Pa; radius range of 1500-1350 km). The data are high signal-to-noise and show these features to be fully resolved and achromatic. The scintillation increases with depth in Pluto's atmosphere and indicates a high-frequency cutoff operating on a broad-band spectrum of gravity waves generated deeper in Pluto's atmosphere. The data are in excellent agreement with atmospheric gravity wave theory (Fritts 1984, RGSP 22, 275). Observations reported here were obtained at the MMT Observatory, a joint facility of The University of Arizona and the Smithsonian Institution. The integration and alignment of both cameras was funded by the Astronomy Camp science education program. We also acknowledge support from NASA's Planetary Astronomy Program via grants NNG04GE48G and NNG04GF25G.
Evidence for a saturated spectrum of atmospheric gravity waves
Smith, Steven A.; Fritts, David C.; Vanzandt, Thomas E.
1987-01-01
The slope and power spectral density of atmospheric velocity fluctuations versus vertical wavenumber at large wavenumbers are observed to be nearly independent of altitude. It is suggested that such a universality is due to saturation of short vertical-scale fluctuations. A brief review of linear gravity wave saturation theory indicates a physical basis for such spectra. It is demonstrated that observed saturation spectra are not solely due to individually saturated waves but most likely result from amplitude limiting instabilities arising from wave superposition. It is also shown that, while the spectrum is saturated at large wavenumbers, the total kinetic energy per unit mass and the characteristic vertical wavelength increase with altitude. Both of these predictions are consistent with observations.
Fritts, D. C.
1989-01-01
Considerable progress was made in understanding gravity waves and their effects in the middle atmosphere during the MAP and MAC periods. During this time, gravity waves were recognized to play a central role in controlling the large scale circulation and the thermal and constituent structure of this region through wave transports of energy and momentum, a significant induced meridional circulation, and through the action of wave induced turbulence. Both theoretical and observational studies also have contributed to the understanding of the gravity wave spectrum, its temporal and spatial variability, and the processes responsible for wave saturation. As a result, the propagation, interactions, and detailed effects of such motions in the middle atmosphere are beginning to be understood. An overview is provided.
Dynamics and Predictability of Deep Propagating Atmospheric Gravity Waves
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
On the role of dust storms in triggering atmospheric gravity waves observed in the middle atmosphere
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S. K. Das
2011-09-01
Full Text Available Lower atmospheric perturbations often produce measurable effects in the middle and upper atmosphere. The present study demonstrates the response of the middle atmospheric thermal structure to the significant enhancement of the lower atmospheric heating effect caused by dust storms observed over the Thar Desert, India. Our study from multi-satellite observations of two dust storm events that occurred on 3 and 8 May 2007 suggests that dust storm events produce substantial changes in the lower atmospheric temperatures as hot spots which can become sources for gravity waves observed in the middle atmosphere.
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Peralta, J.; López-Valverde, M. A. [Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía, 18008 Granada (Spain); Imamura, T. [Institute of Space and Astronautical Science-Japan Aerospace Exploration Agency 3-1-1, Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Read, P. L. [Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford (United Kingdom); Luz, D. [Centro de Astronomia e Astrofísica da Universidade de Lisboa (CAAUL), Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa (Portugal); Piccialli, A., E-mail: peralta@iaa.es [LATMOS, UVSQ, 11 bd dAlembert, 78280 Guyancourt (France)
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.
Evidence of a saturated gravity-wave spectrum throughout the atmosphere
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.
Institute of Scientific and Technical Information of China (English)
吴少平; 易帆
2002-01-01
By using FICE scheme, a numerical simulation of nonlinear propagation of gravity wave packet in three-dimension compressible atmosphere is presented. The whole nonlinear propagation process of the gravity wave packet is shown; the basic characteristics of nonlinear propagation and the influence of the ambient winds on the propagation are analyzed. The results show that FICE scheme can be extended in three-dimension by which the calculation is steady and kept for a long time; the increase of wave amplitude is faster than the exponential increase according to the linear gravity theory; nonlinear propagation makes the horizontal perturbation velocity increase greatly which can lead to enhancement of the local ambient winds; the propagation path and the propagation velocity of energy are different from the results expected by the linear gravity waves theory, the nonlinearity causes the change in propagation characteristics of gravity wave; the ambient winds alter the propagation path and group velocity of gravity wave.
On the nonlinear shaping mechanism for gravity wave spectrum in the atmosphere
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I. P. Chunchuzov
2009-11-01
Full Text Available The nonlinear mechanism of shaping of a high vertical wave number spectral tail in the field of a few discrete internal gravity waves in the atmosphere is studied in this paper. The effects of advection of fluid parcels by interacting gravity waves are taken strictly into account by calculating wave field in Lagrangian variables, and performing a variable transformation from Lagrangian to Eulerian frame. The vertical profiles and vertical wave number spectra of the Eulerian displacement field are obtained for both the case of resonant and non-resonant wave-wave interactions. The evolution of these spectra with growing parameter of nonlinearity of the internal wave field is studied and compared to that of a broad band spectrum of gravity waves with randomly independent amplitudes and phases. The calculated vertical wave number spectra of the vertical displacements or relative temperature fluctuations are found to be consistent with the observed spectra in the middle atmosphere.
Bassiri, Sassan; Hajj, George A.
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.
Song, I. S.; Jee, G.; Kim, B. M.
2015-12-01
Mesoscale gravity waves are simulated by carrying out the specified chemistry whole atmosphere community climate model (SC-WACCM) at the horizontal resolution of about 25 km to understand the origin of gravity waves in the polar mesosphere and lower thermosphere (MLT) and their propagation properties throughout the whole atmosphere. Modeled gravity waves are also compared with gravity-wave activities estimated from meteor radar observations made in Antarctica by Korea Polar Research Institute. For this comparison, SC-WACCM is initialized at a specific date and time using atmospheric state variables from the ground to the thermosphere obtained from various data sets such as operational analyses and empirical wind and temperature model results. Model initial conditions are corrected for mass and dynamical balance to reduce spurious waves due to initial shocks. At conference, preliminary results of the mesoscale SC-WACCM simulation and its comparison with observations will be presented.
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
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S. Watanabe
2014-11-01
Full Text Available The dependence of the gravity wave spectra of energy and momentum flux on the horizontal resolution and time step of atmospheric general circulation models (AGCMs has been thoroughly investigated in the past. In contrast, much less attention has been given to the dependence of these gravity wave parameters on models' vertical resolutions. The present study demonstrates the dependence of gravity wave momentum flux in the stratosphere and mesosphere on the model's vertical resolution, which is evaluated using an AGCM with a horizontal resolution of about 0.56°. We performed a series of sensitivity test simulations changing only the model's vertical resolution above a height of 8 km, and found that inertial gravity waves with short vertical wavelengths simulated at higher vertical resolutions likely play an important role in determining the gravity wave momentum flux in the stratosphere and mesosphere.
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L. Sun
2007-10-01
Full Text Available In order to study the filter effect of the background winds on the propagation of gravity waves, a three-dimensional transfer function model is developed on the basis of the complex dispersion relation of internal gravity waves in a stratified dissipative atmosphere with background winds. Our model has successfully represented the main results of the ray tracing method, e.g. the trend of the gravity waves to travel in the anti-windward direction. Furthermore, some interesting characteristics are manifest as follows: (1 The method provides the distribution characteristic of whole wave fields which propagate in the way of the distorted concentric circles at the same altitude under the control of the winds. (2 Through analyzing the frequency and wave number response curve of the transfer function, we find that the gravity waves in a wave band of about 15–30 min periods and of about 200–400 km horizontal wave lengths are most likely to propagate to the 300-km ionospheric height. Furthermore, there is an obvious frequency deviation for gravity waves propagating with winds in the frequency domain. The maximum power of the transfer function with background winds is smaller than that without background winds. (3 The atmospheric winds may act as a directional filter that will permit gravity wave packets propagating against the winds to reach the ionospheric height with minimum energy loss.
A review of atmospheric gravity waves and travelling ionospheric disturbances: 1982-1995
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K. Hocke
Full Text Available Recent investigations of atmospheric gravity waves (AGW and travelling ionospheric disturbances (TID in the Earth's thermosphere and ionosphere are reviewed. In the past decade, the generation of gravity waves at high latitudes and their subsequent propagation to low latitudes have been studied by several global model simulations and coordinated observation campaigns such as the Worldwide Atmospheric Gravity-wave Study (WAGS, the results are presented in the first part of the review. The second part describes the progress towards understanding the AGW/TID characteristics. It points to the AGW/TID relationship which has been recently revealed with the aid of model-data comparisons and by the application of new inversion techniques. We describe the morphology and climatology of gravity waves and their ionospheric manifestations, TIDs, from numerous new observations.
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O. Onishchenko
2013-03-01
Full Text Available In this paper, we have investigated vortex structures (e.g. convective cells of internal gravity waves (IGWs in the earth's atmosphere with a finite vertical temperature gradient. A closed system of nonlinear equations for these waves and the condition for existence of solitary convective cells are obtained. In the atmosphere layers where the temperature decreases with height, the presence of IGW convective cells is shown. The typical parameters of such structures in the earth's atmosphere are discussed.
Numerical Simulations of Magnetoacoustic-Gravity Waves in the Solar Atmosphere
Murawski, K; McLaughlin, J A; Oliver, R
2012-01-01
We investigate the excitation of magnetoacoustic-gravity waves generated from localized pulses in the gas pressure as well as in vertical component of velocity. These pulses are initially launched at the top of the solar photosphere that is permeated by a weak magnetic field. We investigate three different configurations of the background magnetic field lines: horizontal, vertical and oblique to the gravitational force. We numerically model magnetoacoustic-gravity waves by implementing a realistic (VAL-C) model of solar temperature. We solve two-dimensional ideal magnetohydrodynamic equations numerically with the use of the FLASH code to simulate the dynamics of the lower solar atmosphere. The initial pulses result in shocks at higher altitudes. Our numerical simulations reveal that a small-amplitude initial pulse can produce magnetoacoustic-gravity waves, which are later reflected from the transition region due to the large temperature gradient. The atmospheric cavities in the lower solar atmosphere are foun...
Atmospheric gravity waves observed by an international network of micro-barographs
International Nuclear Information System (INIS)
The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) manages an international network of forty-two operational infra-sound stations recording the pressure fluctuations produced at the ground surface by infrasonic waves. This thesis demonstrates that most of these stations also accurately detect the pressure fluctuations in the entire gravity wave band. This work includes carrying out and analyzing several metrological laboratory experiments and a field campaign (M2008) in Mongolia in 2008. The layout of the experiments as well as the interpretation of their results gave rise to the development of a new linear spectral numerical model able to simulate the generation and propagation of gravity waves. This model was used to quantify the gravity waves produced by the atmospheric cooling that occurs during solar eclipses. The pressure fluctuations expected at ground level were estimated and compared to the data recorded during the 1 August 2008 solar eclipse by the CTBTO and M2008 stations. A detailed data analysis reveals two waves with similar time-frequency characteristics to those simulated for a stratospheric and tropospheric cooling. This constitutes, to our knowledge, a unique result. The validation of worldwide and pluri-annual pressure measurements in the entire gravity wave band allowed the statistical study of gravity wave spectra and atmospheric tides. The work presented throughout this thesis has led to the publication of two articles. A third one is in the drafting process. (author)
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.
A regional study of atmospheric gravity waves using the USArray Transportable Array
Hedlin, M. A. H.; Stephan, C. C.; de Groot-Hedlin, C. D.; Alexander, M. J.; Hoffmann, L.
2015-12-01
The USArray Transportable Array (TA) is a network of approximately 400 seismo-acoustic stations deployed on a 70 km Cartesian grid covering an area of 2,000,000 km2 in the continental United States. The network moves eastward through station redeployments and is now located on the Atlantic coast. This dense network has provided unprecedented opportunities for research in seismology, infrasound and atmospheric science. We have developed a novel technique to investigate gravity wave occurrence and propagation across the network and have applied it to atmospheric pressure data recorded from Jan 1, 2010 through 2014. We divided the stations in this time range into 3,600 non-overlapping triangular arrays (triads). Each triad is most sensitive to propagating gravity waves in the 1-6 hour period range. We report two lines of research with this new dataset. First, we study individual large events in which atmospheric gravity waves are observed to cross the TA. We also study the long-term occurrence statistics of gravity waves and compare them to satellite observations of convective clouds and gravity waves in the stratosphere. We discuss plans for future work when the network is redeployed in Alaska.
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.
Interseasonal Variations in the Middle Atmosphere Forced by Gravity Waves
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.
Directory of Open Access Journals (Sweden)
I. V. Subba Reddy
2005-11-01
Full Text Available MST radars are powerful tools to study the mesosphere, stratosphere and troposphere and have made considerable contributions to the studies of the dynamics of the upper, middle and lower atmosphere. Atmospheric gravity waves play a significant role in controlling middle and upper atmospheric dynamics. To date, frontal systems, convection, wind shear and topography have been thought to be the sources of gravity waves in the troposphere. All these studies pointed out that it is very essential to understand the generation, propagation and climatology of gravity waves. In this regard, several campaigns using Indian MST Radar observations have been carried out to explore the gravity wave activity over Gadanki in the troposphere and the lower stratosphere. The signatures of the gravity waves in the wind fields have been studied in four seasons viz., summer, monsoon, post-monsoon and winter. The large wind fluctuations were more prominent above 10 km during the summer and monsoon seasons. The wave periods are ranging from 10 min-175 min. The power spectral densities of gravity waves are found to be maximum in the stratospheric region. The vertical wavelength and the propagation direction of gravity waves were determined using hodograph analysis. The results show both down ward and upward propagating waves with a maximum vertical wave length of 3.3 km. The gravity wave associated momentum fluxes show that long period gravity waves carry more momentum flux than the short period waves and this is presented.
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.
Murawski, K.; Musielak, Z. E.
2016-09-01
We study the propagation of acoustic-gravity waves in the solar atmosphere. The waves are excited by a space- and time-dependent random driver, whose action mimics turbulence in the upper part of the solar convection zone. Our main goal is to find vertical variations of wave periods of these waves and compare the obtained results to the recent observations of Wiśniewska et al. (2016). We solve numerically the hydrodynamic equations in the solar atmosphere whose temperature is given by the semi-empirical model of Avrett & Loeser (2008). The obtained numerical results show that wave periods vary along vertical direction in agreement with the recent observational data. We discuss physical consequences of our theoretical results.
Gerrard, Andrew J.; Kane, Timothy J.; Eckermann, Stephen D.; Thayer, Jeffrey P.
2004-01-01
We conducted gravity wave ray-tracing experiments within an atmospheric region centered near the ARCLITE lidar system at Sondrestrom, Greenland (67N, 310 deg E), in efforts to understand lidar observations of both upper stratospheric gravity wave activity and mesospheric clouds during August 1996 and the summer of 2001. The ray model was used to trace gravity waves through realistic three-dimensional daily-varying background atmospheres in the region, based on forecasts and analyses in the troposphere and stratosphere and climatologies higher up. Reverse ray tracing based on upper stratospheric lidar observations at Sondrestrom was also used to try to objectively identify wave source regions in the troposphere. A source spectrum specified by reverse ray tracing experiments in early August 1996 (when atmospheric flow patterns produced enhanced transmission of waves into the upper stratosphere) yielded model results throughout the remainder of August 1996 that agreed best with the lidar observations. The model also simulated increased vertical group propagation of waves between 40 km and 80 km due to intensifying mean easterlies, which allowed many of the gravity waves observed at 40 km over Sondrestrom to propagate quasi-vertically from 40-80 km and then interact with any mesospheric clouds at 80 km near Sondrestrom, supporting earlier experimentally-inferred correlations between upper stratospheric gravity wave activity and mesospheric cloud backscatter from Sondrestrom lidar observations. A pilot experiment of real-time runs with the model in 2001 using weather forecast data as a low-level background produced less agreement with lidar observations. We believe this is due to limitations in our specified tropospheric source spectrum, the use of climatological winds and temperatures in the upper stratosphere and mesosphere, and missing lidar data from important time periods.
C. Mercier; Jacobson, A. R.
1997-01-01
In this paper we present a quantitative comparison between a large data base of medium-scale atmospheric gravity waves (AGWs) observed by radio interferometry of transionospheric radio sources and the results of a numerical simulation of the observed effects. The simulation includes: (i) the propagation and dissipation of AGWs up to ionospheric heights and (ii) the calculation of the subsequent slant TEC perturbations integrated along the path to the radio sources. We show that the observed a...
Influences of non-isothermal atmospheric backgrounds on variations of gravity wave parameters
Institute of Scientific and Technical Information of China (English)
LIU Xiao; ZHOU QiHou; YUAN Wei; XU JiYao
2012-01-01
Because of the importance of gravity waves (GWs) in coupling different atmospheric regions,further studies are necessary to investigate the characteristics of GW propagation in a non-isothermal atmosphere.Using a nonlinear numerical model,we simulate the propagation of small amplitude GWs with various wavelengths in different non-isothermal atmospheres.Our results show that the GW vertical wavelength undergoes sharp changes above the stratopause and mesopause region.Specifically,for a GW with an initial vertical wavelength of 5 km,the seasonal background temperature structure difference at 50° latitude can cause the vertical wavelength to vary by ～2 km in the mesosphere and by as large as ～4.5 km in the lower thermosphere.In addition,the GW paths exhibit great divergence in the height range of ～65-110 kin.Our results also show that the variations of GW path,vertical wavelength and horizontal phase velocity are not synchronized in a non-isothermal atmosphere as in an isothermal atmosphere.Despite the fact that all GWs change their characteristics as they propagate upward in a non-isothermal atmosphere,the variations relative to the initial parameters at a reference height are similar for different initial vertical wavelengths.Our results indicate that the changing characteristics of a gravity wave in a non-isothermal atmosphere need to be considered when investigating the relationship of GWs at two different heights.
Newington, Marie
2009-01-01
The detection of upward propagating internal gravity waves in the Sun's chromosphere has recently been reported by Straus et al., who postulated that these may efficiently couple to Alfven waves in magnetic regions. This may be important in transporting energy to higher levels. Here we explore the propagation, reflection and mode conversion of linear gravity waves in a VAL C atmosphere, and find that even weak magnetic fields usually reflect gravity waves back downward as slow magnetoacoustic waves well before they reach the Alfven/acoustic equipartition height at which mode conversion might occur. However, for certain highly inclined magnetic field orientations in which the gravity waves manage to penetrate near or through the equipartition level, there can be substantial conversion to either or both upgoing Alfven and acoustic waves. Wave energy fluxes comparable to the chromospheric radiative losses are expected.
Transition from geostrophic turbulence to inertia-gravity waves in the atmospheric energy spectrum.
Callies, Jörn; Ferrari, Raffaele; Bühler, Oliver
2014-12-01
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
Observation of acoustic-gravity waves in the upper atmosphere during severe storm activity
Hung, R. J.
1975-01-01
A nine-element continuum wave spectrum, high-frequency, Doppler sounder array has been used to detect upper atmospheric wave-like disturbances during periods with severe weather activity, particularly severe thunderstorms and tornadoes. Five events of severe weather activity, including extreme tornado outbreak of April 3, 1974, were chosen for the present study. The analysis of Doppler records shows that both infrasonic waves and gravity waves were excited when severe storms appeared in the north Alabama area. Primarily, in the case of tornado activity, S-shaped Doppler fluctuations or Doppler fold-backs are observed, while quasi-sinusoidal fluctuations are more common in the case of thunderstorm activity. A criterion for the production of Doppler fold-backs is derived and compared with possible tornado conditions.
Rapid propagation of Tsunami-induced gravity waves across the atmosphere
Buhler, Oliver; Wei, Chen; Tabak, Esteban
2014-05-01
We present theoretical and numerical results on large-scale gravity waves that are forced by Tsunamis at the sea surface and subsequently travel rapidly across the atmosphere until they are detectable by remote sensing in the ionosphere an hour or so after their launch. The theoretical possibility of this phenomenon has been known for some time, but only in recent years has detailed data become available that confirms this effect. This has potential impact for remote sensing applied to Tsunami detection as well as to other near-ground processes. Solving this detailed wave problem requires technology somewhat beyond the standard ray-tracing familiar from wave drag parametrizations, as there is no usable scale separation in the vertical. Our method combines Laplace transforms in time with Fourier transforms in the horizontal, which allows us to satisfy the vertical radiation condition correctly, takes into account back-reflection at the tropopause as well as the influence of wind shear, and provides detailed information about the structure of the first arriving waves at 100 km altitude or so. One unexpected outcome is that there is a clearly observable forerunner wave that arrives at the ionosphere in a manner of minutes, which is an acoustic-gravity wave, so its dynamics goes beyond anelastic models and requires the fully compressible Euler equations instead. These results will be illustrated in a number of idealized examples.
Ardhuin, Fabrice
2012-01-01
Oceanic observations, even in very deep water, and atmospheric pressure or seismic records, from anywhere on Earth, contain noise with dominant periods between 3 and 10 seconds, that can be related to surface gravity waves in the oceans. This noise is consistent with a dominant source explained by a nonlinear wave-wave interaction mechanism, and takes the form of surface gravity waves, acoustic or seismic waves. Previous theoretical works on seismic noise focused on surface (Rayleigh) waves, and did not consider finite depth effects on the generating wave kinematics. These finite depth effects are introduced here, which requires the consideration of the direct wave-induced pressure at the ocean bottom, a contribution previously overlooked in the context of seismic noise. That contribution can lead to a considerable reduction of the seismic noise source, which is particularly relevant for noise periods larger than 10 s. The theory is applied to acoustic waves in the atmosphere, extending previous theories that...
Vorontsov, Artem; Andreeva, Elena; Nesterov, Ivan; Padokhin, Artem; Kurbatov, Grigory
2016-04-01
The acoustic-gravity waves (AGW) in the upper atmosphere and ionosphere can be generated by a variety of the phenomena in the near-Earth environment and atmosphere as well as by some perturbations of the Earth's ground or ocean surface. For instance, the role of the AGW sources can be played by the earthquakes, explosions, thermal heating, seisches, tsunami waves. We present the examples of AGWs excited by the tsunami waves traveling in the ocean, by seisches, and by ionospheric heating by the high-power radio wave. In the last case, the gravity waves are caused by the pulsed modulation of the heating wave. The AGW propagation in the upper atmosphere induces the variations and irregularities in the electron density distribution of the ionosphere, whose structure can be efficiently reconstructed by the method of the ionospheric radio tomography (RT) based on the data from the global navigational satellite systems (GNSS). The input data for RT diagnostics are composed of the 150/400 MHz radio signals from the low-orbiting (LO) satellites and 1.2-1.5 GHz radio signals from the high-orbiting (HO) satellites with their orbits at ~1000 and ~20000 km above the ground, respectively. These data enable ionospheric imaging on different spatiotemporal scales with different spatiotemporal resolution and coverage, which is suitable, inter alia, for tracking the waves and wave-like features in the ionosphere. In particular, we demonstrate the maps of the ionospheric responses to the tornado at Moore (Oklahoma, USA) of May 20, 2013, which are reconstructed from the HO data. We present the examples of LORT images containing the waves and wavelike disturbances associated with various sources (e.g., auroral precipitation and high-power heating of the ionosphere). We also discuss the results of modeling the AGW generation by the surface and volumetric sources. The millihertz AGW from these sources initiate the ionospheric perturbation with a typical scale of a few hundred km at the
Calais, E.; Haase, J. S.; Minster, B.
2003-12-01
The Global Positioning System (GPS) is now widely used to measure ionospheric electron content at both global and regional scales. It is also capable of detecting small-scale high-frequency ionospheric disturbances caused by atmospheric acoustic-gravity waves. We show examples of ionospheric perturbations caused by earthquakes, rocket launches, and large surface explosions. The neutral atmospheric waves triggered by these events couple with the motion of free electrons and ionized plasma at ionospheric heights and induce coherent fluctuations of electron densities and ionization layer boundaries that are detectable with GPS. In all cases, the ionospheric perturbations match fairly well observations made through other techniques as well as numerical models. The development of permanent networks of densely spaced and continuously recording GPS stations open up new opportunities for the study of infrasonic waves in the atmosphere and their coupling with small scale processes in the ionosphere. We show examples of infrasonic waves detected using the 250-station GPS network that covers the Los Angeles area (SCIGN). Although the signal-to-noise ratio of these perturbations is relatively small, we show that it can be considerably improved by multi-station array processing techniques derived from seismic array analysis. These techniques can also be used to determine the perturbation propagation azimuth and velocity and, eventually, to recover information about the sources of these perturbations.
Global Propagation of Gravity Waves Generated with the Whole Atmosphere Transfer Function Model
Mayr, H. G.; Talaat, E. R.; Wolven, B. C.
2012-12-01
Gravity waves are ubiquitous phenomena in the Earth's atmosphere, accounting for a significant fraction of its observed variability. These waves, with periods ranging from minutes to hours, are thought to be a major means for exchange of momentum and energy between atmospheric regions. The Transfer Function Model (TFM) describes acoustic gravity waves (AGW) that propagate across the globe in a dissipative static background atmosphere extending from the ground to 700 km. The model is limited to waves with periods force is not important. Formulated in terms of zonal vector spherical harmonics and oscillation frequencies, the linearized equations of energy, mass, and momentum conservation are solved to generate the transfer function (TF) for a chosen height distribution of the excitation source. The model accounts for momentum exchange between atmospheric species (He, O, N2, O2, Ar), which affects significantly the wave amplitudes and phases of thermospheric temperature, densities, and wind fields. Covering a broad range of frequencies and spherical harmonic wave numbers (wavelengths), without limitations, the assembled TF captures the physics that controls the propagation of AGW, and the computational effort is considerable. For a chosen horizontal geometry and impulsive time dependence of the source, however, the global wave response is then obtained in short order. The model is computationally efficient and well suited to serve as an experimental and educational tool for simulating propagating wave patterns on the globe. The model is also semi-analytical and therefore well suited to explore the different wave modes that can be generated under varying dynamical conditions. The TFM has been applied to simulate the AGW, which are generated in the auroral region of the thermosphere by joule heating and momentum coupling due to solar wind induced electric fields [e.g., Mayr et al., Space Science Reviews, 1990]. The auroral source generates three distinct classes of
Turbulent mixing driven by mean-flow shear and internal gravity waves in oceans and atmospheres
Baumert, Helmut Z
2012-01-01
This study starts with balances deduced by Baumert and Peters (2004, 2005) from results of stratified-shear experiments made in channels and wind tunnels by Itsweire (1984) and Rohr and Van Atta (1987), and of free-decay experiments in a resting stratified tank by Dickey and Mellor (1980). Using a modification of Canuto's (2002) ideas on turbulence and waves, these balances are merged with an (internal) gravity-wave energy balance presented for the open ocean by Gregg (1989), without mean-flow shear. The latter was augmented by a linear (viscous) friction term. Gregg's wave-energy source is interpreted on its long-wave spectral end as internal tides, topography, large-scale wind, and atmospheric low-pressure actions. In addition, internal eigen waves, generated by mean-flow shear, and the aging of the wave field from a virginal (linear) into a saturated state are taken into account. Wave packets and turbulence are treated as particles (vortices, packets) by ensemble kinetics so that the loss terms in all thre...
The Influence of Tropospheric Processes in Modeling the Middle Atmosphere with Gravity Waves
Mayr, H. G.; Mengel, J. G.; Drob, D. P.; Porter, H. S.
2002-01-01
Our Numerical Spectral Model (NSM) extends from the ground up into the thermosphere and has a vertical grid point resolution of about 0.5 km to resolve the interactions of gravity waves (GWs) described with Hines' Doppler Spread Parameterization (DSP). This model produces in the stratosphere and mesosphere the major features of QBO, SAO, tides, and planetary waves. The purpose of this paper is to discuss results from an initial study with our 3D model that shows how certain tropospheric processes can affect the dynamics of the middle atmosphere. Under the influence of tropospheric heating, and augmented by GW interactions, two distinct but related processes can be identified. (1) A meridional circulation develops in the stratosphere, with rising motions at low latitudes that are in magnitude comparable to the downward propagation of the QBO. As Dunkerton pointed out, a larger GW source is then required to reproduce the observed QBO, which tends to move us closer to the values recommended for the DSP. This has significant consequences for our model results that describe the upper mesosphere, considering the general importance of GWs for this region and in influencing planetary waves (e.g., 2-day wave) and tides in particular. (2) Tropospheric heating produces zonal jets near the tropopause that are related to latitudinal variations in pressure and reversing temperature variations (resembling the dynamical conditions near the mesopause), which in turn is conducive to generate baroclinic instability. Modeling results show that our ability to generate the QBO critically depends on the magnitude of the temperature reversal that is a measure of this instability. Planetary waves are generated in this process, which can apparently interfere with or augment the GW interactions. As originally demonstrated by Lindzen and Holton, the eastward propagating Kelvin waves and westward propagating Rossby gravity waves (generated by tropospheric convection) can in principle provide
John Z. G. Ma
2016-01-01
We study the modulation of atmospheric nonisothermality and wind shears on the propagation of seismic tsunami-excited gravity waves by virtue of the vertical wavenumber, m (with its imaginary and real parts, m i and m r , respectively), within a correlated characteristic range of tsunami wave periods in tens of minutes. A ge...
Instability of combined gravity-inertial-Rossby waves in atmospheres and oceans
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J. F. McKenzie
2011-06-01
Full Text Available The properties of the instability of combined gravity-inertial-Rossby waves on a β-plane are investigated. The wave-energy exchange equation shows that there is an exchange of energy with the background stratified medium. The energy source driving the instability lies in the background enthalpy released by the gravitational buoyancy force.
It is shown that if the phase speed of the westward propagating low frequency-long wavelength Rossby wave exceeds the Poincaré-Kelvin (or "equivalent" shallow water wave speed, instability arises from the merging of Rossby and Poincaré modes. There are two key parameters in this instability condition; namely, the equatorial/rotational Mach (or Froude number M and the latitude θ_{0} of the β-plane. In general waves equatorward of a critical latitude for given M can be driven unstable, with corresponding growth rates of the order of a day or so. Although these conclusions may only be safely drawn for short wavelengths corresponding to a JWKB wave packet propagating internally and located far from boundaries, nevertheless such a local instability may play a significant role in atmosphere-ocean dynamics.
Gravity wave transmission diagram
Tomikawa, Yoshihiro
2016-07-01
A possibility of gravity wave propagation from a source region to the airglow layer around the mesopause has been discussed based on the gravity wave blocking diagram taking into account the critical level filtering alone. This paper proposes a new gravity wave transmission diagram in which both the critical level filtering and turning level reflection of gravity waves are considered. It shows a significantly different distribution of gravity wave transmissivity from the blocking diagram.
Sensitivity of Middle Atmospheric Analysis to the Representation of Gravity Wave Drag
Li, Shu-Hua; Pawson, Steven; Boville, Byron A.; Lin, S.-J.
2004-01-01
This study examines the sensitivity of middle atmospheric analyses to the representation of gravity wave drag (GWD) in the general circulation model (GCM). A strong sensitivity of temperatures near the stratopause to the inclusion and representation of waves with non-zero phase speeds is isolated; this is consistent with the induced mean meridional circulation. The change (between a control analysis and one with no GWD) decreases with decreasing altitude and has a vertical structure with alternating positive and negative differences that are caused by the constraint on thick-layer radiances offered by near-nadir sounding radiometers. Without the non-zero phase-speed GWI), there is a large observation minus forecast residual that is substantially smaller when these waves are included, indicating the need for these waves in the GCM. Moreover, the sensitivity of analyzed temperatures to the inclusion of these waves reveals the importance of using a non-biased GCM in regions where the observational constraint (thick-layer radiances) is indirect.
The influence of time-dependent wind on gravity-wave propagation in the middle atmosphere
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L. Zhong
Full Text Available Ray-tracing techniques are used to computationally investigate the propagation of gravity waves through the middle atmosphere, as characterized by the vertically varying CIRA-86 wind and temperature models, plus a tidal wind model that varies temporally as well as vertically. For the wave parameters studied here, the background wind variation has a much stronger influence on the ray path and changes in wave characteristics than does the temperature variation. The temporal variation of the tidal component of the wind changes the observed frequency, sometimes substantially, while leaving the intrinsic frequency unaltered. It also renders temporary any critical levels that occur in the tidal region. Different starting times for the rays relative to the tidal phase provide different propagation environments, so that the temporary critical levels appear at different heights. The lateral component of the tidal wind is shown to advect propagating wave packets; the maximum lateral displacement of a packet varies inversely with its vertical group velocity. Time-dependent effects are more pronounced in local winter than in summer.
Acoustic-gravity waves generated by atmospheric and near-surface sources
Kunitsyn, Viacheslav E.; Kholodov, Alexander S.; Krysanov, Boris Yu.; Andreeva, Elena S.; Nesterov, Ivan A.; Vorontsov, Artem M.
2013-04-01
Numerical simulation of the acoustic-gravity waves (AGW) generated by long-period oscillations of the Earth's (oceanic) surface, earthquakes, explosions, thermal heating, seiches, and tsunami is carried out. Wavelike disturbances are quite frequent phenomena in the atmosphere and ionosphere. These events can be caused by the impacts from space and atmosphere, by oscillations of the Earth'as surface and other near-surface events. These wavelike phenomena in the atmosphere and ionosphere appear as the alternating areas of enhanced and depleted density (in the atmosphere) or electron concentration (in the ionosphere). In the paper, AGW with typical frequencies of a few hertz - millihertz are analyzed. AGW are often observed after the atmospheric perturbations, during the earthquakes, and some time (a few days to hours) in advance of the earthquakes. Numerical simulation of the generation of AGW by long-period oscillations of the Earth's and oceanic surface, earthquakes, explosions, thermal heating, seiches, and tsunami is carried out. The AGW generated by the near-surface phenomena within a few hertz-millihertz frequency range build up at the mid-atmospheric and ionospheric altitudes, where they assume their typical spatial scales of the order of a few hundred kilometers. Oscillations of the ionospheric plasma within a few hertz-millihertz frequency range generate electromagnetic waves with corresponding frequencies as well as travelling ionospheric irregularities (TIDs). Such structures can be successfully monitored using satellite radio tomography (RT) techniques. For the purposes of RT diagnostics, 150/400 MHz transmissions from low-orbiting navigational satellites flying in polar orbits at the altitudes of about 1000 km as well as 1.2-1.5 GHz signals form high-orbiting (orbital altitudes about 20000 km) navigation systems like GPS/GLONASS are used. The results of experimental studies on generation of wavelike disturbances by particle precipitation are presented
Convectively Forced Gravity Waves and their Sensitivity to Heating Profile and Atmospheric Structure
Halliday, Oliver; Parker, Douglas; Griffiths, Stephen; Vosper, Simon; Stirling, Alison
2016-04-01
It has been known for some time that convective heating is communicated to its environment by gravity waves. Despite this, the radiation of gravity waves in macro-scale models, which are typically forced at the grid-scale by meso-scale parameterization schemes, is not well understood. We present here theoretical work directed toward improving our fundamental understanding of convectively forced gravity wave effects at the meso-scale, in order to begin to address this problem. Starting with the hydrostatic, non-rotating, 2D, Boussinesq equations in a slab geometry, we find a radiating, analytical solution to prescribed sensible heat forcing for both the vertical velocity and potential temperature response. Both Steady and pulsed heating with adjustable horizontal structure is considered. From these solutions we construct a simple model capable of interrogating the spatial and temporal sensitivity to chosen heating functions of the remote forced response in particular. By varying the assumed buoyancy frequency, the influence of the model stratosphere on the upward radiation of gravity waves, and in turn, on the tropospheric response can be understood. Further, we find that the macro-scale response to convection is highly dependent on the radiation characteristics of gravity waves, which are in turn dependent upon the temporal and spatial structure of the source, and upper boundary condition of the domain.
Directory of Open Access Journals (Sweden)
T. Tsuda
2011-04-01
Full Text Available GPS radio occultation (RO is characterized by high accuracy and excellent height resolution, which has great advantages in analyzing atmospheric structures including small-scale vertical fluctuations. The vertical resolution of the geometrical optics (GO method in the stratosphere is about 1.5 km due to Fresnel radius limitations, but full spectrum inversion (FSI can provide superior resolutions. We applied FSI to COSMIC GPS-RO profiles from ground level up to 30 km altitude, although basic retrieval at UCAR/CDAAC sets the sewing height from GO to FSI below the tropopause. We validated FSI temperature profiles with routine high-resolution radiosonde data in Malaysia and North America collected within 400 km and about 30 min of the GPS RO events. The average discrepancy at 10–30 km altitude was less than 0.5 K, and the bias was equivalent with the GO results.
Using the FSI results, we analyzed the vertical wave number spectrum of normalized temperature fluctuations in the stratosphere at 20–30 km altitude, which exhibits good consistency with the model spectra of saturated gravity waves. We investigated the white noise floor that tends to appear at high wave numbers, and the substantial vertical resolution of the FSI method was estimated as about 100–200 m in the lower stratosphere. We also examined a criterion for the upper limit of the FSI profiles, beyond which bending angle perturbations due to system noises, etc, could exceed atmospheric excess phase fluctuations. We found that the FSI profiles can be used up to about 28 km in studies of temperature fluctuations with vertical wave lengths as short as 0.5 km.
Some characteristics of atmospheric gravity waves observed by radio-interferometry
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Claude Mercier
Full Text Available Observations of atmospheric acoustic-gravity waves (AGWs are considered through their effect on the horizontal gradient G of the slant total electron content (slant TEC, which can be directly obtained from two-dimensional radio-interferometric observations of cosmic radio-sources with the Nançay radioheligraph (2.2^{°}E, 47.3^{°}N. Azimuths of propagation can be deduced (modulo 180^{°}. The total database amounts to about 800 h of observations at various elevations, local time and seasons. The main results are:
a AGWs are partially directive, confirming our previous results.
b The propagation azimuths considered globally are widely scattered with a preference towards the south.
c They show a bimodal time distribution with preferential directions towards the SE during daytime and towards the SW during night-time (rather than a clockwise rotation as reported by previous authors.
d The periods are scattered but are larger during night-time than during daytime by about 60%.
e The effects observed with the solar radio-sources are significantly stronger than with other radio-sources (particularly at higher elevations, showing the role of the geometry in line of sight-integrated observations.
Yiǧit, Erdal; Medvedev, Alexander S.
2016-07-01
Gravity waves are primarily generated in the lower atmosphere, propagate upward, and have profound effects not only in the middle atmosphere but also at much higher altitudes. However, their effects in the upper atmosphere beyond the turbopause ( 105 km) have not been sufficiently studied. Using a general circulating model extending from the lower atmosphere to upper thermosphere and incorporating a whole atmosphere nonlinear parameterization of small-scale GWs developed by Yiǧit et al. (2008)}, we demonstrate that not only GWs penetrate into the thermosphere above the turbopause but also produce substantial dynamical and thermal effects that are comparable to ion drag and Joule heating. During sudden stratospheric warmings, GW propagation in the thermosphere is enhanced by more than a factor of three (Yiǧit and Medvedev, 2012)}, producing appreciable body forcing of up to 600 m s^{-1} day^{-1} around 250-300 km. The resultant impact on the variability of the thermospheric circulation can exceed ± 50% depending on the phase of the sudden warming (Yiǧit et al., 2014)}. References: Yiǧit, E., and A. S. Medvedev (2012), Gravity waves in the thermosphere during a sudden stratospheric warming, Geophys. Res. Lett., 39, L21101, doi:10.1029/2012GL053812. 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. Yiǧit, E., A. S. Medvedev, S. L. England, and T. J. Immel (2014), Simulated vari- ability of the high-latitude thermosphere induced by small-scale gravity waves during a sudden stratospheric warming, J. Geophys. Res. Space Physics, 119, doi:10.1002/2013JA019283.
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V. N. Gubenko
2011-03-01
Full Text Available The new method for the reconstruction of internal gravity wave (IGW parameters from a single vertical temperature profile measurement in the Earth atmosphere has been developed. 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, then analyzed temperature fluctuations can be considered as wave-induced. The method is based on the analysis of relative amplitude thresholds of the temperature wave field and on the linear IGW saturation theory in which amplitude thresholds are restricted by dynamical (shear instability processes in the atmosphere. When the amplitude of an internal gravity wave reaches the shear instability limit, energy is assumed to be dissipated in such a way that the amplitude is maintained at the instability limit as the wave propagates upwards. In order to approbate the method we have used in situ data of simultaneous balloon high-resolution measurements of the temperature and wind velocity in the Earth stratosphere (France where a long-period inertia-gravity wave has been detected. Using the temperature data only, we have reconstructed all the measured wave parameters with uncertainties not larger than 30%. An application of the method to the radio occultation data has given the possibility to identify the IGWs in the Earth stratosphere and to determine the magnitudes of key wave parameters such as the intrinsic frequency, amplitudes of vertical and horizontal perturbations of the wind velocity, vertical and horizontal wavelengths, intrinsic vertical and horizontal phase (and group speeds, kinetic and potential energy, vertical fluxes of the wave energy and horizontal momentum. The obtained results of internal wave studies in the Earth stratosphere deduced from the COSMIC and CHAMP GPS occultation
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V. N. Gubenko
2011-10-01
Full Text Available A new method for the reconstruction of internal gravity wave (IGW parameters from a single vertical temperature profile measurement in the Earth's atmosphere has been developed. 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, then analyzed temperature fluctuations can be considered as wave-induced. The method is based on the analysis of relative amplitude thresholds of the temperature wave field and on the linear IGW saturation theory in which amplitude thresholds are restricted by dynamical (shear instability processes in the atmosphere. When the amplitude of an internal gravity wave reaches the shear instability limit, energy is assumed to be dissipated in such a way that the amplitude is maintained at the instability limit as the wave propagates upwards. In order to approbate the method we have used data of simultaneous high-resolution balloon measurements of the temperature and wind velocity in the Earth's stratosphere over France where a long-period inertia-gravity wave has been detected. Using the radiosonde temperature data only, we have reconstructed all wave parameters, which were determined by radiosondes, with relative deviations not larger than 30%. An application of the method to the radio occultation (RO data has given the possibility to identify the IGWs in the Earth's stratosphere and to determine the magnitudes of key wave parameters such as the intrinsic frequency, amplitudes of vertical and horizontal perturbations of the wind velocity, vertical and horizontal wavelengths, intrinsic vertical and horizontal phase (and group speeds, kinetic and potential energy, vertical fluxes of the wave energy and horizontal momentum. The obtained results of internal wave studies in the Earth's stratosphere
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.
Gong, Shaohua; Yang, Guotao; Dou, Xiankang; Xu, Jiyao; Chen, Chunxia; Gong, Shunsheng
2015-08-01
Atmospheric gravity wave activities in the mesopause region have been observed and statistically investigated with a sodium lidar chain in eastern China. In total, there were 471 gravity waves identified from over 5400 h of observations at Hainan (19.99°N, 110.34°E), Hefei (31.87°N, 117.23°E), and Beijing (40.47°N, 115.97°E). These waves typically had vertical wavelengths of λz = 2 - 4 km, observed periods of Tob = 1 - 4 h, amplitude growth factors of β = - 0.025 ~ + 0.05 km-1, and wave amplitudes of Aeβ * 90km = 1.5 - 6 %. Strong systematic parameter relationships were found, and they agree with the predictions of diffusive filtering theory. Statistical results show that the seasonal variability of gravity wave activity had a summer-maximum and winter-minimum characteristics in the mesopause region over eastern China. A qualitative interpretation is proposed regarding the seasonal and geographic variability observed by the lidar chain, based on analysis of source properties and influences from background wind, which vary by season.
Prasanth, Vishnu
2016-07-01
In this paper, climatological characteristics of the gravity wave activities and thermal structure activities are studied using temperature profiles obtained from Rayleigh lidar located at Reunion Island (20.8°S, 55.5°E) over a period of ~14 years (1994-2007). The study has been performed over the height range from 30 to 65 km. The overall monthly mean temperature shows a maximum of 265-270K at the stratopause height region from ˜44-52km and peaks during the months of March and November. While there is no clear signature of seasonal oscillation in the stratopause height, the stratopause temperature shows distinct maxima during the periods March-April and October-November. The GW characteristics in terms of time (frequency), height (wave number) and GW associated Potential Energy and their seasonal dependences are presented. Generally, the temporal evolution of temperature profile illustrates the downward phase propagation indicating that the energy is propagating upward. The wave activity is clearly visible with the wave periods ranging from 260 min to 32 min. The dominant components have vertical wavelengths in the range of about ~4 km to 35 km. It is found that the seasonal variation of potential energy is maximum during summer in the upper stratosphere and lower mesosphere. A semiannual variation is seen in the gravity wave activity over all height ranges in the months of February and August.
Kuroda, Takeshi; Yiğit, Erdal; Hartogh, Paul
2015-01-01
Global characteristics of the small-scale gravity wave (GW) field in the Martian atmosphere obtained from a high-resolution general circulation model (GCM) are presented for the first time. The simulated GW-induced temperature variances are in a good agreement with available radio occultation data in the lower atmosphere between 10 and 30 km. The model reveals a latitudinal asymmetry with stronger wave generation in the winter hemisphere, and two distinctive sources of GWs: mountainous regions and the meandering winter polar jet. Orographic GWs are filtered while propagating upward, and the mesosphere is primarily dominated by harmonics with faster horizontal phase velocities. Wave fluxes are directed mainly against the local wind. GW dissipation in the upper mesosphere generates body forces of tens of m~s$^{-1}$~sol$^{-1}$, which tend to close the simulated jets. The results represent a realistic surrogate for missing observations, which can be used for constraining GW parameterizations and validating GCM si...
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Huang, K.M. [Wuhan Univ. (China). School of Electronic Information; Chinese Academey of Sciences, Hefei (China). Key Lab. of Geospace Environment; Embry Riddle Aeronautical Univ., Daytona Beach, FL (United States). Dept. of Physical Science; Ministry of Education, Wuhan (China). Key Lab. of Geospace Environment and Geodesy; State Observatory for Atmospheric Remote Sensing, Wuhan (China); Liu, A.Z.; Li, Z. [Embry Riddle Aeronautical Univ., Daytona Beach, FL (United States). Dept. of Physical Science; Zhang, S.D.; Yi, F. [Wuhan Univ. (China). School of Electronic Information; Ministry of Education, Wuhan (China). Key Lab. of Geospace Environment and Geodesy; State Observatory for Atmospheric Remote Sensing, Wuhan (China)
2012-07-01
Nonlinear interactions of gravity waves are studied with a two-dimensional, fully nonlinear model. The energy exchanges among resonant and near-resonant triads are examined in order to understand the spectral energy transfer through interactions. The results show that in both resonant and near-resonant interactions, the energy exchange between two high frequency waves is strong, but the energy transfer from large to small vertical scale waves is rather weak. This suggests that the energy cascade toward large vertical wavenumbers through nonlinear interaction is inefficient, which is different from the rapid turbulence cascade. Because of considerable energy exchange, nonlinear interactions can effectively spread high frequency spectrum, and play a significant role in limiting wave amplitude growth and transferring energy into higher altitudes. In resonant interaction, the interacting waves obey the resonant matching conditions, and resonant excitation is reversible, while near-resonant excitation is not so. Although near-resonant interaction shows the complexity of match relation, numerical experiments show an interesting result that when sum and difference near-resonant interactions occur between high and low frequency waves, the wave vectors tend to approximately match in horizontal direction, and the frequency of the excited waves is also close to the matching value. (orig.)
Instability of coupled gravity-inertial-Rossby waves on a β-plane in solar system atmospheres
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J. F. McKenzie
2009-11-01
Full Text Available This paper provides an analysis of the combined theory of gravity-inertial-Rossby waves on a β-plane in the Boussinesq approximation. The wave equation for the system is fifth order in space and time and demonstrates how gravity-inertial waves on the one hand are coupled to Rossby waves on the other through the combined effects of β, the stratification characterized by the Väisälä-Brunt frequency N, the Coriolis frequency f at a given latitude, and vertical propagation which permits buoyancy modes to interact with westward propagating Rossby waves. The corresponding dispersion equation shows that the frequency of a westward propagating gravity-inertial wave is reduced by the coupling, whereas the frequency of a Rossby wave is increased. If the coupling is sufficiently strong these two modes coalesce giving rise to an instability. The instability condition translates into a curve of critical latitude Θ_{c} versus effective equatorial rotational Mach number M, with the region below this curve exhibiting instability. "Supersonic" fast rotators are unstable in a narrow band of latitudes around the equator. For example Θ_{c}~12° for Jupiter. On the other hand slow "subsonic" rotators (e.g. Mercury, Venus and the Sun's Corona are unstable at all latitudes except very close to the poles where the β effect vanishes. "Transonic" rotators, such as the Earth and Mars, exhibit instability within latitudes of 34° and 39°, respectively, around the Equator. Similar results pertain to Oceans. In the case of an Earth's Ocean of depth 4km say, purely westward propagating waves are unstable up to 26° about the Equator. The nonlinear evolution of this instability which feeds off rotational energy and gravitational buoyancy may play an important role in atmospheric dynamics.
Instability of coupled gravity-inertial-Rossby waves on a {beta}-plane in solar system atmospheres
Energy Technology Data Exchange (ETDEWEB)
McKenzie, J.F. [KwaZulu-Natal Univ., Durban (South Africa). Astrophysics and Cosmology Research Unit, School of Mathematical Sciences; Alabama Univ., AL (United States). Dept. of Physics, CSPAR; King' s College, Cambridge (United Kingdom)
2009-07-01
This paper provides an analysis of the combined theory of gravity-inertial-Rossby waves on a {beta}-plane in the Boussinesq approximation. The wave equation for the system is fifth order in space and time and demonstrates how gravity-inertial waves on the one hand are coupled to Rossby waves on the other through the combined effects of {beta}-, the stratification characterized by the Vaeisaelae-Brunt frequency N, the Coriolis frequency f at a given latitude, and vertical propagation which permits buoyancy modes to interact with westward propagating Rossby waves. The corresponding dispersion equation shows that the frequency of a westward propagating gravity-inertial wave is reduced by the coupling, whereas the frequency of a Rossby wave is increased. If the coupling is sufficiently strong these two modes coalesce giving rise to an instability. The instability condition translates into a curve of critical latitude {theta}{sub c} versus effective equatorial rotational Mach number M, with the region below this curve exhibiting instability. ''Supersonic'' fast rotators are unstable in a narrow band of latitudes around the equator. For example {theta}{sub c}{proportional_to}12 for Jupiter. On the other hand slow ''subsonic'' rotators (e.g. Mercury, Venus and the Sun's Corona) are unstable at all latitudes except very close to the poles where the {beta}- effect vanishes. ''Transonic'' rotators, such as the Earth and Mars, exhibit instability within latitudes of 34 and 39 , respectively, around the Equator. Similar results pertain to Oceans. In the case of an Earth's Ocean of depth 4km say, purely westward propagating waves are unstable up to 26 about the Equator. The nonlinear evolution of this instability which feeds off rotational energy and gravitational buoyancy may play an important role in atmospheric dynamics. (orig.)
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).
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G. Ramkumar
2006-10-01
Full Text Available Altitude profiles of temperature in the stratospheric and mesopheric region from lidar observations at NARL, Gadanki, India, during December 2002–April 2005, as part of ISRO's Middle Atmospheric Dynamics – "MIDAS (2002–2005" program are used to study the characteristics of gravity waves and their seasonal variation. Month-to-month variation of the gravity wave activity observed during the period of December 2002–April 2005 show maximum wave activity, with primary peaks in May 2003, August 2004 and March 2005 and secondary peaks in February 2003 and November 2004. This month-to-month variation in gravity wave activity is linked to the variation in the strength of the sources, viz. convection and wind shear, down below at the tropospheric region, estimated from MST radar measurements at the same location. Horizontal wind shear is found to be mostly correlated with wave activity than convection, and sometimes both sources are found to contribute towards the wave activity.
International Nuclear Information System (INIS)
The theoretical basis for gravity-wave astronomy is described, along with the energy and momentum of gravitational fields. Other topics discussed include:- burst and periodic sources of gravitational waves, the cosmological stochastic background, and the detection of gravitational waves. (U.K.)
Gravity waves and high-altitude CO$_2$ ice cloud formation in the Martian atmosphere
Yiğit, Erdal; Hartogh, Paul
2015-01-01
We present the first general circulation model simulations that quantify and reproduce patches of extremely cold air required for CO$_2$ condensation and cloud formation in the Martian mesosphere. They are created by subgrid-scale gravity waves (GWs) accounted for in the model with the interactively implemented spectral parameterization. Distributions of GW-induced temperature fluctuations and occurrences of supersaturation conditions are in a good agreement with observations of high-altitude CO$_2$ ice clouds. Our study confirms the key role of GWs in facilitating CO$_2$ cloud formation, discusses their tidal modulation, and predicts clouds at altitudes higher than have been observed to date.
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Shao Dong Zhang
2006-12-01
Full Text Available Vertical wave number spectra of inertial gravity waves in the troposphere and lower stratosphere over six stations at latitudes from 20° N to 40° N were statistically studied by using the data from Radiosonde observation on a twice daily basis at 08:00 and 20:00 LT. Statistically, the spectral characteristics seem to be independent of the local observation time, and show considerable conformity between the spectral of zonal and meridional kinetic energy densities. Compared with the spectra of the kinetic energy density, the spectra of the potential energy density are steeper. in addition the characteristic wave numbers of the spectra also show considerable consistency among the observations at different stations. As for the spectral slopes, they are systematically smaller (in magnitude than the canon value of –3, and exhibit slight height, seasonal and latitudinal variability. In addition to these universal characteristics, the spectral structures also exhibit departures and variations, and most of the departures and variations are related to the strong tropospheric jets. Generally, in the case of strong shear due to the tropospheric jet, there usually occur larger characteristic wave numbers and smaller spectral slopes. These departures seem to be persistent and climatological rather than transitory, indicating the significant impacts of the sheared background winds on the spectral structures of gravity waves.
Chefranov, Sergey G
2013-01-01
The condition of internal gravity waves (IGW) parametric excitation in the rotating fluid layer heated from above, with the layer vibration along the vertical axis or with periodic modulation in time of the vertical temperature distribution, is obtained. We show the dual role of the molecular dissipative effects that may lead not only to the wave oscillations damping, but also to emergence of hydrodynamic dissipative instability (DI) in some frequency band of IGW. This DI also may take place for the localized in horizontal plane tornado-like disturbances, horizontal scale of which does not exceed the character vertical scale for the fluid layer of the finite depth. Investigated parametric resonance mechanism of IGW generation in ocean and atmosphere during and before earthquakes allows monitoring of such waves (with double period with respect to the period of vibration or temperature gradient modulation) as precursors of these devastating phenomena.
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John Z. G. Ma
2016-01-01
Full Text Available We study the modulation of atmospheric nonisothermality and wind shears on the propagation of seismic tsunami-excited gravity waves by virtue of the vertical wavenumber, m (with its imaginary and real parts, m i and m r , respectively, within a correlated characteristic range of tsunami wave periods in tens of minutes. A generalized dispersion relation of inertio-acoustic-gravity (IAG waves is obtained by relaxing constraints on Hines’ idealized locally-isothermal, shear-free and rotation-free model to accommodate a realistic atmosphere featured by altitude-dependent nonisothermality (up to 100 K/km and wind shears (up to 100 m/s per km. The obtained solutions recover all of the known wave modes below the 200-km altitude where dissipative terms are assumed negligible. Results include: (1 nonisothermality and wind shears divide the atmosphere into a sandwich-like structure of five layers within the 200-km altitude in view of the wave growth in amplitudes: Layer I (0–18 km, Layer II (18–87 km, Layer III (87–125 km, Layer IV (125–175 km and Layer V (175–200 km; (2 in Layers I, III and V, the magnitude of m i is smaller than Hines’ imaginary vertical wavenumber ( m i H , referring to an attenuated growth in the amplitudes of upward propagating waves; on the contrary, in Layers II and IV, the magnitude of m i is larger than that of m i H , providing a pumped growth from Hines’ model; (3 nonisothermality and wind shears enhance m r substantially at an ∼100-km altitude for a tsunami wave period T t s longer than 30 min. While Hines’ model provides that the maximal value of m r 2 is ∼0.05 (1/km 2 , this magnitude is doubled by the nonisothermal effect and quadrupled by the joint nonisothermal and wind shear effect. The modulations are weaker at altitudes outside 80–140-km heights; (4 nonisothermality and wind shears expand the definition of the observation-defined “damping factor”, β: relative to Hines’ classical wave
Ribstein, Bruno; Achatz, Ulrich; Senf, Fabian
2014-05-01
abstract Gravity waves (GWs) and solar tides (STs) are main constituents of the dynamical coupling between troposphere and mesosphere-lower-thermosphere (MLT). Via momentum deposition, GWs control to a large extent the mesospheric mean circulation. STs are large scale waves, mostly due to tropospheric and stratospheric diurnal heating processes, that modulate all dynamical fields in the mesosphere. GWs ant STs also interact strongly with each other. Conventional GW parameterizations used to describe this interaction (e.g. [1]) neglect the time-dependence and horizontal gradients of the background flow, with fatal effects (e.g. [2]). We study here the propagation of GWs in a time-dependent middle-atmosphere background flow, using a new (caustics free) WKB GW model (ray tracer). The background flow is composed by a climatological mean and tidal fields extracted from a general circulation model (HAMMONIA, see [3]). In order to avoid caustics, inevitable in classic ray-tracer implementations, we implemented a new wave-action phase-space density conservation scheme [4, 5]. The scheme attaches to each ray a finite volume in the location & wavenumber phase-space. The location-wavenumber volume is conserved during the propagation, responding in shape to the local stretching and squeezing in wave-number space. From the propagation of GWs we evaluate the deposition of momentum and buoyancy. Rayleigh-friction and temperature-relaxation coefficients are also evaluated. In this extension of the study by [2] it is shown, with an amplitude scheme more stable against numerical instabilities, due to the avoidance of caustics, that STs (and so the time dependence of the background flow) modulate the propagation of GWs. Via Rayleigh-friction and temperature-relaxation coefficients, we also quantify how the pseudo-momentum-, momentum-, and enthalpy-deposition of GWs can influence the amplitude and the phase structure of STs. Finally, we compare momentum and buoyancy fluxes from the
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
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A. V. Vikulin
2015-09-01
Full Text Available Gravity phenomena related to the Earth movements in the Solar System and through the Galaxy are reviewed. Such movements are manifested by geological processes on the Earth and correlate with geophysical fields of the Earth. It is concluded that geodynamic processes and the gravity phenomena (including those of cosmic nature are related. The state of the geomedium composed of blocks is determined by stresses with force moment and by slow rotational waves that are considered as a new type of movements [Vikulin, 2008, 2010]. It is shown that the geomedium has typical rheid properties [Carey, 1954], specifically an ability to flow while being in the solid state [Leonov, 2008]. Within the framework of the rotational model with a symmetric stress tensor, which is developed by the authors [Vikulin, Ivanchin, 1998; Vikulin et al., 2012a, 2013], such movement of the geomedium may explain the energy-saturated state of the geomedium and a possibility of its movements in the form of vortex geological structures [Lee, 1928]. The article discusses the gravity wave detection method based on the concept of interactions between gravity waves and crustal blocks [Braginsky et al., 1985]. It is concluded that gravity waves can be recorded by the proposed technique that detects slow rotational waves. It is shown that geo-gravitational movements can be described by both the concept of potential with account of gravitational energy of bodies [Kondratyev, 2003] and the nonlinear physical acoustics [Gurbatov et al., 2008]. Based on the combined description of geophysical and gravitational wave movements, the authors suggest a hypothesis about the nature of spin, i.e. own moment as a demonstration of the space-time ‘vortex’ properties.
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.
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
Historical detection of atmospheric impacts by large bolides using acoustic-gravity waves
Energy Technology Data Exchange (ETDEWEB)
ReVelle, D.O.
1995-05-01
During the period from about 1960 to the early 1980`s a number of large bolides (meteor-fireballs) entered the atmosphere which were sufficiently large to generate blast waves during their drag interaction with the air. For example, the remnant of the blast wave from a single kiloton class event was subsequently detected by up to six ground arrays of microbarographs which were operated by the U.S. Air Force during this pre-satellite period. Data have also been obtained from other sources during this period as well and are also discussed in this summary of the historical data. The Air Force data have been analyzed in terms of their observable properties in order to infer the influx rate of NEO`s (near-Earth objects) in the energy range from 0.2 to 1100 kt. The determined influx is in reasonable agreement with that determined by other methods currently available such as Rabinowitz (1992), Ceplecha, (1992; 1994b) and by Chapman and Morrison (1994) despite the fact that due to sampling deficiencies only a portion of the {open_quotes}true{close_quotes} flux of large bodies has been obtained by this method, i.e., only sources at relatively low elevations have been detected. Thus the weak, fragile cometary bodies which do not penetrate the atmosphere as deeply are less likely to have been sampled by this type of detection system. Future work using the proposed C.T.B.T. (Comprehensive Test Ban Treaty) global scale infrasonic network will be likely to improve upon this early estimate of the global influx of NEO`s considerably.
Acoustic-gravity modons in the atmosphere
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L. Stenflo
Full Text Available It is shown that the equations governing low-frequency acoustic-gravity waves in a stable stratified atmosphere can have localized dipole-vortex solutions (modons. They propagate in the horizontal direction with a speed that is larger than that of all possible linear internal waves.
Hocke, Klemens; Lainer, Martin; Moreira, Lorena; Hagen, Jonas; Fernandez Vidal, Susana; Schranz, Franziska
2016-09-01
The temperature profiles of the satellite experiment Aura/MLS are horizontally spaced by 1.5° or 165 km along the satellite orbit. These level-2 data contain valuable information about horizontal fluctuations in temperature, which are mainly induced by inertia-gravity waves. Wave periods of 2-12 h, horizontal wavelengths of 200-1500 km, and vertical wavelengths of 6-30 km efficiently contribute to the standard deviation of the horizontal temperature fluctuations. The study retrieves and discusses the global distributions of inertia-gravity waves in the stratosphere and mesosphere during July 2015 and January 2016. We find many patterns that were previously present in data of TIMED/SABER, Aura/HIRDLS, and ECMWF analysis. However, it seems that Aura/MLS achieves a higher vertical resolution in the gravity wave maps since the maps are derived from the analysis of horizontal fluctuations along the orbit of the sounding volume. The zonal mean of the inertia-gravity wave distribution shows vertical modulations with scales of 10-20 km. Enhanced wave amplitudes occur in regions of increased zonal wind or in the vicinity of strong wind gradients. Further, we find a banana-like shape of enhanced inertia-gravity waves above the Andes in the winter mesosphere. We find areas of enhanced inertia-gravity wave activity above tropical deep convection zones at 100 hPa (z ˜ 13 km). Finally, we study the temporal evolution of inertia-gravity wave activity at 100 hPa in the African longitude sector from December 2015 to February 2016.
Yang, Fanglin; Schlesinger, Michael E.; Andranova, Natasha; Zubov, Vladimir A.; Rozanov, Eugene V.; Callis, Lin B.
2003-01-01
The sensitivity of the middle atmospheric temperature and circulation to the treatment of mean- flow forcing due to breaking gravity waves was investigated using the University of Illinois at Urbana-Champaign 40-layer Mesosphere-Stratosphere-Troposphere General Circulation Model (MST-GCM). Three GCM experiments were performed. The gravity-wave forcing was represented first by Rayleigh friction, and then by the Alexander and Dunkerton (AD) parameterization with weak and strong breaking effects of gravity waves. In all experiments, the Palmer et al. parameterization was included to treat the breaking of topographic gravity waves in the troposphere and lower stratosphere. Overall, the experiment with the strong breaking effect simulates best the middle atmospheric temperature and circulation. With Rayleigh friction and the weak breaking effect, a large warm bias of up to 60 C was found in the summer upper mesosphere and lower thermosphere. This warm bias was linked to the inability of the GCM to simulate the reversal of the zonal winds from easterly to westerly crossing the mesopause in the summer hemisphere. With the strong breaking effect, the GCM was able to simulate this reversal, and essentially eliminated the warm bias. This improvement was the result of a much stronger meridional transport circulation that possesses a strong vertical ascending branch in the summer upper mesosphere, and hence large adiabatic cooling. Budget analysis indicates that 'in the middle atmosphere the forces that act to maintain a steady zonal-mean zonal wind are primarily those associated with the meridional transport circulation and breaking gravity waves. Contributions from the interaction of the model-resolved eddies with the mean flow are small. To obtain a transport circulation in the mesosphere of the UIUC MST-GCM that is strong enough to produce the observed cold summer mesopause, gravity-wave forcing larger than 100 m/s/day in magnitude is required near the summer mesopause. In
Directory of Open Access Journals (Sweden)
G. J. Sofko
2009-01-01
Full Text Available Cases of mesoscale cloud bands in extratropical cyclones are observed a few hours after atmospheric gravity waves (AGWs are launched from the auroral ionosphere. It is suggested that the solar-wind-generated auroral AGWs contribute to processes that release instabilities and initiate slantwise convection thus leading to cloud bands and growth of extratropical cyclones. Also, if the AGWs are ducted to low latitudes, they could influence the development of tropical cyclones. The gravity-wave-induced vertical lift may modulate the slantwise convection by releasing the moist symmetric instability at near-threshold conditions in the warm frontal zone of extratropical cyclones. Latent heat release associated with the mesoscale slantwise convection has been linked to explosive cyclogenesis and severe weather. The circumstantial and statistical evidence of the solar wind influence on extratropical cyclones is further supported by a statistical analysis of high-level clouds (<440 mb extracted from the International Satellite Cloud Climatology Project (ISCCP D1 dataset. A statistically significant response of the high-level cloud area index (HCAI to fast solar wind from coronal holes is found in mid-to-high latitudes during autumn-winter and in low latitudes during spring-summer. In the extratropics, this response of the HCAI to solar wind forcing is consistent with the effect on tropospheric vorticity found by Wilcox et al. (1974 and verified by Prikryl et al. (2009. In the tropics, the observed HCAI response, namely a decrease in HCAI at the arrival of solar wind stream followed by an increase a few days later, is similar to that in the northern and southern mid-to-high latitudes. The amplitude of the response nearly doubles for stream interfaces associated with the interplanetary magnetic field BZ component shifting southward. When the IMF BZ after the stream interface shifts northward, the autumn-winter effect weakens or shifts to lower (mid latitudes
Nakamura, Takuji; Tsutsumi, Masaki; Ejiri, Mitsumu K.; Nishiyama, Takanori; Tomikawa, Yoshihiro; Kogure, Masaru
2016-07-01
Gravity waves generated in the lower atmosphere, or near the surface, propagate upward and transfer significant momentum and energy into the middle atmosphere/lower thermosphere. Recently it is known gravity waves are extensively generated in the high latitudes in the southern hemisphere, but not many have been reported on the generation, propagation and dissipation of such waves. In this study, we investigated gravity wave profiles in the high latitude southern hemisphere by potential energy (Ep) in the height range of 15-70 km from May 2011 to October 2013 by using Rayleigh/Raman lidar located at Syowa station (69S, 40E), in the Antarctic. Above 35km altitude, Ep was maximized during winter. The seasonal dependence of Ep over Syowa was similar to those observed at Davis (69S,79E) [Alexander et al., 2011]. Below 35 km altitude, Ep was enhanced in around May, and did not decrease in September. Almost all monthly mean profiles showed similar growth rate (corresponding scale height of about 12-14 km) above 30 km altitude. Furthermore, almost all Ep profiles have a local minimum around 25 km altitude and a local maximum around 20 km altitude, suggesting significant loss of the gravity waves between 20-25 km. In October 2012, The profile of Ep in October 2012 was quite different from those in the other months. Comparisons with zonal wind in the NASA/MERRA reanalysis data suggests that a height region of weak zonal winds descended earlier in 2012 than in the other years. This also suggests gravity waves below stratosphere include waves with slow phase speed.
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A. Vlasov
2011-11-01
Full Text Available We present a statistical study of Traveling Ionospheric Disturbances (TIDs as observed by the EISCAT Svalbard Radar (ESR during the continuous IPY-run (March 2007–February 2008 with field-aligned measurements. We have developed a semi-automatic routine for searching and extracting Atmospheric Gravity Wave (AGW activity. The collected data shows that AGW-TID signatures are common in the high-latitude ionosphere especially in the field-aligned ion velocity data (244 cases of AGW-TID signatures in daily records, but they can be observed also in electron density (26 cases, electron temperature (12 cases and ion temperature (26 cases. During the IPY campaign (in solar minimum conditions AGW-TID events appear more frequently during summer months than during the winter months. It remains still as a topic for future studies whether the observed seasonal variation is natural or caused by seasonal variation in the performance of the observational method that we use (AGW-TID signature may be more pronounced in a dense ionosphere. In our AGW-TID dataset the distribution of the oscillation periods has two peaks, one around 0.5–0.7 h and the other around 1.1–1.3 h. The diurnal occurrence rate has a deep minimum in the region of magnetic midnight, which might be partly explained by irregular auroral activity obscuring the TID signatures from our detection routines. As both the period and horizontal phase speed estimates (as derived from the classical AGW dispersion relation show values typical both for large scale TIDs and mesoscale TIDs it is difficult to distinguish whether the generator for high-latitude AGW-TIDs resides typically in the troposphere or in the near-Earth space. The results of our statistical analysis give anyway some valuable reference information for the future efforts to learn more about the dominating TID source mechanisms in polar cap conditions, and to improve AGW simulations.
Bakhmetieva, Nataliya V.; Grigoriev; Tolmacheva, Ariadna V.
Artificial periodic irregularities (API) formed by the powerful standing radio waves in the ionospheric plasma give the good chance for the lower ionosphere comprehensive studies. In this paper we present some applications of the API technique for experimental studies of sporadic E-layers (E _{s}), internal gravity waves and turbulent events in the lower ionosphere. API are formed in the field of the standing radio wave produced by interference of the incident wave and reflected one from the ionosphere (in more details about the API technique one can see in the book Belikovich et al., Ionospheric Research by Means of Artificial Periodic Irregularities - Katlenburg-Lindau, Germany. 2002. Copernicus GmbH. ISBN 3-936586-03-9). The spatial period of the irregular structure is equal to the standing wavelength Lambda or one-half the powerful wavelength lambda/2. API diagnostics are carried out at the API relaxation or decay stage by their sounding of probing radio pulses. Based on the measurement of an amplitude and a phase of the API scattered signal their relaxation time and regular vertical plasma velocity are measured. In the E-region of the ionosphere API are formed as a result of the diffusion redistribution of the non-uniformly heated plasma. The relaxation of the periodic structure is specified by the ambipolar diffusion process. The diffusion time is tau=(K (2) D _{a}) (-1) where K=2pi/Lambda and D _{a} is the ambipolar diffusion rate. The atmospheric turbulence causes reduction of the API relaxation time in comparison the diffusion time. Determination of the turbulent velocity is based on this fact. The vertical plasma velocity is determined by measuring the phase of the scattered signal. Atmospheric waves having the periods from 5-10 minutes to 5-6 hours give the contribution to temporal variations of the velocity. Parameters and effects of atmospheric waves and the turbulence on the API relaxation process are presented. Determination of the masses of the
Chakraborty, Suman; Chakrabarti, Sandip Kumar; Sasmal, Sudipta
2016-07-01
An important channel of the lithosphere-atmosphere-ionosphere coupling (LAIC) is the acoustic and gravity wave channel where the atmospheric gravity waves (AGW) play the most important part. Atmospheric waves are excited due to seismic gravitational vibrations before earthquakes and their effects on the atmosphere are the sources for seismo-ionospheric coupling which are manifested as perturbations in Very Low Frequency (VLF)/Low Frequency (LF) signal (amplitude/phase). For our study, we chose the recent major earthquakes that took place in Nepal and Imphal. The Nepal earthquake occurred on 12th May, 2015 at 12:50 pm local time (07:05 UTC) with Richter scale magnitude of M = 7.3 and depth 10 km (6.21 miles) at southeast of Kodari. The Imphal earthquake occurred on 4th January, 2016 at 4:35 am local time (23:05 UTC , 3rd January, UTC) with Richter scale magnitude of M = 6.7 and depth 55 km (34.2 miles). The data has been collected from Ionospheric and Earthquake Research Centre (IERC) of Indian Centre for Space Physics (ICSP) transmitted from JJI station of Japan. We performed both Fast Fourier Transform (FFT) and wavelet analysis on the VLF data for a couple of days before and after the major earthquakes. For both earthquakes, we observed wave like structures with periods of almost an hour before and after the earthquake day. The wave like oscillations after the earthquake may be due to the aftershock effects. We also observed that the amplitude of the wave like structures depends on the location of the epicenter between the transmitting and the receiving points and also on the depth of the earthquake.
Ahmed, B. M.; Eltayeb, I. A.
1980-08-01
The propagation properties of Rossby-gravity waves in an isothermal atmosphere on a beta-plane are investigated in the presence of a latitudinally sheared zonal flow. The perturbation equation is found to possess seven regular singularities provided the fluid is non-Boussinesq, and only five for Boussinesq fluids. In slowly varying shear a local dispersion relation is derived and used to study the wave normal surfaces and ray trajectories. The cross sections of the wave normal surfaces in horizontal planes possess three critical latitudes occurring where the intrinsic frequency hat{ω} takes the values 0, ± N, where N is the Brunt-Vaisalla frequency. The former is the usual Rossby wave critical latitude (R.w.c.l.) and the latter are essentially gravity wave critical latitudes (g.w.c.l.). Waves can propagate only on one side of a R.w.c.l. while propagation is possible on both sides of a g.w.c.l. provided the vertical wavenumber, m, there is real and non-zero. Also for real values of m and provided the atmosphere is non-Boussinesq the g.w.c.l. exhibits valve-like behaviour. Such valve behaviour is shown to be responsible for aiding high frequency waves (i.e. gravity waves) to penetrate jet-like wind streams and may facilitate the transfer of energy and momentum across latitudes. The full wave treatment shows that the system possesses a wave-invariant which has a simple physical interpretation only when m is real in which case it represents the conservation of the total northward wave energy flux. The invariant is used, together with the legitimate solutions near the critical latitudes, to study the influence of each of the critical latitudes on the intensity of the wave. It is found that the R.w.c.l. can be associated with energy absorption or emission, depending on certain specified conditions, but the g.w.c.l. is always associated with energy absorption although the amount of energy absorbed depends crucially on whether m is real or imaginary. The reflexion
Local effects of gravity wave propagation and saturation
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.
Squids, brains and gravity waves
International Nuclear Information System (INIS)
Superconducting quantum interference devices are so sensitive to magnetic flux that they can map the tiny magnetic fields emanating from the human brain and detect the submicroscopic motions of gravity-wave detectors
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. PMID:25353576
Internal wave coupling processes in Earth's atmosphere
Yiğit, Erdal
2014-01-01
This paper presents a contemporary review of vertical coupling in the atmosphere and ionosphere system induced by internal waves of lower atmospheric origin. Atmospheric waves are primarily generated by meteorological processes, possess a broad range of spatial and temporal scales, and can propagate to the upper atmosphere. A brief summary of internal wave theory is given, focusing on gravity waves, solar tides, planetary Rossby and Kelvin waves. Observations of wave signatures in the upper atmosphere, their relationship with the direct propagation of waves into the upper atmosphere, dynamical and thermal impacts as well as concepts, approaches, and numerical modeling techniques are outlined. Recent progress in studies of sudden stratospheric warming and upper atmospheric variability are discussed in the context of wave-induced vertical coupling between the lower and upper atmosphere.
A case study of gravity waves in noctilucent clouds
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P. Dalin
2004-06-01
Full Text Available We present a case study of a noctilucent cloud (NLC display appearing on 10-11 August 2000 over Northern Sweden. Clear wave structures were visible in the clouds and time-lapse photography was used to derive the parameters characterising the gravity waves which could account for the observed NLC modulation. Using two nearby atmospheric radars, the Esrange MST Radar data and Andoya MF radar, we have identified gravity waves propagating upward from the upper stratosphere to NLC altitudes. The wave parameters derived from the radar measurements support the suggestion that gravity waves are responsible for the observed complex wave dynamics in the NLC.
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.
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. PMID:24606251
Hinson, D. P.
1983-01-01
The refractive index of planetary atmospheres at microwave frequencies is discussed. Physical models proposed for the refractive irregularities in the ionosphere and neutral atmosphere serve to characterize the atmospheric scattering structures, and are used subsequently to compute theoretical scintillation spectra for comparison with the Voyager occultation measurements. A technique for systematically analyzing and interpreting the signal fluctuations observed during planetary occultations is presented and applied to process the dual-wavelength data from the Voyager radio occultations by Jupiter, Saturn, and Titan. Results concerning the plasma irregularities in the upper ionospheres of Jupiter and Saturn are reported. The measured orientation of the irregularities is used to infer the magnetic field direction at several locations in the ionospheres of these two planets; the occultation measurements conflict with the predictions of Jovian magnetic field models, but generally confirm current models of Saturn's field. Wave parameters, including the vertical fluxes of energy and momentum, are estimated, and the source of the internal gravity waves discovered in Titan's upper atmosphere is considered.
On the Synchronization of Acoustic Gravity Waves
Lonngren, Karl E.; Bai, Er-Wei
Using the model proposed by Stenflo, we demonstrate that acoustic gravity waves found in one region of space can be synchronized with acoustic gravity waves found in another region of space using techniques from modern control theory.
Waves in vertically inhomogeneous dissipative atmosphere
Dmitrienko, I S
2015-01-01
A method of construction of solution for acoustic-gravity waves (AGW) above a wave source, taking dissipation throughout the atmosphere into account (Dissipative Solution above Source, DSAS), is proposed. The method is to combine three solutions for three parts of the atmosphere: an analytical solution for the upper isothermal part and numerical solutions for the real non-isothermal dissipative atmosphere in the middle part and for the real non-isothermal small dissipation atmosphere in the lower one. In this paper the method has been carried out for the atmosphere with thermal conductivity but without viscosity. The heights of strong dissipation and the total absorption index in the regions of weak and average dissipation are found. For internal gravity waves the results of test calculations for an isothermal atmosphere and calculations for a real non-isothermal atmosphere are shown in graphical form. An algorithm and appropriate code to calculate DSAS, taking dissipation due to finite thermal conductivity i...
Kuroda, Takeshi; Medvedev, Alexander; Yiğit, Erdal; Hartogh, Paul
2016-10-01
Gravity waves (GWs) are small-scale atmospheric waves generated by various geophysical processes, such as topography, convection, and dynamical instability. On Mars, several observations and simulations have revealed that GWs strongly affect temperature and wind fields in the middle and upper atmosphere. We have worked with a high-resolution Martian general circulation model (MGCM), with the spectral resolution of T106 (horizontal grid interval of ~67 km), for the investigations of generation and propagation of GWs. We analyzed for three kinds of wavelength ranges, (1) horizontal total wavenumber s=21-30 (wavelength λ~700-1000 km), (2) s=31-60 (λ~350-700 km), and (3) s=61-106 (λ~200-350 km). Our results show that shorter-scale harmonics progressively dominate with height during both equinox and solstice. We have detected two main sources of GWs: mountainous regions and the meandering winter polar jet. In both seasons GW energy in the troposphere due to the shorter-scale harmonics is concentrated in the low latitudes in a good agreement with observations. Orographically-generated GWs contribute significantly to the total energy of disturbances, and strongly decay with height. Thus, the non-orographic GWs of tropospheric origin dominate near the mesopause. The vertical fluxes of wave horizontal momentum are directed mainly against the larger-scale wind. Mean magnitudes of the drag in the middle atmosphere are tens of m s-1 sol-1, while instantaneously they can reach thousands of m s-1 sol-1, which results in an attenuation of the wind jets in the middle atmosphere and in tendency of their reversal.
Reflection of internal gravity waves from the mesospheric waveguide
International Nuclear Information System (INIS)
Frequency spectrum of internal gravity waves formed at their incidence at the plane atmospheric layer with Brent increased frequency representing a wave guide for IGW, is studied. The amplitude of reflection (passing) coefficient oscillations increases when frequency of incident wave approaches Brent Frequency. 3 refs
Inherently Unstable Internal Gravity Waves
Liang, Y
2016-01-01
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 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.
Directory of Open Access Journals (Sweden)
F. Muto
2009-07-01
Full Text Available As the target earthquake we have taken a huge earthquake (EQ named Miyagi-oki earthquake on 16 August 2005 (with magnitude of 7.2 and we have analyzed the 4 month period including the date of this EQ. In addition to our previous analysis on the nighttime average amplitude (trend and nighttime fluctuation, we have proposed the use of fluctuation power spectra in the frequency rage of atmospheric gravity waves (period=10 min to 100 min as a third parameter of subionospheric VLF/LF propagation characteristics. Then it is found that this third parameter would be of additional importance in confirming the presence of seismo-ionospheric perturbations. Finally, we have discovered an important role of lunar tidal effect in the VLF/LF data, which appears one and two months before this large EQ.
Gravity Waves in Three Dimensions
Gurses, Metin; Tekin, Bayram
2015-01-01
We find the explicit forms of the anti-de Sitter plane, anti-de Sitter spherical, and pp waves that solve both the linearized and exact field equations of the most general higher derivative gravity theory in three dimensions. As a sub-class, we work out the six derivative theory and the critical version of it where the masses of the two spin-2 excitations vanish and the spin-0 excitations decouple.
Exponential asymptotics and gravity waves
Chapman, S. J.; Vanden-Broeck, J.
2006-01-01
The problem of irrotational inviscid incompressible free-surface flow is examined in the limit of small Froude number. Since this is a singular perturbation, singularities in the flow field (or its analytic continuation) such as stagnation points, or corners in submerged objects or on rough beds, lead to a divergent asymptotic expansion, with associated Stokes lines. Recent techniques in exponential asymptotics are employed to observe the switching on of exponentially small gravity waves acro...
Intercomparison of stratospheric gravity wave observations with AIRS and IASI
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L. Hoffmann
2014-08-01
Full Text Available 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 (about 45% that we attribute to the different spatial measurement characteristics of both instruments. We also found differences between day- and nighttime data (about 30% 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
Intercomparison of stratospheric gravity wave observations with AIRS and IASI
Directory of Open Access Journals (Sweden)
L. Hoffmann
2014-12-01
Full Text Available 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 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 5-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
Impact of gravity waves on long-range infrasound propagation
Millet, Christophe; Lott, François; De La Camara, Alvaro
2016-04-01
In this work we study infrasound propagation in acoustic waveguides that support a finite number of propagating modes. We analyze the effects of gravity waves on these acoustic waveguides. Testing sound propagation in such perturbed fields can potentially be used to improve the gravity wave models. A linear solution modeling the interaction between an incoming acoustic wave and a randomly perturbed atmosphere is developed, using the forward-scattering approximation. The wave mode structure is determined by the effective sound speed profile which is strongly affected by gravity wave breaking. The random perturbations are described by a stochastic field predicted by a multiwave stochastic parameterization of gravity waves, which is operational in the LMDz climate model. The justification for this approach is two fold. On the one hand, the use of a few monochromatic waves mimics the observations of rather narrow-banded gravity wave packets in the lower stratosphere. On the other hand, the stochastic sampling of the gravity wave field and the random choice of wave properties deals with the inherent unpredictability of mesoscale dynamics from large scale conditions provided by the meteorological reanalysis. The transmitted acoustic signals contain a stable front and a small-amplitude incoherent coda. A general expression for the stable front is derived in terms of saddle-point contributions. The saddle-points are obtained from a WKB approximation of the vertical eigenvalue problem. This approach extract the dominant effects in the acoustic - gravity wave interaction. We present results that show how statistics of the transmitted signal are related to a few saddle-points and how the GW field can trigger large deviations in the acoustic signals. While some of the characteristics of the stable front can be directly related to that of a few individual gravity waves, it is shown that the amount of the launched gravity waves included in climate models can be estimated using
Institute of Scientific and Technical Information of China (English)
XU; Jiyao(徐寄遥); MA; Ruiping(马瑞平); A.K.Smith
2002-01-01
A nonlinear, compressible, non-isothermal gravity wave model that involves photochemistry is used to study the effects of gravity wave on atmospheric chemical species distributions in this paper. The changes in the distributions of oxygen compound and hydrogen compound density induced by gravity wave propagation are simulated. The results indicate that when a gravity wave propagates through a mesopause region, even if it does not break, it can influence the background distributions of chemical species. The effect of gravity wave on chemical species at night is larger than in daytime.
Satellite observations of the QBO wave driving by Kelvin waves and gravity waves
Ern, Manfred; Preusse, Peter; Kalisch, Silvio; Riese, Martin
2014-05-01
The quasi-biennial oscillation (QBO) of the zonal wind in the tropical stratosphere is an important process in atmospheric dynamics influencing a wide range of altitudes and latitudes. Effects of the QBO are found also in the mesosphere and in the extra-tropics. The QBO even has influence on the surface weather and climate, for example during winter in the northern hemisphere at midlatitudes. Still, climate models have large difficulties in reproducing a realistic QBO. One reason for this deficiency are uncertainties in the wave driving by planetary waves and, in particular, gravity waves that are usually too small-scale to be resolved in global models. Different global equatorial wave modes (e.g., Kelvin waves) have been identified by longitude-time 2D spectral analysis in Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite temperature data, as well as ECMWF temperatures. We find good agreement between SABER satellite observations and ECMWF wave variances in both QBO-related temporal variations and their magnitude. Slow phase speed waves are strongly modulated by the QBO, higher phase speed waves are almost unaffected by the QBO, and ultra-fast equatorial waves can even reach the MLT region. Momentum fluxes and zonal wind drag due to Kelvin waves are derived, and the relative contribution of Kelvin waves to the QBO wind reversal from westward to eastward wind is estimated to be about 30% of the total wave driving. This is in good agreement with the general assumption that gravity waves (GWs) are probably more important for the QBO driving than global-scale waves. This is further supported by SABER and High Resolution Dynamics Limb Sounder (HIRDLS) satellite observations of gravity wave drag in the equatorial region. These observations are compared with the drag still missing in the ECMWF ERA Interim (ERAI) tropical momentum budget after considering zonal wind tendency, Coriolis force, advection terms and drag of resolved global
Role of gravity waves in vertical coupling during sudden stratospheric warmings
Yiğit, Erdal
2016-01-01
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.
Nonlinear interactions between gravity waves and tides
Institute of Scientific and Technical Information of China (English)
LIU Xiao; XU JiYao; MA RuiPing
2007-01-01
In this study, we present the nonlinear interactions between gravity waves (GWs) and tides by using the 2D numerical model for the nonlinear propagation of GWs in the compressible atmosphere. During the propagation in the tidal background, GWs become instable in three regions, that is z = 75-85 km, z =90-110 km and z= 115-130 km. The vertical wavelength firstly varies gradually from the initial 12 km to 27 km. Then the newly generated longer waves are gradually compressed. The longer and shorter waves occur in the regions where GWs propagate in the reverse and the same direction of the horizontal mean wind respectively. In addition, GWs can propagate above the main breaking region (90-110 km). During GWs propagation, not only the mean wind is accelerated, but also the amplitude of tide is amplified. Especially, after GWs become instable, this amplified effect to the tidal amplitude is much obvious.
Nonlinear interactions between gravity waves and tides
Institute of Scientific and Technical Information of China (English)
2007-01-01
In this study, we present the nonlinear interactions between gravity waves (GWs) and tides by using the 2D numerical model for the nonlinear propagation of GWs in the compressible atmosphere. During the propagation in the tidal background, GWs become instable in three regions, that is z = 75―85 km, z = 90―110 km and z = 115―130 km. The vertical wavelength firstly varies gradually from the initial 12 km to 27 km. Then the newly generated longer waves are gradually compressed. The longer and shorter waves occur in the regions where GWs propagate in the reverse and the same direction of the hori-zontal mean wind respectively. In addition, GWs can propagate above the main breaking region (90—110 km). During GWs propagation, not only the mean wind is accelerated, but also the amplitude of tide is amplified. Especially, after GWs become instable, this amplified effect to the tidal amplitude is much obvious.
On the unstable mode merging of gravity-inertial waves with Rossby waves
Mckenzie, J. F.
2011-01-01
We recapitulate the results of the combined theory of gravity-inertial-Rossby waves in a rotating, stratified atmosphere. The system is shown to exhibit a "local" (JWKB) instability whenever the phase speed of the low-frequency-long wavelength westward propagating Rossby wave exceeds the phase speed ("Kelvin" speed) of the high frequency-short wavelength gravity-inertial wave. This condition ensures that mode merging, leading to instability, takes place in some intermediat...
Dissipation of acoustic-gravity waves: an asymptotic approach.
Godin, Oleg A
2014-12-01
Acoustic-gravity waves in the middle and upper atmosphere and long-range propagation of infrasound are strongly affected by air viscosity and thermal conductivity. To characterize the wave dissipation, it is typical to consider idealized environments, which admit plane-wave solutions. Here, an asymptotic approach is developed that relies instead on the assumption that spatial variations of environmental parameters are gradual. It is found that realistic assumptions about the atmosphere lead to rather different predictions for wave damping than do the plane-wave solutions. A modification to the Sutherland-Bass model of infrasound absorption is proposed. PMID:25480091
Observations of gravity wave scales, fluxes, and saturation during MAP
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.
Wave Propagation in Modified Gravity
Lindroos, Jan Ø; Mota, David F
2015-01-01
We investigate the propagation of scalar waves induced by matter sources in the context of scalar-tensor theories of gravity which include screening mechanisms for the scalar degree of freedom. The usual approach when studying these theories in the non-linear regime of cosmological perturbations is based on the assumption that scalar waves travel at the speed of light. Within General Relativity such approximation is good and leads to no loss of accuracy in the estimation of observables. We find, however, that mass terms and non-linearities in the equations of motion lead to propagation and dispersion velocities significantly different from the speed of light. As the group velocity is the one associated to the propagation of signals, a reduction of its value has direct impact on the behavior and dynamics of nonlinear structures within modified gravity theories with screening. For instance, the internal dynamics of galaxies and satellites submerged in large dark matter halos could be affected by the fact that t...
Atmospheric waves as scaling, turbulent phenomena
Directory of Open Access Journals (Sweden)
J. Pinel
2013-06-01
Full Text Available It is paradoxical that while atmospheric dynamics are highly nonlinear and turbulent that atmospheric waves are commonly modelled by linear or weakly nonlinear theories. We postulate that the laws governing atmospheric waves are on the contrary high Reynold's number (Re, emergent laws so that – in common with the emergent high Re turbulent laws – they are also constrained by scaling symmetries. We propose an effective turbulence – wave propagator which corresponds to a fractional and anisotropic extension of the classical wave equation propagator with dispersion relations similar to those of inertial gravity waves (and Kelvin waves yet with an anomalous (fractional order Hwav/2. Using geostationary IR radiances, we estimate the parameters finding that Hwav/2 ≈ 0.17 ± 0.04 (the classical value = 2.
Jonah, O. F.; Kherani, E. A.; De Paula, E. R.
2016-03-01
In the present study, we document daytime total electron content (TEC) disturbances associated with medium-scale traveling ionospheric disturbances (MSTIDs), on few chosen geomagnetically quiet days over Southern Hemisphere of Brazilian longitude sector. These disturbances are derived from TEC data obtained using Global Navigation Satellite System (GNSS) receiver networks. From the keograms and cross-correlation maps, the TEC disturbances are identified as the MSTIDs that are propagating equatorward-eastward, having most of their average wavelengths longer in latitude than in longitude direction. These are the important outcomes of the present study which suggest that the daytime MSTIDs over Southern Hemisphere are similar to their counterparts in the Northern Hemisphere. Another important outcome is that the occurrence characteristics of these MSTIDs and that of atmospheric gravity wave (AGW) activities in the thermosphere are found to be similar on day-to-day basis. This suggests a possible connection between them, confirming the widely accepted AGW forcing mechanism for the generation of these daytime MSTIDs. The source of this AGW is investigated using the Geostationary Operational Environmental Satellite system (GOES) and Constellation Observing System for Meteorology, Ionosphere, and Climate satellite data. Finally, we provided evidences that AGWs are generated by convection activities from the tropospheric region.
Freytag, Bernd; Ludwig, Hans-Guenter; Homeier, Derek; Steffen, Matthias
2010-01-01
Observationally, spectra of brown dwarfs indicate the presence of dust in their atmospheres while theoretically it is not clear what prevents the dust from settling and disappearing from the regions of spectrum formation. Consequently, standard models have to rely on ad hoc assumptions about the mechanism that keeps dust grains aloft in the atmosphere. We apply hydrodynamical simulations to develop an improved physical understanding of the mixing properties of macroscopic flows in M dwarf and brown dwarf atmospheres, in particular of the influence of the underlying convection zone. We performed 2D radiation hydrodynamics simulations including a description of dust grain formation and transport with the CO5BOLD code. The simulations cover the very top of the convection zone and the photosphere including the dust layers for effective temperatures between 900K and 2800K, all with logg=5 assuming solar chemical composition. Convective overshoot occurs in the form of exponentially declining velocities with small s...
VHF radar observations of gravity waves at a low latitude
Directory of Open Access Journals (Sweden)
G. Dutta
Full Text Available Wind observations made at Gadanki (13.5°N by using Indian MST Radar for few days in September, October, December 1995 and January, 1996 have been analyzed to study gravity wave activity in the troposphere and lower stratosphere. Horizontal wind variances have been computed for gravity waves of period (2-6 h from the power spectral density (PSD spectrum. Exponential curves of the form e^{Z}^{/}^{H} have been fitted by least squares technique to these variance values to obtain height variations of the irregular winds upto the height of about 15 km, where Z is the height in kilometers. The value of H, the scale height, as determined from curve fitting is found to be less than the theoretical value of scale height of neutral atmosphere in this region, implying that the waves are gaining energy during their passage in the troposphere. In other words, it indicates that the sources of gravity waves are present in the troposphere. The energy densities of gravity wave fluctuations have been computed. Polynomial fits to the observed values show that wave energy density increases in the troposphere, its source region, and then decreases in the lower stratosphere.
Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; turbulence; waves and tides
Transversally periodic solitary gravity-capillary waves.
Milewski, Paul A; Wang, Zhan
2014-01-01
When both gravity and surface tension effects are present, surface solitary water waves are known to exist in both two- and three-dimensional infinitely deep fluids. We describe here solutions bridging these two cases: travelling waves which are localized in the propagation direction and periodic in the transverse direction. These transversally periodic gravity-capillary solitary waves are found to be of either elevation or depression type, tend to plane waves below a critical transverse period and tend to solitary lumps as the transverse period tends to infinity. The waves are found numerically in a Hamiltonian system for water waves simplified by a cubic truncation of the Dirichlet-to-Neumann operator. This approximation has been proved to be very accurate for both two- and three-dimensional computations of fully localized gravity-capillary solitary waves. The stability properties of these waves are then investigated via the time evolution of perturbed wave profiles. PMID:24399922
Role of Gravity Waves in Determining Cirrus Cloud Properties
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).
LAICE CubeSat mission for gravity wave studies
Westerhoff, John; Earle, Gregory; Bishop, Rebecca; Swenson, Gary R.; Vadas, Sharon; Clemmons, James; Davidson, Ryan; Fanelli, Lucy; Fish, Chad; Garg, Vidur; Ghosh, Alex; Jagannatha, Bindu B.; Kroeker, Erik; Marquis, Peter; Martin, Daniel; Noel, Stephen; Orr, Cameron; Robertson, Robert
2015-10-01
The Lower Atmosphere/Ionosphere Coupling Experiment (LAICE) CubeSat mission will focus on understanding the interaction of atmospheric gravity waves generated by weather systems in the lower atmosphere with the mesosphere, lower thermosphere, and ionosphere (MLTI). Specifically, LAICE will focus on the energy and momentum delivered by these waves and attempt to connect the wave sources and the wave effects in three widely different altitude ranges, substantially adding to our knowledge of critical coupling processes between disparate atmospheric regions. The LAICE mission consists of a 6U CubeSat with a four-instrument payload. The retarding potential analyzer (RPA) will provide in-situ ion density and temperature measurements. A four-channel photometer will measure density and temperature variations in the mesosphere through observations of O2 (0, 0) Atmospheric band and O2 Herzberg I band airglows. There are two pressure sensors that comprise the Space Pressure Suite (SPS): the Space Neutral Pressure Instrument (SNeuPI) and the LAICE Ionization gauge Neutral Atmosphere Sensor (LINAS). Both will provide neutral density measurements, but SNeuPI is a prototype sensor that will be validated by LINAS. This CubeSat mission, scheduled for launch in early 2016 from the International Space Station, provides a cost-effective approach to measuring low altitude in-situ parameters along with simultaneous imaging that is capable of addressing the fundamental questions of atmospheric gravity wave coupling in the MLTI region.
Directory of Open Access Journals (Sweden)
Ze Yu Chen
2008-07-01
Full Text Available The characteristics of dynamical and thermal structures and inertial gravity waves (GWs in the troposphere and lower stratosphere (TLS over Yichang (111°18´ E, 30°42´ N were statistically studied by using the data from intensive radiosonde observations in August 2006 (summer month and January 2007 (winter month on an eight-times-daily basis. The background atmosphere structures observed in different months exhibit evident seasonal differences, and the zonal wind in winter has a prominent tropospheric jet with a maximum wind speed of about 60 ms−1 occurring at the height of 11.5 km. The statistical results of the inertial GWs in our two-month observations are generally consistent with previous observations in the mid-latitudes. In the summer month, the mean intrinsic frequency and vertical wavelength of the inertial GWs in the troposphere are still larger than those in the lower stratosphere with the absence of intensive tropospheric jets, suggesting that the Doppler shifting due to the tropospheric jets cannot completely account for the differences between the GWs in the troposphere and lower stratosphere. Compared with the observations in the summer month, some interesting seasonal characteristics of the GWs are revealed by the observations in the winter month: 1 more and stronger tropospheric GWs are observed in the winter month; 2 less and weaker GWs are observed in the lower stratosphere in winter; 3 the ratio of the mean GW kinetic energy density to potential energy density is smaller than 1 in winter, which contrasts to that in summer. Most of the seasonal differences can be explained by the intensive tropospheric jets in winter. In both the summer and winter months, the fitted spectral slopes of the vertical wave number spectra for GWs are generally smaller than the canonical spectral slope of −3. Correlation analyses suggest that the tropospheric jet induced wind shear is the dominant source for GWs in both the troposphere and
Finite amplitude gravity waves: Harmonics, advective steepening, breaking and saturation
Weinstock, J.
1985-01-01
A simple theory is presented which determines details of the breaking and saturation of a gravity wave as it propagates upward in the atmosphere. Breaking and saturation are here due to nonlinear advection analogous to the breaching of a surface wave and to the breaking of a planetary wave. Much simplification is obtained by the assumption that in a wave packet consisting of a primary wave and its harmonics, the primary wave remains dominant. This assumption, referred to a quasi-monochromatic approximation, is suggested by observations. Determined by this approximate theory are: a detailed picture of the waveform as it steepens and breaks; harmonics of the wave; the turbulence generation; and an underlying relationship between superadiabatic lapse rate and saturation by wave-wave interactions.
f(R) gravity constraints from gravity waves
Vainio, Jaakko
2016-01-01
The recent LIGO observation sparked interest in the field of gravity wave signals. Besides the gravity wave observation the LIGO collaboration used the inspiraling black hole pair to constrain the graviton mass. Unlike general relativity, $f(R)$ theories have a characteristic non-zero mass graviton. We apply the constraint on the graviton mass to viable $f(R)$ models to find the effects on model parameters. We find it possible to constrain the parameter space with the gravity wave based observations. We make a case study for the popular Hu-Sawicki model and find a parameter bracket. The result generalizes to other $f(R)$ theories and can be used to contain the parameter space.
Characteristic of gravity waves resolved in ECMWF
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
Buoyancy waves in Pluto's high atmosphere: Implications for stellar occultations
Hubbard, W B; Kulesa, C A; Benecchi, S D; Person, M J; Elliot, J L; Gulbis, A A S
2009-01-01
We apply scintillation theory to stellar signal fluctuations in the high-resolution, high signal/noise, dual-wavelength data from the MMT observation of the 2007 March 18 occultation of P445.3 by Pluto. A well-defined high wavenumber cutoff in the fluctuations is consistent with viscous-thermal dissipation of buoyancy waves (internal gravity waves) in Pluto's high atmosphere, and provides strong evidence that the underlying density fluctuations are governed by the gravity-wave dispersion relation.
Acoustic-gravity waves, theory and application
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.
Behavior of gravity waves with limited amplitude in the vicinity of critical layer
Institute of Scientific and Technical Information of China (English)
无
2002-01-01
By using the FICE scheme, a numerical simulation of three-dimensional nonlinear propagation of gravity wave packet in a wind-stratified atmosphere is presented. The whole nonlinear propagation process of the gravity wave packet is shown; the propagation behavior of gravity waves in the vicinity of critical layer is analyzed. The results show that gravity waves encounter the critical layer when propagating in the fair winds whose velocities increase with height, and the height of critical layer propagating nonlinearly is lower than that expected by the linear gravity waves theory; the amplitudes of gravity waves increase with height as a whole before gravity waves encounter the critical layer, but the increasing extent is smaller than the result given by the linear theory of gravity waves, while the amplitudes of gravity waves reduce when gravity waves meet the critical layer; the energy of wave decreases with height, especially at the critical layer; the vertical wavelength reduces with the height increasing, but it does not become zero.
Background Lamb waves in the Earth's atmosphere
Nishida, K.; Kobayashi, N.; Fukao, Y.
2013-12-01
Lamb waves of the Earth's atmosphere in the millihertz band have been considered as transient phenomena excited only by large events [e.g. the major volcanic eruption of Krakatoa in 1833, the impact of Siberian meteorite in 1908, the testing of large nuclear tests and the huge earthquakes, Garrett1969]. In a case of the solid Earth, observation of background free oscillations in the millihertz band-now known as Earth's background free oscillations or seismic hum, has been firmly established. Above 5 mHz, their dominant excitation sources are oceanic infragravity waves. At 3.7 and 4.4 mHz an elasto-acoustic resonance between the solid Earth and the atmosphere was observed [Nishida et al., 2000]. These seismic observations show that the contribution of atmospheric disturbances to the seismic hum is dominant below 5 mHz. Such contribution implies background excitations of acoustic-gravity waves in this frequency range. For direct detection of the background acoustic-gravity waves, our group conducted observations using an array of barometers [Nishida et al. 2005]. However, the spatial scale of the array of about 10 km was too small to detect acoustic modes below 10 mHz. Since then, no direct observations of these waves have been reported. In 2011, 337 high-resolution microbarometers were installed on a continental scale at USArray Transportable Array. The large and dense array enables us to detect the background atmospheric waves. Here, we show the first evidence of background Lamb waves in the Earth's atmosphere from 0.2 to 10 mHz, based on the array analysis of microbarometer data from the USArray in 2012. The observations suggest that the excitation sources are atmospheric disturbances in the troposphere. Theoretically, their energy in the troposphere tunnels into the thermosphere at a resonant frequency via thermospheric gravity wave, where the observed amplitudes indeed take a local minimum. The energy leak through the frequency window could partly contribute to
Gravitational waves in geometric scalar gravity
Toniato, J D
2016-01-01
We investigate the description of gravitational waves in the geometric scalar theory of gravity (GSG). The GSG belongs to a class of theories such that gravity is described by a single scalar field and the associated physical metric describing the spacetime is constructed from a disformal transformation of Minkowski geometry. In this theory, gravitational waves have a longitudinal polarization mode, besides others modes that are observer dependent. We examine the orbital variation of a binary system due to the emission of gravitational waves, showing that GSG can also be successful in explaining this phenomena.
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.
Propagation of acoustic gravity waves excited by explosions
International Nuclear Information System (INIS)
Acoustic gravity waves excited by low-altitude nuclear explosions have been observed in the ionosphere, by H.F. Doppler soundings, at horizontal distances from the source between 100 and 1200 km. The characteristics of the initial shock wave, which is observed at short range, are progressively replaced by those of the atmospheric wave guide. In particular, the dispersion properties of the signal observed in the ionosphere at long range are those of the first acoustic and gravity modes. Detailed study of the propagation times to middle and long range shows that the wave guide is mainly excited by the focalisation of acoustic energy which is produced by non-linear mechanisms at an altitude of about 100 km and at a small horizontal distance from the explosion
The Nonlinear Model of the Response of Airglow to Gravity Waves
Institute of Scientific and Technical Information of China (English)
J. Y. Xu; H. Gao; A.V. Mikhalev
2005-01-01
In this paper, we develope a timodependent, nonlinear, photochemical-dynamical 2-D model which is composed of 3 models: dynamical gravity wave model, middle atmospheric photochemical model, and airglow layer photochemical model. We use the model to study the effect of the gravity wave propagation on the airglow layer. The comparison between the effects of the different wavelength gravity wave on the airglow emission distributions is made. When the vertical wavelength of the gravity wave is close to or is shorter than the thickness of the airglow layer, the gravity wave can make complex structure of the airglow layer, such as the double and multi-peak structures of the airglow layer. However, the gravity wave that has long vertical wavelength can make large scale perturbation of the airglow emission distribution.
The gravity wave instability induced by photochemistry in summer polar mesopause region
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The effect of diabatic process due to the photochemical heating and cooling on the gravity wave propagation in middle atmosphere is studied. A linear gravity wave model which considers the diabatic process is established. The unstable region and the growth rate of the gravity wave caused by photochemistry are calculated. And the comparison between the model and the adiabatic gravity wave theory of pure dynamics is made. The results indicate that the photochemical heating process can induce the instability of gravity wave at mesopause. The intensity of the instability becomes stronger as the temperature decreases. The temperature feature and the altitude characteristics of the instability are consistent with the observation. Therefore, the instability of the gravity wave induced by photochemistry may be an important mechanism in polar mesopause region in summer.
Gravitational wave signal from massive gravity
Gumrukcuoglu, A Emir; Lin, Chunshan; Mukohyama, Shinji; Tanahashi, Norihiro
2012-01-01
We discuss the detectability of gravitational waves with a time dependent mass contribution, by means of the stochastic gravitational wave observations. Such a mass term typically arises in the cosmological solutions of massive gravity theories. We conduct the analysis based on a general quadratic action, and thus the results apply universally to any massive gravity theories in which modification of general relativity appears primarily in the tensor modes. The primary manifestation of the modification in the gravitational wave spectrum is a sharp peak. The position and height of the peak carry information on the present value of the mass term, as well as the duration of the inflationary stage. We also discuss the detectability of such a gravitational wave signal using the future-planned gravitational wave observatories.
A Two-Wave Scheme for Orographic Gravity Wave Drag Parameterization
Institute of Scientific and Technical Information of China (English)
WANG Yuan; CAI Ninghao; TANG Jinyun
2008-01-01
When the magnitude of sub-scale ographic forcing is comparable with explicitly ordinary dynamic forcing, the drag effect reduced by ographic gravity wave is to be significant for maintaining dynamic balance of atmo-spheric circulation, as well as the momentum and energy transport. Such sub-scale ographic forcing should be introduced into numerically atmospheric model by means of drag being parameterized. Furthermore, the currently mature ographic gravity wave drag (OGWD) parameterization, i.e., the so-called first-generation(based on lineal single-wave theoretical framework) or the second-generation drag parameterization (includ-ing an important extra forcing by the contribution of critical level absorption), cannot correctly and effectly describe the vertical profile of wave stress under the influence of ambient wind shearing. Based on aforemen-tioned consideration, a new two-wave scheme was proposed to parameterize the ographic gravity wave drag by means of freely propagating gravity waves. It starts with a second order WKB approximation, and treats the wave stress attenuations caused by either the selective critical level absorption or the classical critical level absorption explicitly; while in the regions where critical levels are absent, it transports the wave stress vertically by two sinusoidal waves and deposits them and then damps them according to the wave saturation criteria. This scheme is thus used to conduct some sample computations over the Dabie Mountain region of East China, as an example. The results showed that the new two-wave scheme is able to model the vertical distribution of the wave stress more realistically.
The physics of orographic gravity wave drag
Directory of Open Access Journals (Sweden)
MiguelA CTeixeira
2014-07-01
Full Text Available The drag and momentum fluxes produced by gravity waves generated in flow over orography are reviewed, focusing on adiabatic conditions without phase transitions or radiation effects, and steady mean incoming flow. The orographic gravity wave drag is first introduced in its simplest possible form, for inviscid, linearized, non-rotating flow with the Boussinesq and hydrostatic approximations, and constant wind and static stability. Subsequently, the contributions made by previous authors (primarily using theory and numerical simulations to elucidate how the drag is affected by additional physical processes are surveyed. These include the effect of orography anisotropy, vertical wind shear, total and partial critical levels, vertical wave reflection and resonance, non-hydrostatic effects and trapped lee waves, rotation and nonlinearity. Frictional and boundary layer effects are also briefly mentioned. A better understanding of all of these aspects is important for guiding the improvement of drag parametrization schemes.
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.
On the unstable mode merging of gravity-inertial waves with Rossby waves
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J. F. McKenzie
2011-08-01
Full Text Available We recapitulate the results of the combined theory of gravity-inertial-Rossby waves in a rotating, stratified atmosphere. The system is shown to exhibit a "local" (JWKB instability whenever the phase speed of the low-frequency-long wavelength westward propagating Rossby wave exceeds the phase speed ("Kelvin" speed of the high frequency-short wavelength gravity-inertial wave. This condition ensures that mode merging, leading to instability, takes place in some intermediate band of frequencies and wave numbers. The contention that such an instability is "spurious" is not convincing. The energy source of the instability resides in the background enthalpy which can be released by the action of the gravitational buoyancy force, through the combined wave modes.
Solar cycle variation of gravity waves observed in OH airglow
Gelinas, L. J.; Hecht, J. H.; Walterscheid, R. L.; Reid, I. M.; Woithe, J.; Vincent, R. A.
2013-12-01
Airglow imaging provides a unique means by which to study many wave-related phenomena in the 80 to 100 km altitude regime. Two-dimensional image observations reveal quasi-monochromatic disturbances associated with atmospheric gravity waves (AGWs) as well as small-scale instabilities, often called ripples. Image-averaged temperature and intensity measurements can be used to study the response of the airglow layer to tides and planetary waves, as well as monitor longer-term climatological variations. Here we present results of low and mid-latitude OH airglow observations beginning near solar max of solar cycle 23 and continuing through solar max of cycle 24. Aerospace imagers deployed at Alice Springs (23o42'S, 133o53'E) and Adelaide (34o55'S, 138o36'E) have been operating nearly continuously since ~2001. The imagers employ filters measuring OH Meinel (6, 2) and O2 Atmospheric (0, 1) band emission intensities and temperatures, as well as atmospheric gravity wave parameters. The Aerospace Corporation's Infrared Camera deployed at Maui, HI (20.7N,156.3W), collected more than 700 nights of airglow images from 2002-2005. The camera measures the OH Meinel (4,2) emission at 1.6 um using a 1 second exposure at a 3 second cadence, which allows the study of AGW and ripple features over very short temporal and spatial scales. The camera was relocated to Cerro Pachon, Chile (30.1 S, 70.8 W) and has been operating continuously since 2010. Temperature, intensity and gravity wave climatologies derived from the two Australian airglow imagers span a full solar cycle (solar max to solar max). Emission intensities have been calibrated using background stars, and temperatures have been calibrated with respect to TIMED/SABER temperatures, reducing the influence of instrument degradation on the solar cycle climatology. An automated wave detection algorithm is used to identify quasi monochromatic wave features in the airglow data, including wavelength, wave period and propagation
Directory of Open Access Journals (Sweden)
A. J. Gerrard
2011-05-01
Full Text Available Observations of in-situ generated atmospheric gravity waves associated with a stratospheric temperature enhancement (STE are presented. Two sets of gravity waves are observed by molecular-aerosol lidar in conjunction with the early December 2000 STE event above Sondrestrom, Greenland. The first set of gravity waves shows downward phase progression with a vertical wavelength of ~8 km while the second set shows upward phase progression with a vertical wavelength of ~9 km. With estimates of the background wind fields from synoptic analyses, the various intrinsic gravity wave parameters of these two wave structures are found. The observed waves compare well to numerical modeling predictions, though the potential observation of a downward propagating wave would be unexpected.
Propagation of gravity wave packet near critical level
Institute of Scientific and Technical Information of China (English)
YUE Xianchang; YI Fan
2005-01-01
A couple of two-dimensional linear and fully nonlinear numerical models for compressible atmosphere are used to numerically study the propagation of the gravity wave packet into a mean wind shear. For a linear propagation wave packet, the critical level interactions are in good agreement with the linear critical level theory. The dynamically and convectively unstable regions are formed due to the critical level interaction of a finite-amplitude wave packet, but they would not break. The free exchange of potential energy with kinetic energy in the background atmosphere at rest ceases after entering the mean wind shear. However, it still goes on in the nonlinear propagation. It is shown that the nonlinear effects modify the mean flow markedly, reduce the momentum and energy propagation velocity and drop the elevation of the critical level.The gravity wave packet becomes unstable and breaks down into smaller scales in some regions. It expends much more kinetic energy than potential energy in the early phase of the breakdown. This means that the wave breakdown sets up due to the action of the shear instability rather than a convective one.
Inertio Gravity Waves in the Upper Mesosphere
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.
Cause of winter gravity wave spectrum saturation
Institute of Scientific and Technical Information of China (English)
WU; Yongfu; XU; Jiyao
2005-01-01
This paper utilizes horizontal velocity measurements observed from 19 chaff rockets and nearly simultaneous temperature measurements collected from 19 falling sphere rockets to study the cause of winter gravity wave spectrum saturation. Results suggest that strong horizontal velocity shears larger than 0.04 s-1 are observed to be present at various heights near the winter mesopause. On one single chaff rocket flight, an extremely strong horizontal velocity shear as high as 0.33 s-1 is observed at 87.4 km and is believed to be the strongest value ever measured in the mesosphere. These strong horizontal velocity shears, together with Brunt-V(a)is(a)l(a) frequency squared obtained from the temperature profile, act collectively to yield two dynamical instability regions of Richardson number smaller than 1/4, suggesting that the saturated gravity wave spectrum observed by the chaff rockets in winter is a result of dynamical instability.
Gravity Waves from Chain Inflation
Ashoorioon, Amjad
2008-01-01
Chain inflation proceeds through a series of first order phase transitions, which can release considerable gravitational waves (GW). We demonstrate that bubble collisions can leave an observable signature for future high-frequency probes of GWs, such as advanced LIGO, LISA and BBO. A "smoking gun" for chain inflation would be wiggles in the spectrum (and consequently in the tensor spectral index) due to the multiple phase transitions. The spectrum could also be distinguished from a single first order phase transition by a small difference in the amplitude at low frequency. A second origin of GWs in chain inflation are tensor modes from quantum fluctuations; these GW can dominate and be observed on large scales. The consistency relation between scalar and tensor modes is different for chain inflation than for standard rolling models and is testable by Cosmic Microwave Background experiments. If inflation happened through a series of rapid tunnelings in the string landscape, future high frequency probes of GW c...
Gravity Waves, Chaos, and Spinning Compact Binaries
Levin, Janna
1999-01-01
Spinning compact binaries are shown to be chaotic in the Post-Newtonian expansion of the two body system. Chaos by definition is the extreme sensitivity to initial conditions and a consequent inability to predict the outcome of the evolution. As a result, the spinning pair will have unpredictable gravitational waveforms during coalescence. This poses a challenge to future gravity wave observatories which rely on a match between the data and a theoretical template.
Investigation of gravity waves using horizontally resolved radial velocity measurements
Directory of Open Access Journals (Sweden)
G. Stober
2013-06-01
Full Text Available The Middle Atmosphere Alomar Radar System (MAARSY on the island Andøya in Northern Norway (69.3° N, 16.0° E observes polar mesospheric summer echoes (PMSE. These echoes are used as tracers of atmospheric dynamics to investigate the horizontal wind variability at high temporal and spatial resolution. MAARSY has the capability of a pulse-to-pulse beam steering allowing for systematic scanning experiments to study the horizontal structure of the backscatterers as well as to measure the radial velocities for each beam direction. Here we present a method to retrieve gravity wave parameters from these horizontally resolved radial wind variations by applying velocity azimuth display and volume velocity processing. Based on the observations a detailed comparison of the two wind analysis techniques is carried out in order to determine the zonal and meridional wind as well as to measure first order inhomogeneities. Further, we demonstrate the possibility to resolve the horizontal wave properties, e.g. horizontal wavelength, phase velocity and propagation direction. The robustness of the estimated gravity wave parameters is tested by a simple atmospheric model.
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.
Buoyancy waves in Pluto's high atmosphere: Implications for stellar occultations
Hubbard, W. B.; McCarthy, D. W.; Kulesa, C. A.; Benecchi, S. D.; Person, M. J.; Elliot, J. L.; Gulbis, A.A.S.
2009-01-01
We apply scintillation theory to stellar signal fluctuations in the high-resolution, high signal/noise, dual-wavelength data from the MMT observation of the 2007 March 18 occultation of P445.3 by Pluto. A well-defined high wavenumber cutoff in the fluctuations is consistent with viscous-thermal dissipation of buoyancy waves (internal gravity waves) in Pluto’s high atmosphere, and provides strong evidence that the underlying density fluctuations are governed by the gravity-wave dispersion rela...
Does the Madden-Julian Oscillation Modulate Stratospheric Gravity Waves?
Moss, Andrew; Wright, Corwin; Mitchell, Nicholas
2016-04-01
The circulation of the stratosphere is strongly influenced by the fluxes of gravity waves propagating from tropospheric sources. In the tropics, these gravity waves are primarily generated by convection. The Madden-Julian Oscillation (MJO) dominates the intra-seasonal variability of this convection. However, the connection between the MJO and the variability of stratospheric gravity waves is largely unknown. Here we examine gravity-wave potential energy at a height of 26 km and the upper tropospheric zonal-wind anomaly of the MJO at the 200 hPa level, sorted by the relative phase of the MJO using the RMM MJO indices. We show that a strong anti-correlation exists between gravity-wave potential energy and the MJO eastward wind anomaly. We propose that this correlation is a result of the filtering of ascending waves by the MJO winds. The study provides evidence that the MJO contributes significantly to the variability of stratospheric gravity waves in the tropics.
Wavelet transforms of meteorological parameters and gravity waves
Directory of Open Access Journals (Sweden)
Z. Can
2005-03-01
Full Text Available The main purpose of this paper is to analyze some characteristics of gravity waves (GWs, and seasonal variations of atmospheric waves over Istanbul by using wavelet techniques. Daily radiosonda data of Istanbul in the troposphere and lower stratosphere (1000hPa-30hPa between 1993 and 1997 have been considered. Wavelet analysis based on a computer simulation of data is generally close to the real data when Daubechies wavelet series are used. Daily, monthly, seasonal and annual variations of pressure heights, air temperature and deviations from mean values have been analyzed. Variations show the effects of gravity waves for different pressure levels in the troposphere. These waves lead to the meso-scale wave-form structures in spring, autumn and winter. As a result of this study, wavelet series and transforms for data construction, definition of some discontinuities and the local effects on the signal have been compared with the results of previous studies. The most similar structure between temperature, turbulence parameters and geo-potential height deviations has been defined at the 500-hPa pressure level.
Wave Propagation in Accretion Disks with Self-Gravity
Institute of Scientific and Technical Information of China (English)
LIU Xiao-Ci; YANG Lan-Tian; WU Shao-Ping; DING Shi-Xue
2001-01-01
We extend the research by Lubow and Pringle of axisymmetric waves in accretion disks to the case where self gravity of disks should be considered. We derive and analyse the dispersion relations with the effect of self-gravity. Results show that self-gravity extends the forbidden region of the wave propagation: for high frequency p-modes, self-gravity makes the wavelength shorter and the group velocity larger; for low frequency g-modes, the effect is opposite.
Mesoscale Gravity Wave Variances from AMSU-A Radiances
Wu, Dong L.
2004-01-01
A variance analysis technique is developed here to extract gravity wave (GW) induced temperature fluctuations from NOAA AMSU-A (Advanced Microwave Sounding Unit-A) radiance measurements. By carefully removing the instrument/measurement noise, the algorithm can produce reliable GW variances with the minimum detectable value as small as 0.1 K2. Preliminary analyses with AMSU-A data show GW variance maps in the stratosphere have very similar distributions to those found with the UARS MLS (Upper Atmosphere Research Satellite Microwave Limb Sounder). However, the AMSU-A offers better horizontal and temporal resolution for observing regional GW variability, such as activity over sub-Antarctic islands.
Dipole gravity waves from unbound quadrupoles
Felber, Franklin
2010-01-01
Dipole gravitational disturbances from gravitationally unbound mass quadrupoles propagate to the radiation zone with signal strength at least of quadrupole order if the quadrupoles are nonrelativistic, and of dipole order if relativistic. Angular distributions of parallel-polarized and transverse-polarized dipole power in the radiation zone are calculated for simple unbound quadrupoles, like a linear-oscillator/stress-wave pair and a particle storage ring. Laboratory tests of general relativity through measurements of dipole gravity waves in the source region are proposed. A NASA G2 flywheel module with a modified rotor can produce a post-Newtonian dc bias signal at a gradiometer up to 1 mE. At peak luminosity, the repulsive dipole impulses of proton bunches at the LHC can produce an rms velocity of a high-Q detector surface up to 4 micron/s. Far outside the source region, Newtonian lunar dipole gravity waves can produce a 1-cm displacement signal at LISA. Dipole signal strengths of astrophysical events invol...
Conversion of Internal Gravity Waves into Magnetic Waves
Lecoanet, Daniel; Fuller, Jim; Cantiello, Matteo; Burns, Keaton J
2016-01-01
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) suggests 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 canno...
On the atmospheric internal ship waves
Institute of Scientific and Technical Information of China (English)
桑建国
1997-01-01
The analytical solutions of the atmospheric internal ship waves induced by three-dimensional terrain are obtained by solving the atmospheric wave equation. The solutions show that the waves consist of the untrapped and trapped parts. The patterns of the diverging wave and transverse wave in the untrapped parts are mainly determined by the shape and orientation of the terrain. This kind of wave may transport the wave energy to the upper atmosphere. The patterns of trapped lee waves are decided by the atmospheric conditions such as stratification, mean wind speeds and wind shear.
Cao, Bing; Liu, Alan Z.
2016-07-01
Many long-term observations, such as airglow imaging, have shown that gravity waves exist in the mesopause region most of the time. These waves deposit momentum and energy into the background atmosphere when dissipating, and thus exert strong influence to the atmosphere. In this study, we focus on (1) the climatology of gravity waves characteristics, (2) the intermittency of gravity wave momentum flux and (3) the duration/lifespan of gravity wave events. These properties have important implications for gravity wave parameterizations. This study is based on multi-year all sky OH airglow observations obtained at Maui, HI (20.7° N, 156.3° W) and the Andes Lidar Observatory in Chile (30.3° S, 70.7° W). The statistical distribution of intrinsic wave parameters and the momentum flux are analyzed. The probability density functions of gravity wave momentum flux and duration can be described by simple functions and are related to the gravity wave intermittency. The probability distributions of the two sites have some similarity but with noticeable differences, indicating different effects of the background flow and wave source on the gravity wave intermittency in the mesopause region.
Nonstationary Gravity Wave Forcing of the Stratospheric Zonal Mean Wind
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.
Deep-water gravity waves: theoretical estimating of wave parameters
Mindlin, Ilia M
2014-01-01
This paper addresses deep-water gravity waves of finite amplitude generated by an initial disturbance to the water. It is assumed that the horizontal dimensions of the initially disturbed body of the water are much larger than the magnitude of the free surface displacement in the origin of the waves. Initially the free surface has not yet been displaced from its equilibrium position, but the velocity field has already become different from zero. This means that the water at rest initially is set in motion suddenly by an impulse. Duration of formation of the wave origin and the maximum water elevation in the origin are estimated using the arrival times of the waves and the maximum wave-heights at certain locations obtained from gauge records at the locations, and the distances between the centre of the origin and each of the locations. For points situated at a long distance from the wave origin, forecast is made for the travel time and wave height at the points. The forecast is based on the data recorded by th...
Mixa, T.; Fritts, D. C.; Laughman, B.; Wang, L.; Kantha, L. H.
2015-12-01
Multiple observations provide compelling evidence that gravity wave dissipation events often occur in multi-scale environments having highly-structured wind and stability profiles extending from the stable boundary layer into the mesosphere and lower thermosphere. Such events tend to be highly localized and thus yield local energy and momentum deposition and efficient secondary gravity wave generation expected to have strong influences at higher altitudes [e.g., Fritts et al., 2013; Baumgarten and Fritts, 2014]. Lidars, radars, and airglow imagers typically cannot achieve the spatial resolution needed to fully quantify these small-scale instability dynamics. Hence, we employ high-resolution modeling to explore these dynamics in representative environments. Specifically, we describe numerical studies of gravity wave packets impinging on a sheet of high stratification and shear and the resulting instabilities and impacts on the gravity wave amplitude and momentum flux for various flow and gravity wave parameters. References: Baumgarten, Gerd, and David C. Fritts (2014). Quantifying Kelvin-Helmholtz instability dynamics observed in noctilucent clouds: 1. Methods and observations. Journal of Geophysical Research: Atmospheres, 119.15, 9324-9337. Fritts, D. C., Wang, L., & Werne, J. A. (2013). Gravity wave-fine structure interactions. Part I: Influences of fine structure form and orientation on flow evolution and instability. Journal of the Atmospheric Sciences, 70(12), 3710-3734.
Simulation of response of sodium layer to the propagation of gravity wave
Institute of Scientific and Technical Information of China (English)
XU Jiyao
2004-01-01
A time-dependent two-dimensional photochemical-dynamical coupling gravity wave model of sodium layer is developed, which combines the sodium photochemical theory, a time-dependent two-dimensional atmospheric photochemical model, a two-dimensional gravity wave model, and the International Reference Ionosphere model (IRI-95)with the diabatic process induced by photochemical reactions and the transport of chemical species by gravity waves included. The pseudospectral method is used in the horizontal direction, the finite difference approximations are used in vertical direction z and time t. And FICE method is used to solve the model. The simulation results indicate that intense perturbations of the sodium layer can be induced by the propagation of gravity waves. The results are consistent with the observations.
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'. PMID:27550763
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
Wave Equations for Discrete Quantum Gravity
Gudder, Stan
2015-01-01
This article is based on the covariant causal set ($c$-causet) approach to discrete quantum gravity. A $c$-causet $x$ is a finite partially ordered set that has a unique labeling of its vertices. A rate of change on $x$ is described by a covariant difference operator and this operator acting on a wave function forms the left side of the wave equation. The right side is given by an energy term acting on the wave function. Solutions to the wave equation corresponding to certain pairs of paths in $x$ are added and normalized to form a unique state. The modulus squared of the state gives probabilities that a pair of interacting particles is at various locations given by pairs of vertices in $x$. We illustrate this model for a few of the simplest nontrivial examples of $c$-causets. Three forces are considered, the attractive and repulsive electric forces and the strong nuclear force. Large models get much more complicated and will probably require a computer to analyze.
Ionospheric acoustic and gravity waves associated with midlatitude thunderstorms
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.
AdS Waves as Exact Solutions to Quadratic Gravity
Gullu, Ibrahim; Sisman, Tahsin Cagri; Tekin, Bayram
2011-01-01
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.
Mesosphere Dynamics with Gravity Wave Forcing. 2; Planetary Waves
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 Ripple over Marine Stratocumulus Clouds
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.
Gravity wave penetration into the thermosphere: sensitivity to solar cycle variations and mean winds
Directory of Open Access Journals (Sweden)
D. C. Fritts
2008-12-01
Full Text Available We previously considered various aspects of gravity wave penetration and effects at mesospheric and thermospheric altitudes, including propagation, viscous effects on wave structure, characteristics, and damping, local body forcing, responses to solar cycle temperature variations, and filtering by mean winds. Several of these efforts focused on gravity waves arising from deep convection or in situ body forcing accompanying wave dissipation. Here we generalize these results to a broad range of gravity wave phase speeds, spatial scales, and intrinsic frequencies in order to address all of the major gravity wave sources in the lower atmosphere potentially impacting the thermosphere. We show how penetration altitudes depend on gravity wave phase speed, horizontal and vertical wavelengths, and observed frequencies for a range of thermospheric temperatures spanning realistic solar conditions and winds spanning reasonable mean and tidal amplitudes. Our results emphasize that independent of gravity wave source, thermospheric temperature, and filtering conditions, those gravity waves that penetrate to the highest altitudes have increasing vertical wavelengths and decreasing intrinsic frequencies with increasing altitude. The spatial scales at the highest altitudes at which gravity wave perturbations are observed are inevitably horizontal wavelengths of ~150 to 1000 km and vertical wavelengths of ~150 to 500 km or more, with the larger horizontal scales only becoming important for the stronger Doppler-shifting conditions. Observed and intrinsic periods are typically ~10 to 60 min and ~10 to 30 min, respectively, with the intrinsic periods shorter at the highest altitudes because of preferential penetration of GWs that are up-shifted in frequency by thermospheric winds.
Simulations of Atmospheric Neutral Wave Coupling to the Ionosphere
Siefring, C. L.; Bernhardt, P. A.
2005-12-01
The densities in the E- and F-layer plasmas are much less than the density of background neutral atmosphere. Atmospheric neutral waves are primary sources of plasma density fluctuations and are the sources for triggering plasma instabilities. The neutral atmosphere supports acoustic waves, acoustic gravity waves, and Kelvin Helmholtz waves from wind shears. These waves help determine the structure of the ionosphere by changes in neutral density that affect ion-electron recombination and by neutral velocities that couple to the plasma via ion-neutral collisions. Neutral acoustic disturbances can arise from thunderstorms, chemical factory explosions and intentional high-explosive tests. Based on conservation of energy, acoustic waves grow in amplitude as they propagate upwards to lower atmospheric densities. Shock waves can form in an acoustic pulse that is eventually damped by viscosity. Ionospheric effects from acoustic waves include transient perturbations of E- and F-Regions and triggering of E-Region instabilities. Acoustic-gravity waves affect the ionosphere over large distances. Gravity wave sources include thunderstorms, auroral region disturbances, Space Shuttle launches and possibly solar eclipses. Low frequency acoustic-gravity waves propagate to yield traveling ionospheric disturbances (TID's), triggering of Equatorial bubbles, and possible periodic structuring of the E-Region. Gravity wave triggering of equatorial bubbles is studied numerically by solving the equations for plasma continuity and ion velocity along with Ohms law to provide an equation for the induced electric potential. Slow moving gravity waves provide density depressions on bottom of ionosphere and a gravitational Rayleigh-Taylor instability is initiated. Radar scatter detects field aligned irregularities in the resulting plasma bubble. Neutral Kelvin-Helmholtz waves are produced by strong mesospheric wind shears that are also coincident with the formation of intense E-layers. An
New Gravity Wave Treatments for GISS Climate Models
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.
Electromagnetic inertio-gravity waves in the ionospheric E-layer
Energy Technology Data Exchange (ETDEWEB)
Kaladze, T D [Physics Department, GC University, Lahore 54000 (Pakistan); Pokhotelov, O A [Automatic Control and Systems Engineering, University of Sheffield, Sheffield (United Kingdom); Stenflo, L [Department of Plasma Physics, Umeaa University, SE-90187 Umeaa (Sweden); Shah, H A [Physics Department, GC University, Lahore 54000 (Pakistan); Jandieri, G V [Physics Department, Georgian Technical University, 77 Kostava Street, 0175 Tbilisi (Georgia)
2007-10-15
The effect of the Ampere force on inertio-gravity (IG) waves in the partially ionized ionospheric E-layer is considered. Electromagnetic IG waves are then studied. It is shown that the free energy necessary for linear instability of electromagnetic IG waves arises from the field-aligned current. Furthermore, it is found that atmospheric vortex motions can induce substantial variations in the geomagnetic field and field-aligned currents.
Directory of Open Access Journals (Sweden)
M. Sivakandan
2015-08-01
Full Text Available The image observations of mesospheric O(1S 558 nm have been performed from a low latitude Indian station, Gadanki (13.5° N; 79.2° E using a CCD based all sky camera system. Based on three years (from year 2012 to the year 2014 of image data during March–April, we characterize the small scale gravity wave properties. We noted 50 strong gravity wave event and 19 ripple events to occur. The horizontal wavelengths of the gravity waves are found to vary from 12 to 42 km with the phase velocity ranging from 20 to 90 km. In most cases, these waves were propagating towards north with only a few occasions of southward propagation. The outgoing longwave radiation data suggest that lower atmospheric convection was most possible reason for the generation of the waves observed in the airglow data.
Rossby Wave Instability with Self-Gravity
Lovelace, R V E
2012-01-01
The Rossby wave instability (RWI) in non-self-gravitating discs can be triggered by a bump at a radius $r_0$ in the disc surface mass-density (which is proportional to the inverse potential vorticity). It gives rise to a growing non-axisymmetric perturbation [$\\propto \\exp(im\\phi)$, $m=1,2..$] in the vicinity of $r_0$ consisting of anticyclonic vortices which may facilitate planetesimal growth in protoplanetary discs. Here, we analyze a continuum of thin disc models ranging from self-gravitating to non-selfgravitating. The key quantities determining the stability/instability are: (1) the parameters of the bump (or depression) in the disc surface density, (2) the Toomre $Q$ parameter of the disc (a non-self-gravitating disc has $Q\\gg1$), and (3) the dimensionless azimuthal wavenumber of the perturbation $\\bar{k}_\\phi =mQh/r_0$, where $h$ is the half-thickness of the disc. For discs stable to axisymmetric perturbations ($Q>1$), the self-gravity has a significant role for $\\bar{k}_\\phi \\pi/2$ the self-gravity i...
Realistic inflation models and primordial gravity waves
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.
Freely decaying weak turbulence for sea surface gravity waves
Onorato, M.; Osborne, A. R.; Resio, D.; Pushkarev, A.; Zakharov, V.; Serio, M.; Brandini, C.
2002-01-01
We study numerically the generation of power laws in the framework of weak turbulence theory for surface gravity waves in deep water. Starting from a random wave field, we let the system evolve numerically according to the nonlinear Euler equations for gravity waves in infinitely deep water. In agreement with the theory of Zakharov and Filonenko, we find the formation of a power spectrum characterized by a power law of the form of $|{\\bf k}|^{-2.5}$.
Surface gravity waves at equilibrium with a steady wind
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.
A Comparison Between Gravity Wave Momentum Fluxes in Observations and Climate Models
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.
Infra-Gravity Wave Generation by the Shoaling Wave Groups over Beaches
Institute of Scientific and Technical Information of China (English)
LIN Yu-Hsien; HWUNG Hwung-Hweng
2012-01-01
A physical parameter,μb,which was used to meet the forcing of primary short waves to be off-resonant before wave breaking,has been considered as an applicable parameter in the infra-gravity wave generation.Since a series of modulating wave groups for different wave conditions are performed to proceed with the resonant mechanism of infragravity waves prior to wave breaking,the amplitude growth of incident bound long wave is assumed to be simply controlled by the normalized bed slope,βb.The results appear a large dependence of the growth rate,α,of incident bound long wave,separated by the three-array method,on the normalized bed slope,βb.High spatial resolution of wave records enables identification of the cross-correlation between squared short-wave envelopes and infra-gravity waves.The crossshore structure of infra-gravity waves over beaches presents the mechanics of incident bound- and outgoing free long waves with the formation of free standing long waves in the nearshore region.The wave run-up and amplification of infra-gravity waves in the swash zone appear that the additional long waves generated by the breaking process would modify the cross-shore structure of free standing long waves.Finally,this paper would further discuss the contribution of long wave breaking and bottom friction to the energy dissipation of infra-gravity waves based on different slope conditions.
Possibility of measuring gravity-wave momentum flux by single beam observation of MST radar
Liu, C. H.
1986-01-01
Vincent and Reid (1983) proposed a technique to measure gravity-wave momentum fluxes in the atmosphere by mesosphere-stratosphere-troposphere (MST) radars using two or more radar beams. Since the vertical momentum fluxes are assumed to be due to gravity waves, it appears possible to make use of the dispersion and polarization relations for gravity waves in extracting useful information from the radar data. In particular, for an oblique radar beam, information about both the vertical and the horizontal velocities associated with the waves are contained in the measured Doppler data. Therefore, it should be possible to extract both V sub Z and V sub h from a single beam observational configuration. A procedure is proposed to perform such an analysis. The basic assumptions are: the measured velocity fluctuations are due to gravity waves and a separable model gravity-wave spectrum of the Garrett-Munk type that is statistically homogeneous in the horizontal plane. Analytical expressions can be derived that relate the observed velocity fluctuations to the wave momentum flux at each range gate. In practice, the uncertainties related to the model parameters and measurement accuracy will affect the results. A MST radar configuration is considered.
LINEAR GRAVITY WAVES ON MAXWELL FLUIDS OF FINITE DEPTH
Institute of Scientific and Technical Information of China (English)
ZHANG Qinghe; SUN Yabin
2004-01-01
Linear surface gravity waves on Maxwell viscoelastic fluids with finite depth are studied in this paper. A dispersion equation describing the spatial decay of the gravity wave in finite depth is derived. A dimensionless memory (time) number θ is introduced. The dispersion equation for the pure viscous fluid will be a specific case of the dispersion equation for the viscoelastic fluid as θ = 0. The complex dispersion equation is numerically solved to investigate the dispersion relation. The influences of θ and water depth on the dispersion characteristics and wave decay are discussed. It is found that the role of elasticity for the Maxwell fluid is to make the surface gravity wave on the Maxwell fluid behave more like the surface gravity wave on the inviscid fluid.
Bruntz, R. J.; Paxton, L. J.; Miller, E. S.; Bust, G. S.; Mayr, H. G.
2015-12-01
The Transfer Function Model (TFM) has been used in numerous studies to simulate gravity waves. In the TFM, the time dependence is formulated in terms of frequencies, and the horizontal wave pattern on the globe is formulated in terms of vector spherical harmonics. For a wide range of frequencies, the equations of mass, energy and momentum conservation are solved to compile a transfer function. The transfer function can then be easily combined with a time-dependent source whose spatial extent is also expressed in spherical harmonics, to produce a global atmospheric response, including gravity waves. This approach has significant benefits in that the solution is grid-independent (without any inherent limits on resolution), and the solutions do not suffer from singularities at the poles. We will show results from our simulations that couple the output of the TFM to an ionospheric model, to predict traveling ionospheric disturbances (TIDs) driven by the simulated gravity waves.
Nonlocal resonances in weak turbulence of gravity-capillary waves.
Aubourg, Quentin; Mordant, Nicolas
2015-04-10
We report a laboratory investigation of weak turbulence of water surface waves in the gravity-capillary crossover. By using time-space-resolved profilometry and a bicoherence analysis, we observe that the nonlinear processes involve three-wave resonant interactions. By studying the solutions of the resonance conditions, we show that the nonlinear interaction is dominantly one dimensional and involves collinear wave vectors. Furthermore, taking into account the spectral widening due to weak nonlinearity explains why nonlocal interactions are possible between a gravity wave and high-frequency capillary ones. We observe also that nonlinear three-wave coupling is possible among gravity waves, and we raise the question of the relevance of this mechanism for oceanic waves. PMID:25910127
A Simple Theory of Capillary-Gravity Wave Turbulence
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.
Massive gravitational waves in Chern-Simons modified gravity
Energy Technology Data Exchange (ETDEWEB)
Myung, Yun Soo; Moon, Taeyoon, E-mail: ysmyung@inje.ac.kr, E-mail: tymoon@inje.ac.kr [Institute of Basic Science and Department of Computer Simulation, Inje University, Gimhae 621-749 (Korea, Republic of)
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.
AdS Waves as Exact Solutions to Quadratic Gravity
Gullu, Ibrahim; Gurses, Metin; Sisman, Tahsin Cagri; Tekin, Bayram(Department of Physics, Middle East Technical University, 06800 Ankara, Turkey)
2011-01-01
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.
Angular Momentum Transport via Internal Gravity Waves in Evolving Stars
Fuller, Jim; Cantiello, Matteo; Brown, Ben
2014-01-01
Recent asteroseismic advances have allowed for direct measurements of the internal rotation rates of many sub-giant 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 sub-giants, 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 sub-giant branch when stars have surface temperatures of roughly 5500 K. However, gravity waves can s...
Laser Source for Atomic Gravity Wave Detector Project
National Aeronautics and Space Administration — Develop an Atom Interferometry-based gravity wave detector (vs Optical Interferometry). Characterize a high power laser. Use Goddard Space Flight Center Mission...
The study and applications of photochemical-dynamical gravity wave model Ⅰ--Model description
Institute of Scientific and Technical Information of China (English)
XU; Jiyao(徐寄遥); MA; Ruiping(马瑞平); A.K.Smith
2002-01-01
A two-dimensional, nonlinear, compressible, diabatic, nonhydrostatic photochemical- dynamical gravity wave model has been advanced. The model includes diabetic process produced by photochemistry and the effect of gravity wave on atmospheric chemical species. In the horizontal direction, the pseudospectral method is used. The finite difference approximations are used in vertical direction z and time t. The FICE method is used to solve the model. The model results on small amplitude fluctuation are very close to those of linear theory, which demonstrates the correctness of the model.
(abstract) Tropospheric Calibration for the Mars Observer Gravity Wave Experiment
Walter, Steven J.; Armstrong, John
1994-01-01
In spring 1993, microwave radiometer-based tropospheric calibration was provided for the Mars Observer gravitational wave search. The Doppler shifted X-band radio signals propagating between Earth and the Mars Observer satellite were precisely measured to determine path length variations that might signal passage of gravitational waves. Experimental sensitivity was restricted by competing sources of variability in signal transit time. Principally, fluctuations in the solar wind and ionospheric plasma density combined with fluctions in tropospheric refractivity determined the detection limit. Troposphere-induced path delay fluctions are dominated by refractive changes caused by water vapor inhomogeneities blowing through the signal path. Since passive microwave remote sensing techniques are able to determine atmospheric propagation delays, radiometer-based tropospheric calibration was provided at the Deep Space Network Uranus tracking site (DSS-15). Two microwave water vapor radiometers (WVRs), a microwave temperature profiler (MTP), and a ground based meterological station were deployed to determine line-of-sight vapor content and vertical temperature profile concurrently with Mars Observer tracking measurements. This calibration system provided the capability to correct Mars Observer Doppler data for troposphere-induced path variations. We present preliminary analysis of the Doppler and WVR data sets illustrating the utility of WVRs to calibrate Doppler data. This takes an important step toward realizing the ambitious system required to support future Ka-band Cassini satellite gravity wave tropospheric calibration system.
Wrasse, Cristiano M.; Gobbi, Delano; Buriti, Ricardo; Bageston, José Valentin; Medeiros, Amauri; Paulino, Igo; Cosme Alexandre Figueiredo, M.; Takahashi, Hisao; Azambuja, Rodrigo
2016-07-01
All-sky imager was used to observe the wave activity in the mesosphere and a ground network of GPS receivers were used to make detrended Total Electron Content (dTEC) maps to monitor the ionosphere. The wave activity was observed on September 16th 2015 over the southeast region in Brazil. The gravity wave characteristics and the atmospheric conditions for wave propagation will be presented and discussed. The gravity wave source was associated with strong tropospheric convection.
Magellan radio occultation measurements of atmospheric waves on Venus
Hinson, David P.; Jenkins, J. M.
1995-01-01
Radio occultation experiments were conducted at Venus on three consecutive orbits of the Magellan spacecraft in October 1991. Each occultation occurred over the same topography (67 deg N, 127 deg E) and at the same local time (22 hr 5 min), but the data are sensitive to zonal variations because the atmosphere rotates significantly during one orbit. Through comparisons between observations and predictions of standard wave theory, we have demonstrated that small-scale oscillations in retrieved temperature profiles as well as scintillations in received signal intensity are caused by a spectrum of vertically propagating internal gravity waves. There is a strong similarity between the intensity scintillations observed here and previous measurements, which pertain to a wide range of locations and experiment dates. This implies that the same basic phenomenon underlies all the observations and hence that gravity waves are a persistent, global feature of Venus' atmosphere. We obtained a fairly complete characterization of a gravity wave that appears above the middle cloud in temperature measurements on all three orbits. The amplitude and vertical wavelength are about 4 K and 2.5 km respectively, at 65 km. A model for radiative damping implies that the wave intrinsic frequency is approximately 2 x 10(exp 4) rad/sec, the corresponding ratio between horizontal and vertical wavelengths is approximately 100. The wave is nearly stationary relative to the surface or the Sun. Radiative attenuation limits the wave amplitude at altitudes above approximately 65 km, leading to wave drag on the mean zonal winds of about +0.4 m/sec per day (eastward). The sign, magnitude, and location of this forcing suggest a possible role in explaining the decrease with height in the zonal wind speed that is believed to occur above the cloud tops. Temperature oscillations with larger vertical wavelengths (5-10 km) were also observed on all three orbits, but we are able unable to interpret these
Yigit, E.; Medvedev, A. S.; Aylward, A. D.; Hartogh, P.; Harris, M. J.
2009-01-01
A nonlinear spectral gravity wave (GW) drag parameterization systematically accounting for breaking and dissipation in the thermosphere developed by Yigit et al. (2008) has been implemented into the University College London Coupled Middle Atmosphere-Thermosphere-2 (CMAT2) general circulation model (GCM). The dynamical role of GWs propagating upward from the lower atmosphere has been studied in a series of GCM tests for June solstice conditions. The results suggest that GW drag is not only no...
Interaction of modulated gravity water waves of finite depth
Giannoulis, Ioannis
2016-10-01
We consider the capillary-gravity water wave problem of finite depth with a flat bottom of one or two horizontal dimensions. We derive the modulation equations of leading and next-to-leading order in the hyperbolic scaling for three weakly amplitude-modulated plane wave solutions of the linearized problem in the absence of quadratic and cubic resonances. We justify the derived system of macroscopic equations in the case of gravity waves using the stability of the finite depth water wave problem on the time scale O (1 / ɛ).
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
Tidal and gravity waves study from the airglow measurements at Kolhapur (India)
Indian Academy of Sciences (India)
R N Ghodpage; Devendraa Siingh; R P Singh; G K Mukherjee; P Vohat; A K Singh
2012-12-01
Simultaneous photometric measurements of the OI 557.7 nm and OH (7, 2) band from a low latitude station, Kolhapur (16.8°N, 74.2°E) during the period 2004–2007 are analyzed to study the dominant waves present in the 80–100 km altitude region of the atmosphere. The nocturnal intensity variations of different airglow emissions are observed using scanning temperature controlled filter photometers. Waves having period lying between 2 and 12 hours have been recorded. Some of these waves having subharmonic tidal oscillation periods 4, 6, 8 and 12 hours propagate upward with velocity lying in the range 1.6–11.3 m/s and the vertical wave length lying between 28.6 and 163 kms. The other waves may be the upward propagating gravity waves or waves resulting from the interaction of inter-mode tidal oscillations, interaction of tidal waves with planetary waves and gravity waves. Some times, the second harmonic wave has higher vertical velocity than the corresponding fundamental wave. Application of these waves in studying the thermal structure of the region is discussed.
Antarctic MLT Gravity Wave Momentum Flux Observed by the Davis MST Radar
Love, P. T.; Murphy, D. J.
2015-12-01
The MST radar at Davis Station, Antarctica, 68.6 S 78.0 E, was used to make dual coplanar beam measurements of short period (12-60 minutes) gravity wave momentum flux in the mesopause region during the southern hemisphere summer of 2014-2015. Mean zonal and meridional momentum flux estimates are eastward and southward respectively, throughout the region and season, with a bias towards both larger mean flux and number of eastward and southward propagating waves. Lognormal distributions of the absolute momentum flux attributable to individual wave events are broadly consistent with satellite and other middle atmosphere gravity wave observation and modelling techniques, with greater than 40% of the total flux being contributed by the largest 10% of wave events. Estimates of flux divergence are made during periods where sufficient density of observations exist. Ray tracing methods are employed to identify potential source regions and mechanisms to aid the development of meteorologically interactive parameterization schemes for the region.
Massive gravitational waves in Chern-Simons modified gravity
Myung, Yun Soo; Moon, Taeyoon(Institute of Basic Science and Department of Computer Simulation, Inje University, Gimhae, 621-749, Korea)
2014-01-01
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 $\\theta=x/\\mu$ 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 $\\Psi_4$, implying thre...
No further gravitational wave modes in F(T) gravity
International Nuclear Information System (INIS)
We explore the possibility of further gravitational wave modes in F(T) gravity, where T is the torsion scalar in teleparallelism. It is explicitly demonstrated that gravitational wave modes in F(T) gravity are equivalent to those in General Relativity. This result is achieved by calculating the Minkowskian limit for a class of analytic function of F(T). This consequence is also confirmed by the preservative analysis around the flat background in the weak field limit with the scalar–tensor representation of F(T) gravity
No further gravitational wave modes in F(T) gravity
Energy Technology Data Exchange (ETDEWEB)
Bamba, Kazuharu, E-mail: bamba@kmi.nagoya-u.ac.jp [Kobayashi–Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Nagoya 464-8602 (Japan); Capozziello, Salvatore, E-mail: capozziello@na.infn.it [Kobayashi–Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Nagoya 464-8602 (Japan); Dipartimento di Fisica, Università di Napoli “Federico II” (Italy); INFN Sez. di Napoli, Compl. Univ. di Monte S. Angelo, Edificio G, Via Cinthia, I-80126 Napoli (Italy); De Laurentis, Mariafelicia, E-mail: felicia@na.infn.it [Kobayashi–Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Nagoya 464-8602 (Japan); Dipartimento di Fisica, Università di Napoli “Federico II” (Italy); INFN Sez. di Napoli, Compl. Univ. di Monte S. Angelo, Edificio G, Via Cinthia, I-80126 Napoli (Italy); Nojiri, Shin' ichi, E-mail: nojiri@phys.nagoya-u.ac.jp [Kobayashi–Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Nagoya 464-8602 (Japan); Department of Physics, Nagoya University, Nagoya 464-8602 (Japan); Sáez-Gómez, Diego, E-mail: diego.saezgomez@uct.ac.za [Kobayashi–Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Nagoya 464-8602 (Japan); Astrophysics, Cosmology and Gravity Centre (ACGC) and Department of Mathematics and Applied Mathematics, University of Cape Town, Rondebosch 7701, Cape Town (South Africa); Fisika Teorikoaren eta Zientziaren Historia Saila, Zientzia eta Teknologia Fakultatea, Euskal Herriko Unibertsitatea, 644 Posta Kutxatila, 48080 Bilbao (Spain)
2013-11-25
We explore the possibility of further gravitational wave modes in F(T) gravity, where T is the torsion scalar in teleparallelism. It is explicitly demonstrated that gravitational wave modes in F(T) gravity are equivalent to those in General Relativity. This result is achieved by calculating the Minkowskian limit for a class of analytic function of F(T). This consequence is also confirmed by the preservative analysis around the flat background in the weak field limit with the scalar–tensor representation of F(T) gravity.
Direct numerical simulations of gravity-capillary wave turbulence
Deike, Luc; Fuster, Daniel; Berhanu, Michael; Falcon, Eric
2012-11-01
Direct numerical simulation of the full two phase Navier-Stokes equations, including surface tension are performed, using the code Gerris (Popinet, 2009), in order to investigate gravity-capillary wave turbulence. Wave turbulence concerns the study of the statistical and dynamical properties of a set of nonlinear interacting waves (Zakharov, 1992). Waves at the air-water interface, initially at rest, are excited at low wave-numbers and a stationary wave turbulence state is obtained after a time long enough (typically 30 periods of the wave forcing period). The space-time wave height power spectrum is calculated for both capillary and gravity waves regimes. The observed dispersion relation is in agreement with the theoretical one for linear gravity-capillary wave. The wave height power spectrum in the wave-number-space or in the frequency-space exhibit a power law and will be discussed with respects of weak turbulence theory (Zakharov, 2012). Finally the scaling of the spectrum with the injected power will be compared with theoretical and experimental works.
On the parameterization scheme of gravity wave drag effect on the mean zonal flow of mesosphere
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
Based on McFarlane's parameterization scheme of gravity wave drag, a refined gravity-wave-drag scheme is presented. Both the drag effect of the momentum flux and the dissipation effect of gravity wave breaking on the mean zonal flow are included in the refined parameterization scheme. The dissipation effect can be formulated with the gravity wave numbers and the mean quantities. The refined parameterization scheme may represent a complete drag effect of stationary gravity wave breaking on the mean zonal flow.
Pisoft, Petr; Sacha, Petr; Kuchar, Ales
2015-04-01
The gravity waves spectrum is shaped not only by different sources but it also reflects tropospheric background conditions contributing to filtering of various gravity waves. This could be most easily illustrated for the propagation of the orographic gravity waves that are critically filtered when the wind speed is zero. This condition is ensured in case of the directional shear exceeding 180°. Above regions where it is fulfilled, one can rule out the possibility of orographic GW modes contributing to the observed GW activity and vice versa regions of small wind rotation in the lower levels are often precursors of enhanced GW activity higher. In this study, we have performed a global analysis of the background conditions with a focus on the rotation of the ground level winds. We have analyzed MERRA and JRA-55 time series. The results provided climatology of atmospheric regions with the conditions favorable for the upward propagation of the orographic gravity waves from the troposphere into the stratosphere. The regions are detected mainly over areas where tropospheric and stratospheric jets coincide. The study is supplemented by a global analysis of the fields of potential energy of disturbances as a proxy for gravity waves activity using COSMIC GPS RO data.
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. PMID:27136878
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
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.
Institute of Scientific and Technical Information of China (English)
HUANG KaiMing; ZHANG ShaoDong; YI Fan; CHEN ZeYu
2009-01-01
On the basis of previous parameterization schemes, considering both the wave breaking and absorbed at critical level, a parameterization with a continuous spectrum of gravity waves is realized by intro-ducing a momentum flux density function for the wave spectrum, and then the parameterization scheme of the gravity waves is improved. Choosing parameter values of the background atmosphere and waves based on the observations, a more realistic equatorial quasi-biennial oscillation (QBO)driven by the incorporated drag from the planetary and gravity waves can be simulated. The numerical results indicate that the forcing magnitude of the planetary and gravity waves varies with the wind field,and in some phases of the QBO, the contribution of the gravity waves is comparable with that of the planetary waves. After the QBO is steadily formed, its amplitude and period and wind configuration are relevant to the effect of vertical diffusion and the momentum flux distribution with spectrum, however,independent of the initial background wind field. Moreover, for any given nonzero initial background wind, a steady QBO can be finally generated due to the incorporated drag from the planetary and grav-ity waves.
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.
Observation of resonant interactions among surface gravity waves
Bonnefoy, F; Michel, G; Semin, B; Humbert, T; Aumaître, S; Berhanu, M; Falcon, E
2016-01-01
We experimentally study resonant interactions of oblique surface gravity waves in a large basin. Our results strongly extend previous experimental results performed mainly for perpendicular or collinear wave trains. We generate two oblique waves crossing at an acute angle, while we control their frequency ratio, steepnesses and directions. These mother waves mutually interact and give birth to a resonant wave whose properties (growth rate, resonant response curve and phase locking) are fully characterized. All our experimental results are found in good quantitative agreement with four-wave interaction theory with no fitting parameter. Off-resonance experiments are also reported and the relevant theoretical analysis is conducted and validated.
The response of plasma density to breaking inertial gravity wave in the lower regions of ionosphere
Energy Technology Data Exchange (ETDEWEB)
Tang, Wenbo, E-mail: Wenbo.Tang@asu.edu; Mahalov, Alex, E-mail: Alex.Mahalov@asu.edu [School of Mathematical and Statistical Sciences, Arizona State University, Tempe, Arizona 85287 (United States)
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.
PP-waves with torsion and metric-affine gravity
Pasic, Vedad; Vassiliev, Dmitri
2005-01-01
A classical pp-wave is a 4-dimensional Lorentzian spacetime which admits a nonvanishing parallel spinor field; here the connection is assumed to be Levi-Civita. We generalise this definition to metric compatible spacetimes with torsion and describe basic properties of such spacetimes. We use our generalised pp-waves for constructing new explicit vacuum solutions of quadratic metric-affine gravity.
Triad resonance between gravity and vorticity waves in vertical shear
Drivas, Theodore D.; Wunsch, Scott
2016-07-01
Weakly nonlinear theory is used to explore the effect of vertical shear on surface gravity waves in three dimensions. An idealized piecewise-linear shear profile motivated by wind-driven profiles and ambient currents in the ocean is used. It is shown that shear may mediate weakly nonlinear resonant triad interactions between gravity and vorticity waves. The triad results in energy exchange between gravity waves of comparable wavelengths propagating in different directions. For realistic ocean shears, shear-mediated energy exchange may occur on timescales of minutes for shorter wavelengths, but slows as the wavelength increases. Hence this triad mechanism may contribute to the larger angular spreading (relative to wind direction) for shorter wind-waves observed in the oceans.
Diffraction of acoustic-gravity waves in the presence of a turning point.
Godin, Oleg A
2016-07-01
Acoustic-gravity waves (AGWs) in an inhomogeneous atmosphere often have caustics, where the ray theory predicts unphysical, divergent values of the wave amplitude and needs to be modified. Unlike acoustic waves and gravity waves in incompressible fluids, AGW fields in the vicinity of a caustic have never been systematically studied. Here, asymptotic expansions of acoustic gravity waves are derived in the presence of a turning point in a horizontally stratified, moving fluid such as the atmosphere. Sound speed and the background flow (wind) velocity are assumed to vary gradually with height, and slowness of these variations determines the large parameter of the problem. It is found that uniform asymptotic expansions of the wave field in the presence of a turning point can be expressed in terms of the Airy function and its derivative. The geometrical, or Berry, phase, which arises in the consistent Wentzel-Kramers-Brillouin approximation for AGWs, plays an important role in the caustic asymptotics. In the dominant term of the uniform asymptotic solution, the terms with the Airy function and its derivative are weighted by the cosine and sine of the Berry phase, respectively. The physical meaning and corollaries of the asymptotic solutions are discussed. PMID:27475153
Baumgarten, Gerd; Fiedler, Jens; Hildebrand, Jens; Lübken, Franz-Josef
2016-04-01
The observation of wind and temperature perturbations by gravity waves propagating throughout the strato- and mesosphere is a challenging task. Both the kinetic and potential energy density can be derived and yield information about ensemble mean properties of gravity waves. We measure temperatures and winds with the Doppler Rayleigh/Mie/Raman lidar at the ALOMAR research station in Northern Norway (69N, 16E). Using two independently steerable telescopes and lasers we are able to measure vertical profiles of two wind components and temperatures simultaneously. The observations can be performed even under sunlit conditions, which is essential for measuring atmospheric perturbations over several days and during summer at this location. We report on the first observation of persistent inertia gravity wave signatures in the horizontal wind and temperature. The measurements cover the altitude range from 20 km to about 80 km during night and to about 70 km during daytime. For one case with observations lasting more than 50 hours, we find amplitudes of 5 to 25 m/s and 1 to 8 K in wind and temperature, respectively. The measured kinetic to potential energy density ratio is about 10, indicating that the majority of variability is due to waves with intrinsic frequencies close to the inertial frequency. The entire wave field is mainly characterized by the presence of multiple waves, however quasi-monochromatic waves can be identified at limited times and allow a more detailed analysis of wave properties like propagation direction, amplitudes and the momentum flux.
Reflection and Ducting of Gravity Waves Inside the Sun
MacGregor, K. B.; Rogers, T.M.
2011-01-01
Internal gravity waves excited by overshoot at the bottom of the convection zone can be influenced by rotation and by the strong toroidal magnetic field that is likely to be present in the solar tachocline. Using a simple Cartesian model, we show how waves with a vertical component of propagation can be reflected when traveling through a layer containing a horizontal magnetic field with a strength that varies with depth. This interaction can prevent a portion of the downward-traveling wave en...
Efficient computation of capillary-gravity generalized solitary waves
Dutykh, Denys; Duran, Angel
2015-01-01
This paper is devoted to the computation of capillary-gravity solitary waves of the irrotational incompressible Euler equations with free surface. The numerical study is a continuation of a previous work in several points: an alternative formulation of the Babenko-type equation for the wave profiles, a detailed description of both the numerical resolution and the analysis of the internal flow structure under a solitary wave. The numerical code used in this study is provided in open source for interested readers.
Properties of surface waves in granular media under gravity
International Nuclear Information System (INIS)
Acoustical waves propagating along the free surface of granular media under gravity are investigated in the framework of elasticity theory. The influence of stress on a surface wave is analyzed. The results have shown that two types of surface waves, namely sagittal and transverse modes exist depending on initial stress states, which may have some influence on the dispersion relations of surface waves, but the influence is not great. Considering that the present experimental accuracy is far from distinguishing this detail, the validity of elasticity theory on the surface waves propagating in granular media can still be maintained. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
Numerical simulations of ionospheric oscillations caused by coseismic atmospheric waves
Matsumura, M.; Shinagawa, H.; Tsugawa, T.; Saito, A.; Otsuka, Y.; Iyemori, T.
2012-12-01
Following the Mw=9.0 Tohoku earthquake on March 11, 2011, oscillations of total electric content (TEC) were observed in the ionosphere. They propagated with velocities of 140-780m/s from the tsunami source point, and had circular wave fronts [Tsugawa et al., 2011]. The purpose of this study is to simulate these oscillations and to elucidate the generation mechanism of them. In this study, we describe numerical simulations using a coupled model of a two-dimensional tsunami and a three-dimensional atmosphere and ionosphere. Velocity of the sea surface displacement generated by tsunami is implemented in the atmosphere-ionosphere model as the lower boundary condition. The simulations elucidate followings: (1) Oscillations of 420-780m/s are caused by secondary acoustic and gravity waves generated in the thermosphere. They are generated by primary acoustic waves triggered by the sea-surface displacement at the tsunami source point. (2) Oscillations of 140-290m/s are caused by gravity waves generated by tsunami and the tsunami source. They propagate to the thermosphere and attenuate over F1 region. This indicates that the TEC oscillations of 140-290m/s are mainly contributed by F1 or E region.
Snively, J. B.
2013-09-01
Numerical model results demonstrate that acoustic waves generated by tropospheric sources may produce cylindrical "concentric ring" signatures in the mesospheric hydroxyl airglow layer. They may arrive as precursors to upward propagating gravity waves, generated simultaneously by the same sources, and produce strong temperature perturbations in the thermosphere above. Transient and short-lived, the acoustic wave airglow intensity and temperature signatures are predicted to be detectable by ground-based airglow imaging systems and may provide new insight into the forcing of the upper atmosphere from below.
Testing Relativistic Gravity and Detecting Gravitational Waves in Space
Ni, Wei-Tou
2010-01-01
For testing gravity and detecting gravitational waves in space, deep-space laser ranging using drag-free spacecraft is a common method. Deep space provides a large arena and a long integration time. Laser technology provides measurement sensitivity, while drag-free technology ensures that gravitational phenomenon to be measured with least spurious noises. In this talk, we give an overview of motivations and methods of various space missions/proposals testing relativistic gravity and detecting...
Properties of QBO and SAO Generated by Gravity Waves
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
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
Simultaneous rocket and MST radar observation of an internal gravity wave breaking in the mesosphere
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.
Validation of the CUTLASS HF radar gravity wave observing capability using EISCAT CP-1 data
Directory of Open Access Journals (Sweden)
N. F. Arnold
Full Text Available Quasi-periodic fluctuations in the returned ground-scatter power from the SuperDARN HF radars have been linked to the passage of medium-scale gravity waves. We have applied a technique that extracts the first radar range returns from the F-region to study the spatial extent and characteristics of these waves in the CUTLASS field-of-view. Some ray tracing was carried out to test the applicability of this method. The EISCAT radar facility at Tromsø is well within the CUTLASS field-of-view for these waves and provides a unique opportunity to assess independently the ability of the HF radars to derive gravity wave information. Results from 1st March, 1995, where the EISCAT UHF radar was operating in its CP-1 mode, demonstrate that the radars were in good agreement, especially if one selects the electron density variations measured by EISCAT at around 235 km. CUTLASS and EISCAT gravity wave observations complement each other; the former extends the spatial field of view considerably, whilst the latter provides detailed vertical information about a range of ionospheric parameters.
Key words. Ionosphere (ionosphere – atmosphere interactions · Meteorology and atmospheric dynamics (thermospheric dynamics · Radio science (ionospheric propagations
Dynamics of Gravity-Capillary Solitary Waves in Deep Water
Wang, Zhan
2012-01-01
The dynamics of solitary gravity-capillary water waves propagating on the surface of a three-dimensional fluid domain is studied numerically. In order to accurately compute complex time dependent solutions, we simplify the full potential flow problem by taking a cubic truncation of the scaled Dirichlet-to-Neumann operator for the normal velocity on the free surface. This approximation agrees remarkably well with the full equations for the bifurcation curves, wave profiles and the dynamics of solitary waves for a two-dimensional fluid domain. Fully localised solitary waves are then computed in the three-dimensional problem and the stability and interaction of both line and localized solitary waves are investigated via numerical time integration of the equations. The solitary wave branches are indexed by their finite energy at small amplitude, and the dynamics of the solitary waves is complex involving nonlinear focussing of wave packets, quasi-elastic collisions, and the generation of propagating, spatially lo...
Wave heating of the solar atmosphere.
Arregui, Iñigo
2015-05-28
Magnetic waves are a relevant component in the dynamics of the solar atmosphere. Their significance has increased because of their potential as a remote diagnostic tool and their presumed contribution to plasma heating processes. We discuss our current understanding of coronal heating by magnetic waves, based on recent observational evidence and theoretical advances. The discussion starts with a selection of observational discoveries that have brought magnetic waves to the forefront of the coronal heating discussion. Then, our theoretical understanding of the nature and properties of the observed waves and the physical processes that have been proposed to explain observations are described. Particular attention is given to the sequence of processes that link observed wave characteristics with concealed energy transport, dissipation and heat conversion. We conclude with a commentary on how the combination of theory and observations should help us to understand and quantify magnetic wave heating of the solar atmosphere. PMID:25897091
Wave heating of the solar atmosphere.
Arregui, Iñigo
2015-05-28
Magnetic waves are a relevant component in the dynamics of the solar atmosphere. Their significance has increased because of their potential as a remote diagnostic tool and their presumed contribution to plasma heating processes. We discuss our current understanding of coronal heating by magnetic waves, based on recent observational evidence and theoretical advances. The discussion starts with a selection of observational discoveries that have brought magnetic waves to the forefront of the coronal heating discussion. Then, our theoretical understanding of the nature and properties of the observed waves and the physical processes that have been proposed to explain observations are described. Particular attention is given to the sequence of processes that link observed wave characteristics with concealed energy transport, dissipation and heat conversion. We conclude with a commentary on how the combination of theory and observations should help us to understand and quantify magnetic wave heating of the solar atmosphere.
Interactions between small and medium scale gravity waves in the mesosphere and lower thermosphere
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.
Gravitational Waves in Effective Quantum Gravity
Calmet, Xavier; Kuntz, Iberê; Mohapatra, Sonali
2016-01-01
In this short paper we investigate quantum gravitational effects on Einstein's equations using effective field theory techniques. We consider the leading order quantum gravitational correction to the wave equation. Besides the usual massless mode, we find a pair of modes with complex masses. These massive particles have a width and could thus lead to a damping of gravitational waves if excited in violent astrophysical processes producing gravitational waves such as e.g. black hole mergers. We...
Gravitational Waves in Effective Quantum Gravity
Calmet, Xavier; Mohapatra, Sonali
2016-01-01
In this short paper we investigate quantum gravitational effects on Einstein's equations using effective field theory techniques. We consider the leading order quantum gravitational correction to the wave equation. Besides the usual massless mode, we find a pair of modes with complex masses. These massive particles have a width and could thus lead to a damping of gravitational waves if excited in violent astrophysical processes producing gravitational waves such as e.g. black hole mergers. We discuss the consequences for gravitational wave events such as GW 150914 recently observed by the Advanced LIGO collaboration.
Gravitational Waves in Effective Quantum Gravity
Calmet, Xavier; Kuntz, Iberê; Mohapatra, Sonali
2016-08-01
In this short paper we investigate quantum gravitational effects on Einstein's equations using Effective Field Theory techniques. We consider the leading order quantum gravitational correction to the wave equation. Besides the usual massless mode, we find a pair of modes with complex masses. These massive particles have a width and could thus lead to a damping of gravitational waves if excited in violent astrophysical processes producing gravitational waves such as e.g. black hole mergers. We discuss the consequences for gravitational wave events such as GW 150914 recently observed by the Advanced LIGO collaboration.
Waveguide gravity disturbances in vertically inhomogeneous dissipative atmosphere
Rudenko, G V
2015-01-01
Trapped atmosphere waves, such as IGW waveguide modes and Lamb modes, are described using dissipative solution above source (DSAS) (Dmitrienko and Rudenko, 2016). Accordingly this description, the modes are disturbances penetrating without limit in the upper atmosphere and dissipating their energy throughout the atmosphere; leakage from a trapping region to the upper atmosphere is taken in consideration. The DSAS results are compared to those based on both accurate and WKB approximated dissipationless equations. It is shown that the spatial and frequency characteristics of modes in the upper atmosphere calculated by any of the methods are close to each other and are in good agreement with the observed characteristics of traveling ionospheric disturbances.
On Wave Processes in the Solar Atmosphere
Musielak, Z. E.
1998-01-01
This grant was awarded by NASA/MSFC to The University of Alabama in Huntsville (UAH) to investigate the physical processes responsible for heating and wind acceleration in the solar atmosphere, and to construct theoretical, self-consistent and time-dependent solar wind models based on the momentum deposition by finite amplitude and nonlinear Alfven waves. In summary, there are three main goals of the proposed research: (1) Calculate the wave energy spectra and wave energy fluxes carried by magnetic non- magnetic waves. (2) Find out which mechanism dominates in supplying the wave energy to different parts of the solar atmosphere. (3) Use the results obtained in (1) and (2) to construct theoretical, self-consistent and time- dependent models of the solar wind. We have completed the first goal by calculating the amount of non-radiative energy generated in the solar convection zone as acoustic waves and as magnetic tube waves. To calculate the amount of wave energy carried by acoustic waves, we have used the Lighthill-Stein theory for sound generation modified by Musielak, Rosner, Stein & Ulmschneider (1994). The acoustic wave energy fluxes for stars located in different regions of the Hertzsprung-Russell (H-R) diagram have also been computed. The wave energy fluxes carried by longitudinal and transverse waves along magnetic flux tubes have been calculated by using both analytical and numerical methods. Our analytical approach is based a theory developed by Musielak, Rosner & Ulmschnelder and Musielak, Rosner, Gall & Ulmschneider, which allows computing the wave energy fluxes for linear tube waves. A numerical approach has been developed by Huang, Musielak & Ulmschneider and Ulmschneider & Musielak to compute the energy fluxes for nonlinear tube waves. Both methods have been used to calculate the wave energy fluxes for stars located in different regions of the HR diagram (Musielak, Rosner & Ulmschneider 1998; Ulmschneider, Musielak & Fawzy 1998). Having obtained the
Koch, Steven E.; Einaudi, F.; Dorian, Paul B.; Lang, Stephen; Heymsfield, Gerald M.
1993-01-01
A summary of the results of a detailed study of the vertical structure of mesoscale gravity waves conducted during the Cooperative Convective Precipitation Experiment (CCOPE) is presented. Pressure perturbation fields derived from the Doppler wind fields are compared with the vertical structure of eigenfunctions resulting from a solution to the Taylor-Goldstein linear wave equation for an atmosphere whose mean state is described by vertical profiles obtained from a representative CCOPE sounding. An analysis of the potential for shear instability is also performed on all of the soundings taken on this day to assess the representativeness of the one chosen for the linear theoretical analysis.
Generation of internal gravity waves by penetrative convection
Pinçon, C; Goupil, M J
2015-01-01
The rich harvest of seismic observations over the past decade provides evidence of angular momentum redistribution in stellar interiors that is not reproduced by current evolution codes. In this context, transport by internal gravity waves can play a role and could explain discrepancies between theory and observations. The efficiency of the transport of angular momentum by waves depends on their driving mechanism. While excitation by turbulence throughout the convective zone has already been investigated, we know that penetrative convection into the stably stratified radiative zone can also generate internal gravity waves. Therefore, we aim at developing a semianalytical model to estimate the generation of IGW by penetrative plumes below an upper convective envelope. We derive the wave amplitude considering the pressure exerted by an ensemble of plumes on the interface between the radiative and convective zones as source term in the equation of momentum. We consider the effect of a thermal transition from a c...
Role of the basin boundary conditions in gravity wave turbulence
Deike, Luc; Gutiérrez-Matus, Pablo; Jamin, Timothée; Semin, Benoit; Aumaitre, Sébastien; Berhanu, Michael; Falcon, Eric; BONNEFOY, Félicien
2014-01-01
Gravity wave turbulence is studied experimentally in a large wave basin where irregular waves are generated unidirectionally. The role of the basin boundary conditions (absorbing or reflecting) and of the forcing properties are investigated. To that purpose, an absorbing sloping beach opposite to the wavemaker can be replaced by a reflecting vertical wall. We observe that the wave field properties depend strongly on these boundary conditions. Quasi-one dimensional field of nonlinear waves propagate before to be damped by the beach whereas a more multidirectional wave field is observed with the wall. In both cases, the wave spectrum scales as a frequency-power law with an exponent that increases continuously with the forcing amplitude up to a value close to -4, which is the value predicted by the weak turbulence theory. The physical mechanisms involved are probably different according to the boundary condition used, but cannot be easily discriminated with only temporal measurements. We have also studied freely...
Nonlinear interactions between gravity waves and background winds
Institute of Scientific and Technical Information of China (English)
Liu Xiao; Xu Jiyao
2007-01-01
Using the nonlinear propagating gravity waves (GW) model in the two-dimensional compressible atmosphere and the linear GW theory, the process of GW propagation in different background winds, e.g. the direction of the background wind is opposite to (dead wind) or the same as (tail wind) the direction of the horizontal phase velocity of GW, is studied. The results show that the dead wind prolongs the vertical wavelength and accelerates GW propagation. Therefore, GW propagates up to a higher height becomes instable in a short time and eventually induces an inverse jet flow. Then, the vertical wavelength is becoming short due to the nonlinear interactions between GW and the inverse jet flow. The vertical wavelength and group velocity decrease after GW propagates into the tail wind. The initial instable time is delayed. Although most of GW is trapped in the instable region, some of GW propagates above the instable region.Compared with GW propagation in the tail wind, the nonlinear interactions between GW and the dead wind are also strong. In contrast,the linear GW theory predicts that GW can propagate freely in the dead wind. The vertical wavelength simulated by the nonlinear numerical model is different from that predicted by the linear theory greatly after GW propagates into the dead wind.
Tropical Gravity Wave Momentum Fluxes and Latent Heating Distributions
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.
Active Absorption of Irregular Gravity Waves in BEM-Models
DEFF Research Database (Denmark)
Brorsen, Michael; Frigaard, Peter
1992-01-01
The boundary element method is applied to the computation of irregular gravity waves. The boundary conditions at the open boundaries are obtained by a digital filtering technique, where the surface elevations in front of the open boundary are filtered numerically yielding the velocity...... to be prescribed at the boundary. By numerical examples it is shown that well designed filters can reduce the wave reflection to a few per cent over a frequency range corresponding to a Jonswap spectrum....
Characteristics of Gravity Waves over an Antarctic Ice Sheet during an Austral Summer
Directory of Open Access Journals (Sweden)
Daniela Cava
2015-08-01
Full Text Available While occurrences of wavelike motion in the stable boundary layer due to the presence of a significant restoring buoyancy force are rarely disputed, their modalities and interaction with turbulence remain a subject of active research. In this work, the characteristics of gravity waves and their impact on flow statistics, including turbulent fluxes, are presented using data collected above an Antarctic Ice sheet during an Austral Summer. Antarctica is an ideal location for exploring the characteristics of gravity waves because of persistent conditions of strong atmospheric stability in the lower troposphere. Periods dominated by wavelike motion have been identified by analysing time series measured by fast response instrumentation. The nature and characteristic of the dominant wavy motions are investigated using Fourier cross-spectral indicators. Moreover, a multi-resolution decomposition has been applied to separate gravity waves from turbulent fluctuations in case of a sufficiently defined spectral gap. Statistics computed after removing wavy disturbances highlight the large impact of gravity waves on second order turbulent quantities including turbulent flux calculations.
Magnetoacoustic Waves in the Solar Stratified Atmosphere
Institute of Scientific and Technical Information of China (English)
郑惠南; 王水; 吴式灿; 李波
2001-01-01
The propagation of magnetoacoustic waves in the solar atmosphere consisting of the photosphere, chromosphere and corona has been studied numerically by time-dependent multi-dimensional magnetohydrodynamic (MHD) simulation. Pressure disturbances are introduced at the bottom of the chromosphere and at the bottom of the corona, respectively. The computational results show that incurred fast and slow MHD waves propagate away from the source of the disturbances. The fast MHD wave propagates as an expansive wave in the radial direction, while the slow one steepens and it may evolve into a slow shock. We suggest that the extreme ultraviolet imaging telescope wave observed by the SOHO and Moreton wave are a fast MHD wave propagating in the corona and in the chromosphere, respectively.
Cosmic Tsunamis in Modified Gravity: Scalar waves disrupting screening mechanisms
Hagala, R; Mota, D F
2016-01-01
Extending General Relativity by adding extra degrees of freedom is a popular approach to explain 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 the screening mechanisms, thereby spoiling the viability of modified gravity theories. Specifically, we show that the waves produced can increase the amplitude of the fifth force and the Parametrized Post Newtonian parameters by several orders of magnitude.
Gravity Wave Variances and Propagation Derived from AIRS Radiances
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).
On the kurtosis of deep-water gravity waves
Fedele, Francesco
2014-01-01
In this paper, we revisit Janssen's (2003) formulation for the dynamic excess kurtosis of weakly nonlinear gravity waves at deep water. For narrowband directional spectra, the formulation is given by a sixfold integral that depends upon the Benjamin-Feir index and the parameter $R=\\sigma_{\\theta}^{2}/2\
Field verification of ADCP surface gravity wave elevation spectra
Hoitink, A.J.F.; Peters, H.C.; Schroevers, M.
2007-01-01
Acoustic Doppler current profilers (ADCPs) can measure orbital velocities induced by surface gravity waves, yet the ADCP estimates of these velocities are subject to a relatively high noise level. The present paper introduces a linear filtration technique to significantly reduce the influence of noi
Brissaud, Quentin; Martin, Roland; Garcia, Raphaël F.; Komatitsch, Dimitri
2016-07-01
Acoustic and gravity waves propagating in planetary atmospheres have been studied intensively as markers of specific phenomena such as tectonic events or 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 modelled in a 3-D attenuating and windy atmosphere extending from the ground to the upper thermosphere. Thus, in order to provide an efficient numerical tool at the regional or global scale, we introduce a finite difference in the time domain (FDTD) approach that relies on the linearized compressible Navier-Stokes equations with a background flow (wind). One significant benefit of such a method is its versatility because it handles both acoustic and gravity waves in the same simulation, which enables one to observe interactions between them. Simulations can be performed for 2-D or 3-D realistic cases such as tsunamis in a full MSISE-00 atmosphere or gravity-wave generation by atmospheric explosions. We validate the computations by comparing them to analytical solutions based on dispersion relations in specific benchmark cases: an atmospheric explosion, and a ground displacement forcing.
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.
Gravity's shadow the search for gravitational waves
Collins, Harry
2004-01-01
According to the theory of relativity, we are constantly bathed in gravitational radiation. When stars explode or collide, a portion of their mass becomes energy that disturbs the very fabric of the space-time continuum like ripples in a pond. But proving the existence of these waves has been difficult; the cosmic shudders are so weak that only the most sensitive instruments can be expected to observe them directly. Fifteen times during the last thirty years scientists have claimed to have detected gravitational waves, but so far none of those claims have survived the scrutiny of the scie
Dust gravitational drift wave in complex plasma under gravity
International Nuclear Information System (INIS)
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
Electromagnetic inertio-gravity waves in the Earth's ionosphere
Kaladze, T. D.; Tsamalashvili, L. V.; Kahlon, L. Z.
2011-05-01
Propagation of electromagnetic inertio-gravity (IG) waves in the partially ionized ionospheric E- and F-layers is considered in the shallow water approximation. Accounting of the field-aligned current is the main novelty of the investigation. Existence of two new eigen-frequencies for fast and slow electromagnetic waves is revealed in the ionospheric E-layer. It is shown that in F-layer slowly damping new type of inertial-fast magnetosonic waves can propagate. Slowly damping low-frequency oscillations connected with the field-aligned conductivity are found. Broad spectrum of oscillations is investigated.
The Binary Pulsar: Gravity Waves Exist.
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)
Testing Gravity with Gravitational Wave Source Counts
Calabrese, Erminia; Spergel, David N
2016-01-01
We show that the gravitational wave source counts distribution can test how gravitational radiation propagates on cosmological scales. This test does not require obtaining redshifts for the sources. If the signal-to-noise from a gravitational wave source is proportional to the strain then it falls as $R^{-1}$, thus we expect the source counts to follow $dN/dS \\propto S^{-4}$. However, if gravitational waves decay as they propagate or can propagate into other dimensions, then there can be deviations from this generic prediction. We consider the possibility that the signal-to-noise falls as $R^{-\\gamma}$, where $\\gamma=1$ recovers the expected predictions in a Euclidean uniformly-filled universe. We forecast the sensitivity of future observations in constraining gravitational wave physics using this method by simulating sources distributed over a finite range of signal-to-noise. We first consider the case of few objects, 7 sources, with a signal-to-noise from 8 to 24, and impose a lower limit on $\\gamma$, findi...
Formation of ice supersaturation by mesoscale gravity waves
Directory of Open Access Journals (Sweden)
P. Spichtinger
2005-01-01
Full Text Available We investigate the formation and evolution of an ice-supersaturated region (ISSR that was detected by means of an operational radiosonde sounding launched from the meteorological station of Lindenberg on 21 March 2000, 00:00 UTC. The supersaturated layer was 5 situated below the local tropopause, between 320 and 408 hPa altitude. Our investigation uses satellite imagery (METEOSAT, AVHRR and analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF. Mesoscale simulations reveal that the ISSR was formed by a temporary vertical uplift of upper tropospheric air parcels by 20 to 40 hPa in 1 to 2 h. This resulted in a significant local increase of the 10 specific humidity by the moisture transport from below. The ascent was triggered by the superposition of two internal gravity waves, a mountain wave induced by flow past the Erzgebirge and Riesengebirge south of Lindenberg, and an inertial gravity wave excited by the anticyclonically curved jet stream over the Baltic Sea. The wave-induced ISSR was rather thick with a depth of about 2 km. The wave-induced upward motion 15 causing the supersaturation also triggered the formation of a cirrus cloud. METEOSAT imagery shows that the cirrus cloud got optically thick within two hours. During this period another longer lasting thin but extended cirrus existed just beneath the tropopause. The wave-induced ISSR disappeared after about half a day in accordance with the decaying wave activity.
What gravity waves are telling about quantum spacetime
Arzano, Michele; Calcagni, Gianluca
2016-01-01
We discuss various modified dispersion relations motivated by quantum gravity which might affect the propagation of the recently observed gravitational-wave signal of the event GW150914. We find that the bounds set by the data on the characteristic quantum-gravity mass scale $M$ are too weak to constrain these scenarios and, in general, much weaker than the expected $M> 10^4\\,\\text{eV}$ for a correction to the dispersion relation linear in $1/M$. We illustrate this issue by giving lower bound...
Energy Technology Data Exchange (ETDEWEB)
Rechou, A. [La Reunion Univ., St. Denis Messag, Ile de La Reunion (France). Lab. de l' Atmosphere et des Cyclones; Arnault, J.; Dalin, P.; Kirkwood, S. [Swedish Institute of Space Physics, Kiruna (Sweden)
2013-03-01
Orography is a well-known source of gravity and inertia-gravity waves in the atmosphere. Other sources, such as convection, are also known to be potentially important but the large amplitude of orographic waves over Scandinavia has generally precluded the possibility to study such other sources experimentally in this region. In order to better understand the origin of stratospheric gravity waves observed by the VHF radar ESRAD (Esrange MST radar) over Kiruna, in Arctic Sweden (67.88 N, 21.10 E), observations have been compared to simulations made using the Weather Research and Forecasting model (WRF) with and without the effects of orography and clouds. This case study concerns gravity waves observed from 00:00 UTC on 18 February to 12:00 UTC on 20 February 2007. We focus on the wave signatures in the static stability field and vertical wind deduced from the simulations and from the observations as these are the parameters which are provided by the observations with the best height coverage. As is common at this site, orographic gravity waves were produced over the Scandinavian mountains and observed by the radar. However, at the same time, southward propagation of fronts in the Barents Sea created short-period waves which propagated into the stratosphere and were transported, embedded in the cyclonic winds, over the radar site. (orig.)
Electromagnetic internal gravity waves in the Earth's ionospheric E-layer
Energy Technology Data Exchange (ETDEWEB)
Kaladze, T.D., E-mail: tamaz_kaladze@yahoo.com [I. Vekua Institute of Applied Mathematics, Tbilisi State University, 2 University str., 0186 Tbilisi, Georgia (United States); Tsamalashvili, L.V.; Kaladze, D.T. [I. Vekua Institute of Applied Mathematics, Tbilisi State University, 2 University str., 0186 Tbilisi, Georgia (United States)
2011-12-05
In the Earth's ionospheric E-layer existence of the new waves connecting with the electromagnetic nature of internal gravity waves is shown. They represent the mixture of the ordinary internal gravity waves and the new type of dispersive Alfven waves. -- Highlights: ► Existence of electromagnetic internal gravity waves in the ionospheric E-layer is shown. ► Electromagnetic nature of internal gravity waves is described. ► Appearance of the new dispersive Alfven waves is shown.
Testing gravity with gravitational wave source counts
Calabrese, Erminia; Battaglia, Nicholas; Spergel, David N.
2016-08-01
We show that the gravitational wave source counts distribution can test how gravitational radiation propagates on cosmological scales. This test does not require obtaining redshifts for the sources. If the signal-to-noise ratio (ρ) from a gravitational wave source is proportional to the strain then it falls as {R}-1, thus we expect the source counts to follow {{d}}{N}/{{d}}ρ \\propto {ρ }-4. However, if gravitational waves decay as they propagate or propagate into other dimensions, then there can be deviations from this generic prediction. We consider the possibility that the strain falls as {R}-γ , where γ =1 recovers the expected predictions in a Euclidean uniformly-filled Universe, and forecast the sensitivity of future observations to deviations from standard General Relativity. We first consider the case of few objects, seven sources, with a signal-to-noise from 8 to 24, and impose a lower limit on γ, finding γ \\gt 0.33 at 95% confidence level. The distribution of our simulated sample is very consistent with the distribution of the trigger events reported by Advanced LIGO. Future measurements will improve these constraints: with 100 events, we estimate that γ can be measured with an uncertainty of 15%. We generalize the formalism to account for a range of chirp masses and the possibility that the signal falls as {exp}(-R/{R}0)/{R}γ .
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
Effective viscosity of grease ice in linearized gravity waves
de Carolis, G; Pignagnoli, L; Carolis, Giacomo de; Olla, Piero; Pignagnoli, Luca
2004-01-01
Grease ice is an agglomeration of disc-shaped ice crystals, named frazil ice, which forms in turbulent waters of the Polar Oceans and in rivers as well. It has been recognized that the properties of grease ice to damp surface gravity waves could be explained in terms of the effective viscosity of the ice slurry. This paper is devoted to the study of the dynamics of a suspension of disc-shaped particles in a gravity wave field. For dilute suspensions,depending on the strength and frequency of the external wave flow, two orientation regimes of the particles are predicted: a preferential orientation regime with the particles rotating in coherent fashion with the wave field, and a random orientation regime in which the particles oscillate around their initial orientation while diffusing under the effect of Brownian motion. For both motion regimes, the effective viscosity has been derived as a function of the wave frequency, wave amplitude and aspect ratio of the particles. Model predictions have been validated ag...
Global Gravity Wave Variances from Aura MLS: Characteristics and Interpretation
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.
Electromagnetic internal gravity waves in the Earth's ionospheric E-layer
Kaladze, T. D.; Tsamalashvili, L. V.; Kaladze, D. T.
2011-12-01
In the Earth's ionospheric E-layer existence of the new waves connecting with the electromagnetic nature of internal gravity waves is shown. They represent the mixture of the ordinary internal gravity waves and the new type of dispersive Alfven waves.
Steady periodic gravity waves with surface tension
Walsh, Samuel
2009-01-01
In this paper we consider two-dimensional, stratified, steady water waves propagating over an impermeable flat bed and with a free surface. The motion is assumed to be driven by capillarity (that is, surface tension) on the surface and a gravitational force acting on the body of the fluid. We prove the existence of global continua of classical solutions that are periodic and traveling. This is accomplished by first constructing a 1-parameter family of laminar flow solutions, $\\mathcal{T}$, then applying bifurcation theory methods to obtain local curves of small amplitude solutions branching from $\\mathcal{T}$ at an eigenvalue of the linearized problem. Each solution curve is then continued globally by means of a degree theoretic theorem in the spirit of Rabinowitz. Finally, we complement the degree theoretic picture by proving an alternate global bifurcation theorem via the analytic continuation method of Dancer.
Viscous damping of gravity waves over a permeable bed
Directory of Open Access Journals (Sweden)
K. K. Puri
1978-01-01
Full Text Available The damping of gravity waves over the surface of a layer of viscous fluid which overlies a porous bed saturated with the same fluid is studied. It is shown that viscosity may not be the dominant influence in the damping mechanism; the damping effects due to percolation in the fixed bed may be of the same or even higher order than those due to viscosity.
Global bifurcation of steady gravity water waves with critical layers
Constantin, Adrian; Strauss, Walter; Varvaruca, Eugen
2014-01-01
We construct large families of two-dimensional travelling water waves propagating under the influence of gravity in a flow of constant vorticity over a flat bed. A Riemann-Hilbert problem approach is used to recast the governing equations as a one-dimensional elliptic pseudo-differential equation with a scalar constraint. The structural properties of this formulation, which arises as the Euler-Lagrange equation of an energy functional, enable us to develop a theory of analytic global bifurcat...
LINEAR THEORY OF GRAVITY WAVES ON A VOIGT VISCOELASTIC MEDIUM
Institute of Scientific and Technical Information of China (English)
Zhang Qinghe; Wu Yongsheng; Zhao Zidan
2000-01-01
Linear surface gravity waves on a semi-infinite incompressible Voigt medium are studied in this paper. Three dimensionless parameters, the dimensionless viscoelastic parameter θ, the dimensionless wave number and the dimensionless sur face tension are introduced. A dimensionless characteristic equation describing the waves is derived. This is a sixth order complex algebraic equation which is solved to give the complex dispersion relation. Based on the numerical solution, two critical values of θ, θA = 0.607 and θB = 2.380, which represent the appearance of the cutoff region and the disappearance of the strong dispersion region, are found. The effects of θ on the characteristic equation and the properties of the waves are discussed.
Resonant nonlinear interactions between atmospheric waves in the polar summer mesopause region
Institute of Scientific and Technical Information of China (English)
刘仁强; 易帆
2003-01-01
Data obtained from the mobile SOUSY VHF radar at And(ya/Norway in summer 1987 have been used to study the nonlinear interactions between planetary waves, tides and gravity waves in the polar mesosphere, and the instability of background atmosphere above the mesopause. It is observed that 35-h planetary wave, diurnal, semidiurnal and terdiurnal tides are the prominent perturbations in the Lomb-Scargle spectra of the zonal wind component. By inspecting the frequency combinations, several triads are identified. By bispectral analysis it is shown that most bispectral peaks stand for quadratic coupling between tidal harmonics or between tide and planetary or gravity wave, and the height dependence of bispectral peaks reflects the variation of wave-wave interactions. Above the mesopause, the occurrence heights of the maximum L-S power spectral peaks corresponding to the prominent wave components tend to increase with their frequencies. This may result from the process in which two low frequency waves interact to generate a high frequency wave. Intensities of the planetary wave and tides increase gradually, arrive at their maxima, and then decay quickly in turn with increasing height. This kind of scene correlates with a "chain" of wave-wave resonant interactions that shifts with height from lower frequency segment to higher frequency segment. By instability analysis, it is observed that above the mesopause, the Richardson number becomes smaller and smaller with height, implying that the turbulent motion grows stronger and stronger and accordingly the background atmosphere more and more instable. It is suggested that the wave-wave sum resonant interaction and the wave dissipation due to instability are two dominant dynamical processes that occur in the mesopause region. The former invokes the energy transfer from lower frequency waves to higher frequency waves. The latter results in the heating of the atmosphere and accelerating of the background flow.
A Wave Theory for the Onset and Initial Growth of Condensation in the Atmosphere.
Chimonas, G.; Einaudi, F.; Lalas, D. P.
1980-04-01
Pre-storm conditions are often characterized by an atmosphere in the presence of rather strong wind shears and a temperature inversion. The latter acts as a lid for moisture in the boundary layer. In this paper we discuss the possibility that a gravity wave generated by wind shear can reach sufficiently large amplitude to induce condensation. We show that under certain circumstances the ensuing heat release takes place in such a phase with respect to the initial gravity wave so as to reinforce it, substantially increasing its rate of growth. Thus, the lifting due to the wave will grow and so will the condensation. By showing that in the early stages after the first condensation occurs, we have a positive feedback between the gravity wave and the induced condensation, we strengthen the case for gravity waves as possible lifting agents leading to condensation and eventually to convection. The present calculations are not meant to describe the system after the onset of convection and as such they differ from existing CISK theories. The results also appear to indicate that the presence of a critical level in the region of large relative humidity may be a prerequisite for a strong feedback between the gravity wave and the induced condensation.
Experimental study of three-wave interactions among capillary-gravity surface waves
Haudin, Florence; Deike, Luc; Jamin, Timothée; Falcon, Eric; Berhanu, Michael
2016-01-01
In propagating wave systems, three or four-wave resonant interactions constitute a classical non-linear 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 spatio-temporal one (Diffusive Light Photography), a third wave of smaller amplitude is detected, verifying the three-wave resonance conditions in frequency and in wavenumber. 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 non-linear 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-w...
Empirical Mode Decomposition of the atmospheric wave field
Directory of Open Access Journals (Sweden)
A. J. McDonald
2007-03-01
Full Text Available This study examines the utility of the Empirical Mode Decomposition (EMD time-series analysis technique to separate the horizontal wind field observed by the Scott Base MF radar (78° S, 167° E into its constituent parts made up of the mean wind, gravity waves, tides, planetary waves and instrumental noise. Analysis suggests that EMD effectively separates the wind field into a set of Intrinsic Mode Functions (IMFs which can be related to atmospheric waves with different temporal scales. The Intrinsic Mode Functions resultant from application of the EMD technique to Monte-Carlo simulations of white- and red-noise processes are compared to those obtained from the measurements and are shown to be significantly different statistically. Thus, application of the EMD technique to the MF radar horizontal wind data can be used to prove that this data contains information on internal gravity waves, tides and planetary wave motions.
Examination also suggests that the EMD technique has the ability to highlight amplitude and frequency modulations in these signals. Closer examination of one of these regions of amplitude modulation associated with dominant periods close to 12 h is suggested to be related to a wave-wave interaction between the semi-diurnal tide and a planetary wave. Application of the Hilbert transform to the IMFs forms a Hilbert-Huang spectrum which provides a way of viewing the data in a similar manner to the analysis from a continuous wavelet transform. However, the fact that the basis function of EMD is data-driven and does not need to be selected a priori is a major advantage. In addition, the skeleton diagrams, produced from the results of the Hilbert-Huang spectrum, provide a method of presentation which allows quantitative information on the instantaneous period and amplitude squared to be displayed as a function of time. Thus, it provides a novel way to view frequency and amplitude-modulated wave phenomena and potentially non
Formation of ice supersaturation by mesoscale gravity waves
Directory of Open Access Journals (Sweden)
P. Spichtinger
2005-01-01
Full Text Available We investigate the formation and evolution of an ice-supersaturated region (ISSR that was detected by means of an operational radiosonde sounding launched from the meteorological station of Lindenberg on 21 March 2000, 00:00 UTC. The supersaturated layer was situated below the local tropopause, between 320 and 408 hPa altitude. Our investigation uses satellite imagery from METEOSAT and the Advanced Very High Resolution Radiometer (AVHRR and analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF. Mesoscale simulations reveal that the ISSR was formed by a temporary vertical uplift of upper tropospheric air parcels by 20 to 40 hPa in 1 to 2 h. This resulted in a significant local increase of the specific humidity by the moisture transport from below. The ascent was triggered by the superposition of two internal gravity waves, a mountain wave induced by flow past the Erzgebirge and Riesengebirge south of Lindenberg, and an inertial gravity wave excited by the anti-cyclonically curved jet stream over the Baltic Sea. The wave-induced ISSR was rather thick with a depth of about 2 km. The wave-induced upward motion causing the supersaturation also triggered the formation of a cirrus cloud. METEOSAT imagery shows that the cirrus cloud got optically thick within two hours. During this period another longer lasting thin but extended cirrus existed just beneath the tropopause. The wave-induced ISSR disappeared after about half a day in accordance with the decaying wave activity.
Medvedev, Alexander S; Yiğit, Erdal; Feofilov, Artem G; Forget, François; Hartogh, Paul
2015-01-01
Observations show that the lower thermosphere of Mars ($\\sim$100--140 km) is up to 40 K colder than the current general circulation models (GCMs) can reproduce. Possible candidates for physical processes missing in the models are larger abundances of atomic oxygen facilitating stronger CO$_2$ radiative cooling, and thermal effects of gravity waves. Using two state-of-the-art Martian GCMs, the Laboratoire de M\\'et\\'eorologie Dynamique and Max Planck Institute models that self-consistently cover the atmosphere from the surface to the thermosphere, these physical mechanisms are investigated. Simulations demonstrate that the CO$_2$ radiative cooling with a sufficiently large atomic oxygen abundance, and the gravity wave-induced cooling can alone result in up to 40 K colder temperature in the lower thermosphere. Accounting for both mechanisms produce stronger cooling at high latitudes. However, radiative cooling effects peak above the mesopause, while gravity wave cooling rates continuously increase with height. A...
Yamanaka, M. D.
1989-01-01
In MAP observations, it was found that: (1) gravity waves in selected or filtered portions of data are fit for monochromatic structures, whereas (2) those in fully continuous and resolved observations take universal continuous spectra. It is possible to explain (2) by dispersion of quasi-monochromatic (or slowly varying) wave packets observed locally as (1), since the medium atmosphere is unsteady and nonuniform. Complete verification of the wave-mean flow interactions by tracking individual wave packets seems hopeless, because the wave induced flow cannot be distinguished from the basic flow independent of the waves. Instead, the primitive picture is looked at before MAP, that is, the atmosphere is just like an entertainment stage illuminated by cocktail lights of quasi-monochromatic gravity waves. The wave parameters are regarded as functions of time and spatial coordinates. The observational evidences (1) and (2) suggest that the wave parameter field is rather homogeneous, which can be explained by interference of quasi-monochromatic wave packets.
Gravity Wave and Turbulence Transport of Heat and Na in the Mesopause Region over the Andes
Guo, Yafang; Liu, Alan Z.
2016-07-01
The vertical heat and Na fluxes induced by gravity waves and turbulence are derived based on over 600 hours of observations from the Na wind/temperature lidar located at Andes lidar Observatory (ALO), Cerro Pachón, Chile. In the 85-100 km region, the annual mean vertical fluxes by gravity waves show downward heat transport with a maximum of 0.78K m/s at 90 km, and downward Na transport with a maximum of 210 m/s/cm3 at 94km. The maximum cooing rate reaches -24 K/d at 94km. The vertical fluxes have strong seasonal variations, with large differences in magnitudes and altitudes of maximum fluxes between winter and summer. The vertical fluxes due to turbulence eddies are also derived with a novel method that relates turbulence fluctuations of temperature and vertical wind with photon count fluctuations at very high resolution (25 m, 6 s). The results show that the vertical transports are comparable to those by gravity waves and they both play significant roles in the atmospheric thermal structure and constituent distribution. This direct measure of turbulence transport also enables estimate of the eddy diffusivity for heat and constituent in the mesopause region.
Experimental study of three-wave interactions among capillary-gravity surface waves.
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. PMID:27176393
Recent progress in mesospheric gravity wave studies using nightglow imaging system
Energy Technology Data Exchange (ETDEWEB)
Taylor, Michael J.; Pendleton Junior, William R.; Pautet, Pierre-Dominique; Zhao, Yucheng; Olsen, Chris; Babu, Hema Karnam Surendra [Center for Atmospheric and Space Sciences, Utah State University, Logan, Utah (United States); Medeiros, Amauri F. [Universidade Federal de Campina Grande, Centro de Ciencias e Tecnologia, Unidade Academica de Fisica, Campina Grande, PB (Brazil); Takahashi, Hisao, E-mail: mtaylor@cc.usu.edu, E-mail: wpen@cc.usu.edu, E-mail: dominiquepautet@gmail.com, E-mail: yucheng@cc.usu.edu, E-mail: cmellob@gmail.com, E-mail: hema_sb@rediffmail.com, E-mail: afragoso@df.ufcg.edu.br, E-mail: hisaotak@laser.inpe.br [INPE, Sao Jose dos Campos, SP (Brazil)
2007-07-01
A variety of optical remote sensing techniques have now revealed a rich spectrum of wave activity in the upper atmosphere. Many of these perturbations, with periodicities ranging from {approx} 5 min to many hours and horizontal scales of a few tens of km to several thousands km, are due to freely propagating atmospheric gravity waves and forced tidal oscillations. Passive optical observations of the spatial and temporal characteristics of these waves in the mesosphere and lower thermosphere (MLT) region ( {approx} 80-100 km) are facilitated by several naturally occurring, vertically distinct nightglow layers. This paper describes the use of state-of-the-art ground-based CCD imaging techniques to detect these waves in intensity and temperature. All-sky (180 deg ) image measurements are used to illustrate the characteristics of small-scale, short period ( < 1 hour) waves and to investigate their seasonal propagation and momentum impact on the MLT region. These results are then contrasted with measurements of mesospheric temperature made using a new temperature mapping imaging system capable of determining induced temperature amplitudes of a large range of wave motions and investigating night-to-night and seasonal variability in mesospheric temperature. (author)
Plane-wave analysis of solar acoustic-gravity waves: A (slightly) new approach
Bogart, Richard S.; Sa, L. A. D.; Duvall, Thomas L., Jr.; Haber, Deborah A.; Toomre, Juri; Hill, Frank
1995-01-01
The plane-wave decomposition of the acoustic-gravity wave effects observed in the photosphere provides a computationally efficient technique that probes the structure of the upper convective zone and boundary. In this region, the flat sun approximation is considered as being reasonably accurate. A technique to be used for the systematic plane-wave analysis of Michelson Doppler imager data, as part of the solar oscillations investigation, is described. Estimates of sensitivity are presented, and the effects of using different planar mappings are discussed. The technique is compared with previous approaches to the three dimensional plane-wave problem.
Gravity wave structure between 60 and 90 km inferred from Space Shuttle reentry data
Fritts, David C.; Blanchard, Robert C.; Coy, Lawrence
1989-01-01
Density fluctuations obtained along seven Space Shuttle reentry tracks are used to examine the horizontal structure and the vertical distribution of density variance in the mesosphere and lower thermosphere. The tracks lie primarily over open ocean at middle and low latitudes and represent the only measurements of horizontal atmospheric structure at these heights available to date. The density fluctuations are interpreted in terms of gravity-wave motions and reveal significant density (and velocity) variance at horizontal scales ranging from about 10 to 1000 km. Fluctuation amplitudes are used to infer corresponding velocity perturbations and characteristic vertical scales and frequencies of the wave spectrum. Results suggest that the mean velocity variance is smaller over the Pacific ocean than over major land masses, and that the variance increases with height in a manner consistent with that expected in the present of wave saturation processes.
Kuroda, T.; Medvedev, A. S.; Kasaba, Y.; Hartogh, P.
2016-09-01
The CO2 snowfalls in winter polar atmosphere have been simulated by a MGCM. Our results show that they are strongly modulated by the synoptic dynamical features such as baroclinic planetary waves, as well as by gravity waves in smaller scale.
Serva, Federico; Cagnazzo, Chiara; Riccio, Angelo
2016-04-01
The effects of the propagation and breaking of atmospheric gravity waves have long been considered crucial for their impact on the circulation, especially in the stratosphere and mesosphere, between heights of 10 and 110 km. These waves, that in the Earth's atmosphere originate from surface orography (OGWs) or from transient (nonorographic) phenomena such as fronts and convective processes (NOGWs), have horizontal wavelengths between 10 and 1000 km, vertical wavelengths of several km, and frequencies spanning from minutes to hours. Orographic and nonorographic GWs must be accounted for in climate models to obtain a realistic simulation of the stratosphere in both hemispheres, since they can have a substantial impact on circulation and temperature, hence an important role in ozone chemistry for chemistry-climate models. Several types of parameterization are currently employed in models, differing in the formulation and for the values assigned to parameters, but the common aim is to quantify the effect of wave breaking on large-scale wind and temperature patterns. In the last decade, both global observations from satellite-borne instruments and the outputs of very high resolution climate models provided insight on the variability and properties of gravity wave field, and these results can be used to constrain some of the empirical parameters present in most parameterization scheme. A feature of the NOGW forcing that clearly emerges is the intermittency, linked with the nature of the sources: this property is absent in the majority of the models, in which NOGW parameterizations are uncoupled with other atmospheric phenomena, leading to results which display lower variability compared to observations. In this work, we analyze the climate simulated in AMIP runs of the MAECHAM5 model, which uses the Hines NOGW parameterization and with a fine vertical resolution suitable to capture the effects of wave-mean flow interaction. We compare the results obtained with two
Gravity Waves characteristics and their impact on turbulent transport above an Antarctic Ice Sheet
Cava, Daniela; Giostra, Umberto; Katul, Gabriel
2016-04-01
Turbulence within the stable boundary layer (SBL) remains a ubiquitous feature of many geophysical flows, especially over glaciers and ice-sheets. Although numerous studies have investigated various aspects of the boundary layer motion during stable atmospheric conditions, a unified picture of turbulent transport within the SBL remains elusive. In a strongly stratified SBL, turbulence generation is frequently associated with interactions with sub-meso scale motions that are often a combination of gravity waves (GWs) and horizontal modes. While some progress has been made in the inclusion of GW parameterisation within global models, description and parameterisation of the turbulence-wave interaction remain an open question. The discrimination between waves and turbulence is a focal point needed to make progress as these two motions have different properties with regards to heat, moisture and pollutant transport. In fact, the occurrence of GWs can cause significant differences and ambiguities in the interpretation of turbulence statistics and fluxes if not a priori filtered from the analysis. In this work, the characteristics of GW and their impact on turbulent statistics were investigated using wind velocity components and scalars collected above an Antarctic Ice sheet during an Austral Summer. Antarctica is an ideal location for exploring the characteristics of GW because of persistent conditions of strongly stable atmospheric stability in the lower troposphere. Periods dominated by wavy motions have been identified by analysing time series measured by fast response instrumentation. The GWs nature and features have been investigated using Fourier cross-spectral indicators. The detected waves were frequently characterised by variable amplitude and period; moreover, they often produced non-stationarity and large intermittency in turbulent fluctuations that can significantly alter the estimation of turbulence statistics in general and fluxes in particular. A multi
What gravity waves are telling about quantum spacetime
Arzano, Michele; Calcagni, Gianluca
2016-06-01
We discuss various modified dispersion relations motivated by quantum gravity which might affect the propagation of the recently observed gravitational-wave signal of the event GW150914. We find that the bounds set by the data on the characteristic quantum-gravity mass scale M are too weak to constrain these scenarios and, in general, much weaker than the expected M >104 eV for a correction to the dispersion relation linear in 1 /M . We illustrate this issue by giving lower bounds on M , plus an upper bound coming from constraints on the size of a quantum ergosphere. We also show that a phenomenological dispersion relation ω2=k2(1 +α kn/Mn) is compatible with observations and, at the same time, has a phenomenologically viable mass M >10 TeV only in the quite restrictive range 0 models.
Gravitational Waves and the Fate of Scalar-Tensor Gravity
Bettoni, Dario; Hinterbichler, Kurt; Zumalacárregui, Miguel
2016-01-01
We investigate the propagation speed of gravitational waves (GWs) in generic scalar-tensor gravity. A difference in the speed of gravity relative to the speed of light can be caused by the emergence of a disformal geometry in the gravitational sector. This requires the background scalar configuration to both spontaneously break Lorentz symmetry and couple to second derivatives of the metric perturbations through the Weyl tensor or higher derivatives of the scalar. The latter requirement allows a division of gravitational theories into two families: those that predict that GWs propagate exactly at the speed of light and those that allow for anomalous speed. Neutron star binary mergers and other GW events with an associated electromagnetic counterpart can place extremely tight constraints on the speed of GWs relative to the speed of light. However, such observations become impossible if the speed is modified too much, as predicted by some models of cosmic acceleration. Complementary measurements of the speed of...
A semiclassical Hamiltonian for plane waves in loop quantum gravity
Neville, Donald E
2013-01-01
This is the first of two papers which study the semiclassical limit of a loop quantum gravity (LQG) canonical quantization of unidirectional plane gravity waves. Initially I formulate an exact LQG in which each triad, E^x_X for example, grasps only one of the x holonomies present at the vertex. Field strengths are non-local, constructed from holonomies which connect two neighboring vertices of the spin network. The equations are simplified using a semiclassical approximation, meaning eigenvalues of the volume operator are assumed to be large enough that the [volume, holonomy] commutators may be replaced by their quantum field theory limits. Additionally, SU(2) holonomies are expanded in sines and cosines, sines are assumed small, and terms quadratic in sines are dropped. In the semiclassical limit many non-local features disappear. However, differences replace derivatives with respect to z, the propagation direction; and semiclassical triads grasp both holonomies present at each vertex. Gauge-fixing constrain...
Characteristics of gravity waves generated in a baroclinic instability simulation
Directory of Open Access Journals (Sweden)
Y.-H. Kim
2015-11-01
Full Text Available An idealized baroclinic instability case is simulated using a ~ 10 km resolution global model to investigate the characteristics of gravity waves (GWs generated in the baroclinic life cycle. Three groups of GWs (W1–W3 appear around the high-latitude surface trough at the mature stage of the baroclinic wave. They have horizontal and vertical wavelengths of 40–400 and 2.9–9.8 km, respectively, in the upper troposphere. The two-dimensional phase-velocity spectrum of the waves is arc-shaped with a peak at 17 m s−1 eastward, which is difficult for the waves to propagate upward through the tropospheric westerly jet. At the breaking stage of the baroclinic wave, a midlatitude surface low is isolated from the higher-latitude trough, and two groups of quasi-stationary GWs (W4 and W5 appear near the surface low. These waves have horizontal and vertical wavelengths of 60–400 and 4.9–14 km, respectively, and are able to propagate vertically for long distances. The generation mechanism of the simulated GWs is discussed.
Planetary and Gravity Waves in the Mesosphere and Lower Thermosphere
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.
Internal gravity waves: Analysis using the periodic, inverse scattering transform
Directory of Open Access Journals (Sweden)
W. B. Zimmerman
1999-01-01
Full Text Available The discrete periodic inverse scattering transform (DPIST has been shown to provide the salient features of nonlinear Fourier analysis for surface shallow water waves whose dynamics are governed by the Korteweg-de Vries (KdV equation - (1 linear superposition of components with power spectra that are invariants of the motion of nonlinear dispersive waves and (2 nonlinear filtering. As it is well known that internal gravity waves also approximately satisfy the KdV equation in shallow stratified layers, this paper investigates the degree to which DPIST provides a useful nonlinear spectral analysis of internal waves by application to simulations and wave tank experiments of internal wave propagation from localized dense disturbances. It is found that DPIST analysis is sensitive to the quantity λ = (r/6s * (ε/μ2, where the first factor depends parametrically on the Richardson number and the background shear and density profiles and the second factor is the Ursell number-the ratio of the dimensionless wave amplitude to the dimensionless squared wavenumber. Each separate wave component of the decomposition of the initial disturbance can have a different value, and thus there is usually just one component which is an invariant of the motion found by DPIST analysis. However, as the physical applications, e.g. accidental toxic gas releases, are usually concerned with the propagation of the longest wavenumber disturbance, this is still useful information. In cases where only long, monochromatic solitary waves are triggered or selected by the waveguide, the entire DPIST spectral analysis is useful.
Lay, E. H.; Shao, X. M.; Kendrick, A.
2014-12-01
Gravity waves with periods greater than 5 minutes and acoustic waves with periods between 3 and 5 minutes have been detected at ionospheric heights (250-350 km) and associated with severe thunderstorms. Modeling results support these findings, indicating that acoustic waves should be able to reach 250-350 km within ~250 km horizontally of the source, and gravity waves should be able to propagate significantly further. However, the mechanism by which the acoustic waves are generated and the ubiquity of occurrence of both types of wave is unknown. We use GPS total electron content measurements to detect gravity and acoustic waves in the ionosphere. We perform a statistical study from 2005 May - July to compare the occurrence rate and horizontal extent of the waves to storm size and convective height from NEXRAD radar measurements. It is found that both gravity waves and acoustic wave horizontal extent is primarily associated with storm size and not convective height.
Gravity wave influence on NLC: experimental results from ALOMAR, 69° N
Directory of Open Access Journals (Sweden)
H. Wilms
2013-12-01
Full Text Available The influence of gravity waves on noctilucent clouds (NLC at ALOMAR (69° N is analysed by relating gravity wave activity to NLC occurrence from common-volume measurements. Gravity wave kinetic energies are derived from MF-radar wind data and filtered into different period ranges by wavelet transformation. From the dataset covering the years 1999–2011, a direct correlation between gravity wave kinetic energy and NLC occurrence is not found, i.e., NLC appear independently of the simultaneously measured gravity wave kinetic energy. In addition, gravity wave activity is divided into weak and strong activity as compared to a 13 yr mean. The NLC occurrence rates during strong and weak activity are calculated separately for a given wave period and compared to each other. Again, for the full dataset no dependence of NLC occurrence on relative gravity wave activity is found. However, concentrating on 12 h of NLC detections during 2008, we do find an NLC-amplification with strong long-period gravity wave occurrence. Our analysis hence confirms previous findings that in general NLC at ALOMAR are not predominantly driven by gravity waves while exceptions to this rule are at least possible.
The criterion of gravity wave instability induced by photochemistry in summer polar mesopause region
Institute of Scientific and Technical Information of China (English)
徐寄遥; 吴永富; 王咏梅; 傅利平
2002-01-01
This paper studies the effect of photochemistry on the gravity wave instability in summer polar mesopause region. The calculation method of the effects of eddy viscosity, conductivity and eddy diffusion of chemical species on the gravity wave instability induced by photochemistry are studied. The critical wavelength of the instability is given in this paper. The influences of some parameters on it are discussed. The study shows that the gravity wave instability induced by photochemistry is sensitive to the temperature and atomic oxygen profiles.
First champ mission results for gravity, magnetic and atmospheric studies
Lühr, Hermann; Schwintzer, Peter
2003-01-01
In the summer of 2000 the German geo-research satellite CHAMP was launched into orbit. Its innovative payload arrangement and the low intial orbit allow CHAMP to simultaneously collect and almost continuously analyse precise data relating to gravity and magnetic fields at low altitude. In addition to this CHAMP also measures the neutral atmosphere and ionosphere using GPS techniques. Eighteen months after the launch, CHAMP research groups from all over the world met at the Geo-Forschungs-Zentrum in Potsdam for an initial exchange of experiences and results. The main outcome of this user meeting is summarized in this volume. Apart from technical information about the mission, the book offers a comprehensive insight into the present status of CHAMP data exploitation for Earth system research and practical applications in geodesy, geophysics and meteorology.
Numerical Simulation of Hydrodynamic Behaviors of Gravity Cage in Waves
Institute of Scientific and Technical Information of China (English)
ZHAO Yun-peng; LI Yu-cheng; DONG Guo-hai; GUI Fu-kun
2007-01-01
This paper aims at investigation of the dynamic properties of gravity cage exposed to waves by use of a numerical model. The numerical model is developed, based on lumped mass method to set up the equations of motion of the whole cage; meanwhile the solutions of equations are solved by the Runge-Kutta-Verner fifth-order and sixth-order method. Physical model tests have been carried out to examine the validity of the numerical model. The results by the numerical simulation agree well with the experimental data.
Long-period unstable gravity-waves and associated VHF radar echoes
Directory of Open Access Journals (Sweden)
R. M. Worthington
Full Text Available VHF atmospheric radar is used to measure the wind velocity and radar echo power related to long-period wind perturbations, including gravity waves, which are observed commonly in the lower stratosphere and tropopause region, and sometimes in the troposphere. These wind structures have been identified previously as either inertia-gravity waves, often associated with jet streams, or mountain waves. At heights of peak wind shear, imbalances are found between the echo powers of a symmetric pair of radar beams, which are expected to be equal. The largest of these power differences are found for conditions of simultaneous high wind shear and high aspect sensitivity. It is suggested that the effect might arise from tilted specular reflectors or anisotropic turbulent scatterers, a result of, for example, Kelvin-Helmholtz instabilities generated by the strong wind shears. This radar power-difference effect could offer information about the onset of saturation in long-period waves, and the formation of thin layers of turbulence.
Seasonal changes in gravity wave activity measured by lidars at mid-latitudes
Directory of Open Access Journals (Sweden)
M. Rauthe
2008-07-01
Full Text Available More than 230 nights of temperature measurements between 1 and 105 km have been performed at the Leibniz-Institute of Atmospheric Physics in Kühlungsborn with a combination of two different lidars, i.e. a Rayleigh-Mie-Raman lidar and a potassium lidar. About 1700 h of measurements have been collected between 2002 and 2006. Apart from some gaps due to the adverse weather conditions the measurements are well distributed throughout the year. Comprehensive information about the activity of medium- and low-frequency gravity waves was extracted from this data set. The dominating vertical wavelengths found are between 10 and 20 km and do not show any seasonal variation. In contrast the temperature fluctuations due to gravity waves experience a clear annual cycle with a maximum in winter. The most significant differences exist around 60 km where the fluctuations in winter are more than two times larger than they are in summer. Only small seasonal differences are observed above 90 km and below 35 km. Generally, the fluctuations grow from about 0.5 K up to 8 K between 20 and 100 km. Damping of waves is observed at nearly all altitudes and in all seasons. The planetary wave activity shows a similar structure in altitude and season as the gravity wave activity which indicates a strong coupling between the processes of the different scales. Combining the monthly mean temperatures and the fluctuations we show that the transition between winter and summer season and vice versa seems to start in the mesopause region and to penetrate downward.
Quantum Gravity Explanation of the Wave-Particle Duality
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.
Spatiotemporal measurement of surfactant distribution on gravity-capillary waves
Strickland, Stephen L; Daniels, Karen E
2015-01-01
Materials adsorbed to the surface of a fluid -- for instance, crude oil, biogenic slicks, or industrial/medical surfactants -- will move in response to surface waves. Due to the difficulty of non-invasive measurement of the spatial distribution of a molecular monolayer, little is known about the dynamics that couple the surface waves and the evolving density field. Here, we report measurements of the spatiotemporal dynamics of the density field of an insoluble surfactant driven by gravity-capillary waves in a shallow cylindrical container. Standing Faraday waves and traveling waves generated by the meniscus are superimposed to create a non-trivial surfactant density field. We measure both the height field of the surface using moir\\'e-imaging, and the density field of the surfactant via the fluorescence of NBD-tagged phosphatidylcholine, a lipid. Through phase-averaging stroboscopically-acquired images of the density field, we determine that the surfactant accumulates on the leading edge of the traveling menis...
Linear theory of the response of Na mixing ratio to gravity waves
Institute of Scientific and Technical Information of China (English)
XU Jiyao; JI Qiao; WU Mingliang
2003-01-01
The influence of gravity waves on the sodium layer is studied by using a linear photochemical-dynamical coupling gravity wave model. The model includes the background photochemistry and the photochemical reactions in the sodium layer. The amplitude and phase difference of the response of sodium mixing ratio to gravity waves are calculated. The results indicate that the lower part of sodium layer is the most sensitive region responding to gravity waves. The perturbation of sodium mixing ratio is in phase with temperature in the lower part of the layer. However, it is out of phase with temperature fluctuation in the upper part.
Constraining modified theories of gravity with gravitational wave stochastic background
Maselli, Andrea; Ferrari, Valeria; Kokkotas, Kostas; Schneider, Raffaella
2016-01-01
The direct discovery of gravitational waves has finally opened a new observational window on our Universe, suggesting that the population of coalescing binary black holes is larger than previously expected. These sources produce an unresolved background of gravitational waves, potentially observables by ground-based interferometers. In this paper we investigate how modified theories of gravity, modeled using the ppE formalism, affect the expected signal, and analyze the detectability of the resulting stochastic background by current and future ground-based interferometers. We find the constraints that AdLIGO would be able to set on modified theories, showing that they may significantly improve the current bounds obtained from astrophysical observations of binary pulsars.
What gravity waves are telling about quantum spacetime
Arzano, Michele
2016-01-01
We discuss various modified dispersion relations motivated by quantum gravity which might affect the propagation of the recently observed gravitational-wave signal of the event GW150914. We find that the bounds set by the data on the characteristic quantum-gravity mass scale $M$ are too weak to constrain these scenarios and, in general, much weaker than the expected $M> 10^4\\,\\text{eV}$ for a correction to the dispersion relation linear in $1/M$. We illustrate this issue by giving lower bounds on $M$, plus an upper bound coming from constraints on the size of a quantum ergosphere. We also show that a phenomenological dispersion relation $\\omega^2 = k^2(1+\\alpha k^n/M^n)$ is compatible with observations and, at the same time, has a phenomenologically and theoretically viable mass $10\\,\\text{TeV}
A comprehensive observational filter for satellite infrared limb sounding of gravity waves
Trinh, Thai; Kalisch, Silvio; Preusse, Peter; Chun, Hye Yeong; Eckermann, Stephen D.; Ern, Manfred; Riese, Martin
2015-04-01
Infrared limb sounding provides valuable observations for understanding the dynamics of the middle atmosphere. For the interpretation of gravity wave (GW) observations, the observational filter plays a crucial role. We describe a comprehensive observational filter for this technique. Both instrument visibility and observation geometry are considered in this filter with a high level of accuracy. Four main aspects that influence the GW spectrum are discussed thoroughly. They are: (1) visibility filter, (2) projection of the horizontal wavelength on the tangent-point track, (3) aliasing effect, and (4) calculation of the observed vertical wavelength. Gravity waves simulated by coupling a convective GW source (CGWS) scheme with the gravity wave regional or global ray tracer (GROGRAT) are used as an example for applying the observational filter. The observation geometries of the satellite instruments SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) and HIRDLS (High Resolution Dynamics Limb Sounder) are considered. The visibility filter is found to be the most important aspect: it strongly influences the GWMF spectrum for both instruments. The second important aspect is aliasing for SABER, and projection on tangent-point track for HIRDLS. It is shown that the retrieval (a part of the "visibility filter" process) significantly affects the vertical wavelength distribution. For some cases, the short-horizontal-scale spectrum might be projected towards longer horizontal wavelengths where the original spectrum was not located. Also, GWMF values at very short horizontal wavelengths were significantly decreased due to the observational filter. In addition, we discuss the interpretation of observed data using this observational filter, as well as its applicability to other types of instruments.
Gravitational Wave Memory: A New Approach to Study Modified Gravity
Du, Song Ming
2016-01-01
It is well known that two types of gravitational wave memory exist in general relativity (GR): the linear memory and the non-linear, or Christodoulou memory. These effects, especially the latter, depend on the specific form of 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 gravitational wave, respectively. In particular, 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 gravitation...
Yiğit, Erdal; Liu, Guiping; Medvedev, Alexander S; Mahaffy, Paul R; Kuroda, Takeshi; Jakosky, Bruce M
2015-01-01
First high-altitude observations of gravity wave (GW)-induced CO$_2$ density perturbations in the Martian thermosphere retrieved from NASA's NGIMS instrument on board the MAVEN satellite are presented and interpreted using the extended GW parameterization of Yi\\u{g}it et al. [2008] and the Mars Climate Database as an input. Observed relative density perturbations between 180-220 km of 20-40 % demonstrate appreciable local time, latitude, and altitude variations. Modeling for the spatiotemporal conditions of the MAVEN observations suggests that GWs can directly propagate from the lower atmosphere to the thermosphere, produce appreciable dynamical effects, and likely contribute to the observed fluctuations. Modeled effects are somewhat smaller than the observed but their highly variable nature is in qualitative agreement with observations. Possible reasons for discrepancies between modeling and measurements are discussed.
Identification of gravity wave sources using reverse ray tracing over Indian region
Directory of Open Access Journals (Sweden)
M. Pramitha
2014-07-01
Full Text Available Reverse ray tracing method is successfully implemented for the first time in the Indian region for identification of the sources and propagation characteristics of the gravity waves observed using airglow emissions from Gadanki (13.5° N, 79.2° E and Hyderabad (17.5° N, 78.5° E. Wave amplitudes are also traced back for these wave events by including both radiative and diffusive damping. Background temperature and wind data obtained from MSISE-90 and HWM-07 models, respectively, are used for the ray tracing. For Gadanki region suitability of these models is tested. Further, a climatological model of background atmosphere for Gadanki region has been developed using a long-term of nearly 30 years of observations available from a variety of ground-based (MST radar, radiosonde, MF radar, rocket-, and satellite-borne measurements. For considering real-time atmospheric inputs, ERA-Interim products are utilized. By this reverse ray method, the source locations for nine wave events could be identified to be in the upper troposphere, whereas, for five other events the waves seem to have been ducted in the mesosphere itself. Uncertainty in locating the terminal points in the horizontal direction is estimated to be within 50–100 and 150–300 km for Gadanki and Hyderabad wave events, respectively. This uncertainty arises mainly due to non-consideration of the day-to-day variability in tidal amplitudes. As no convection in-and-around the terminal points are noticed, it is unlikely to be the source. Interestingly, large (~9 m s−1 km−1 vertical shear in the horizontal wind is noted near the ray terminal points (at 10–12 km altitude and is identified to be the source for generating the nine wave events. Conditions prevailing at the terminal points for each of the 14 events are also provided. These events provide leads to a greater understanding of the tropical lower and upper atmospheric coupling through gravity waves.
Observations of acoustic-gravity waves in the troposphere by lidar
Borchevkina, Olga; Karpov, Ivan
2015-04-01
Many experimental researches reveal disturbances of the parameters of the upper atmosphere and ionosphere caused by the development of strong weather disturbances, seismic events on the surface, a tsunami generated by an underwater earthquake. The physical mechanisms that implement these various communication layers of the atmosphere and determine the morphological characteristics of ionospheric disturbances, remain insufficiently understood. Hypotheses about the influence of the processes in the lower atmosphere on the condition of the upper atmosphere and ionosphere are based on the concept of generation of acoustic-gravity (AGW) and internal gravity (IGW) waves in the lower atmosphere and their distribution in the upper atmosphere. That is why, the study of the processes of generation AGW in the lower atmosphere is interest to confirm the validity of such representations. Regular source of perturbations of all layers of the atmosphere is the solar terminator (ST). Observations perturbation parameters of the atmosphere and ionosphere during the passage of the ST will determine the frequency spectrum of the resulting disturbances. The paper presents the results of experimental researches, which demonstrating an increase of wave activity with periods of AGW and IGW in the observations of the lower atmosphere during the passage of the solar terminator. Observations of variations in the parameters of the lower atmosphere during the passage of ST were performed by the lidar. The observations were carried out in Kaliningrad (52N, 22 E) in 2012-2014. Analysis of the observations focused on the allocation of variations with periods ranging from 2 to 20 min., caused by the generation of AGW in ST. The duration of each observation was for several hours. This allows us to consider the dynamics of changes in the characteristics of such variations during observations. Analysis of the results of observations revealed a number of features in the dynamics of AGW during the
Reflection and Ducting of Gravity Waves Inside the Sun
MacGregor, K B
2011-01-01
Internal gravity waves excited by overshoot at the bottom of the convection zone can be influenced by rotation and by the strong toroidal magnetic field that is likely to be present in the solar tachocline. Using a simple Cartesian model, we show how waves with a vertical component of propagation can be reflected when traveling through a layer containing a horizontal magnetic field with a strength that varies with depth. This interaction can prevent a portion of the downward-traveling wave energy flux from reaching the deep solar interior. If a highly reflecting magnetized layer is located some distance below the convection zone base, a duct or wave guide can be set up, wherein vertical propagation is restricted by successive reflections at the upper and lower boundaries. The presence of both upward- and downward-traveling disturbances inside the duct leads to the existence of a set of horizontally propagating modes that have significantly enhanced amplitudes. We point out that the helical structure of these ...
Small divisor problem in the theory of three-dimensional water gravity waves
Iooss, Gérard; Plotnikov, Pavel
2009-01-01
We consider doubly-periodic travelling waves at the surface of an infinitely deep perfect fluid, only subjected to gravity $g$ and resulting from the nonlinear interaction of two simply periodic travelling waves making an angle $2\\theta $ between them. \
Characteristics of equatorial gravity waves derived from mesospheric airglow imaging observations
Directory of Open Access Journals (Sweden)
S. Suzuki
2009-04-01
Full Text Available We present the characteristics of small-scale (<100 km gravity waves in the equatorial mesopause region derived from OH airglow imaging observations at Kototabang (100.3° E, 0.2° S, Indonesia, from 2002 to 2005. We adopted a method that could automatically detect gravity waves in the airglow images using two-dimensional cross power spectra of gravity waves. The propagation directions of the waves were likely controlled by zonal filtering due to stratospheric mean winds that show a quasi-biennial oscillation (QBO and the presence of many wave sources in the troposphere.
Baumgarten, G.; Fiedler, J.; Hildebrand, J.; Lübken, F.-J.
2015-12-01
We report on the first observation of persistent inertia gravity wave signatures in the horizontal wind and temperature by Doppler Rayleigh lidar in the middle atmosphere. The observations were performed at the Arctic Lidar Observatory for Middle Atmosphere Research station in northern Norway (69°N,16°E) between 21 and 23 January 2012. The measurements cover the altitude range from 20 km to about 80 km during nighttime and to about 70 km during daytime. We observe amplitudes of 5 to 25 m/s and 1 to 8 K in wind and temperature, respectively. The measured kinetic to potential energy density ratio is about 10, indicating that the majority of variability is due to waves with intrinsic frequencies close to the inertial frequency. The entire wavefield is mainly characterized by the presence of multiple waves; however, quasi-monochromatic waves could be identified at limited times around 60 km altitude with a mean momentum flux in direction of propagation of 3.8 m2/s2.
Examining Traveling Waves in Mars Atmosphere Reanalyses
Greybush, Steven J.; Wilson, R. John
2015-11-01
Synoptic-scale eddies (traveling waves) are a key feature of the variability of Mars atmosphere weather in the extratropics, and are linked to the initiation of dust storms. Mars reanalyses, which combine satellite observations with simulations from a Mars Global Climate Model (MGCM), provide a four-dimensional picture of the evolution of these waves in terms of temperature, winds, pressure, and aerosol fields. The Ensemble Mars Atmosphere Reanalysis System (EMARS) has created multiple years of Mars weather maps through the assimilation of Thermal Emission Spectrometer (TES) and Mars Climate Sounder (MCS) temperature profiles using the ensemble Kalman filter and the GFDL MGCM. We investigate the robustness of the synoptic eddies to changes in the aerosol fields, model parameters, data assimilation system design, and observation dataset (TES vs. MCS). We examine the evolution of wavenumber regimes, their seasonal evolution, and interannual variability. Finally, reanalysis fields are combined with spacecraft visible imagery (e.g. MGS Mars Orbital Camera), demonstrating the link between meteorological fields (temperature, pressure, and wind) and dust fronts.
On reduced models for gravity waves generated by moving bodies
Trinh, Philippe H
2015-01-01
In 1982, Marshall P. Tulin published a report proposing a framework for reducing the equations for gravity waves generated by moving bodies into a single nonlinear differential equation solvable in closed form [Proc. 14th Symp. on Naval Hydrodynamics, 1982, pp.19-51]. Several new and puzzling issues were highlighted by Tulin, notably the existence of weak and strong wave-making regimes, and the paradoxical fact that the theory seemed to be applicable to flows at low speeds, "but not too low speeds". These important issues were left unanswered, and despite the novelty of the ideas, Tulin's report fell into relative obscurity. Now thirty years later, we will revive Tulin's observations, and explain how an asymptotically consistent framework allows us to address these concerns. Most notably, we will explain, using the asymptotic method of steepest descents, how the production of free-surface waves can be related to the arrangement of integration contours connected to the shape of the moving body. This approach p...
Dislocations in magnetohydrodynamic waves in a stellar atmosphere.
López Ariste, A; Collados, M; Khomenko, E
2013-08-23
We describe the presence of wave front dislocations in magnetohydrodynamic waves in stratified stellar atmospheres. Scalar dislocations such as edges and vortices can appear in Alfvén waves, as well as in general magnetoacoustic waves. We detect those dislocations in observations of magnetohydrodynamic waves in sunspots in the solar chromosphere. Through the measured charge of all the dislocations observed, we can give for the first time estimates of the modal contribution in the waves propagating along magnetic fields in solar sunspots.
Plane wave holonomies in quantum gravity. II. A sine wave solution
Neville, Donald E.
2015-08-01
This paper constructs an approximate sinusoidal wave packet solution to the equations of canonical gravity. The theory uses holonomy-flux variables with support on a lattice (LHF =lattice-holonomy flux ). There is an SU(2) holonomy on each edge of the LHF simplex, and the goal is to study the behavior of these holonomies under the influence of a passing gravitational wave. The equations are solved in a small sine approximation: holonomies are expanded in powers of sines and terms beyond sin2 are dropped; also, fields vary slowly from vertex to vertex. The wave is unidirectional and linearly polarized. The Hilbert space is spanned by a set of coherent states tailored to the symmetry of the plane wave case. Fixing the spatial diffeomorphisms is equivalent to fixing the spatial interval between vertices of the loop quantum gravity lattice. This spacing can be chosen such that the eigenvalues of the triad operators are large, as required in the small sine limit, even though the holonomies are not large. Appendices compute the energy of the wave, estimate the lifetime of the coherent state packet, discuss circular polarization and coarse-graining, and determine the behavior of the spinors used in the U(N) SHO realization of LQG.
Holographic p-wave superfluid in Gauss-Bonnet gravity
Liu, Shancheng; Jing, Jiliang
2016-01-01
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.
Scattering of gravity waves in subcritical flows over an obstacle
Robertson, Scott; Parentani, Renaud
2016-01-01
We numerically study the scattering coefficients of linear water waves on stationary flows above a localized obstacle. We compare the scattering on trans- and subcritical flows, and then focus on the latter which have been used in recent analog gravity experiments. The main difference concerns the magnitude of the mode amplification: whereas transcritical flows display a large amplification (which is generally in good agreement with the Hawking prediction), this effect is heavily suppressed in subcritical flows. This is due to the transmission across the obstacle for frequencies less than some critical value. As a result, subcritical flows display high- and low-frequency behaviors separated by a narrow band around the critical frequency. In the low-frequency regime, transmission of long wavelengths is accompanied by non-adiabatic scattering into short wavelengths, whose spectrum is approximately linear in frequency. By contrast, in the high-frequency regime, no simple description seems to exist. In particular...
Janches, Diego; Fritts, David C.; Riggin, Dennis M.; Sulzer, Michael P.; Gonzalez, Sixto
2006-09-01
We report here and in a companion paper by Fritts et al. (2006a) on a new use of the UHF radar at the Arecibo Observatory in Puerto Rico. We have employed the 430 MHz radar for incoherent scatter measurements of radial wind spectra at altitudes from ˜71 to 95 km using the Gregorian and line-feed antennas to define beam angles inclined 15° to the east and west of zenith. We find that the two beams define radial velocities with sufficient accuracy to characterize both the gravity waves and the momentum fluxes due to these waves over the majority of the observed altitude range during daylight hours. The characteristics of the gravity waves inferred from these measurements include (1) vertical scales ranging from ˜2 to 20 km, (2) downward phase progression of the dominant gravity waves up to ˜5 ms-1, and (3) vertical wave number spectra having slopes near a value (-3) expected for saturated gravity waves. Gravity wave frequency spectra and momentum fluxes are addressed in the companion paper.
Axisymmetric Waves in Isothermal Accretion Discs with Vertical Self-Gravity
Institute of Scientific and Technical Information of China (English)
LIU Xiao-Ci; YANG Lan-Tian; WU Shao-Ping; DING Shi-Xue
2001-01-01
We extend the research of axisymmetric waves in accretion discs with three-dimensional structure to the case that vertical self-gravity of the discs is included. We derive and analyze the dispersion relation and solve the eigenfunctions numerically. The following results have been reached: vertical self-gravity expands the forbidden region of the wave propagation. As the influence of the vertical self-gravity increases, the group velocities of the waves get smaller and the vertical nodes of the wave shrink to the middle plane of the disc.
Diffraction and Dissipation of Atmospheric Waves in the Vicinity of Caustics
Godin, O. A.
2015-12-01
A large and increasing number of ground-based and satellite-borne instruments has been demonstrated to reliably reveal ionospheric manifestations of natural hazards such as large earthquakes, strong tsunamis, and powerful tornadoes. To transition from detection of ionospheric manifestations of natural hazards to characterization of the hazards for the purposes of improving early warning systems and contributing to disaster recovery, it is necessary to relate quantitatively characteristics of the observed ionospheric disturbances and the underlying natural hazard and, in particular, accurately model propagation of atmospheric waves from the ground or ocean surface to the ionosphere. The ray theory has been used extensively to model propagation of atmospheric waves and proved to be very efficient in elucidating the effects of atmospheric variability on ionospheric signatures of natural hazards. However, the ray theory predicts unphysical, divergent values of the wave amplitude and needs to be modified in the vicinity of caustics. This paper presents an asymptotic theory that describes diffraction, focusing and increased dissipation of acoustic-gravity waves in the vicinity of caustics and turning points. Air temperature, viscosity, thermal conductivity, and wind velocity are assumed to vary gradually with height and horizontal coordinates, and slowness of these variations determines the large parameter of the problem. Uniform asymptotics of the wave field are expressed in terms of Airy functions and their derivatives. The geometrical, or Berry, phase, which arises in the consistent WKB approximation for acoustic-gravity waves, plays an important role in the caustic asymptotics. In addition to the wave field in the vicinity of the caustic, these asymptotics describe wave reflection from the caustic and the evanescent wave field beyond the caustic. The evanescent wave field is found to play an important role in ionospheric manifestations of tsunamis.
Joint Geophysical Imaging of the Utah Area Using Seismic Body Waves, Surface Waves and Gravity Data
Zhang, H.; Maceira, M.; Toksoz, M. N.; Burlacu, R.; Yang, Y.
2009-12-01
We present a joint geophysical imaging method that makes use of seismic body wave arrival times, surface wave dispersion measurements, and gravity data to determine three-dimensional (3D) Vp and Vs models. An empirical relationship mapping densities to Vp and Vs for earth materials is used to link them together. The joint inversion method takes advantage of strengths of individual data sets and is able to better constrain the velocity models from shallower to greater depths. Combining three different data sets to jointly invert for the velocity structure is equivalent to a multiple-objective optimization problem. Because it is unlikely that the different “objectives” (data types) would be optimized by the same parameter choices, some trade-off between the objectives is needed. The optimum weighting scheme for different data types is based on relative uncertainties of individual observations and their sensitivities to model parameters. We will apply this joint inversion method to determine 3D Vp and Vs models of the Utah area. The seismic body wave arrival times are assembled from waveform data recorded by the University of Utah Seismograph Stations (UUSS) regional network for the past 7 years. The surface wave dispersion measurements are obtained from the ambient noise tomography study by the University of Colorado group using EarthScope/USArray stations. The gravity data for the Utah area is extracted from the North American Gravity Database managed by the University of Texas at El Paso. The preliminary study using the seismic body wave arrival times indicates strong low velocity anomalies in middle crust beneath some known geothermal sites in Utah. The joint inversion is expected to produce a reasonably well-constrained velocity structure of the Utah area, which is helpful for characterizing and exploring existing and potential geothermal reservoirs.
Differences in gravity wave drag between realistic oblique and assumed vertical propagation
Kalisch, Silvio; Preusse, Peter; Ern, Manfred; Eckermann, Stephen D.; Riese, Martin
2014-09-01
Gravity wave (GW) parametrizations for general circulation models (GCMs) restrict the propagation of GWs to the vertical direction. The influence of this vertical-only propagation assumption on the distribution of GW drag (GWD) has not yet been investigated. Thus, we present results of two global GW ray tracing simulations, one with full three-dimensional propagation (GWO) and a second one with vertical-only propagation (GWV) of GWs for January and July 2008. The Gravity wave Regional Or Global RAy Tracer (GROGRAT) was used to perform these simulations with a global homogeneous and isotropic launch distribution. Both simulations, GWO and GWV, are analyzed with respect to GWD in the zonal and meridional direction. The location of zonal GWD maxima changes. GWO shows in comparison to GWV a poleward shift of zonal GWD in both seasons with increased GWD at the summer stratopause. The meridional GWD is much stronger in the GWO case, spatially correlated with the zonal drag, and is generally poleward directed. These features in zonal and meridional drag are consistent with a general prevalence of poleward propagation of GWs. Additional simulations suggest that this is due to the Coriolis effect as well as wind filtering around the tropopause, allowing more GWs to propagate into the middle atmosphere. We infer how GWs of different horizontal wavelengths and phase speeds cause the main differences in GWD in the middle atmosphere. A simple test for GCMs is proposed to assess the effects of the altered meridional drag on the general circulation and the interaction with planetary waves.
Slope wavenumber spectrum models of capillary and capillary-gravity waves
Institute of Scientific and Technical Information of China (English)
贾永君; 张杰; 王岩峰
2010-01-01
Capillary and capillary-gravity waves possess a random character, and the slope wavenumber spectra of them can be used to represent mean distributions of wave energy with respect to spatial scale of variability. But simple and practical models of the slope wavenumber spectra have not been put forward so far. In this article, we address the accurate definition of the slope wavenumber spectra of water surface capillary and capillary-gravity waves. By combining the existing slope wavenumber models and using th...
A two-dimensional Stockwell transform for gravity wave analysis of AIRS measurements
Hindley, Neil P.; Smith, Nathan D.; Wright, Corwin J.; Rees, D. Andrew S.; Mitchell, Nicholas J.
2016-06-01
Gravity waves (GWs) play a crucial role in the dynamics of the earth's atmosphere. These waves couple lower, middle and upper atmospheric layers by transporting and depositing energy and momentum from their sources to great heights. The accurate parameterisation of GW momentum flux is of key importance to general circulation models but requires accurate measurement of GW properties, which has proved challenging. For more than a decade, the nadir-viewing Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite has made global, two-dimensional (2-D) measurements of stratospheric radiances in which GWs can be detected. However, one problem with current one-dimensional methods for GW analysis of these data is that they can introduce significant unwanted biases. Here, we present a new analysis method that resolves this problem. Our method uses a 2-D Stockwell transform (2DST) to measure GW amplitudes, horizontal wavelengths and directions of propagation using both the along-track and cross-track dimensions simultaneously. We first test our new method and demonstrate that it can accurately measure GW properties in a specified wave field. We then show that by using a new elliptical spectral window in the 2DST, in place of the traditional Gaussian, we can dramatically improve the recovery of wave amplitude over the standard approach. We then use our improved method to measure GW properties and momentum fluxes in AIRS measurements over two regions known to be intense hotspots of GW activity: (i) the Drake Passage/Antarctic Peninsula and (ii) the isolated mountainous island of South Georgia. The significance of our new 2DST method is that it provides more accurate, unbiased and better localised measurements of key GW properties compared to most current methods. The added flexibility offered by the scaling parameter and our new spectral window presented here extend the usefulness of our 2DST method to other areas of geophysical data analysis and beyond.
Dislocations in magnetohydrodynamic waves in a stellar atmosphere
Ariste, A López; Khomenko, E
2013-01-01
We describe the presence of wavefront dislocations in magnetohydrodynamic waves in stratified stellar atmospheres. Scalar dislocations such as edges and vortices can appear in Alfv\\'en waves, as well as in general magneto-acoustic waves. We detect those dislocations in observations of magnetohydrodynamic waves in sunspots in the solar chromosphere. Through the measured charge of all the dislocations observed, we can give for the first time estimates of the modal contribution in the waves propagating along magnetic fields in solar sunspots.
Majda, Andrew J.; Khouider, Boualem; Frenkel, Yevgeniy
2015-02-01
Atmospheric convection has the striking capability to organize itself into a hierarchy of cloud clusters and super-clusters on scales ranging from the convective cell of a few kilometres to planetary scale disturbances such as the Madden-Julian oscillation. It is widely accepted that this phenomenon is due in large part to the two-way coupling between convective processes and equatorially trapped waves and planetary scale flows in general. However, the physical mechanisms responsible for this multiscale organization and the associated across-scale interactions are poorly understood. The two main peculiarities of the tropics are the vanishing of the Coriolis force at the equator and the abundance of mid-level moisture. Here we test the effect of these two physical properties on the organization of convection and its interaction with gravity waves in a simplified primitive equation model for flows parallel to the equator. Convection is represented by deterministic as well as stochastic multicloud models that are known to represent organized convection and convectively coupled waves quite well. It is found here that both planetary rotation and mid-troposphere moisture are important players in the diminishing of organized convection and convectively coupled gravity wave activity in the subtropics and mid-latitudes. The meridional mean circulation increases with latitude while the mean zonal circulation is much shallower and is dominated by mid-level jets, reminiscent of a second baroclinic mode circulation associated with a congestus mode instability in the model. This is consistent with the observed shallow Hadley and Walker circulations accompanied by congestus cloud decks in the higher latitude tropics and sub-tropics. Moreover, deep convection activity in the stochastic model simulations becomes very patchy and unorganized as the computational domain is pushed towards the subtropics and mid-latitudes. This is consistent with previous work based on cloud resolving
Jensen, Eric J.
2016-01-01
Recent investigations of the influence of atmospheric waves on ice nucleation in cirrus have identified a number of key processes and sensitivities: (1) ice concentrations produced by homogeneous freezing are strongly dependent on cooling rates, with gravity waves dominating upper tropospheric cooling rates; (2) rapid cooling driven by high-frequency waves are likely responsible for the rare occurrences of very high ice concentrations in cirrus; (3) sedimentation and entrainment tend to decrease ice concentrations as cirrus age; and (4) in some situations, changes in temperature tendency driven by high-frequency waves can quench ice nucleation events and limit ice concentrations. Here we use parcel-model simulations of ice nucleation driven by long-duration, constant-pressure balloon temperature time series, along with an extensive dataset of cold cirrus microphysical properties from the recent ATTREX high-altitude aircraft campaign, to statistically examine the importance of high-frequency waves as well as the consistency between our theoretical understanding of ice nucleation and observed ice concentrations. The parcel-model simulations indicate common occurrence of peak ice concentrations exceeding several hundred per liter. Sedimentation and entrainment would reduce ice concentrations as clouds age, but 1-D simulations using a wave parameterization (which underestimates rapid cooling events) still produce ice concentrations higher than indicated by observations. We find that quenching of nucleation events by high-frequency waves occurs infrequently and does not prevent occurrences of large ice concentrations in parcel simulations of homogeneous freezing. In fact, the high-frequency variability in the balloon temperature data is entirely responsible for production of these high ice concentrations in the simulations.
A survey of atmospheric wave recording at Blacknest
International Nuclear Information System (INIS)
Techniques are described for recording atmospheric waves at the AWRE Blacknest Research Centre. Examples, with interpretative comments, of various types of atmospheric waves observed over a period of several years are illustrated in a series of figures taken from a representative selection of Blacknest records. (author)
Directory of Open Access Journals (Sweden)
L. Thomas
Full Text Available Radar measurements at Aberystwyth (52.4° N, 4.1° W of winds at tropospheric and lower stratospheric heights are shown for 12-13 March 1994 in a region of highly curved flow, downstream of the jet maximum. The perturbations of horizontal velocity have comparable amplitudes in the troposphere and lower stratosphere with downward and upward phase propagation, respectively, in these two height regions. The sense of rotation with increasing height in hodographs of horizontal perturbation velocity derived for hourly intervals show downwards propagation of energy in the troposphere and upward propagation in the lower stratosphere with vertical wavelengths of 1.7 to 2.3 km. The results indicate inertia-gravity waves propagating in a direction similar to that of the jet stream but at smaller velocities. Some of the features observed contrast with those of previous observations of inertia-gravity waves propagating transverse to the jet stream. The interpretation of the hodographs to derive wave parameters has taken account of the vertical shear of the background wind transverse to the direction of wave propagation.
Key words. Meteorology and atmospheric dynamics (mesoscale meteorology; middle atmosphere dynamics; waves and tides
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.
Energy Technology Data Exchange (ETDEWEB)
Leutbecher, M. [DLR Deutsches Zentrum fuer Luft- und Raumfahrt e.V., Wessling (Germany). Inst. fuer Physik der Atmosphaere
1998-07-01
Flow over mountains in the stably stratified atmosphere excites gravity waves. The three-dimensional propagation of these waves into the stratosphere is studied using linear theority as well as idealized and realistic numerical simulations. Stagnation, momentum fluxes and temperature anomalies are analyzed for idealized types of flow. Isolated mountains with elliptical contours are considered. The unperturbed atmosphere has constant wind speed and constant static stability or two layers (troposphere/stratosphere) of constant stability each. Real flow over orography is investigated where gravity waves in the stratosphere have been observed. Characteristics of the gravity wave event over the southern tip of Greenland on 6 January 1992 were recorded on a flight of the ER-2 at an altitude of 20 km. In the second case polar stratospheric clouds (PSC) were observed by an airborne Lidar over Northern Scandinavia on 9 January 1997. The PSC were induced by temperature anomalies in orographic gravity waves. (orig.)
Capillary-gravity waves on a liquid film of arbitrary depth: analysis of the wave resistance.
Wędołowski, Karol; Napiórkowski, Marek
2013-10-01
We discuss the wave resistance in the case of an externally perturbed viscous liquid film of arbitrary thickness. Emphasis is placed on the dependence of the wave resistance on the film thickness H, the length scale b characterizing the external perturbation, and its velocity V. In particular, the effectiveness of the mechanisms of capillary-gravity waves and the viscous dissipation localized in the vicinity of the perturbation are compared and discussed as functions of H and V. We show that, in general, the wave resistance is a nonmonotonous function of H with a maximum whose amplitude and position depend on b and V. In the case of small H the wave resistance depends on a parameter S proportional V/H(3). We find three different regimes of this parameter in which the wave resistance behaves like S(r) with the exponent r equal to 1, 1/3, and -1. These results are also obtained independently within the thin liquid film approximation. This allows us to assess the range of validity of the thin liquid film approximation in various cases, in particular its dependence on the perturbation length scale b. PMID:24229283
Towards a coupled ocean-wave-atmosphere four dimensional data assimilation system
Ngodock, Hans; Carrier, Matthew; Amerault, Clark; Campbell, Timothy; Holt, Teddy; Xu, Liang; Rowley, Clark
2015-04-01
Individual 4dvar systems have been developed at the Naval Research Laboratory (NRL) for the ocean model (Navy coastal ocean model, NCOM), the wave model (simulating waves in the nearshore, SWAN) and the atmospheric component of the coupled ocean-atmosphere mesoscale prediction system (COAMPS). Although the three models within COAPMS are coupled in the forward integration, the initialization of each model is done separately. The coupled system forecast is hindered, however, by the lack of a fully coupled and dynamically balanced ocean-atmosphere analysis. A recent work by Ngodock and Carrier (2013) has highlighted this shortcoming with the NCOM-4DVAR, showing that while the NCOM-4DVAR is able to adjust the ocean state properly, the resulting ocean forecast degrades quickly due to the fact that the atmospheric state has not also been adjusted relative to the ocean observations. Likewise, . Currently, the coupled model is initialized using separate analyses for the ocean and atmosphere that do not account for observations in the adjacent fluid. The lack of a coupled analysis produces shocks in the coupled model in the form of gravity waves that degrade the information gained through DA and increase the error in the coupled forecast. The goal of this presentation is to describe ongoing developments at NRL in building a fully coupled ocean-wave-atmosphere four-dimensional variational (4dvar) data assimilation system using the Earth System Modeling Framework (ESMF).
Effects of anisotropy on the frequency spectrum of gravity waves observed by MST radar
Liu, C. H.
1986-01-01
In the investigation of gravity waves using mesosphere-stratosphere-troposphere radar data, model gravity-wave spectra have been used. In these model spectra, one usually assumes azimuthal symmetry. The effect of spectral anisotropy on the observed spectrum is studied here. It is shown that for a general Garrett-Munk-type spectrum, the anisotropy does not affect the frequency spectrum observed by the vertically beamed radar. For the oblique beam, however, the observed frequency spectrum is changed. A general gravity wave spectrum including azimuthal anisotropy is considered.
HIRDLS observations of global gravity wave absolute momentum fluxes: A wavelet based approach
John, Sherine Rachel; Kishore Kumar, Karanam
2016-02-01
Using wavelet technique for detection of height varying vertical and horizontal wavelengths of gravity waves, the absolute values of gravity wave momentum fluxes are estimated from High Resolution Dynamics Limb Sounder (HIRDLS) temperature measurements. Two years of temperature measurements (2005 December-2007 November) from HIRDLS onboard EOS-Aura satellite over the globe are used for this purpose. The least square fitting method is employed to extract the 0-6 zonal wavenumber planetary wave amplitudes, which are removed from the instantaneous temperature profiles to extract gravity wave fields. The vertical and horizontal wavelengths of the prominent waves are computed using wavelet and cross correlation techniques respectively. The absolute momentum fluxes are then estimated using prominent gravity wave perturbations and their vertical and horizontal wavelengths. The momentum fluxes obtained from HIRDLS are compared with the fluxes obtained from ground based Rayleigh LIDAR observations over a low latitude station, Gadanki (13.5°N, 79.2°E) and are found to be in good agreement. After validation, the absolute gravity wave momentum fluxes over the entire globe are estimated. It is found that the winter hemisphere has the maximum momentum flux magnitudes over the high latitudes with a secondary maximum over the summer hemispheric low-latitudes. The significance of the present study lies in introducing the wavelet technique for estimating the height varying vertical and horizontal wavelengths of gravity waves and validating space based momentum flux estimations using ground based lidar observations.
Directory of Open Access Journals (Sweden)
Joel Arnault
2012-02-01
Full Text Available Gravity waves generated by the Vestfjella Mountains (in western Droning Maud Land, Antarctica, southwest of the Finnish/Swedish Aboa/Wasa station have been observed with the Moveable atmospheric radar for Antarctica (MARA during the SWEDish Antarctic Research Programme (SWEDARP in December 2007/January 2008. These radar observations are compared with a 2-month Weather Research Forecast (WRF model experiment operated at 2 km horizontal resolution. A control simulation without orography is also operated in order to separate unambiguously the contribution of the mountain waves on the simulated atmospheric flow. This contribution is then quantified with a kinetic energy budget analysis computed in the two simulations. The results of this study confirm that mountain waves reaching lower-stratospheric heights break through convective overturning and generate inertia gravity waves with a smaller vertical wavelength, in association with a brief depletion of kinetic energy through frictional dissipation and negative vertical advection. The kinetic energy budget also shows that gravity waves have a strong influence on the other terms of the budget, i.e. horizontal advection and horizontal work of pressure forces, so evaluating the influence of gravity waves on the mean-flow with the vertical advection term alone is not sufficient, at least in this case. We finally obtain that gravity waves generated by the Vestfjella Mountains reaching lower stratospheric heights generally deplete (create kinetic energy in the lower troposphere (upper troposphere–lower stratosphere, in contradiction with the usual decelerating effect attributed to gravity waves on the zonal circulation in the upper troposphere–lower stratosphere.
An efficient numerical method for 3D viscous ship hydrodynamics with free-surface gravity waves
Lewis, M.R.; Koren, B.; Groth, C.; Zingg, D.W.
2006-01-01
A new numerical method for water flows with free-surface gravity waves is investigated. The method is first analyzed with respect to the existence of steady free-surface waves, and the dispersion properties of these waves. Next, the method is used to compute the free water surface generated by a sta
Directory of Open Access Journals (Sweden)
S. Vijaya Bhaskara Rao
2008-06-01
range of −2 to −2.8. The significance of the present study lies in using the ten years of data to estimate the monthly mean vertical wave number spectra of gravity waves, which will find their application in representing the realistic gravity wave characteristics in atmospheric models.
Interpretation of ground-based radiometric observations in terms of a gravity wave model
Canavero, F. G.; Einaudi, F.; Westwater, E. R.; Falls, M. J.; Schroeder, J. A.
1990-01-01
An analysis is presented of 2-hour and 4-hour segments of data taken at Denver, Colorado, on February 3, 1984, by a ground-based radiometer designed and operated by the Wave Propagation Laboratory of the National Oceanic and Atmospheric Administration (NOAA). The zenith-viewing instrument has two moisture-sensing and four temperature-sensing channels. It is demonstrated that a peak at a period of 10 min, present in the spectra of the measured brightness temperature and of the derived geopotential heights, thicknesses, and vertically integrated water vapor content, is due to an internal gravity wave generated by wind shear in the jet aloft. This analysis shows that the radiometer has the sensitivity to detect such disturbances and that the mathematical inversion technique used to retrieve the geopotential field and other integrated quantities retains the derived information as well. Finally, a linear expression is derived which relates the brightness temperature to the atmospheric temperature, density, humidity, and cloud liquid perturbation fields.
Stratospheric gravity wave momentum flux from radio occultations
Schmidt, T.; Alexander, P.; Torre, A.
2016-05-01
Triples of GPS radio occultation (RO) temperature data are used to derive horizontal and vertical gravity wave (GW) parameters in the stratosphere between 20 km and 40 km from which the vertical flux of horizontal momentum is determined. Compared to previous studies using RO data, better limiting values for the sampling distance (Δd≤250 km) and the time interval (Δt≤15 min) are used. For several latitude bands the mean momentum fluxes (MFs) derived in this study are considerably larger than MF from other satellite missions based on horizontal wavelengths calculated between two adjacent temperature profiles along the satellite track. Error sources for the estimation of MF from RO data and the geometrical setup for the applied method are investigated. Another crucial issue discussed in this paper is the influence of different background separation methods to the final MF. For GW analysis a measured temperature profile is divided into a fluctuation and a background and it is assumed that the fluctuation is caused by GWs only. For the background separation, i.e., the detrending of large-scale processes from the measured temperature profile, several methods exist. In this study we compare different detrending approaches and for the first time an attempt is made to detrend RO data with ERA-Interim data from the European Centre for Medium-Range Weather Forecasts. We demonstrate that the horizontal detrending based on RO data and ERA-Interim gives more consistent results compared with a vertical detrending.
Stratospheric gravity wave momentum fluxes from radio occultations
Schmidt, Torsten; Wickert, Jens; De la Torre, Alejandro; Alexander, Peter; Llamedo, Pablo; Ramezani Ziarani, Maryam
2016-07-01
Triples of GPS radio occultation (RO) temperature data are used to derive horizontal and vertical gravity wave (GW) parameters in the stratosphere between 20 km and 40 km from which the vertical flux of horizontal momentum is determined. Compared to previous studies using RO data better limiting values for the sampling distance (Δdprofiles along the satellite track. Error sources for the estimation of MF from RO data and the geometrical setup for the applied method is investigated. Another crucial issue discussed in the presentation is the influence of different background separation methods to the final MF. For GW analysis a measured temperature profile is divided into a fluctuation and a background and it is assumed that the fluctuation is caused by GWs only. For the background separation, i.e. the detrending of large-scale processes from the measured temperature profile, several methods exist. In this study we compare different detrending approaches including a new attempt by detrending RO data with ERA-Interim data from the European Centre for Medium-Range Weather Forecasts. We demonstrate that the horizontal detrending based on RO data and ERA-Interim gives more consistent results compared with a vertical detrending.
Directory of Open Access Journals (Sweden)
J. L. Innis
Full Text Available Zenith-directed Fabry-Perot Spectrometer (FPS and 3-Field Photometer (3FP observations of the λ630 nm emission (~240 km altitude were obtained at Davis station, Antarctica, during the austral winter of 1999. Eleven nights of suitable data were searched for significant periodicities common to vertical winds from the FPS and photo-metric variations from the 3FP. Three wave-like events were found, each of around one or more hours in duration, with periods around 15 minutes, vertical velocity amplitudes near 60 ms^{–1} , horizontal phase velocities around 300 ms^{–1} , and horizontal wavelengths from 240 to 400 km. These characteristics appear consistent with polar cap gravity waves seen by other workers, and we conclude this is a likely interpretation of our data. Assuming a source height near 125 km altitude, we determine the approximate source location by calculating back along the wave trajectory using the gravity wave property relating angle of ascent and frequency. The wave sources appear to be in the vicinity of the poleward border of the auroral oval, at magnetic local times up to 5 hours before local magnetic midnight.
Key words. Meteorology and atmospheric dynamics (thermospheric dynamics; waves and tides
National Aeronautics and Space Administration — Gravity wave detection using space-based long-baseline laser interferometric sensors imposes stringent noise requirements on the system components, including the...
Background gravity wave activity and its variability as determined from Dynasonde data
Negrea, C.; Zabotin, N. A.; Bullett, T. W.; Rietveld, M.
2014-12-01
The importance of gravity waves for the dynamics of the thermosphere-ionosphere system is a well-known fact. Numerical models of the thermosphere-ionosphere must account for gravity wave effects by using various parameterization schemes with currently unknown levels of accuracy. There are several existing methods allowing for the detection of individual instances of gravity wave manifestations. However, little information exists regarding the background wave spectrum and its variability in the thermosphere. We employ Travelling Ionospheric Disturbances (TID's) as tracers for gravity wave propagation, using results of Dynasonde data analysis as the starting point in our calculations. Data from the Wallops Island (VA), San Juan (Puerto Rico), Boulder (CO), Tromso and Svalbard (Norway) instruments are used. The interval between the sounding sessions is 2 minutes and the NeXtYZ inversion procedure (a part of the Dynasonde software package) allows us to obtain a vertical resolution for the parameters of ionospheric plasma in real height better than 1 km. The full output of the inversion procedure consists of height profiles of electron density, X (East-West) and Y (North-South) tilts of the constant plasma density contours and Doppler velocities, all of which showing persistent signs of gravity wave induced TID's. We demonstrate using a few examples that the characteristics of the observed TID's are in good agreement with the dispersion relation describing gravity waves. The ionospheric tilt measurements allow for determination of the direction of propagation for every wave mode. For each calendar month of 2013, the tilt spectra is obtained as a function of altitude using a Lomb-Scargle Welch implementation. The analysis is applied to all 6 stations proving unprecedented geographical coverage. The result is a complete picture of the altitude, temporal and location variability of gravity wave activity in the accessible thermospheric altitude interval with included
Zabotin, Nikolay; Negrea, Catalin; Godin, Oleg A.; Rietveld, Michael; Bullett, Terence; Zabotina, Liudmila
2015-04-01
Propagation conditions for thermospheric gravity waves in the Polar Regions are characterized by combination of several unique factors including interactions with the Auroral activity and the polar vortex. Tropospheric sources of the acoustic gravity waves (AGWs), such as wind disturbances caused by mountain relief, are likely to be complemented by energy and momentum depositions associated with fluxes of energetic particles from above. We apply recently developed Dynasonde techniques to study peculiarities of the gravity wave characteristics over Northern Scandinavia. A week-long (adjacent to the summer 2014 Solstice) data series for this study has been obtained with the Dynasonde system at the EISCAT's Tromsø Observatory operating continuously with sounding session periodicity equal to 2 min. A component of Dynasonde data analysis software, the inversion procedure NeXtYZ, has been used to attribute plasma density, plasma contour tilts, and line-of-sight Doppler values to the altitudes in real space with 1 km resolution. The temporal and spatial resolution allows visualization of the phase fronts of the traveling ionospheric disturbances (TIDs) and measuring the full set of parameters (both vertical and horizontal) of TID activity in the upper atmosphere between the base of the E layer and the maximum of F layer, where the ionospheric plasma can reflect the radar's signal. We verify the nature of the activity for selected spectral peaks by substituting the TID parameters into the dispersion relation describing acoustic-gravity waves. Application of the Lomb-Scargle periodogram technique to the tilt data provides useful insight into the dynamics of spectral composition of the TIDs, which we compare to results of a similar analysis obtained for mid-latitude (Wallops Island, VA) Dynasonde location. Interference of wave packets and multi-path propagation are more frequent in polar thermosphere compared to mid-latitude situation. Backtracking of selected waves to
Bulatov, Vitaly V
2012-01-01
In this paper, we consider fundamental problems of the dynamics of internal gravity waves. We present analytical and numerical algorithms for calculating the wave fields for a set of values of the parameters, as observed in the ocean. We show that our mathematical models can describe the wave dynamics of the Arctic Basin, taking into account the actual physical characteristics of sea water, topography of its floor, etc. The numerical and analytical results show that the internal gravity waves have a significant effect on underwater sea objects in the Arctic Basin.
Frequency variations of gravity waves interacting with a time-varying tide
Energy Technology Data Exchange (ETDEWEB)
Huang, C.M.; Zhang, S.D.; Yi, F.; Huang, K.M.; Gan, Q.; Gong, Y. [Wuhan Univ., Hubei (China). School of Electronic Information; Ministry of Education, Wuhan, Hubei (China). Key Lab. of Geospace Environment and Geodesy; State Observatory for Atmospheric Remote Sensing, Wuhan, Hubei (China); Zhang, Y.H. [Nanjing Univ. of Information Science and Technology (China). College of Hydrometeorolgy
2013-11-01
Using a nonlinear, 2-D time-dependent numerical model, we simulate the propagation of gravity waves (GWs) in a time-varying tide. Our simulations show that when aGW packet propagates in a time-varying tidal-wind environment, not only its intrinsic frequency but also its ground-based frequency would change significantly. The tidal horizontal-wind acceleration dominates the GW frequency variation. Positive (negative) accelerations induce frequency increases (decreases) with time. More interestingly, tidal-wind acceleration near the critical layers always causes the GW frequency to increase, which may partially explain the observations that high-frequency GW components are more dominant in the middle and upper atmosphere than in the lower atmosphere. The combination of the increased ground-based frequency of propagating GWs in a time-varying tidal-wind field and the transient nature of the critical layer induced by a time-varying tidal zonal wind creates favorable conditions for GWs to penetrate their originally expected critical layers. Consequently, GWs have an impact on the background atmosphere at much higher altitudes than expected, which indicates that the dynamical effects of tidal-GW interactions are more complicated than usually taken into account by GW parameterizations in global models.
Southern Argentina Agile Meteor Radar: Initial assessment of gravity wave momentum fluxes
Fritts, D. C.; Janches, D.; Hocking, W. K.
2010-10-01
The Southern Argentina Agile Meteor Radar (SAAMER) was installed on Tierra del Fuego (53.8°S) in May 2008 and has been operational since that time. This paper describes tests of the SAAMER ability to measure gravity wave momentum fluxes and applications of this capability during different seasons. Test results for specified mean, tidal, and gravity wavefields, including tidal amplitudes and gravity wave momentum fluxes varying strongly with altitude and/or time, suggest that the distribution of meteors throughout the diurnal cycle and averaged over a month allows characterization of both monthly mean profiles and diurnal variations of the gravity wave momentum fluxes. Applications of the same methods for real data suggest confidence in the monthly mean profiles and the composite day diurnal variations of gravity wave momentum fluxes at altitudes where meteor counts are sufficient to yield good statistical fits to the data. Monthly mean zonal winds and gravity wave momentum fluxes exhibit anticorrelations consistent with those seen at other midlatitude and high-latitude radars during austral spring and summer, when no strong local gravity wave sources are apparent. When stratospheric variances are significantly enhanced over the Drake Passage “hot spot” during austral winter, however, MLT winds and momentum fluxes over SAAMER exhibit very different correlations that suggest that MLT dynamics are strongly influenced by strong local gravity wave sources within this “hot spot.” SAAMER measurements of mean zonal and meridional winds at these times and their differences from measurements at a conjugate site provide further support for the unusual momentum flux measurements.
Energy Technology Data Exchange (ETDEWEB)
Peralta, J.; López-Valverde, M. A. [Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía, 18008 Granada (Spain); Imamura, T. [Institute of Space and Astronautical Science-Japan Aerospace Exploration Agency 3-1-1, Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan); Read, P. L. [Clarendon Laboratory, Department of Physics, University of Oxford, Parks Road, Oxford (United Kingdom); Luz, D. [Centro de Astronomia e Astrofísica da Universidade de Lisboa (CAAUL), Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa (Portugal); Piccialli, A., E-mail: peralta@iaa.es [LATMOS, UVSQ, 11 bd dAlembert, 78280 Guyancourt (France)
2014-07-01
This paper is the second in 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 where 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 second part, we study the waves' solutions when several atmospheric approximations are applied: Lamb, surface, and centrifugal waves. Lamb and surface waves are found to be quite similar to those in a geostrophic regime. By contrast, centrifugal waves turn out to be a special case of Rossby waves that arise in atmospheres in cyclostrophic balance. Finally, we use our results to identify the nature of the waves behind atmospheric periodicities found in polar and lower latitudes of Venus's atmosphere.
Surface wave propagation characteristics in atmospheric pressure plasma column
International Nuclear Information System (INIS)
In the typical experiments of surface wave sustained plasma columns at atmospheric pressure the ratio of collision to wave frequency (ν/ω) is much greater than unity. Therefore, one might expect that the usual analysis of the wave dispersion relation, performed under the assumption ν/ω = 0, cannot give adequate description of the wave propagation characteristics. In order to study these characteristics we have analyzed the wave dispersion relationship for arbitrary ν/ω. Our analysis includes phase and wave dispersion curves, attenuation coefficient, and wave phase and group velocities. The numerical results show that a turning back point appears in the phase diagram, after which a region of backward wave propagation exists. The experimentally observed plasma column is only in a region where wave propagation coefficient is higher than the attenuation coefficient. At the plasma column end the electron density is much higher than that corresponding to the turning back point and the resonance
Directory of Open Access Journals (Sweden)
M. Ern
2006-06-01
Full Text Available In order to incorporate the effect of gravity waves (GWs on the atmospheric circulation most global circulation models (GCMs employ gravity wave parameterization schemes. To date, GW parameterization schemes in GCMs are used without experimental validation of the set of global parameters assumed for the GW launch spectrum. This paper focuses on the Warner and McIntyre GW parameterization scheme. Ranges of parameters compatible with absolute values of gravity wave momentum flux (GW-MF derived from CRISTA-1 and CRISTA-2 satellite measurements are deduced for several of the parameters and the limitations of both model and measurements are discussed. The findings presented in this paper show that the initial guess of spectral parameters provided by Warner and McIntyre (2001 are some kind of compromise with respect to agreement of absolute values and agreement of the horizontal structures found in both measurements and model results. Better agreement can be achieved by using a vertical wavenumber launch spectrum with a wider saturated spectral range and reduced spectral power in the unsaturated part. Still, even global features of the measurements remain unmatched, and it is inevitable to provide a globally varying source distribution in future.
Wavemaker theories for acoustic-gravity waves over a finite depth
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
Logarithmic AdS waves and Zwei-Dreibein gravity
Bergshoeff, Eric A.; Goya, Andres F.; Merbis, Wout; Rosseel, Jan
2014-01-01
We show that the parameter space of Zwei-Dreibein Gravity (ZDG) in AdS(3) exhibits critical points, where massive graviton modes coincide with pure gauge modes and new 'logarithmic' modes appear, similar to what happens in New Massive Gravity. The existence of critical points is shown both at the li
Linear surface capillary-gravity short-crested waves on a current
Institute of Scientific and Technical Information of China (English)
HUANG Hu
2008-01-01
One of the forward situations in the study of water waves is the basic three-dimensional surface wave motion of short-crested waves. Capillary waves result in rich effects concerned closely with remote sensing in the open ocean. Ocean currents experience a complete process in surface wave motion. Based on the above ideas, a linear dynamical system of surface capillary-gravity short-crested waves is developed by considering the current effects, thus leading to the following analytical expressions of the kinematic and dynamic variables: the wave height, the wave steepness, the phase velocity, the wave-particle velocities, accelerations and trajectories and the wave pressure. A number of the classi-cal, typical and latest special wave cases can arise from these expressions.
Wave-Modulated CO2 Condensation in Mars' Polar Atmosphere
Banfield, D.; Neumann, G. A.
2016-09-01
We have identified regions where atmospheric waves would be expected to significantly modulate CO2 cloud formation in Mars' polar winters. We have correlated this with MOLA cloud identifications but, surprisingly, only poor correlations were found.
Energy Technology Data Exchange (ETDEWEB)
Liu, X. [Chinese Academy of Sciences, Beijing (China). State Key Lab. of Space Weather; Henan Normal Univ., Xinxiang (China). College of Mathematics and Information Science; Xu, J. [Chinese Academy of Sciences, Beijing (China). State Key Lab. of Space Weather; Yue, J. [National Center for Atmospheric Research, Boulder, CO (United States). High Altitude Observatory; Hampton Univ., VA (United States). Atmospheric and Planetary Sciences; Vadas, S.L. [North West Research Associates, Inc., Boulder, CO (United States)
2013-03-01
We study the momentum deposition in the thermosphere from the dissipation of small amplitude gravity waves (GWs) within a wave packet using a fully nonlinear two-dimensional compressible numerical model. The model solves the nonlinear propagation and dissipation of a GW packet from the stratosphere into the thermosphere with realistic molecular viscosity and thermal diffusivity for various Prandtl numbers. The numerical simulations are performed for GW packets with initial vertical wavelengths ({lambda}{sub z}) ranging from 5 to 50 km. We show that {lambda}{sub z} decreases in time as a GW packet dissipates in the thermosphere, in agreement with the ray trace results of Vadas and Fritts (2005) (VF05). We also find good agreement for the peak height of the momentum flux (z{sub diss}) between our simulations and VF05 for GWs with initial {lambda}{sub z} {<=} 2{pi}H in an isothermal, windless background, where H is the density scale height.We also confirm that z{sub diss} increases with increasing Prandtl number. We include eddy diffusion in the model, and find that the momentum deposition occurs at lower altitudes and has two separate peaks for GW packets with small initial {lambda}{sub z}. We also simulate GW packets in a non-isothermal atmosphere. The net {lambda}{sub z} profile is a competition between its decrease from viscosity and its increase from the increasing background temperature. We find that the wave packet disperses more in the non-isothermal atmosphere, and causes changes to the momentum flux and {lambda}{sub z} spectra at both early and late times for GW packets with initial {lambda}{sub z} {>=} 10 km. These effects are caused by the increase in T in the thermosphere, and the decrease in T near the mesopause. (orig.)
Meteotsunamis: atmospherically induced destructive ocean waves in the tsunami frequency band
Directory of Open Access Journals (Sweden)
S. Monserrat
2006-01-01
Full Text Available In light of the recent enhanced activity in the study of tsunami waves and their source mechanisms, we consider tsunami-like waves that are induced by atmospheric processes rather than by seismic sources. These waves are mainly associated with atmospheric gravity waves, pressure jumps, frontal passages, squalls and other types of atmospheric disturbances, which normally generate barotropic ocean waves in the open ocean and amplify them near the coast through specific resonance mechanisms (Proudman, Greenspan, shelf, harbour. The main purpose of the present study is to describe this hazardous phenomenon, to show similarities and differences between seismic and meteorological tsunamis and to provide an overview of meteorological tsunamis in the World Ocean. It is shown that tsunamis and meteotsunamis have the same periods, same spatial scales, similar physical properties and affect the coast in a comparably destructive way. Some specific features of meteotsunamis make them akin to landslide-generated tsunamis. The generation efficiency of both phenomena depend on the Froude number (Fr, with resonance taking place when Fr~1.0. Meteotsunamis are much less energetic than seismic tsunamis and that is why they are always local, while seismic tsunamis can have globally destructive effects. Destructive meteotsunamis are always the result of a combination of several resonant factors; the low probability of such a combination is the main reason why major meteotsunamis are infrequent and observed only at some specific locations in the ocean.
Wave analysis in the atmosphere of Venus below 100-km altitude, simulated by the LMD Venus GCM
Lebonnois, Sébastien; Sugimoto, Norihiko; Gilli, Gabriella
2016-11-01
A new simulation of Venus atmospheric circulation obtained with the LMD Venus GCM is described and the simulated wave activity is analyzed. Agreement with observed features of the temperature structure, static stability and zonal wind field is good, such as the presence of a cold polar collar, diurnal and semi-diurnal tides. At the resolution used (96 longitudes × 96 latitudes), a fully developed superrotation is obtained both when the simulation is initialized from rest and from an atmosphere already in superrotation, though winds are still weak below the clouds (roughly half the observed values). The atmospheric waves play a crucial role in the angular momentum budget of the Venus's atmospheric circulation. In the upper cloud, the vertical angular momentum is transported by the diurnal and semi-diurnal tides. Above the cloud base (approximately 1 bar), equatorward transport of angular momentum is done by polar barotropic and mid- to high-latitude baroclinic waves present in the cloud region, with frequencies between 5 and 20 cycles per Venus day (periods between 6 and 23 Earth days). In the middle cloud, just above the convective layer, a Kelvin type wave (period around 7.3 Ed) is present at the equator, as well as a low-latitude Rossby-gravity type wave (period around 16 Ed). Below the clouds, large-scale mid- to high-latitude gravity waves develop and play a significant role in the angular momentum balance.
Eckermann, S. D.; Wu, D. L.
2012-01-01
Orographic gravity-wave (OGW) parameterizations in models produce waves over subtropical mountain ranges in Australia and Africa that propagate into the stratosphere during austral winter and deposit momentum, affecting weather and climate. Satellite sensors have measured stratospheric GWs for over a decade, yet find no evidence of these waves. So are parameterizations failing here? Here we argue that the short wavelengths of subtropical OGWs place them near or below the detection limits of satellite sensors. To test this hypothesis, we reanalyze nine years of stratospheric radiances from the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua satellite during austral winter, applying new averaging techniques to maximize signal-to-noise and improve thresholds for OGW detection. Deep climatological enhancements in stratospheric OGW variance over specific mountain ranges in Australia and southern Africa are revealed for the first time, which exhibit temporal and vertical variations consistent with predicted OGW responses to varying background winds.
Stochastic Background of Gravitational Waves as a Benchmark for Extended Theories of Gravity
Capozziello, S.; De Laurentis, M.; Francaviglia, M.
2008-01-01
The cosmological background of gravitational waves can be tuned by Extended Theories of Gravity. In particular, it can be shown that assuming a generic function f(R) of the Ricci scalar R gives a parametric approach to control the evolution and the production mechanism of gravitational waves in the early Universe.
Gravity waves on water with non-uniform depth and current
Booij, N.
1981-01-01
A mathematical model for the combined refraction-diffraction of linear periodic gravity waves on water is developed, in which the influence of inhomogeneities of depth and current is taken into account. The model is used to compute partial reflection of waves a gully or an undersea slope, with influ
Simulation and Observation of Acoustic-Gravity Waves in the Ionosphere
Kunitsyn, Viacheslav; Andreeva, Elena; Krysanov, Boris; Nesterov, Ivan
Atmospheric and ionospheric perturbations associated with the acoustic-gravity waves (AGW) with typical frequencies of a few hertz -millihertz are considered. These events may be caused by the influence from space and atmosphere as well as by oscillations of the Earth surface and other near-surface phenomena. The surface sources include long-period oscillations of the Earth's surface, earthquakes, explosions, thermal heating, seisches and tsunami waves. The wavelike phenomena manifest themself as travelling disturbances of air (in the atmosphere) and of electron density (in the ionosphere). Travelling ionospheric disturbances (TIDs) are well detected by radio physical methods. AGW generation by near-surface sources is modeled by the numerical solution of the equation of geophysical fluid dynamics for different sources in two-dimensional non-linear dissipative compressible atmosphere. The numerical calculations are based on the FCT (Flux Corrected Transport) technique of the second order accuracy in time and space. Different scenarios of AGW generation are analyzed. The AGW caused by the surface sources within a few hertz-millihertz frequency band appear at the altitudes of middle atmosphere and ionosphere as the disturbances with typical scales from a few kilometers to several hundreds kilometers. Such structures can be successfully monitored by the methods of satellite radio tomography (RT). For the purposes of RT diagnostics of such disturbances, low-orbiting navigational satellites like Transit and Tsikada and high-orbiting navigation systems GPS/GLONASS are used. The results of numerical modeling of AGW generation by the surface sources are compared with the data of RT sounding. Also, generation of AGW by volumetric sources such as particle precipitation, rocket launching, heating by high-frequency radiation and other are considered. The obtained results proved the capability of RT methods of detecting and distinguishing between TIDs caused by AGW generated by
A Coupled Atmospheric and Wave Modeling System for Storm Simulations
DEFF Research Database (Denmark)
Du, Jianting; Larsén, Xiaoli Guo; Bolanos, R.
2015-01-01
This study aims at improving the simulation of wind and waves during storms in connection with wind turbine design and operations in coastal areas. For this particular purpose, we investigated the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) Modeling System which couples the Weather ...
Directory of Open Access Journals (Sweden)
Antonio Gledson Goulart
2013-12-01
Full Text Available In this paper, the equation for the gravity wave spectra in mean atmosphere is analytically solved without linearization by the Adomian decomposition method. As a consequence, the nonlinear nature of problem is preserved and the errors found in the results are only due to the parameterization. The results, with the parameterization applied in the simulations, indicate that the linear solution of the equation is a good approximation only for heights shorter than ten kilometers, because the linearization the equation leads to a solution that does not correctly describe the kinetic energy spectra.
Conservation laws of wave action and potential enstrophy for Rossby waves in a stratified atmosphere
Straus, D. M.
1983-01-01
The evolution of wave energy, enstrophy, and wave motion for atmospheric Rossby waves in a variable mean flow are discussed from a theoretical and pedagogic standpoint. In the absence of mean flow gradients, the wave energy density satisfies a local conservation law, with the appropriate flow velocity being the group velocity. In the presence of mean flow variations, wave energy is not conserved, but wave action is, provided the mean flow is independent of longitude. Wave enstrophy is conserved for arbitrary variations of the mean flow. Connections with Eliassen-Palm flux are also discussed.
Directory of Open Access Journals (Sweden)
N. P. Hindley
2015-02-01
Full Text Available During austral winter the mountains of the southern Andes and Antarctic Peninsula are a known hot spot of intense gravity wave momentum flux. There also exists a long leeward region of increased gravity wave energy that sweeps eastwards from the mountains out over the Southern Ocean, the source of which has historically proved difficult to determine. In this study we use Global Positioning System (GPS Radio Occultation (RO data from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC satellite constellation to investigate the distribution, variability and sources of waves in the hot spot region and over the Southern Ocean. We present evidence that suggests a southward focusing of waves into the stratospheric jet from sources to the north. We also describe a wavelet analysis technique for the quantitative identification of individual waves from COSMIC temperature profiles. This analysis reveals different geographical regimes of wave amplitude and short-timescale variability in the wave field over the Southern Ocean. Finally, we take advantage of the large numbers of closely spaced pairs of profiles from the deployment phase of the COSMIC constellation in 2006 to make estimates of gravity wave horizontal wavelengths. We show that, given sufficient numbers of these pairs, GPS-RO can then produce physically reasonable estimates of stratospheric gravity wave momentum flux in the hot spot region that are consistent with other studies. The results are discussed in the context of previous satellite and modelling studies to build up a better picture of the nature and origins of waves in the southern winter stratosphere.
Wu, Dong L.; Gong, Jie
2011-01-01
Tropical anvil clouds play important roles in redistributing energy, water in the troposphere. Interacting with dynamics at a wide range of spatial and temporal scales, they can become organized internally and form structured cells, transporting momentum vertically and laterally. To quantify small-scale structures inside cirrus and anvils, we study view-dependence of the cloud-induced radiance from Atmospheric Infrared Sounder (AIRS) using channels near CO2 absorption line. The analysis of tropical eight-year (30degS-30degN, 2003-2010) data suggests that AIRS east-views observe 10% more anvil clouds than westviews during day (13:30 LST), whereas east-views and westviews observe equally amount of clouds at midnight (1 :30 LST). For entire tropical averages, AIRS oblique views observe more anvils than the nadir views, while the opposite is true for deep convective clouds. The dominance of cloudiness in the east-view cannot be explained by AIRS sampling and cloud microphysical differences. Tilted and banded anvil structures from convective scale to mesoscale are likely the cause of the observed view-dependent cloudiness, and gravity wave-cloud interaction is a plausible explanation for the observed structures. Effects of the tilted and banded cloud features need to be further evaluated and taken into account potentially in large-scale model parameterizations because of the vertical momentum transport through cloud wave breaking.
Atom Interferometry for detection of Gravity Waves-a Project
National Aeronautics and Space Administration — Atom interferometers are more sensitive to inertial effects. This is because atoms in their inertial frame are ideal test masses for detection of gravity effects...
deWit, R J; Espy, P J; Orsolini, Y J; Limpasuvan, V; Kinnison, D E
2016-01-01
Studies of vertical and interhemispheric coupling during Sudden Stratospheric Warmings (SSWs) suggest that gravity wave (GW) momentum flux divergence plays a key role in forcing the middle atmosphere, although observational validation of GW forcing is limited. We present a whole atmosphere view of zonal winds from the surface to 100 km during the January 2013 major SSW, together with observed GW momentum fluxes in the mesopause region derived from uninterrupted high-resolution meteor radar observations from an All-Sky Interferometric Meteor Radar system located at Trondheim, Norway (63.4 $^{\\circ}$N, 10.5 $^{\\circ}$E). Observations show GW momentum flux divergence 6 days prior to the SSW onset, producing an eastward forcing with peak values of $\\sim$+145 $\\pm$ 60m $s^{-1}$ $d^{-1}$. As the SSW evolves, GW forcing turns westward, reaching a minimum of $\\sim$-240 $\\pm$ 70 m $s^{-1}$ $d^{-1}$ $\\sim$+18 days after the SSW onset. These results are discussed in light of previous studies and simulations using the Wh...
International Nuclear Information System (INIS)
We have been investigating high-power radio wave-induced acoustic gravity waves (AGWs) at Gakona, Alaska, using the High-frequency Active Aurora Research Program (HAARP) heating facility (i.e. HF heater) and extensive diagnostic instruments. This work was aimed at performing a controlled study of the space plasma turbulence triggered by the AGWs originating from anomalous heat sources, as observed in our earlier experiments at Arecibo, Puerto Rico (Pradipta 2007 MS Thesis MIT Press, Cambridge, MA). The HF heater operated in continuous wave (CW) O-mode can heat ionospheric plasmas effectively to yield a depleted magnetic flux tube as rising plasma bubbles (Lee et al 1998 Geophys. Res. Lett. 25 579). Two processes are responsible for the depletion of the magnetic flux tube: (i) thermal expansion and (ii) chemical reactions caused by heated ions. The depleted plasmas create large density gradients that can augment spread F processes via generalized Rayleigh–Taylor instabilities (Lee et al 1999 Geophys. Res. Lett. 26 37). It is thus expected that the temperature of neutral particles in the heated ionospheric region can be increased. Such a heat source in the neutral atmosphere may potentially generate AGWs in the form of traveling ionospheric plasma disturbances (TIPDs). We should point out that these TIPDs have features distinctively different from electric and magnetic field (ExB) drifts of HF wave-induced large-scale non-propagating plasma structures. Moreover, it was noted in our recent study of naturally occurring AGW-induced TIDs that only large-scale AGWs can propagate upward to reach higher altitudes. Thus, in our Gakona experiments we select optimum heating schemes for HF wave-induced AGWs that can be distinguished from the naturally occurring ones. The generation and propagation of AGWs are monitored by MUIR (Modular Ultra high-frequency Ionospheric Radar), Digisonde and GPS/low-earth-orbit satellites. Our theoretical and experimental studies have shown
Pradipta, R.; Lee, M. C.
2013-07-01
We have been investigating high-power radio wave-induced acoustic gravity waves (AGWs) at Gakona, Alaska, using the High-frequency Active Aurora Research Program (HAARP) heating facility (i.e. HF heater) and extensive diagnostic instruments. This work was aimed at performing a controlled study of the space plasma turbulence triggered by the AGWs originating from anomalous heat sources, as observed in our earlier experiments at Arecibo, Puerto Rico (Pradipta 2007 MS Thesis MIT Press, Cambridge, MA). The HF heater operated in continuous wave (CW) O-mode can heat ionospheric plasmas effectively to yield a depleted magnetic flux tube as rising plasma bubbles (Lee et al 1998 Geophys. Res. Lett. 25 579). Two processes are responsible for the depletion of the magnetic flux tube: (i) thermal expansion and (ii) chemical reactions caused by heated ions. The depleted plasmas create large density gradients that can augment spread F processes via generalized Rayleigh-Taylor instabilities (Lee et al 1999 Geophys. Res. Lett. 26 37). It is thus expected that the temperature of neutral particles in the heated ionospheric region can be increased. Such a heat source in the neutral atmosphere may potentially generate AGWs in the form of traveling ionospheric plasma disturbances (TIPDs). We should point out that these TIPDs have features distinctively different from electric and magnetic field (ExB) drifts of HF wave-induced large-scale non-propagating plasma structures. Moreover, it was noted in our recent study of naturally occurring AGW-induced TIDs that only large-scale AGWs can propagate upward to reach higher altitudes. Thus, in our Gakona experiments we select optimum heating schemes for HF wave-induced AGWs that can be distinguished from the naturally occurring ones. The generation and propagation of AGWs are monitored by MUIR (Modular Ultra high-frequency Ionospheric Radar), Digisonde and GPS/low-earth-orbit satellites. Our theoretical and experimental studies have shown that
Hydrodynamic coefficients of a simplified floating system of gravity cage in waves
Institute of Scientific and Technical Information of China (English)
Chang-wen WU; Fu-kun GUI; Yu-cheng LI; Wei-huan FANG
2008-01-01
Numerical simulation and experimental tests were carried out to examine the hydrodynamic behaviors of a double-column floating system of gravity cage under wave conditions. A floating system of gravity cage can be treated as a small-sized floating structure when compared with the wavelengths. The main problem in calculating the wave loads on the small-sized floating structure is to obtain the reasonable force coefficients, which may differ from a submerged structure. In this paper, the floating system of gravity cage is simplified to a 2D problem, where the floating system is set symmetrically under wave conditions. The motion equations were deduced under wave conditions and a specific method was proposed to resolve the problem of wave forces acting on a small-sized floating system of gravity cage at water surface. Results of the numerical method were compared with those from model tests and the hydrodynamic coefficients Cn and C?were studied. It is found that Cn ranges from 0.6 to 1.0 while C?is between 0.4 and 0.6 in this study. The results are useful for research on the hydrodynamic behavior of the deep-water gravity sea cages.
Indian Academy of Sciences (India)
Sushil Kumar Addy; Nil Ratan Chakraborty
2005-02-01
This paper deals with the effect of temperature on gravity waves in a compressible liquid layer over a solid half-space. It has been assumed that the liquid layer is under the action of gravity, while the solid half-space is under the inﬂuence of initial compressive hydrostatic stress. When the temperature of the half-space is altered, gravity waves propagate through the liquid layer along with sub-oceanic Rayleigh waves in the system. A new frequency equation has been derived here for gravity waves and sub-oceanic Rayleigh waves. It has been shown graphically that the phase velocity of gravity waves is inﬂuenced signiﬁcantly by the initial compressive hydrostatic stress present in the solid half-space, for a particular value of the phase velocity of sub-oceanic Rayleigh waves and different coupling co-efﬁcients of the temperature.
Current effects on scattering of surface gravity waves by bottom topography
Magne, R; Ardhuin, Fabrice; Magne, Rudy
2005-01-01
Scattering of random surface gravity waves by small amplitude topography in the presence of a uniform current is investigated theoretically. This problem is relevant to ocean waves propagation on shallow continental shelves where tidal currents are often significant. A perturbation expansion of the wave action to second order in powers of the bottom amplitude yields an evolution equation for the wave action spectrum. A scattering source term gives the rate of exchange of the wave action spectrum between wave components, with conservation of the total action at each absolute frequency. With and without current, the scattering term yields reflection coefficients for the amplitudes of waves that converge, in the limit of small bottom amplitudes and small Froude numbers, to the results of previous theories for monochromatic waves propagating in one dimension over sinusoidal bars. Over sandy continental shelves, tidal currents are known to generate sandwaves with scales comparable to those of surface waves. Applic...
Proposed observations of gravity waves from the early Universe via "Millikan oil drops"
Chiao, R Y
2006-01-01
Pairs of Planck-mass drops of superfluid helium coated by electrons (i.e., ``Millikan oil drops''), when levitated in a superconducting magnetic trap, can be efficient quantum transducers between electromagnetic (EM) and gravitational (GR) radiation. This leads to the possibility of a Hertz-like experiment, in which EM waves are converted at the source into GR waves, and then back-converted at the receiver from GR waves back into EM waves. Detection of the gravity-wave analog of the cosmic microwave background using these drops can discriminate between various theories of the early Universe.
A Parabolic Equation Approach to Modeling Acousto-Gravity Waves for Local Helioseismology
Del Bene, Kevin; Lingevitch, Joseph; Doschek, George
2016-07-01
A wide-angle parabolic-wave-equation algorithm is developed and validated for local-helioseismic wave propagation. The parabolic equation is derived from a factorization of the linearized acousto-gravity wave equation. We apply the parabolic-wave equation to modeling acoustic propagation in a plane-parallel waveguide with physical properties derived from helioseismic data. The wavenumber power spectrum and wave-packet arrival-time structure for receivers in the photosphere with separation up to 30° is computed, and good agreement is demonstrated with measured values and a reference spectral model.
A Parabolic Equation Approach to Modeling Acousto-Gravity Waves for Local Helioseismology
Del Bene, Kevin; Lingevitch, Joseph; Doschek, George
2016-08-01
A wide-angle parabolic-wave-equation algorithm is developed and validated for local-helioseismic wave propagation. The parabolic equation is derived from a factorization of the linearized acousto-gravity wave equation. We apply the parabolic-wave equation to modeling acoustic propagation in a plane-parallel waveguide with physical properties derived from helioseismic data. The wavenumber power spectrum and wave-packet arrival-time structure for receivers in the photosphere with separation up to 30° is computed, and good agreement is demonstrated with measured values and a reference spectral model.
Detectability of bi-gravity with graviton oscillations using gravitational wave observations
Narikawa, Tatsuya; Tagoshi, Hideyuki; Tanaka, Takahiro; Kanda, Nobuyuki; Nakamura, Takashi
2014-01-01
The gravitational waveforms in the ghost-free bi-gravity theory exhibit deviations from those in general relativity. The main difference is caused by graviton oscillations in the bi-gravity theory. We investigate the prospects for the detection of the corrections to gravitational waveforms from coalescing compact binaries due to graviton oscillations and for constraining bi-gravity parameters with the gravitational wave observations. We consider the bi-gravity model discussed by the De Felice-Nakamura-Tanaka subset of the bi-gravity model, and the phenomenological model in which the bi-gravity parameters are treated as independent variables. In both models, the bi-gravity waveform shows strong amplitude modulation, and there can be a characteristic frequency of the largest peak of the amplitude, which depends on the bi-gravity parameters. We show that there is a detectable region of the bi-gravity parameters for the advanced ground-based laser interferometers, such as Advanced LIGO, Advanced Virgo, and KAGRA....
Interaction of acoustic-gravity waves with an elastic shelf-break
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.
Mesospheric Non-Migrating Tides Generated With Planetary Waves: II Influence of Gravity Waves
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.
Directory of Open Access Journals (Sweden)
N. J. Mitchell
Full Text Available The EISCAT VHF radar (69.4°N, 19.1°E has been used to record vertical winds at mesopause heights on a total of 31 days between June 1990 and January 1993. The data reveal a motion field dominated by quasi-monochromatic gravity waves with representative apparent periods of ~30–40 min, amplitudes of up to ~2.5 m s^{–1} and large vertical wavelength. In some instances waves appear to be ducted. Vertical profiles of the vertical-velocity variance display a variety of forms, with little indication of systematic wave growth with height. Daily mean variance profiles evaluated for consecutive days of recording show that the general shape of the variance profiles persists over several days. The mean variance evaluated over a 10 km height range has values from 1.2 m^{2}s^{–2} to 6.5 m^{2}s^{–2} and suggests a semi-annual seasonal cycle with equinoctial minima and solsticial maxima. The mean vertical wavenumber spectrum evaluated at heights up to 86 km has a slope (spectral index of –1.36 ± 0.2, consistent with observations at lower heights but disagreeing with the predictions of a number of saturation theories advanced to explain gravity-wave spectra. The spectral slopes evaluated for individual days have a range of values, and steeper slopes are observed in summer than in winter. The spectra also appear to be generally steeper on days with lower mean vertical-velocity variance.
Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides
The Role of Gravity Waves in the Formation and Organization of Clouds during TWPICE
Energy Technology Data Exchange (ETDEWEB)
Reeder, Michael J. [Monash University; Lane, Todd P. [University of Melbourne; Hankinson, Mai Chi Nguyen [Monash University
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
Stoneley waves in a non-homogeneous orthotropic granular medium under the influence of gravity
Directory of Open Access Journals (Sweden)
S. M. Ahmed
2005-01-01
Full Text Available The aim of this paper is to investigate the Stoneley waves in a non-homogeneous orthotropic granular medium under the influence of a gravity field. The frequency equation obtained, in the form of a sixth-order determinantal expression, is in agreement with the corresponding result when both media are elastic. The frequency equation when the gravity field is neglected has been deduced as a particular case.
Torsion Wave Solutions in Yang-Mielke Theory of Gravity
Pasic, Vedad
2015-01-01
The approach of metric-affine gravity initially distinguishes it from Einstein's general relativity. Using an independent affine connection produces a theory with 10+64 unknowns. We write down the Yang-Mills action for the affine connection and produce the Yang-Mills equation and the so called complementary Yang-Mills equation by independently varying with respect to the connection and the metric respectively. We call this theory the Yang-Mielke theory of gravity. We construct explicit spacetimes with pp-metric and purely axial torsion and show that they represent a solution of Yang-Mills theory. Finally we compare these spacetimes to existing solutions of metric-affine gravity and present future research possibilities.
Dalakishvili, Giorgi; Didebulidze, Goderdzi G.; Matiashvili, Giorgi
2016-04-01
The horizontal tidal wind in the mesosphere lower thermosphere region (MLT) is considered as a source of atmospheric gravity waves (AGWs) and vortical type perturbations generation. It is shown that at mid-latitude these atmospheric waves, evolving in the tidal wind, can lead to vertical convergence of heavy metallic ions of this region and Formation of sporadic E (Es) layer. The process of sporadic E formation by short-period AGWs (close to Bunt-Vaisala period) and by the stationary type vortical perturbations with the same spatial scale, excited in the horizontal shear flow is demonstrated using numerical simulations. The possibility of oscillation of Es layers electron/ions density by period less than BV period under influence of short-period AGWs is shown and the possible coupling of these processes with quasi-periodic echoes is also noted. In our numerical experiment the mid-latitude nighttime Es layers formed under influence of these atmospheric waves, which are possibly generated by horizontal tidal wind, mostly move downward, this is an observed phenomena. It is noted that investigation of sporadic E formation by atmospheric waves evolving in the tidal wind is important for study of the in situ developing processes in the lower thermosphere determining atmosphere-ionosphere dynamical coupling as well as for revealing their possible dynamical coupling with lower atmosphere. Acknowledgements: This work has been supported by Shota Rustaveli National Science Foundation grant No 31/81 and the Shota Rustaveli National Science Foundation grant No FR/51/6-300/14.
International Nuclear Information System (INIS)
On 1998 November 14, Saturn and its rings occulted the star GSC 0622-00345. The occultation latitude was 55.05 S. This paper analyzes the 2.3 μm light curve derived by Harrington and French. A fixed-baseline isothermal fit to the light curve has a temperature of 140 ± 3 K, assuming a mean molecular mass of 2.35 AMU. The thermal profile obtained by numerical inversion is valid between 1 and 60 μbar. The vertical temperature gradient is > 0.2 K km-1 more stable than the adiabatic lapse rate, but it still shows the alternating-rounded-spiked features seen in many temperature gradient profiles from other atmospheric occultations and usually attributed to breaking gravity (buoyancy) waves. We conduct a wavelet analysis of the thermal profile, and show that, even with our low level of noise, scintillation due to turbulence in Earth's atmosphere can produce large temperature swings in light-curve inversions. Spurious periodic features in the 'reliable' region of a wavelet amplitude spectrum can exceed 0.3 K in our data. We also show that gravity-wave model fits to noisy isothermal light curves can lead to convincing wave 'detections'. We provide new significance tests for localized wavelet amplitudes, wave model fits, and global power spectra of inverted occultation light curves by assessing the effects of pre- and post-occultation noise on these parameters. Based on these tests, we detect several significant ridges and isolated peaks in wavelet amplitude, to which we fit a gravity wave model. We also strongly detect the global power spectrum of thermal fluctuations in Saturn's atmosphere, which resembles the 'universal' (modified Desaubies) curve associated with saturated spectra of propagating gravity waves on Earth and Jupiter.
Influence of short gravity waves on thermal radio emission of water surface
Ilin, V. A.; Naumov, A. A.; Rayzer, V. Y.; Filonovich, S. R.; Etkin, V. S.
1985-06-01
An experimental study is presented of the thermal radio emission caused by short waves, accompanied by a quantitative interpretation of the data obtained. Emphasis is on an analysis of the variation in radio brightness contrast as a function of steepness of the short gravity waves, measured by means of a high-frequency radiometer operating in the lambda = 0.8 cm range. Waves were artificially generated in a small channel, wavelength 8 to 40 cm, height 0.6 to 3 cm. Due to the high sensitivity of the radiometric apparatus used, effects were recorded which were related to the influence of the profile and steepness of the short gravity waves. The possibility of using the geometrical optics approximation for quantitative interpretation of the experimental data is demonstrated. The model is based on essentially non-Gaussian statistics of slopes corresponding to quasimonochromatic waves of finite amplitude.
Simulation of breaking gravity waves during the south foehn of 7 - 13 January 1996
Energy Technology Data Exchange (ETDEWEB)
Schmid, H.; Doernbrack, A.
1998-07-01
A high-resolution mesoscale model with horizontal mesh size of 6 km is applied to simulate upper-level wave breaking above the Alps during a south foehn event in January 1996. The model reproduces the key synoptic and mesoscale features of cross-alpine airflow during foehn. High-resolution radiosonde ascents at Munich and Innsbruck are used to evaluate the quality of the model simulations. The simulations predict breaking gravity waves above the jet stream in a layer between 10 and 15 km altitude where the shear is maximum. In part of the foehn period a critical level is present at about 200 hPa that results in wave steepening below and no wave activity aloft. Regions where aircraft report clear-air turbulence encounters agree reasonably with the simulated locations of gravity wave breaking. (orig.)
Estimations of model parameters for gravity wave spectra observed by MST radar
Scheffler, A. O.; Liu, C. H.; Franke, S. J.
1989-01-01
The general theory of MST radar observations of gravity wave spectra is developed. This effort extends the previous results to include anisotropy and Doppler effects for the spectra, as well as the consequences for the multibeam configuration. The relationships between the observed one- or two-dimensional spectra for the line-of-sight velocity in the gravity wave spectra are derived. Expressions for cross spectra, as well as covariances between velocities observed on different beams, are computed. Using these results, studies are carried out to show how model parameters for gravity wave spectra can be estimated from the observed quantities. Model parameters include the variance, power law indices, anisotropy parameters, Doppler parameters, mean scale sizes, etc. Cases with different numbers of beams are investigated.
Characterizing the propagation of gravity waves in 3D nonlinear simulations of solar-like stars
Alvan, L.; Strugarek, A.; Brun, A. S.; Mathis, S.; Garcia, R. A.
2015-09-01
Context. The revolution of helio- and asteroseismology provides access to the detailed properties of stellar interiors by studying the star's oscillation modes. Among them, gravity (g) modes are formed by constructive interferences between progressive internal gravity waves (IGWs), propagating in stellar radiative zones. Our new 3D nonlinear simulations of the interior of a solar-like star allows us to study the excitation, propagation, and dissipation of these waves. Aims: The aim of this article is to clarify our understanding of the behavior of IGWs in a 3D radiative zone and to provide a clear overview of their properties. Methods: We use a method of frequency filtering that reveals the path of individual gravity waves of different frequencies in the radiative zone. Results: We are able to identify the region of propagation of different waves in 2D and 3D, to compare them to the linear raytracing theory and to distinguish between propagative and standing waves (g-modes). We also show that the energy carried by waves is distributed in different planes in the sphere, depending on their azimuthal wave number. Conclusions: We are able to isolate individual IGWs from a complex spectrum and to study their propagation in space and time. In particular, we highlight in this paper the necessity of studying the propagation of waves in 3D spherical geometry, since the distribution of their energy is not equipartitioned in the sphere.
Impact of rotation on stochastic excitation of gravity and gravito-inertial waves in stars
Mathis, S.; Neiner, C.; Tran Minh, N.
2014-05-01
Context. Gravity waves (or their signatures) are detected in stars thanks to helio- and asteroseismology, and they may play an important role in the evolution of stellar angular momentum. Moreover, a previous observational study of the CoRoT target HD 51452 demonstrated the potential strong impact of rotation on the stochastic excitation of gravito-inertial waves in stellar interiors. Aims: Our goal is to explore and unravel the action of rotation on the stochastic excitation of gravity and gravito-inertial waves in stars. Methods: The dynamics of gravito-inertial waves in stellar interiors in both radiation and in convection zones is described with a local non-traditional f-plane model. The coupling of these waves with convective turbulent flows, which leads to their stochastic excitation, is studied in this framework. Results: First, we find that in the super-inertial regime in which the wave frequency is twice as high as the rotation frequency (σ > 2Ω), the evanescence of gravito-inertial waves in convective regions decreases with decreasing wave frequency. Next, in the sub-inertial regime (σ modified by rotation. Indeed, the turbulent energy cascade towards small scales is slowed down, and in the case of rapid rotation, strongly anisotropic turbulent flows are obtained that can be understood as complex non-linear triadic interactions of propagative inertial waves. These different behaviours, due to the action of the Coriolis acceleration, strongly modify the wave coupling with turbulent flows. On one hand, turbulence weakly influenced by rotation is coupled with evanescent gravito-inertial waves. On the other hand, rapidly rotating turbulence is intrinsically and strongly coupled with sub-inertial waves. Finally, to study these mechanisms, the traditional approximation cannot be assumed because it does not properly treat the coupling between gravity and inertial waves in the sub-inertial regime. Conclusions: Our results demonstrate the action of rotation on
Bostater, Charles R.; Yang, Bingyu
2014-10-01
Imaging of shallow waters using high resolution video imagery is described. Common to mono, stereo and trinocular imaging approaches from ground and airborne platforms is the need to validate the surface water wave field measurements, particularly the amplitude and specular reflectance of water surface small gravity waves. A technique for calibration and validation of water surface gravity wave field energy spectra is described. Results demonstrate the value of video imagery where water level staff gauges with approximately with 0.5 cm wave height accuracy are easily sensed using high definition videography. Essentially, a staff gauge placed in shallow water constructed from PVC materials with custom colored line coding are imaged at 30 H or high frame rates, followed by frame by frame analyses in order to detect the water level measured at 0.5 cm height intervals. The image based time series allow the development of shallow water gravity wave energy spectra using standard FFT analysis procedures. Spectral models based upon peak frequency, for example, are then used in a two dimensional water surface wave simulation model that generates radiative transfer based hyperspectral images of the water surface wave field. The simulated and observed water surface wave patch fields are compared by extracting vertical or horizontal transects within observed and simulated imagery. The approach allows one to developed spectral energy model probability distributions at low cost. The novel noncontact video sensing and image analysis methodology used to calibrate and validate shallow water gravity wave models yield a means for ultimately calculating bottom boundary velocities under measured or simulated wave fields. These boundary layer velocities can cause migration and horizontal particle fluxes (g cm-2 s-1), resuspension, settling, and increased turbidity during dredging operations, but not necessarily due to waterway dredging operations and activities.
Hima Bindu, H.; Venkat Ratnam, M.; Yesubabu, V.; Narayana Rao, T.; Kesarkar, Amit; Naidu, C. V.
2016-11-01
Characteristics of gravity waves (GWs) generated due to tropical cyclone (TC) Phailin (2013) that occurred over Bay of Bengal are investigated using the Weather Research and Forecast (WRF) model simulations from its depression stage to weakening stage (10-14 October 2013). Two types of numerical experiments are conducted with and without assimilating conventional and satellite observations using the 3-Dimentional Variational (3DVAR) technique. The results show that the experiment without assimilating any observations (control) has produced a large difference in terms of track and intensity with observed best track estimates of IMD. Similar features are noticed also in winds, reflectivity and independent GPS Radio Occultation (temperature) and radiosonde (temperature and winds) profiles. The experiment with assimilation significantly reduced the observed differences in all the above mentioned parameters. A close match of the assimilated outputs with observations prompted us to use it to identify the TC generated GW characteristics. GW perturbation components are extracted from the three day mean (4-7 October 2013) calm background atmosphere prior to the formation of depression. When compared to the control run, assimilated outputs show a clear increase in all the gravity wave parameters except the amplitudes where control run wave amplitudes are found to be stronger than the assimilated outputs. Fast Fourier transform (FFT) analysis in the time domain revealed dominance of GWs with periods of 2-4 h. Band pass filtered vertical velocity perturbations for these periods showed clear downward phase propagation (0.05-0.07 ms- 1) in the upper troposphere and lower stratosphere (UTLS) at different latitude/longitude positions away from the centre of the TC revealing an upward energy propagation of generated GWs. Interestingly, an increase in GW activity during the landfall of the TC is found. FFT in the vertical domain revealed vertical wavelengths ranging from 3 to 8 km
Measurement of TID and Gravity Wave Parameters Using An HF Doppler System
Wene, G. P.; Crowley, G.; Fessler, B. W.; Bronn, J. S.
2005-05-01
The manifestation of atmospheric gravity waves (AGWs) in the ionosphere is called a traveling ionospheric disturbance (TID). TIDs can be thought of as traveling corrugations in the ionosphere, and as such can seriously affect HF radio communications and surveillance systems. They may indirectly play a greater role in disrupting communications by triggering the growth of ionospheric instabilities, resulting in scintillation of radio signals. It is therefore of great interest to monitor TIDs on a routine basis, and to correlate their properties with other phenomena. In this paper, we present data from a unique radio technique for measuring TID properties such as their spectrum, and their spectrally resolved propagation characteristics. One of the most sensitive methods for detecting transient changes in the ionosphere is the HF Doppler technique operating in the 3-10 MHz band. HF Doppler systems have advantages over all other techniques for the measurement of TID characteristics. They are more amenable to analysis than data from ionosonde chains, and their time resolution (30 sec) is much higher than that of ionosondes . Unlike total electron content (TEC) methods, which respond to height-integrated TID effects, the HF Doppler radar responds to TIDs at the altitude of the radio reflection point. Finally, HF Doppler systems have low power consumption, so that both spatial and temporal resolution can be maintained for many days without the costs that would be associated with an incoherent-scatter radar. SwRI recently designed, built and deployed an HF Doppler sounding system in Texas, to investigate TIDs. The TIDDBIT radar consisted of three transmitters (Austin, Uvalde and St. Hedwig) and a receiver in San Antonio, Texas. Using a cross-spectral analysis technique, TID speeds and azimuths were obtained for each wave frequency. We provide a synoptic survey of the TID characteristics observed over Texas during January-March 2002. The Doppler system provides an accurate
Wu, Dong L.; Zhang, Fuqing
2004-01-01
Satellite microwave data are used to study gravity wave properties and variabilities over the northeastern United States and the North Atlantic in the December-January periods. The gravity waves in this region, found in many winters, can reach the stratopause with growing amplitude. The Advanced Microwave Sounding Unit-A (AMSU-A) observations show that the wave occurrences are correlated well with the intensity and location of the tropospheric baroclinic jet front systems. To further investigate the cause(s) and properties of the North Atlantic gravity waves, we focus on a series of wave events during 19-21 January 2003 and compare AMSU-A observations to simulations from a mesoscale model (MM5). The simulated gravity waves compare qualitatively well with the satellite observations in terms of wave structures, timing, and overall morphology. Excitation mechanisms of these large-amplitude waves in the troposphere are complex and subject to further investigations.
Influence of atmospheric waves on the formation and maintenance of
Kuroda, Yuhji
2016-04-01
The formation and maintenance of the subtropical jet during the Northern Hemisphere winter was examined using new analysis method that can isolate the responses to specific forcings within meteorological data. It is found that atmospheric waves play a crucial role in the climatological maintenance, the month-to-month, and the day-to-day variabilities of the jet. Climatologically, stationary waves, which reach up to 1.4 m/s/day, are the greatest accelerator of the jet core, whereas synoptic waves decelerate the jet core. For the month-to-month variability of the jet, stationary waves are the primary driver of the jet, followed by synoptic waves. On the other hand, Low-Frequency Transient (LFT) waves, whose frequency falls between stationary and synoptic waves, act to suppress the variability. However, synoptic waves play a key role in creating the variability on a monthly scale, whereas stationary waves work only for the maintenance of the jet. Regarding the day-to-day variability of the jet, the most important driver of eddies originates from the interference between synoptic waves and the mixing of stationary and LFT waves.
Computation of 3D steady Navier-Stokes flow with free-surface gravity waves
Lewis, M. R.; Koren, Barry; Raven, H.C.
2003-01-01
In this paper an iterative method for the computation of stationary gravity-wave solutions is investigated, using a novel formulation of the free-surface (FS) boundary-value problem. This method requires the solution of a sequence of stationary Reynolds-Averaged Navier-Stokes subproblems employing the so-called quasi free-surface condition. The numerical performance of this new approach is investigated for two test cases. The first test case involves the computation of the 3D gravity-wave pat...
Surface gravity wave transformation across a platform coral reef in the Red Sea
Lentz, S. J.; Churchill, J. H.; Davis, K. A.; Farrar, J. T.
2016-01-01
The transformation of surface gravity waves across a platform reef in the Red Sea is examined using 18 months of observations and a wave transformation model developed for beaches. The platform reef is 200 m across, 700 m long, and the water depth varies from 0.3 to 1.2 m. Assuming changes in wave energy flux are due to wave breaking and bottom drag dissipation, the wave transformation model with optimal parameters characterizing the wave breaking (γm = 0.25) and bottom drag (hydrodynamic roughness zo = 0.08 m) accounts for 75%-90% of the observed wave-height variance at four sites. The observations and model indicate that wave breaking dominates the dissipation in a 20-30 m wide surf zone while bottom drag dominates the dissipation over the rest of the reef. Friction factors (drag coefficients) estimated from the observed wave energy balance range from fw = 0.5 to fw = 5 and increase as wave-orbital displacements decrease. The observed dependence on wave-orbital displacement is roughly consistent with extrapolation of an empirical relationship based on numerous laboratory studies of oscillatory flow. As a consequence of the dependence on wave-orbital displacement, wave friction factors vary temporally due to changes in water depth and incident wave heights, and spatially across the reef as the waves decay.
Pantillon, Florian P; Charbonnel, Corinne
2007-01-01
This is the third in a series of papers that deal with angular momentum transport by internal gravity waves. We concentrate on the waves excited by core convection in a 3Msun, Pop I main sequence star. Here, we want to examine the role of the Coriolis acceleration in the equations of motion that describe the behavior of waves and to evaluate its impact on angular momentum transport. We use the so-called traditional approximation of geophysics, which allows variable separation in radial and horizontal components. In the presence of rotation, the horizontal structure is described by Hough functions instead of spherical harmonics. The Coriolis acceleration has two main effects on waves. It transforms pure gravity waves into gravito-inertial waves that have a larger amplitude closer to the equator, and it introduces new waves whose restoring force is mainly the conservation of vorticity. Taking the Coriolis acceleration into account changes the subtle balance between prograde and retrograde waves in non-rotating ...
Gravitational and torsion waves in linearised teleparallel gravity
de Andrade, L. C. Garcia
2002-01-01
Spin-2, spin-1 and spin-0 modes in linearised teleparallelism are obtained where the totally skew-symmetric complex contortion tensor generates scalar torsion waves and the symmetric contortion in the last two indices generates gravitational waves as gravitational perturbations of flat spacetime with contortion tensor. A gedanken experiment with this gravitational-torsion wave hitting a ring of spinless particles is proposed which allows us to estimate the contortion of the Earth by making us...
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.
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.
2002-09-01
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.
Climatology of extratropical atmospheric wave packets in the northern hemisphere
Grazzini, Federico
2010-01-01
Planetary and synoptic scale wave-packets represents one important component of the atmospheric large-scale circulation. These dissipative structures are able to rapidly transport eddy kinetic energy, generated locally (e.g. by baroclinic conversion), downstream along the upper tropospheric flow. The transported energy, moving faster than individual weather systems, will affect the development of the next meteorological system on the leading edge of the wave packet, creating a chain of connections between systems that can be far apart in time and space, with important implications on predictability. In this work we present a different and novel approach to investigate atmospheric variability, based on the objective recognition of planetary and synoptic wave packets. We have developed an objective tracking algorithm which allows to extract relevant statistical properties of the wave trains as a function of their dominant wavelength. We have applied the algorithm to the daily analysis (every 12h) from 1958-2009...
Rayleigh lidar observations of gravity wave activity in the upper stratosphere at Urbana, Ill.
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.
Inter-hemispheric Comparison of Mesospheric Short-period Gravity Wave Propagation
Nielsen, K.; Taylor, M. J.; Collins, R. L.; Irving, B. K.; Negale, M.; Siskind, D. E.; Eckermann, S. D.; Hoppel, K.; Harvey, V.; Russell, J. M.
2011-12-01
Mesospheric short-period (≤1-hr) gravity waves are of great importance for dynamics in the mesosphere-lower thermosphere (MLT) region, and are typically measured by instruments capable of high temporal and/or spatial resolutions such as lidars and airglow imagers. These waves have been studied extensively at low- and mid-latitudes where known wave sources are well established. The results show strong dependence on the background wind and temperature fields, which can act as a barrier prohibiting vertical propagation of the waves, as well as providing a ducted environment in which the waves can travel large horizontal distances. In fact, results show that up to 75% of these waves may exhibit ducted wave motion. Recent airglow imaging measurements over Antarctica have revealed a large number of short-period gravity waves in absence of the prominent wave sources present at lower latitudes. In contrast to results at lower latitudes, very few waves (˜5%) observed over Halley (76°S) exhibited Doppler ducted motion. In this work, we utilize airglow imagery, SABER temperature measurements, together with the Navy's high-altitude numerical weather prediction system, NOGAPS-ALPHA, to investigate propagation conditions (particularly, the role of thermal ducting) over Rothera (68°S). Data acquired from a newly installed airglow imager operating at Poker Flat, Alaska (65°N) and the co-located lidar provide an opportunity to perform an inter-hemispheric comparison of propagation conditions over two polar sites at similar latitudes.
Energy spectrum of ensemble of weakly nonlinear gravity-capillary waves on a fluid surface
Tobisch, Elena
2014-01-01
In this Letter we regard nonlinear gravity-capillary waves with parameter of nonlinearity being $\\varepsilon \\sim 0.1 \\div 0.25$. For this nonlinearity time scale separation does not occur and kinetic wave equation does not hold. An energy cascade in this case is built at the dynamic time scale (D-cascade) and is computed by the increment chain equation method first introduced in \\emph{Kartashova, \\emph{EPL} \\textbf{97} (2012), 30004.} We compute for the first time an analytical expression for the energy spectrum of nonlinear gravity-capillary waves as an explicit function depending on the ratio of surface tension to the gravity acceleration. It is shown that its two limits - pure capillary and pure gravity waves on a fluid surface - coincide with the previously obtained results. We also discuss relations of the model of D-cascade with a few known models used in the theory of nonlinear waves such as Zakharov's equation, resonance of the modes with nonlinear Stokes corrected frequencies and Benjamin-Feir index...
Waves in the martian atmosphere: Observations, Theory, and Application
Murphy, James
2001-11-01
Ongoing spacecraft exploration and numerical model studies indicate the presence in the martian atmosphere of migrating thermal waves with structures extending from the surface to at least 100 kilometers altitude. High frequency atmospheric waves are both a direct (westward travelling) and indirect (eastward travelling) response to the diurnal variations of solar heating and cooling. The eastward travelling waves are the result of longitudinal asymmetries in the thermal forcing, generated by topography and atmospheric dust on Mars. Quantification of these waves offers both a window into the physical state of the martian atmosphere (dust load, temperature structure, wind field structure) as well as a tool by which the state of the martian thermosphere can be ‘predicted’ for spacecraft aerobraking and aerocapture purposes. We will discuss the current theoretical understanding of these wave phenomena, the observational record of the same, and the ongoing employment of this growing understanding in the current aerobraking activities of the Mars ’01 Odyssey orbiter (due to arrive into orbit about Mars on Oct. 24, 2001). This work is funded by NASA’s Mars Data Analysis Program and by the Mars Exploration Office at JPL.
Swell impact on wind stress and atmospheric mixing in a regional coupled atmosphere-wave model
DEFF Research Database (Denmark)
Wu, Lichuan; Rutgersson, Anna; Sahlée, Erik;
2016-01-01
-wave-coupled regional climate model, separately and combined. The swell influence on atmospheric mixing is introduced into the atmospheric mixing length formula by adding a swell-induced contribution to the mixing. The swell influence on the wind stress under wind-following swell, moderate-range wind, and near...... reduces the near-surface wind speed. Introducing the wave influence roughness length has a larger influence than does adding the swell influence on mixing. Compared with measurements, adding the swell influence on both atmospheric mixing and wind stress gives the best model performance for the wind speed...... when developing climate models....
On the Dynamics of Two-Dimensional Capillary-Gravity Solitary Waves with a Linear Shear Current
Directory of Open Access Journals (Sweden)
Dali Guo
2014-01-01
Full Text Available The numerical study of the dynamics of two-dimensional capillary-gravity solitary waves on a linear shear current is presented in this paper. The numerical method is based on the time-dependent conformal mapping. The stability of different kinds of solitary waves is considered. Both depression wave and large amplitude elevation wave are found to be stable, while small amplitude elevation wave is unstable to the small perturbation, and it finally evolves to be a depression wave with tails, which is similar to the irrotational capillary-gravity waves.
Ultralong atmospheric waves and a long-range forecasting
KURBATKIN, G. P.
2011-01-01
A hydrodynamic model of a long-range forecasting of planetary waves is described. In developing this model a priori meteorological information together with the theory of atmospheric instability was used. To solve the filtered multi-level model the spectral method of spherical harmonics was applied. The most large-scale harmonics of “climatic sources” were computed from the acquired data on the state of the atmosphere during a long period of time. Heating and dissipation were estimated with t...
Surface Gravity Waves: Resonance in a Fish Tank
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…
On the linear approximation of gravity wave saturation in the mesosphere
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.
Observations of gravity waves in the upper and lower stratosphere by lidar and ozonesondes
Directory of Open Access Journals (Sweden)
N. J. Mitchell
Full Text Available Lidar observations of Rayleigh backscatter and temperature profiles measured by ozonesondes have been used to investigate gravity waves in the upper and lower stratosphere, respectively, over Aberystwyth (52.4°N, 4.1°W. Both data sets have been used to investigate the vertical wavenumber spectrum of the wave field at high wavenumbers. Similar analytic techniques applied to each data set enable direct comparison of the spectra. The possibility of laminar structures generated by differential advection contaminating gravity-wave fields deduced from temperature and/or density measurement is discussed and the behaviour of the wave-field mean potential energy reveals a seasonal cycle throughout the stratosphere with a late winter maximum and a summer minimum.
The instability of counter-propagating kernel gravity waves in a constant shear flow
Umurhan, O M; Harnik, N; Lott, F
2007-01-01
The mechanism describing the recently developed notion of kernel gravity waves (KGWs) is reviewed and such structures are employed to interpret the unstable dynamics of an example stratified plane parallel shear flow. This flow has constant vertical shear, is infinite in the vertical extent, and characterized by two density jumps of equal magnitude each decreasing successively with height, in which the jumps are located symmetrically away from the midplane of the system. We find that for a suitably defined bulk-Richardson number there exists a band of horizontal wavenumbers which exhibits normal-mode instability. The instability mechanism closely parallels the mechanism responsible for the instability seen in the problem of counter-propagating Rossby waves. In this problem the instability arises out of the interaction of counter-propagating gravity waves. We argue that the instability meets the Hayashi-Young criterion for wave instability. We also argue that the instability is the simplest one that can arise ...
Trapping and instability of directional gravity waves in localized water currents.
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. PMID:25019886
Intercomparisons of HIRDLS, COSMIC and SABER for the detection of stratospheric gravity waves
Directory of Open Access Journals (Sweden)
C. J. Wright
2011-01-01
Full Text Available Colocated temperature profiles from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC, High Resolution Dynamics Limb Sounder (HIRDLS and the Sounding of the Atmosphere by Broadband Emission Radiometry (SABER mission are compared over the years 2006–2007 to assess their relative performances for the detection of stratospheric gravity waves. Two methods are used, one based on a simple comparison of the standard deviations and correlation coefficients of high-pass filtered profiles from each instrument, and the other based on Stockwell transform analyses of the profiles for vertical wavelength and temperature perturbation scales. It is concluded, when allowing for their different vertical resolution capabilites, that the three instruments reproduce each other's results for magnitude and vertical scale of perturbations to within their resolution limits in approximately 50% of cases, but with a positive frequency and temperature bias in the case of COSMIC. This is possibly indicative of a slightly higher vertical resolution being available to the constellation than estimated.
Effect of Gravity Waves Generated in the Monsoon Region on Polar Mesospheric Clouds
Thurairajah, B.; Bailey, S. M.; Carstens, J. N.; Siskind, D. E.
2015-12-01
Gravity Waves (GWs) play an important role in both the formation and destruction of polar mesospheric clouds. In summer, while vertically propagating GWs induce a residual circulation that cools the summer mesosphere and therefore supports the formation of PMCs, observation and modeling studies have also shown that short period GWs can additionally destroy PMCs. In this study we analyze the effect of non-vertical propagation of GWs on PMCs using temperature data from the SABER instrument on TIMED satellite and PMC occurrence frequency from the CIPS instrument on the AIM satellite. During the 2007 PMC season, time series of GWs over the monsoon region at 50 km and PMCs over the polar region at 84 km have a correlation coefficient of 0.9. SABER GW amplitude and momentum flux over the monsoon region show a poleward tilt with altitude. This slanted structure suggests a poleward, but non-vertical, propagation of GWs facilitated by the easterly winds associated with the monsoon circulation, thus indicating a possible source of high latitude middle atmospheric GWs.
Kelley, M. C.; Pfaff, R. F., Jr.; Dao, E. V.; Holzworth, R. H., II
2014-12-01
With the increase in solar activity, the Communications/Outage Forecast System satellite (C/NOFS) now goes below the F peak. As such, we now can study the development of Convective Ionospheric Storms (CIS) and, most importantly, large-scale seeding of the low growth-rate Rayleigh-Taylor (R-T) instability. Two mechanisms have been suggested for such seeding: the Collisional Kelvin-Helmholtz Instability (CKHI) and internal atmospheric gravity waves. A number of observations have shown that the spectrum of fully developed topside structures peaks at 600 km and extends to over 1000 km. These structures are exceedingly difficult to explain by CKHI. Here we show that sinusoidal plasma oscillations on the bottomside during daytime develop classical R-T structures on the nightside with the background 600 km structure still apparent. In two case studies, thunderstorm activity was observed east of the sinusoidal features in the two hours preceding the C/NOFS passes. Thus, we argue that convective tropospheric storms are a likely source of these sinusoidal features.
Absolute parallelism, modified gravity, and suppression of gravitational short waves
Zhogin, I L
2011-01-01
There is a unique variant of Absolute Parallelism, which is very simple as it has no free parameters: nothing (nor D=5) can be changed if to keep the theory safe from emerging singularities of solutions. On the contrary, eternal solutions of this theory, due to the linear instability of the trivial solution, should be of great complexity which can in some scenarios (with a set of slowly varying parameters of solutions) provide a few phenomenological models including a modified (better to say, new or another) gravity and an expanding-shell cosmology (the longitudinal polarization gives the anti-Milne model). The former looks (mostly) like a variant of tensor-Ricci-squared gravity on a brane of a huge scale L along the extra-dimension. The correction to Newton's law of gravity, which depends in this theory on two parameters (bi-Laplace equation) and behaves as 1/r on large scales, r>L (kpc>L>pc), can start from zero (the Rindler term vanishes) if a constraint is imposed on these parameters. On further considera...
Tsunami and acoustic-gravity waves in water of constant depth
Energy Technology Data Exchange (ETDEWEB)
Hendin, Gali; Stiassnie, Michael [Faculty of Civil and Environmental Engineering, Technion – Israel institute of technology, Haifa 32000 (Israel)
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.
Tsunami and acoustic-gravity waves in water of constant depth
International Nuclear Information System (INIS)
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
Tsunami and acoustic-gravity waves in water of constant depth
Hendin, Gali; Stiassnie, Michael
2013-08-01
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.
Directory of Open Access Journals (Sweden)
X. Liu
2013-01-01
Full Text Available We study the momentum deposition in the thermosphere from the dissipation of small amplitude gravity waves (GWs within a wave packet using a fully nonlinear two-dimensional compressible numerical model. The model solves the nonlinear propagation and dissipation of a GW packet from the stratosphere into the thermosphere with realistic molecular viscosity and thermal diffusivity for various Prandtl numbers. The numerical simulations are performed for GW packets with initial vertical wavelengths (λ_{z} ranging from 5 to 50 km. We show that λ_{z} decreases in time as a GW packet dissipates in the thermosphere, in agreement with the ray trace results of Vadas and Fritts (2005 (VF05. We also find good agreement for the peak height of the momentum flux (z_{diss} between our simulations and VF05 for GWs with initial λ_{z} ≤ 2π H in an isothermal, windless background, where H is the density scale height. We also confirm that z_{diss} increases with increasing Prandtl number. We include eddy diffusion in the model, and find that the momentum deposition occurs at lower altitudes and has two separate peaks for GW packets with small initial λ_{z}. We also simulate GW packets in a non-isothermal atmosphere. The net λ_{z} profile is a competition between its decrease from viscosity and its increase from the increasing background temperature. We find that the wave packet disperses more in the non-isothermal atmosphere, and causes changes to the momentum flux and λ_{z} spectra at both early and late times for GW packets with initial λ_{z} ≥ 10 km. These effects are caused by the increase in T in the thermosphere, and the decrease in T near the mesopause.
Propagation of High Frequency Waves in the Quiet Solar Atmosphere
AndiÄ, Aleksandra
2008-01-01
High-frequency waves (5 mHz to 20mHz) have previously been suggested as a source of energy accounting partial heating of the quiet solar atmosphere. The dynamics of previously detected high-frequency waves is analysed here. Image sequences are taken using the German Vacuum Tower Telescope (VTT), Observatorio del Teide, Izana, Tenerife, with a Fabry-Perot spectrometer. The data were speckle reduced and analyzed with wavelets. Wavelet phase-difference analysis is performed to determine whether the waves propagate. We observe the propagation of waves in the frequency range 10mHz to 13mHz. We also observe propagation of low-frequency waves in the ranges where they are thought to be evanescent in regions where magnetic structures are present.
Propagation of High Frequency Waves in the Quiet Solar Atmosphere
Directory of Open Access Journals (Sweden)
Andić, A.
2008-12-01
Full Text Available High-frequency waves (5 mHz to 20 mHz have previously been suggested as a source of energy accounting for partial heating of the quiet solar atmosphere. The dynamics of previously detected high-frequency waves is analysed here. Image sequences were taken by using the German Vacuum Tower Telescope (VTT, Observatorio del Teide, Izana, Tenerife, with a Fabry-Perot spectrometer. The data were speckle reduced and analysed with wavelets. Wavelet phase-difference analysis was performed to determine whether the waves propagate. We observed the propagation of waves in the frequency range 10 mHz to 13 mHz. We also observed propagation of low-frequency waves in the ranges where they are thought to be evanescent in the regions where magnetic structures are present.
Mars Gravity Field and Upper Atmosphere from MGS, Mars Odyssey, and MRO
Genova, A.; Goossens, S. J.; Lemoine, F. G.; Mazarico, E.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.
2015-12-01
The NASA orbital missions Mars Global Surveyor (MGS), Mars Odyssey (ODY), and Mars Reconnaissance Orbiter (MRO) have been exploring and monitoring the planet Mars since 1997. MGS executed its mapping mission between 1999 and 2006 in a frozen sun-synchronous, near-circular, polar orbit with the periapsis altitude at ~370 km and the dayside equatorial crossing at 2 pm Local Solar Time (LST). The spacecraft was equipped with onboard instrumentation to acquire radio science data and to measure spacecraft ranges to the Martian surface (Mars Orbiter Laser Altimeter). These measurements resulted in static and time-varying gravity field and high-resolution global topography of the planet. ODY and MRO are still orbiting about Mars in two different sun-synchronous orbits, providing radio tracking data that indirectly measure both the static and time-varying gravity field and the atmospheric density. The orbit of ODY has its periapsis at ~390 km altitude and descending node at 4-5 pm LST. However, the spacecraft also collected measurements at lower altitudes (~220 km) in 2002 prior to the mapping phase. Since November 2006, MRO is in a low-altitude orbit with a periapsis altitude of 255 km and descending node at 3 pm LST. Radio data from MRO help improve the resolution of the static gravity field and measure the mass distribution of the polar caps, but the atmospheric drag at those altitudes may limit the benefits of these radio tracking observations. We present a combined solution of the Martian gravity field to degree and order 110 and atmospheric density profiles with radio tracking data from MGS, ODY and MRO. The gravity field solution is combined with the MOLA topography yielding an updated map of Mars crustal thickness. We also show our solution of the Love number k2 and time-variable gravity zonal harmonics (C20 and C30, in particular). The recovered atmospheric density profiles may be used in atmospheric models to constrain the long-term variability of the
Pramitha, M.; Venkat Ratnam, M.; Leena, P. P.; Krishna Murthy, B. V.; Vijaya Bhaskar Rao, S.
2016-07-01
In the present study, sources for the inertia-gravity waves (IGWs) that are observed in the troposphere and lower stratosphere during different seasons over a tropical station Gadanki (13.5°N, 79.2°E), India, have been identified. For this we have used long-term high resolution radiosonde observations of horizontal winds and temperature during May 2006 to March 2014. The IGW parameters are extracted using Stokes method. Rotary analysis is applied to the wind data to find the vertical direction of propagation. Dominant vertical wavelengths for these waves are obtained from FFT in the altitude domain as well as from apparent frequency method. The vertical and horizontal wavelengths are found to be in the range of 2-5 km (1-3 km) and 500-1500 km (1000-2000 km) in the troposphere (stratosphere), respectively. Using Stokes parameter method we have obtained the statistics of the number of the waves which are monochromatic. GROGRAT model with ERA-Interim data as the background atmosphere is used to identify the terminal (and source) points (sources) for the observed waves. In general, 53% of the waves observed over this location have convection as source and for only 38% of the cases vertical shear in the horizontal wind is identified as a source. For the rest of the 9% of the cases, these two sources are not found to be active.
Gravitational waves during inflation from a 5D large-scale repulsive gravity model
Reyes, Luz Marina; Aguilar, José Edgar Madriz; Bellini, Mauricio
2012-01-01
We investigate, in the transverse traceless (TT) gauge, the generation of the relic background of gravitational waves, generated during an early inflationary stage, on the framework of a large-scale repulsive gravity model. We calculate the spectrum of the tensor metric fluctuations of an effective 4D Schwarzschild-de-Sitter metric, which is obtained after implementing a planar coordinate transformation on a 5D Ricci-flat metric solution, in the context of a non-compact Kaluza-Klein theory of gravity. We found that the spectrum is nearly scale invariant under certain conditions. One interesting aspect of this model is that is possible to derive dynamical field equations for the tensor metric fluctuations, valid not just at cosmological scales, but also at astrophysical scales, from the same theoretical model. The astrophysical and cosmological scales are determined by the gravity- antigravity radius, which is a natural length scale of the model, that indicates when gravity becomes repulsive in nature.
Scalar Gravitational Waves in the Effective Theory of Gravity
Mottola, Emil
2016-01-01
As a low energy effective field theory, classical General Relativity receives an infrared relevant modification from the conformal trace anomaly of the energy-momentum tensor of massless, or nearly massless, quantum fields. The local form of the effective action associated with the trace anomaly is expressed in terms of a dynamical scalar field that couples to the conformal factor of the spacetime metric, allowing it to propagate over macroscopic distances. Linearized around flat spacetime, this semi-classical EFT admits scalar gravitational wave solutions in addition to the transversely polarized tensor waves of the classical Einstein theory. The amplitude, Hamiltonian, energy flux, and quantization of the scalar wave modes are discussed. Astrophysical sources for scalar gravitational waves are considered, with the excited gluonic condensates in the interiors of neutron stars in merger events with other compact objects likely to provide the strongest burst signals.
Feasibility study of a zero-gravity (orbital) atmospheric cloud physics experiments laboratory
Hollinden, A. B.; Eaton, L. R.
1972-01-01
A feasibility and concepts study for a zero-gravity (orbital) atmospheric cloud physics experiment laboratory is discussed. The primary objective was to define a set of cloud physics experiments which will benefit from the near zero-gravity environment of an orbiting spacecraft, identify merits of this environment relative to those of groundbased laboratory facilities, and identify conceptual approaches for the accomplishment of the experiments in an orbiting spacecraft. Solicitation, classification and review of cloud physics experiments for which the advantages of a near zero-gravity environment are evident are described. Identification of experiments for potential early flight opportunities is provided. Several significant accomplishments achieved during the course of this study are presented.
HF Doppler observations of gravity waves during the 16 February 1980 solar eclipse
Energy Technology Data Exchange (ETDEWEB)
Hanuise, C.; Broche, P. (Toulon Univ., 83 (France). Lab. de Sondages Electromagnetiques de l' Environnement Terrestre); Ogubazghi, G. (Addis Ababa Univ. (Ethiopia))
1982-11-01
Observations by the HF Doppler technique of the ionospheric effects of the 16 February 1980 solar eclipse in Africa are presented. Some oscillations which are detected at two stations can be attributed to a travelling coherent structure. Its characteristics are consistent with a gravity wave generated by the eclipse.
HF Doppler observations of gravity waves during the 16 February 1980 solar eclipse
International Nuclear Information System (INIS)
Observations by the HF Doppler technique of the ionospheric effects of the 16 February 1980 solar eclipse in Africa are presented. Some oscillations which are detected at two stations can be attributed to a travelling coherent structure. Its characteristics are consistent with a gravity wave generated by the eclipse. (author)
On the time varying horizontal water velocity of single, multiple, and random gravity wave trains
Wells, D.R.
1964-01-01
In this dissertation some characteristics of the horizontal water velocity for single, multiple, and random gravity wave trains are studied. This work consists of two parts, an analogue study and hydraulic measurements. An important aspect in this work is to suggest the horizontal water velocity asy
The electromagnetic afterglows of gravitational waves as a test for Quantum Gravity
Abramowicz, M A; Ellis, G F R; Meissner, K A; Wielgus, M
2016-01-01
We argue that if particularly powerful electromagnetic afterglows of the gravitational waves bursts will be observed in the future, this could be used as a strong observational support for some suggested quantum alternatives for black holes (e.g., firewalls and gravastars). A universal absence of powerful afterglows should be taken as a suggestive argument against such hypothetical quantum-gravity objects.
Coupling Atmosphere and Waves for Coastal Wind Turbine Design
DEFF Research Database (Denmark)
Bolanos, Rodolfo; Larsén, Xiaoli Guo; Petersen, Ole S.;
2014-01-01
Offshore wind farms in coastal areas are considered by the Danish government to contribute to the goal of having 50% of the energy consumption from renewable sources by 2025. Therefore, new coastal developments will take place in Danish areas. The impact of waves on atmosphere is most often descr...
Frolov, Vladimir; Chernogor, Leonid; Rozumenko, Victor
The Radiophysical Research Institute (Nizhny Novgorod, Russia) and Kharkiv V. N. Karazin National University (Kharkiv, Ukraine) have studied opportunities for the effective generation of acoustic gravity waves (AGWs) in 3 - 180-min period range. The excitation of such waves was conducted for the last several years using the SURA heating facility (Nizhny Novgorod). The detection of the HF-induced AGWs was carried out in the Radiophysical Observatory located near Kharkiv City at a distance of about 960 km from the SURA. A coherent radar for vertical sounding, an ionosonde, and magnetometer chains were used in our measurements. The main results are the following (see [1-5]): 1. Infrasound oscillation trains with a period of 6 min are detected during periodic SURA heater turn-on and -off. Similar oscillation trains are detected after long time pumping, during periodic transmissions with a period of 20 s, as well as after pumping turn-off. The train recordings begin 28 - 54 min after the heater turn-on or -off, and the train propagation speeds are about 300 - 570 m/s, the value of which is close to the sound speed at upper atmospheric altitudes. The amplitude of the Doppler shift frequency is of 10 - 40 mHz, which fits to the 0.1 - 0.3% electron density disturbances at ionospheric altitudes. The amplitude of the infrasound oscillations depends on the SURA mode of operation and the state of the upper atmosphere and ionosphere. 2. High-power radio transmissions stimulate the generation (or enhancement) of waves at ionospheric altitudes in the range of internal gravity wave periods. The HF-induced waves propagate with speeds of 360 - 460 m/s and produce changes in electron density with amplitudes of 2 - 3%. The generation of such periodic perturbations is more preferable with periods of 10 - 60 minutes. Their features depend significantly on the heater mode of operation. It should be stressed that perturbation intensity increases when a pumping wave frequency approaches
International Nuclear Information System (INIS)
Complete text of publication follows. The role of short scale high frequency gravity waves in the upper mesosphere lower thermosphere (UMLT) region is now well appreciated. Still their global distribution and source regions are not well known. All-sky imaging of nightglow emissions provide a unique way to study the high frequency waves in the UMLT region. In this work we have studied the characteristics of the waves observed in OH Meinel band emissions over Tirunelveli (8.7degN, 77.8degE) during January and February months of 2007. We have concentrated on the OH band observations because they have better SNR than other emissions and also wave activity is more in OH than other nightglow. From Indian sector, this is the first statistical study of short period waves with nightglow imaging. Our study shows the predominance of meridionally propagating waves indicating wind filtering effects in the lower atmospheric region. Such predominant meridional propagation during solstice periods is also seen from few other sites. Apart from that considerable number of waves propagated towards northwest direction. This may be an indication for existence of strong source region situated to the southeast of the observation site. It should be noted that the strong convective activity over and around Indonesian region is situated southeast to Tirunelveli. The average wavelength and apparent phase velocity of the observed waves are 17.7 km and 52.0 m/s respectively. These parameters are obtained from observations made during winter period only. A wider picture will be available once the characterization is over for a wider dataset covering other seasons also.
Local Dynamics of Baroclinic Waves in the Martian Atmosphere
Kavulich, Michael J.
2013-11-01
The paper investigates the processes that drive the spatiotemporal evolution of baroclinic transient waves in the Martian atmosphere by a simulation experiment with the Geophysical Fluid Dynamics Laboratory (GFDL) Mars general circulation model (GCM). The main diagnostic tool of the study is the (local) eddy kinetic energy equation. Results are shown for a prewinter season of the Northern Hemisphere, in which a deep baroclinic wave of zonal wavenumber 2 circles the planet at an eastward phase speed of about 70° Sol-1 (Sol is a Martian day). The regular structure of the wave gives the impression that the classical models of baroclinic instability, which describe the underlying process by a temporally unstable global wave (e.g., Eady model and Charney model), may have a direct relevance for the description of the Martian baroclinic waves. The results of the diagnostic calculations show, however, that while the Martian waves remain zonally global features at all times, there are large spatiotemporal changes in their amplitude. The most intense episodes of baroclinic energy conversion, which take place in the two great plain regions (Acidalia Planitia and Utopia Planitia), are strongly localized in both space and time. In addition, similar to the situation for terrestrial baroclinic waves, geopotential flux convergence plays an important role in the dynamics of the downstream-propagating unstable waves. © 2013 American Meteorological Society.
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.
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. PMID:26331898
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.
Directory of Open Access Journals (Sweden)
Q. Li
2011-08-01
Full Text Available An all-sky airglow imager (ASAI was installed at Xinglong, in northern China (40.2° N, 117.4° E in November 2009 to study the morphology of atmospheric gravity waves (AGWs in the mesosphere and lower thermosphere (MLT region. Using one year of OH airglow imager data from December 2009 to November 2010, the characteristics of short-period AGWs are investigated and a yearlong AGW climatology in northern China is first ever reported. AGW occurrence frequency in summer and winter is higher than that in equinoctial months. Observed bands mainly have horizontal wavelengths from 10 to 35 km, observed periods from 4 to 14 min and observed horizontal phase speeds in the range of 30 to 60 m s^{−1}. Most of the bands propagate in the meridional direction. The propagation directions of the bands show a strong southwestward preference in winter, while almost all bands propagate northeastward in summer. Although the wind filtering in the middle atmosphere may control AGW propagations in the zonal direction, the non-uniform distribution of wave sources in the lower atmosphere may contribute to the anisotropy in the meridional direction in different seasons. Additionally, as an indication of local instability, the characteristics of ripples are also analyzed. It also shows seasonal variations, occurring more often in summer and winter and mainly moving westward in summer and eastward in winter.
Energy Technology Data Exchange (ETDEWEB)
Li, Q.; Yuan, W. [Chinese Academy of Sciences, Beijing (China). State Key Lab. of Space Weather; Chinese Academy of Sciences, Beijing (China). Graduate Univ.; Xu, J. [Chinese Academy of Sciences, Beijing (China). State Key Lab. of Space Weather; Yue, J. [National Center for Atmospheric Research, Boulder, CO (United States). High Altitude Observatory; Liu, X. [Chinese Academy of Sciences, Beijing (China). State Key Lab. of Space Weather; Henan Normal Univ., Xinxiang (China). College of Mathematics and Information Science
2011-07-01
An all-sky airglow imager (ASAI) was installed at Xinglong, in northern China (40.2 N, 117.4 E) in November 2009 to study the morphology of atmospheric gravity waves (AGWs) in the mesosphere and lower thermosphere (MLT) region. Using one year of OH airglow imager data from December 2009 to November 2010, the characteristics of short-period AGWs are investigated and a yearlong AGW climatology in northern China is first ever reported. AGW occurrence frequency in summer and winter is higher than that in equinoctial months. Observed bands mainly have horizontal wavelengths from 10 to 35 km, observed periods from 4 to 14 min and observed horizontal phase speeds in the range of 30 to 60ms{sup -1}. Most of the bands propagate in the meridional direction. The propagation directions of the bands show a strong southwestward preference in winter, while almost all bands propagate northeastward in summer. Although the wind filtering in the middle atmosphere may control AGW propagations in the zonal direction, the nonuniform distribution of wave sources in the lower atmosphere may contribute to the anisotropy in the meridional direction in different seasons. Additionally, as an indication of local instability, the characteristics of ripples are also analyzed. It also shows seasonal variations, occurring more often in summer and winter and mainly moving westward in summer and eastward in winter. (orig.)
Gravity solitary waves with polynomial decay to exponentially small ripples at infinity
Lombardi, E; Iooss, Gérard
2003-01-01
International audience In this paper, we study the travelling gravity waves of velocity c in a system of two layers of perfect fluids, the bottom one being infinitely deep, the upper one having a finite thickness h. We assume that the flow is potential, and the dimensionless parameters are the ratio between densities ρ = ρ2/ρ1 and λ=gh/c^2. For ε = 1 − λ(1 − ρ) near 0 + , the existence of periodic travelling waves of arbitrary small amplitude and the existence of generalized solitary waves...
The Influence of Surface Gravity Waves on Marine Current Turbine Performance
Lust, E.; Luznik, L.; Flack, K. A.; Walker, J.; Van Benthem, M.
2013-12-01
Surface gravity waves can significantly impact operating conditions for a marine current turbine, imparting unsteady velocities several orders of magnitude larger than the ambient turbulence. The influence of surface waves on the performance characteristics of a two-bladed horizontal axis marine current turbine was investigated experimentally in a large towing tank facility at the United States Naval Academy. The turbine model had a 0.8 m diameter (D) rotor with a NACA 63-618 cross section, which is Reynolds number independent with respect to lift coefficient in the operating range of Rec ≈ 4 x 105. The torque, thrust and rotational speed were measured at a range of tip speed ratios (TSR) from 5 tidal turbine, towing-tank experiments, surface gravity waves, fatigue loading, phase averaging
Gravity surface wave turbulence in a laboratory flume
Denissenko, Petr; Lukaschuk, Sergei; Nazarenko, Sergey
2006-01-01
We present experimental results for water wave turbulence excited by piston-like programmed wavemakers in a water flume with horisontal dimensions 6x12x1.5 meters. Our main finding is that for a wide range of excitation amplitudes the energy spectrum has a power-law scaling, $E_\\omega \\sim \\omega^{-\
Waves in the Ocean and the Atmosphere: Introduction to Wave Dynamics
Samelson, Roger M.
Anyone who has stood on a ship or a beach will recognize that wave motions are an essential element of the ocean environment. And in its deeps, along its margins and across its basins, the ocean seethes with a wide spectrum of slow-moving interior waves that are invisible to the casual eye of the surface observer. Their influence may ultimately be felt across the globe, on land as well as at sea, for years, decades, or centuries. The winds that buffet a land-locked observer may seem less like waves and more akin to the continuous rush of water through a pipe or down a river channel. However, viewed from a broader perspective, even the ever-changing weather patterns of the Earth's atmosphere have their own particular wave dynamics. With Waves in the Ocean and the Atmosphere: Introduction to Wave Dynamics, leading geophysical fluid dynamicist Joseph Pedlosky provides an accessible and authoritative theoretical introduction to the wide variety of wave motions that occur in the planetary fluid environment. This is a fine book, tailor-made for graduate teaching, but also suitable for use as a desk reference for the basic elements of oceanic and atmospheric wave dynamics. The oceanographic perspective is emphasized. Aside from a few, largely cosmetic typographical errors, the only disappointment is that it does not go on a little longer: chapters on acoustic waves, tides, coastal-trapped ocean waves, and some pointers toward the many fascinating phenomena of nonlinear wave dynamics would have been welcome extensions, and one can hope that they may be added to a future edition.
Directory of Open Access Journals (Sweden)
E. A. K. Ford
2008-02-01
Full Text Available Data from the Fabry-Perot Interferometers at KEOPS (Sweden, Sodankylä (Finland, and Svalbard (Norway, have been analysed for gravity wave activity on all the clear nights from 2000 to 2006. A total of 249 nights were available from KEOPS, 133 from Sodankylä and 185 from the Svalbard FPI. A Lomb-Scargle analysis was performed on each of these nights to identify the periods of any wave activity during the night. Comparisons between many nights of data allow the general characteristics of the waves that are present in the high latitude upper thermosphere to be determined. Comparisons were made between the different parameters: the atomic oxygen intensities, the thermospheric winds and temperatures, and for each parameter the distribution of frequencies of the waves was determined. No dependence on the number of waves on geomagnetic activity levels, or position in the solar cycle, was found. All the FPIs have had different detectors at various times, producing different time resolutions of the data, so comparisons between the different years, and between data from different sites, showed how the time resolution determines which waves are observed. In addition to the cutoff due to the Nyquist frequency, poor resolution observations significantly reduce the number of short-period waves (<1 h period that may be detected with confidence. The length of the dataset, which is usually determined by the length of the night, was the main factor influencing the number of long period waves (>5 h detected. Comparisons between the number of gravity waves detected at KEOPS and Sodankylä over all the seasons showed a similar proportion of waves to the number of nights used for both sites, as expected since the two sites are at similar latitudes and therefore locations with respect to the auroral oval, confirming this as a likely source region. Svalbard showed fewer waves with short periods than KEOPS data for a season when both had the same time resolution data
Atmospheric Refractive Electromagnetic Wave Bending and Propagation Delay
Mangum, Jeffrey G
2014-01-01
In this tutorial we summarize the physics and mathematics behind refractive electromagnetic wave bending and delay. Refractive bending and delay through the Earth's atmosphere at both radio/millimetric and optical/IR wavelengths are discussed, but with most emphasis on the former, and with Atacama Large Millimeter Array (ALMA) applications in mind. As modern astronomical measurements often require sub-arcsecond position accuracy, care is required when selecting refractive bending and delay algorithms. For the spherically-uniform model atmospheres generally used for all refractive bending and delay algorithms, positional accuracies $\\lesssim 1^{\\prime\\prime}$ are achievable when observing at zenith angles $\\lesssim 75^\\circ$. A number of computationally economical approximate methods for atmospheric refractive bending and delay calculation are presented, appropriate for astronomical observations under these conditions. For observations under more realistic atmospheric conditions, for zenith angles $\\gtrsim 75^...
Institute of Scientific and Technical Information of China (English)
Debashis NATH; CHEN Wen
2013-01-01
Over the tropics,convection,wind shear (i.e.,vertical and horizontal shear of wind and/or geostrophic adjustment comprising spontaneous imbalance in jet streams) and topography are the major sources for the generation of gravity waves.During the summer monsoon season (June-August) over the Indian subcontinent,convection and wind shear coexist.To determine the dominant source of gravity waves during monsoon season,an experiment was conducted using mesosphere-stratosphere-troposphere (MST) radar situated at Gadanki (13.5°N,79.2°E),a tropical observatory in the southern part of the Indian subcontinent.MST radar was operated continuously for 72 h to capture high-frequency gravity waves.During this time,a radiosonde was released every 6 h in addition to the regular launch (once daily to study low-frequency gravity waves) throughout the season.These two data sets were utilized effectively to characterize the jet stream and the associated gravity waves.Data available from collocated instruments along with satellite-based brightness temperature (TBB) data were utilized to characterize the convection in and around Gadanki,Despite the presence of two major sources of gravity wave generation (i.e.,convection and wind shear) during the monsoon season,wind shear (both vertical shear and geostrophic adjustment) contributed the most to the generation of gravity waves on various scales.
Scintillation index of optical wave propagating in turbulent atmosphere
Institute of Scientific and Technical Information of China (English)
Rao Rui-Zhong
2009-01-01
A concise expression of the scintillation index is proposed for a plane optical wave and a spherical optical wave both propagating in a turbulent atmosphere with a zero inner scale and a finite inner scale under an arbitrary fluc- tuation condition. The expression is based on both the results in the Rytov approximation under a weak fluctuation condition and the numerical results in a strong fluctuation regime. The maximum value of the scintillation index and its corresponding Rytov index axe evaluated. These quantities are affected by the ratio of the turbulence inner scale to the Frcsnel size.
Wavemaker theories for acoustic-gravity waves over a finite depth
Tian, Miao
2016-01-01
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 and triad wave-wave interaction, in the current study we are interested in their generation by wave-structure interaction with possible implication 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, 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 de...
Observation of mesospheric gravity waves at Comandante Ferraz Antarctica Station (62° S
Directory of Open Access Journals (Sweden)
P. B. Souza
2009-06-01
Full Text Available An airglow all-sky imager was operated at Comandante Ferraz Antarctica Station (62.1° S, 58.4° W, between April and October of 2007. Mesospheric gravity waves were observed using the OH airglow layer during 43 nights with good weather conditions. The waves presented horizontal wavelengths between 10 and 60 km and observed periods mainly distributed between 5 and 20 min. The observed phase speeds range between 5 m/s and 115 m/s; the majority of the wave velocities were between 10 and 60 m/s. The waves showed a preferential propagation direction towards the southwest in winter (May to July, while during spring (August to October there was an anisotropy with a preferential propagation direction towards the northwest. Unusual mesospheric fronts were also observed. The most probable wave source could be associated to orographic forcing, cold fronts or strong cyclonic activity in the Antarctica Peninsula.
Gamow, George
2003-01-01
A distinguished physicist and teacher, George Gamow also possessed a special gift for making the intricacies of science accessible to a wide audience. In Gravity, he takes an enlightening look at three of the towering figures of science who unlocked many of the mysteries behind the laws of physics: Galileo, the first to take a close look at the process of free and restricted fall; Newton, originator of the concept of gravity as a universal force; and Einstein, who proposed that gravity is no more than the curvature of the four-dimensional space-time continuum.Graced with the author's own draw
Inverting for a deterministic surface gravity wave using the sensitivity-kernel approach.
Roux, Philippe; Nicolas, Barbara
2014-04-01
The dynamic imaging of a deterministic gravity wave propagating at an air-water interface requires continuous sampling of every point at this interface. This sampling can be done acoustically using waves that propagate in the water column but have specular reflection points that fully scan the air-water interface. This study aims to perform this complex task experimentally, with identical ultrasonic source and receiver arrays that face each other in a 1-m-long, 5-cm-deep fluid waveguide, and with frequencies in the MHz range. The waveguide transfer matrix is recorded 100 times per second between the source-receiver arrays, while a gravity wave is generated at the air-water interface. Through the beamforming process, a large set of acoustic multi-reverberated beams are isolated and identified that interact with the air-water interface. The travel-time and amplitude modulations of each eigenbeam are measured when the surface gravity wave travels through the source-receiver plane. Linear inversion of the travel-time and amplitude perturbations is performed from a few thousand eigenbeams using diffraction-based sensitivity kernels. Inversion results using travel-times, amplitudes, or these two observables together, lead to accurate spatial-temporal patterns of the surface deformation. The advantages and limitations of the method are discussed. PMID:25234978
New gravity-capillary waves at low speeds. Part 1: Linear geometries
Trinh, Philippe H
2015-01-01
When traditional linearised theory is used to study gravity-capillary waves produced by flow past an obstruction, the geometry of the object is assumed to be small in one or several of its dimensions. In order to preserve the nonlinear nature of the obstruction, asymptotic expansions in the low-Froude or low-Bond number limits can be derived, but here, the solutions invariably predict a waveless surface at every order. This is because the waves are in fact, exponentially small, and thus beyond-all-orders of regular asymptotics; their formation is a consequence of the divergence of the asymptotic series and the associated Stokes Phenomenon. By applying techniques in exponential asymptotics to this problem, we have discovered the existence of new classes of gravity-capillary waves, from which the usual linear solutions form but a special case. In this paper, we present the initial theory for deriving these waves through a study of gravity-capillary flow over a linearised step; this will be done using two approa...
The influence of the atmosphere on geoid and potential coefficient determinations from gravity data
Rummel, R.; Rapp, R. H.
1976-01-01
For the precise computation of geoid undulations the effect of the attraction of the atmosphere on the solution of the basic boundary value problem of gravimetric geodesy must be considered. This paper extends the theory of Moritz for deriving an atmospheric correction to the case when the undulations are computed by combining anomalies in a cap surrounding the computation point with information derived from potential coefficients. The correction term is a function of the cap size and the topography within the cap. It reaches a value of 3.0 m for a cap size of 30 deg, variations on the decimeter level being caused by variations in the topography. The effect of the atmospheric correction terms on potential coefficients is found to be small, reaching a maximum of 0.0055 millionths at n = 2, m = 2 when terrestrial gravity data are considered. The magnitude of this correction indicates that in future potential coefficient determination from gravity data the atmospheric correction should be made to such data.
Ionospheric manifestations of acoustic-gravity waves under quiet and disturbed conditions
Barabash, Vladimir; Chernogor, Leonid; Panasenko, Sergii; Domnin, Igor
2014-05-01
We present the observation results of wave disturbances in the ionosphere, which are known to be manifestations of atmospheric acoustic-gravity waves (AGWs). The observations have been conducted under quiet and naturally or artificially disturbed conditions by ionosonde and incoherent scatter radar located near Kharkiv, Ukraine. Wave disturbance parameters under quiet conditions were obtained and analysed during geophysical periods including vernal and autumn equinoxes as well as summer and winter solstices. The prevailing oscillation in ionospheric F2- layer had the period of 140 - 200 min and relative amplitude of 0.1 - 0.2. The duration of this oscillation changed from 5 - 7 to 24 hours, depending on a season. The amplitude of fluctuations with other periods was noticeably smaller. The time intervals at which the intensity of incoherent scatter signals varied quasi-periodically in the altitude range from 150 to 300 km were detected. The parameters of these variations were estimated using statistical analysis and bandpass filtering. The periods of wave processes were shown to be of 30 - 120 min, there durations did not exceed of 2 - 6 periods and relative amplitudes usually ranged from 0.03 to 0.15. The phase of oscillations was detected to propagate downwards. The vertical phase velocity of travelling ionospheric disturbances (TIDs) was estimated to be in the range from 50 to 200 m/s and increased with altitude. The observations of the partial solar eclipse on January, 4, 2011 near Kharkiv were used to study the ionospheric parameters in naturally disturbed conditions. The F2-layer critical frequency dropped by a factor of 2.1. The time delay of these variations with respect to the main magnitude of the solar disk obscuration was equal to about 16 minutes. The virtual height of signal reflection near the maximum of the F2-layer ionization increased by 70 km, and the height of the model parabolic layer increased by 10 km. Some decrease in electron density and
Energy Technology Data Exchange (ETDEWEB)
Wrasse, Cristiano Max [Universidade do Vale do Paraiba (UNIVAP), Instituto de Pesquisa e Desenvolvimento (IPeD), Sao Jose dos Campos, SP (Brazil); Takahashi, Hisao; Fechine, Joaquim; Denardini, Clezio Marcos [Instituto Nacional de Pesquisas Espaciais (INPE), Sao Jose dos Campos, SP (Brazil); Wickert, Jens, E-mail: cmw@univap.br, E-mail: hisaotak@laser.inpe.br, E-mail: joaquim@laser.inpe.br, E-mail: denardin@dae.inpe.br, E-mail: jens.wickert@gfz-potsdam.de [GeoForschungsZentrum, Potsdam (GFZ), Department of Geodesy and Remote Sensing (Germany)
2007-07-01
Stratospheric gravity wave activities were deduced from GPS radio occultation temperature profiles obtained by CHAMP satellite between 2001 and 2005. Potential energy profiles are used to analyze the gravity wave activity over South America. The results showed an inter-annual variation of the potential energy integrated between 24 and 34 km of altitude. The gravity wave activity is more concentrated around the equatorial region. In order to evaluate the seasonal variation of the gravity wave activity, a mean potential energy was determined over (10 deg N-10 deg S) and (100 deg W-20 deg W). The results showed a lower gravity wave activity during winter time, while during spring time the mean potential energy showed an increase in the wave activity. The results of the mean potential energy also showed that the gravity wave activity in the lower stratosphere exhibits a higher wave activity during 2002 and 2004 and a lower wave activity during 2003 and 2005. (author)
Corda, Christian
2012-01-01
Towards the goal to quantize gravity, in this short review we discuss an intermediate step which consists in extending the picture of standard General Relativity by considering Extended Theories of Gravity. In this tapestry, the equations to quantize are not the standard Einstein field equations of General Relativity, but the extended Einstein field equations of such Extended Theories. The traditional relation between mass-energy and space-time curvature, which founds standard General Relativity, results modified in this new picture and, at least at the linearized approximation, variations of the space-time curvature generate the mass-energy. Various problems of the Dark Universe, Dark Energy, Dark Matter and Pioneer anomaly, can be, in principle, solved through this approach, while a definitive endorsement for Extended Theories of Gravity could arrive from the realization of a consistent gravitational wave astronomy. We also discuss the quantization of both mass-energy and space-time curvature in the early U...
Ripening of splashed 4He crystals by acoustic waves with and without gravity
International Nuclear Information System (INIS)
By developing a refrigerator compatible with the parabolic flight of a small jet plane, 4He crystals in a superfluid were obtained in zero-gravity conditions at 0.6 K. We report Ostwald ripening of these crystals in the superfluid after being splashed by acoustic waves. Ostwald ripening is a process in which smaller crystals melt and larger ones grow to minimize the overall surface energy. Under gravity on the ground, this ripening was not apparent because it stopped growing at a capillary length of about 1 mm; crystals at lower positions grew to minimize the gravitational energy. Without gravity, however, Ostwald ripening was observed up to the order of 10 mm, a much greater length than the 1 mm due to the infinitely long capillary length, exhibiting a novel evolution of the crystal shape driven solely by the surface energy. (paper)
Harms, Jan; Dorsher, Steven; Mandic, Vuk
2009-01-01
In this paper, we develop a new approach to gravity-gradient noise subtraction for underground gravitational-wave detectors in homogeneous rock. The method is based on spatial harmonic expansions of seismic fields. It is shown that gravity-gradient noise produced by seismic fields from distant sources, stationary or non-stationary, can be calculated from seismic data measured locally at the test mass. Furthermore, the formula is applied to seismic fields from stationary local sources. It is found that gravity gradients from these fields can be subtracted using local seismic measurements. The results are confirmed numerically with a finite-element simulation. A new seismic-array design is proposed that provides the additional information about the seismic field required to ensure applicability of the approach to realistic scenarios even with inhomogeneous rock and non-stationary local sources.
Johnson-McDaniel, Nathan; Ghosh, Abhirup; Ghosh, Archisman; Samajdar, Anuradha; Ajith, Parameswaran; Del Pozzo, Walter
2016-03-01
We describe a variety of self-consistent modifications of the effective-one-body framework that yield kludge modified gravity inspiral-merger-ringdown (IMR) waveforms. These waveforms do not correspond to any particular modified theory of gravity, but offer parametrized deviations from general relativity in various regimes. They can thus be used to test the performance of various gravitational wave tests of general relativity (GR). As an example, we introduce the IMR consistency test, which tests for consistency between the estimations of the final mass and spin from the inspiral and merger-ringdown portions of a binary black hole waveform. We show that for reasonable source parameters and SNRs in Advanced LIGO, this test is able to detect a deviation from GR with high confidence for certain modifications of the GR energy flux that are not constrained by observations of the double pulsar. We also consider the performance of a parameterized test of GR on these kludge modified gravity waveforms.
Greco, R. V.; Eaton, L. R.; Wilkinson, H. C.
1974-01-01
The work is summarized which was accomplished from January 1974 to October 1974 for the Zero-Gravity Atmospheric Cloud Physics Laboratory. The definition and development of an atmospheric cloud physics laboratory and the selection and delineation of candidate experiments that require the unique environment of zero gravity or near zero gravity are reported. The experiment program and the laboratory concept for a Spacelab payload to perform cloud microphysics research are defined. This multimission laboratory is planned to be available to the entire scientific community to utilize in furthering the basic understanding of cloud microphysical processes and phenomenon, thereby contributing to improved weather prediction and ultimately to provide beneficial weather control and modification.
Karlstrom, L.; Dunham, E. M.
2013-12-01
Volcanic conduits are strongly stratified multiphase mixtures of magma, bubbles and crystals exhibiting vertical gradients in density and pressure that drive flow. We examine the behavior of perturbations to this stratification in a model of multiphase flow through a cylindrical conduit using analytic and numerical linear stability analysis. Magma is idealized as a mixture of gas and liquid phases, accounting for compressibility of both phases, viscosity of the mixture, and a finite exsolution time for mass exchange between the phases. Short time variations in conduit flow variables are characterized by three modes of wave motion. Two modes correspond to sound waves that travel up and down the conduit, while the third is an internal gravity wave arising from restoring forces due to differences in density. When perturbed downward, a fluid parcel in the stratified magma is surrounded by more dense fluid and feels an upward restoring force from buoyancy. That restoring force can be reduced by compression of the fluid parcel by the greater pressures at depth that act to increase its density. These three modes of wave motion are characterized by several competing timescales. The timescale for viscous damping τ D sets the decay time of flow perturbations and the damping of sound waves and internal gravity waves propagating through the magma. The timescale of gravity wave oscillation, τ G (inverse of buoyancy frequency N), measures adjustment of perturbations to density and pressure differences in the vertically stratified magma. Finally, a timescale for volatile diffusion τ V measures adjustment of the gas phase mass fraction to its equilibrium solubility value. We examine perturbations to a magmastatic base state and to a base state of steady flow. Initial analytic results with frozen coefficients for a magmastatic and vertically unbounded conduit suggest that when τ V > τ G and τ D > τ G, τ V, the base state is unstable to harmonic perturbations in flow
Long-Term Observation of Small and Medium-Scale Gravity Waves over the Brazilian Equatorial Region
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.
Walterscheid, R. L.; Christensen, A. B.
2014-12-01
Equatorial regions are the scene of prolific generation of gravity waves by deep tropical convection. Waves generated by deep convection have appreciable energy at frequencies and spatial scales that are able to reach altitudes in the Middle Atmosphere and Lower Thermosphere (MLT) and above where they may attain significant amplitudes. A portion of these waves have scales and amplitudes large enough to be detected by space borne instruments. We have analyzed temperature data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite for sub-tidal scale fluctuations. Filtering was applied both vertically and horizontally to extract wave variances. We have examined the variances at equatorial latitudes for the altitude region between 70 and 120 km and have have characterized them as a function of season, local time intervals, geographical location and altitude. We find large variances in locations of where convection is particularly prolific (e.g., western South Pacific) and at altitudes where wave trapping is known to be favored (e.g., the lower thermospheric duct). The locations of significant variances persist from year to year. Variances of on the order of a few tens of degrees are found. We have also performed simulations of the response to deep tropical convection with the The Aerospace Corporation Dynamical Model (ADM). This model is a time dependent, high-resolution fully compressible dynamical model that has been used to examine the MLT wave response to intense cellular convection in northern Australia. The background thermal structure for the present simulations was obtained from TIMED/SABER data averaged over low latitudes by season and local time. Our simulations give wave amplitudes that agree reasonably well with the observed amplitudes and show layering that is consistent with the observations. We will show the results of our analysis of
Rotating black holes in a draining bathtub: superradiant scattering of gravity waves
Richartz, Mauricio; Liberati, Stefano; Weinfurtner, Silke
2014-01-01
In a draining rotating fluid flow background, surface perturbations behave as a scalar field on a rotating effective black hole spacetime. We propose a new model for the background flow which takes into account the varying depth of the water. Numerical integration of the associated Klein-Gordon equation using accessible experimental parameters shows that gravity waves in an appropriate frequency range are amplified through the mechanism of superradiance. Our numerical results suggest that the observation of this phenomenon in a common fluid mechanical system is within experimental reach. Unlike the case of wave scattering around Kerr black holes, which depends only on one dimensionless background parameter (the ratio $a/M$ between the specific angular momentum and the mass of the black hole), our system depends on two dimensionless background parameters, namely the normalized angular velocity and surface gravity at the effective black hole horizon.
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.
Towards field and laboratory experiments with ocean acoustic-gravity waves
Oliveira, Tiago; Kadri, Usama; Lin, Ying-Tsong; Morozov, Andrey
2016-04-01
Acoustic-gravity waves (AGWs) can be generated in the ocean by mechanical energy transfer from the Earth's crust (e.g. earthquakes or volcanoes) and by energy transfer occurring at the water surface (e.g. interaction of opposing gravity waves, ice-quakes or localized pressure changes). Recent theoretical studies shed light on the underlying physics of the generation and propagation of AGWs in the ocean. However, these theories are yet to be verified further with very challenging field experiments due to the associated low frequency signals required, and ambient disturbances involved. Here, we present a unique setup of field experiments and large scale laboratory tests to verify the main physical properties of AGWs in ocean generated by different types of sources. We also present a novel methodology to generate and measure AGWs in the ocean.
Inertia-gravity waves in inertially stable and unstable shear flows
Lott, François; Vanneste, Jacques
2015-01-01
An inertia-gravity wave (IGW) propagating in a vertically sheared, rotating stratified fluid interacts with the pair of inertial levels that surround the critical level. An exact expression for the form of the IGW is derived here in the case of a linear shear and used to examine this interaction in detail. This expression recovers the classical values of the transmission and reflection coefficients $|T|=\\exp(-\\pi \\mu )$ and $|R|=0$, where $\\mu^2=J(1+\
Arrival-time fluctuations of coherent reflections from surface gravity water waves.
Badiey, Mohsen; Eickmeier, Justin; Song, Aijun
2014-05-01
Arrival time fluctuations of coherent reflections from surface gravity waves are examined. A two-dimensional ray model with an evolving rough sea surface is used to explain the mechanism and formation of the deterministic striation patterns due to the surface reflection. Arrival time predictions from the ray model match qualitatively well with the measurements from bidirectional acoustic transmissions in a water depth of 100 m. PMID:24815293
The COBE cosmic 3 K anisotropy experiment: A gravity wave and cosmic string probe
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.
Symmetries In Evolving Space-time and Their Connection To High-frequency Gravity Wave Production
Beckwith, A W
2008-01-01
We present how a worm hole bridge from a prior to the present universe allows us to use symmetry arguments which allow us to generate relic gravity waves, and also non massless gravitons. The relic gravitons are produced due to thermal / vacuum energy transferral from a prior universe using a pseudo time dependent version of the Wheeler De Witt equation as presented by Crowell (2005)
Lang, Benjamin; Jacobeit, Jucundus; Beck, Christoph; Philipp, Andreas
2015-04-01
The climate research program "Medium-range Climate Predictions" (MiKlip), funded by the Federal Ministry of Education and Research in Germany (BMBF), has the aim to develop a climate model system (MPI-ESM) that can provide reliable decadal predictions of climate, including extreme weather events. A substantial part of the development process is a comprehensive model validation. Within MiKlip, it includes comparisons of model simulations and observations in order to allow statements about the performance of the model and to give particular recommendations for the further development of the model. The research project "Validation of Atmospheric Dynamics" (VADY), conducted by the cooperation partners "Institute of Geography at the University of Augsburg" (IGUA) and the "German Aerospace Centre" (DLR), contributes to model validation within MiKlip with a special focus on atmospheric waves and circulation dynamics. Within the framework of VADY, DLR validates the representation of atmospheric waves on different levels and scales based on suitable activity indices (e.g. the so-called large-scale dynamical activity index (LDAI), which is a measure for the activity of planetary waves). The focus of IGUA is on the model validation with respect to the representation of atmospheric circulation types, dynamical modes and the teleconnectivity of the atmospheric circulation. Currently, the connection between LDAI and atmospheric circulation types on different levels and for different seasons in the North Atlantic-European region is analysed by considering, in particular, the North Atlantic Oscillation. Results will be shown for the connection between LDAI and atmospheric circulation types and subsequently for the representation of the identified connections in the decadal-prediction model system of MPI-ESM.
Properties of internal planetary-scale inertio gravity waves in the mesosphere
H. G. Mayr; J. G. Mengel; E. R. Talaat; H. S. Porter; Chan, K. L.
2004-01-01
International audience At high latitudes in the upper mesosphere, horizontal wind oscillations have been observed with periods around 10h. Waves with such a period are generated in our Numerical Spectral Model (NSM), and they are identified as planetary-scale inertio gravity waves (IGW). These IGWs have periods between 9 and 11h and appear above 60km in the zonal mean (m=0), as well as in m=1 to 4, propagating eastward and westward. Under the influence of the Coriolis force, the amplitudes...
E. A. K. Ford; A. L. Aruliah; Griffin, E. M.; I. McWhirter
2008-01-01
Data from the Fabry-Perot Interferometers at KEOPS (Sweden), Sodankyla (Finland), and Svalbard (Norway), have been analysed for gravity wave activity on all the clear nights from 2000 to 2006. A total of 249 nights were available from KEOPS, 133 from Sodankyla and 185 from the Svalbard FPI. A Lomb-Scargle analysis was performed on each of these nights to identify the periods of any wave activity during the night. Comparisons between many nights of data allow the general characteristics of the...
E. A. K. Ford; A. L. Aruliah; Griffin, E. M.; I. McWhirter
2008-01-01
Data from the Fabry-Perot Interferometers at KEOPS (Sweden), Sodankylä (Finland), and Svalbard (Norway), have been analysed for gravity wave activity on all the clear nights from 2000 to 2006. A total of 249 nights were available from KEOPS, 133 from Sodankylä and 185 from the Svalbard FPI. A Lomb-Scargle analysis was performed on each of these nights to identify the periods of any wave activity during the night. Comparisons between many nights of data allow the general char...
Second generation diffusion model of interacting gravity waves on the surface of deep fluid
Directory of Open Access Journals (Sweden)
A. Pushkarev
2004-01-01
Full Text Available We propose a second generation phenomenological model for nonlinear interaction of gravity waves on the surface of deep water. This model takes into account the effects of non-locality of the original Hasselmann diffusion equation still preserving important properties of the first generation model: physically consistent scaling, adherence to conservation laws and the existence of Kolmogorov-Zakharov solutions. Numerical comparison of both models with the original Hasselmann equation shows that the second generation models improves the angular distribution in the evolving wave energy spectrum.
Gravitational waves from quasicircular black-hole binaries in dynamical Chern-Simons gravity.
Yagi, Kent; Yunes, Nicolás; Tanaka, Takahiro
2012-12-21
Dynamical Chern-Simons gravity cannot be strongly constrained with current experiments because it reduces to general relativity in the weak-field limit. This theory, however, introduces modifications in the nonlinear, dynamical regime, and thus it could be greatly constrained with gravitational waves from the late inspiral of black-hole binaries. We complete the first self-consistent calculation of such gravitational waves in this theory. For favorable spin orientations, advanced ground-based detectors may improve existing solar system constraints by 6 orders of magnitude. PMID:23368447
Effects of Shelves on Amplification of Long Waves Generated by Atmospheric Pressure Differences
Duha Metin, Ayse; Cevdet Yalciner, Ahmet; Ozyurt Tarakcıoglu, Gulizar; Zaytsev, Andrey
2016-04-01
Meteotsunami is a type of long period ocean wave generated by different types of meteorological disturbances such as atmospheric gravity waves, spatial and temporal pressure distributions and squall lines. The main idea behind the occurrence of this type of long wave is that low atmospheric pressure leads to static water level rise in a part of the marine area and high atmospheric pressure leads to static water level drop in another zone. Then, it causes deformation of the water level throughout the entire sea area. The relation between the pressure difference and change of water level from normal position (η =0.99Δ P where η is the water level change (cm) according to the pressure difference from normal pressure Δ P) can be used to determine the sea level deformation. The relation represents that 1 hPa decrease in air pressure causes 1 cm rise in mean sea level. Due to the spatial and temporal changes of atmospheric pressure, the respective small amplitude long waves propagate along the entire marine area. This type of tsunami-like waves can propagate through long distances and can also be amplified due to resonant effects in the enclosed basins, offshore shelves, and nearshore/offshore coastal morphology. Therefore, it can result in considerable amplifications and causes unexpected effects in some coastal regions. This study is mainly focused on understanding of amplification of long waves generated by atmospheric pressure differences when they encounter the offshore shelves while it is propagating towards to the shore. The problem is investigated by numerically solving nonlinear shallow water equations by using regular shaped basins with different depth and shelf characteristics. In all cases, the rectangular shape large basin is triggered by spatial and temporal distributions of atmospheric pressure. The water depth and shelf formation is changed for different cases. Initially, a deep flat bottom basin is used in simulations and the reference data of water
Scattering of gravity waves by a porous rectangular barrier on a seabed
Institute of Scientific and Technical Information of China (English)
孟庆瑞; 卢东强
2016-01-01
Within the frame of linear potential flow theory, the impact of a porous rectangular barrier on a seabed on the dynamic characteristics of gravity waves is investigated. The porous barrier can be regarded as an abstract representative such as a seabed plant, a wave breaker, inhomogeneous topography, and trussed supporting of ocean engineering platform, etc. In the process of mathematical modeling, the method of matched eigenfunction expansions is employed for analysis, where a newly defined form of inner product is introduced to improve the simplicity of derivation. Under this definition, the inner product is automatically orthogonal, which will provide great simplification to obtain the expansion coefficients. Once the wave numbers for the fluid region and the barrier region are obtained, the reflection and transmission coefficients of the wave motion can readily be calculated.
Directional Filtering Due to Mesospheric Wind Shear on the Propagation of Acoustic-gravity Waves
Institute of Scientific and Technical Information of China (English)
YU Yonghui; CHEN Wei; WANG Yachong
2013-01-01
Gravity waves with periods close to the Brunt-V(a)is(a)l(a) period of the upper troposphere are often observed at mesopause altitudes as short period,quasi-monochromatic waves.The assumption that these short period waves originate in the troposphere may be problematic because their upward propagation to the mesosphere and lower thermosphere region could be significantly impeded due to an extended region of strong evanescence above the stratopause.To reconcile this apparent paradox,an alternative explanation is proposed in this paper.The inclusion of mean winds and their vertical shears is sufficient to allow certain short period waves to remain internal above the stratopause and to propagate efficiently to higher altitudes.A time-dependent numerical model is used to demonstrate the feasibility of this and to determine the circumstances under which the mesospheric wind shears play a role in the removal and directional filtering of short period gravity waves.Finally this paper concludes that the combination of the height-dependent mean winds and the mean temperature structure probably explains the existence of short period,quasi-monochromatic structures observed in airglow images of mesopause region.
Hogg, C. A. R.; Pietrasz, V. B.; Ouellette, N. T.; Koseff, J. R.
2015-12-01
Desalination of seawater offers a source of potable water in arid regions and during drought. However, hypersaline discharge from desalination facilities presents environmental risks, particularly to benthic organisms. The risks posed by salt levels and chemical additives, which can be toxic to local ecosystems, are typically mitigated by ensuring high levels of dilution close to the source. We report on laboratory flume experiments examining how internal waves at the pycnocline of a layered ambient density stratification influence the transport of hypersaline effluent moving as a gravity current down the slope. We found that some of the hypersaline fluid from the gravity current was diverted away from the slope into an intrusion along the pycnocline. A parametric study investigated how varying the energy of the internal wave altered the amount of dense fluid that was diverted into the pycnocline intrusion. The results are compared to an analytical framework that compares the incident energy in the internal wave to potential energy used in diluting the gravity current. These results are significant for desalination effluents because fluid diverted into the intrusion avoids the ecologically sensitive benthic layer and disperses more quickly than if it had continued to propagate along the bed.
QBO modulation of the mesopause gravity wave momentum flux over Tierra del Fuego
Wit, R. J.; Janches, D.; Fritts, D. C.; Hibbins, R. E.
2016-04-01
The interannual variability of the mesosphere and lower thermosphere (MLT) gravity wave momentum flux over southern midlatitudes (53.7°S) has been studied using more than 7 years of meteor radar observations at Río Grande, Argentina. A modulation, with periods similar to that of the equatorial stratospheric quasi-biennial oscillation (QBO), is observed in the vertical flux of zonal as well as meridional momentum. The QBO signal is largest in the zonal component during summer and is in phase with the stratospheric QBO at 50 hPa (˜21 km). The relation between the stratospheric QBO and the QBO modulation in the MLT gravity wave forcing (derived from the divergence of the momentum flux) was found to be consistent with that expected from the Holton-Tan effect coupled to the interhemispheric coupling mechanism. These results provide the first observational support for the existence of the midlatitude gravity wave forcing anomalies as hypothesized in the interhemispheric coupling mechanism.
Influence of tides and gravity waves on layering processes in the polar summer mesopause region
Directory of Open Access Journals (Sweden)
P. Hoffmann
2008-12-01
Full Text Available Polar Mesosphere Summer Echoes (PMSE have been studied at Andenes (69° N, 16° E, Norway, using VHF radar observations since 1994. One remarkable feature of these observations is the fact that {during 50% of the time,} the radar echoes occur in the form of two or more distinct layers. In the case of multiple PMSE layers, statistical analysis shows that the lower layer occurs at a mean height of ~83.4 km, which is almost identical to the mean height of noctilucent clouds (NLC derived from observation with the ALOMAR Rayleigh/Mie/Raman lidar at the same site. To investigate the layering processes microphysical model simulations under the influence of tidal and gravity waves were performed. In the presence of long period gravity waves, these model investigations predict an enhanced formation of multiple PMSE layer structures, where the lower layer is a consequence of the occurrence of the largest particles at the bottom of the ice cloud. This explains the coincidence of the lowermost PMSE layers and NLC. During periods with enhanced amplitudes of the semidiurnal tide, the observed NLC and PMSE show pronounced tidal structures comparable to the results of corresponding microphysical simulations. At periods with short period gravity waves there is a tendency for a decreasing occurrence of NLC and for variable weak PMSE structures.
Small-scale topology of solar atmosphere dynamics I: wave sources and wave diffraction
Hoekzema, N.M.; Rutten, R.J.; Brandt, P.N.; Shine, R.A.
2001-01-01
We study the small-scale topology of dynamical phenomena in the quiet-sun internet w ork atmosphere,using short-duration Fourier analysis of high-resolution filtergram sequences to obtain statistical estimates for the co-location probability of different fine-structure elements and wave modes. In th
Waves and Magnetism in the Solar Atmosphere (WAMIS)
Ko, Y. K.; Auchere, F.; Casini, R.; Fineschi, S.; Gibson, S. E.; Knoelker, M.; Korendyke, C.; Laming, J. M.; Mcintosh, S. W.; Moses, J. D.; Romoli, M.; Rybak, J.; Socker, D. G.; Strachan, L.; Tomczyk, S.; Vourlidas, A.; Wu, Q.
2014-12-01
Magnetic fields in the solar atmosphere provide the energy for most varieties of solar activity, including high-energy electromagnetic radiation, solar energetic particles, flares, and coronal mass ejections, as well as powering the solar wind. Despite the fundamental role of magnetic fields in solar and heliospheric physics, there exists only very limited measurements of the field above the base of the corona. What is needed are direct measurements of not only the strength and orientation of the magnetic field but also the signatures of wave motions in order to better understand coronal structure, solar activity and the role of MHD waves in heating and accelerating the solar wind. Fortunately, the remote sensing instrumentation used to make magnetic field measurements is also well suited for measuring the Doppler signature of waves in the solar structures. With this in mind, we are proposing the WAMIS (Waves and Magnetism in the Solar Atmosphere) investigation. WAMIS will take advantage of greatly improved infrared (IR) detectors, forward models, advanced diagnostic tools and inversion codes to obtain a breakthrough in the measurement of coronal magnetic fields and in the understanding of the interaction of these fields with space plasmas. This will be achieved with a high altitude balloon borne payload consisting of a coronagraph with an IR spectro-polarimeter focal plane assembly. The balloon platform provides minimum atmospheric absorption and scattering at the IR wavelengths in which these observations are made. Additionally, a NASA long duration balloon flight mission from the Antarctic can achieve continuous observations over most of a solar rotation, covering all of the key time scales for the evolution of coronal magnetic fields. With these improvements in key technologies along with experience gained from current ground-based instrumentation, WAMIS will provide a low-cost mission with a high technology readiness leve.
Directory of Open Access Journals (Sweden)
John Z. G. Ma
2015-10-01
Full Text Available The effect of an ionospheric dynamo electric field on the electron density and total electron content (TEC perturbations in the F layer (150–600 km altitudes is investigated at two arbitrarily selected locations (noted as 29° N and 60° N in latitudes in the presence of seismic tsunami-excited gravity waves propagating in a stratified, nondissipative atmosphere where vertical gradients of atmospheric properties are taken into consideration. Generalized ion momentum and continuity equations are solved, followed by an analysis of the dynamo electric field (E. The E -strength is within several mV/m, determined by the zonal neutral wind and meridional geomagnetic field. It is found that, at the mid-latitude location, n0 e is dominated by the atmospheric meridional wind when E = 0, while it is determined by the zonal wind when E ≠ 0. The perturbed TEC over its unperturbed magnitude lies in around 10% at all altitudes for E = 0, while it keeps the same percentage at most altitudes for E ≠ 0, except a jump to >25% in the F2-peak layer (300–340 km in height. By contrast, at the low-latitude location, the TEC jump is eliminated by the locally enhanced background electron density.
2D instabilities of surface gravity waves on a linear shear current
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
Alfv\\'en Wave Driven High Frequency Waves in the Solar Atmosphere: Implications for Ion Heating
Kaghashvili, Edisher Kh
2014-01-01
This work is an extension of Kaghashvili [1999] where ion-cyclotron wave dissipation channel for Alfv\\'en waves was discussed. While our earlier study dealt with the mode coupling in the commonly discussed sense, here we study changes in the initial waveform due to interaction of the initial driver Alfv\\'en wave and the plasma inhomogeneity, which are implicitly present in the equations, but were not elaborated in Kaghashvili [1999]. Using a cold plasma approximation, we show how high frequency waves (higher than the initial driver Alfv\\'en wave frequency) are generated in the inhomogeneous solar plasma flow. The generation of the high frequency forward and backward propagating modified fast magnetosonic/whistler waves as well as the generation of the driven Alfv\\'en waves is discussed in the solar atmosphere. The generated high frequency waves have a shorter dissipation timescale, and they can also resonant interact with particles using both the normal cyclotron and anomalous cyclotron interaction channels. ...
Waves in the Martian Atmosphere: Results from MGS Radio Occultations
Flasar, F. M.; Hinson, D. P.; Tyler, G. L.
1999-01-01
Temperatures retrieved from Mars Global Surveyor radio occultations have been searched for evidence of waves. Emphasis has been on the initial series of occultations between 29 deg N and 64 deg S, obtained during the early martian southern summer, L(sub s) = 264 deg - 308 deg. The profiles exhibit an undulatory behavior that is suggestive of vertically propagating waves. wavelengths approximately 10 km are often dominant, but structure on smaller scales is evident. The undulatory structure is most pronounced between latitudes 29 deg N and 10 deg S, usually in regions of "interesting" topography, e.g., in the Tharsis region and near the edge of Syrtis Major. Several temperature profiles, particularly within 30 deg of the equator, exhibit lapse rates that locally become superadiabatic near the 0.4-mbar level or at higher altitudes. This implies that the waves are "breaking" and depositing horizontal momentum into the atmosphere. Such a deposition may play an important role in modulating the atmospheric winds, and characterizing the spatial and temporal distribution of these momentum transfers can provide important clues to understanding how the global circulation is maintained.
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.
Direct measurement of dispersion relation for directional random surface gravity waves
Magnus Arnesen Taklo, Tore; Trulsen, Karsten; Krogstad, Harald; Nieto Borge, José Carlos
2014-05-01
Linear wave theory is widely used to model for instance response of ocean structures and ships to water surface gravity waves and assumes that the water surface can be modeled as a linear superposition of regular waves satisfying the linear dispersion relation. The linear dispersion relation is often taken for granted for the interpretation of wave measurements. The interpretation of nautical radar images currently depends on the linear dispersion relation as a prerequisite, Nieto Borge et al. (J. Atmos. Ocean Tech., 2004, vol. 21, pp. 1291-1300). Krogstad & Trulsen (Ocean Dynamics, 2010, vol. 60, pp. 973-991) carried out numerical simulations in one horizontal dimension with the nonlinear Schrödinger equation NLS and the modified nonlinear Schrödinger equation MNLS. From wavenumber-frequency spectra obtained from the simulated unidirectional surfaces they found that nonlinear evolution of unidirectional wave fields may cause deviation from the linear dispersion relation. Extending the work by Krogstad & Trulsen (2010) we carried out experiments with unidirectional waves with fixed wave steepness and various bandwidths in a narrow wave tank. These experiments verified the results obtained from the simulations with the (M)NLS models and showed that the directly measured dispersion relation deviated from the linear dispersion relation for sufficiently narrow bandwidths. For broad bandwidths, however, the linear dispersion relation was satisfied, suggesting validity of linear wave theory. By further analysis of the experimental data we suggest that the occurence of the deviation depends on steepness and spectral bandwidth. Recently we have extended the work by Krogstad & Trulsen (2010) to two horizontal dimensions using the MNLS equation and simulated directional random surface gravity waves with bandwidths ranging from narrow to relatively broad. The wavenumber-frequency spectra obtained from these simulated directional surfaces also show deviation from the linear
Louie, J. N.; Basler-Reeder, K.; Kent, G. M.; Pullammanappallil, S. K.
2015-12-01
Simultaneous joint seismic-gravity optimization improves P-wave velocity models in areas with sharp lateral velocity contrasts. Optimization is achieved using simulated annealing, a metaheuristic global optimization algorithm that does not require an accurate initial model. Balancing the seismic-gravity objective function is accomplished by a novel approach based on analysis of Pareto charts. Gravity modeling uses a newly developed convolution algorithm, while seismic modeling utilizes the highly efficient Vidale eikonal equation traveltime generation technique. Synthetic tests show that joint optimization improves velocity model accuracy and provides velocity control below the deepest headwave raypath. Detailed first arrival picking followed by trial velocity modeling remediates inconsistent data. We use a set of highly refined first arrival picks to compare results of a convergent joint seismic-gravity optimization to the Plotrefa™ and SeisOpt® Pro™ velocity modeling packages. Plotrefa™ uses a nonlinear least squares approach that is initial model dependent and produces shallow velocity artifacts. SeisOpt® Pro™ utilizes the simulated annealing algorithm and is limited to depths above the deepest raypath. Joint optimization increases the depth of constrained velocities, improving reflector coherency at depth. Kirchoff prestack depth migrations reveal that joint optimization ameliorates shallow velocity artifacts caused by limitations in refraction ray coverage. Seismic and gravity data from the San Emidio Geothermal field of the northwest Basin and Range province demonstrate that joint optimization changes interpretation outcomes. The prior shallow-valley interpretation gives way to a deep valley model, while shallow antiformal reflectors that could have been interpreted as antiformal folds are flattened. Furthermore, joint optimization provides a clearer image of the rangefront fault. This technique can readily be applied to existing datasets and could
NUMERICAL STUDIES OF INTERNAL SOLITARY WAVE GENERATION AND EVOLUTION BY GRAVITY COLLAPSE
Institute of Scientific and Technical Information of China (English)
LIN Zhen-hua; SONG Jin-bao
2012-01-01
In this study,an analysis on the internal wave generation via the gravity collapse mechanism is carried out based on the theoretical formulation and the numerical simulation.With the linear theoretical model,a rectangle shape wave is generated and propagates back and forth in the domain,while a two-dimensional non-hydrostatic numerical model could reproduce all the observed phenomena in the laboratory experiments conducted by Chen et al.(2007),and the related process realistically.The model results further provide more quantitative information in the whole domain,thus allowing an in depth understanding of the corresponding internal solitary wave generation and propagation.It is shown that the initial type of the internal wave is determined by the relative height between the perturbation and the environmental density interface,while the final wave type is related to the relative height of the upper and lower layers of the environmental fluid.The shape of the internal wave generated is consistent with that predicted by the KdV and EKdV theories if its amplitude is small,as the amplitude becomes larger,the performance of the EKdV becomes better after the wave adjusts itself to the ambient stratification and reaches an equilibrium state between the nonlinear and dispersion effects.The evolution of the mechanical energy is also analyzed.
Yang, Tae-Yong; Kwak, Young-Sil; Kim, Yong-Ha
2015-12-01
Previously, all-sky airglow images observed at Shigaraki (34.9° N, 136.1° E), Japan, during 2004 and 2005 were analyzed in relation to those observed at Mt. Bohyun (36.2° N, 128.9° E) for a comparison of their gravity wave characteristics (Kim et al. 2010). By applying the same selection criteria of waves and cloud coverages as in the case of Mt. Bohyun all-sky images, we derived apparent wavelengths, periods, phase velocities, and monthly occurrence rates of gravity waves at Shigaraki in this study. The distributions of wavelengths, periods, and speeds derived for Shigaraki were found to be roughly similar to those for Mt. Bohyun. However, the overall occurrence rates of gravity waves at Shigaraki were 36% and 34% for OI 557.7 nm and OH Meinel band airglow layers, respectively, which were significantly higher than those at Mt. Bohyun. The monthly occurrence rates did not show minima near equinox months, unlike those for Mt. Bohyun. Furthermore, the seasonal preferential directions that were clearly apparent for Mt. Bohyun were not seen in the wave propagation trends for Shigaraki. These differences between the two sites imply different origins of the gravity waves near the Korean peninsula and the Japanese islands. The gravity waves over the Japanese islands may originate from sources at various altitudes; therefore, wind filtering may not be effective in causing any seasonal preferential directions in the waves in the airglow layers. Our analysis of the Shigaraki data supports recent theoretical studies, according to which gravity waves can be generated from in situ sources, such as mesosphere wind shear or secondary wave formation, in the mesosphere.
Framework of Distributed Coupled Atmosphere-Ocean-Wave Modeling System
Institute of Scientific and Technical Information of China (English)
WEN Yuanqiao; HUANG Liwen; DENG Jian; ZHANG Jinfeng; WANG Sisi; WANG Lijun
2006-01-01
In order to research the interactions between the atmosphere and ocean as well as their important role in the intensive weather systems of coastal areas, and to improve the forecasting ability of the hazardous weather processes of coastal areas, a coupled atmosphere-ocean-wave modeling system has been developed.The agent-based environment framework for linking models allows flexible and dynamic information exchange between models. For the purpose of flexibility, portability and scalability, the framework of the whole system takes a multi-layer architecture that includes a user interface layer, computational layer and service-enabling layer. The numerical experiment presented in this paper demonstrates the performance of the distributed coupled modeling system.
Gravitational waves during inflation from a 5D large-scale repulsive gravity model
Energy Technology Data Exchange (ETDEWEB)
Reyes, Luz M., E-mail: luzmarinareyes@gmail.com [Departamento de Matematicas, Centro Universitario de Ciencias Exactas e ingenierias (CUCEI), Universidad de Guadalajara (UdG), Av. Revolucion 1500, S.R. 44430, Guadalajara, Jalisco (Mexico); Moreno, Claudia, E-mail: claudia.moreno@cucei.udg.mx [Departamento de Matematicas, Centro Universitario de Ciencias Exactas e ingenierias (CUCEI), Universidad de Guadalajara (UdG), Av. Revolucion 1500, S.R. 44430, Guadalajara, Jalisco (Mexico); Madriz Aguilar, Jose Edgar, E-mail: edgar.madriz@red.cucei.udg.mx [Departamento de Matematicas, Centro Universitario de Ciencias Exactas e ingenierias (CUCEI), Universidad de Guadalajara (UdG), Av. Revolucion 1500, S.R. 44430, Guadalajara, Jalisco (Mexico); Bellini, Mauricio, E-mail: mbellini@mdp.edu.ar [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata (UNMdP), Funes 3350, C.P. 7600, Mar del Plata (Argentina); Instituto de Investigaciones Fisicas de Mar del Plata (IFIMAR) - Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET) (Argentina)
2012-10-22
We investigate, in the transverse traceless (TT) gauge, the generation of the relic background of gravitational waves, generated during the early inflationary stage, on the framework of a large-scale repulsive gravity model. We calculate the spectrum of the tensor metric fluctuations of an effective 4D Schwarzschild-de Sitter metric on cosmological scales. This metric is obtained after implementing a planar coordinate transformation on a 5D Ricci-flat metric solution, in the context of a non-compact Kaluza-Klein theory of gravity. We found that the spectrum is nearly scale invariant under certain conditions. One interesting aspect of this model is that it is possible to derive the dynamical field equations for the tensor metric fluctuations, valid not just at cosmological scales, but also at astrophysical scales, from the same theoretical model. The astrophysical and cosmological scales are determined by the gravity-antigravity radius, which is a natural length scale of the model, that indicates when gravity becomes repulsive in nature.
Gravitational waves during inflation from a 5D large-scale repulsive gravity model
Reyes, Luz M.; Moreno, Claudia; Madriz Aguilar, José Edgar; Bellini, Mauricio
2012-10-01
We investigate, in the transverse traceless (TT) gauge, the generation of the relic background of gravitational waves, generated during the early inflationary stage, on the framework of a large-scale repulsive gravity model. We calculate the spectrum of the tensor metric fluctuations of an effective 4D Schwarzschild-de Sitter metric on cosmological scales. This metric is obtained after implementing a planar coordinate transformation on a 5D Ricci-flat metric solution, in the context of a non-compact Kaluza-Klein theory of gravity. We found that the spectrum is nearly scale invariant under certain conditions. One interesting aspect of this model is that it is possible to derive the dynamical field equations for the tensor metric fluctuations, valid not just at cosmological scales, but also at astrophysical scales, from the same theoretical model. The astrophysical and cosmological scales are determined by the gravity-antigravity radius, which is a natural length scale of the model, that indicates when gravity becomes repulsive in nature.
Arun, K. G.; Pai, Archana
2013-01-01
Gravitational wave (GW) observations of coalescing compact binaries will be unique probes of strong-field, dynamical aspects of relativistic gravity. We present a short review of various schemes proposed in the literature to test general relativity (GR) and alternative theories of gravity using inspiral waveforms. Broadly these schemes may be classified into two types: model dependent and model independent. In the model dependent category, GW observations are compared against a specific waveform model representative of a particular theory or a class of theories such as scalar-tensor theories, dynamical Chern-Simons theory and massive graviton theories. Model independent tests are attempts to write down a parametrized gravitational waveform where the free parameters take different values for different theories and (at least some of) which can be constrained by GW observations. We revisit some of the proposed bounds in the case of downscaled LISA configuration (eLISA) and compare them with the original LISA configuration. We also compare the expected bounds on alternative theories of gravity from ground-based and space-based detectors and find that space-based GW detectors can test GR and other theories of gravity with unprecedented accuracies. We then focus on a recent proposal to use singular value decomposition of the Fisher information matrix to improve the accuracies with which post-Newtonian theory can be tested. We extend those results to the case of space-based detector eLISA and discuss its implications.
Regional variations of mesospheric gravity-wave momentum flux over Antarctica
Directory of Open Access Journals (Sweden)
P. J. Espy
2006-03-01
Full Text Available Images of mesospheric airglow and radar-wind measurements have been combined to estimate the difference in the vertical flux of horizontal momentum carried by high-frequency gravity waves over two dissimilar Antarctic stations. Rothera (67° S, 68° W is situated in the mountains of the Peninsula near the edge of the wintertime polar vortex. In contrast, Halley (76° S, 27° W, some 1658 km to the southeast, is located on an ice sheet at the edge of the Antarctic Plateau and deep within the polar vortex during winter. The cross-correlation coefficients between the vertical and horizontal wind perturbations were calculated from sodium (Na airglow imager data collected during the austral winter seasons of 2002 and 2003 at Rothera for comparison with the 2000 and 2001 results from Halley reported previously (Espy et al., 2004. These cross-correlation coefficients were combined with wind-velocity variances from coincident radar measurements to estimate the daily averaged upper-limit of the vertical flux of horizontal momentum due to gravity waves near the peak emission altitude of the Na nightglow layer, 90km. The resulting momentum flux at both stations displayed a large day-to-day variability and showed a marked seasonal rotation from the northwest to the southwest throughout the winter. However, the magnitude of the flux at Rothera was about 4 times larger than that at Halley, suggesting that the differences in the gravity-wave source functions and filtering by the underlying winds at the two stations create significant regional differences in wave forcing on the scale of the station separation.
,
2012-01-01
During previous numerical experiments on isotropic turbulence of surface gravity waves we observed formation of the long wave background (condensate). It was shown (Korotkevich, Phys. Rev. Lett. vol. 101 (7), 074504 (2008)), that presence of the condensate changes a spectrum of direct cascade, corresponding to the flux of energy to the small scales from pumping region (large scales). Recent experiments show that the inverse cascade spectrum is also affected by the condensate. In this case mechanism proposed as a cause for the change of direct cascade spectrum cannot work. But inverse cascade is directly influenced by the linear dispersion relation for waves, as a result direct measurement of the dispersion relation in the presence of condensate is necessary. We performed the measurement of this dispersion relation from the direct numerical experiment. The results demonstrate that in the region of inverse cascade influence of the condensate cannot be neglected.
Experimental study of tsunami-type waves impact on soil at foundations of offshore gravity platforms
Directory of Open Access Journals (Sweden)
N.D. Belyaev
2014-10-01
Full Text Available Scouring, caused by waves, currents and races of ship propellers, has been a subject of theoretical investigations, physical modeling in hydraulic laboratories and full-scale experiments in several countries. The results reported on these tests usually recommend formulas and diagrams to determine water velocities that can be used to estimate the risk of scouring and design the required protection measures. The results of the physical modeling of interaction of long tsunami-type waves with an offshore gravity platform are presented in this article. The reaction of seabed soil to wave impact at the platform foundation has been studied and the obtained results have been analyzed. Conclusions about changes in the seabed profile, density of the top layers of the seabed soil and their influence on the platform stability have been made.