Articoli di riviste: "Gravity waves"

1

Naciri, Mamoun, e Chiang C. Mei. "Evolution of short gravity waves on long gravity waves". Physics of Fluids A: Fluid Dynamics 5, n. 8 (agosto 1993): 1869–78. http://dx.doi.org/10.1063/1.858812.

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Dias, Frédéric, e Christian Kharif. "NONLINEAR GRAVITY AND CAPILLARY-GRAVITY WAVES". Annual Review of Fluid Mechanics 31, n. 1 (gennaio 1999): 301–46. http://dx.doi.org/10.1146/annurev.fluid.31.1.301.

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3

Akers, Benjamin F., David M. Ambrose e J. Douglas Wright. "Gravity perturbed Crapper waves". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 470, n. 2161 (8 gennaio 2014): 20130526. http://dx.doi.org/10.1098/rspa.2013.0526.

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Crapper waves are a family of exact periodic travelling wave solutions of the free-surface irrotational incompressible Euler equations; these are pure capillary waves, meaning that surface tension is accounted for, but gravity is neglected. For certain parameter values, Crapper waves are known to have multi-valued height. Using the implicit function theorem, we prove that any of the Crapper waves can be perturbed by the effect of gravity, yielding the existence of gravity–capillary waves nearby to the Crapper waves. This result implies the existence of travelling gravity–capillary waves with multi-valued height. The solutions we prove to exist include waves with both positive and negative values of the gravity coefficient. We also compute these gravity perturbed Crapper waves by means of a quasi-Newton iterative scheme (again, using both positive and negative values of the gravity coefficient). A phase diagram is generated, which depicts the existence of single-valued and multi-valued travelling waves in the gravity–amplitude plane. A new largest water wave is computed, which is composed of a string of bubbles at the interface.

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4

Beya, Jose, William Peirson e Michael Banner. "ATTENUATION OF GRAVITY WAVES BY TURBULENCE". Coastal Engineering Proceedings 1, n. 32 (2 febbraio 2011): 3. http://dx.doi.org/10.9753/icce.v32.waves.3.

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We report new laboratory measurements of the interaction between mechanically-generated gravity waves and turbulence generated by simulated rain. Wave attenuation coefficients and vertical profiles of turbulent velocity fluctuations were measured. Observations are in broad agreement with Teixeira and Belcher (2002) despite substantial differences between assumed and measured turbulence profiles. Wave attenuation due to surface turbulence appears to be stronger than theoretical estimates. These finding could have significant implications for the next generation of spectral wave models and the understanding of wave dissipation processes.

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5

Kenyon, Kern E. "Frictionless Surface Gravity Waves". Natural Science 12, n. 04 (2020): 199–201. http://dx.doi.org/10.4236/ns.2020.124017.

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6

SUN, TIEN-YU, e KAI-HUI CHEN. "ON INTERNAL GRAVITY WAVES". Tamkang Journal of Mathematics 29, n. 4 (1 dicembre 1998): 249–69. http://dx.doi.org/10.5556/j.tkjm.29.1998.4254.

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We are concerned with the steady wave motions in a 2-fluid system with constant densities. This is a free boundary problem in which the lighter fluid is bounded above by a free surface and is separated from the heavier one down below by an interface. By using a contractive mapping principle type argument. a constructive proof to the existence of some of these exact periodic internal gravity waves is proveded.

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Vikulin, A. V., A. A. Dolgaya e S. A. Vikulina. "Geodynamic waves and gravity". Geodynamics & Tectonophysics 5, n. 1 (2014): 291–303. http://dx.doi.org/10.5800/gt-2014-5-1-0128.

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8

Longuet-Higgins, M. S. "Bifurcation in gravity waves". Journal of Fluid Mechanics 151, n. -1 (febbraio 1985): 457. http://dx.doi.org/10.1017/s0022112085001057.

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9

Pizzo, Nick E. "Surfing surface gravity waves". Journal of Fluid Mechanics 823 (16 giugno 2017): 316–28. http://dx.doi.org/10.1017/jfm.2017.314.

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A simple criterion for water particles to surf an underlying surface gravity wave is presented. It is found that particles travelling near the phase speed of the wave, in a geometrically confined region on the forward face of the crest, increase in speed. The criterion is derived using the equation of John (Commun. Pure Appl. Maths, vol. 6, 1953, pp. 497–503) for the motion of a zero-stress free surface under the action of gravity. As an example, a breaking water wave is theoretically and numerically examined. Implications for upper-ocean processes, for both shallow- and deep-water waves, are discussed.

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10

STENFLO, L., e P. K. SHUKLA. "Nonlinear acoustic–gravity waves". Journal of Plasma Physics 75, n. 6 (11 marzo 2009): 841–47. http://dx.doi.org/10.1017/s0022377809007892.

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AbstractPrevious results on nonlinear acoustic–gravity waves are reconsidered. It turns out that the mathematical techniques used are somewhat similar to those already adopted by the plasma physics community. Consequently, a future interaction between physicists in different fields, e.g. in meteorology and plasma physics, can be very fruitful.

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11

Miles, Alan J., e B. Roberts. "Magnetoacoustic-gravity surface waves". Solar Physics 141, n. 2 (ottobre 1992): 205–34. http://dx.doi.org/10.1007/bf00155176.

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Miles, Alan J., H. R. Allen e B. Roberts. "Magnetoacoustic-gravity surface waves". Solar Physics 141, n. 2 (ottobre 1992): 235–51. http://dx.doi.org/10.1007/bf00155177.

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13

Lomnitz, Cinna. "Gravity waves in earthquakes?" Engineering Geology 29, n. 1 (giugno 1990): 95–97. http://dx.doi.org/10.1016/0013-7952(90)90084-e.

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14

Hassler, Donald M. "Drowning in Gravity Waves". Academic Questions 30, n. 3 (15 luglio 2017): 342. http://dx.doi.org/10.1007/s12129-017-9644-6.

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15

Gonz�lez, Alejandro G., e Julio Gratton. "Magnetoacoustic surface gravity waves". Solar Physics 134, n. 2 (agosto 1991): 211–32. http://dx.doi.org/10.1007/bf00152645.

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16

Hara, Tetsu, Kurt A. Hanson, Erik J. Bock e B. Mete Uz. "Observation of hydrodynamic modulation of gravity-capillary waves by dominant gravity waves". Journal of Geophysical Research: Oceans 108, n. C2 (febbraio 2003): n/a. http://dx.doi.org/10.1029/2001jc001100.

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17

Hankinson, Mai C. N., M. J. Reeder e T. P. Lane. "Gravity waves generated by convection during TWP-ICE: I. Inertia-gravity waves". Journal of Geophysical Research: Atmospheres 119, n. 9 (13 maggio 2014): 5269–82. http://dx.doi.org/10.1002/2013jd020724.

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18

Gnevyshev, Vladimir, e Sergei Badulin. "Wave Patterns of Gravity–Capillary Waves from Moving Localized Sources". Fluids 5, n. 4 (24 novembre 2020): 219. http://dx.doi.org/10.3390/fluids5040219.

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We study wave patterns of gravity–capillary waves from moving localized sources within the classic setup of the problem of ship wakes. The focus is on the co-existence of two wave systems with opposite signatures of group velocity relative to the localized source. It leads to the problem of choice of signs for phase functions of the gravity (“slow”) and capillary (“fast”) branches of the dispersion relation: the question generally ignored when constructing phase patterns of the solutions. We detail characteristic angles of the wake patterns: (i) angle of demarcation of gravity and capillary waves—“the phase Mach” cone, (ii) angle of the minimal group velocity of gravity–capillary waves—“the group Mach” cone, (iii, iv) angles of cusps of isophases that appear after a threshold current speed. The outer cusp cone is naturally associated with the classic cone of Kelvin for pure gravity waves. The inner one results from the effect of capillarity and tends to the “group Mach” pattern at high speeds of current. Amplitudes of the wave patterns are estimated within the recently proposed approach of reference functions for the problem of propagation of packets of linear dispersive waves. The effect of shape is discussed for elliptic reference sources.

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19

Naeser, Harald. "The Capillary Waves’ Contribution to Wind-Wave Generation". Fluids 7, n. 2 (10 febbraio 2022): 73. http://dx.doi.org/10.3390/fluids7020073.

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Published theories and observations have shown that dissipation of gravity waves implies frequency downshifting of wave energy. Hence, for wind-waves, the wind energy input to the highest frequencies is of special interest. Here it is shown that this input is vital, because the direct wind energy input obtained by the air-pressure’s work on most gravity waves is slightly less than what the waves need to grow. Further, the wind’s input of the angular momentum that waves need to grow is found to be absent at most gravity wave frequencies. The capillary waves that appear at the surface of the sea when the wind is blowing solve these problems. To demonstrate this, an extension of linear wave theory is established to study possibilities and limitations for transfer of energy and angular momentum from the wind to waves through these frequencies. The theory describes regular, gravity–capillary waves with constant amplitude under laminar conditions. It includes surface tensions, viscosity, gravity and a wind-generated shear current, and shows that these waves—contrary to most gravity waves—receive more energy from the wind than they dissipate and angular momentum they cannot keep. Hence, the problem of the missing input of energy and angular momentum from wind to gravity waves is solved by transfers through the capillary waves. This implies that capillary waves are vital to obtain growing gravity waves.

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20

Wang, Xiujuan, Lingkun Ran, Yanbin Qi, Zhongbao Jiang, Tian Yun e Baofeng Jiao. "Analysis of Gravity Wave Characteristics during a Hailstone Event in the Cold Vortex of Northeast China". Atmosphere 14, n. 2 (20 febbraio 2023): 412. http://dx.doi.org/10.3390/atmos14020412.

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Based on high-resolution pressure data collected by a microbarograph and Fourier transform (FFT) data processing, a detailed analysis of the frequency spectra characteristics of gravity waves during a hailstone event in the cold vortex of Northeast China (NECV) on 9 September 2021 is presented. The results show that the deep NECV served as the large-scale circulation background for the hailstone event. The development of hailstones was closely related to gravity waves. In different hail stages, the frequency spectra characteristics of gravity waves were obviously different. One and a half hours before hailfall, there were gravity wave precursors with periods of 50–180 min and corresponding amplitudes ranging from 30 to 60 Pa. During hailfall, the center amplitudes of the gravity waves were approximately 50 Pa and 60 Pa, with the corresponding period ranges expanding to 60–70 min and 160–240 min. Simultaneously, hailstones initiated shorter periods (26–34 min) of gravity waves, with the amplitudes increasing to approximately 12–18 Pa. The relationship between hailstones and gravity waves was positive. After hailfall, gravity waves weakened and dissipated rapidly. As shown by the reconstructed gravity waves, key periods of gravity wave precursors ranged from 50–180 min, which preceded hailstones by several hours. When convection developed, there was thunderstorm high pressure and an outflow boundary. The airflow converged and diverged downstream, resulting in the formation of gravity waves and finally triggering hailfall. Gravity wave predecessors are significant for hail warnings and artificial hail suppression.

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21

Lingevitch, Joseph F., Michael D. Collins e William L. Siegmann. "Parabolic equations for gravity and acousto-gravity waves". Journal of the Acoustical Society of America 105, n. 6 (giugno 1999): 3049–56. http://dx.doi.org/10.1121/1.424634.

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22

Laxague, Nathan J. M., Milan Curcic, Jan-Victor Bjorkqvist e Brian K. Haus. "Gravity-Capillary Wave Spectral Modulation by Gravity Waves". IEEE Transactions on Geoscience and Remote Sensing 55, n. 5 (maggio 2017): 2477–85. http://dx.doi.org/10.1109/tgrs.2016.2645539.

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23

Yasui, Ryosuke, Kaoru Sato e Yasunobu Miyoshi. "The Momentum Budget in the Stratosphere, Mesosphere, and Lower Thermosphere. Part II: The In Situ Generation of Gravity Waves". Journal of the Atmospheric Sciences 75, n. 10 (ottobre 2018): 3635–51. http://dx.doi.org/10.1175/jas-d-17-0337.1.

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The contributions of gravity waves to the momentum budget in the mesosphere and lower thermosphere (MLT) is examined using simulation data from the Ground-to-Topside Model of Atmosphere and Ionosphere for Aeronomy (GAIA) whole-atmosphere model. Regardless of the relatively coarse model resolution, gravity waves appear in the MLT region. The resolved gravity waves largely contribute to the MLT momentum budget. A pair of positive and negative Eliassen–Palm flux divergences of the resolved gravity waves are observed in the summer MLT region, suggesting that the resolved gravity waves are likely in situ generated in the MLT region. In the summer MLT region, the mean zonal winds have a strong vertical shear that is likely formed by parameterized gravity wave forcing. The Richardson number sometimes becomes less than a quarter in the strong-shear region, suggesting that the resolved gravity waves are generated by shear instability. In addition, shear instability occurs in the low (middle) latitudes of the summer (winter) MLT region and is associated with diurnal (semidiurnal) migrating tides. Resolved gravity waves are also radiated from these regions. In Part I of this paper, it was shown that Rossby waves in the MLT region are also radiated by the barotropic and/or baroclinic instability formed by parameterized gravity wave forcing. These results strongly suggest that the forcing by gravity waves originating from the lower atmosphere causes the barotropic/baroclinic and shear instabilities in the mesosphere that, respectively, generate Rossby and gravity waves and suggest that the in situ generation and dissipation of these waves play important roles in the momentum budget of the MLT region.

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24

Christodoulides, P., e F. Dias. "Resonant capillary–gravity interfacial waves". Journal of Fluid Mechanics 265 (25 aprile 1994): 303–43. http://dx.doi.org/10.1017/s0022112094000856.

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Two-dimensional space-periodic cabillary–gravity waves at the interface between two fluids of different densities are considered when the second harmonic and the fundamental mode are near resonance. A weakly nonlinear analysis provides the equations (normal form), correct to third order, that relate the wave frequency with the amplitudes of the fundamental mode and of the second harmonic for all waves with small energy. A study of the normal form for waves which are also periodic in time reveals three possible types of space- and time-periodic waves: the well-known travelling and standing waves as well as an unusual class of three-mode mixed waves. Mixed waves are found to provide a connection between standing and travelling waves. The branching behaviour of all types of waves is shown to depend strongly on the density ratio. For travelling waves the weakly nonlinear results are confirmed numerically and extended to finite-amplitude waves. When slow modulations in time of the amplitudes are considered, a powerful geometrical method is used to study the resulting normal form. Finally a discussion on modulational stability suggests that increasing the density ratio has a stabilizing effect.

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25

Hankinson, Mai C. N., M. J. Reeder e T. P. Lane. "Gravity waves generated by convection during TWP-ICE: 2. High-frequency gravity waves". Journal of Geophysical Research: Atmospheres 119, n. 9 (13 maggio 2014): 5257–68. http://dx.doi.org/10.1002/2013jd020726.

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26

Mehta, Dhvanit, Andrew J. Gerrard, Yusuke Ebihara, Allan T. Weatherwax e Louis J. Lanzerotti. "Short-period mesospheric gravity waves and their sources at the South Pole". Atmospheric Chemistry and Physics 17, n. 2 (20 gennaio 2017): 911–19. http://dx.doi.org/10.5194/acp-17-911-2017.

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Abstract. The sourcing locations and mechanisms for short-period, upward-propagating gravity waves at high polar latitudes remain largely unknown. Using all-sky imager data from the Amundsen–Scott South Pole Station, we determine the spatial and temporal characteristics of 94 observed small-scale waves in 3 austral winter months in 2003 and 2004. These data, together with background atmospheres from synoptic and/or climatological empirical models, are used to model gravity wave propagation from the polar mesosphere to each wave's source using a ray-tracing model. Our results provide a compelling case that a significant proportion of the observed waves are launched in several discrete layers in the tropopause and/or stratosphere. Analyses of synoptic geopotentials and temperatures indicate that wave formation is a result of baroclinic instability processes in the stratosphere and the interaction of planetary waves with the background wind fields in the tropopause. These results are significant for defining the influences of the polar vortex on the production of these small-scale, upward-propagating gravity waves at the highest polar latitudes.

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Subba Reddy, I. V., D. Narayana Rao, A. Narendra Babu, M. Venkat Ratnam, P. Kishore e S. Vijaya Bhaskara Rao. "Studies on atmospheric gravity wave activity in the troposphere and lower stratosphere over a tropical station at Gadanki". Annales Geophysicae 23, n. 10 (30 novembre 2005): 3237–60. http://dx.doi.org/10.5194/angeo-23-3237-2005.

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Abstract. 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.

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Lecoanet, D., G. M. Vasil, J. Fuller, M. Cantiello e K. J. Burns. "Conversion of internal gravity waves into magnetic waves". Monthly Notices of the Royal Astronomical Society 466, n. 2 (15 dicembre 2016): 2181–93. http://dx.doi.org/10.1093/mnras/stw3273.

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Henderson, Stephen M., R. T. Guza, Steve Elgar e T. H. C. Herbers. "Refraction of Surface Gravity Waves by Shear Waves". Journal of Physical Oceanography 36, n. 4 (1 aprile 2006): 629–35. http://dx.doi.org/10.1175/jpo2890.1.

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Abstract Previous field observations indicate that the directional spread of swell-frequency (nominally 0.1 Hz) surface gravity waves increases during shoreward propagation across the surf zone. This directional broadening contrasts with the narrowing observed seaward of the surf zone and predicted by Snell’s law for bathymetric refraction. Field-observed broadening was predicted by a new model for refraction of swell by lower-frequency (nominally 0.01 Hz) current and elevation fluctuations. The observations and the model suggest that refraction by the cross-shore currents of energetic shear waves contributed substantially to the observed broadening.

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Yih, Chia-Shun, e Songping Zhu. "Patterns of ship waves. II. Gravity-capillary waves". Quarterly of Applied Mathematics 47, n. 1 (1 marzo 1989): 35–44. http://dx.doi.org/10.1090/qam/987893.

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Williams, Paul D., Thomas W. N. Haine e Peter L. Read. "Inertia–Gravity Waves Emitted from Balanced Flow: Observations, Properties, and Consequences". Journal of the Atmospheric Sciences 65, n. 11 (1 novembre 2008): 3543–56. http://dx.doi.org/10.1175/2008jas2480.1.

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Abstract This paper describes laboratory observations of inertia–gravity waves emitted from balanced fluid flow. In a rotating two-layer annulus experiment, the wavelength of the inertia–gravity waves is very close to the deformation radius. Their amplitude varies linearly with Rossby number in the range 0.05–0.14, at constant Burger number (or rotational Froude number). This linear scaling challenges the notion, suggested by several dynamical theories, that inertia–gravity waves generated by balanced motion will be exponentially small. It is estimated that the balanced flow leaks roughly 1% of its energy each rotation period into the inertia–gravity waves at the peak of their generation. The findings of this study imply an inevitable emission of inertia–gravity waves at Rossby numbers similar to those of the large-scale atmospheric and oceanic flow. Extrapolation of the results suggests that inertia–gravity waves might make a significant contribution to the energy budgets of the atmosphere and ocean. In particular, emission of inertia–gravity waves from mesoscale eddies may be an important source of energy for deep interior mixing in the ocean.

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Melville, W. Kendall, e Alexey V. Fedorov. "The equilibrium dynamics and statistics of gravity–capillary waves". Journal of Fluid Mechanics 767 (18 febbraio 2015): 449–66. http://dx.doi.org/10.1017/jfm.2014.740.

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AbstractRecent field observations and modelling of breaking surface gravity waves suggest that air-entraining breaking is not sufficiently dissipative of surface gravity waves to balance the dynamics of wind-wave growth and nonlinear interactions with dissipation for the shorter gravity waves of $O(10)$ cm wavelength. Theories of parasitic capillary waves that form at the crest and forward face of shorter steep gravity waves have shown that the dissipative effects of these waves may be one to two orders of magnitude greater than the viscous dissipation of the underlying gravity waves. Thus the parasitic capillaries may provide the required dissipation of the short wind-generated gravity waves. This has been the subject of speculation and conjecture in the literature. Using the nonlinear theory of Fedorov & Melville (J. Fluid Mech., vol. 354, 1998, pp. 1–42), we show that the dissipation due to the parasitic capillaries is sufficient to balance the wind input to the short gravity waves over some range of wave ages and wave slopes. The range of gravity wave lengths on which these parasitic capillary waves are dynamically significant approximately corresponds to the range of short gravity waves that Cox & Munk (J. Mar. Res., vol. 13, 1954, pp. 198–227) found contributed significantly to the mean square slope of the ocean surface, which they measured to be proportional to the wind speed. Here we show that the mean square slope predicted by the theory is proportional to the square of the friction velocity of the wind, ${u_{\ast }}^{2}$, for small wave slopes, and approximately $u_{\ast }$ for larger slopes.

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Lane, Todd P., e Jason C. Knievel. "Some Effects of Model Resolution on Simulated Gravity Waves Generated by Deep, Mesoscale Convection". Journal of the Atmospheric Sciences 62, n. 9 (1 settembre 2005): 3408–19. http://dx.doi.org/10.1175/jas3513.1.

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Abstract Over the past decade, numerous numerical modeling studies have shown that deep convective clouds can produce gravity waves that induce a significant vertical flux of horizontal momentum. Such studies used models with horizontal grid spacings of O(1 km) and produced strong gravity waves with horizontal wavelengths greater than about 20 km. This paper is an examination of how simulated gravity waves and their momentum flux are sensitive to model resolution. It is shown that increases in horizontal resolution produce more power in waves with shorter horizontal wavelengths. This change in the gravity waves’ spectra influences their vertical propagation. In some cases, gravity waves that were vertically propagating in coarse simulations become vertically trapped in fine simulations, which strongly influences the vertical flux of horizontal momentum.

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Khan, Mehtab A., Simon J. Watson, Dries J. N. Allaerts e Matthew Churchfield. "Recommendations on setup in simulating atmospheric gravity waves under conventionally neutral boundary layer conditions". Journal of Physics: Conference Series 2767, n. 9 (1 giugno 2024): 092042. http://dx.doi.org/10.1088/1742-6596/2767/9/092042.

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Abstract Wind farm-induced atmospheric gravity waves have been the subject of recent research as they can impact wind farm performance. Pressure variations associated with gravity waves can contribute to the global blockage effect and wind farm wake recovery. Therefore, accurate numerical simulation of flow fields, where wind-farm-induced gravity waves may be produced, is important. Three main considerations in such simulations are the overall domain size, the use of Rayleigh damping near domain boundaries to dampen gravity waves, and advection damping at the inlet to prevent spurious oscillations. Often these considerations are treated ad hoc rather than systematically. This work aims to test and extend the systematic modelling of internal gravity waves proposed in a preliminary investigation to modelling of both internal and trapped gravity waves. The preliminary study identifies the length scales to set the domain and damping layer sizes and the time scale to configure the Rayleigh damping coefficient but under linearly stratified conditions. Large eddy simulations of flow through a wind farm canopy are performed under conventionally neutral boundary layer (CNBL) conditions to test the validity of proposed setups for CNBL conditions. Background atmospheric parameters, such as Froude number (Fr), inversion height (Hi ), and inversion layer Froude number (Fri ) control most of the atmospheric gravity wave characteristics. We validated for CBNL conditions that the effective wavelengths of the internal gravity waves are the correct length scale to configure the domain size and damping layer thickness. Likewise, the optimum damping coefficient to dampen the internal gravity waves relates to the free atmosphere’s buoyancy frequency or buoyant perturbations’ time scale. We infer that the damping coefficient in the inversion layer may relate to the inversion buoyancy frequency to effectively dampen the trapped gravity waves. Moreover, the advection damping length is linked to the horizontal wavelength of the trapped gravity waves in the inversion layer to prevent spurious waves at the inlet by retaining wave energy accumulation.

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Zülicke, Christoph, e Dieter Peters. "Parameterization of Strong Stratospheric Inertia–Gravity Waves Forced by Poleward-Breaking Rossby Waves". Monthly Weather Review 136, n. 1 (1 gennaio 2008): 98–119. http://dx.doi.org/10.1175/2007mwr2060.1.

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Abstract The link between poleward-breaking Rossby waves and stratospheric inertia–gravity waves is examined. With a visual inspection of Ertel’s potential vorticity maps based on ECMWF analyses it was found that Rossby wave–breaking events occurred over northern Europe in about 40% of the winter days in 1999–2003. The majority of them were breaking poleward downstream. A total of 10 field campaigns were performed in the winters of 1999–2002 at Kühlungsborn, Germany (54°N, 12°E). They are related to such events and can be considered as representative for poleward-breaking Rossby waves. Inertia–gravity wave properties are diagnosed from radiosonde observations. They appeared to be shallower, slower, and stronger than the climatological mean for the north German lowlands. Hence, Rossby wave–breaking events are linked with strong stratospheric inertia–gravity wave activity. A novel parameterization of inertia–gravity wave generation and propagation is proposed. The stratospheric inertia–gravity wave action in the 16–20-km height range was parameterized with the synoptic-scale cross-stream ageostrophic wind, which accounts for imbalances in the upper-tropospheric jet streak. This empirical relationship is supported with quasigeostrophic theory. Effects of damping and critical level absorption are taken into account with Wentzel–Kramers–Brillouin theory. For verification of the parameterization with homogeneous meteorological fields in space and time, the 10 field campaigns were hindcasted with the nonhydrostatic fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model. About 80% of the variance in inertia–gravity wave action was found to be explained. For the 10 campaigns a close link was found between the poleward-breaking Rossby waves and the strong stratospheric inertia–gravity waves. The role of the polar vortex was twofold: first, it forced the poleward-oriented Rossby waves to break downstream and to form strong tropospheric jet streaks generating inertia–gravity waves. Second, the strong winds in the stratosphere favored the upward propagation of the inertia–gravity waves. The proposed new parameterization of inertia–gravity wave generation and propagation was validated and can be used to deduce mesoscale wave intensity from synoptic flow characteristics during poleward Rossby wave–breaking events.

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Voisin, Bruno. "Internal wave generation in uniformly stratified fluids. Part 1. Green's function and point sources". Journal of Fluid Mechanics 231 (ottobre 1991): 439–80. http://dx.doi.org/10.1017/s0022112091003464.

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In both Boussinesq and non-Boussinesq cases the Green's function of internal gravity waves is calculated, exactly for monochromatic waves and asymptotically for impulsive waves. From its differentiation the pressure and velocity fields generated by a point source are deduced. by the same method the Boussinesq monochromatic and impulsive waves radiated by a pulsating sphere are investigated.Boussinesq monochromatic waves of frequency ω < N are confined between characteristic cones θ = arccos(ω/N) tangent to the source region (N being the buoyancy frequency and θ the observation angle from the vertical). In that zone the point source model is inadequate. For the sphere an explicit form is given for the waves, which describes their conical 1/r½ radial decay and their transverse phase variations.Impulsive waves comprise gravity and buoyancy waves, whose separation process is non-Boussinesq and follows the arrival of an Airy wave. As time t elapses, inside the torus of vertical axis and horizontal radius 2Nt/β for gravity waves and inside the circumscribing cylinder for buoyancy waves, both components become Boussinesq and have wavelengths negligible compared with the scale height 2/β of the stratification. Then, gravity waves are plane propagating waves of frequency N cos θ, and buoyancy waves are radial oscillations of the fluid at frequency N; for the latter, initially propagating waves comparable with gravity waves, the horizontal phase variations have vanished and the amplitude has become insignificant as the Boussinesq zone has been entered. In this zone, outside the torus of vertical axis and horizontal radius Nta, a sphere of radius a [Lt ] 2/β is compact compared with the wavelength of the dominant gravity waves. Inside the torus gravity waves vanish by destructive interference. For the remaining buoyancy oscillations the sphere is compact outside the vertical cylinder circumscribing it, whereas the fluid is quiescent inside this cylinder.

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37

Fabris, Júlio C., Marcelo H. Alvarenga, Mahamadou Hamani Daouda e Hermano Velten. "Nonconservative Unimodular Gravity: Gravitational Waves". Symmetry 14, n. 1 (6 gennaio 2022): 87. http://dx.doi.org/10.3390/sym14010087.

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Unimodular gravity is characterized by an extra condition with respect to general relativity, i.e., the determinant of the metric is constant. This extra condition leads to a more restricted class of invariance by coordinate transformation: The symmetry properties of unimodular gravity are governed by the transverse diffeomorphisms. Nevertheless, if the conservation of the energy–momentum tensor is imposed in unimodular gravity, the general relativity theory is recovered with an additional integration constant which is associated to the cosmological term Λ. However, if the energy–momentum tensor is not conserved separately, a new geometric structure appears with potentially observational signatures. In this text, we consider the evolution of gravitational waves in a nonconservative unimodular gravity, showing how it differs from the usual signatures in the standard model. As our main result, we verify that gravitational waves in the nonconservative version of unimodular gravity are strongly amplified during the evolution of the universe.

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38

Bakas, Nikolaos A., e Brian F. Farrell. "Gravity Waves in a Horizontal Shear Flow. Part II: Interaction between Gravity Waves and Potential Vorticity Perturbations". Journal of Physical Oceanography 39, n. 3 (1 marzo 2009): 497–511. http://dx.doi.org/10.1175/2008jpo3837.1.

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Abstract Interaction among potential vorticity perturbations and propagating internal gravity waves in a horizontally sheared zonal flow is investigated. In the strong stratification limit, an initial vorticity perturbation weakly excites two propagating gravity waves while the density component of the potential vorticity perturbation is significantly amplified, potentially leading to convective collapse. If stratification is sufficiently weak, a strong coupling between vorticity perturbations and gravity waves is found and spontaneous gravity wave generation occurs. This coupling can be traced to the nonnormal interaction between the potential vorticity and gravity wave manifolds in the weak stratification limit. Vorticity perturbations amplify in energy due to downgradient Reynolds stress when their phase lines tilt against the shear and the large growth attained is transferred to propagating gravity waves. When the flow geometry is such that the excited gravity waves are confined in the vicinity of the vorticity perturbation by their trapping levels, an overall convective collapse of this region can be anticipated. On the other hand, when the flow geometry permits wave propagation, significant gravity wave emission occurs.

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39

Salmon, Rick. "Variational treatment of inertia–gravity waves interacting with a quasi-geostrophic mean flow". Journal of Fluid Mechanics 809 (14 novembre 2016): 502–29. http://dx.doi.org/10.1017/jfm.2016.693.

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The equations for three-dimensional hydrostatic Boussinesq dynamics are equivalent to a variational principle that is closely analogous to the variational principle for classical electrodynamics. Inertia–gravity waves are analogous to electromagnetic waves, and available potential vorticity (i.e. the amount by which the potential vorticity exceeds the potential vorticity of the rest state) is analogous to electric charge. The Lagrangian can be expressed as the sum of three parts. The first part corresponds to quasi-geostrophic dynamics in the absence of inertia–gravity waves. The second part corresponds to inertia–gravity waves in the absence of quasi-geostrophic flow. The third part represents a coupling between the inertia–gravity waves and quasi-geostrophic motion. This formulation provides the basis for a general theory of inertia–gravity waves interacting with a quasi-geostrophic mean flow.

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40

van Holten, Jan. "The Gravity of Light-Waves". Universe 4, n. 10 (18 ottobre 2018): 110. http://dx.doi.org/10.3390/universe4100110.

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Light waves carry along their own gravitational field; for simple plain electromagnetic waves, the gravitational field takes the form of a p p -wave. I present the corresponding exact solution of the Einstein–Maxwell equations and discuss the dynamics of classical particles and quantum fields in this gravitational and electromagnetic background.

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41

Kenyon, Kern E. "Upwelling by Surface Gravity Waves". Natural Science 09, n. 05 (2017): 133–35. http://dx.doi.org/10.4236/ns.2017.95013.

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42

Kenyon, Kern E. "Downwelling by Surface Gravity Waves?" Natural Science 09, n. 05 (2017): 143–44. http://dx.doi.org/10.4236/ns.2017.95015.

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43

Sturani, Riccardo. "Fundamental Gravity and Gravitational Waves". Symmetry 13, n. 12 (10 dicembre 2021): 2384. http://dx.doi.org/10.3390/sym13122384.

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While being as old as general relativity itself, the gravitational two-body problem has never been under so intense investigation as it is today, spurred by both phenomenological and theoretical motivations. The observations of gravitational waves emitted by compact binary coalescences bear the imprint of the source dynamics, and as the sensitivity of detectors improve over years, more accurate modeling is being required. The analytic modeling of classical gravitational dynamics has been enriched in this century by powerful methods borrowed from field theory. Despite being originally developed in the context of fundamental particle quantum scatterings, their applications to classical, bound system problems have shown that many features usually associated with quantum field theory, such as, e.g., divergences and counterterms, renormalization group, loop expansion, and Feynman diagrams, have only to do with field theory, be it quantum or classical. The aim of this work is to present an overview of this approach, which models massive astrophysical objects as nonrelativistic particles and their gravitational interactions via classical field theory, being well aware that while the introductory material in the present article is meant to represent a solid background for newcomers in the field, the results reviewed here will soon become obsolete, as this field is undergoing rapid development.

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44

Kanev, N. G., e M. A. Mironov. "Resonance Absorption of Gravity Waves". Fluid Dynamics 56, n. 5 (settembre 2021): 678–84. http://dx.doi.org/10.1134/s0015462821050062.

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45

Varma, Dheeraj, Manikandan Mathur e Thierry Dauxois. "Instabilities in internal gravity waves". Mathematics in Engineering 5, n. 1 (2022): 1–34. http://dx.doi.org/10.3934/mine.2023016.

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<abstract><p>Internal gravity waves are propagating disturbances in stably stratified fluids, and can transport momentum and energy over large spatial extents. From a fundamental viewpoint, internal waves are interesting due to the nature of their dispersion relation, and their linear dynamics are reasonably well-understood. From an oceanographic viewpoint, a qualitative and quantitative understanding of significant internal wave generation in the ocean is emerging, while their dissipation mechanisms are being debated. This paper reviews the current knowledge on instabilities in internal gravity waves, primarily focusing on the growth of small-amplitude disturbances. Historically, wave-wave interactions based on weakly nonlinear expansions have driven progress in this field, to investigate spontaneous energy transfer to various temporal and spatial scales. Recent advances in numerical/experimental modeling and field observations have further revealed noticeable differences between various internal wave spatial forms in terms of their instability characteristics; this in turn has motivated theoretical calculations on appropriately chosen internal wave fields in various settings. After a brief introduction, we present a pedagogical discussion on linear internal waves and their different two-dimensional spatial forms. The general ideas concerning triadic resonance in internal waves are then introduced, before proceeding towards instability characteristics of plane waves, wave beams and modes. Results from various theoretical, experimental and numerical studies are summarized to provide an overall picture of the gaps in our understanding. An ocean perspective is then given, both in terms of the relevant outstanding questions and the various additional factors at play. While the applications in this review are focused on the ocean, several ideas are relevant to atmospheric and astrophysical systems too.</p></abstract>

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46

Kenyon, Kern E. "Gravity Forcing of Surface Waves." Physics Essays 19, n. 1 (1 marzo 2006): 83–90. http://dx.doi.org/10.4006/1.3025786.

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47

Stevens, Jonathan. "The Ringing of Gravity Waves". Science News 154, n. 18 (31 ottobre 1998): 275. http://dx.doi.org/10.2307/4011052.

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48

Lehn, Waldemar H., Wayne K. Silvester e David M. Fraser. "Mirages with atmospheric gravity waves". Applied Optics 33, n. 21 (20 luglio 1994): 4639. http://dx.doi.org/10.1364/ao.33.004639.

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49

Guerreiro, Thiago. "Quantum effects in gravity waves". Classical and Quantum Gravity 37, n. 15 (13 luglio 2020): 155001. http://dx.doi.org/10.1088/1361-6382/ab9d5d.

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50

Wang, Tao, Tian‐Fu Gao e Li Ma. "Moments of internal gravity waves". Journal of the Acoustical Society of America 109, n. 5 (maggio 2001): 2422. http://dx.doi.org/10.1121/1.4744572.

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