Acoustic radiation by ocean surface waves

2000 ◽  
Vol 415 ◽  
pp. 1-21 ◽  
Author(s):  
STEVE ARENDT ◽  
DAVID C. FRITTS
Keyword(s):  
Surface Waves ◽  
Gravity Waves ◽  
Acoustic Waves ◽  
Acoustic Radiation ◽  
Three Dimensional ◽  
Phase Speed ◽  
Ocean Surface ◽  
Surface Gravity ◽  
Ocean Surface Waves ◽  
Surface Gravity Waves

We calculate the radiation of acoustic waves into the atmosphere by surface gravity waves on the ocean surface. We show that because of the phase speed mismatch between surface gravity waves and acoustic waves, a single surface wave radiates only evanescent acoustic waves. However, owing to nonlinear terms in the acoustic source, pairs of ocean surface waves can radiate propagating acoustic waves if the two surface waves propagate in almost equal and opposite directions. We derive an analytic expression for the acoustic radiation by a pair of ocean surface waves, and then extend the result to the case of an arbitrary spectrum of ocean surface waves. We present some examples for both the two-dimensional and three-dimensional regimes. Of particular note are the findings that the efficiency of acoustic radiation increases at higher wavenumbers, and the fact that the directionality of the acoustic radiation is often independent of the shape of the spectrum.

scholarly journals VISIR-1.b: ocean surface gravity waves and currents for energy-efficient navigation

2019 ◽  
Vol 12 (8) ◽  
pp. 3449-3480 ◽  
Author(s):  
Gianandrea Mannarini ◽  
Lorenzo Carelli
Keyword(s):  
Energy Efficiency ◽  
Gravity Waves ◽  
Ocean Surface ◽  
Surface Gravity ◽  
Ocean Current ◽  
Ship Routing ◽  
Surface Gravity Waves ◽  
Waves And Currents ◽  
The Impact

Abstract. The latest development of the ship-routing model published in Mannarini et al. (2016a) is VISIR-1.b, which is presented here. The new version of the model targets large ocean-going vessels by considering both ocean surface gravity waves and currents. To effectively analyse currents in a graph-search method, new equations are derived and validated against an analytical benchmark. A case study in the Atlantic Ocean is presented, focussing on a route from the Chesapeake Bay to the Mediterranean Sea and vice versa. Ocean analysis fields from data-assimilative models (for both ocean state and hydrodynamics) are used. The impact of waves and currents on transatlantic crossings is assessed through mapping of the spatial variability in the tracks, an analysis of their kinematics, and their impact on the Energy Efficiency Operational Indicator (EEOI) of the International Maritime Organization. Sailing with or against the main ocean current is distinguished. The seasonal dependence of the EEOI savings is evaluated, and greater savings with a higher intra-monthly variability during winter crossings are indicated in the case study. The total monthly mean savings are between 2 % and 12 %, while the contribution of ocean currents is between 1 % and 4 %. Several other ocean routes are also considered, providing a pan-Atlantic scenario assessment of the potential gains in energy efficiency from optimal tracks, linking them to regional meteo-oceanographic features.

What happens to the ocean surface gravity waves when ENSO and MJO phases combine during the extended boreal winter?

2019 ◽  
Vol 54 (3-4) ◽  
pp. 1407-1424 ◽  
Author(s):  
Victor A. Godoi ◽  
Felipe M. de Andrade ◽  
Tom H. Durrant ◽  
Audalio R. Torres Júnior
Keyword(s):  
Gravity Waves ◽  
Ocean Surface ◽  
Surface Gravity ◽  
Boreal Winter ◽  
Surface Gravity Waves

scholarly journals TOMOGRAPHY OF THE SOLAR INTERIOR

2006 ◽  
Vol 21 (22) ◽  
pp. 1701-1715 ◽  
Author(s):  
L. GIZON
Keyword(s):  
Gravity Waves ◽  
Acoustic Waves ◽  
Solar Surface ◽  
Three Dimensional ◽  
Magnetic Activity ◽  
Solar Interior ◽  
Turbulent Convection ◽  
Convective Structures ◽  
Surface Gravity Waves ◽  
Rich Spectrum

Solar oscillations consist of a rich spectrum of internal acoustic waves and surface gravity waves, stochastically excited by turbulent convection. They have been monitored almost continuously over the last ten years with high-precision Doppler images of the solar surface. The purpose of helioseismology is to retrieve information about the structure and the dynamics of the solar interior from the frequencies, phases and amplitudes of solar waves. Methods of analysis are being developed to make three-dimensional images of subsurface motions and temperature inhomogeneities in order to study convective structures and regions of magnetic activity, like sunspots.

Array measurements of atmospheric pressure fluctuations above surface gravity waves

1981 ◽  
Vol 102 ◽  
pp. 1-59 ◽  
Author(s):  
R. L. Snyder ◽  
F. W. Dobson ◽  
J. A. Elliott ◽  
R. B. Long
Keyword(s):  
Gravity Waves ◽  
Atmospheric Pressure ◽  
Pressure Sensors ◽  
Phase Speed ◽  
Limited Range ◽  
Surface Gravity ◽  
Wave Number ◽  
Surface Gravity Waves ◽  
Array Measurements ◽  
Wave Induced

A joint experiment to study microscale fluctuations of atmospheric pressure above surface gravity waves was conducted in the Bight of Abaco, Bahamas, during November and December 1974. Field hardware included a three-dimensional array of six wave sensors and seven air-pressure sensors, one of which was mounted on a wave follower. The primary objectives of the study were to resolve differences in previous field measurements by Dobson (1971), Elliott (1972b) and Snyder (1974), and to estimate the vertical profile of wave-induced pressure and the corresponding input of energy and momentum to the wave field.Analysis of a pre-experiment intercalibration of instruments and of 30 h of field data partially removes the discrepancy between the previous measurements of the wave-induced component of the pressure and gives a consistent picture of the profile of this pressure over a limited range of dimensionless height and wind speed. Over this range the pressure decays approximately exponentially without change of phase; the decay is slightly less steep than predicted by potential theory. The corresponding momentum transfer is positive for wind speeds exceeding the phase speed. Extrapolation of present results to higher frequencies suggests that the total transfer is a significant fraction of the wind stress (0·1 to 1·0, depending on dimensionless fetch).Analysis of the turbulent component of the atmospheric pressure shows that the ‘intrinsic’ downwind coherence scale is typically an order-of-magnitude greater than the crosswind scale, consistent with a ‘frozen’ turbulence hypothesis. These and earlier data of Priestley (1965) and Elliott (1972c) suggest a horizontally isotropic ‘intrinsic’ turbulent pressure spectrum which decays ask−νwherekis the (horizontal) wave-number and ν is typically −2 to −3; estimates of this spectrum are computed for the present data. The implications of these findings for Phillips’ (1957) theory of wave growth are examined.

scholarly journals Wave-Slope Soaring of the Brown Pelican

2021 ◽  
Author(s):  
Ian Stokes ◽  
Andrew Lucas
Keyword(s):  
Gravity Waves ◽  
Ground Effect ◽  
Ocean Surface ◽  
The Body ◽  
Surface Gravity ◽  
Cost Of Transport ◽  
Surface Gravity Waves ◽  
Wave Slope ◽  
Ocean Conditions ◽  
Wave Induced

Abstract Background: From the laboratory at Scripps Institution of Oceanography, it is common to see the brown pelican (Pelecanus occidentalis) traveling along the crests of ocean waves just offshore of the surf zone. When flying in this manner, the birds can travel long distances without flapping, centimeters above the ocean's surface. Here we derive a theoretical framework for assessing the energetic savings related to this behavior, `wave-slope soaring,' in which an organism in flight takes advantage of localized updrafts caused by traveling ocean surface gravity waves. Methods: The energy cost of steady, constant altitude flight in and out of ground effect are analyzed as controls. Potential flow theory is used to quantify the ocean wave-induced wind associated with near-shoaling, weakly nonlinear, shallow water ocean surface gravity waves moving through an atmosphere initially at rest. Using perturbation theory and the Green's function for Laplace's equation in 2D with Dirichlet boundary conditions, we obtain integrals for the horizontal and vertical components of the wave-induced wind in a frame of reference moving with the wave. Wave-slope soaring flight is then analyzed using an energetics-based approach for waves under a range of ocean conditions and the body plan of P. occidentalis . Results: For ground effect flight, we calculate a ~ 15 - 25% reduction in cost of transport as compared with steady, level flight out of ground effect. When wave-slope soaring is employed at flight heights ≤ 2m in typical ocean conditions (2m wave height, 15s period), we calculate 60-70% reduction in cost of transport as compared with flight in ground effect. A relatively small increase in swell amplitude or decrease in flight height allows up to 100% of the cost of transport to be offset by wave-slope soaring behavior. Conclusions: The theoretical development presented here suggests there are energy savings associated with wave-slope soaring. Individual brown pelicans may significantly decrease their cost of transport utilizing this mode of flight under typical ocean conditions. Thus wave-slope soaring may provide fitness benefit to these highly mobile organisms that depend on patchy prey distribution over large home ranges.

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