123,191 research outputs found

    Observations of internal waves generated by an anticyclonic eddy: a case study in the ice edge region of the Greenland Sea

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    Internal waves in the ocean play an important role in turbulence generation due to wave-breaking processes and mixing of the ocean. Airborne radar images of internal waves and ocean eddies north of Svalbard suggested that ocean eddies could generate internal waves. Here, we test this hypothesis using data from a dedicated internal wave experiment in the Greenland Sea. Internal waves with dominant frequencies of 1–3 cycles per hour and amplitudes up to 15 m were observed using three thermistor chains suspended from a drifting array conveniently placed on the ice in a triangle with sides of several km. Analysis shows that internal waves propagated westwards with a speed of about 0.2 m/s and wavelength of 0.4–1.0 km, away from an anticyclonic ocean eddy located just east of the array. This was consistent with the remote-sensing observations of internal waves whose surface signature was imaged by an airborne radar in the western part of this eddy, and with theories that eddies and vortexes can directly generate internal waves. This case study supports our hypothesis that ocean eddies can be the direct sources of internal waves reported here for the first time and not only enhancing the local internal wave field by draining energy from the eddies, as studied previously. The present challenge is to explore the role of eddies as a new source in generating internal waves in the global ocean

    Remote Internal Wave Forcing of Regional Ocean Simulations Near the U.S. West Coast

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    Low mode internal waves are able to propagate across ocean basins and modulate ocean dynamics thousands of kilometers away from their generation sites. In this study, the impact of remotely generated internal waves on the internal wave energetics near the U.S. West Coast is investigated with realistically forced regional ocean simulations. At the open boundaries, we impose high-frequency oceanic state variables obtained from a global ocean simulation with realistic atmospheric and astronomical tidal forcing. We use the Discrete Fourier Transform (DFT) technique in separating ingoing and outgoing internal tide energy fluxes at the open boundaries in order to quantify internal tide reflections. Although internal tide reflections are reduced with increasing sponge viscosity and/or sponge layer width, reflection coefficients (λ) can be as high as 73%. In the presence of remote internal waves, the model variance and spatial correlations become more in agreement with both mooring and altimetry datasets. The results confirm that an improved internal wave continuum can be achieved in regional models with remote internal wave forcing at the open boundaries. However, care should be taken to avoid excessive reflections of internal waves from the interior at these boundaries

    Internal Waves Generated from Asymmetric Topographies

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    Internal waves are a key part of the energy budget of the ocean and atmosphere. The generation of internal waves in the ocean from tides is dependent on the frequency of oscillation, the profile of the underwater mountain range, and the density of water in the surrounding ocean. A study of the effect of an asymmetric mountain range, with varying pro-files, on the generation of internal waves is presented. Results begin to indicate that the wave is mostly similar when generated on either side of the topography, but might extend to higher wavenumbers in Fourier space when generated on the wide side

    Propagating and evanescent internal waves in a deep ocean model

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    We present experimental and computational studies of the propagation of internal waves in a stratified fluid with an exponential density profile that models the deep ocean. The buoyancy frequency profile N(z)N(z) (proportional to the square root of the density gradient) varies smoothly by more than an order of magnitude over the fluid depth, as is common in the deep ocean. The nonuniform stratification is characterized by a turning depth zcz_c, where N(zc)N(z_c) is equal to the wave frequency ω\omega and N(z<zc)<ωN(z < z_c) < \omega. Internal waves reflect from the turning depth and become evanescent below the turning depth. The energy flux below the turning depth is shown to decay exponentially with a decay constant given by kc k_c, which is the horizontal wavenumber at the turning depth. The viscous decay of the vertical velocity amplitude of the incoming and reflected waves above the turning depth agree within a few percent with a previously untested theory for a fluid of arbitrary stratification [Kistovich and Chashechkin, J. App. Mech. Tech. Phys. 39, 729-737 (1998)].Comment: 13 pages, 4 figures, 4 table

    Hamiltonian formalism and the Garrett-Munk spectrum of internal waves in the ocean

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    Wave turbulence formalism for long internal waves in a stratified fluid is developed, based on a natural Hamiltonian description. A kinetic equation appropriate for the description of spectral energy transfer is derived, and its self-similar stationary solution corresponding to a direct cascade of energy toward the short scales is found. This solution is very close to the high wavenumber limit of the Garrett-Munk spectrum of long internal waves in the ocean. In fact, a small modification of the Garrett-Munk formalism includes a spectrum consistent with the one predicted by wave turbulence.Comment: 4 pages latex fil

    An Experimental Investigation of Evanescent Wave Propagation Through a Turning Depth

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    Internal waves are complex phenomena which occur uniquely in fluids which are stratified, or have varying density with respect to height. This occurs within the ocean and the atmosphere. One well known method of internal wave generation is tidal flow over oceanic bathymetry. However, in some locations, the natural frequency of the deep ocean is less than the tidal frequency and thus only evanescent waves are generated. While evanescent waves generally dissipate quickly after formation, it is been observed that if these waves travel into a stronger stratification, they can become propagating internal waves. Presented here is an experimental investigation of this internal wave generation mechanism. Specifically, internal wave energy transfer through a turning depth for a range of stratification profiles and turning depth locations is explored

    The relation of gravity waves and turbulence in the mesosphere

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    Since researchers couldn't prove that the mesospheric turbulence layers are generated by the simultaneously existing short-period gravity waves, they invoked other generation mechanisms than wave breaking. Possible mechanisms like lateral convection (Rottger 1980a), quasi-geostrophic flows at mesoscales (Lilly, 1983) or vortical modes of motion as seen in the ocean (Muller and Pujalet, 1984) could be candidates. Researchers are inclined to see a connection of these layers or laminae with very-long-period internal waves because of the periodicity in their vertical structure and their long mean persistency. Rottger (1980b) had proposed that such structures are due the modulation of the me an temperature and wind profiles by internal waves. The superposition of random or short-term wave-induced wind and temperature fluctuations with the background profile, modulated by very-long-period waves (quasi-inertia waves) then would yield the observed effects, and could explain the vertical periodicity, the long-term mean persistency as well as some short-term variability of their intensity
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