Horizontal dispersion of near-inertial oscillations in a turbulent mesoscale eddy field

We study the dispersion of wind-induced near-inertial oscillations (NIOs) in a fully turbulent baroclinic mesoscale eddy field characterized by a continuous wavenumber spectrum. The influence of the eddy field on the horizontal dispersion of the different NIO modes is analyzed using a vertical normal mode expansion. Previous studies have identified two dispersion regimes: trapping and strong dispersion. We examine the modes in physical and spectral space to assess which regime prevails,Numerical and analytical results show the prevalence of a trapping regime. For each NIO mode, there exists a critical horizontal wavenumber. k(c), that separates large-scale NIO structures, where trapping dominates, from the much less energetic small-scale NIO structures, where strong dispersion dominates. The maximum efficiency of dispersion for scales close to k(c) concentrates NIO kinetic energy at these scales.The wavenumber k(c) results from a balance between refraction and dispersion. This balance first occurs at the highest wavenumber. Thereafter. k(c), which has dimensional expression k(c)(2) = pi/(ftR(m)(2)), decreases with time at a rate inversely proportional to the radius of deformation, R-m, of the baroclinic NIO mode considered, As a consequence, at any given time, higher NIO baroclinic mode energy can mostly be found in small-scale negative vorticity structures, such as filaments near sharp vorticity fronts, whereas lower NIO mode energy is concentrated within the core of mesoscale anticyclonic vortices. For large times, a saturation mechanism stops the time-evolution of k(c) at a value close to the peak of the kinetic energy spectrum of the QG flow field.


Refraction, Horizontal dispersion, Wind induced oscillations, Eddy field

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Klein Patrice, Smith Stefan Llewellyn (2001). Horizontal dispersion of near-inertial oscillations in a turbulent mesoscale eddy field. Journal of Marine Research. 59 (5). 697-723. https://archimer.ifremer.fr/doc/00000/799/

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