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Notes on “The degree of anisotropy for mid-ocean currents from satellite observations and an eddy-permitting model simulation” by Huang et al. (JGR, 2007)


In this paper, the authors quantify the anisotropy of the surface geostrophic velocity derived from satellite observations and of the surface and deep (1000 m) geostrophic velocity obtained in a numerical model of the Pacific Ocean. It is found that the surface flow changes from isotropic at weekly time scale to purely zonal for seasonal and annual averages. This behavior is found in the simulation at depth as well suggesting that long vertical scale at low frequency.


  • The authors start the paper by noticing that the anisotropy in zonal velocity (U) found recently in observations and numerical simulations does not necessarily suggest zonal jets. Because of the geostrophic relationship between the velocity field and the sea surface anomaly (SSA), a white spectrum of SSA in both the zonal and meridional directions results into an anisotropic spectrum in U and in the meridional velocity V, with more energy in the zonal direction at long scale in U and more energy in the meridional direction at long scale in V; in this case, no zonal jets form. However, the spectrum of U and V together stays white suggesting that U and V be considered to together to study the actual anisotropy of the velocity flow.