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Diagnosing Surface Mixed Layer Dynamics from High-Resolution Satellite Observations: Numerical Insights

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  • 1 Laboratoire de Physique des Océans, IFREMER-CNRS-IRD-UBO, Plouzané, France
  • | 2 LOCEAN, IPSL, Paris, France
  • | 3 Laboratoire d'Océanographie Spatiale, IFREMER, Plouzané, France
  • | 4 Laboratoire de Physique des Océans, IFREMER-CNRS-IRD-UBO, Plouzané, France
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Abstract

High-resolution numerical experiments of ocean mesoscale eddy turbulence show that the wind-driven mixed layer (ML) dynamics affects mesoscale motions in the surface layers at scales lower than O(60 km). At these scales, surface horizontal currents are still coherent to, but weaker than, those derived from sea surface height using geostrophy. Vertical motions, on the other hand, are stronger than those diagnosed using the adiabatic quasigeotrophic (QG) framework. An analytical model, based on a scaling analysis and on simple dynamical arguments, provides a physical understanding and leads to a parameterization of these features in terms of vertical mixing. These results are valid when the wind-driven velocity scale is much smaller than that associated with eddies and the Ekman number (related to the ratio between the Ekman and ML depth) is not small. This suggests that, in these specific situations, three-dimensional ML motions (including the vertical velocity) can be diagnosed from high-resolution satellite observations combined with a climatological knowledge of ML conditions and interior stratification.

Corresponding author address: Patrice Klein, Laboratoire de Physique des Océans, Ifremer-CNRS-UBO-IRD, 29280 Plouzané, France. E-mail: patrice.klein@ifremer.fr

Abstract

High-resolution numerical experiments of ocean mesoscale eddy turbulence show that the wind-driven mixed layer (ML) dynamics affects mesoscale motions in the surface layers at scales lower than O(60 km). At these scales, surface horizontal currents are still coherent to, but weaker than, those derived from sea surface height using geostrophy. Vertical motions, on the other hand, are stronger than those diagnosed using the adiabatic quasigeotrophic (QG) framework. An analytical model, based on a scaling analysis and on simple dynamical arguments, provides a physical understanding and leads to a parameterization of these features in terms of vertical mixing. These results are valid when the wind-driven velocity scale is much smaller than that associated with eddies and the Ekman number (related to the ratio between the Ekman and ML depth) is not small. This suggests that, in these specific situations, three-dimensional ML motions (including the vertical velocity) can be diagnosed from high-resolution satellite observations combined with a climatological knowledge of ML conditions and interior stratification.

Corresponding author address: Patrice Klein, Laboratoire de Physique des Océans, Ifremer-CNRS-UBO-IRD, 29280 Plouzané, France. E-mail: patrice.klein@ifremer.fr
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