Ocean turbulence at meso and submesoscales: connection between surface and interior dynamics

Abstract

High resolution simulations of ocean turbulence with Rossby number of order one have revealed that upper layer dynamics significantly differs from the interior dynamics. As reported before, upper layer dynamics is characterized with shallow velocity spectrum corresponding to kinetic energy distributed over a spectral range from mesoscales to small scales. This dynamics is driven by small-scale frontogenesis related to surface density anomalies. Interior dynamics is characterized by steeper velocity spectrum and is driven by the potential vorticity anomalies set up by the interior baroclinic instability. Impact of the divergent motions related to surface frontogenesis leads to a warming of the upper layers, a cyclone dominance and a negative skewness of the isopycnal displacements. On the contrary, divergent motions in the interior lead to a cooling of the deeper layers, an anticylone dominance and a positive skewness of the isopycnal displacements. These different ageostrophic processes are consistent with an SQG regime extended to Rossby number of order one on one hand and an interior QG regime extended to Rossby number of order one on the other hand, as proposed by previous studies. Synthesis of these characteristics suggest a connection between upper and deeper layers, induced by the divergent motions, through which small scales near the surface interact with mesoscales in the interior.

Keywords:

• Ocean turbulence
• Ageostrophic effects
• Boundary-interior connection

Acknowledgements

Discussions with Bach Lien Hua and Xavier Capet (coauthors of some of the papers reviewed in this study) are warmly acknowledged. This work is supported by IFREMER and CNRS (FRANCE). Numerical simulations reported here were done on the Earth Simulator (Yokohama, Japan) whose access has been possible through a M.O.U. signed between IFREMER, CNRS, and JAMSTEC. Patrice Klein, Guillaume Roullet and Sylvie Le Gentil also acknowledge the support from the French ANR (Agence Nationale pour la Recherche, Contract no ANR-05-CIGC-010).