Radiation and Dissipation of Internal Waves Generated by Geostrophic Motions Impinging on Small-Scale Topography: Theory

• Published in: Journal of Physical Oceanography
• Main Authors: Nikurashin, M, Ferrari, R
• Format: Article in Journal/Newspaper
• Language: English
• Published: Amer Meteorological Soc 2010
• Subjects: Earth Sciences; Oceanography; Physical Oceanography; Drake Passage
• Online Access: https://doi.org/10.1175/2009JPO4199.1; http://ecite.utas.edu.au/79715

Observations and inverse models suggest that small-scale turbulent mixing is enhanced in the SouthernOcean in regions above rough topography. The enhancement extends O(1) km above the topography, suggestingthat mixing is supported by the breaking of gravity waves radiated from the ocean bottom. In thisstudy, it is shown that the observed mixing rates can be sustained by internal waves generated by geostrophicmotions flowing over bottom topography. Weakly nonlinear theory is used to describe the internal wavegeneration and the feedback of the waves on the zonally averaged flow. Vigorous inertial oscillations aredriven at the ocean bottom by waves generated at steep topography. The wave radiation and dissipation atequilibrium is therefore the result of both geostrophic flow and inertial oscillations differing substantiallyfrom the classical lee-wave problem. The theoretical predictions are tested versus two-dimensional highresolutionnumerical simulations with parameters representative of Drake Passage. This work suggests thatmixing in Drake Passage can be supported by geostrophic motions impinging on rough topography ratherthan by barotropic tidal motions, as is commonly assumed.