A parameterization of local and remote tidal mixing

Type Article
Date 2020-05
Language English
Author(s) Lavergne C.1, Vic Clement2, Madec G1, 3, Roquet F.4, Waterhouse A. F.5, Whalen C. B.6, Cuypers Y.1, Bouruet‐aubertot P.1, Ferron Bruno2, Hibiya T.7
Affiliation(s) 1 : LOCEAN Laboratory Sorbonne Université‐CNRS‐IRD‐MNHN Paris, France
2 : LOPS Laboratory, UBO‐IFREMER‐CNRS‐IRD Plouzané ,France
3 : LJK Laboratory, Université Grenoble Alpes‐INRIA‐CNRS Grenoble, France
4 : Department of Marine Sciences University of Gothenburg Gothenburg ,Sweden
5 : Scripps Institution of Oceanography University of California California, USA
6 : Applied Physics Laboratory University of Washington Washington, USA
7 : Department of Earth and Planetary Science, Graduate School of Science The University of Tokyo Tokyo, Japan
Source Journal Of Advances In Modeling Earth Systems (1942-2466) (American Geophysical Union (AGU)), 2020-05 , Vol. 12 , N. 5 , P. e2020MS002065 (25p.)
DOI 10.1029/2020MS002065
WOS© Times Cited 5
Keyword(s) ocean mixing, internal tides, parameterization, energy dissipation

Vertical mixing is often regarded as the Achilles' heel of ocean models. In particular, few models include a comprehensive and energy‐constrained parameterization of mixing by internal ocean tides. Here, we present an energy‐conserving mixing scheme which accounts for the local breaking of high‐mode internal tides and the distant dissipation of low‐mode internal tides. The scheme relies on four static two‐dimensional maps of internal tide dissipation, constructed using mode‐by‐mode Lagrangian tracking of energy beams from sources to sinks. Each map is associated with a distinct dissipative process and a corresponding vertical structure. Applied to an observational climatology of stratification, the scheme produces a global three‐dimensional map of dissipation which compares well with available microstructure observations and with upper‐ocean finestructure mixing estimates. This relative agreement, both in magnitude and spatial structure across ocean basins, suggests that internal tides underpin most of observed dissipation in the ocean interior at the global scale. The proposed parameterization is therefore expected to improve understanding, mapping and modelling of ocean mixing Plain Language Summary When tidal ocean currents flow over bumpy seafloor, they generate internal tidal waves. Internal waves are the subsurface analogue of surface waves that break on beaches. Like surface waves, internal tidal waves often become unstable and break into turbulence. This turbulence is a primary cause of mixing between stacked ocean layers—a key process regulating ocean currents and biology and a key ingredient of computer models of the global ocean. In this article, a three‐dimensional global map of mixing induced by internal tidal waves is presented. This map incorporates a large variety of energy pathways from the generation of tidal waves to turbulence, accounting for the conservation of energy. The map is compared to available observations of turbulence across the globe and found to reproduce with good fidelity the main patterns identified in observations. This relatively good agreement suggests that internal tidal waves are the main source of turbulence in the subsurface ocean, and implies that the map may serve a range of applications. In particular, the three‐dimensional map provides an efficient and realistic means to represent mixing by internal tidal waves in global ocean models.

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Lavergne C., Vic Clement, Madec G, Roquet F., Waterhouse A. F., Whalen C. B., Cuypers Y., Bouruet‐aubertot P., Ferron Bruno, Hibiya T. (2020). A parameterization of local and remote tidal mixing. Journal Of Advances In Modeling Earth Systems, 12(5), e2020MS002065 (25p.). Publisher's official version : https://doi.org/10.1029/2020MS002065 , Open Access version : https://archimer.ifremer.fr/doc/00624/73573/