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Water Mass Transformation Budgets in Finite-Volume Generalized Vertical Coordinate Ocean Models
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  • Henri Francois Drake,
  • Shanice Bailey,
  • Raphael Dussin,
  • Stephen M Griffies,
  • John P Krasting,
  • Graeme Alastair MacGilchrist,
  • Geoffrey J Stanley,
  • Jan-Erik Tesdal,
  • Jan David Zika
Henri Francois Drake
University of California, Irvine

Corresponding Author:[email protected]

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Shanice Bailey
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Raphael Dussin
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Stephen M Griffies
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John P Krasting
Geophysical Fluid Dynamics Laboratory
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Graeme Alastair MacGilchrist
Princeton University
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Geoffrey J Stanley
University of Victoria
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Jan-Erik Tesdal
Princeton University
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Jan David Zika
University of New South Wales
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Water mass transformation theory provides conceptual tools that in principle enable innovative analyses of numerical ocean models; in practice, however, these methods can be challenging to implement and interpret, and therefore remain under-utilized. Most prior work evaluates only some of the simpler or more accessible terms in the water mass budget; meanwhile, the few full budget calculations in the literature are either limited to idealized model configurations and geometrically-simple domains or else have required heroic efforts that are neither scalable to large data sets nor portable to other ocean models or research questions. We begin with a pedagogical derivation of key results of classical water mass transformation theory. We then describe best practices for diagnosing each of the water mass budget terms from the output of Finite-Volume Generalized Vertical Coordinate (FV-GVC) ocean models, including the identification of a non-negligible remainder term as the spurious numerical mixing due to advection scheme discretization errors. We illustrate key aspects of the methodology through an example application to diagnostics from a polygonal region of a Baltic Sea regional configuration of the Modular Ocean Model v6 (MOM6). We verify the convergence of our WMT diagnostics by brute-force, comparing time-averaged diagnostics on various vertical grids to timestep-averaged diagnostics on the native model grid. Finally, we briefly describe a stack of xarray-enabled Python packages for evaluating WMT budgets in FV-GVC models, which is intended to be model-agnostic and available for community use and development.
09 Apr 2024Submitted to ESS Open Archive
11 Apr 2024Published in ESS Open Archive