Water mass transformation budgets in finite‐volume generalized vertical coordinate ocean models

Water Mass Transformation (WMT) 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. Our aim is to demonstrate the feasibility of diagnosing all terms in the water mass budget and to exemplify their usefulness for scientific inquiry and model development by quantitatively relating water mass changes, overturning circulations, boundary fluxes, and interior mixing. We begin with a pedagogical derivation of key results of classical WMT 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 the analysis of a polygonal region of the Greater Baltic Sea in a regional demonstration simulation using the Modular Ocean Model v6 (MOM6). We verify the convergence of our WMT diagnostics by brute‐force, comparing time‐averaged (“offline”) diagnostics on various vertical grids to timestep‐averaged (“online”) 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 (culminating in the new xwmb package), which is intended to be model‐agnostic and available for community use and development.

To Access Resource:

Questions? Email Resource Support Contact:

  • opensky@ucar.edu
    UCAR/NCAR - Library

Resource Type publication
Temporal Range Begin N/A
Temporal Range End N/A
Temporal Resolution N/A
Bounding Box North Lat N/A
Bounding Box South Lat N/A
Bounding Box West Long N/A
Bounding Box East Long N/A
Spatial Representation N/A
Spatial Resolution N/A
Related Links

Related Software #1 : MOM6 model source code/run-time parameters and analysis notebooks used in the Drake et al. (JAMES) water mass transformation budget paper

Additional Information N/A
Resource Format PDF
Standardized Resource Format PDF
Asset Size N/A
Legal Constraints

Copyright author(s). This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.


Access Constraints None
Software Implementation Language N/A

Resource Support Name N/A
Resource Support Email opensky@ucar.edu
Resource Support Organization UCAR/NCAR - Library
Distributor N/A
Metadata Contact Name N/A
Metadata Contact Email opensky@ucar.edu
Metadata Contact Organization UCAR/NCAR - Library

Author H. F. Drake
Bailey, S.
Dussin, Raphael
Griffies, S. M.
Krasting, J.
MacGilchrist, G.
Stanley, G.
Tesdal, J.
Zika, J. D.
Publisher UCAR/NCAR - Library
Publication Date 2025-03-01T00:00:00
Digital Object Identifier (DOI) Not Assigned
Alternate Identifier N/A
Resource Version N/A
Topic Category geoscientificInformation
Progress N/A
Metadata Date 2025-07-10T19:54:04.351318
Metadata Record Identifier edu.ucar.opensky::articles:43164
Metadata Language eng; USA
Suggested Citation H. F. Drake, Bailey, S., Dussin, Raphael, Griffies, S. M., Krasting, J., MacGilchrist, G., Stanley, G., Tesdal, J., Zika, J. D.. (2025). Water mass transformation budgets in finite‐volume generalized vertical coordinate ocean models. UCAR/NCAR - Library. https://n2t.net/ark:/85065/d7sn0fc4. Accessed 05 August 2025.

Harvest Source