MOM output diagnostics

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MOM output is managed through the FMS diagnostics manager, and configured using the diag_table file. This page describes the format of diag_table records and how to manage output diagnostic in MOM.


diag_table configuration files contain two types of records:

  • Files: NetCDF output files containing MOM4 output
  • Fields: Individual data fields (such as velocity or temperature) to be saved.

Output file specification

diag_table files begin with output file records. An example output file is shown below:

"ocean_snap", 5, "days", 1, "days", "Time"

Each field is discussed below (in order of appearance)

  • "ocean_snap": The filename of a target netCDF output file. A .nc extension will be appended to the filename.
  • 5, "days": The output frequency for variables in this file, followed by units. Standard calendar units can be used (days, hours, etc.).
  • 1, "days": Output time axis unit of measurement (with units).
  • "Time": Time axis variable name in the netCDF file.

Output frequency and other time-related information is associated with individual files. For this reason, variables with similar output rates should generally be grouped together in the same file.

Field specification

Example field record:

"ocean_model", "u", "u", "ocean_snap", "all", .false., "none", 2

  • "ocean_model": MOM5 module containing the diagnostic variable. This is typically attributed to a particular submodel, such as "ocean model" or "ice_model".
  • "u", "u": The MOM5 registered variable name, and the output netCDF variable name, respectively. The first must match the variable name in the MOM5 source code, but the second can be renamed by the user.
  • "ocean_snap": The output file (defined in the diag_table file record) which will store this variable.
  • "all": The sampling rate of the variable. "all" means that the variable is sampled for every value on the time axis (as specified in the file record).
  • .false.: Time averaging between output times. .true. saves the time-averaged values between time sampling rates, while .false. returns snapshots of the fields at each point on the time axis.
  • "none": Optional arguments, usually defined in MOM5. "none" denotes no optional arguments.
  • 2: Output data type.

Four output data types are supported:

  • 1: Double-precision (64-bit) floating point
  • 2: Single-precision (32-bit) floating point
  • 4: 16-bit integer packed variables (typically used for long-term archival)
  • 8: 8-bit integer-packed variables (untested)

Creating new variables

To create new variables for output not included in the default version requires a modification of the MOM4 source code.