Customize MOM output

Customize MOM output#

Adding MOM6 Diagnostics#

MOM6 diagnostics are controlled through a file called diag_table.

During case setup, CESM generates a template file named:

Buildconf/momconf/diag_table.unresolved

To customize the diagnostics that MOM6 outputs, copy this file into your SourceMods directory:

cp Buildconf/momconf/diag_table.unresolved SourceMods/src.mom/diag_table

You can then edit SourceMods/src.mom/diag_table to add, remove, or modify diagnostic output fields.

Note CESM regenerates files in Buildconf during case setup. Therefore, user modifications should be made in SourceMods/src.mom/diag_table, which will override the default version and be preserved during subsequent builds.

The diag_table specifies:

  • Which variables to output

  • How frequently they are written

  • Whether they are snapshots or time averages

  • Which output files they are written to

Finding Available Diagnostics#

The set of available diagnostics depends on the MOM6 configuration being used. After running the model, MOM6 writes a file named:

available_diags.000000

in the run directory. This file contains a complete list of diagnostics available for your configuration.

To view the available diagnostics:

cd $RUNDIR
less available_diags.000000

or search for a specific variable:

grep temp available_diags.000000

Before adding new diagnostics to the diag_table, it is often helpful to inspect available_diags.000000 to determine the exact diagnostic names recognized by MOM6.

File Section#

This section of diag_table defines an arbitrary number of files that will be created. The general format of each entry is

"file_name", output_freq, "output_freq_units", 1, "time_axis_units", "time_axis_name"

For example:

"ocean_monthly", 1, "months", 1, "days", "time"

creates a file named ocean_monthly.nc with output written every month.

Common examples include:

"ocean_hourly", 1, "hours", 1, "days", "time"
"ocean_daily", 1, "days", 1, "days", "time"
"ocean_monthly", 1, "months", 1, "days", "time"
"ocean_annual", 12, "months", 1, "days", "time"

Field Section#

This section of diag_table defines an arbitrary number of fields that will be created in an output file. The general format of each entry is

"module_name", "field_name", "output_name", "file_name", "time_sampling", "reduction_method", "regional_section", packing

For example:

"ocean_model", "thetao", "thetao", "ocean_monthly", "all", "mean", "none", 2

writes monthly mean potential temperature thetao to the file ocean_monthly.nc.

Changing the Output Frequency#

To change monthly output to daily output, modify the file section entry:

"ocean_daily", 1, "days", 1, "days", "time"

and update the corresponding field section entries to write to the new file:

"ocean_model", "thetao", "thetao", "ocean_daily", "all", "mean", "none", 2

Snapshots versus Time Averages#

The output frequency determines when data are written, while the reduction method determines how data are accumulated between writes.

Common reduction methods (specified in the field section) are:

"none"    # instantaneous snapshot
"mean"    # time average
"min"     # minimum value
"max"     # maximum value

For example:

"ocean_model", "SSH", "SSH", "ocean_daily", "all", "none", "none", 2

writes a daily snapshot of sea surface height, while

"ocean_model", "thetao", "thetao", "ocean_daily", "all", "mean", "none", 2

writes a daily mean temperature.

Note: Increasing the output frequency or adding a large number of diagnostics can significantly increase output volume and reduce model throughput. Start with a small number of diagnostics and increase the frequency only when needed.

For additional details about the diag_table format and MOM6 diagnostics, see MOM6 documentation.

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