experiment.nml

experiment.nml#

The experiment namelist defines the experiment metadata required for CMIP7 output. It captures the experiment identity, the parent/child branch information, the variant label components, and the temporal coverage of the run. These are the metadata elements used to construct the CMIP7 Data Reference Syntax (DRS) and to describe how a simulation relates to its parent run.

The CMIP7 guidance defines these as part of the required and conditionally required global attributes for model output. In particular, the experiment identifier, the activity, the variant indices, and the parent experiment information should be consistent with the registered experiment definition and the model branch history.

&experiment
 casename               = 'n1850.ne16pg3_tn14.noresm3_0_beta22.bdmc2_1p2.20260811',
 osubdir                = 'NorESM3-LM/piControl/v20260914',
 experiment_id          = 'piControl',
 parent_experiment_id   = 'piControl-spinup',
 parent_experiment_rip  = 'r1i1p1',
 parent_time_units      = 'days since 0421-01-01',
 history                = '',
 realization_index      = 'r1',
 initialization_index   = 'i1',
 physics_index          = 'p1',
 forcing_index          = 'f1',
 branch_time            = 0.,
 year1                  = 1346,
 yearn                  = 1395,
 month1                 = 1,
 monthn                 = 12,
 activity_id            = 'CMIP',
 parent_activity_id     = 'CMIP',
 parent_variant_label   = 'r1i1p1f1',
 parent_mip_era         = 'CMIP7',
 mip_era                = 'CMIP7',
 branch_time_in_child   = 0.0D0,
 branch_time_in_parent  = 430700.0D0,
 scanallfiles           = .false.
/

Key CMIP7 concepts#

The most important fields in this namelist are:

  • experiment_id: the short label identifying the experiment, such as piControl, historical, or abrupt-4xCO2.

  • activity_id: the activity responsible for the experiment and the data, such as CMIP.

  • realization_index, initialization_index, physics_index, forcing_index: the four parts of the CMIP7 variant label, usually combined as r<i>i<p>f<...> or r1i1p1f1.

  • parent_experiment_id, parent_variant_label, parent_mip_era: the metadata needed to trace the run back to the parent simulation when the current experiment is a branch.

  • branch_time_in_child and branch_time_in_parent: the times at which the branch occurred in the child and parent simulations.

Field descriptions#

keyword

CMIP7-aligned description

casename

Name of the model run or case, typically containing the model, experiment, ensemble member, and run date.

osubdir

Output subdirectory path describing the archive location for the experiment and version in the CMIP7 directory hierarchy.

experiment_id

Short experiment identifier, as defined in the CMIP7 controlled vocabulary for experiment labels.

parent_experiment_id

Experiment label of the parent simulation from which the current experiment was branched.

parent_experiment_rip

Parent run variant identifier, typically in the form r...i...p...f..., used to identify the parent ensemble member.

parent_time_units

Time units used in the parent simulation, for example days since 0421-01-01.

history

Optional CF-style processing history describing how the dataset was produced or transformed.

realization_index

Realization index, part of the CMIP7 variant label; for example r1, r2, or r12.

initialization_index

Initialization index, part of the CMIP7 variant label; for example i1 or i196001.

physics_index

Physics index, part of the CMIP7 variant label; for example p1 or p3.

forcing_index

Forcing index, part of the CMIP7 variant label; for example f1 or f6.

branch_time

Time in the child simulation at which the branch from the parent simulation occurred, expressed in the child time units.

year1

First year of the temporal coverage represented by the output file or dataset.

yearn

Final year of the temporal coverage represented by the output file or dataset.

month1

First month of the temporal coverage represented by the output file or dataset.

monthn

Final month of the temporal coverage represented by the output file or dataset.

activity_id

Activity acronym for the experiment, such as CMIP, as defined in the CMIP7 controlled vocabularies.

parent_activity_id

Activity acronym of the parent experiment.

parent_variant_label

Full parent simulation variant label identifying the parent realization, initialization, physics, and forcing indices.

parent_mip_era

MIP era associated with the parent experiment, such as CMIP6 or CMIP7.

mip_era

MIP era for the dataset; CMIP7 files should use CMIP7.

branch_time_in_child

Time in the child simulation when the branch occurred, expressed in the child simulation’s time units and calendar.

branch_time_in_parent

Time in the parent simulation when the branch occurred, expressed in the parent simulation’s time units and calendar.

scanallfiles

Logical switch controlling whether all files in the target output set are scanned when determining file coverage.

Note

For CMIP7, these values should be internally consistent with the registered experiment definition, the source_id, and the variant information used in the file metadata. When a simulation is a branch of an earlier experiment, the parent metadata must clearly record the parent experiment identity, the parent variant label, and the parent branch time so that users can trace the lineage of the simulation.

Important

Code and dataset versions: The processed dataset version should match the code release tag. This keeps the output traceable and reproducable. It will be easiber to identify errors in the CMORized and published datasets, and facilitate the data errata record and retract processes.