2. Experiments

NorESM is part of the CESM family of earth system models and shares a lot of the configuration options with CESM. Many of the simulation configuration settings are defined by the so-called compsets.

For a quick-start guide on how to create, configure, build, and submit a NorESM experiment, see the Newbies guide. More details are provided below, for the more advanced users.

2.1. Create and configure a new case

To start a new experiment you need to create and configure a case. After running the


script, a case folder <path_to_case_dir>/<casename> is created that contains set-up files for your experiment. Then, after running the


script, several other files and directories needed to build the case are created, including the user namelists files.

The case folder contains predefined namelists (with namelist settings partly depending on compset option). The default namelist options for the case can be overwritten by changing/adding the new namelist options in the user_nl_<component> file.

The create_newcase script includes a --compset option. A compset, or component set, is a collection of predefined setting that defines your experiment set-up, including which model components that should be activated. Some of the available compsets are described below.

2.1.1. Compsets

Compsets, or component sets, specify which component models will be used in your simulation along with which forcing files, and even which physics options to use. Each compset has a long name (lname) and an alias. For instance N1850 is the alias for the NorESM compset for pre-industrial (1850) conditions. The long name for N1850 is


The long name generally follows the notation


(see the help section of the file <noresm_base>/cime_config/config_compsets.xml for details). The compsets can also include information on which grids are scientifically supported (see below for details).

To find all predefined compsets:

  • coupled simulations <noresm_base>/cime_config/config_compsets.xml

  • AMIP-type (atmsophere/land-only) simulations <noresm_base>/components/cam/cime_config/config_compsets.xml

  • stand-alone experiments with the sea-ice model <noresm_base>/components/cice/cime_config/config_compsets.xml

  • stand-along experiments with the land model <noresm_base>/components/clm/cime_config/config_compsets.xml

  • Stand-alone experiments with the ocean model <noresm_base>/components/blom/cime_config/config_compsets.xml

The compsets starting with N are NorESM coupled configurations. Compsets starting with NF are NorESM AMIP (atmosphere/land-only) configurations. Some examples are:

  • N1850 and N1850frc2: Coupled configuration for NorESM for pre-industrial (1850) conditions.

  • NHIST and NHISTfrc2: Historical configuration from 1850 up to year 2015 (see detailed description below; ‘Create your own compsets for AMIP simulations’)

  • NSSP126frc2, NSSP245frc2, NSSP370frc2, NSSP585frc2: Future scenario compsets from 2015 to 2100

  • NFHISTnorpddmsbc: AMIP simulation with time-evolving prescribed observed values for SSTs and sea ice and upper-ocean DMS values derived from a fully coupled NorESM2 simulation for present-day conditions

frc2 compsets: The frc2 option uses differently organized emission files. The frc2 files are located in


The frc2 files were created to avoid the occurence of random mid-month model crashes. These crashes are related to the reading of emission files, but are still under investigation. To make sure that you are using the frc2 files, choose a compsets including frc2 or if you want to create a new compset add


to NORESM2. For a detailed description, see the section on creating your own compset below.

For an overview of the compsets provided for CESM2, please see: http://www.cesm.ucar.edu/models/cesm2/config/compsets.html.

2.1.2. Creating your own compset

The essential file to edit for a new coupled NorESM compset is


and for a new AMIP NorESM compset is


Coupled simulation

This examples shows how to simply add the “N1850frc2” compset to config_compsets.xml. In <noresm_base>/cime_config/config_compsets.xml the N1850frc2 is set as



  • <alias>COMPSETNAME</alias> sets the compsets name used when building a new case, make sure to use a new and unique name

  • ‘_’ is used as a separator between model components: _<MODEL>

  • ‘%’ is used to to set components-specific configurations

So for the N1850frc2 compset, the different parts of the lname have the following meaning:

  • 1850_CAM60%NORESM%FRC2
    • Forcing and input files read from pre-industrial conditions (1850). If you need a historical run replace 1850 with HIST

    • Build CAM6.0 (the atmosphere model) with NorESM configuration and FRC2 organized emission files

    • Build CLM5 (land model) with Biogeochemistry and prognotic crop package

    • Build CICE (sea-ice model) with NorESM2-CMIP6 setup

    • Build BLOM (ocean model) including iHAMOCC biogeochemistry model

    • Build MOSART (river runoff model) with default configurations

    • The SGLC (land-ice) and SWAV (ocean-wave) models are not interactive, but used only to satisy the interface requirements

    • ocean biogeochemistry model iHAMOCC run with interactive DMS

The details of the compset i.e. which models components and component-specific configurations to use are set in


It is possible to use the long name (lname) to select a compset then creating a new case.

AMIP simulation

For details about AMIP simulation compsets, please see Atmosphere

2.1.3. Resolution and grids

The model resolution is set when the case is created (with the --res option). Below some common resolutions are listed.

Atmospheric grids

f19_f19 - atm lnd 1.9x2.5
f09_f09 - atm lnd 0.9x1.25

Ocean grids

tnx1v4   - tripolar ocn ice 1-degree grid
tnx2v1   - tripolar ocn ice 2-degree grid
tx0.25v4 - tripolar ocn ice 1/4-degree grid


f19_tn14   - atm lnd 1.9x2.5, ocnice tnx1v4  [CMIP6 grid, NorESM2-LM]
f09_tn14   - atm lnd 0.9x1.25, ocnice tnx1v4  [CMIP6 grid, NorESM2-MM]
f09_tn0254 - atm lnd 0.9x1.25, ocnice tnx0.25v4

A complete list of model grids can be found here:


2.1.4. Supported grids

Most compsets contain an entries listing which which grid(s) are scientifically supported for that compset

<science_support grid="xxx"/> fields

When a compset has a scientifically-supported grid, you can create a new case (with the create_newcase script) without having to use the option --run-unsupported. If the compset does not list any scientifically-supported grids, or if you want to use a grid configuration is not included in the definition of the compset, the


option is required when a case is created or the create_newcase script will fail.

2.1.5. User modifications (usermods)

Several configuration options are available in the user modification (usermod) directories under <noresm_base>/cime_config/usermods_dirs/. The sets of usermods contain pre-defined user namelists for the atmosphere (cam) and land (clm) components that have been used for specific experiments, such as the CMIP6 DECK experiments. Within the user namelists, the lists of output variables and output frequencies has been modified and/or extended with additional output variables. In addition, the usermodes include one SourceMod (SourceMods/src.cam/preprocessorDefinitions.h) which defines whether AEROFFL and AEROCOM are activated to produce extra aerosol diagnostics (for more details about the aerosol diagnostics see Aerosol diagnostics and output)

The usermods under <noresm_base>/cime_config/usermods_dirs/ include:

cmip6_noresm_DECK (AEROFFL)
cmip6_noresm_hifreq (high frequency output, AEROFFL)
cmip6_noresm_hifreq_xaer (high frecuency output, AEROFFL and AEROCOM)
cmip6_noresm_keyCLIM (used for KeyCLIM experiments, AEROFFL)
cmip6_noresm_xaer (AEROFFLand AEROCOM)

To activate the cmip6_noresm_DECK usermod, run the create_newcase script with the option --user-mods-dir cmip6_noresm_DECK.

Remember that the amount of diagnostics and the output frequency have a huge impact on both the run time and storage.

For more details, check this folder


2.1.6. Create a clone case

The create_clone script in the <noresm_base>/cime/scripts folder allows you to create a clone of an already existing case:

./create_clone --clone <full-path-to-experiment-to-be-cloned> --case <full-path-to-cloned-experiment>

Creating a clone case can be very useful if you want to recreate an existing case or if you want to create a perturbed version. The clone will be set up as if it was created with the same create_newcase options as the existing case (except the case name) and will have identical env_*.xml, user_nml_<component> and SourceMods files (these files can of course be modified before building the case).

2.1.7. The xmlchange and xmlquery scripts

The xmlchange and xmlquery scripts are located in your case folder and lets you change or query the contents of variables in the evn_*.xml files without entering the files. There are two advantages of using xmlchange to edit the xml files rather than doing by hand: (1) the xmlchange script checks that the new setting is valid and (2) the change is echoed to the CaseStatus file, thus automatically documented. To change from the default ndays to nmonths

./xmlchange STOP_OPTION=nmonths

It’s also possible to change several variables at once, for instance

./xmlchange STOP_OPTION=nmonths,STOP_N=14

See the header of xmlchange and xmlquery for more details and examples.

2.1.8. Forcing

Please see Input data sets

2.1.9. Choosing output

please see NorESM2 output

2.1.10. Setting up a nudged simulation

please see Nudged experiments

2.2. Building the case

The case is built by


All user modifications to env_run.xml, env_mach_pes.xml, env_batch.xml must be done before case.build is invoked. This is also the case for the aforementioned user-made namelists: i.e. user_nl_cam, user_nl_cice, user_nl_clm, user_nl_blom, user_nl_cpl).

If you want to ensure your case is ready for submission, you can run


which will:

  • Ensure that all of the env_*.xml files are in sync with the locked files

  • Create namelists (thus verifying that there will be no problems with namelist generation)

  • Ensure that the build is complete

Running this is completely optional: these checks will be done automatically when running case.submit. However, you can run this if you want to perform these checks without actually submitting the case.

As a last step, remember to copy restart files to run directory if you are running a branch run or a hybrid run.

2.3. Submitting the case

The case is submitted by