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 user namelists files.

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.

The case folder contains predefined namelist (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.

Several configuration options are available in the usermods directories in <noresm_base>/cime_config/usermods_dirs/. These folders contain information about output variables and frequencies from clm (land) and cam (atmosphere). In addition one SourceMod is included in SourceMods/src.cam/preprocessorDefinitions.h to define if AEROFFL and AEROCOM are included for extra aerosol diagnostics (for more details about the aerosol diagnostics see ??)

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

--user-mods-dir cmip6_noresm_*

cmip6_noresm_DECK (AEROFFL)
cmip6_noresm_hifreq (high frequency output, AEROFFL)
cmip6_noresm_hifreq_xaer (high frecuency output, AEROFFL and AEROCOM)
cmip6_noresm_xaer (AEROFFLand AEROCOM)

For more details about the user-mod-dir options, check this folder


2.2. 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.

2.3. Create a clone case

To create clone cases from a control case can be very useful for e.g. sensitivity studies. If you want to make a copy of a case (i.e. identical ./create_newcase command and identical env_*.xml, user_nml_<component> and SourceMods files) that can be done by the use of ./create_clone. You only need to give the casename of the new case and the casename of the case which sholud be cloned (copied). The case will have identical set up (env_*.xml, user_nml_<component> files and SourceMods) as the clone, but these files can of course be modified before building the case.

2.4. 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 scientifcally supported (see below for details).

All predefined compsets for coupled simulations can be found in


Predefined compsets for AMIP-type (atmsophere/land-only) simulations can be found in


Predefined compsets for running the sea-ice model as a stand-alone model cam be found in


Predefined compsets for running the land model as a stand-alone model can be found in


Predefined compsets for running the ocean model as a stand-alone model can be found in


The compsets starting with N are NorESM coupled configurations. Compsets starting with NF are NorESM AMIP (atmosphere only) configurations. Some examples are given below.

N1850 and N1850frc2

Coupled configuration for NorESM for pre-industrial (1850) conditions.


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


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 emission files

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


A new set of emission files have been made 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 use the newest emission files choose compsets including frc2 or if you want to create a new compset add


to NORESM2. For a detailed description, see 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.

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.

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


It is also possible to just add that line (without the <lname>) when creating a new case.

‘_’ seperates between model components


and ‘%’ sets the component-specific configuration



  • 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

AMIP simulation

For details about AMIP simulation compsets, please see Atmosphere

2.6. 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.

2.7. Submitting the case

The case is submitted by


2.7.1. Resolution

Model resolution is set when the case is created. Below some common resolutions are listed. A complete list of model grids can be found here:


2.8. Atmospheric grids

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

2.9. Ocean grids

Currently, BLOM supports three resolutions, nominal 2,1, and 1/4 degrees in a tripolar grid configuration:

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

2.10. Coupled

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

2.10.1. Forcing

Please see Input data sets

2.10.2. Choosing output

please see NorESM2 output

2.10.3. Setting up a nudged simulation

please see Nudged experiments