NCAS Computational Modelling Services

Unified Model

UKESM1-coupled Release Notes

Release notes for the fully coupled configurations of version 1 of the UK Earth System Model (UKESM1).

An atmosphere-only (AMIP) configuration of UKESM1 is also available for use.

Model and suite specifications

The current version of UKESM1 has an atmospheric resolution of N96 (~140 km) and a one degree resolution in the ocean. The vertical resolution is 85 levels in the atmosphere and 75 levels in the ocean.

Each configuration of the model is distributed and run as a Rose suite.

Note that links to suites (and to a couple of other pages) require access to the Met Office Science Repository Service (MOSRS) - see the introduction to UKESM for more details.

historical, pre-industrial control

There are two fully coupled UKESM1 configurations which each make use of all model components: one with science settings for a historical experiment, and one with settings for a pre-industrial control experiment.

UM versionhistoricalpre-industrial control

abrupt4xCO2, 1%CO2

Configurations for abrupt4xCO2 and 1%CO2 experiments can be created using the pre-industrial control experiment as a starting point.

To create a suite for the abrupt4xCO2 experiment, first make a copy of the pre-industrial control suite, then in um -> namelist -> UM Science Settings -> Section 01-02 - Radation -> GAS MMRs, set co2_mmr=1.72728e-03.

To create a suite for the 1xCO2 experiment, first make a copy of the pre-industrial control suite, then in um -> namelist -> UM Science Settings -> Section 01-02 - Radation -> GAS MMRs -> Varying gas MMRs, set l_clmchfcg=.true. to enable time-varying GHGs. Finally, in the sub-panel Varying CO2 MMRs, set


See below for more on the science settings of the model.

Running on the Met Office HPC

By default, each UKESM1 suite is set up to run the model on the Met Office HPC (i.e. suite conf -> Machine Options -> Site at which model is being run is set to MetO Cray). The suite offers several options for specifying how the model is to be run, including:

  • login node to be used for submission to Met Office HPC: suite conf -> Machine Options -> MetO Cray login node
  • Met Office queue to which jobs will be submitted: suite conf -> Machine Options -> HPC queue

Options for specifying the account under which jobs will be run are available in suite conf -> Project Accounting:

  • Select Use default account to use the default account for your department.
  • If this is set to false, then choose an option from the Account menu.
  • If the option is other, then enter the account explicitly in ‘Other’ user account.

Running on other machines

The model may be run on other (i.e. non-Met Office) machines. See the introduction to UKESM1 for more on available resources and how to access them. More specific instructions for suite settings for different machines are given in the following subsections.


To run on Monsoon, the Met Office / NERC collaborative platform, set suite conf -> Machine Options -> Site at which model is being run to MONSooN.

Output files created by the suite running on Monsoon may be archived via the Met Office Operational Storage Environment (MOOSE). The options for requesting this can be found under the postproc -> Post Processing - common settings control panel. Set archive_command to Moose and provide (or check) values for further options in the subpanel Moose Archiving. See below for more on the non_duplexed_set option.

Note that you must have a MOOSE account before archiving will work - see below for help.


Rewrite for ARCHER2 suites

To run on Archer2, the NERC platform, set suite “conf -> Machine Options -> Site at which model is being run” to Archer2 and set these other Machine Options:

Use Environment Modules to Custom module files Science Configuration Module Name to GC3-PrgEnv/2.0/90386 Module file location to /work/y07/y07/umshared/moci/modules/modules In addition, the following tests (see below) must be turned off when running on Archer:

Test restartability Test rigorous compiler option Test PE decomposition change Archive integrity CPMIP Analysis -> CPMIP load balancing analysis Output files created by the suite running on Archer may be archived to disk. The options for requesting this can be found under the postproc -> Post Processing - common settings control panel. Set archive_command to Archer and provide values for archive_root_path and archive_name in the subpanel Archer Archiving to specify the location of the archived files on Archer.

Following archiving, the files may be optionally transferred to a remote machine such as JASMIN. Provide values for remote_host (the address of the remote machine) and transfer_dir (the location of the archived files on the remote machine) in the subpanel JASMIN Transfer. In addition, transferring must be turned on by setting suite conf -> Build and Run -> PP Transfer to true.

Note that, before transfer from Archer to JASMIN can work, some setup of communications (specifically, both between PUMA and Archer data transfer node?, and between Archer data transfer node and JASMIN?) is required.

Using the model in a CMIP6 production run

Using the model in a CMIP6 production run requires the provision of extra information (for example, the MIP and the experiment to which the run is contributing). This information must be specified in the suite, and the suite will check its validity. See ​here on MOSRS for more details about this information.

By default, the suite is not set up to run in full CMIP6 production mode, so this information is not required. To change this, set “suite info -> project” to u-cmip6 (which will expose the interface in suite info for collecting this information) and set “suite conf -> Project Accounting -> CMIP6 Experiment” to true (which will turn on the validation of the information). More information on setting up a CMIP6 experiment is available ​here on MOSRS.

Archiving of duplexed data

When running on Met Office machines (including Monsoon), the suite will, by default, archive a single copy of its data to MOOSE. For critical model runs, this setting may be changed to archive two copies of the data (i.e. duplex) by switching non_duplexed_set in “postproc -> Post Processing-common settings -> Moose Archiving” to false. Further guidance on when to choose this option is available at ​MassNonDuplexPolicy (Note that this link only works from within the Met Office).

Compute Resource Usage

The compute resources used by the suite can be set via parameters on the “suite conf -> Machine Options” and “suite conf -> Domain Decomposition” control panels. The following discussion is specific to the Met Office HPC for the most part, but may still be helpful for users of other machines.

The type of compute node can be set via “suite conf -> Machine Options -> XC40 core type”: a Haswell node has 32 cores, while Broadwell has 36.

The suite is currently set up in “suite conf -> Domain Decomposition” to use 36 nodes (see below for more details on how this is calculated). An alternative setup uses 19 nodes. Parameter settings for both setups are:

Parameter36 node suite19 node suite
Atmosphere: Processes East-West3232
Atmosphere: Processes North-South1818
IO Server Processes00
OpenMP threads for the atmosphere21
NEMO: Number of processes East-West129
NEMO: Number of processes North-South98
NEMO: Number of processes in XIOS server66
OpenMP threads for the ocean11

Note that the ocean must be rebuilt (by setting “suite conf -> Build and Run -> Build Ocean” to true) whenever the NEMO parameters in the table are changed during a run.

Setting these parameters to other values may require load balancing to ensure that HPC resources are being used in the most efficient fashion.

Calculation of node count

On “Domain Decomposition -> Atmosphere”, the number of processes used by the UM can be set via “Atmosphere: Processes East-West” and “Atmosphere: Processes North-South”; additional processes for the IO Server may be requested using “IO Server Processes”. Finally, “OpenMP threads for the atmosphere” sets the number of threads for each process; multiplying this by the number of processes gives the number of compute tasks.

Using the parameter values for the 36 node suite, the number of tasks used by the UM is (32 * 18 + 0) * 2 = 1152. Dividing by the number of cores per node (in this case 36) and rounding up (because different executables cannot run on the same node) gives 32 compute nodes used by the atmosphere.

A similar calculation may be performed for the settings on “Domain Decomposition -> Ocean”; using “NEMO: Number of processes East-West”, “NEMO: Number of processes North-South” and “OpenMP threads” for the ocean to give 12 * 9 * 1 = 108 tasks, or 3 compute nodes used by the ocean.

Finally, on the same control panel, “NEMO: Number of processes in XIOS server” is set to 6, which equates to 1 compute node used by XIOS.

Thus, the total number of nodes used by the suite is 32 + 3 + 1 = 36.

Tests in the suite

The suite contains options for testing different aspects of the model including reproducible restarting, changes in processor decomposition, comparison to known good output and integrity of archived files. Some of these tests may be of more interest to developers than general users of the model; they can be turned on or off via the “suite conf -> Testing” control panel.

Testing for PE decomposition change

Changing the PE decomposition will change the results of the model because of the behaviour of the chemistry solver within the UM. Thus, by default, the Test PE decomposition change test (see “suite conf -> Testing”) will fail, and so this test has been turned off. There is a version of the chemistry solver which does not change results; this can be selected by setting l_ukca_asad_columns=.true. in app/um/rose-app.conf. With this option selected, the PE decomposition change test should pass.

Note that we do not select this version of the chemistry solver by default because it has a performance overhead; specifically, it causes an atmosphere-only job to run about 10% slower than when running with l_ukca_asad_columns=.false.

It should be noted that changing the PE decomposition for the ocean in UKESM will also change results because this changes results for both the iceberg code in NEMO and for the CICE code. This behaviour cannot be rectified by setting a single variable (that is, there is no analogue of l_ukca_asad_columns for NEMO and CICE).

Science notes

The historical release job differs from the first member of the CMIP6 historical ensemble (u-bb075) in the following ways:

  • The anthropogenic SO2 emission ancillaries were produced using different methodologies. The resulting SO2 emission in the model is nearly identical but has differences at the bit level.
  • It includes a fix for the aerosol plume scavenging diagnostic 38900-38932 to ensure that they bit-compare across differing processor decompositions. The difference appears at only a small number of points where the value is very close to zero.

The piControl release job differs from the CMIP6 piControl run (u-aw310) in the following ways:

  • The anthropogenic emission height is different. In the release job all anthropogenic SO2 is emitted at the surface, consistent with the model’s treatment of other anthropogenic emissions (except NOx emissions from aircraft which are supplied with a vertical emission profile). In the CMIP6 piControl, around 30% of anthropogenic emissions were released at 500m. Because the 1850 anthropogenic emissions are tiny relative to natural emissions from volcanoes and the ocean, this difference in emission height makes no meaningful difference to the SO2 burden or the aerosol simulation.
  • The release job includes several diagnostic fixes which were not included in the CMIP6 piControl run. These include:
    • The fix to plume scavenging diagnostics described above
    • Corrections to diagnostics 30312, 30313, 30298 which were corrupted in the CMIP6 piControl
    • Addition of some other diagnostics to CMIP6 PP streams

Known issues

  • All Stash items spanning 38:485 to 38:545: Aerosol surface conc., concn., load diagnostics: Due to the way STASH is handling and processing these items, they will be output as exactly 1/3rd of their actual value. The values of these items must therefore be scaled by a factor of 3.0.
  • The ocean diagnostic variable tnpeo [Tendency of ocean potential energy content, with units of W/m2] is calculated incorrectly. The value of this item should therefore be ignored.
  • Development work on the coupled configurations (including instructions on how to upgrade suites, where necessary) is documented in ticket #651 on MOSRS.


  • NERC users requiring assistance running this suite on NERC machines (ARCHER2 & Monsoon) should raise a ticket on the NCAS-CMS helpdesk.
  • Users running this suite on other machines should contact local support services.