UKESM1.1-coupled Release Notes

Release notes for the fully coupled configurations of version 1.1 of the UK Earth System Model (UKESM).

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

clim_fcg_levls_co2=4.3182e-04
clim_fcg_nyears_co2=1
clim_fcg_rates_co2=1.0
clim_fcg_years_co2=1849

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

Running on the Met Office HPC

By default, each UKESM1.1 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). Each 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.

Archiving of duplexed data

When running on Met Office machines (including Monsoon3), 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:

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 suite conf -> 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 suite conf -> 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 um -> namelist -> UM Science Settings -> Section 34 - UKCA: UK Aerosols and chemistry -> Chemistry -> l_ukca_asad_columns to true. 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 option turned off.

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).

Known issues

• Development work on the UKESM1.1 um12.1 configurations (including instructions on how to upgrade suites, where necessary) is documented in ticket #830 on MOSRS.

Support

• NERC users requiring assistance running this suite on NERC machines (ARCHER2 & Monsoon3) should raise a ticket on the NCAS-CMS helpdesk.
• Users running this suite on other machines should contact local support services.