7. Further Exercises (2)

The exercises in this section are all optional. We suggest you pick and choose the exercises that you feel are most relevant to the work you are/will be doing.

Note

Use your copy of suite u-cc654 for these exercises unless otherwise specified.

7.1. Post-Processing (archive and transfer of model data)

When your model runs it outputs data onto the ARCHER2 /work disk (/projects on Monsoon2). If you are running a long integration and/or at high resolution data will mount up very quickly and you will need to move the data off of ARCHER2; for example to JASMIN. The post-processing app (postproc) is used within cycling suites to automatically archive model data and can be optionally configured to transfer the data from ARCHER2 to the JASMIN data facility. The app archives and deletes model output files, not only for the UM, but also NEMO and CICE in coupled configurations.

Let’s try configuring your suite to archive to a staging location on ARCHER2:

  • Switch on post-processsing in window suite conf –> Tasks

The post-processing is configured under the postproc section:

  • Select the Archer archiving system in window Post Processing - common settings.

A couple of new entries will have appeared in the index panel, Archer Archiving and JASMIN Transfer, identified with the blue dots.

You now need to specify where you want your archived data to be copied to:

  • In the Archer Archiving panel set archive_root_dir to be /work/n02/n02/<userid>/archive. The archive_name (suite id) will be automatically appended to this.

You will need to run the model for at least 1 day as archiving doesn’t work for periods of less than 1 day. Change the run length and cycling frequency to be 1 day. This should complete in about 5 minutes so set the wallclock time to be 10 minutes.

Run the suite.

Once the run has completed go to the archive directory for this cycle (e.g. /nerc/n02/n02/<userid>/<suiteid>/19880901T0000Z) and you should see several files have been copied over (e.g cc654a.pc19880901_00.pp).

Data files that have been archived and are no longer required by the model for restarting or for calculating means (seasonal, annual, etc) are deleted from the suite History_Data directory. Go to the History_Data directory for your suite and confirm that this has happened. This run is reinitialising the pc data stream every 6 hours and you should see that it has only removed data files for this stream up to 18:00hrs, the cc654a.pc19880901_18.pp file is still present. This file contains data for the hours 18-24 and would be required by the model in order to restart. Equally seasonal mean files would not be fully archived until the end of the year, after the annual mean has been created.

Note

The post-processing app can also be configured to transfer the archived data over to JASMIN. Details on how to do this are available on the CMS website: http://cms.ncas.ac.uk/wiki/Docs/PostProcessingApp

7.2. Using IO Servers

Older versions of the UM did not have IO servers, which meant that all reading and writing of fields files went through a single processor (pe0). When the model is producing lots of data and is running on many processors, this method of IO is very inefficient and costly - when pe0 is writing data, all the other processors have to wait around doing nothing but still consuming AUs. Later UM versions, including UM 10.5, have IO servers which are processors dedicated to performing IO and which work asynchronously with processors doing the computation.

Here’s just a taste of how to get this working in your suite.

Set the suite to run for 1 day with an appropriate cycling frequency, then check that OpenMP is switched on as this is needed for the IO servers to work.

Hint

Search for openmp in the rose edit GUI

Navigate to suite conf –> Domain Decomposition –> Atmosphere and check the number of OpenMP threads is set to 2. Set the number of IO Server Processes to 8.

Save and then Run the suite.

You will see lots of IO server log files in ~/cylc-run/<suitename>/work/<cycle>/atmos_main which can be ignored for the most part.

Try repeating the Change the dump frequency experiment with the IO servers switched on - you should see much faster performance.

7.3. Writing NetCDF output from the UM

Until UM vn10.9, only fields-file output was available from the UM - bespoke NetCDF output configurations did exist but not on the UM trunk. The suite used in most of these Section 7 exercises is vn11.7, hence supports both fields-file and NetCDF output data formats.

Enable NetCDF

Make sure that IO Server Processes variable is set to 0.

Navigate to um –> namelist –> Model Input and Output –> NetCDF Output Options and set l_netcdf to true. Several fields will appear which allow you to configure various NetCDF options. For this exercise, leave them at their chosen values.

Set NetCDF Output Streams

Expand the NetCDF Output Streams section. A single stream - nc0 - already exists; select it to display its content. As a useful comaprison, expand the Model Output Streams section and with the middle mouse button select pp0. Observe that the only significant differences between pp0 and nc0 are the values of file_id and filename_base. Data compression options for nc0 are revealed if l_compress is set to true. NetCDF deflation is a computationally expensive process best handled asynchronously to computation and as yet not fully implemented through the UM IO Server scheme (but under active development.) For many low- to medium-resolution models and, depending precisely on output profiles, high-resolution models also, use of UM-NetCDF without IO servers still provides significant benefits over fields-file output since using it avoids the need for subsequent file format conversion.

Right-click on nc0 and select Clone this section. Edit the settings of the newly cloned section appropriately to make the new stream similar to pp1 (ie. edit filename_base and all the reinitialisation variables). It is sensible to change the name of the new stream from 1 to something more meaningful, nc1 for example (right click on 1, select Rename a section, and change …nc(1) to …nc (nc1)).

Direct output to the nc streams

Expand STASH Requests and Profiles, then expand Usage Profiles. Assign nc streams to usage profiles - in this suite, UPA and UPB are assigned to pp0 and pp1 respectively (where can you see this?). Edit these Usage profiles to refer to nc0 and nc1 respectively. Run the STASH Macros (if you need a reminder see Section 6), save the changes, and run the suite. Check that the NetCDF output is what you expected.

Try adding more nc streams to mimic the pp stream behaviour.

7.4. Running the coupled model

The coupled model consists of the UM Atmosphere model coupled to the NEMO ocean and CICE sea ice models. The coupled configuration used for this exercise is the UKESM Historical configuration with an N96 resolution for the atmosphere and a 1 degree ocean - you will see this written N96 ORCA1.

Checkout and run the suite

Checkout and open the suite u-ce119. The first difference you should see is in the naming of the apps; there is a separate build app for the um and ocean, called fcm_make_um and fcm_make_ocean respectively. Similarly there are separate apps for the atmos and ocean model settings, called um and nemo_cice.

Make the usual changes required to run the suite (i.e. set username, account code, queue). If you are following the tutorial as part of an organised training event, select one of the special queues, otherwise, select to run in the short queue.

Check that the suite is set to build the UM, Ocean, and Drivers as well as run the reconfiguration and model.

Run the suite.

Exploring the suite

Whilst the suite is compiling and running which will take around 40 minutes, take some time to look around the suite.

  • How many nodes is the atmosphere running on?

  • How many nodes is the ocean running on?

  • What is the cycling frequency?

The version of NEMO used in this suite (and most suites you will come across) uses the XML IO Server (XIOS) to wite its diagnostic output. XIOS runs on dedicated nodes (one node in this case). Running squeue will show three status entries corresponding to the Atmosphere, Ocean, and XIOS components of the coupled suite. XIOS is running in multiple-file mode with 6 servers.

  • Can you see where the NEMO model settings appear?

Look under Run settings (namrun). The variables nn_stock and nn_write control the frequency of output files.

  • How often are NEMO restart files written?

Hint

The NEMO timestep length is set as variable rn_rdt

Now browse the CICE settings.

  • Can you find what the CICE restart frequency is set to?

NEMO, CICE and XIOS are developed separately from the UM, and you should have seen that they work in very different ways. See the following websites for documentation:

Output files

Log files

NEMO logging information is written to:

~/cylc-run/<suitename>/work/<cycle>/coupled/ocean.output

CICE logging information is written to:

~/cylc-run/<suitename>/work/<cycle>/coupled/ice_diag.d

If the model fails some error messages may also be written to the file ~/cylc-run/<suitename>/work/<cycle>/coupled/debug.root.01 or debug.root.02

When something goes wrong with the coupled model it can be tricky to work out what has gone wrong. NEMO errors may not appear at the end of the file but will be flagged with the string E R R O R.

Restart files

Restart files go to the subdirectories NEMOhist and CICEhist in the standard data directory ~/cylc-run/<suitename>/share/data/History_Data.

Diagnostic files

Diagnostic files are left in the ~/cylc-run/<suitename>/work/<cycle>/coupled/ directory.

CICE files start with <suitename>i. Once your suite has run you should see the following CICE file (and more):

archer$ ls ce119i*
ce119i.10d.1850-01-10.nc

NEMO diagnostic files are named <suitename>o*grid_[TUVW]*. To see what files are produced, run:

archer$ ls ce119o*grid*

In this case each XIOS IO server writes to a separate file. To concatenate these into a global file use the rebuild_nemo tool, e.g.:

archer$ rebuild_nemo ce119o_1d_18500101_18500110_grid_T 6

Note

The coupled atmos-ocean model setup is complex so we recommend you find a suite already setup for your needs. If you find you do need to modify a coupled suite setup please contact NCAS-CMS for advice.

7.5. Running the Nesting Suite

The Nesting Suite drives a series of nested limited area models (LAM) from a global model. It allows the user to specify the domains and it then automatically creates the required ancillary files and lateral boundary condition files.

Checkout and run the suite

Checkout and open the suite u-ce122. There are a number of tasks for creating ancillary files (ancil_* and ants_*). The global model set up is in glm_um and the LAMs are in um. The task um-createbc creates the lateral boundary condition files.

Under suite conf –> jinja2:suite.rc are the main panels for controlling the Nesting Suite. Make the usual changes required to run the suite (i.e. set username, account code, queue).

If following the tutorial as part of an organised training event, select one of the special queues, otherwise, select the short queue.

Run the suite.

This particular suite has a global model and one limited area model. It should complete in about 45 - 60 minutes.

Exploring the Suite

The Driving Model set up panel allows the user to specify the resolution of the global model and the number of nested regions.

The Nested Region 1 set up panel specifies the latitude and longitude of the centre of the first nested region. All the other limited area models have the same centre.

A useful way to get this information is to use Google Maps. Find the place you want as a centre and then press control-left mouse and a little window with the latitude and longitude appears.

  • Can you find out where the first LAM is located?

Hint

Look at the orography file output during the ancillary creation.

The resolution 1 set up panel specifies the grid and the run length.

The Config 1 set up panel specifies the science configuration to be run. Each LAM can have multiple science configurations.

Initial Data

The initial data for the global model is in share/cycle/<cycle time>/glm/ics

The initial data for the first LAM is in share/cycle/<cycle time>/Regn1/resn_1/RA1M/ics

The RA1M is the name you gave to the first science configuration.

The LBCs for the first LAM are in share/cycle/<cycle time>/Regn1/resn_1/RA1M/lbcs.

The ancillary files

These are in share/data/ancils/Regn1/resn_1

The output files

The global model output is in share/cycle/<cycle time>/glm/um. This also contains contains the data for creating the LBC files (umglaa_cb*) for the first LAM.

Diagnostic files can be found under work/<cycle time> in an application directory. For example, the region1 forecast diagnostics is in work/<cycle time>/Regn1_resn_1_RA1M_um_fcst_000. This will include the pe_output files.

The output for the first LAM is in share/cycle/<cycle time>/Regn1/resn_1/RA1M/um.

Further Information

This has been a very brief overview of the functionality of the Nesting Suite. The Nesting Suite is developed and maintained by Stuart Webster at the Met Office. He has a web page all about the Nesting Suite at https://code.metoffice.gov.uk/trac/rmed/wiki/suites/nesting. This includes a more detailed tutorial.