How do we actually run very high resolution climate simulations?

By: Annette Osprey

Excessive decision modelling

Operating very detailed and superb scale (“excessive decision”) simulations of the Earth’s ambiance is significant for understanding modifications to the Earth’s local weather, notably excessive occasions and high-impact climate [1]. Nevertheless, every simulation is 1) time-consuming to arrange – scientists spend numerous time designing the experiments and perfecting the underlying science, and a pair of) costly to run – it could take many months to finish a multi-decade simulation on 1000’s of CPUs. However the information from every simulation could also be used many instances for many different purposes.

Beneath the hood

There’s numerous technical work that’s executed “underneath the hood” to ensure the simulations run as seamlessly and effectively as potential and the outcomes safely moved to an information archive the place they are often made out there to others. That is the work that we do in NCAS-CMS (the Nationwide Centre for Atmospheric Science’s Computational Modelling Companies group), alongside our colleagues at CEDA (the Centre for Environmental Information Evaluation) and the UK Met Workplace. My position is to work with the HRCM (Excessive Decision Local weather Modelling) staff, serving to scientists to arrange and handle these very large-scale simulations.

CMS is liable for ensuring the simulation code, the Met Office Unified Model (UM), runs on the nationwide supercomputer, Archer2, for tutorial researchers across the UK. In addition to constructing, testing and debugging totally different variations of the code, we have to set up the supporting software program that’s required to really run the UM (we name this the “software program infrastructure”). This contains code libraries, experiment and workflow administration instruments [2], and software program for processing enter and output information. That is all specialist code that we have to configure for our specific methods and the wants of our customers, and generally we have to complement this with our personal code.

Sturdy workflows

We name the end-to-end technique of working a simulation the “workflow”. This includes 1) organising the experiment (choosing the code model, scientific settings, and enter information), 2) working the simulation on the supercomputer, 3) processing the output information, 4) then archiving the information to the nationwide information centre Jasmin, the place we are able to have a look at the outcomes and share with different scientists. When working very excessive decision and/or long-running simulations we want this course of to be as seamless as potential. We don’t need to must maintain manually restarting the experiment or troubleshooting technical points.

Moreover, the quantity of information that’s generated from these excessive decision simulations is extremely giant. It’s too giant to retailer all the information on the supercomputer, and it may well generally take so long as the simulation to maneuver the information to the archive. The answer due to this fact, is to course of and archive the information because the simulation is working. We construct this into the workflow in order that it may be executed robotically, and we now have as most of the duties working concurrently potential (this is called “concurrency”).

The HRCM workflow








Determine 1: An instance workflow for a UM simulation with information archiving to Jasmin, displaying a number of duties working concurrently.

The picture exhibits the workflow we now have arrange for our newest excessive decision simulations. We cut up the simulation into chunks, working 1 month at a time. As soon as one month has accomplished, we set the following month working and start processing the information we simply produced. The workflow design signifies that the processing could be executed concurrently the following simulation month is working. First we carry out any transformations on the information, then we start copying it to Jasmin. We generate distinctive hashes (checksums) that we use to confirm the information copy is equivalent to the unique, in order that we are able to safely delete it, clearing area for forthcoming information. Then we add the information to the Jasmin long run tape archive, and we might put some information in a workspace the place scientists can evaluation the progress of the simulation.

Serving to local weather scientists get on with science

The advances that we make for the excessive decision simulations are made out there to our different customers, regardless of the dimension of the run. Ideally the workflow design signifies that the one consumer involvement is to start out the run going. In actuality, in fact, generally the machine goes down, connections are misplaced, the mannequin crashes, (or the experiment wasn’t arrange appropriately!) Thus, we now have constructed a stage of resilience into our workflow that signifies that we are able to take care of failures successfully. So, scientists can concentrate on organising the experiment and analysing the outcomes, with out worrying too a lot about how the simulation runs.


[1] Roberts, M. J., et al. (2018). “The Advantages of World Excessive Decision for Local weather Simulation: Course of Understanding and the Enabling of Stakeholder Selections on the Regional Scale” in Bulletin of the American Meteorological Society, 99(11), 2341-2359, doi:

[2] H. Oliver et al. (2019). “Workflow Automation for Biking Methods,” in Computing in Science & Engineering, 21(4), 7-21, doi:

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