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Introduction
OpenIFS is an ECMWF led project which provides an easy-to-use, exportable version of the IFS system in use at ECMWF for operational weather forecasting. The project aims to develop and promote research, teaching and training on numerical weather prediction (NWP) and NWP-related topics with academic and research institutions.
In this tutorial, OpenIFS has been pre-installed for you. If you want to learn more about how OpenIFS can be downloaded, configured and installed, please see the OpenIFS website at: http://software.ecmwf.int/oifs/.
In this tutorial..
What you will do:
- Explore installed OpenIFS files.
- Run T21 model forecast.
- Verify model works in serial (1 process) and parallel (2 tasks & 2 threads).
- Carry out acceptance test.
- Use the model namelist to change settings
- Explore model output data (GRIB)
At the end of this tutorial, you will:
- learnt about how OpenIFS is installed and organised.
- run it at T21 resolution and know how to run it serially (1 process) and in parallel with both MPI & OpenMP.
- know how to use grib tools to look at model output.
OpenIFS directories
In this section we:
- Set the OpenIFS environment
- Examine the OpenIFS installation
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- OpenIFS has been precompiled on the virtual machine.
- All source code has been removed due to licensing restrictions.
- OpenIFS builds 'out-of-source'; object (.o) and executables are not mixed with source code.
OpenIFS T21 test forecasts
In this section of the tutorial, we'll run the pre-compiled OpenIFS model on a simple T21 forecast.
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Whenever the model fails, it will produce this traceback (controlled by DR_HOOK=1 in the job file).
Single process test
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Copy the file namelists and run the model with a single task and single thread by executing the job script:
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This test runs only 6 timesteps.
Model output
The model writes its output to a several files.
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Look at the output from the model in the NODE_001.01 file from this successful run. Note the output of the model namelists and the statistics printed at the end. IFS has very comprehensive logging output which is useful for debugging and understanding the model's performance. Look at the grib output files using the grib commands. |
Parallel runs
These next short tests verify the model works correctly with either OpenMP parallel threading, MPI tasks and both and follow on from the serial tests above.
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Look in the NODE_001.01 output file for the line: "NUMBER OF TASKS 2" to verify that two MPI tasks was used.
Mixed mode: OpenMP/MPI
The model can also be set to use NPROC=2 and OMP_NUM_THREADS=2 to use a total of 4 processes. However, this would require a computer with at least 4 cores to see any benefit and is not beneficial on the virtual machine.
Acceptance testing
The final step is to check the model is producing the numerical answers within acceptable limits, even if it runs the short tests above without failing. OpenIFS includes code that will compute internal statistical norms and compare against numbers supplied by ECMWF. The file: ref_021_0144 in the t21test directory contains statistical norms computed by the model run at ECMWF.
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As long as the model reports 'calculations are correct' and the error is less than a few percent then the model is behaving satisfactorily in your compilation and run environment.
How to control model output
In this section, the main NAMELIST variables that control the output of the model are presented.
If you have time, try changing the variables, run the model and using the grib_ls and grib_dump commands to view the output grib file contents.
How to control output frequency
The namelist variables that determine the output from the model as it runs are:
Namelist : NAMCT0
LFPOS - this should be set TRUE in order to turn on model output and diagnostics.
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NPOSTS & NHISTS - these are integer arrays that control the write times of the history files. They can be used for non-regular output intervals.
Examples
Regular output at fixed timesteps
NFRHIS=4,
NFRPOS=4,
NPOSTS=0,
NHISTS=0,
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For this to work correctly, |
Non-regular output
NFRHIS=1, NFRPOS=1, NHISTS(0)=3, NHISTS(1:3)=0,-3,-9, NPOSTS(0)=-3, NPOSTS(1:3)=0,-3,-9,
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In this example, the model will write 3 separate output files at the first timestep (0hrs), 3hrs and 9hrs and then no more regardless of how long the model runs for.
How to change the output variables and post-processing
The namelist NAMFPC is the main namelist for the post-processing. Variables in this list can be sensitive to changes as many combinations are possible but not all work.
Model level output
To control model level output the following namelist variables (in NAMFPC) are used:
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