Introduction

This page describes the files typically found in an OpenIFS 43r3 experiment. Experiment files are provided by the OpenIFS team at ECMWF as gzipped tarfile. These files provide initial and boundary conditions and currently are provided on request to the user for download via ftp.ecmwf.int.

Note that the experiment ID forms part of the name for all binary ICM* GRIB files. The experiment ID is also stored inside each GRIB file. Grib tools can be used to modify the experiment ID if required. Users should not just copy the files to a new name.

Overview of an Initial File Archive

The table below shows an initial data produced by provided in order to run OpenIFS for a 48 hour forecast with experiment ID h9wu, starting on 1990-01-01 at 00 UTC using a Tco159 cubic octahedral grid with 91 vertical model levels.

The files will be provided by OpenIFS at ECMWF as a gzipped tar archive, which can be uncompressed and unpacked byusing:

% tar xvzf h9wu_19900101.tgz

If your version of the 'tar' command does not support the 'z' uncompress option, do it in two stages using the 'gunzip' command first and then 'tar xvf' on the resulting file.

The directory structure consists of a top-level directory named after the experiment ID, which differs for each experiment (h9wu in the example below), and subdirectories for all available start dates (here only one start date, 1990010100). The subdirectory ecmwf contains namelist files and several pre-run log file outputs to compare your experiment against.

Contents of the Initial Data Files

In the following sections the content of the individual GRIB initial files is further explained. Click on the parameters in the table in order to link to the ECMWF GRIB parameter database for a more comprehensive description of the variables.

ICMCL****INIT

This file provides surface boundary conditions for the duration of the experiment. The data in this file is interpolated from climatological monthly means to daily values at 12:00 UTC over the duration of the forecast experiment (FCLENGTH). 

Origin of the climatological data (climate.v015 for OpenIFS 43r3) and further details are in the IFS documentation, Part IV (Physical Processes) Chapter 11. The data sets that are used for the climatology are described in Section 11.2. 

During the preparation process of initial data packages climatological SSTs (which originate from ERA-40) are replaced with daily values from more recent meteorological reanalyses, e.g. such as ERA5.

ICMGG****INIT

The data in this file contains the initial conditions at the start of the experiment. 

Parameters that are not available from requested analyses type (e.g. ERA5) will be substituted from the climatological files described above. 

ICMGG****INIUA

This file contains "upper atmosphere" initial data, see the above section for the origin of the data. 

ICMSH****INIT

This file contains initial data in spectral formulation, see the above section for the origin of the data. 

Other Files in the Experiment Directory

The experiment directory contains the initial data files described above. Moreover, other files and symbolic links are created when the model is run for the first time.

OpenIFS run script:
It verifies the required environment variables and file paths and creates symbolic links to other climatological and grid-related data directories.
It calls the binary model executable to start the experiment.
Once the experiment has completed the script carries out housekeeping procedures and initiates first post-processing steps of the Grib output files.

How do I start the experiment?

If all the environment variables are set and the symbolic file path links exist and are valid, the experiment could in principle be started by executing the model binary master.exe with appropriate command line parameters, as it is done in the oifs_run script:

master.exe -r -e -n

In practice this method is not recommended.  It is far better to make use of the provided service script oifs_run which verifies all the settings and if necessary creates the missing links. It calls the executable by invoking the MPI environment (which may well be hardware dependent) and will initiate postprocessing of the experiment results by moving the Grib model output to a target directory and concatenates according to time step. oifs_run can be called with command line parameters which are passed on to the model executable. If no command line parameters are provided oifs_run will substitute with default values for experiment ID, grid resolution, number of tasks and threads, etc. which are likely to be of no use. Therefore the command line parameters need to be set. By calling oifs_run the model will run interactively in the login shell.

oifs_run -r -e -n

Passing on the appropriate command line parameters can further be simplified by writing a brief job script which itself calls oifs_run with the required parameters. This job script is either run.ccb or run.ws.  run.ccb is a batch script which can be submitted to the Cray PBS schedule using the qsub ./run.ccb command.  run.ws is a shell script which can be called interactively from the command line and simply calls oifs_run.