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A. The 'T' refers to the spectral truncation of the model and the number following is the highest retained wavenumber. A spectral method, based on spherical harmonic expansion is used in the model, for example to compute some horizontal derivatives. The 'T' means the model uses a 'triangular' truncation in spectral space to decide the retained spherical harmonics. The number following the 'T' is the highest retained wave number. For more information on the spectral truncation and resolution of the model and the model grid, the IFS documentation is recommended reading.

T159 is approximately 125km resolution, T255 - 80km, T511 - 40km, T799 - 25km, T1279 - 16km.

A. This depends on the grid used. For medium and high resolutions, the model uses a 'reduced Gaussian grid' with reduced numbers of gridpoints along a latitude circle towards the poles. Full quadratic and linear grids are also possible. This table shows the correspondence between spectral resolution and lat/lon resolution. The grid definitions can also be found here: reduced gaussian grid definitions.

A. The OpenIFS model is based on the main IFS code though without some functionality such as data assimilationis only capable of forecasts. The first OpenIFS version was based on cycle 38 release 1 (known as CY38R1). More information is found on the page comparing OpenIFS .v. IFS.

Information on scientific & technical changes between cycles cycle releases is available on the main ECMWF website.

A. The model writes its output in GRIB format using WMO FM-92 GRIB edition 1 and edition 2 messages. ECMWF provides the GRIB_API software for handling and manipulating grib data using either command line tools and a programming library for C, Fortran and Python.

For plotting GRIB data, ECMWF provides the MetView software, which is freely available under the Apache license.

Note that the OpenIFS model outputs a mix of GRIB edition 1 & 2 messages in a single file. Unlike MetView, not all GRIB software available on the Internet can read such files and extra steps may be necessary to separate the messages before use if you want to use 3rd party software.

A. The model can be run in 'reference' mode where it computes statistical numerical norms and compares against values calculated at ECMWF. Please see 'Testing the Installation' for more details.

A. The timestep depends on the horizontal and vertical resolution, the type of grid (full or reduced Gaussian), whether Eulerian or semi-Lagrangian (SL) transport is used and whether the 2 or 3 time-level SL scheme is used. The recommended default is the 2 time-level SL scheme. For this configuration suggested timesteps are: T21 - T159 : 60mins, T213 -T319 : 20mins, T511 and above : 10mins. If the 2 time-level scheme is not used, these timesteps should be halved. If Eulerian, not SL transport is used, these timesteps should be a quarter. For more details, see the code in the routine sudyn.F90 which has approximate values for the timestep (n.b. the NAMDYN namelist variable TSTEP is in units of secs).

Note the model will calculate the optimum timestep for its particular configuration. This value is written to the NODE_001.01 output file. Look for the line:
PTSTEP_OPT (optimal timestep computed in SUTSTEP) 0.36000000E+04
to see the recommended value in seconds.

A. The file 'MCICA' is a climatological input file the model needs. The model expects to read the climatological files from a sub-directory called 'ifsdata' in the directory containing the executable. Normally this is a link to where you installed the ifs data files. See Downloading OpenIFS for more details on how to download and install the data files.

A. This usually indicates an error in the GRIB file or GRIB_API configuration rather than the model. See the GRIB FAQ on this page, or email openifs-support@ecmwf.int and include the model output file (NODE_001.01) and the job log.

A. This could be for a number of reasons. However, a common one is that when compiled optimized the model requires more memory.  With the optimized settings OpenMP is enabled. This causes the model to require more what's known as 'stack memory'. To increase your stack memory to the maximum allowed on your system, use the command 'ulimit -s unlimited'. If that does not solve your problem, email openifs-support@ecmwf.int.

A. This normally means that the OpenMP stacksize is not large enough. The default per process stack size limit is too low and needs to be increased. Check the value of the OMP_STACKSIZE environment variable.

A. This could be for a number of reasons. One possibility is that the model is configured as if running at ECMWF where it writes file to a special database. Check that the NODE_001.01 output file and make sure that in namelist NAMCT0, the variable LFDBOP is .FALSE. and in namelist NAMPAR1, the variable NOUTTYPE=1. If this is the ok, then please see our HowTo on changing the model output or contact openifs-support@ecmwf.int.