Q. What does the 'T' mean in 'T511', 'T1279' etc? A. The 'T' refers to the spectral truncation of the model and the number after 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, the IFS documentation is recommended reading. T159 is approximately 125km resolution, T255 - 80km, T511 - 40km, T1279 - 25km. Q. How do I know the grid from from the 'T' number? 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. Q. What is the difference between IFS/OpenIFS model versions? A. The OpenIFS model is based on the main IFS code though without some functionality such as data assimilation. 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 releases is available on the main ECMWF website. Q. What format is the model output? 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. Q. How do I check the model is working correctly on my system after I've installed it? 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. Q. OpenIFS fails with an error message from GRIB_API. 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. Q. OpenIFS fails (segmentation violation) when compiled with optimized compiler options ('opt' configuration) but works without any optimization ('noopt' configuration). 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. |