OpenIFS programme

The ECMWF OpenIFS programme provides an easy-to-use, exportable version of the IFS in use at ECMWF for operational weather forecasting. The programme aims to develop and promote research, teaching and training on numerical weather prediction (NWP) and NWP-related topics with academic and research institutions.

Use of OpenIFS on topics of interest to the Centre and member states is encouraged. Research topics at ECMWF are described in more detail on the main ECMWF site. Enquiries regarding potential collaborations are welcome.

OpenIFS provides the forecast-only capability of IFS (no data assimilation), stays close to operational version and supports operational configurations. For more details see how OpenIFS compares with IFS.

OpenIFS is supported by a small team at ECMWF for technical & scientific assistance, however, there are limited resources for detailed scientific help.

The OpenIFS model 'package' includes not just the model itself but acceptability tests for compilers/hardware, example case studies, plotting & analysis tools and so on. The model is intended for research and educational use by Universities,  research organisations and individual researchers on their own computer systems. It is not provided for any real-time forecasting. ECMWF does not provide facilities to run OpenIFS on its computer systems.

Documentation, install instructions, frequently asked questions and other help information can all be found on this website. User forums are also available. Support is provided for a range of hardware platforms and compilers.

Please note that OpenIFS is licensed software and not open-source nor in the public domain. Licenses are free of charge and typically granted as site licenses.

About IFS

The ECMWF Integrated Forecasting System (IFS) is ECMWF's modelling and data assimilation computer program for global numerical weather prediction (NWP). IFS is a collaborative effort that started between ECMWF and Meteo-France, and today involves many ECMWF member-states and associated consortia of the national meteorological services.

Dynamical core

The dynamical core of IFS is hydrostatic, two-time-level, semi-implicit, semi-Lagrangian and applies spectral transforms between grid-point space (where the physical parametrizations and advection are calculated) and spectral space.

The evolution equations of the IFS are a terrain following mass-based vertical coordinate (Simmons and Burridge, 1981), solving the hydrostatic, shallow-atmosphere equations (Ritchie et al., 1995). The solution procedure uses the spectral transform method. The first spectral transform model was introduced into operations at ECMWF in April 1983. Spectral transforms on the sphere involve discrete spherical harmonics transformations between physical (gridpoint) space and spectral (spherical-harmonics) space. This technique has been successfully combined with semi-implicit time stepping (Robert et al., 1972), where the resulting Helmholtz problem is solved in spectral space, and the unconditional stability of semi-Lagrangian (SL) advection (Temperton et al., 2001), where the only limiting factor on the time step is the magnitude of local truncation errors.

The horizontal resolution of IFS has approximately doubled every 8 years, with approximately 9km global grid resolution (and an effective resolution of ~36km) in 2016.

Physics

In global atmospheric models, subgrid-scale parametrisations describe the effect of unresolved processes on the resolved scale (e.g. surface exchange, convection, gravity wave drag, vertical diffusion), but also describe diabatic effects such as radiation and water phase changes.

The IFS has a comprehensive package of sub-grid parametrization schemes representing radiative transfer, convection, clouds, surface exchange, turbulent mixing, sub-grid-scale orographic drag and non-orographic gravity wave drag. The radiation scheme is based on the Rapid Radiation Transfer Model (RRTM) (Mlawer et al., 1997) with cloud radiation interactions using the Monte Carlo Independent Column Approximation (McICA) (Morcrette et al., 2008). Radiation calculations of short- and longwave radiative fluxes are done less frequently than the timestep of the model and on a coarser grid.

The moist convection scheme uses the mass-flux approach and represents deep (including congestus), shallow and mid-level (elevated moist layers) convection (Bechtold et al. (2014). Clouds and large-scale precipitation are parametrized with prognostic equations for cloud liquid, cloud ice, rain and snow water contents and a sub-grid fractional cloud cover.

The land surface parametrization scheme represents the surface  fluxes of energy / water and corresponding sub-surface quantities. It uses a tiled approach (TESSEL) representing different sub-grid surface types for vegetation, bare soil, snow and open water (Balsamo et al., 2009). Turbulent diffusion and exchange with the surface are represented on the basis of Monin-Obukhov similarity in the surface layer and an Eddy-Diffusivity Mass-Flux (EDMF) framework above the surface layer (Kohler et al., 2011).

Unresolved orographic effects are represented in the Turbulent Orographic Form Drag (TOFD) scheme for the scales smaller than 5 km (Beljaars et al., 2004) and in the low level blocking and gravity wave scheme for the larger scales (Lott and Miller, 1997). Non-orographic gravity waves are parametrized according to Orr et al. (2010).

At the sea surface, the IFS has a two-way coupling to the WAve Model (WAM, Hasselmann et al., 1988). The coupling with WAM is performed every time step whereby WAM is forced by IFS 10-metre wind speeds while the IFS is forced by surface roughness over sea.

The latest scientific documentation of IFS with detailed descriptions of the dynamical core and the physical parametrization package is available from here.

Further information

Further information about OpenIFS, IFS and ECMWF can be found on this website and on the main ECMWF website.

Questions and queries about OpenIFS can be addressed to : openifs-support@ecmwf.int.