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The Icosahedral Nonhydrostatic Weather and Climate Model (ICON) is being deployed for numerical forecasting for the Swiss meteorological service, MeteoSwiss, as part of the ICON-22 project. This will replace the COSMO forecasting model that is currently being used.

Project start01.10.2019
Project end31.12.2024
StatusCurrent projects
  • Measurement & forecasting systems


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Swiss federal authoritiesSwiss federal authorities

Weather-dependent decisions are made on a daily basis in many sectors of the Swiss economy, not least in agriculture and the energy industry. Weather forecasts are also central to the operation of early warning systems for extreme weather events such as flooding, storms and hail. Numerical weather forecast models form the basis for weather forecasts and warnings produced by MeteoSwiss. They simulate the state of the atmosphere in the near future and produce probability forecasts for various parameters such as precipitation and temperature. These are then further processed into data products that can be employed in decision-making. To continuously improve the quality of these important functions, the forecast models must be developed on an ongoing basis.

MeteoSwiss currently produces its forecasts using two different ensemble configurations of the COSMO forecasting model (COSMO-1E and COSMO-2E). The model that is to succeed COSMO has been developed alongside ongoing operations over the past few years under the auspices of the German Meteorological Service (DWD) and the Max Planck Institute for Meteorology (MPI-M). Now that the strategic decision has been made by the COSMO consortium to replace COSMO with ICON, all further development of COSMO has been ended and the international developer community is refocusing its efforts on ICON. With the switch from COSMO to ICON, MeteoSwiss is hoping for an improvement in forecast quality and computer infrastructure, as well as synergy with ongoing research projects (GLORI-A, EXCLAIM).

The project: ICON-22

The goal of the project is to deploy ICON in the operational forecasting business of MeteoSwiss. The most important factor is that the new models, ICON-CH1-EPS and ICON-CH2-EPS, surpass (or at least equal) the existing COSMO-1E and COSMO-2E models in terms of quality, so that verification – in other words, the comparison of forecasts with measured data – generally produces better results. To achieve this, the existing ICON model must be adapted to the special needs and circumstances of Switzerland.

At the same time that the new model is introduced, an upgrade of the computing infrastructure at the Swiss National Supercomputing Centre at ETH Zurich (CSCS) will be carried out. This will enable ICON to operate on the new ALPS High-Performance Computing Platform in the CSCS, in so-called virtual clusters with a dedicated software environment.

Another major step forward is the adaptation of the data flows for the downstream applications that are deployed for producing a wide variety of data products. To this end, post-processing will be optimised on ICON test runs, which will be instigated as part of ICON-22.

From COSMO to ICON: an improved model

Like COSMO, ICON is a numerical model that describes the processes relevant to weather forecasting and calculates what the state of the atmosphere will be in the near future. However, there are some important differences between the two models, as outlined below:

While COSMO uses a regular geographical (latitudinal/longitudinal) grid, the ICON concept is based on a triangular (icosahedral) grid. The advantage of this is that the grid elements no longer differ in their actual size, thus avoiding any grid distortion due to the meridians converging towards the Earth’s poles. ICON also enables better reproduction of the complex and detailed Alpine topography of Switzerland. The new formulation of the flow equations allows the use of steeper mountain slopes than the COSMO model could cater for. The resulting, more detailed modelling of the surface also helps to improve the model predictions. The new nesting option in ICON (i.e. the possibility of calculating individual areas with a higher spatial resolution in the model calculation) carries the benefit of using the computing power in a targeted way, thus reducing the operating costs of the model. Since 2016, MeteoSwiss has also been the first weather service in the world to run an operational weather model (COSMO) on a graphics-card (GPU) based computer structure. Because of the lower hardware and energy costs associated with GPUs, ICON is also being optimised for operation on this basis under the ICON-22 project.

Research projects involving ICON: GLORI-A and EXCLAIM

The ICON model framework brings next-generation weather modelling to Switzerland and forms the basis of research projects in which MeteoSwiss plays a significant contributory role within the international ICON developer community. These primarily consist of advancements in forecasting performance that will improve weather and impact forecasting, as well as the user-friendliness of the output data.

Conducted at the ETH Centre for Climate Systems Modelling (C2SM), the EXCLAIM project is developing an exascale computing and data platform for weather and climate modelling based on the ICON model, which is able to model the regional to global atmosphere-land-ocean system at a far higher spatial resolution than has previously been possible.

The GLORI-A (GLObal to Regional ICON Alpine Digital Twin) project is working on a configurable, high-resolution digital twin based on ICON’s predictive capabilities. GLORI-A will enable users and decision-makers to access customised forecasting products for applications such as flood, air quality and energy production forecasting. This “on demand” functionality combines weather and impact forecasting and can be configured by users to suit their individual needs.

COSMO and ICON: The successful international cooperation continues

The development of the ICON model goes back some 20 years and has been driven primarily by the German Meteorological Service and the Max Planck Institute for Meteorology. The ICON developer community, of which MeteoSwiss is also a member, has grown steadily since its inception and is now much larger than the COSMO consortium, since it not only consists of national weather services but also research institutions. This successful international cooperation is fundamental to the operation and further development of the highly complex ICON Model Framework. ICON enables weather forecasting based on next-generation science and technology and therefore serves as a reliable basis for decision-making in Swiss society.