ICON (weather forecast model)

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The ICON model (short for icosahedral non-hydrostatic , English for "icosahedral non-hydrostatic") is a computer program that the German Weather Service (DWD) uses to create global weather forecasts . The weather model was developed jointly by the DWD and the Max Planck Institute for Meteorology .

Name and basic principles

To create the ICON calculation grid, an icosahedron is placed in the globe, the sides of which are subdivided until the desired mesh size of 13 km is reached.

The name ICON refers to two basic properties of the program: It regards the atmosphere as a non- hydrostatic fluid and uses a computational grid , which is based on an icosahedron imagined in the earth . By dividing the twenty faces of the icosahedron over and over again, a fine-meshed grid of triangles is created that spans the entire globe. Specifically, the German Weather Service currently uses almost 3 million such triangular grid cells for its global weather forecast, which corresponds to a mesh size of around 13 km. In each of these triangles, ICON solves the non-hydrostatic equations at 90 different altitudes. This results in a total of approximately 265 million grid points. The advantage of the icosahedral grid is that all grid cells are roughly the same size, which is not the case with a conventional grid (e.g. based on the geographic coordinate system ) (since the length of the parallels decreases towards the poles).

For the calculation of a 7-day forecast, the program on the mainframe computer of the DWD needs about an hour and produces about 900  gigabytes of data. For each grid point worldwide, it concerns air density and (potential) temperature (derived from the air pressure ), wind speed and direction , water vapor , cloud water , cloud ice, rain and snow as well as over land temperature and soil water and ice content for seven layers of soil. These properties are to be regarded as mean values ​​for the entire respective grid cell.

meaning

According to its own information, the German Weather Service is only one of fourteen weather services worldwide that operate such a global weather model. Other weather services use so-called section models that only model a specific region. However, such models are always dependent on the data of a global model. The DWD also uses the data from ICON as a “drive” ( boundary conditions ) for its ocean wave model, the RLM weather model of the German Armed Forces and the ICON-EU Europe section, which is itself based on ICON . The latter in turn provides the boundary conditions for the COSMO-DE model , which covers Germany, Austria and Switzerland with a higher resolution of 2.8 km.

history

ICON is a joint project of the German Weather Service and the Max Planck Institute for Meteorology (MPI-Met) in Hamburg. While the DWD uses the model as an operational weather model, the MPI uses it as a climate model . ICON's predecessor is GME (Global Model Europe), which was operational from 1999 and was replaced by ICON in January 2015 . A few months later in June 2015, the Europe section ICON-EU replaced the COSMO-EU that had been used until then .

Web links

literature

  • Günther Zängl, Daniel Reinert, Pilar Rípodas, Michael Baldauf: The ICON (ICOsahedral Non ‐ hydrostatic) modeling framework of DWD and MPI ‐ M: Description of the non ‐ hydrostatic dynamical core. In: Quarterly Journal of the Royal Meteorological Society . 141, 2015, ISSN  0035-9009 , pp. 563-579 ( doi: 10.1002 / qj.2378 ).