Icosahedral non-hydrostatic model at Institute of Atmospheric Physics

The ICON-IAP model is a non-hydrostatic and compressible global atmospheric model and is based on an icosahedral grid. In such a setting, the Earth surfaces is tessalated into a hexagons and 10 pentagons. The areas of those grid boxes vary only slightly over the globe. In contrast, grid boxes of a geographical coordinate systme would become very small near the poles and give rise to numerical problems. The C-grid discretization of ICON-IAP allows for a good numerical representation of gravity waves. The model contains simple parameterizations for moist physics and turbulence. Some options are available for artifical forcings (Held-Suarez-forcing). The horizontal momentum diffusion is treated with a traditional Smagorinsky scheme in dependence on the local wind shear.

Innovative aspects of ICON-IAP numerics are

  • the fulfillment of conservations laws for mass and energy due to the usage of discrete Poisson brackets
  • the fulfillment of the linear dependency of overspecified horizontal wind components in the hexagonal C-grid (3 instead of 2 horizontal wind components)
  • the treatment of subgrid-scale terms under consideration of the second law of thermodynamics (positive internal entropy production)

Applications of the ICON-IAP model at IAP are

  • the study of propagation and breaking of gravity waves at small scales (2D model version)
  • the analysis of general atmospheric dynamics (imbalance and stratified macroturbulence)


An extensive model documentation is here and details on the implementation of three-dimensional turblence are here.