The coupled Earth-System Model ICON-ESM: developments for physical and technical coupling on unstructured grids

Coupling atmosphere and ocean models on grids with different resolution results in diverse representation of coastlines or sea ice edges. Therefore the coupling fluxes of energy, water, and momentum calculated by the sub-models can strongly deviate within one grid-point. These fluxes need specific consideration in order to connect the corresponding sub-models with respect to the physical properties. Here, we present a physical and technical solution within ICON-ESM. It was implemented by (1) using a partial land-sea-mask on the coarser (atmosphere) grid, by (2) aggregating the coupling fluxes on three parts (land, sea ice, open ocean) of each grid-point, and (3) by property-dependent selection of interpolation methods provided by the YAC-coupler.