Coupled model development (ECHAM5-FESOM)
A new global coupled climate model has recently been established at AWI. The atmospheric component is the general circulation model ECHAM5 developed at the Max Planck Institute for Meteorology (MPI) whereas the ocean and sea-ice module is represented by the Finite-Element Sea-Ice Ocean Model (FESOM).
Figure 1: Average mean sea level pressure [hPa] for the months December-February (DJF) as simulated by ECHAM5-FESOM.
In contrast to more traditional climate models we hereby try a new approach by coupling an ocean model based on unstructured meshes to an atmospheric component based on regular grids. This is a non-trivial technical task and has been achieved by means of both a regular exchange mesh (on the ocean side) and the parallel OASIS4 coupler. Since coastlines are defined differently in the ocean and atmospheric part, a pattern interpolation technique conserving net fluxes has been applied in the coupling procedure.
The new climate model supports variable resolution ocean meshes. Thus it allows to resolve key regions like the North Atlantic, the tropics, coastlines or narrow straits without involving additional nesting techniques.
Figure 2: Average mean sea level pressure [hPa] for the months June-August (JJA) as simulated by ECHAM5-FESOM.
With the help of such coupled setup we aim to improve current climate predictions, study the response to the Greenland ice-sheet melting, reveal impacts of the El Niño-Southern Oscillation (ENSO) onto a global climate and to improve our understanding of atmosphere-ocean feedbacks. The unconventional setup of ECHAM5-FESOM is also eminently suited to answer the questions to the role of mesh resolution and different coupling strategies in simulating the climate state.
The current setup is being validated on multidecadal time scales. First simulations suggest that the model provides in most cases both a reasonable mean climate state (see figures 1 and 2 for the average mean sea level pressure) and the climate variability within the spread of other models.