The recently established AWI Climate Model (AWI-CM), a coupled configuration of the Finite
Element Sea Ice-Ocean Model (FESOM) with the atmospheric model ECHAM6, uses a novel
multi-resolution approach: Its ocean component builds on a finite element dynamical core
supporting unstructured triangular surface grids, allowing to distribute the grid points in a
flexible manner. This allows to concentrate resolution in dynamically important regions, with a
continuous transition zone to the coarser resolution in other areas. The model is an ideal tool to
study the influence of explicit resolution of smaller scales in dedicated experiments. The unique
– spatially seamless – approach might also be of benefit when it comes to temporally seamless
prediction, bridging the gap between numerical weather prediction and climate models.
A first benchmark set-up of AWI-CM with moderate resolution in the atmosphere (T63) and
25km in key ocean areas, e.g. around the equator, achieved a similar overall simulation
performance in a long control simulation compared to well-established CMIP5 models. In
particular, the (isotropically) increased equatorial resolution considerably increased the realism
of TIW activity and ENSO-related variability compared to standard resolutions.
The potential of AWI-CM is further exploited within the EU project PRIMAVERA in the
HighResMIP of CMIP6, where we plan to contribute simulations with eddy-resolving resolutions
(1/12° or 9-10 km) in key areas of the global ocean, such as the Gulf Stream-North Atlantic
Current region, the Agulhas retroflection zone, or the Arctic basin. First simulations show
distinct improvements with respect to the development of deep temperature and salinity biases
in the North Atlantic Ocean and an overall improvement of surface biases. At even higher
resolutions of 4.5 km locally in the Arctic, linear kinematic features emerge in the simulated sea
ice distribution with potentially strong impacts on air-sea fluxes in the coupled system. Although
the tested set-ups are computationally very demanding (with numbers of grid points
comparable to a regular 0.25° grid), the throughput is high at about 8 simulated years per day
because of high scalability. In addition, we are about to finish the development of a finite
volume version of the ocean model code (FESOM 2). It is already faster than the original FESOM
version by a factor of two to three, which will further enlarge the set of computationally feasible
applications
