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We developed a new version of the Alfred Wegener Institute Climate Model (AWI-CM3), which has higher skills in representing the observed climatology and better computational efficiency than its predecessors. Its ocean component FESOM2 (Finite-volumE Sea ice–Ocean Model) has the multi-resolution functionality typical of unstructured-mesh models while still featuring a scalability and efficiency similar to regular-grid models. The atmospheric component OpenIFS (CY43R3) enables the use of the latest developments in the numerical-weather-prediction community in climate sciences. In this paper we describe the coupling of the model components and evaluate the model performance on a variable-resolution (25–125 km) ocean mesh and a 61 km atmosphere grid, which serves as a reference and starting point for other ongoing research activities with AWI-CM3. This includes the exploration of high and variable resolution and the development of a full Earth system model as well as the creation of a new sea ice prediction system. At this early development stage and with the given coarse to medium resolutions, the model already features above-CMIP6-average skills (where CMIP6 denotes Coupled Model Intercomparison Project phase 6) in representing the climatology and competitive model throughput. Finally we identify remaining biases and suggest further improvements to be made to the model. [ABSTRACT FROM AUTHOR]

The article reports that the Fifth Workshop on Systematic Errors in Weather and Climate Models was organized by Environment and Climate Change Canada under the auspices of the Working Group on Numerical Experimentation. It notes that the jointly sponsored by the Commission of Atmospheric Sciences of the World Meteorological Organization. The use of explicit simulations, such as large-eddy simulations on wide geographical domains, gives rise to new opportunities to improve parameterizations.

Existing CMIP-type climate scenario simulations are known to be vulnerable to model errors which are most noticeable in the North Atlantic. These errors are generally attributed to the imperfectness of parameterizations and the lack of ocean model resolution. However, resolving ocean mesoscales globally requires high computational resources. An alternative is to use climate models operating on unstructured meshes, allowing one to vary spatial model resolution in a way that ocean eddy dynamics is explicitly resolved only in most energetically important places. The FESOM-ECHAM climate setup offers this variable mesh functionality for the ocean. The successor version of the Finite-volumE Sea ice–Ocean circulation Model (FESOM v.2.0) has been recently released and is based on the finite volume approach with the cell centered placement of horizontal velocities (quasi-B-grid). It ensures a significant improvement in the computational performance of the ocean component (by a factor of 3 compared to the previous version). In the current work we validate the FESOM2-ECHAM climate setup using HighResMIP protocol and different ocean resolutions in the otherwise unchanged climate configurations. In particular we compare coarse and eddy-resolving ocean setups and analyze the related differences in the simulated North Atlantic climate. [ABSTRACT FROM AUTHOR]