Towards multi-resolution global climate modeling with ECHAM6–FESOM. Part I: model formulation and mean climate

TLDR

In principle, the multi‑resolution approach allows enhanced horizontal resolution in dynamically active regions while keeping a coarse resolution elsewhere. In this study only moderate refinement of the unstructured ocean grid is applied, with resolution varying from about 25 km in the northern North Atlantic and tropics to about 150 km in parts of the open ocean, and the results serve as a benchmark for future variable‑resolution versions. The coupled model combines ECHAM6 with the finite‑element sea ice‑ocean model FESOM, details its formulation, and describes its performance in simulating observed aspects of the mean climate. The model realistically simulates many observed climate aspects, performs at least as well as some of the most sophisticated CMIP5 models, but shares substantial shortcomings in simulating the North Atlantic circulation.

Abstract

A new climate model has been developed that employs a multi-resolution dynamical core for the sea ice-ocean component. In principle, the multi-resolution approach allows one to use enhanced horizontal resolution in dynamically active regions while keeping a coarse-resolution setup otherwise. The coupled model consists of the atmospheric model ECHAM6 and the finite element sea ice-ocean model (FESOM). In this study only moderate refinement of the unstructured ocean grid is applied and the resolution varies from about 25 km in the northern North Atlantic and in the tropics to about 150 km in parts of the open ocean; the results serve as a benchmark upon which future versions that exploit the potential of variable resolution can be built. Details of the formulation of the model are given and its performance in simulating observed aspects of the mean climate is described. Overall, it is found that ECHAM6–FESOM realistically simulates many aspects of the observed climate. More specifically it is found that ECHAM6–FESOM performs at least as well as some of the most sophisticated climate models participating in the fifth phase of the Coupled Model Intercomparison Project. ECHAM6–FESOM shares substantial shortcomings with other climate models when it comes to simulating the North Atlantic circulation.