ICON‐O: The Ocean Component of the ICON Earth System Model ‐ Global Simulation Characteristics and Local Telescoping Capability

We describe the ocean general circulation model Icosahedral Nonhydrostatic Weather and Climate Model (ICON-O) of the Max Planck Institute for Meteorology, which forms the ocean-sea ice component of the Earth system model ICON-ESM. ICON-O relies on innovative structure-preserving finite volume numerics. We demonstrate the fundamental ability of ICON-O to simulate key features of global ocean dynamics at both uniform and non-uniform resolution. Two experiments are analyzed and compared with observations, one with a nearly uniform and eddy-rich resolution of similar to 10 km and another with a telescoping configuration whose resolution varies smoothly from globally similar to 80 to similar to 10 km in a focal region in the North Atlantic. Our results show first, that ICON-O on the nearly uniform grid simulates an ocean circulation that compares well with observations and second, that ICON-O in its telescope configuration is capable of reproducing the dynamics in the focal region over decadal time scales at a fraction of the computational cost of the uniform-grid simulation. The telescopic technique offers an alternative to the established regionalization approaches. It can be used either to resolve local circulation more accurately or to represent local scales that cannot be simulated globally while remaining within a global modeling framework.