The North Atlantic mean state in eddy-resolving coupled models: a multimodel study

Ocean mesoscale structures, which are parameterized in standard resolution models, play an important role in featuring global ocean dynamics. Here we study the effects of increasing model ocean resolution to eddy-resolving scales on the representation of the North Atlantic mean state, by comparing an ensemble of four HighResMIP coupled historical simulations with nominal ocean resolutions of at least 1/10° – corresponding to the models CESM1-CAM5-SE-HR, EC-Earth3P-VHR, HadGEM3-GC31-HH, and MPI-ESM1-2-ER – to a baseline of 39 Coupled Model Intercomparison Project phase 6 (CMIP6) simulations at coarser resolution. Despite a warm and salty bias at the surface, we find generally improved vertical stratification in the Labrador (LS) and western Irminger Seas (IS) in the high resolution ensemble, leading to stronger deep water convection in that region, in closer agreement with observations. Both the overturning and barotropic circulations of the North Atlantic present significant improvements in the eddy-resolving models: the Atlantic Meridional Overturning Circulation (AMOC) is weaker than for lower resolution models and closer to RAPID observations; the paths, strength, and structure of the Gulf Stream (GS), North Atlantic Current (NAC), and subpolar gyre (SPG) are also improved, resulting into reduced surface temperature and salinity biases north of Cape Hatteras (NCH) and in the Central North Atlantic (CNA).