Meridional heat transport in the North Atlantic: Effects of ocean and atmosphere grid resolutions in FOCI-OpenIFS-AGRIF 3.0

Abstract. We present results of a new coupled climate model configurations named FOCI-OpenIFS-AGRIF 3.0. Advancing from the Flexible Ocean and Climate Infrastructure version 1 (FOCI1, Matthes et al., 2020), the new configuration employs the OpenIFS atmosphere model for improved computational scaling at high grid resolutions. Moreover, a novel coupling technique is developed to enable direct exchange of surface fluxes between an embedded zoom in the ocean model (AGRIF) and the atmosphere component through the coupler in addition to the coupling between the global atmosphere and global ocean. We discuss major differences between three configurations: one with low resolution in ocean (1/2^◦, 25–50 km) and in atmosphere (∼100 km), one with the refined 1/10^◦ (5–10 km) ocean grid in the North Atlantic but still low resolution atmosphere, and a third one with additionally globally enhanced atmosphere resolution at ∼31 km and 50% more vertical levels. The regionally eddy-rich ocean yields an improved North Atlantic Current path and enhanced northward volume and heat transport simulating a stronger subpolar gyre. Increasing the atmospheric resolution to better match the refined ocean grid yields larger winter heat loss over the subpolar North Atlantic thereby reducing the ocean heat transport into the Nordic Seas despite an unaltered volume transport compared to the configuration with only enhanced ocean resolution. We conclude that just increasing ocean grid resolution shifts meridional heat transport from the atmosphere to the ocean in the North Atlantic region. For a realistic balance between ocean and atmosphere transport matching grid resolutions are required to properly simulate heat exchange at subpolar latitudes.