Improvement of a Large-Scale Circulation Simulation in an Ocean-Sea Ice Model with High Resolution

The impact of resolution on the large-scale features in an ocean-sea ice coupled model (CAS-LICOM3) is communicated in this paper through three aspects. First, a refined resolution accelerates temperature and salinity drifts at a basin-averaged scale by facilitating exchanges among basins, subsequently reducing global-averaged drifts. This amplification of basin-scale exchanges is associated with an accelerated large-scale circulation, leading to a more rapid equilibration of temperature and salinity near 200 meters. Second, the refined resolution yields improved simulations of large-scale temperature, salinity, and currents, particularly evident in regions such as the Gulf Stream and its extension. Positive feedback mechanisms, such as improved undercurrents and a stronger Atlantic Meridional Ocean Circulation (AMOC), enhance temperature and salinity distributions, further improving the large-scale circulation. Subsurface improvements near 300 m are linked to improved simulations of equatorial undercurrents, Gulf Stream dynamics, and the Deep Western Boundary Current, leading to a more realistic representation of AMOC and high-latitude deep-water formation. However, limitations in vertical resolution may obscure finer-scale improvements in subsurface and deep-ocean processes. Despite having little impact on the temporal variability of phenomena such as ENSO, Indian Ocean Dipole (IOD), PDO, and AMO, the refined resolution enhances the strengths of their variabilities.