Improvement of large-scale circulation simulation in an ocean-sea ice model with high-resolution

The impact of the resolution on the large-scale features in an ocean-sea ice coupled model (CAS-LICOM3) is represented in this paper through three aspects. Firstly, 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. Secondly, 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 AMOC, enhance temperature and salinity distributions, which further improve large-scale circulation. Subsurface improvements near 300 m are linked to better 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 little impact on the temporal variability of phenomena such as ENSO, IOD, PDO, and AMO, the refined resolution enhances the strengths of their variabilities.