Updated sea ice code and atmospheric forcing improve the Antarctic summer sea ice of an ocean model

The ocean and sea ice play an important role in the Antarctic climate system, and the atmosphere plays an important role in forcing the sea ice and the ocean. A better understanding of these interactions is needed to understand recent changes and anticipate future changes in the Antarctic. ​ We present a regional ocean model MetROMS-UHel for a quarter-degree resolution domain of the Antarctic Ocean. MetROMS-UHel is based on the MetROMS-Iceshelf model that uses ROMS (Regional Ocean Modeling System), with ocean-ice shelf thermodynamics. For the sea ice, MetROMS-Iceshelf uses CICE (Community Ice CodE) 5.1.2., while MetROMS-UHel has been updated to CICE 6.3.1. We run both models with two different atmospheric forcings, ERA-Interim (ECMWF Re-Analysis ERA-Interim from 1992 to 2018) and ERA5 (ECMWF Reanalysis v5 from 1992 to 2023). The atmospheric reanalysis plays an important role in the results, and this way we see which changes are due to the updated sea-ice model and which are from the updated atmospheric forcing. The models simulate the interannual variability of the Antarctic sea ice extent reasonably well. The sea ice extent is similar for all model runs and close to observed in all seasons except JFM. In JFM the extent varies between the models especially in the Ross and Weddell Seas, with the largest, and closest to observed extent produced by the MetROMS-UHel CICE 6, ERA5 run. Important watermasses are well represented by the models, with cold waters being slightly fresher in the MetROMS-UHel runs.