Assessing the new version of the CMCC Global Ocean Reanalysis System (C-GLORS)

Over the past decade, CMCC has focused on developing state-of-the-art global ocean reanalyses that can be suited for diverse purposes, from climate studies to initialization of forecasting systems and downscaling applications. The robustness of the C-GLORS series on key oceanic variables has been demonstrated through its participation in numerous reanalysis inter-comparison projects and is continuously monitored as part of the GREP ensemble product (GLOBAL_MULTIYEAR_PHY_ENS_001_031) within the CMEMS catalogue. The latest consolidated version, C-GLORSv8, spans the altimetry era from 1993 to the present. The same spatial resolution as version 7 is preserved, alongside substantial upgrades. New advances consider the use of hourly ERA5 atmospheric reanalysis, the inclusion of a sea-level spatial unbias scheme, a new multi-category sea-ice model and a bivariate SIC/SIT assimilation system.

The new product shows a reduced temperature bias within the upper 1500m, leading to a more accurate depiction of global ocean heat content.  The new configuration has a lower error in sea-level anomaly, and a more realistic representation of the salinity field in the Southern Ocean, especially during the pre-argo era. Furthermore, the new system shows higher surface eddy activity and a more realistic surface eddy kinetic energy field, leading to an improved representation of mesoscale dynamics. In addition, the system demonstrates enhanced ocean convection and a more accurate representation of sea ice extent at both poles, including a reduced low bias in Southern Hemisphere sea ice volume.