| Summary: | This paper is the first part of a twofold contribution dedicated to the new version of the Louvain-la-Neuve sea ice model LIM3. In this part, LIM3 is described and its results are compared with observations. LIM3 is a C-grid dynamic–thermodynamic model, including the representation of the subgrid-scale distributions of ice thickness, enthalpy, salinity and age. Brine entrapment and drainage as well as brine impact on ice thermodynamics are explicitly included. LIM3 is embedded into the ocean modelling system NEMO, using OPA9, a hydrostatic, primitive equation, finite difference ocean model in the 2° × 2°cos configuration ORCA2. Model performance is evaluated by performing a hindcast of the Arctic and Antarctic sea ice packs, forced by a combination of daily NCEP/NCAR reanalysis data and various climatologies. The annual cycle of sea ice growth and decay is very realistically captured with ice area, thickness, drift and snow depth in good agreement with observations. In the Arctic, the simulated geographical distributions of ice thickness and concentration are significantly improved when compared with earlier versions of LIM. Model deficiencies feature an overestimation (underestimation) of ice thickness in the Beaufort gyre (around the North Pole) as well as an underestimation of ice thickness in the Southern Ocean. The simulated first year/multiyear sea ice limit agrees with observations. The values and distribution of sea ice age in the perennial ice zone are different from satellite-derived values, which is attributed to the different definitions of ice age. In conclusion, in light of the exhaustive sea ice analysis presented here, LIM3 is found to be an appropriate tool for large-scale sea ice and climate simulations.
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