Implementation and evaluation of open boundary conditions for sea ice in a regional coupled ocean (ROMS 3.7) and sea ice (CICE 5.1.2) modelling system.

The Los Alamos Sea Ice Model (CICE) is used by several Earth System Models where sea ice boundary conditions are not necessary, given their global scope. However, regional and local implementations of sea ice models require boundary conditions describing the time changes of the sea ice and snow being exchanged across the boundaries of the model domain. These boundary conditions include but are not limited to: (i) drift direction and velocity; (ii) concentration; (iii) thickness (of the ice and snow); (iv) thermodynamic conditions (with emphasis on sea ice and snow temperature or enthalpy); (v) salinity. The physical detail of these boundary conditions regarding, for example, the usage of different sea ice size categories or the vertical resolution of thermodynamic properties, must also be taken into account when matching them with the requirements of a specific implementation of a sea ice model. Available satellite products do not include all required fields described above. Therefore, the most straightforward way of getting sea ice boundary conditions is from a larger scale model. The main goal of our study is to describe and evaluate the implementation of time-varying sea ice boundaries in the CICE model using two regional coupled ocean-sea ice models, covering a large part of the Barents Sea and areas around Svalbard: the Barents-2.5 km, implemented at the Norwegian Meteorological Institute (MET), and the S4K, implemented at the Norwegian Polar Institute (NPI). We use the TOPAZ4 model and a Pan-Arctic 4 km-resolution model (A4) model to generate the boundary conditions for the sea ice and the ocean. The Barents-2.5 km model is MET Norway's main forecasting model for ocean state and sea ice in the Barents Sea. The S4K model covers a similar domain but it is used mainly for research purposes. Obtained results show significant improvements in the performance of the Barents-2.5 km model after the implementation of the time-varying boundary conditions. The performance of the S4K model in terms of sea ice and snow thickness is comparable to that of the TOPAZ4 system but with more accurate results regarding the oceanic component. The implementation of time-varying boundary conditions described in this study is similar regardless of the CICE versions used in different models. [ABSTRACT FROM AUTHOR]