Abstract
Abstract. The second part of the assessment and evaluation of the unstructured-mesh Finite-volumE Sea ice–Ocean Model version 2.0 (FESOM2.0) is presented. It focuses on the performance of partial cells and embedded sea ice and the effect of mixing parameterisations available through the Community Vertical Mixing (CVMix) package. It is shown that partial cells and embedded sea ice lead to significant improvements in the representation of the Gulf Stream and North Atlantic Current and the circulation of the Arctic Ocean. In addition to the already existing Pacanowski and Phillander (fesom_PP) and K-profile (fesom_KPP) parameterisations for vertical mixing in FESOM2.0, we document the impact of several mixing parameterisations from the CVMix project library. Among them are the CVMix versions of Pacanowski and Phillander (cvmix_PP) and K-profile (cvmix_KPP) parameterisations; the tidal mixing parameterisation (cvmix_TIDAL); a vertical mixing parameterisation based on turbulent kinetic energy (cvmix_TKE); and a combination of cvmix_TKE and the recent scheme for the computation of the Internal Wave Dissipation, Energy, and Mixing (IDEMIX) parameterisation. IDEMIX parameterises the redistribution of internal wave energy through wave propagation, non-linear interactions and the associated imprint on the vertical background diffusivity. Further, the benefit from using a parameterisation of Southern Hemisphere sea ice melt season mixing in the surface layer (MOMIX) for reducing Southern Ocean hydrographic biases in FESOM2.0 is presented. We document the implementation of different model components and illustrate their behaviour. This paper serves primarily as a reference for FESOM users but is also useful to the broader modelling community.
Highlights
Global unstructured-mesh ocean models start to be widely used in climate studies, including the recent CMIP6 simulations (Semmler et al, 2020), structured-mesh ocean general circulation models are still more mature in terms of features, functionality and complexity due to their long development history
This paper describes the two new features introduced into FESOM2.0 – partial cells and embedded sea ice – and the implementation of the vertical mixing library Community Vertical Mixing (CVMix), together with the elaboration of the effect of melt season mixing in the surface layer (MOMIX)
These new features expand the functionality of FESOM2.0, its applicability and its ability to be better compared to other state-of-the-art ocean general circulation models
Summary
Global unstructured-mesh ocean models start to be widely used in climate studies, including the recent CMIP6 simulations (Semmler et al, 2020), structured-mesh ocean general circulation models are still more mature in terms of features, functionality and complexity due to their long development history. It parameterises the wind-driven mixing in the Southern Ocean, especially when there is insufficient mixing during the melt seasons when other mixing schemes are used It is used in FESOM2.0 to improve the otherwise too low stratification in the Southern Ocean and Weddell Sea. The intention of this paper is to document the performance of the newly implemented features, i.e. partial bottom cells, embedded sea ice, the vertical mixing parameterisations that come with the implementation of CVMix, and the local mixing parameterisation of Timmerman and Beckmann (2004), based on comparing the associated hydrographic biases, changes in vertical convection and differences in the meridional overturning circulation using a relatively coarse reference mesh.
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