Abstract
Abstract. A set of hindcast simulations with the new version 3.6 of the Nucleus for European Modelling of the Ocean (NEMO) ocean–ice model in the ORCA1 configuration and forced by the DRAKKAR Forcing Set version 5.2 (DFS5.2) atmospheric data was performed from 1958 to 2012. Simulations differed in their sea-ice component: the old standard version Louvain-la-Neuve Sea Ice Model (LIM2) and its successor LIM3. Main differences between these sea-ice models are the parameterisations of sub-grid-scale sea-ice thickness distribution, ice deformation, thermodynamic processes, and sea-ice salinity. Our main objective was to analyse the response of the ocean–ice system sensitivity to the change in sea-ice physics. Additional sensitivity simulations were carried out for the attribution of observed differences between the two main simulations.In the Arctic, NEMO-LIM3 compares better with observations by realistically reproducing the sea-ice extent decline during the last few decades due to its multi-category sea-ice thickness. In the Antarctic, NEMO-LIM3 more realistically simulates the seasonal evolution of sea-ice extent than NEMO-LIM2. In terms of oceanic properties, improvements are not as evident, although NEMO-LIM3 reproduces a more realistic hydrography in the Labrador Sea and in the Arctic Ocean, including a reduced cold temperature bias of the Arctic Intermediate Water at 250 m. In the extra-polar regions, the oceanographic conditions of the two NEMO-LIM versions remain relatively similar, although they slowly drift apart over decades. This drift is probably due to a stronger deep water formation around Antarctica in LIM3.
Highlights
Sea ice is an important part of Earth’s climate system because it effectively regulates the amount of energy being transferred between the atmosphere and oceans (Vaughan et al, 2013)
Nucleus for European Modelling of the Ocean (NEMO)-la-Neuve Sea Ice Model (LIM) simulations started from the state of no motion in January 1958, with initial conditions for ocean temperature and salinity derived from Polar Hydrographic Climatology version 3 (PHC3) (Steele et al, 2001), and ended in December 2012
Grid forced by the DFS5.2 atmospheric data
Summary
Sea ice is an important part of Earth’s climate system because it effectively regulates the amount of energy being transferred between the atmosphere and oceans (Vaughan et al, 2013). The impacts of the Arctic warming on lower latitudes are masked by the large internal climatic variability and the detection of robust signals is very difficult due to relatively short time series of reliable observational data (Koenigk and Brodeau, 2016). These observational shortcomings can partly be overcome by analysing long climate model experiments, which optimally should incorporate the most realistic sea-ice models to minimise the model uncertainty
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