ALBERT

Description: Tides are proved to have a significant effect on the ocean and climate. Previous modelling research either adds a tidal mixing parameterisation or an explicit tidal forcing to the ocean models. However, no research compares the two approaches in the same framework. Here we implement both schemes in a general ocean circulation model and assess both methods by comparing the results. The aspects for comparison involve hydrography, sea ice, meridional overturning circulation (MOC), vertical diffusivity, barotropic streamfunction and energy diagnostics. We conclude that although the mesh resolution is poor in resolving internal tides in most mid-latitude and shelf-break areas, explicit tidal forcing still shows stronger tidal mixing at the Kuril–Aleutian Ridge and the Indonesian Archipelago than the tidal mixing parameterisation. Beyond that, the explicit tidal forcing method leads to a stronger upper cell of the Atlantic MOC by enhancing the Pacific MOC and the Indonesian Throughflow. Meanwhile, the tidal mixing parameterisation leads to a stronger lower cell of the Atlantic MOC due to the tidal mixing in deep oceans. Both methods maintain the Antarctic Circumpolar Current at a higher level than the control run by increasing the meridional density gradient. We also show several phenomena that are not considered in the tidal mixing parameterisation, for example, the changing of energy budgets in the ocean system, the bottom drag induced mixing on the continental shelves and the sea ice transport by tidal motions. Due to the limit of computational capacity, an internal-tide-resolving simulation is not feasible for climate studies. However, a high-resolution short-term tidal simulation is still required to improve parameters and parameterisation schemes in climate studies.

Description: The continuing retreat of sea ice affects the Arctic mesoscale eddies, and its future evolution will strongly influence air-sea-ice interactions. However, knowledge of eddy activity is limited to sparse observations and coarse resolution models. How future eddies and their effects will evolve remains uncertain. Here, we apply the global unstructured model FESOM2 for 143 years of 4.5 km-Arctic simulations up to 2100 and 1 km-Arctic simulations for 5 years from 2010; 2090 to reveal the interactions between eddies, winds, sea ice and the energy budget of eddy kinetic energy (EKE) in a high resolution view. We demonstrate a significant increase in future Arctic EKE from 0-200 m, which is stronger in summer when sea ice melts. The future abundance of EKE can be explained by an increase in winter eddy generation and a decrease in summer eddy dissipation. This also leads to an enhancement of the horizontal velocity field, thus filling the Arctic Ocean with eddies in the future.