The tidal effects in the Finite-volumE Sea ice–Ocean Model (FESOM2.1): a comparison between parameterised tidal mixing and explicit tidal forcing

Abstract

Abstract. 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.

The Role of Tidal Mixing in Shaping Early Eocene Deep Ocean Circulation and Oxygenation

“…Since the seminal work of Munk (1966), great efforts have been made to understand what controls diapycnal mixing in the ocean interior (e.g., MacKinnon et al., 2017; Munk & Wunsch, 1998; St. Laurent & Garrett, 2002) and to refine the parameterizations of vertical diffusivity in ocean general circulation models (GCM) (e.g., Bryan & Lewis, 1979; de Lavergne et al., 2020; Gargett, 1984; Jayne, 2009; Melet et al., 2016; Saenko & Merryfield, 2005; Schmittner & Egbert, 2014; Simmons et al., 2004; Song et al., 2023). Recent work has comprehensively reviewed what is currently known about the role of ocean mixing in the climate system (de Lavergne et al., 2022; Melet et al., 2022; Whalen et al., 2020) and, in particular, the contribution of different internal wave processes (e.g., near‐field and far‐field internal tide dissipation, lee wave dissipation and wind‐induced near‐inertial wave energy dissipation) to the total mixing.…”

Quantifying numerical mixing in a tidally forced global eddy-permitting ocean model

“…Improvements in fidelity resulting from the inclusion of tidal forcing in OGCMs have also been found outside ice-covered regions. Song et al (2023) compared global implementations of the Finite-volumE Sea ice-Ocean Model (FESOM2.1) with and without explicit tidal forcing, concluding that tides strengthened both the upper and lower cells of the global overturning circulation, as well as the Antarctic Circumpolar Current (ACC). Katavouta et al (2022) reported a marked improvement in the representation of critical water masses in a regional 1/12 • model of the Indonesian Archipelago when tides were present.…”