The Impact of Abyssal Mixing Parameterizations in an Ocean General Circulation Model

Abstract

A parameterization of vertical diffusivity in ocean general circulation models has been implemented in the ocean model component of the Community Climate System Model (CCSM). The parameterization represents the dynamics of the mixing in the abyssal ocean arising from the breaking of internal waves generated by the tides forcing stratified flow over rough topography. This parameterization is explored over a range of parameters and compared to the more traditional ad hoc specification of the vertical diffusivity.Diapycnal mixing in the ocean is thought to be one of the primary controls on the meridional overturning circulation and the poleward heat transport by the ocean. When compared to the traditional approach with uniform mixing, the new mixing parameterization has a noticeable impact on the meridional overturning circulation; while the upper limb of the meridional overturning circulation appears to be only weakly impacted by the transition to the new parameterization, the deep meridional overturning circulation is significantly strengthened by the change. The poleward ocean heat transport does not appear to be strongly affected by the mixing in the abyssal ocean for reasonable parameter ranges. The transport of the Antarctic Circumpolar Current through the Drake Passage is related to the amount of mixing in the deep ocean. The new parameterization is found to be energetically consistent with the known constraints on the ocean energy budget.

The Norwegian Earth System Model, NorESM1-M – Part 1: Description and basic evaluation of the physical climate

“…Further, a portion of the energy extracted from the mean flow by the bottom drag is used to drive diapycnal mixing (Legg et al, 2006). Tidally driven diapycnal mixing is parameterized according to Simmons et al (2004) using the estimated tidal energy dissipation by Jayne (2009).…”

The Finite Element Sea Ice-Ocean Model (FESOM) v.1.4: formulation of an ocean general circulation model

“…Concentrating intense mixing above rough topography where major tidal energy dissipates was found to be preferable for representing deep ocean stratification and Southern Ocean heat uptake in climate models (Saenko, 2006;Exarchou et al, 2013). The model sensitivity study by Jayne (2009) shows that using the tidal mixing parametrization proposed by St Laurent et al (2002) can significantly enhance the deep cell of the meridional overturning circulation (MOC) in comparison with only using an ad hoc background vertical diffusivity, although the upper cell of the MOC and the poleward heat transport (the often used diagnostics for adjudging climate models) are not strongly affected by this parametrization. Present climate and earth system models tend to use the St Laurent et al (2002) parametrization instead of the Bryan and Lewis (1979) type of background diffusivity (e.g.…”

Variability of the Turbulent Kinetic Energy Dissipation along the A25 Greenland–Portugal Transect Repeated from 2002 to 2012

“…In the formulation Eq. (2), k is an adjustable parameter (Jayne and St. Laurent 2001;Jayne 2009). As Jayne and St. Laurent (2001) stressed, Eq.…”