التفاصيل البيبلوغرافية
| العنوان: |
A Simple Eddy Potential Vorticity Flux Closure. |
| المؤلفون: |
Eden, Carsten |
| المصدر: |
Journal of Advances in Modeling Earth Systems; Oct2023, Vol. 15 Issue 10, p1-10, 10p |
| مصطلحات موضوعية: |
VORTEX motion, BAROCLINICITY, LARGE eddy simulation models, EDDIES, TURBULENCE, ATMOSPHERIC models, FRICTION |
| مستخلص: |
It is shown that within the limits of quasi‐geostrophic scaling, biharmonic mixing of potential vorticity is equivalent to biharmonic lateral friction together with biharmonic isopycnal thickness mixing in primitive equations, all with the same viscosity. The problem of unbalanced zonal forces related to the planetary vorticity gradient disappears using a biharmonic instead of a harmonic closure. The former is appropriate for eddy‐permitting ocean models which are replacing now more and more the non‐eddy‐resolving model versions in coupled state‐of‐the‐art climate models. Numerical experiments demonstrate that including biharmonic thickness mixing has some benefits regarding stronger eddy production in marginally eddying ocean models, in particular when the grid size is larger than the baroclinic Rossby radius. Going to finer grids where relative vorticity dominates, however, using only biharmonic friction becomes similar to biharmonic mixing of potential vorticity, justifying the long‐standing use of biharmonic friction in reasonably well resolved eddy‐permitting ocean models. Plain Language Summary: The fluctuating oceanic flow on scales of 50–100 km can be well described by the lateral transport of a quantity called potential vorticity, from which the transport velocity can by obtained in turn, and which is therefore sufficient to describe all important aspects of the flow. The effect of turbulence on these scales on the larger scales can therefore be described by lateral mixing of potential vorticity. This mixing effect can be implemented in ocean models which only resolve the largest scales of the turbulence—so‐called eddy‐permitting models—by relating the turbulent transport of potential vorticity fluctuations to the gradient of the Laplacian of the potential vorticity variations on the larger scales, called biharmonic mixing of potential vorticity. It is shown here that in the momentum equation of eddy‐permitting models, this biharmonic mixing of potential vorticity becomes biharmonic lateral mixing of momentum together with a term akin to vertical mixing of the Laplacian of momentum with several physical interpretations, which is here called biharmonic isopycnal thickness mixing. It is also shown in numerical experiments that including this biharmonic isopycnal thickness mixing has benefits regarding stronger and more realistic turbulence production in eddy‐permitting models on very coarse lateral grid resolution. Key Points: Biharmonic mixing of potential vorticity is equivalent to biharmonic lateral friction together with biharmonic isopycnal thickness mixing in primitive equationsIncluding biharmonic isopycnal thickness mixing allows for stronger eddy production in marginally eddying ocean modelsOn finer grids, using only biharmonic friction becomes similar to biharmonic mixing of potential vorticity [ABSTRACT FROM AUTHOR] |
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