[MITgcm-support] bottomDragQuadratic magnitude

[Martin Losch]

Hi Dong,

I don’t have a good answer for this, but keep in mind that the bottom drag will be applied as a body force to the bottom-most grid cell, i.e. there is a scaling with the grid cell width implied, so that for thin cells the drag will be smaller. To overcome this, a logarithmic law of the wall is implemented for the drag, see https://mitgcm.readthedocs.io/en/latest/algorithm/algorithm.html#vertical-dissipation, eq 2.121 and 2.122, maybe that can be useful for you. With the formulae you could also estimate the bottom drag as a function of roughness length, which may be the more universal parameter.

Martin

> On 28. May 2024, at 12:34, Dong Jian (ENV - Postgraduate Researcher) <D.Jian at uea.ac.uk> wrote:
> 
> Hi, Dear MITgcm-ers
>  
> I am wondering if anyone has experience with the choice of bottomDragQuadratic coefficient? Typical values I can refer to are bottomDragQuadratic = 1.E-3, or bottomDragQuadratic=2.5E-3.
>  
> But I am testing a regional model over very rough topography, I do find larger bottomDragQuadratic (even much larger than 2.5E-3 ) gives a closer transport and more similar circulation pattern compared with reanalysis, is there a limit value on the choice of bottomDragQuadratic?
>  
> Thanks in advance!
> Dong
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