[MITgcm-support] Adding a strictly westward advective velocity on the LLC grids

[Martin Losch]

Hi Julian,

did you get an answer to this?

On the model grid I would compute the advective fluxes on the grid in both directions (i and j, or u and v). Then there are the fields AngleCS and AngleSN which contain the cos/sin of the angle of the “grid north” (i.e. the j-direction) with geographical north. These angles are for the cell centres, the advective fluxes are for the cell interfaces, so some interpolation is required, I guess.
The westward direction would be: flxugrid * AngleCS + flxvgrid * AngleSN. Similarly the northward direction would (-flxugrid*AngleSN + flxvgrd*AngleCS)  (and as usual I never know about the sign of the sin-term, could be the other way around).

Does that answer your question?

Martin

> On 26. Oct 2021, at 10:16, Julian Mak <jclmak at ust.hk> wrote:
> 
> Dear MITgcm users/developers,
> 
> Probably a niche question: I have something I am looking to advect on the LLC
> grid (in this case some parameterised energy at the depth mean velocity and
> westward by the Rossby phase speed). To my understanding (please correct if I am
> wrong) the depth mean velocity is essentially trivial to construct, and
> computing the relevant advective tendencies on the center grid points is just
> the usual procedures. But is there an easy way to make sure that I construct a
> velocity field that is strictly westwards for the Rossby wave part on the LLC
> grid? Failing that, any guidance on what routines to look into would be
> appreciated.
> 
> Best wishes,
> Julian
> 
> -- 
> Julian Mak,
> Department of Ocean Science,
> Hong Kong University of Science and Technology,
> Clearwater Bay,
> Hong Kong
> e-mail: jclmak at ust.hk
> www: https://julianmak.github.io/
> _______________________________________________
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> MITgcm-support at mitgcm.org
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