[MITgcm-devel] momentum OBCS implemetation

[Menemenlis, Dimitris (3248)]

Jean-Michel, suggestion is good.
Go ahead and change seaice_obcs

Cheers

Dimitris Menemenlis

On Apr 29, 2011, at 8:11 AM, Jean-Michel Campin wrote:

> Hi,
> 
> I did some changes last month (once again) in OBCS implementation for 
> tracer, using maskInC,W,S in pkg/generic_advdiff/ S/R for all the 
> wider-stencil scheme (assuming zero gradient beyond the OB), 
> so that the calls to OBCS_COPY_TRACER (that I added last November !)
> are no longer needed (just removed yesterday).
> 
> The main motivation for this is that it's cleaner (e.g., for biharmonic diffusion), 
> the OB border-line can be more general (concave interior) with OB closer to 
> each-other (Olx grid-points separation instead of 2xOlx) and it can be extended 
> to the momentum whereas the OBCS_COPY_TRACER approach is more difficult for U,V.
> 
> Going to apply the same idea to the momentum, starting with biharmonic 
> viscosity (& leaving the 4th Order coriolis for later).
> In short, the changes are (like zero gradient beyond the OB):
> - to multiply divergence (& tension) by maksInC
> - to multiply horiz. grad of vorticity by maskInW/S
> Additional changes are needed in mom_calc_visc.F (Leith & Smagorinsky)
> but even the changes outside mom_calc_visc will already affects the computed 
> viscosity. So I was going to check-in these changes all at once.
> 
> From early tests, it seems that the effects of these changes from the computed 
> viscosity (Leith) are of the same order that the one from biharmonic viscosity.
> 
> The debug parameter I added (OBCS_uvApplyFac) should allow to confirm
> that the results no longer depend on normal-component being applied 
> to the 2nd grid-point (=beyond the OB).
> 
> But one issue with those changes is that very few test-exp are currently
> testing momentum wider-stencil scheme with OBCS (in fact, only dome results
> are affected). Would be good to test biharmonic diffusivity (un-tested),
> constant biharmonic visc (in flux-form) and zStar could be added to the list.
> I propose to:
> - slightly change exp4 (add Non-Hydrostatic and small viscA4)
> - add 2nd exp4 test with zStar (and time-varying OBC ?), but not yet ready.
> And was thinking of adding small diffK4T,diffK4S into seaice_obcs to
> test biharmonic diffusivity. Other exp using OBCS are not as good test,
> either 2-D or starting with weak T,S horiz gradient or don't have the 
> 4 types of OB (N,S,E,W).
> Dimitris, is it OK with you ? (and in this case would add a comment line 
>  next to these 2 param in seaice_obcs/input/data); 
> or should I add a secondary test ? (But is it worth to have 2 tests with so 
> little differences in parameter list ?).
> 
> Cheers,
> Jean-Michel
> 
> 
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