[MITgcm-support] Questions about the OBCS Package

[Matthew Mazloff]

Hi Benjamin

i) The state will simply be prescribed on the open boundary. 

ii) sorry, I don’t use it


I’m not sure your setup — you could provide more info. But most likely my advice will be to make a restoring region that is perhaps 10 cells thick and has a bathymetry with no gradient normal to the boundary. (That way you will not be forcing a normal flow that immediately has divergence from topographic gradients.) Prescribe the normal flow and T and S (and SSH if necessary for your setup) that you want. Set tangential flow to 0 and have a restoring on this tangential flow, which will damp the open boundary waveguide. 

These things I am suggested are intended to limit unphysical vertical flows. 

Open boundaries are no fun,
Matt



> 
> On Jun 10, 2016, at 9:45 AM, Benjamin Ocampo <rurik at ualberta.ca> wrote:
> 
> Hi All:
> 
> I have a couple questions about the OBCS package with regards to
> regional modelling at the poles:
> 
> i)   If I do not use Orlanski, Stevenson or Sponge configuration
>      with the OBCS package, what method or algorithm does 
>      OBCS use to simulate Open Boundary Conditions (OBC)?
> 
> ii)  Although I have read [Orlanski, 1976], I am still a little bit 
>      confused with the paper. As far as my understanding goes, 
>      the Orlanski OBC solves for the time dependent phase speed 
>      C of the fluid characteristic variable phi at grid points lying on 
>      (N-1) where N is the index locating the horizontal boundary
>      sets the C at horizontal boundaries so long as C is b/w some
>      range. Algorithm wise, what are the advantages and
>      disadvantages of using the Orlanski configuration? When is
>      the Orlanski configuration appropriate to use.
> 
> Cheers,
> Benjamin
>              
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