[MITgcm-support] Strange U-velocity and V-velocity on North, East

[Martin Losch]

Hi Camille,

I think there is nothing to worry about. 

I think you can write OB_Jsouth = 170*1,30*0, (if your first 170 grid points are water and the last 30 grid points are land), and similar for OB_Iwest, if you want to get rid of the artifacts in surface_temp.png, but they won’t do any harm.
The artifacts in surface_zonal_velocity.png, surface_meridional_velocity.png are also harmless. I assume that you are using the mnc package (netcdf). When the velocity fields are “exchanged”, ie, when the halos are updated (I am dropping the k-dimension here), U(1,:) is copied to U(Nx+1,:), and V(:,1) is copied to V(:,Ny+1). mnc writes U(1:Nx+1,:) and V(:,1:Ny+1), so that you see part of the halo. This may not be too useful for non-periodic boundary conditions, but is useful in other cases.

Martin

> On 17 Mar 2017, at 10:53, Camille Mazoyer <mazoyer at univ-tln.fr> wrote:
> 
> Dear all,
> 
> I'm wondering if my OBCs are well imposed. Could you advice me about it. In attach, u and v surface velocity  and surface temperature for a given time. I also give you the depth in my area, so you can have an idea of the masks variables.
> 
> The OBC are only in South and West, as you can see on the depth file.
> 
> My grid is NX:200, NY: 100, NZ:75. In data.obcs, I write OB_Jsouth = 200*1 and OB_Iwest = 100*1, so I imposed on OBC also on land. I know this is not the best way, but I had problems to impose it correctly. So I thought they won't be fluxes on land thanks to the mask vairables, and I will be ok like this. Do you think It's ok?
> 
>  1 # Open-boundaries
>    2  &OBCS_PARM01
>    3
>    4  OBCSfixTopo=.TRUE.,
>    5  OB_Jsouth = 200*1,
>    6  OB_Iwest = 100*1,
>    7
>    8  useOBCSprescribe = .TRUE.,
>    9  useOBCSsponge = .TRUE.,
>   10
>   16  useOBCSbalance = .TRUE.,
>   18  OBCS_balanceFacW =1,
>   19  OBCS_balanceFacS =1,
>   20
> 
> However, I have a strange velocities behaviour. In attached, you can see surface velocities for a given time. I see an east zonal velocity on land and I don't explain it. It's the same behaviour for meridional north velocity. Does anyone have an idea about what's going on?
> 
> Just to be sure, could you confirm it:
> 
> - in my case, dimensions binaries files for West OBC are NY x Nz x NTIMES for all variables
> 
> - in my case, dimensions binaries files for South OBC are NX x Nz x NTIMES for all variables
> 
> As the velocities are staggered, as you said this week in http://mitgcm.org/pipermail/mitgcm-support/2017-March/010924.html, I imposed for Western boundary (NY x Nz x NTIMES) arrays:
> 
> U(i=2,j=1:NY,k=1:NZ)
> 
> V(i=1,j=2:NY+1,k=1:NZ)
> 
> Temp, Sal (i=1,j=1:NY,k=1:NZ)
> 
> Thanks for your help,
> 
> Camille
> 
> 
> -- 
> ------------------------------------------
> Camille Mazoyer
> Phd Student
> Mediterranean Institute of Oceanography (MIO)
> Institut de Mathématiques de Toulon (IMATH)
> Université de TOULON
> Bat X - CS 60584
> 83041 TOULON cedex 9
> France
> tel: +33.4.94.14.24.50
> Email: mazoyer at univ-tln.fr
> http://mio.pytheas.univ-amu.fr/
> http://imath.fr/
> 
> <grid.png><surface_temp.png><surface_zonal_velocity.png><surface_meridional_velocity.png>_______________________________________________
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