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

[Camille Mazoyer]

Hi Martin,

Thanks for your fast answer.

Le 17/03/2017 à 14:32, Martin Losch a écrit :
> 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.
Ok, I will try your advice. I already tried it, but maybe I didn't write 
it as you propose, and I writed it with a bug.
So If I write OB_Jsouth = 170*1,30*0, I give (170,NZ) arrays for all 
variables on south OBC. Is that right?
> The artifacts in surface_zonal_velocity.png, surface_meridional_velocity.png are also harmless. I assume that you are using the mnc package (netcdf).
Yes, i'm using it.
> 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.
Ok I understand it better now. Thanks a lot.


Camille
>
> 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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>
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-- 
------------------------------------------
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/