[MITgcm-support] Questions about MITgcm setup

[Jean-Michel Campin]

Hi Kaushal,

I just came back from vacations so I did not have a chance to answer your email before.
In general, for this type of question, I would recommend to send it 9after subscribing)
to the mitgcm-support list, since others might have encountered similar problem ir have 
good suggestions.

Anyway, regarding this:
> Is MITgcm's setup periodic in the x and the y direction?
Yes, unless you are using Open-boundary conditions (pkg/obcs). And if there is a row or column
of land-points, this will close the domain and the periodicity will be irrelevant.

And for this part:
> Why do I get the correct answer for simulation B. 
I am not sure if, in this case, you have included or not a row of land point (i.e., zero depth) 
in your bathymetry file. So not clear to me.

> I see that the value of USidDrag at both y=0 and y=Ly are not zero. How do I implement free-slip at both the northern and the southern boundaries but no-slip at the eastern and the western boundaries?

The safest way would be to change/customize the code instead of relying on "thin-wall" + no_slip_sides=T,
because the fact that "thin-wall" does not work for no_slip_sides BC does not mean that it
behaves as a free-slip BC.

Cheers,
Jean-Michel

On Thu, Jun 06, 2024 at 09:36:45PM +0000, Kaushal Gianchandani wrote:
> Hello Jean-Michel
> 
> I had a few questions regarding the option of including thin walls in MITgcm simulations. I am playing with the barotropic gyre example in MITgcm, and I want to implement freeslip at the southern boundary (y=0) and the northern boundary (y=Ly) and no slip on the sides.  In the Params.h file, it states that the thin walls can be specified using the addSwallFile. I did 2 simulations:
> 
>   1.
> I specified a 2d array in the addSwallFile that has 1s at both the first and last index in the y direction.  When I look at the velocity fields, I see that the U field has non-zero values in at the southern edge (y=0) but the values at the northern edge (y=Ly) look like random noise.
>   2.
> I specified a 2d array in the addSwallFile that has 1s only at the first index in the y direction (at y=0).  The U fields at y=0 and y=Lx are identical in this case.
> 
> 
> Here are my questions:
> 
>   1.
> Why do I get the correct answer for simulation B. Is MITgcm's setup periodic in the x and the y direction?
>   2.
> I see that the value of USidDrag at both y=0 and y=Ly are not zero. How do I implement free-slip at both the northern and the southern boundaries but no-slip at the eastern and the western boundaries?
> 
> I will really appreciate your help regarding this. Thank you.
> 
> Kind regards,
> Kaushal.