[MITgcm-support] On the set up of the OBCS volume conservation in a regional simulation with curvilinear grid

[Martin Losch]

Hi Chengyan,

AngelCS/SN are the cos/sin of the angle the grid makes with geographical north.The velocities are still aligned with the grid, so that **only if** you want velocities in the zonal and meridional direction you need to rotate them.

The same combination of variables (as you noted) describe the flux through the open boundary conditions in any grid.

If you want to use velocities from a polar spherical grid as open boundary conditions for a general curvilinear grid that is not aligned with the meridians and parallels, then you need to rotate these velocities into the direction of the curvilinear grid (which is given locally by AngleCS/SN).

Does that make sense?

Martin

> On 27. Aug 2019, at 04:27, whale <250107302 at qq.com> wrote:
> 
> Dear friends,
> I am a little confused by the setting of volume conservation in a regional simulation.
> I had set up a regional model in Prydz Bay based on the spherical grid (usingSphericalPolarGrid=.TRUE.,). By following the suggestion in historical emails, the volume conservation can be set as follows:
> V*DRF*DXG*hFacS；U*DRF*DYG*hFacW; Here, the volume calculated by these flux at the OBCS should be 0 to keep the volume conservation;
> Now, I want to set up a regional model based on the curvilinear grid (usingCurvilinearGrid=.TRUE.). As I see, the velocity in the curvilinear grid are rotated by the AngleCS/SN.data files. So, I am a little confused with what should I do with the velocity field applied at the OBCS. Should I rotate the velocity fields applied at the OBCS to keep the volume conservation in a curvilinear grid simulation. Or, Should I just apply the velocity filed as what I had did in the spherical grid simulation, and the model can adjust the velocity fields by itself.
> Cheers
> Chengyan
>  
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