[MITgcm-support] SSH drift with sponge-OBCS & OBCSbalance

[Matthew Mazloff]

Hi Yang

I have never seen SSH be unbalanced with 
OBCSbalance = true
How slow is the drift? Could it be associated with something else (e.g. freshwater or heat forcing)?

Regarding " have the bathy gradient normal to the wall = 0 in the sponge; turn off tangential velocity; making the corners in the sponge layer have depth 0”
These are not really for balance. These are to prevent a spurious wave guide, spurious mixing, and forced divergence at the boundary.

Matt



> On Apr 12, 2019, at 8:49 AM, yang zhibin <853245241 at qq.com> wrote:
> 
> Hi all,
> 
> Recently I am running a regional model with OBCS. For the purpose of volum balance, I use OBCSbalance. However, there still exist SSH drift (though slow). 
> I checked the previous maillist and found a similar question about five years ago (http://mailman.mitgcm.org/pipermail/mitgcm-support/2014-July/009288.html). Thanks to the reply of previous modeler on this question.
> In that mail, Mattew gave a complex process to solve this problem (e.g. have the bathy gradient normal to the wall = 0 in the sponge; turn off tangential velocity; making the corners in the sponge layer have depth 0). I wonder if the zero tangential velocity could affect inner or the sponge layer? In the end, Mattew also suggest use RBCS  instead of OBCS. But could the volum balance without OBCSbalance?
> 
> Cheers,
> Yang
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