[MITgcm-devel] changing OBC in multiDim advection

[Menemenlis, Dimitris (3248)]

Jean-Michel, does this mean that seaice obcs should
not be used with multiDim advection?

Michael is running a hi-res Pine Island Bay configuration.
He uses seaice_advscheme = 7 and he has some sea ice
artifacts at the boundary.  I would be curious to know if these
artifacts go away after you add OBCS_APPLY in seaice_advection.F

D.

On Oct 28, 2010, at 7:34 AM, Jean-Michel Campin wrote:

> Hi,
> 
> I am planning to change the OBC in multiDim advection (gad_advection.F):
> Currently: 
> 1) calculate "future" OB values (obcs_calc) at the beginning
>  of the time step.
> 2) after updating the local tracer field (in gad_advection.F) with
> X-advective flux, we apply the "future" OB value before computing 
> fluxes in Y-direction.
> 
> There is no clear reason to use, at this stage, the "future" OB value
> rather than the current OB value (i.e., corresponding to the current time step).
> And as a matter of fact, I prefer the alternative way (use current OB value)
> to compute all explicit contribution, and it's also much simpler.
> 
> One might think that using value at current-time + deltaT/2 would be 
> more accurate (would be more complicated for sure), but it's not necessary 
> the case if other than horizontal advection (e.g., forcing, vertical 
> processes) dominate the evolution of tracer near OB regions.
> 
> I propose to change step-2 to use the current OB value (instead of future 
> one). This will change the results when multi-dim is used for a tracer 
> (active or passive) which has time-varying OBC.
> 
> I did not see any "OBCS_APPLY" calls within "seaice_advection.F", 
> and propose, later on, to implement the new method (using "current 
> OB values") in seaice_advection.F.
> 
> Is it OK for everybody ?
> 
> Cheers,
> Jean-Michel
> 
> 
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