[MITgcm-support] Behavior of Ptracers at Orlanski boundary

[Jean-Michel Campin]

Hi Yilang,

Did you try, for each passive tracer "iTr":
 OBCS_u1_adv_Tr(iTr) = 1,
This will force to use 1rst Order upwind advection-scheme at OB location 
but only in the case of an outflow. This could help the passive tracer to
leave the domain without accumulating.
An example can be found here:
 verification/so_box_biogeo/input/data.obcs

Cheers,
Jean-Michel

On Fri, Apr 12, 2019 at 09:41:44AM +0200, Martin Losch wrote:
> Hi Yilang,
> 
> I think that your only way out is to change the boundary conditions for the passive tracers. You obviously read this old post. Now you know what I mean by ???keep your fingers crossed???.
> 
> As a quick fix, I usually try to use some approximate v.Neumann BC, but that???s already implemented in the example given in the old post <http://mailman.mitgcm.org/pipermail/mitgcm-support/2012-October/008012.html>
> 
> If that doesn???t help you???ll probably have to try to implement Orlanski BC???s for passive tracers ???
> 
> Martin
> 
> > On 11. Apr 2019, at 21:51, Yilang Xu <yxu at whoi.edu> wrote:
> > 
> > Hi everyone, 
> >  
> > As MITgcm suggests, the implementation of Orlanski OBCS and Ptracers together is not recommended by the current version of the code. Following some previous discussions
> > (e.g., http://mailman.mitgcm.org/pipermail/mitgcm-support/2012-October/008012.html), I comment out the part that stops the model in obcs_calc.F and obcs_check.F. 
> >  
> > As a result, the model behaves well until the ptracer reaches the Orlanski boundary. I notice the occurrence of instability or aggregation of ptracer when it comes near boundary cells. 
> > I wonder if there is any solution to this problem. Appreciate your help. 
> >  
> > Thanks,
> > Yilang
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> 
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