[MITgcm-support] Behavior of Ptracers at Orlanski boundary

[Yilang Xu]

Hi Martin and Jean-Michel, 

 

Thanks very much for your advice. I set up a test case and add " OBCS_u1_adv_Tr(1) = 1," in data.obcs, but the plot behaves the same as the case does without it. Generally, the problem is that the ptracer starts to accumulate to a large number after it reaches the Orlanski boundary. I am trying to use ptracer to mimic salt. They behave relatively in a similar way except for the cells near the boundary. I have attached a vertical slice of the ptracer for demonstration. 

 

My current implementation is the same as suggested in the old post (http://mailman.mitgcm.org/pipermail/mitgcm-support/2012-October/008012.html). Ptracer is resotred by RBCS on a small surface area, and " OBCS_u1_adv_Tr(1) = 1," is the only ptracer-related line in data.obcs (but this did not change any behavior). I am wondering what could be improved if I want to advect the ptracer out properly. Implementing Orlanski BC for ptracers could be a choice in the future. 

 

Thanks,

Yilang

 

 

On 4/12/19, 12:03, "MITgcm-support on behalf of Jean-Michel Campin" <mitgcm-support-bounces at mitgcm.org on behalf of jmc at mit.edu> wrote:

 

    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

    > > _______________________________________________

    > > MITgcm-support mailing list

    > > MITgcm-support at mitgcm.org

    > > http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support

    > 

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