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--></style></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoPlainText>Hi Martin and Jean-Michel, <o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>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. <o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>My current implementation is the same as suggested in the old post (<a href="http://mailman.mitgcm.org/pipermail/mitgcm-support/2012-October/008012.html">http://mailman.mitgcm.org/pipermail/mitgcm-support/2012-October/008012.html</a>). 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. <o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>Thanks,<o:p></o:p></p><p class=MsoPlainText>Yilang<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText>On 4/12/19, 12:03, "MITgcm-support on behalf of Jean-Michel Campin" <mitgcm-support-bounces@mitgcm.org on behalf of jmc@mit.edu> wrote:<o:p></o:p></p><p class=MsoPlainText><o:p> </o:p></p><p class=MsoPlainText> Hi Yilang,<o:p></o:p></p><p class=MsoPlainText> <o:p></o:p></p><p class=MsoPlainText> Did you try, for each passive tracer "iTr":<o:p></o:p></p><p class=MsoPlainText> OBCS_u1_adv_Tr(iTr) = 1,<o:p></o:p></p><p class=MsoPlainText> This will force to use 1rst Order upwind advection-scheme at OB location <o:p></o:p></p><p class=MsoPlainText> but only in the case of an outflow. This could help the passive tracer to<o:p></o:p></p><p class=MsoPlainText> leave the domain without accumulating.<o:p></o:p></p><p class=MsoPlainText> An example can be found here:<o:p></o:p></p><p class=MsoPlainText> verification/so_box_biogeo/input/data.obcs<o:p></o:p></p><p class=MsoPlainText> <o:p></o:p></p><p class=MsoPlainText> Cheers,<o:p></o:p></p><p class=MsoPlainText> Jean-Michel<o:p></o:p></p><p class=MsoPlainText> <o:p></o:p></p><p class=MsoPlainText> On Fri, Apr 12, 2019 at 09:41:44AM +0200, Martin Losch wrote:<o:p></o:p></p><p class=MsoPlainText> > Hi Yilang,<o:p></o:p></p><p class=MsoPlainText> > <o:p></o:p></p><p class=MsoPlainText> > 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”.<o:p></o:p></p><p class=MsoPlainText> > <o:p></o:p></p><p class=MsoPlainText> > 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><o:p></o:p></p><p class=MsoPlainText> > <o:p></o:p></p><p class=MsoPlainText style='text-indent:10.5pt'>> If that doesn’t help you’ll probably have to try to implement Orlanski BC’s for passive tracers …<o:p></o:p></p><p class=MsoPlainText> > <o:p></o:p></p><p class=MsoPlainText> > Martin<o:p></o:p></p><p class=MsoPlainText> > <o:p></o:p></p><p class=MsoPlainText> > > On 11. Apr 2019, at 21:51, Yilang Xu <yxu@whoi.edu> wrote:<o:p></o:p></p><p class=MsoPlainText> > > <o:p></o:p></p><p class=MsoPlainText> > > Hi everyone, <o:p></o:p></p><p class=MsoPlainText> > > <o:p></o:p></p><p class=MsoPlainText> > > 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<o:p></o:p></p><p class=MsoPlainText> > > (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. <o:p></o:p></p><p class=MsoPlainText> > > <o:p></o:p></p><p class=MsoPlainText> > > 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. <o:p></o:p></p><p class=MsoPlainText> > > I wonder if there is any solution to this problem. Appreciate your help. <o:p></o:p></p><p class=MsoPlainText> > > <o:p></o:p></p><p class=MsoPlainText> > > Thanks,<o:p></o:p></p><p class=MsoPlainText> > > Yilang<o:p></o:p></p><p class=MsoPlainText> > > _______________________________________________<o:p></o:p></p><p class=MsoPlainText> > > MITgcm-support mailing list<o:p></o:p></p><p class=MsoPlainText> > > MITgcm-support@mitgcm.org<o:p></o:p></p><p class=MsoPlainText> > > http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support<o:p></o:p></p><p class=MsoPlainText> > <o:p></o:p></p><p class=MsoPlainText> > _______________________________________________<o:p></o:p></p><p class=MsoPlainText> > MITgcm-support mailing list<o:p></o:p></p><p class=MsoPlainText> > MITgcm-support@mitgcm.org<o:p></o:p></p><p class=MsoPlainText> > http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support<o:p></o:p></p><p class=MsoPlainText> _______________________________________________<o:p></o:p></p><p class=MsoPlainText> MITgcm-support mailing list<o:p></o:p></p><p class=MsoPlainText> MITgcm-support@mitgcm.org<o:p></o:p></p><p class=MsoPlainText> http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support<o:p></o:p></p><p class=MsoPlainText> <o:p></o:p></p><p class=MsoPlainText> <o:p></o:p></p></div></body></html>