[MITgcm-support] ptracer and default boundary conditions

[Jody Klymak]

Hi Dan,

I’ve not used ptracers before. But depending on your flow, I think it might be hard to get d(u C)/dx = 0 at the boundaries.  Just based on instinct, I would use a sponge for this problem, probably using rbcs.  But maybe dC/dx = 0 is close enough for your purposes - i.e. your downstream flow doesn’t have a lot of irregularities, internal waves, etc.  

Cheers,   Jody



> On 7 Apr 2017, at  12:08 PM, Daniel Goldberg <dngoldberg at gmail.com> wrote:
> 
> many thanks matt.
> 
> going by verification/exp4, this is simply defining (for the western boundary)
> 
> OBWptrFile(1) = [filename]
> 
> correct? (I only have one tracer)
> 
> thanks
> dan
> 
> On Fri, Apr 7, 2017 at 8:03 PM, Matthew Mazloff <mmazloff at ucsd.edu <mailto:mmazloff at ucsd.edu>> wrote:
> I believe default is Neumann boundary conditions. To get what you want you need Dirichlet, so you need to prescribe an open boundary file with values all 0
> 
> -Matt
> 
> 
> 
> 
>> On Apr 7, 2017, at 11:32 AM, Daniel Goldberg <dngoldberg at gmail.com <mailto:dngoldberg at gmail.com>> wrote:
>> 
>> Hello All
>> 
>> It's my first time using ptracers. In my setup I am using OBCS at all boundaries, specifying U and V (inflow in some places, out in others). I am not using Orlanski or Stevens bc's. I want the tracer to simply be advected out with the outgoing flow, and incoming flow to have zero tracer concentration, and I have not defined any boundary files for ptracers in data.obcs. 
>> 
>> My assumption is that by default I will get this (simple outflow, no inflow), but the online ptracer documentation does not explicitly say this, so I would just like to make sure.
>> 
>> Thanks very much!
>> Dan
>> 
>> -- 
>> 
>> Daniel Goldberg, PhD
>> Lecturer in Glaciology
>> School of Geosciences, University of Edinburgh
>> Geography Building, Drummond Street, Edinburgh EH8 9XP
>> 
>> 
>> em: D <mailto:dgoldber at mit.edu>an.Goldberg at ed.ac.uk <mailto:an.Goldberg at ed.ac.uk>
>> web: http://ocean.mit.edu/~dgoldberg <http://ocean.mit.edu/~dgoldberg>_______________________________________________
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> 
> 
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> 
> 
> 
> -- 
> 
> Daniel Goldberg, PhD
> Lecturer in Glaciology
> School of Geosciences, University of Edinburgh
> Geography Building, Drummond Street, Edinburgh EH8 9XP
> 
> 
> em: D <mailto:dgoldber at mit.edu>an.Goldberg at ed.ac.uk <mailto:an.Goldberg at ed.ac.uk>
> web: http://ocean.mit.edu/~dgoldberg <http://ocean.mit.edu/~dgoldberg>_______________________________________________
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--
Jody Klymak    
http://web.uvic.ca/~jklymak/





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