[MITgcm-support] ptracer and default boundary conditions

[Daniel Goldberg]

Hello Jody

On Fri, Apr 7, 2017 at 8:50 PM, Jody Klymak <jklymak at uvic.ca> wrote:

> 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
>

as i understood it, this is what matt said would happen by default (matt
said it is Neumann by default). this would cause the domain to fill up with
the tracer over time, as there is an internal source. i do not want this!!!!

in a simulation with OBCS prescribing e.g. salt and velocities, outgoing
velocity will remove salt from the domain. this is what i want. from what
matt said, i need to specify OBCS files for the tracer as i would for salt,
and set them uniformly to zero. i have done this, and will see if it works..

thanks
dan


> 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> 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>
>> 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 <dgoldber at mit.edu>an.Goldberg at ed.ac.uk
>> web: 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 <dgoldber at mit.edu>an.Goldberg at ed.ac.uk
> web: http://ocean.mit.edu/~dgoldberg
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>
> --
> Jody Klymak
> http://web.uvic.ca/~jklymak/
>
>
>
>
>
>
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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 <dgoldber at mit.edu>an.Goldberg at ed.ac.uk
web: http://ocean.mit.edu/~dgoldberg
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