[MITgcm-support] MITgcm-support Digest, Vol 167, Issue 21

Jody Klymak jklymak at uvic.ca
Wed May 24 10:23:37 EDT 2017 

> 
> @Jody: Can I force the boundary with Orlanski using the OBCStides option? Further, for  wave generation, shouldn't prescribing the tidal forcing only at the boundaries not generate waves since there is a phase lag within the domain and all regions won't experience the same velocity at the same time.

I’m not sure about the OBCSTides option.  I think that may work.

If you have open boudnaries, where you have to prescribe the velocity *and* a body force, they won’t match perfectly, and the generated surface wave will have some standing wave components.  I don’t think there is any benefit to also specifying a body force, and in fact only confusion will result.  The only time I’d specify a body force was when I had a periodic domain or if I was forcing a closed basin.

No matter what you do, all regions won’t experience the same velocity at the same time.  The barotropic velocity is set by the surface wave and that takes a finite amount of time to propagate.  on the other hand, the wavelength is often long compared to any region of interest, so the barotropic velocity is near constant.

Cheers,   Jody


> 
> -Hanut
> 
> 
> On Wed, May 24, 2017 at 1:03 PM, <mitgcm-support-request at mitgcm.org <mailto:mitgcm-support-request at mitgcm.org>> wrote:
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> Today's Topics:
> 
>    1. Tidal forcing with Orlanski boundary conditions.
>       (Hanut Vemulapalli)
>    2. Re: Tidal forcing with Orlanski boundary  conditions. (Jody Klymak)
>    3. Re: Tidal forcing with Orlanski boundary  conditions.
>       (Jean-Michel Campin)
>    4. Re: ideal age tracer (Alexandre Pohl)
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Tue, 23 May 2017 22:42:29 +0530
> From: Hanut Vemulapalli <hanut2 at gmail.com <mailto:hanut2 at gmail.com>>
> To: mitgcm-support at mitgcm.org <mailto:mitgcm-support at mitgcm.org>
> Subject: [MITgcm-support] Tidal forcing with Orlanski boundary
>         conditions.
> Message-ID:
>         <CAC9SbcbjP_WKpSiWP_p=KGw7+HXv5E3qgvuPQyxL0XwhECbtHg at mail.gmail.com <mailto:KGw7%2BHXv5E3qgvuPQyxL0XwhECbtHg at mail.gmail.com>>
> Content-Type: text/plain; charset="utf-8"
> 
> Hi all,
> 
> I am trying to simulate gravity waves produced by a gaussian topography in
> uniform stratificaiton. I have a 2D simulation with unit depth in the
> y-coordinate. I am giving tidal forcing to the model in
> code/external_forcing.F by adding the following lines .
> 
> DO j=0,sNy+1
>   DO i=1,sNx+1
>           gU(i,j,kLev,bi,bj) = gU(i,j,kLev,bi,bj) +
> 0.02*0.00014*cos(0.00014*myTime)
>   ENDDO
> ENDDO
> 
> 
> I am prescribing Orlanski boundary condition at the east and west
> boundaries.
> However, the velocity magnitude tends to very small values of the order
> 1E-5 times the tidal amplitude (i.e 1E-12) once I prescribe open boundary
> condition at the east and west boundaries.
> Can anyone tell me where I am going wrong.
> 
> Thanks in advance.
> 
> Best regards
> Hanut
> 
> 
> 
> 
>   <https://mailtrack.io/ <https://mailtrack.io/>> Sent with Mailtrack
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> 
> ------------------------------
> 
> Message: 2
> Date: Tue, 23 May 2017 10:27:21 -0700
> From: Jody Klymak <jklymak at uvic.ca <mailto:jklymak at uvic.ca>>
> To: mitgcm-support at mitgcm.org <mailto:mitgcm-support at mitgcm.org>
> Subject: Re: [MITgcm-support] Tidal forcing with Orlanski boundary
>         conditions.
> Message-ID: <64DBA29B-9BBC-4315-B5E9-3854BBD74356 at uvic.ca <mailto:64DBA29B-9BBC-4315-B5E9-3854BBD74356 at uvic.ca>>
> Content-Type: text/plain; charset="utf-8"
> 
> Hi Hanut,
> 
> The boundary conditions need to be altered to force the flow through them as well.  Orlanski will allow a mode-1 wave to pass, but without modification will set the barotropic velocity to zero.  The body force should still move the water around in the interior, but your boundary conditions will be set to zero barotropic flow.  I think ye olde internal wave examples modify `calc_obcs.F`, but you don?t need to do this anymore.
> 
> For a radiating internal wave problem I recommend using obcs or rbcs and force a sponged velocity at the boundaries, and I do not use orlanski etc.  The sponge needs to be wide and gentle enough to absorb internal waves without reflection.
> 
> An example setup (with steady forcing, but how to setup oscilatory forcing should be clear from `gendata.py`) is at
> 
> https://github.com/jklymak/MITgcmExampleSteadyGauss <https://github.com/jklymak/MITgcmExampleSteadyGauss> <https://github.com/jklymak/MITgcmExampleSteadyGauss <https://github.com/jklymak/MITgcmExampleSteadyGauss>>
> 
> I think you can use the external forcing of the boundary with Orlanski BC instead of a sponge.
> 
> I think you can also do all this with a body force as well, but you would want to be sure that your body force and BC forcing are in sync.
> 
> If your domain is long compared to the surface tidal wave, you may also want to lag one end of the domain relative to the other to allow the tidal waves to be in sync.
> 
> Cheers,   Jody
> 
> 
> 
> in data &PARAM03:
> 
> `
> 
> # Forcing for boundary condition files
>  periodicExternalForcing=.TRUE.,
> # 1/12th M2 tidal period...
>  externForcingPeriod = 3720.,
> # one tidal period (12 records need to be in OBEuFile, etc)
>  externForcingCycle = 44640.,
> `
> 
> and in data.obcs:
> 
> `
> 
> # Open-boundaries
>  &OBCS_PARM01
>  OB_Iwest=1*1,
>  OB_Ieast=1*-1,
>  OB_Jnorth=80*0,
>  OB_Jsouth=80*0,
>  useOBCSsponge=.TRUE.,
>  useOBCSprescribe=.TRUE.,
>  OBEuFile = 'Ue.bin',
>  OBWuFile = 'Uw.bin',
>  OBEtFile = 'Te.bin',
>  OBWtFile = 'Tw.bin',
>  /
> 
> # Orlanski parameters
>  &OBCS_PARM02
> /
> 
> # Sponge layer parameters
>  &OBCS_PARM03
>  Urelaxobcsinner=1000.,
>  Urelaxobcsbound=100.,
>  Vrelaxobcsinner=1000.0,
>  Vrelaxobcsbound=100.0,
>  spongeThickness=10,
>  /`
> 
> 
> 
> 
> 
> > On May 23, 2017, at  10:12 AM, Hanut Vemulapalli <hanut2 at gmail.com <mailto:hanut2 at gmail.com>> wrote:
> >
> > Hi all,
> >
> > I am trying to simulate gravity waves produced by a gaussian topography in uniform stratificaiton. I have a 2D simulation with unit depth in the y-coordinate. I am giving tidal forcing to the model in code/external_forcing.F by adding the following lines .
> >
> > DO j=0,sNy+1
> >   DO i=1,sNx+1
> >           gU(i,j,kLev,bi,bj) = gU(i,j,kLev,bi,bj) + 0.02*0.00014*cos(0.00014*myTime)
> >   ENDDO
> > ENDDO
> >
> >
> > I am prescribing Orlanski boundary condition at the east and west boundaries.
> > However, the velocity magnitude tends to very small values of the order 1E-5 times the tidal amplitude (i.e 1E-12) once I prescribe open boundary condition at the east and west boundaries.
> > Can anyone tell me where I am going wrong.
> >
> > Thanks in advance.
> >
> > Best regards
> > Hanut
> >
> >
> >
> >
> >  ?  <https://mailtrack.io/ <https://mailtrack.io/>>Sent with Mailtrack <https://mailtrack.io/install?source=signature&lang=en&referral=hanut2@gmail.com&idSignature=22 <https://mailtrack.io/install?source=signature&lang=en&referral=hanut2@gmail.com&idSignature=22>>_______________________________________________
> > MITgcm-support mailing list
> > MITgcm-support at mitgcm.org <mailto:MITgcm-support at mitgcm.org>
> > http://mitgcm.org/mailman/listinfo/mitgcm-support <http://mitgcm.org/mailman/listinfo/mitgcm-support>
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> ------------------------------
> 
> Message: 3
> Date: Tue, 23 May 2017 14:36:22 -0400
> From: Jean-Michel Campin <jmc at mit.edu <mailto:jmc at mit.edu>>
> To: mitgcm-support at mitgcm.org <mailto:mitgcm-support at mitgcm.org>
> Subject: Re: [MITgcm-support] Tidal forcing with Orlanski boundary
>         conditions.
> Message-ID: <20170523183622.GA30290 at ocean.mit.edu <mailto:20170523183622.GA30290 at ocean.mit.edu>>
> Content-Type: text/plain; charset=us-ascii
> 
> Hi Hanut,
> 
> Subroutines in external_forcing.F have been retired since Aug 2014
> and replaced with the ones in apply_forcing.F
> They are just kept in case someone has a customized version and want
> to keep it (and in this case, need to compile with #define USE_OLD_EXTERNAL_FORCING
> in CPP_OPTIONS.h). Are you in this case ?
> 
> Cheers,
> Jean-Michel
> 
> On Tue, May 23, 2017 at 10:42:29PM +0530, Hanut Vemulapalli wrote:
> > Hi all,
> >
> > I am trying to simulate gravity waves produced by a gaussian topography in
> > uniform stratificaiton. I have a 2D simulation with unit depth in the
> > y-coordinate. I am giving tidal forcing to the model in
> > code/external_forcing.F by adding the following lines .
> >
> > DO j=0,sNy+1
> >   DO i=1,sNx+1
> >           gU(i,j,kLev,bi,bj) = gU(i,j,kLev,bi,bj) +
> > 0.02*0.00014*cos(0.00014*myTime)
> >   ENDDO
> > ENDDO
> >
> >
> > I am prescribing Orlanski boundary condition at the east and west
> > boundaries.
> > However, the velocity magnitude tends to very small values of the order
> > 1E-5 times the tidal amplitude (i.e 1E-12) once I prescribe open boundary
> > condition at the east and west boundaries.
> > Can anyone tell me where I am going wrong.
> >
> > Thanks in advance.
> >
> > Best regards
> > Hanut
> >
> >
> >
> >
> >   <https://mailtrack.io/ <https://mailtrack.io/>> Sent with Mailtrack
> > <https://mailtrack.io/install?source=signature&lang=en&referral=hanut2@gmail.com&idSignature=22 <https://mailtrack.io/install?source=signature&lang=en&referral=hanut2@gmail.com&idSignature=22>>
> 
> > _______________________________________________
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> > MITgcm-support at mitgcm.org <mailto:MITgcm-support at mitgcm.org>
> > http://mitgcm.org/mailman/listinfo/mitgcm-support <http://mitgcm.org/mailman/listinfo/mitgcm-support>
> 
> 
> 
> 
> ------------------------------
> 
> Message: 4
> Date: Wed, 24 May 2017 09:39:46 +0200
> From: Alexandre Pohl <pohl at cerege.fr <mailto:pohl at cerege.fr>>
> To: mitgcm-support at mitgcm.org <mailto:mitgcm-support at mitgcm.org>
> Subject: Re: [MITgcm-support] ideal age tracer
> Message-ID: <D4AF3406-1AD2-4D6E-8954-0472AA41F675 at cerege.fr <mailto:D4AF3406-1AD2-4D6E-8954-0472AA41F675 at cerege.fr>>
> Content-Type: text/plain; charset=us-ascii
> 
> Hi Jean-Michel,
> 
> Thank you for your answer. I will take a look at these files, to see if it is feasible make such an ideal age tracer work with the dic pkg.
> 
> I think that it would be really helpful to have this output to interpret changes in oxygen concentration in the ocean between different model runs.
> 
> Cheers,
> Alexandre
> 
> 
> ------------------------------
> 
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> 
> 
> End of MITgcm-support Digest, Vol 167, Issue 21
> ***********************************************
> 
> 
> 
> -- 
> Hanut Vemulapalli
> Btech Undergraduate
> Aerospace Engineering
> IIT-Madras
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> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-support

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