[MITgcm-support] only eta as open boundary ?

[Jean-Michel Campin]

Hi Kaveh,

I think there has been some discussions you can find in the support archive:
For instance, when I type "eta at OBCS" on the MTgcm seach tool,
the 1rst one that come up:
 http://mitgcm.org/pipermail/mitgcm-support/2005-October/003491.html
contains some relevant information for your case.
And just to repeat it, the way OBC are implemented in MITgcm is that
the flow is prescribed (or computed, e.g. if using Orlanski) at the OB
and the pressure gradient accross the OB does not enter the equations.

Cheers,
Jean-Michel

On Mon, Feb 01, 2016 at 10:56:38AM +0100, kaveh Purkiani wrote:
> Dear Martin,
> 
> I tried with all values larger than 0, 1 to 4, none of them could help this
> to solve.
> I will have a look at documentation again and report you back soon.
> 
> Kaveh.
> 
> On Mon, Feb 1, 2016 at 10:45 AM, Martin Losch <Martin.Losch at awi.de> wrote:
> 
> > I suggest to read the documentation to learn about the parameters
> > necessary for the nonlinear free surface:
> > <http://mitgcm.org/public/r2_manual/latest/online_documents/node42.html>
> > where you will see, that ???1??? is not the appropriate choice for
> > nonlinFreeSurf
> >
> > Also, did you find a verification example with obcs and nonlinear free
> > surface? I suggest verifcation/exp4/input.nlfs
> >
> > Martin
> >
> > > On 01 Feb 2016, at 10:35, kaveh Purkiani <kavehpurkiani at googlemail.com>
> > wrote:
> > >
> > > Dear Martin,
> > >
> > > I use nonlinearFreesurf in my configuration similar to as sinusoidal
> > elevation (simple M2) at BC. Also the  nonlinFreeSurf = 1 at data namelist.
> > > Should not this work? and show non-zero elevation inside the model as
> > well as boundaries?
> > >
> > > The method for converting the elevation into bartropic velocities seems
> > to work, but I wanted to apply a realistic condition to the model (
> > components of M2, M4, S2 and O1 ) therefore, using eta BC seems to be more
> > accurate.
> > >
> > > regards
> > >
> > > Kaveh.
> > >
> > >
> > > On Mon, Feb 1, 2016 at 10:23 AM, Martin Losch <Martin.Losch at awi.de>
> > wrote:
> > > Kaveh,
> > >
> > > you probably use a linear free surface in your model configuration? With
> > a ***linear*** free surface, the open boundary conditions for Eta have no
> > effect (basically, there are none to be specified). But your method of
> > converting the elevation into bartropic velocities seems to work, doesn???t
> > it?
> > >
> > > Otherwise you need to use a non-linear free surface, which will make the
> > experiment more complicated.
> > >
> > > Martin
> > >
> > > > On 30 Jan 2016, at 20:50, kaveh Purkiani <kavehpurkiani at googlemail.com>
> > wrote:
> > > >
> > > > Hi MITgcm users,
> > > >
> > > > I have been trying to use eta as the only boundary condition in
> > > > a configuration.
> > > >
> > > > below you see the relative part of configuration regarding the bcs at
> > data and data.obcs
> > > >
> > > > data
> > > >
> > > >  periodicExternalForcing=.TRUE.,
> > > >  externForcingPeriod=900.,
> > > >  externForcingCycle =43200.,
> > > >  &
> > > >
> > > >
> > > > data.obcs
> > > >
> > > >  OBCSfixTopo=.FALSE.,
> > > >  OB_Jnorth= 80*-1,
> > > >  OB_Jsouth= 80*1,
> > > >  OB_Ieast = 42*-1,
> > > >  OB_Iwest = 42*1,
> > > >  useOBCSprescribe = .TRUE.,
> > > >
> > > >  OBNetaFile = 'OBNeta.bin', (Nx,time)
> > > >  OBSetaFile = 'OBSeta.bin', (Nx,time)
> > > >  OBWetaFile = 'OBWeta.bin', (Ny,time)
> > > >  OBEetaFile = 'OBEeta.bin', (Ny,time)
> > > >
> > > > The boundary conditions are obviously read in (only at boundaries
> > output shows identical to what is prescribed as boundary condition),
> > > >  but they are not applied inside the domain. Except the boundaries,
> > rest of the domain does not show any elevation.
> > > >
> > > > When I convert the sea surface elevation (eta) into barotropic
> > velocity and prescribe the OB(N,S,E,W)(u,v) and no elevation at boundaries,
> > it works
> > > > properly, with meaningful eta, zonal and meridional values.
> > > >
> > > > I appreciate any suggestions.
> > > >
> > > > regards,
> > > >
> > > > Kaveh.
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > _______________________________________________
> > > > MITgcm-support mailing list
> > > > MITgcm-support at mitgcm.org
> > > > http://mitgcm.org/mailman/listinfo/mitgcm-support
> > >
> > >
> > > _______________________________________________
> > > MITgcm-support mailing list
> > > MITgcm-support at mitgcm.org
> > > http://mitgcm.org/mailman/listinfo/mitgcm-support
> > >
> > > _______________________________________________
> > > MITgcm-support mailing list
> > > MITgcm-support at mitgcm.org
> > > http://mitgcm.org/mailman/listinfo/mitgcm-support
> >
> >
> > _______________________________________________
> > MITgcm-support mailing list
> > MITgcm-support at mitgcm.org
> > http://mitgcm.org/mailman/listinfo/mitgcm-support
> >

> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-support