[MITgcm-support] is Orlanski radiation condition working in the rotating rank of MITgcm?

[Yi-Chih Huang]

Hello Martin,

    I am using the curvilinear coordinate on the rotating_tank for
latitudes 75N-90N by applying the old grids on MITgcm_contrib/arctic40km/
and MITgcm_contrib/arctic/cs_4km.  Generally, the numerical disturbances
occurred around the lateral boundary and moved back to the center of the
domain.  Thus, the default lateral boundary condition does not seem to be
good enough to handle these disturbances.  My experiences with Orlanski
radiation condition were really good.  Therefore, I updated b.c. by
adding obcs in code/packages.conf and having a run/data.obcs as I showed
earlier.  Although no error messages about boundary condition are in the
logfiles of execution, the output patterns are almost exactly the same as
the original one.  If my updating processes for b.c. was wrong, what else
should I do to make it working?

    By the way, I will change the radius of the planet.  Those old gids on
MITgcm_contrib/arctic40km/ and MITgcm_contrib/arctic/cs_4km will not be
suitable for my work on curvilinear coordinates accordingly.  Can I change
the radius of the planet and focus on latitudes 75N-90N by working on the
grids of CS or LLC?  I know very little about them.

    Thanks,

          Yi-Chih

Date: Fri, 14 Dec 2018 13:50:11 +0100
From: Martin Losch <Martin.Losch at awi.de>
To: MITgcm Support <mitgcm-support at mitgcm.org>
Subject: Re: [MITgcm-support] is Orlanski radiation condition working
        in the rotating rank of MITgcm?
Message-ID: <CABCD918-87C9-43E4-9B04-053E15DE67EF at awi.de>
Content-Type: text/plain; charset="utf-8"

Hi Yi-Chih,

I can only guess what you are trying to do: You use the
verification/rotating_tank setup, you probably change f0 from 0.5 to
something more ?polar?, e.g. 1.45e-4 for a latitude of 85.5 degN, but then
your grid spacing needs to be adjusted (from the lab-scales in the original
rotating_tank experiment), etc ? There are many places, where you may not
satify stability criteria. See here <
https://mitgcm.readthedocs.io/en/latest/examples/examples.html> for
examples of stability criteria in other tutorial experiments.

Introducing open boundary conditions to get rid of grid scale noise is not
a good idea. Normally open boundar condition tend to be more of a problem
than a solution.

Martin

On Fri, Dec 14, 2018 at 8:27 AM Yi-Chih Huang <dscpln at gmail.com> wrote:

> Dear MITgcm experts,
>
>     I ran into numerical disturbances around the boundary working on the
> rotating rank of MITgcm in the Arctic regions.  I tried to apply Orlanski
> radiation condition to the rotating rank in data.obcs below.  However, the
> patterns with the data.obcs are almost the same as the original one.
> There is no error message in the log files.  Do you think Orlanski
> radiation condition is working in the rotating rank of MITgcm?  How should
> I update the boundary conditions on MITgcm?
>
> # Open-boundaries
>  &OBCS_PARM01
>  OB_Ieast=102*-1,
>  OB_Iwest=102*1,
>  OB_Jnorth=130*-1,
>  OB_Jsouth=130*1,
>  useOrlanskiEast=.TRUE.,
>  useOrlanskiWest=.TRUE.,
>  useOrlanskiNorth=.TRUE.,
>  useOrlanskiSouth=.TRUE.,
> # useOBCSbalance=.TRUE.,
> # OBCS_balanceFacW= 1.,
> # OBCS_balanceFacN= 0.,
>  OBCS_monitorFreq=3000.,
>  &
>
>  &OBCS_PARM02
>  CMAX=0.5,
>  cvelTimeScale=10000.,
>  useFixedCEast=.FALSE.,
>  useFixedCWest=.FALSE.,
>  &
>
>     Thanks much,
>
>                Yi-Chih
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.mitgcm.org/pipermail/mitgcm-support/attachments/20181214/2e2f8e73/attachment.html>