[MITgcm-support] nonhydrostatic w boundary condition

[grisouard]

Hi everyone,

I use the OBCS package intensively for internal wave problems and always
have encountered witht these problems. I usually have been able to cope
with them rather than suppressing them. Not sure if the problems you
encounter are the same as mine, but I am quite interested in this
discussion.

I have been told a while ago that a possiblity is that these problems
arise beacause the pressure is not prescribed along with U, V, W and T/S.
I have been advised to take a look two papers, I am afraid I am not
proficient enough in numerics to know if they are relevant, may somebody
make good use of them:
http://dx.doi.org/10.1016/j.ocemod.2009.02.010 (the more relevant I think)
http://dx.doi.org/10.1175/JTECH1930.1

As a remark, I had sent a configuration (input and code directories)
involving this problem on this list on Jan 26th, without much success. My
email was probably too long, my bad.

Cheers,
Nicolas


> Thanks Martin for your response. So it looks like whenever
> INTEGR_CONTINUITY is called, w is computed via INTEGRATE_FOR_W, then
OBCS_APPLY_W applies boundary values for W.
>
> I have been trying to use sponge layer to relax interior solutions to
the boundary without much success. I am wondering the following: I have
been running model in nonhydrostatic mode WITHOUT specifying W open
boundary values. If I am not mistaken, in this configuration all OB?w
will be set to zero in OBCS_INIT_VARIABLES. Then when OBCS_APPLY_W is
called the boundary value for W obtained via continuity is replaced by
zero. Then zero would always be used for boundary values when w is
timestepped, would it not? And since there is no sponge code for W as of
yet, would this be conducive to reflections/boundary noise?
>
> Thanks,
>
> David
>
>
> Thanks
>
> On 04/19/10 02:15, Martin Losch wrote:
>> In nonhydrostatic mode, vertical velocities are still computed from
"div
>> U = 0". If the 3D pressure solver has converged perfectly, this wVel is
the same as the one obtained from stepping the w-equation. If not (in
practice you have only finite accuracy), the differences are small, and
you have to make a decision which equation you want to satisfy, dw/dt =
Gw, or delU=0. In the MITgcm, delU=0, as far as I know. However, W at
the open boundary is reset to the prescribed value (see
>> integr_continuity).
>> If (div U) is not zero, you'll generally get extra sources in the
tracer
>> equations. I bet that this will also happen along the open boundaries.
Martin
>> On Apr 16, 2010, at 7:42 PM, David Hebert wrote:
>>> In nonhydrostatic mode it looks like it is possible to prescribe all
components (u,v,w) of velocity at the boundaries. Is that right? Are
there consequences if continuity ("del dot U") is not strictly
matched?
>>> Thanks,
>>> David
>>> _______________________________________________
>>> 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
>
> --
> David A. Hebert
> Naval Research Lab
> Stennis Space Center, MS 39529
> david.hebert at nrlssc.navy.mil
> Phone: (228) 688-5846
> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-support
>


-- 
Nicolas GRISOUARD
PhD Student - ERES research group
Laboratoire des Ecoulements Geophysiques et Industriels
BP 53
38041 Grenoble cedex 9 France
tel : +33 (0)476 825 037 - fax : +33 (0)476 827 022
http://nicolas.grisouard.free.fr