[MITgcm-support] [Fwd: Auto-discard notification]

[Ed Hill]

-----Forwarded Message-----
> From: Jake Gebbie <gebbie at eps.harvard.edu>
> To: Martin Losch <mlosch at awi-bremerhaven.de>
> Cc: MITgcm Support <mitgcm-support at mitgcm.org>, gebbie at eps.harvard.edu
> Subject: Re: OBCS
> Date: Mon, 25 Oct 2004 09:30:18 -0400
> 
> 
> Hi Martin:  My memory is fading at this point, but here's my assessment.
> 
> If you're setting the o.b. points to be the outermost grid-points in the
> domain, then the vertical velocity field (or sea surface height) at those
> points don't affect the interior solution. In other words, those points
> don't get used in the global pressure solver. But the large or strange
> values should be only on the open boundaries and not in the interior.
> 
> So, to be clear, what are the coordinates of the "corner" versus the open
> boundary coordinates?
> 
> One other idea: I believe the CD scheme and open boundaries are
> incompatible (can anyone else back me up?). Is CD turned off?
> 
> Dan Lea has also found that there was a missing exchange in the OB
> routines. Hopefully, it has found its way into the main trunk.
> 
> Cheers,
> --Jake

> 
> On Mon, 25 Oct 2004, Martin Losch wrote:
> 
> > Hi,
> >
> > I have made an obseration  with the OBCS package, and I can't quite
> > figure out what it is, mayby someone can help:
> >
> > I have a box with 4 open boundaries, where I prescribe U and V (and T
> > and S). From looking at obcs_apply_uv (which is called from dynamics
> > and momentum_correction_step, so before integr_continuity), I would
> > think that u(1,:) = u(1-1,:)=u_obcs(east),
> > u(nx,:)=u(nx+1,:)=u_obcs(west), v(:,1)=v(:,1-1)=u_obcs(south), and
> > v(:,ny)=v(:,ny+1)=v_obcs(north). So at the corners, dw/dz = du/dx+dv/dy
> > = 0 and w(z) = const.
> > But that's not what I observe. There is a vertical profile (nearly
> > linear in 3 of 4 corners). This w a the corners is more or less
> > consistent (smooth transition) with surrounding points at the southern
> > points (iy=1), but very singular at the at the northern points
> > (iy=sNy). In fact, w is large (factor 100 larger than interior) and
> > positive at (ix=1,iy=sNy) and large and negative at (ix=sNx,iy=sNy).
> >
> > This looks very much like a bug to me, but before I spend too much time
> > on hunting it down, I would like to know if anyone has made similar
> > observations. Maybe there's a simple explanation, why at these corners
> > w has to be so strange ...
> >
> > Martin
> >
-- 
Edward H. Hill III, PhD
office:  MIT Dept. of EAPS;  Rm 54-1424;  77 Massachusetts Ave.
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