[MITgcm-devel] Fwd: [MITgcm-support] GM: Skew flux vs Advective form
Jean-Michel Campin
jmc at ocean.mit.edu
Fri Jun 14 14:45:42 EDT 2013
Hi Martin,
two things:
The messages from Lars Czeschel are relative to the layers diagnostics.
Is it a pkg/layers problem (with the skew flux) or not just a diagnostics
problem but a more serious pkg/gmredi problem ?
And what was the specific point that Carsten mentioned to you ?
And the older message (from Christopher Wolfe, Jan 2008) that Lars pointed
to: http://mitgcm.org/pipermail/mitgcm-support/2008-January/005180.html
is about difference between advective form and skew flux form
plus the issue of monotonicity of the scheme.
I looked for a reply to this message but did not find one.
I can certainly answer something to this old message, if this is
useful for anyone.
Cheers,
Jean-Michel
On Fri, Jun 14, 2013 at 11:35:26AM +0200, Martin Losch wrote:
> Hi guys,
>
> I just got a call from Carsten Eden, who wanted to raise awareness for the apparent problem with the skew flux formulation of GM. Here's the thread again: <http://mitgcm.org/pipermail/mitgcm-support/2013-June/008344.html>
>
> Do you agree, that this is a serious issue? How can we fix that? May the adjoint stability even be affected in a positive way by this?
>
> Martin
>
> Begin forwarded message:
>
> > From: Lars Czeschel <lars.czeschel at zmaw.de>
> > Subject: Re: [MITgcm-support] GM: Skew flux vs Advective form
> > Date: June 12, 2013 12:50:08 PM GMT+02:00
> > To: <mitgcm-support at mitgcm.org>
> > Reply-To: <mitgcm-support at mitgcm.org>
> >
> > Hi Ryan,
> > it seems it is not a problem of the layer diagnostic.
> > I calculated the eddy-MOC from the bolus velocities in z-levels
> > for the 'tutorial_global_oce_latlon' for year 10 with similar results.
> >
> > I attached some figures showing the global eddy MOC for both cases and the differences.
> > The last two figures show the eddy MOC in the deepest level to give an impression of the
> > divergence when using the skew flux formulation.
> >
> > I also attached the matlab code in case I am missing something in my calculation.
> >
> > Thanks, Lars
> >
> >
> >
> >
> >
> >
> >
> > %Eddy MOC from skew flux formulation
> > clear all
> > % load data
> > DXG = rdmds('DXG');
> > hFacS = rdmds('hFacS');
> > YG = rdmds('YG');
> > DRF = rdmds('DRF');
> > DRF = squeeze(DRF);
> > KWY = rdmds('GM_Kwy-T.0000172800');
> >
> > % compute mer. bolus velocity
> > KWY(:,:,16)=0.0;
> > for i=1:90
> > for j=1:40
> > for k=1:15
> > Vb(i,j,k)=KWY(i,j,k+1)*0.5-KWY(i,j,k)*0.5;
> > end
> > end
> > end
> > DX=repmat(DXG,[1,1,15]);
> > ddz=repmat(DRF,[1, 40, 90]);
> > ddz=permute(ddz,[3 2 1]);
> > n=find(hFacS > 0);
> > Vb(n)=Vb(n)./(ddz(n).*hFacS(n));
> >
> > % integrate MOC
> > Xint=sum(Vb.*DX.*hFacS);
> > Xint=squeeze(Xint);
> > dz=repmat(DRF,[1,40]);
> > dz=permute(dz,[2 1]);
> > MOC=cumsum(Xint.*dz./1e6, 2);
> >
> > %Plotting
> > [hcl cl]=contourf(YG(1,:),cumsum(DRF),MOC',[-30:5:-10 -10:2:10 10:5:30 ]);
> > set(gca,'YDIR','reverse')
> > clabel(hcl,cl)
> > caxis([-30,30])
> > colorbar
> > title('Skew Flux MOC [Sv]');
> >
> > ----
> >
> > %Eddy MOC from advective formulation
> > clear all
> > DXG = rdmds('DXG');
> > hFacS = rdmds('hFacS');
> > YG = rdmds('YG');
> > DRF = rdmds('DRF');
> > DRF = squeeze(DRF);
> > PSIY = rdmds('GM_PsiYtave.0000172800');
> >
> > % compute mer. bolus velocity
> > PSIY(:,:,16)=0.0;
> > for i=1:90
> > for j=1:40
> > for k=1:15
> > Vb(i,j,k)=PSIY(i,j,k+1)-PSIY(i,j,k);
> > end
> > end
> > end
> > DX=repmat(DXG,[1,1,15]);
> > ddz=repmat(DRF,[1, 40, 90]);
> > ddz=permute(ddz,[3 2 1]);
> > n=find(hFacS > 0);
> > Vb(n)=Vb(n)./(ddz(n).*hFacS(n));
> >
> > % compute eddy MOC
> > Xint=sum(Vb.*DX.*hFacS);
> > Xint=squeeze(Xint);
> > dz=repmat(DRF,[1,40]);
> > dz=permute(dz,[2 1]);
> > MOC=cumsum(Xint.*dz./1e6, 2);
> >
> > %Plotting
> > [hcl cl]=contourf(YG(1,:),cumsum(DRF),MOC',[-30:5:-10 -10:2:10 10:5:30 ]);
> > set(gca,'YDIR','reverse')
> > clabel(hcl,cl)
> > caxis([-30,30])
> > colorbar
> > title('Advective form MOC [Sv]');
> >
> >
> >
> >
> > On 06.06.2013, at 18:04, Ryan Abernathey wrote:
> >
> >> Lars,
> >> Unfortunately, I can't really comment on climatological differences between the skew flux vs adv form.
> >> But I am curious whether using adv form fixed the problems you were having with the layers diagnostics.
> >> -Ryan
> >>
> >
> >>
> >> On Thu, Jun 6, 2013 at 2:24 AM, Lars Czeschel <lars.czeschel at zmaw.de> wrote:
> >> Hi all,
> >>
> >> i am running a 1deg global model with version MITgcm_63q. Using the layers pkg I noticed
> >> that my global overturning in density space is divergent (up to 5 Sv in ACC latitudes).
> >> Without bolus velocities or using ' GM_AdvForm = .TRUE.,' in data.gmredi
> >> the overturning becomes non-divergent.
> >>
> >> As we used the skew flux version frequently in the past (which is also the default) I hoped to find
> >> a bug in the layers pkg but without success. As a further test I ran the tutorial example
> >> 'tutorial_global_oce_latlon' for 10 years with GM_AdvForm = .False. compared
> >> to GM_AdvForm = .TRUE. in data.gmredi. I attached the quite strong differences in theta (z=85m)
> >> below.
> >>
> >> To my understanding the differences should be very small even if the small slope assumption
> >> is made using the skew flux version.
> >>
> >> Did I miss something here or do we have an undiscovered bug in the skew flux code and
> >> the advective form should be recommended ?
> >>
> >> Thanks , Lars
> >>
> >> p.s: Several years ago Christopher Wolfe reported a related problem
> >> http://mitgcm.org/pipermail/mitgcm-support/2008-January/005180.html
> >>
> >>
> >> ----------------------------------------------
> >> Lars Czeschel
> >> Theoretical Oceanography
> >> Institut für Meereskunde
> >> KlimaCampus Universität Hamburg
> >> Bundesstr. 53
> >> 20146 Hamburg
> >>
> >>
> >> _______________________________________________
> >> MITgcm-support mailing list
> >> MITgcm-support at mitgcm.org
> >> http://mitgcm.org/mailman/listinfo/mitgcm-support
> >>
> >>
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> >> http://mitgcm.org/mailman/listinfo/mitgcm-support
> >
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