[MITgcm-support] Re: viscosity questions

[Martin.Losch at awi.de]

Jean-Michel, Dimitris,

thanks again for your comments. I don't think that KPP is the problem as I get noise also without it. With advScheme 33, I 
tried different diffusivities (smaller than those used with advScheme 2) and also no explicit diffusivity, but none seemed to 
work properly.

I have tried to use a combination of 33 and 2 as Jean-Michel suggests, but I had to turn off multidimadvection (=.false.) for 
that, so that the solution looks very different, but the noise is not gone.

For now, I have 3 series of plots to look at, if anyone is interested. For these plots I have reduced the domain (gulf of elat 
at the northern end of the red sea) to get faster results. I started from rest and ran the model for 30 days and forcing with 
homogeneous wind stress (wind from the south). "data" is attached, no other packages used (except for diagnostics). 
horizontal resolution is 900m. advection 33 with no explicit diffusivity.
Shown are temperatures at layers 1,5,10 with velocity vectors, nothing is scaled for plotting. On the left is a run with 
viscC2Smag=1 and on the right with viscC4Smag=1. In particular, level 5 has a lot of noise that persists for 30 days. The 
noise in level 10 appears to fade away towards the end of the intergration period. I do not show W, because that's noisy 
all the way, nothing to learn. horizontal velocities are more or less smooth (they are affected by the noise in the density 
field, of course, but the viscosity seems to damp this away along the boundaries, where viscAh/4 is high, not so much in 
the interior where viscAh/4 is low. The plots of Ah/4 are not smooth). 

here are the plots (approx 2MB each):
http://mitgcm.org/~mlosch/eilat_temp1.ps.gz
http://mitgcm.org/~mlosch/eilat_temp5.ps.gz
http://mitgcm.org/~mlosch/eilat_temp10.ps.gz

In the full domain the noise is even more pronounced. 

M.

Martin Losch
Alfred Wegener Institute 
Postfach 120161, 27515 Bremerhaven, Germany; 
Tel./Fax: ++49(0471)4831-1872/1797



----- Original Message -----
From: Jean-Michel Campin <jmc at ocean.mit.edu>
Date: Friday, November 17, 2006 2:31 am
Subject: Re: [MITgcm-support] Re: viscosity questions

> Hi Martin,
> 
> Looks like an interesting problem !
> No obvious noise on uVel,vVel. What about wVel ?
> Also, the noise on T,S, is it a steady noise or oscillating/fast-
> growing ?
> 
> I did not use very often this option, but you can try to
> keep the 33 advection scheme for the horizontal, and switch back
> to 2nd order in the vertical (at least for a test):
> tempAdvScheme=33,
> tempVertAdvScheme=2,
> 
> Jean-Michel
> 
> On Thu, Nov 16, 2006 at 11:34:32PM +0200, Martin.Losch at awi.de wrote:
> > Hi, 
> > thanks for the KPP suggestion. However, I never had any problems 
> with KPP, and this time again, KPP is not the culprit. I 
> > turned it of (use cAdjFreq=-1) and the problem persists.
> > 
> > Again: 
> > with temp/saltAdvScheme = 2 and diffK4T/S = 1.e6, I can suppress 
> the noise, but
> > with temp/saltAdvScheme = 33 and diffK4T/S = 1.e6, there is a lot 
> of noise (also with diffK4T/S smaller or 0), 
> > staggerTimeStep = .true.. That's what's really puzzling me. I 
> though that the advection scheme 33 (DST3FL) is extremely 
> > stable and should remove all grid scale noise (in my previous 
> experience it does exactly that). Why not now?
> > 
> > Martin
> > 
> > Martin Losch
> > Alfred Wegener Institute 
> > Postfach 120161, 27515 Bremerhaven, Germany; 
> > Tel./Fax: ++49(0471)4831-1872/1797
> > 
> > 
> > 
> > ----- Original Message -----
> > From: Dimitris Menemenlis <menemenlis at sbcglobal.net>
> > Date: Thursday, November 16, 2006 9:09 pm
> > Subject: Re: [MITgcm-support] Re: viscosity questions
> > 
> > > KPP does have a computational grid-scale mode in T/S, 
> especially 
> > > visible at 
> > > Equator, in my experience.  That's why those horizontal 121 
> filters 
> > > were added. 
> > >  The recommended filters are on by default in KPP_OPTIONS.h.  
> But 
> > > worth trying 
> > > with KPP off.  D.
> > > _______________________________________________
> > > 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
>