[MITgcm-devel] tutorial_global_oce_latlon documentation

[Jean-Michel Campin]

Hi,

I've tried to use the same procedure as for s_examples/held_suarez_cs/
to get an updated version of the parameter files that are described in
the manual, section 3.12, "Global Ocean Simulation at 4^o Resolution". 
This could help in maintaining the manual up-to-date (cf message
below). 

But I stopped when I realised that most of the description is
in fact related to verification/exp2 instead of tutorial_global_oce_latlon.
(I've just added a warning at the beginning of the section).
If someone find some-time to update it, he/she is welcome.

Cheers,
Jean-Michel

On Mon, Apr 11, 2011 at 12:11:53PM -0700, Krishnakumar Rajagopalan wrote:
> Hi All,
> I have an update on the temperature drift in tutorial. 
> In the write up of the Global Ocean Simulation at 4 deg resolution (in the .pdf 
> manual), 
> 
> the horizontal diffusion coefficient for salt and theta, diffKh  is set at  
> 1.E3. 
> 
> But, the tutorial is configured to use the GMREDI package, thus diffKh has to be 
> zero. Note that the \input\data  of this tutorial
> is correct with diffKh=0 in the input file.
> I think it would be good if the manual (.pdf document) is  revised. I followed 
> the manual and did many runs with diffKh=1e3 and GMREDI package, only realizing
> the mistake after reading  the writeup on \tutorial_cfc_offline where it is 
> spelled out that
> when GMREDI package is used, diffKh must be zero.
> 
> I think when we set diffKh to some value, and also use GMREDI package, the 
> diffusive flux,
> df gets calculated once outside the GMREDI_XTRANSPORT subroutine, before being 
> incremented
> within GMREDI_XTRANSPORT. A configuration check to tell users to ensure diffKh=0 
> when
> using GMREDI scheme would be great.
> 
>  The attached figure (a) shows two cases where GMREDI package is used. In case 
> 1, diffkH
> for salt and theta is set as 1e3. In case 2 diffKh=0. Thus case 2 is the correct 
> setting.
> The results show that the overshoot of theta is larger in case 1.
> Danabasoglu (Ocean Modelling 7 (2004); 323-341; Fig1) showed that the mean theta
> increases to about 4.25 degrees when the tracer and momentum time step are 
> different and stays constant
> thereafter. However, in my case (case 2), the mean theta is seen to reduce after 
> reacing a maximum of about
> 4.15 deg. Any ideas on why this is happening is most welcome. ( I am yet to run 
> cases where the
> tracer and momentum time steps are equal)
>  
> 
> Thanks in advance
> 
> Krishnakumar
> 
> 
> 
> 
> ________________________________
> From: Krishnakumar Rajagopalan <krishna_raj_2010 at yahoo.com>
> To: mitgcm-support at mitgcm.org
> Sent: Tue, March 15, 2011 7:03:32 PM
> Subject: Re: [MITgcm-support] Temperature drift in tutorial ( 
> tutorial_global_oce_latlon: Global Ocean Simulation at 4◦ Resolution).
> 
> 
> Hi Martin,
> 
> Thanks a lot for your reply and pointing to the reference.
> 
> Best regards
> 
> Krishnakumar
> 
> 
> 
> 
> ________________________________
> From: Martin Losch <Martin.Losch at awi.de>
> To: mitgcm-support at mitgcm.org
> Sent: Mon, March 14, 2011 9:31:22 PM
> Subject: Re: [MITgcm-support] Temperature drift in tutorial ( 
> tutorial_global_oce_latlon: Global Ocean Simulation at 4◦ Resolution).
> 
> Hi Krishnakumar,
> 
> This behavior is expected: The tutorial_global_oce_latlon is forced by a hea 
> flux that is globally balanced (should lead to no net temperature drift), AND a 
> restoring term. This restoring term ( -(lev_sst.bin - theta)/tauThetaClimRelax ) 
> causes the drift until the model has reached an equilibrium with this forcing 
> (the same is true for salinity: fresh water flux plus restoring to sss). This 
> can take very long, see e.g.
> Gokhan Danabasoglu , Ocean Modelling 7 (2004) 323–341, A comparison of global 
> ocean general circulation model solutions obtained with synchronous and 
> accelerated integration methods
> where the spin up takes up to 10,000 years. That's just the way it is.
> 
> If you want to get rid of the mean temperature trend then you have get rid of 
> the restoring terms, but that will most likely give you a strange circulation.
> 
> Martin
> 
> 
> On Mar 14, 2011, at 8:01 PM, Krishnakumar Rajagopalan wrote:
> 
> > Hi All,
> > 
> > 
> > 
> > We ran the tutorial (tutorial_global_oce_latlon) for a thousand years and find 
> >that there is a drift in the temperature.  See the attached figure which shows, 
> >for example,  the temperature at longitude=158deg and latitude= 2deg, for some 
> >depths;  the temperature at 3010m fails to reach a steady state even after 
> >1000yrs. Although the annual integral of Qnet equals zero, the annual integral 
> >of heat flux flowing into the computational domain due the relaxation term is 
> >not. Could this be a reason for the drift in temperature? Is there any 
> >setting/method to reduce this (drift in temperature).  Our study also shows that 
> >the temperature drift persists even on a higher resolution grid.
> > 
> > 
> > 
> > Thanks in advance
> > 
> > 
> > 
> > Krishnakumar
> > 
> > 
> > 
> > (University of Hawaii at Manoa)
> > 
> > 
> > <mitgcm_jpg.jpg>_______________________________________________
> > MITgcm-support mailing list
> > MITgcm-support at mitgcm.org
> > http://mitgcm.org/mailman/listinfo/mitgcm-support
> 
> 
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> 
>       


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