[MITgcm-support] GM: Skew flux vs Advective form

[Jean-Michel Campin]

Hi Lars,

I've just looked at the cvs-history of pkg/layers, and few things
have been fixed since checkpoint MITgcm_63q. 
In particular, on Jan 9, 2013, we got the revision 1.5 of file layers_fluxcalc.F 
with this comment:
> Fix GM flow when using Skew Flux form.
This might answer your 1rst point (divergent overturning).

I also wrote something to the support list yesterday redarging this:
> p.s: Several years ago Christopher Wolfe reported a related problem
> http://mitgcm.org/pipermail/mitgcm-support/2008-January/005180.html

Cheers,
Jean-Michel

On Thu, Jun 06, 2013 at 11:24:27AM +0200, Lars Czeschel 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
> 


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