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

[Lars Czeschel]

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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