[MITgcm-devel] equation of state -- JMD95Z versus others

[Jean-Michel Campin]

Hi Dan,

I am moving this to devel (so that others can comment).

There is a problem (in MITgcm) when using EOS in p with Non-Hydrostatic (NH),
since the non hydrostatic contribution is not acounting for.

Apart from this, I am not very comfortable with EOS in p and Boussinesq aprox
(but may be it's just me), and physical reasons are not very clear to me since
it's a compressible effect in a fully imcompressible (Boussinesq) formulation.
For instance, when SSH changes, the hydrostic pressure will not change by
the same amount within the water column (because d.SSH > 0 implies d.rho > 0
and an increase of P-Hyd larger at great depth than near surface).
Also this contribution is instantaneous (Hydrostatic Aprox) but is not 
part of the implicit surface pressure solver and there is an open question
there whether or not it could be a stability issue (I don't think it's an issue
with earth ocean).

You might want to check Griffies & Adcroft, 2008, Geophys. Monograph Series 177.
and references inside.

Cheers,
Jean-Michel

On Fri, Jan 16, 2015 at 11:46:38AM +0000, Daniel Goldberg wrote:
> Hi J-M
> 
> I am starting to put together a document to send to Jim (the BAS postdoc).
> I have a question about EOS. Back during the summer when I was doing the
> tests of modifying Ro_surf in ISOMIP, I was using a linear EOS to
> completely ignore any complications of EOS from changing ksurfc. But I
> don't think we will be able to get away with that going forward, as the EOS
> gets quite nonlinear in the ice shelf problem..
> 
> Is there an advantage to using a z-dependent rather than p-dependent EOS? I
> cannot remember whether density (and this pressure) with a z-dependent EOS
> would be affected less than with a pressure-dependent one when kSurfC is
> incremented or decremented. I just remember that the pressure-dependent one
> is problematic.
> 
> (should this conversation go on mitgcm-devel? i'm assuming not but can move
> it there.)
> 
> Thanks
> Dan
> 
> -- 
> 
> Daniel Goldberg, PhD
> Lecturer in Glaciology
> School of Geosciences, University of Edinburgh
> Geography Building, Drummond Street, Edinburgh EH8 9XP
> 
> 
> em: D <dgoldber at mit.edu>an.Goldberg at ed.ac.uk
> web: http://ocean.mit.edu/~dgoldberg