[MITgcm-support] ISOMIP compressibility

[Martin Losch]

Arran,

the isomip verification experiment uses hydrostatic (because nonHydrostatic=.FALSE. in data, defining ALLOW_NONHYDROSTATIC only compiles the code) and incompressible equations.

In general, I have always thought the the non-hydrostatic code always uses incompressible equations.

I am not entirely sure about the documentation, but 1.5.1.4 (where you find eq 1.98-1.103) also contains the statement that “it is the hydrostatic () form of these equations that are used throughout the ocean modelling community …”
I agree that this is a little misleading. But note, that 1.100 (non-divergent velocity field) implies incompressibility, so I am not quite sure what the section heading means here, maybe someone else can explain.

Martin

> On 3. Nov 2021, at 21:11, Arran Whiteford <arran.whiteford at vuw.ac.nz> wrote:
> 
> Hullo,
> 
> I'm trying to figure out what versions of the Boussinesq equations the ISOMIP tutorial example is solving 
> https://github.com/MITgcm/MITgcm/tree/master/verification/isomip
> 
> It includes non hydrostatic code.
> #define ALLOW_NONHYDROSTATIC https://github.com/MITgcm/MITgcm/blob/master/verification/isomip/code/CPP_OPTIONS.h
> 
> In the MITgcm documents it explains:
> 1.3.4.4.2. Ocean
> Non-hydrostatic forms of the incompressible Boussinesq equations in z- coordinates are supported - see eqs. (1.98) to (1.103).
> 
> BUT eqns (1.98) to (1.103) are not the incompressible eqns, they are the semi-compressible.
> https://mitgcm.readthedocs.io/en/latest/overview/hydrostatic.html
> 
> In the non-hydrostatic ocean model all terms in equations Eqs.(1.29 →
> 1.31) are retained.
> 
> Which is true? Is the nonhydrostatic code running incompressible or semi-compressible Boussinesq equations?
> 
> Thanks,
> Arran
> 
> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support

-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 1665 bytes
Desc: not available
URL: <http://mailman.mitgcm.org/pipermail/mitgcm-support/attachments/20211104/41395728/attachment.p7s>