[MITgcm-support] Nonlinear equations of state

Tue Mar 12 21:49:25 EDT 2024

Hi,

Just to add a little precision: the choice of what pressure goes into non-linear seawater EOS
can be set in "data", in same namelist as eosType, with:
 selectP_inEOS_Zc = 0 : to use  -rhoConst * gravity * z
 selectP_inEOS_Zc = 1 : same as above, only function of z, but more accurate
 selectP_inEOS_Zc = 2 : to use model hydrostatic pressure
 selectP_inEOS_Zc = 3, only with nonHydrostatic=T : to use model full (hydrostatic+non-hydrostatics) 
                      pressure

And what has been describe here earlier in this thread is still valid, but just reflects the default
setting of selectP_inEOS_Zc (e.g., if not set in "data" and eosType='MDJWF' --> selectP_inEOS_Zc 
will be set to 2 ; and if not set in "data" and eosType='JMD95Z',  --> selectP_inEOS_Zc = 0)

Note that the value of selectP_inEOS_Zc is reported in STDOUT (config-summary).

Cheers,
Jean-Michel

On Tue, Mar 12, 2024 at 08:49:26AM -0700, Paola Cessi wrote:
> Hi Dave,
> 
> another issue of using a complex EoS such as TEOS-10 in a model which makes the Boussinesq approximation is that proper conservation of total energy (including internal energy) is lost unless some care is taken. For example, with the Boussinesq approximation the dependence of the EoS on the pressure, p, must be through the term  p = -rhoConst*gravity*z, not the in situ pressure. If the actual in situ pressure  is used in a Boussinesq model, then there is an inconsistent energy budget. 
> 
> This is explained in detail in the attached paper. If you are using an incompressible, Boussinesq model use JMD95Z, not JMD95P.
> 
> Cheers,
> Paola
> 
> 
> 
> > On Mar 12, 2024, at 4:44 AM, Dave Munday - BAS <danday at bas.ac.uk> wrote:
> > 
> > Thanks Martin. That???s quite reassuring that I haven???t made a daft choice with at least trying out MDJWF. TEOS-10 would have been nice, but I???m quite happy to do without for now.
> > 
> > D
> > 
> >> On 12 Mar 2024, at 09:16, Martin Losch <Martin.Losch at awi.de> wrote:
> >> 
> >> Hi Dave,
> >> 
> >> JMD95Z (based on Jackett and McDougall 1995) is basically a ???re-tuned??? UNESCO formula (UNESCO for in-situ temperature and JMD95Z for potential temperature), both use p = -rhoConst*gravity*z as an approximation for pressure.
> >> JMD95Z uses the actual hydrostatic pressure (lagged by one timestep), and hence requires a little more computation
> >> MDJWF implements McDougall, et al (2003). The EOS is based on a different fromula and principles and contains fewer terms, so that the authors (?) claim that there fewer computations involved, hence it should be faster. This EOS also uses the hydrostatic pressure of the previous time step
> >> 
> >> In practice, the EOS is not the bottleneck of any simulation, so that I would not expect any significant speed differences. For potential temperature I wouild use MDJWF, just because it is ???newer???. 
> >> 
> >> There???s also TEOS10, which requires that ???THETA??? and ???SALT??? are interpreted as conservative temperature and absolute salinity. This implementation is not quite complete yet, see PR #812: https://github.com/MITgcm/MITgcm/pull/812 <https://urldefense.com/v3/__https://github.com/MITgcm/MITgcm/pull/812__;!!Mih3wA!DjhCnEwPZhyprmcYr_89m6KqNgmJNB21EC-PMgNe0EpUy6Vm-BFs2jS5snW4uYL1HBOPG_wQVFB303U$>
> >> 
> >> Martin
> >> 
> >>> On 11. Mar 2024, at 18:35, Dave Munday - BAS <danday at bas.ac.uk> wrote:
> >>> 
> >>> Dear MITgcm-ers,
> >>> 
> >>> I???ve just been trying to make a decision about which particular nonlinear EOS to use for a very long-running two basin sector model with biogeochemistry. In reading the docs the MDJWF EOS is described as ???more accurate and less expensive???, which is appealing when running models for 10-20 000 years. A lot of the verification experiments are set to use JMD95Z or JMD95P. Is there a reason to prefer them over MDJWF?
> >>> 
> >>> Many thanks,
> >>> 
> >>> Dave
> >>> 
> >>> 
> >>> This email and any attachments are intended solely for the use of the named recipients. If you are not the intended recipient you must not use, disclose, copy or distribute this email or any of its attachments and should notify the sender immediately and delete this email from your system. UK Research and Innovation (UKRI) has taken every reasonable precaution to minimise risk of this email or any attachments containing viruses or malware but the recipient should carry out its own virus and malware checks before opening the attachments. UKRI does not accept any liability for any losses or damages which the recipient may sustain due to presence of any viruses.
> >>> 
> >>> _______________________________________________
> >>> MITgcm-support mailing list
> >>> MITgcm-support at mitgcm.org
> >>> http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support <https://urldefense.com/v3/__http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support__;!!Mih3wA!DjhCnEwPZhyprmcYr_89m6KqNgmJNB21EC-PMgNe0EpUy6Vm-BFs2jS5snW4uYL1HBOPG_wQUnvZ4sk$>
> >> 
> >> _______________________________________________
> >> MITgcm-support mailing list
> >> MITgcm-support at mitgcm.org
> >> http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support <https://urldefense.com/v3/__http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support__;!!Mih3wA!DjhCnEwPZhyprmcYr_89m6KqNgmJNB21EC-PMgNe0EpUy6Vm-BFs2jS5snW4uYL1HBOPG_wQUnvZ4sk$>
> > 
> > _______________________________________________
> > MITgcm-support mailing list
> > MITgcm-support at mitgcm.org
> > https://urldefense.com/v3/__http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support__;!!Mih3wA!DjhCnEwPZhyprmcYr_89m6KqNgmJNB21EC-PMgNe0EpUy6Vm-BFs2jS5snW4uYL1HBOPG_wQUnvZ4sk$ 
> 

> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support