[MITgcm-support] Nonlinear equations of state

[Dave Munday - BAS]

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

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

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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.mitgcm.org/pipermail/mitgcm-support/attachments/20240312/08eb4101/attachment-0001.html>