<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><div class=""></div><div class=""><br class="webkit-block-placeholder"></div><div><blockquote type="cite" class=""><div class="">On Mar 12, 2024, at 4:44 AM, Dave Munday - BAS <<a href="mailto:danday@bas.ac.uk" class="">danday@bas.ac.uk</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
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<span style="caret-color: rgb(0, 0, 0);" class="">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.</span>
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<div style="caret-color: rgb(0, 0, 0);" class="">D</div>
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<div class="">On 12 Mar 2024, at 09:16, Martin Losch <<a href="mailto:Martin.Losch@awi.de" class="">Martin.Losch@awi.de</a>> wrote:</div>
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Hi Dave,
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<div class="">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.</div>
<div class="">JMD95Z uses the actual hydrostatic pressure (lagged by one timestep), and hence requires a little more computation</div>
<div class="">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</div>
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<div class="">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”. </div>
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<div class="">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: <a href="https://urldefense.com/v3/__https://github.com/MITgcm/MITgcm/pull/812__;!!Mih3wA!DjhCnEwPZhyprmcYr_89m6KqNgmJNB21EC-PMgNe0EpUy6Vm-BFs2jS5snW4uYL1HBOPG_wQVFB303U$" class="">https://github.com/MITgcm/MITgcm/pull/812</a></div>
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<div class="">Martin</div>
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<div class="">On 11. Mar 2024, at 18:35, Dave Munday - BAS <<a href="mailto:danday@bas.ac.uk" class="">danday@bas.ac.uk</a>> wrote:</div>
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<div class="">Dear MITgcm-ers,<br class="">
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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?<br class="">
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Many thanks,<br class="">
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Dave<br class="">
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