<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="">Dear Xiaozhou, did anybody respond to your question?<div class=""><br class=""><div class="">It is possible to reduce (but not completely eliminate) spurious mixing by choosing a different advection scheme.<div class="">I am partial to:</div><div class=""><br class=""></div><div class=""><div class="">C ENUM_OS7MP :: 7th Order One Step method with Monotonicity Preserving Limiter</div><div class=""> INTEGER ENUM_OS7MP</div><div class=""> PARAMETER(ENUM_OS7MP=7)</div><div class=""><br class=""></div><div class="">which you set in the “data” runtime parameter file using: </div><div class=""><div class=""> tempAdvScheme=7,</div><div class=""> saltAdvScheme=7,</div></div><div class=""><br class=""></div><div class="">Prather advection:</div><div class=""><br class=""></div><div class=""><div class="">C ENUM_SOM_PRATHER :: 2nd Order-Moment Advection Scheme, Prather, 1986</div><div class=""> INTEGER ENUM_SOM_PRATHER</div><div class=""> PARAMETER(ENUM_SOM_PRATHER=80)</div><div class=""><br class=""></div><div class="">C ENUM_SOM_LIMITER :: 2nd Order-Moment Advection Scheme, Prather Limiter</div><div class=""> INTEGER ENUM_SOM_LIMITER</div><div class=""> PARAMETER(ENUM_SOM_LIMITER=81)</div></div><div class=""><br class=""></div><div class="">is supposed to be even less diffusive but more expensive to compute.</div><div class=""><br class=""></div><div class="">There is a nice discussion on advection schemes in the MITgcm user manual:</div><div class=""><a href="http://mitgcm.org/sealion/online_documents/node71.html" class="">http://mitgcm.org/sealion/online_documents/node71.html</a></div><div class=""><a href="http://mitgcm.org/sealion/online_documents/node76.html" class="">http://mitgcm.org/sealion/online_documents/node76.html</a></div><div class=""><a href="http://mitgcm.org/sealion/online_documents/node81.html" class="">http://mitgcm.org/sealion/online_documents/node81.html</a></div><div class=""><br class=""></div><div class="">Cheers, Dimitris</div><div class=""><br class=""></div><div><br class=""><blockquote type="cite" class=""><div class="">On Jan 29, 2021, at 9:58 AM, Ruan Xiaozhou <<a href="mailto:saberruan@hotmail.com" class="">saberruan@hotmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
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Dear MITgcm users,
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<div class="">Hope this message finds you well. I’ve been running simple 2D simulations with internal tides driven by oscillatory mean flows over rough bathymetry. When diagnosing the volume-integrated tracer variance budget, although the l.h.s. (time-tendency)
and r.h.s (advection + diffusion) terms balance exactly, I found some extra destruction of variance coming from the volume integral of the advection term using nonlinear advection schemes (scheme 33) which is as large as the diffusion term. Theoretically this
volume integral of variance advection should vanish... Switching to a centered 2nd order scheme (scheme 2) kills this contribution but the total variance destruction rate becomes about twice as large which, according to the output, can be explained by the
noisy tracer field and thus a larger gradient term.</div>
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<div class="">I was wondering if anyone had experience beating down this *spurious* contribution from the advection term? I noticed this contribution not only in the variance budget but also other 2nd order budgets involving a volume integral.</div>
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<div class="">Cheers,</div>
<div class="">Xiaozhou</div>
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--<br class="">
Xiaozhou Ruan</div>
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Postdoctoral researcher</div>
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Department of Earth, Atmospheric and Planetary Sciences</div>
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Massachusetts Institute of Technology<br class="">
54-1622<br class="">
Cambridge, MA 02139</div>
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email: <a href="mailto:xiaozhour@caltech.edu" class="">xruan@mit.edu</a></div>
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web: <a href="https://urldefense.us/v3/__http://www.its.caltech.edu/*xruan__;fg!!PvBDto6Hs4WbVuu7!YRuAOFjbX-Ud-ObyNQx3QCA_mHxkdrR9q1gbhLpGtf0UsoeYre8nvFKMppLmQdKyrxkxhE2anEU$" style="orphans: auto; widows: auto;" class="">http://www.mit.edu/~xruan</a></div>
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