[MITgcm-support] Spurious mixing with internal tides

[Ruan Xiaozhou]

Dear MITgcm users,

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.

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.

Cheers,
Xiaozhou
--
Xiaozhou Ruan
Postdoctoral researcher
Department of Earth, Atmospheric and Planetary Sciences
Massachusetts Institute of Technology
54-1622
Cambridge, MA  02139

email: xruan at mit.edu<mailto:xiaozhour at caltech.edu>
web:   http://www.mit.edu/~xruan<http://www.its.caltech.edu/~xruan>


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