2004 LOM Workshop

Monday 10:15 - 10:35 a.m.

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Numerical Cabbeling of Dissipative and Monotone Tracer Advection Schemes

Mohamed Iskandarani, Eric Chassignet and Trevor J. McDougall
UM
miskandarani@rsmas.miami.edu

ABSTRACT

We investigate the spurious, and numerically induced, cabbeling caused by the inherent numerical dissipation of tracer advection schemes. This spurious cabbeling is the numerical analog of natural cabbeling, the process by which the nonlinear equation of states leads to denser water when water particles of nearly equal densities, but with different temperature and salt properties, mix. The spurious mixing can be exacerbated by the flux- and slope-limiting mechanisms used to prevent Gibbs oscillations from occuring. The impact of four classical advection schemes (Centered Difference, MPDATA, UTOPIA and WENO) on numerical cabbeling is studied. The experiment consists of advecting two passive tracers, that initially combine to yield a constant density, in a square basin driven by a double-gyre circulation. Most of the spurious cabbeling is caused by the deformational flow field, and occurs primarily in the western boundary current region and the eastward jet. Centered schemes with no numerical dissipation can lead to the production of negative anomalies, whereas only positive density anomalies are seen with dissipative schemes like WENO and UTOPIA. At coarse resolution, numerical cabbeling is most significant in deep layers with weak stratification, irrespective of the numerical scheme used.

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LOM Users' Workshop, February 9-11, 2004