Stellar mixing. III. The case of a passive tracer

Details Stellar mixing. III. The case of a passive tracer Stellar mixing. III. The case of a passive tracer

Apr 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011a%26a...528a..78c&link_type=abstract

Astronomy & Astrophysics, Volume 528, id.A78

Astronomy and Astrophysics

Astrophysics

Diffusion, Instabilities, Turbulence, Stars: Interiors, Convection, Methods: Analytical

Scientific paper

In Papers I-II, we derived the expressions for the turbulent diffusivities of momentum, temperature T, and mean molecular weight μ. Since the scalar T-μ fields are active tracers (by influencing the density and thus the velocity field), whereas passive tracers such as 7Li are carried along by the flow without influencing it, it would be unjustified to use the diffusivities of the T-μ fields to represent the diffusivity of passive tracers. In this paper, we present the first derivation of a passive tracer diffusivity. Some key results are: a) In the general 3D case, the passive tracer diffusivity is a tensor given in algebraic form; b) the diffusivity tensor depends on shear, vorticity, T, and μ-gradients, thus including double diffusion and differential rotation; c) in the 1D version of the model, the passive tracer diffusivity is a scalar denoted by Kc; d) in doubly stable regimes, ∇μ > 0, ∇ - ∇ad < 0, Kc is nearly the same as those of the T-μ fields; e) in semi-convection regimes, ∇μ > 0, ∇ - ∇ad > 0, Kc is larger than that of the μ-field; f) in salt fingers regimes ∇μ < 0,∇ - ∇ad < 0, Kc is smaller than that of the μ-field; and finally, g) in the only case we know of a direct measurement of a passive tracer diffusivity, the oceanographic North Atlantic Tracer Release Experiment (NATRE), the model reproduces the data quite closely.
This work is dedicated to Aura Sofia Canuto.

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