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01.23.11: Notes on “Effects of variable and anisotropic diffusivities in a steady-state diffusion model” by Armi and Haidvogel (1982)

The authors show how gradient in diffusivity can generate advective-like feature in a tracer field.

“An additional complication studied here is the effect of anisotropy in the diffusivity field. This is suggested by the dynamical constarint due to the variation of planetary vorticity in the north-south direction and no such constraint in the east-west direction. Freeland et al. (1975) also present observational evidence from the dispersion of SOFAR floats for a small anisotropy of the horizontal diffusivity.”

Interesting. Needs to look at this paper.

“Although the classical interpretation of tongues of various properties [..] has been as an advective-diffusive attribute, the catalog of purely diffusive solutions shown here suggests that any interpretation of tongue-like property distributions need to be put forth with caution when little is known about the degree of anisotropy or variability of the supposed Fickian diffusivity field.”

“[V]ariations of the diffusivity act much like an additional advective field in the direction from high to low eddy diffusivity.”