A simple differential diffusion model to account for the discrepancy between Ra-223- and Ra-224-based eddy diffusivities

作者：Stachelhaus Scott L^*; Moran S Bradley

来源：Journal of Geophysical Research, 2012, 117: C03004.

DOI：10.1029/2011JC007500

A series of Ra-223 (t(1/2) = 11.4 d) and Ra-224 (t(1/2) = 3.66 d) measurements made in the Mid-Atlantic Bight yield eddy diffusivity (K) estimates of 1.2 +/- 0.3 x 102 m(2) s(-1) and 1.4 +/- 0.2 x 102 m(2) s(-1), respectively. These results fall in line with previous studies from multiple locations throughout the ocean, in which Ra-224-based eddy diffusivities invariably exceed those determined using Ra-223. Such a pattern conflicts with the Fickian model for eddy diffusivity, in which K is constant. Moreover, this trend runs counter to the length scale-dependent view of eddy diffusion, which suggests that K values estimated using Ra-223 should exceed those of Ra-224, because the length scale of the former is greater than that of the latter. A finite mixing-length model based on the concept of differential diffusion is used to provide an explanation for this discrepancy.

• 出版日期2012-3-1