Publication

2005-06

English

http://archimer.ifremer.fr/doc/2005/publication-456.pdf (1.04 Mo)

2005 Cambridge University Press

Ollitrault Michel¹, Gabillet Céline², De Verdiere Alain Colin³

1 : IFREMER, Ctr Brest, Lab Phys Oceans, F-29280 Plouzane, France.
2 : Inst Rech Ecole Navale, F-29240 Brest, France.
3 : Univ Bretagne Occidentale, Lab Phys Oceans, F-29285 Brest, France.

Journal of fluid mechanics (0022-1120) (Cambridge univ. Press), 2005-06 , Vol. 533 , P. 381-407

22

Physical Oceanography

Taylor dispersion, Dispersion, Atlantic circulation, Particule pairs

As two fluid particles separate in time, the entire spectrum of eddy motions is being sampled from the smallest to the largest scales. In large-scale geophysical systems for which the Earth rotation is important, it has been conjectured that the relative diffusivity should vary respectively as D-2 and D-4/3 for distances respectively smaller and larger than a well-defined forcing scale of the order of the internal Rossby radius (with D the r.m.s. separation distance). Particle paths data from a mid-latitude float experiment in the central part of the North Atlantic appear to support these statements partly: two particles initially separated by a few km within two distinct clusters west and east of the mid-Atlantic ridge, statistically dispersed following a Richardson regime (D-2 similar to t(3) asymptotically) for r.m.s. separation distances between 40 and 300 km, in agreement with a D-4/3 law. At early times, and for smaller separation distances, an exponential growth, in agreement with a D-2 law, was briefly observed but only for the eastern cluster (with an e-folding time around 6 days). After a few months or separation distances greater than 300km, the relative dispersion slowed down naturally to the Taylor absolute dispersion regime.