Open ocean regimes of relative dispersion

Type Article
Date 2005-06
Language English
Author(s) Ollitrault Michel1, Gabillet Céline2, De Verdiere Alain Colin3
Affiliation(s) 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.
Source Journal of fluid mechanics (0022-1120) (Cambridge univ. Press), 2005-06 , Vol. 533 , P. 381-407
DOI 10.1017/S0022112005004556
WOS© Times Cited 52
Keyword(s) Taylor dispersion, Dispersion, Atlantic circulation, Particule pairs
Abstract 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.
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