Open ocean regimes of relative dispersion.

• Published in: Journal of Fluid Mechanics
• Main Authors: Ollitrault, Michel, Gabillet, Céline, Colin De Verdiere, Alain
• Other Authors: Laboratoire de physique des océans (LPO), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche de l'Ecole Navale (IRENAV), Université de Bordeaux (UB)-Institut Polytechnique de Bordeaux-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Arts et Métiers Sciences et Technologies, HESAM Université (HESAM)-HESAM Université (HESAM)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2005
• Subjects: [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; Mid-Atlantic Ridge; North Atlantic
• Online Access: https://hal.archives-ouvertes.fr/hal-00308726; https://doi.org/10.1017/S0022112005004556

International audience 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 ($D^{2}\,{\sim}\,t^{3}$ 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 300 km, the relative dispersion slowed down naturally to the Taylor absolute dispersion regime.