Lagrangian Velocity Spectra at 700 m in the Western North Atlantic.

• Main Authors: Rupolo, Volfango, Artale, Vincenzo, Hua, Bach Lien, Provenzale, Antonello
• Other Authors: Italian National agency for new technologies, Energy and sustainable economic development Frascati (ENEA), 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), Instituto di Cosmogeofisica, CNR Corso Fiume
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 1996
• Subjects: [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography; North Atlantic
• Online Access: https://hal.science/hal-00268745; https://doi.org/10.1175/1520-0485(1996)026<1591:LVSAMI>2.0.CO;2

International audience Pending an appropriate scaling of each trajectory by its Lagrangian integral timescale TL, there exists a generic shape of the Lagrangian frequency spectrum for the trajectories of the 700-m dataset in western North Atlantic, which are stationary on the timescale of 200 days. The generic spectral shape contains a plateau at the lowest frequencies extending up to ν0∼(30TL)−1, a power-law behavior with an intermediate spectral slope α = 0.25 between ν0 and ν1∼(3∼4TL)−1, and a steeper slope n ≥ 3 at larger frequencies. Such a steep slope at large frequencies implies that most of Lagrangian dispersion can be ascribed to low and intermediate frequency motions. The variance of the Lagrangian acceleration computed from such a spectrum is finite, indicating continuous particle accelerations and supporting a truly Lagrangian behavior of the 700-m floats. The existence of an intermediate power-law behavior in the spectrum can be linked with the trapping of some trajectories by persistent energetic structures and is associated with a tendency for anomalous diffusion lasting up to 10TL. The authors also introduce an alternative method for computing TL from a yardstick measure of Lagrangian decor-relation length from each individual trajectory.