Title :

Impact of ageostrophic dynamics on the predictability of Lagrangian trajectories in surface-ocean turbulence

Author(s) :

Maalouly, Michael [Auteur]
Unité de Mécanique de Lille - ULR 7512 [UML]
Lapeyre, Guillaume [Auteur]
Institut Pierre-Simon-Laplace [IPSL (FR_636)]
Berti, Stefano [Auteur]
Unité de Mécanique de Lille - ULR 7512 [UML]

Journal title :

Physical Review Fluids

Pages :

104503

Publisher :

American Physical Society

Publication date :

2024-10-24

ISSN :

2469-990X

HAL domain(s) :

Planète et Univers [physics]/Océan, Atmosphère

English abstract : [en]

Turbulent flows at the surface of the ocean deviate from geostrophic equilibrium on scales smaller than about 10 km. These scales are associated with important vertical transport of active and passive tracers, and should ...
Show more >Turbulent flows at the surface of the ocean deviate from geostrophic equilibrium on scales smaller than about 10 km. These scales are associated with important vertical transport of active and passive tracers, and should play a prominent role in the heat transport at climatic scales and for plankton dynamics. Measuring velocity fields on such small scales is notoriously difficult but new, high-resolution satellite altimetry is starting to reveal them. However, the satellite-derived velocities essentially represent the geostrophic flow component, and the impact of unresolved ageostrophic motions on particle dispersion needs to be understood to properly characterize transport properties. Here, we investigate ocean fine-scale turbulence using a model that represents some of the processes due to ageostrophic dynamics. We take a Lagrangian approach and focus on the predictability of the particle dynamics, comparing trajectories advected by either the full flow or by its geostrophic component only. Our results indicate that, over long times, relative dispersion is marginally affected by the filtering of the ageostrophic component. Nevertheless, advection by the filtered flow leads to an overestimation of the typical pair-separation rate, and to a bias on trajectories (in terms of displacement from the actual ones), whose importance grows with the Rossby number. We further explore the intensity of the transient particle clustering induced by ageostrophic motions and find that it can be significant, even for small flow compressibility. Indeed, we show that clustering is here due to the interplay between compressibility and persistent flow structures that trap particles, enhancing their aggregation.Show less >

Language :

Anglais

Peer reviewed article :

Oui

Audience :

Internationale

Popular science :

Non

Comment :

18 pages, 10 figures

Collections :

• Unité de Mécanique de Lille (UML) - ULR 7512

Source :

Harvested from HAL