Barotropic vorticity balance of the North Atlantic subpolar gyre in an eddy-resolving model

• Published in: Ocean Science
• Main Authors: Le Corre, Mathieu, Gula, Jonathan, Tréguier, Anne-Marie
• Other Authors: Laboratoire d'Océanographie Physique et Spatiale (LOPS), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), UBO, Region Bretagne through ISblue, Interdisciplinary graduate school for the blue planet ANR-17-EURE-0015, ANR-17-EURE-0015,ISBlue,Interdisciplinary Graduate School for the Blue planet(2017)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: [SDV.MP]Life Sciences [q-bio]/Microbiology and Parasitology; Curl; North Atlantic
• Online Access: https://hal.science/hal-02933376; https://hal.science/hal-02933376/document; https://hal.science/hal-02933376/file/os-16-451-2020.pdf; https://doi.org/10.5194/os-16-451-2020

International audience The circulation in the North Atlantic subpolar gyre is complex and strongly influenced by the topography. The gyre dynamics are traditionally understood as the result of a topographic Sverdrup balance, which corresponds to a first-order balance between the planetary vorticity advection, the bottom pressure torque, and the wind stress curl. However, these dynamics have been studied mostly with noneddy-resolving models and a crude representation of the bottom topography. Here we revisit the barotropic vorticity balance of the North Atlantic subpolar gyre using a new eddy-resolving simulation (with a grid space of approximate to 2 km) with topography-following vertical coordinates to better represent the mesoscale turbulence and flow-topography interactions. Our findings highlight that, locally, there is a first-order balance between the bottom pressure torque and the nonlinear terms, albeit with a high degree of cancellation between them. However, balances integrated over different regions of the gyre - shelf, slope, and interior - still highlight the important role played by nonlinearities and bottom drag curls. In particular, the Sverdrup balance cannot describe the dynamics in the interior of the gyre. The main sources of cyclonic vorticity are nonlinear terms due to eddies generated along eastern boundary currents and time-mean nonlinear terms in the northwest corner. Our results suggest that a good representation of the mesoscale activity and a good positioning of mean currents are two important conditions for a better representation of the circulation in the North Atlantic subpolar gyre.