Laboratory modelling of momentum transport by internal gravity waves and eddies in the Antarctic circumpolar current

• Main Authors: Sommeria, Joël, Ajayi, Adekunle-Opeoluwa, Raja, Keshav Jayakrishnan, Staquet, Chantal, Viboud, Samuel, Voisin, Bruno
• Other Authors: Laboratoire des Écoulements Géophysiques et Industriels Grenoble (LEGI ), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes 2016-2019 (UGA 2016-2019 )
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2016
• Subjects: [PHYS.MECA.MEFL]Physics [physics]/Mechanics [physics]/Fluid mechanics [physics.class-ph]; Antarctic; Southern Ocean; The Antarctic; Antarc*
• Online Access: https://hal.science/hal-01938043; https://hal.science/hal-01938043/document; https://hal.science/hal-01938043/file/ejh2016-sommeria.pdf

International audience Wakes in stratified fluids have been an active field of research of Emil Hopfinger (e.g. Hopfinger (1987) - J. Geophys. Research) topics undergoes new developments in the context of the dynamics of the Antarctic Circumpolar current, a strong source of ocean mixing with impact on Earth climate. Recent field campaigns in the Southern Ocean have revealed that the interaction of this current with bottom topography can radiate internal gravity waves whose momentum transport contributes to friction (Naveira-Garabato et al. 2004, Nikurashin & Ferrari 2010). An additional contribution to friction is due the eddy wakes produced behind obstacles. These problems have been much studied in the context of atmospheric dynamics, and several laboratories experiments in a linearly stratified fluid have been performed, for instance Baines (1995), Dalziel et al. (2011). Those previous experiments were however constrained by lateral boundaries and did not reach the fully turbulent regime for the eddy wakes. Moreover the Coriolis effect was not investigated although it is much relevant in the oceanic case due to the small Rossby number.We have reproduced the wake of a spherical cap in a linearly stratified fluid on the ‘Coriolis’ rotating platform, 13 m in diameter. A uniform circular current around the tank is produced by a small change of tank rotation speed (spinup) which persists by inertia for the duration of the experiment, typically 15 minutes, over which the flow conditions can be considered quasi-steady with a slow decay by friction. The sphere radius is 80 cm, and the cap height is 20 cm (69 cm in diameter) while the total water depth is 90 cm. The non-rotating case is obtained by introducing a small tank rotation while the water remains at rest by inertia. This is compared to a rotating case with a ratio $f/N = 2.5$ of the Coriolis parameter $f$ to the buoyancy frequency $N = 0.5\;\mathrm{s}^{-1}$. The flow velocity is varied from 3 cm/s to 12 cm/s which allows us to cover the relevant range of ...