Large-amplitude internal tides, solitary waves, and turbulence in the central Bay of Biscay

Xu Hu Xie (1, 2) , Yannis Cuypers (3, 4) , Pascale Bouruet-Aubertot (3, 4) , Bruno Ferron (5) , Annick Pichon (6) , Antonio Lourenço (7) , Norbert Cortes (5)

1 LOCEAN - Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques
2 Laboratory of Tropical Oceanography
3 IPSO - Interactions et Processus au sein de la couche de Surface Océanique
4 SURF - Échanges dans la couche de surface : des pôles aux tropiques
5 LPO - Laboratoire de physique des océans
6 Centre Militaire d'Océanographie
7 DITM - Développement Instrumental et Techniques Marines

Microstructure and fine-scale measurements collected in the central Bay of Biscay during the MOUTON experiment are analyzed to investigate the dynamics of internal waves and associated mixing. Large-amplitude internal tides (ITs) that excite internal solitary waves (ISWs) in the thermocline are observed. ITs are dominated by modes 3 and 4, while ISWs projected on mode 1 that is trapped in the thermocline. Therein, ITs generate a persistent narrow shear band, which is strongly correlated with the enhanced dissipation rate in the thermocline. This strong dissipation rate is further reinforced in the presence of ISWs. Dissipation rates during the period without ISWs largely agree with the MacKinnon-Gregg scaling proposed for internal wavefields dominated by a low-frequency mode, while they show poor agreement with the Gregg-Henyey parameterization valid for internal wavefields close to the Garrett-Munk model. The agreement with the MacKinnon-Gregg scaling is consistent with the fact that turbulent mixing here is driven by the low-frequency internal tidal shear.

Mots clés: Bay of Biscay; turbulence; solitary waves; internal tides

Domaines: Océanographie

Xu Hu Xie, Yannis Cuypers, Pascale Bouruet-Aubertot, Bruno Ferron, Annick Pichon, et al.. Large-amplitude internal tides, solitary waves, and turbulence in the central Bay of Biscay. Geophysical Research Letters, 2013, 40 (11), pp.2748-2754. ⟨10.1002/grl.50533⟩. ⟨hal-00852194⟩