Vertical mixing estimates along hydrological sections en Atlantique Nord in North Atlantic

• Main Author: Kokoszka, Florian
• Other Authors: 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), Université de Bretagne occidentale - Brest, Herlé Mercier, Bruno Ferron
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2012
• Subjects: North Atlantic; Hydrological Section; Data Analysis; InternalWaves; Thorpe Scales; Garrett and Munk Model; Turbulence; Vertical Mixing; Dissipation; Fine-structure; Micro-structure; Parameterizations; Topography; Atantique Nord; Section Hydrologique; Analyse de données; Ondes Internes; Echelles de Thorpe; Modèle de Garrett et Munk; Mélange vertical; Finestructure; Microstructure; Paramétrisations; Topographie; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Greenland; Mid-Atlantic Ridge; Munk
• Online Access: https://theses.hal.science/tel-02071038; https://theses.hal.science/tel-02071038/document; https://theses.hal.science/tel-02071038/file/These-2012-EDSM-Oceanographie_physique-KOKOSZKA_Florian.pdf

Vertical mixing in the ocean contributes to sustain the Meridionnal Overturning. Circulation (MOC) by allowing the renewal of deep waters. A section across the MOC is performed by the hydrological radial OVIDE repeated every two years between Portugal and Greenland since 2002. The energy required for mixing is provided by internal waves generated by wind and tides and micro-structure measurements(VMP) in 2008 show intensified values of dissipation Evmp in the main thermocline and near topographies. Our study is based on these observations and aims tostudy the vertical fine-scale structure of the ocean. Estimates of the dissipation E due to internal waves are made with CTD and LADCP measurements. The comparison with VMP measurements allow us to optimize the parameterization of E by framing the observations by factor 3 and their mean values at ±30%. The systematic application to the OVIDE dataset provides a mapping of the mixing across the basin. Geographical distribution of the vertical diffusion K is similar along the five sections, with values near10−4m2/s in the main thermocline and at the bottom of topographies, and near 10−5m2/s in the ocean interior. Regional differences are present and K can belocally close to 10−3m2/s. Application to FOUREX1997 datas et reveals an increase of K along the Mid-Atlantic Ridge, where the average values are 2 to 3stronger than along OVIDE sections. The spatial distribution of Thorpe scales LT appears to be correlated with internal waves mixing patterns. Nevertheless dissipation estimates based on LT overestimates Evmp by a 10 to 100 factor, which maybe due to misrepresentation of the stage of turbulence development in the ocean. Some mechanisms that can generate internal waves are proposed. Probable sites where tidal generation could occur are located using a simple model of wave beam trajectory. A possible correlation between geostrophic flows and internal waves is considered in the main thermocline. Finally the study of Turnerangles shows that double-diffusion instabilities ...