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Characterizing turbulent overturns in CTD-data
van Haren, H.; Gostiaux, L. (2014). Characterizing turbulent overturns in CTD-data. Dyn. Atmos. Oceans 66: 58-76.
In: Dynamics of atmospheres and oceans. Elsevier: Amsterdam; New York; Oxford; Tokyo. ISSN 0377-0265, more
Peer reviewed article  

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Author keywords
    Overturn character; Rankine vortex model; Vertical profile (CTD) observations

Authors  Top 
  • van Haren, H., more
  • Gostiaux, L.

    We are concerned with the shape of overturns due to irreversible effects of turbulent mixing through internal wave breaking in the ocean. Vertical (z) overturn displacements (d) are computed from ship-borne SeaBird-911 CTD-data using the well-established method of reordering unstable portions in vertical density profiles. When displayed as a function of z, the displacements d(z) reveal a characteristic zigzag shape. Here, we primarily investigate the particular slope (z/d) of this zigzag signature after assigning the displacements to the end-point depths. Using model-overturns we show that this slope equals ½ for a solid-body-rotation, while a more sophisticated Rankine-vortex overturn-model, here employed in the vertical, has slopes slightly >½ in the interior and >1 along the sides. In the case of a near-homogeneous layer, displacement-points fill a parallelogram with side-edges having a slope of 1. The models are used to interpret overturn shapes in NE-Atlantic-Ocean-data from moderately deep, turbulent waters above Rockall Bank (off Ireland) and from deep, weakly stratified waters above Mount Josephine (off Portugal). These are compared with salinity-compensated intrusion data in Mediterranean-outflow-waters in the Canary Basin. Dynamically, most overturns are found to resemble the half-turn Rankine-vortex model and very few a, small-only, solid-body-rotation. Additionally, the usefulness and uselessness of upcast-CTD-data are discussed for overturn characterization.

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