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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. hdl.handle.net/10.1016/j.dynatmoce.2014.02.001
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.

Abstract
    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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