Abstract
Oceanic density overturns are commonly used to parameterize the dissipation rate of turbulent kinetic energy. This method assumes a linear scaling between the Thorpe length scale LT and the Ozmidov length scale LO. Historic evidence supporting LTLO has been shown for relatively weak shear-driven turbulence of the thermocline; however, little support for the method exists in regions of turbulence driven by the convective collapse of topographically influenced overturns that are large by open-ocean standards. This study presents a direct comparison of LT and LO, using vertical profiles of temperature and microstructure shear collected in the Luzon Strait-a site characterized by topographically influenced overturns up to 100) m in scale. The comparison is also done for open-ocean sites in the Brazil basin and North Atlantic where overturns are generally smaller and due to different processes. Akey result is that LT/LO increases with overturn size in a fashion similar to that observed in numerical studies of Kelvin-Helmholtz (K-H) instabilities for all sites but is most clear in data from the Luzon Strait. Resultant bias in parameterized dissipation is mitigated by ensemble averaging; however, a positive bias appears when instantaneous observations are depth and time integrated. For a series of profiles taken during a spring tidal period in the Luzon Strait, the integrated value is nearly an order of magnitude larger than that based on the microstructure observations. Physical arguments supporting LT LO are revisited, and conceptual regimes explaining the relationship between LT/LO and a nondimensional overturn size ĽT are proposed. In a companion paper, Scotti obtains similar conclusions from energetics arguments and simulations.
Recommended Citation
B. D. Mater et al., "Biases in Thorpe-scale Estimates of Turbulence Dissipation. Part I: Assessments from Large-scale overturns in Oceanographic Data," Journal of Physical Oceanography, vol. 45, no. 10, pp. 2497 - 2521, American Meteorological Society, Jan 2015.
The definitive version is available at https://doi.org/10.1175/JPO-D-14-0128.1
Department(s)
Civil, Architectural and Environmental Engineering
Publication Status
Full Access
Keywords and Phrases
Atm/Ocean Structure/Phenomena; Circulation/Dynamics; Diapycnal mixing; Mixing; Models and modeling; Observational techniques and algorithms; Oceanic; Parameterization; Profilers; Small scale processes; Turbulence
International Standard Serial Number (ISSN)
1520-0485; 0022-3670
Document Type
Article - Journal
Document Version
Final Version
File Type
text
Language(s)
English
Rights
© 2025 American Meteorological Society, All rights reserved.
Publication Date
01 Jan 2015
Comments
National Science Foundation, Grant OCE-1151838