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Tidal mixing in sill regions: influence of sill depth and aspect ratio

Xing, Jiuxing; Davies, Alan M.. 2011 Tidal mixing in sill regions: influence of sill depth and aspect ratio. Ocean Dynamics, 61 (10). 1697-1717. 10.1007/s10236-011-0441-4

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Abstract/Summary

A non-hydrostatic model in cross-sectional form with an idealized sill is used to examine the influence of sill depth (h s) and aspect ratio upon internal motion. The model is forced with a barotropic tide and internal waves and mixing occurs at the sill. Calculations using a wide sill and quantifying the response using power spectra show that for a given tidal forcing namely Froude number F r as the sill depth (h s) increases the lee wave response and vertical mixing decrease. This is because of a reduction in across sill velocity U s due to increased depth. Calculations show that the sill Froude number F s based on sill depth and across sill velocity is one parameter that controls the response at the sill. At low F s (namely F s ≪ 1) in the wide sill case, there is little lee wave production, and the response is in terms of internal tides. At high F s, calculations with a narrow sill show that for a given F s value, the lee wave response and internal mixing increase with increasing aspect ratio. Calculations using a narrow sill with constant U s show that for small values of h s, a near surface mixed layer can occur on the downstream side of the sill. For large values of h s, a thick well-mixed bottom boundary layer occurs due to turbulence produced by the lee waves at the seabed. For intermediate values of h s, “internal mixing” dominates the solution and controls across thermocline mixing

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1007/s10236-011-0441-4
Programmes: Oceans 2025 > Next generation ocean prediction systems
ISSN: 1616-7341
Additional Keywords: INTERNAL WAVES; SILLS; MIXING; TIDES
NORA Subject Terms: Marine Sciences
Date made live: 27 Oct 2011 11:43
URI: http://nora.nerc.ac.uk/id/eprint/15626

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