Accession Number : ADA307391

Title :   Tidally-Forced Vorticity, Diurnal Shear and Turbulence Atop Fieberling Seamount,

Corporate Author : WASHINGTON UNIV SEATTLE DEPT OF OCEANOGRAPHY

Personal Author(s) : Kunze, Eric ; Toole, John M.

PDF Url : ADA307391

Report Date : MAR 1996

Pagination or Media Count : 76

Abstract : Fine- and microstructure profiles collected over Fieberling Seamount at 32 deg 26'N in the eastern North Pacific reveal three intensified phenomena co-existing in a 200-m thick layer atop the summit plain: (i) an anticyclonic vortex cap of core relative vorticity O.50f, (ii) diurnal shear of 15 cm s-1/40 m, and (iii) turbulence levels corresponding to an eddy diffusivity Kp is approx. 0.0001 m2 s-1. The vortex cannot be explained solely by Taylor-Proudman dynamics because of its O.3fN(2) negative potential vorticity anomaly. The fortnightly cycle in the vortex's strength suggests that it is at least partially maintained against dissipative erosion by rectification of diurnal tides. Baroclinic diurnal fluctuations are slightly subinertial and the diurnal kinetic energy also tracks the beating of the barotropic K1 and O1 diurnal tides. Their horizontal structure closely resembles a seamount-trapped topographic wave. However, counterclockwise turning with depth of the horizontal velocity vector and the 180 deg phase difference between radial velocity Ur' and vertical displacement Z' = -T'/Tz (producing a net positive radial heat-flux) are more consistent with an upward-propagating vortex-trapped near-inertial internal wave. The slightly subinertial frequency is allowed by the strong negative vorticity of the vortex cap. A vortex-trapped wave would encounter a vertical critical layer at the top of the cap where its energy would be lost to turbulence. High observed turbulence levels of E=3 x 10(-8) W kg-1 imply decay times for the wave and vortex of less than 3 days, emphasizing the strongly forced nature of the system. Inferred eddy diffusivities two orders of magnitude larger than those found in the ocean interior suggest that, locally, seamounts are important sites for diapycnal transport.

Descriptors :   *TURBULENCE, *VORTICES, *OCEAN TIDES, *SEAMOUNTS, MATHEMATICAL MODELS, MICROSTRUCTURE, OCEAN WAVES, OCEAN CURRENTS, TIME SERIES ANALYSIS, DISSIPATION, EDDIES(FLUID MECHANICS), TURBULENT BOUNDARY LAYER, HIGH RESOLUTION, OCEANOGRAPHIC DATA, BATHYMETRY, CONTINENTAL SLOPES, PROFILES, KINETIC ENERGY, SALINITY, HEAT FLUX, INVISCID FLOW, VISCOUS FLOW, STRATIFICATION, OCEAN MODELS, OCEAN BOTTOM TOPOGRAPHY, DIURNAL VARIATIONS, NORTH PACIFIC OCEAN, OCEAN BASINS, SHEAR FLOW, AXISYMMETRIC FLOW, TURBULENT DIFFUSION, RADIAL VELOCITY.

Subject Categories : Physical and Dynamic Oceanography

Distribution Statement : APPROVED FOR PUBLIC RELEASE