Rainville Luc

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  • Preprint
    The Kuroshio Extension and its recirculation gyres
    ( 2009-07-01) Jayne, Steven R. ; Hogg, Nelson G. ; Waterman, Stephanie N. ; Rainville, Luc ; Donohue, Kathleen A. ; Watts, D. Randolph ; Tracey, Karen L. ; McClean, Julie L. ; Maltrud, Mathew E. ; Qiu, Bo ; Chen, Shuiming ; Hacker, Peter
    This paper reports on the strength and structure of the Kuroshio Extension and its recirculation gyres. In the time average, quasi-permanent recirculation gyres are found to the north and south of the Kuroshio Extension jet. The characteristics of recirculation gyres are determined from the combined observations from the Kuroshio Extension System Study (KESS) field program program (June 2004 – June 2006) and include current meters, pressure and current recording inverted echo sounders, and sub-surface floats. The position and strength of the recirculation gyres simulated by a high-resolution numerical model are found to be consistent with the observations. The circulation pattern that is revealed is of a complex system of multiple recirculation gyres that are embedded in the crests and troughs of the quasi-permanent meanders of the Kuroshio Extension. At the location of the KESS array, the Kuroshio Extension jet and its recirculation gyres transport of about 114 Sv. This represents a 2.7-fold increase in the transport of the current compared to the Kuroshio’s transport at Cape Ashizuri before it separates from the coast and flows eastward into the open ocean. This enhancement in the current’s transport comes from the development of the flanking recirculation gyres. Estimates from an array of inverted echo sounders and a high-resolution ocean general circulation model are of similar magnitude.
  • Article
    Dynamics in the deep Canada Basin, Arctic Ocean, inferred by thermistor chain time series
    (American Meteorological Society, 2007-04) Timmermans, Mary-Louise ; Melling, Humfrey ; Rainville, Luc
    A 50-day time series of high-resolution temperature in the deepest layers of the Canada Basin in the Arctic Ocean indicates that the deep Canada Basin is a dynamically active environment, not the quiet, stable basin often assumed. Vertical motions at the near-inertial (tidal) frequency have amplitudes of 10– 20 m. These vertical displacements are surprisingly large considering the downward near-inertial internal wave energy flux typically observed in the Canada Basin. In addition to motion in the internal-wave frequency band, the measurements indicate distinctive subinertial temperature fluctuations, possibly due to intrusions of new water masses.
  • Article
    Diurnal and semidiurnal internal tide energy flux at a continental slope in the South China Sea
    (American Geophysical Union, 2008-03-25) Duda, Timothy F. ; Rainville, Luc
    Barotropic (surface) and baroclinic (internal) tides were measured at four mooring sites during a field investigation of acoustic propagation characteristics and physical oceanography in the northern South China Sea. The mooring positions were in a line moving up the shallow portion of a continental slope at water depths between 350 and 85 m. Using time series of temperature and velocity, at several depths, 1-month series of semidiurnal and diurnal species internal tidal energy flux vectors were computed for three sites, with a 14-day series computed for the fourth (shallow) site. The internal tides had a temporal signature that was not in complete accord with the barotropic tides, showing an enhancement of diurnal internal tides with respect to semidiurnal. Bathymetric slope, barotropic tidal fluid particle trajectories, and scale of generation site versus internal tide wavelength are investigated as possible causes of the differing response of the species.
  • Preprint
    Formation of Subtropical Mode Water in a high-resolution ocean simulation of the Kuroshio Extension region
    ( 2007-03-09) Rainville, Luc ; Jayne, Steven R. ; McClean, Julie L. ; Maltrud, Mathew E.
    A high-resolution numerical model is used to examine the formation and variability of the North Pacific Subtropical ModeWater (STMW) over a 3-year period. The STMW distribution is found to be highly variable in both space and time, a characteristic often unexplored because of sparse observations or the use of coarse resolution simulations. Its distribution is highly dependent on eddies, and where it was renewed during the previous winter. Although the potential vorticity fluxes associated with down-front winds can be of the same order of magnitude or even greater than the diabatic ones due to air-sea temperature differences, the latter dominate the potential vorticity budget on regional and larger scales. Air-sea fluxes, however, are dominated by a few strong wind events, emphasizing the importance of short time scales in the formation of mode waters. In the Kuroshio Extension region, both advection and mixing play important roles to remove the STMW from the formation region.
  • Article
    Direct breaking of the internal tide near topography : Kaena Ridge, Hawaii
    (American Meteorological Society, 2008-02) Klymak, Jody M. ; Pinkel, Robert ; Rainville, Luc
    Barotropic to baroclinic conversion and attendant phenomena were recently examined at the Kaena Ridge as an aspect of the Hawaii Ocean Mixing Experiment. Two distinct mixing processes appear to be at work in the waters above the 1100-m-deep ridge crest. At middepths, above 400 m, mixing events resemble their open-ocean counterparts. There is no apparent modulation of mixing rates with the fortnightly cycle, and they are well modeled by standard open-ocean parameterizations. Nearer to the topography, there is quasi-deterministic breaking associated with each baroclinic crest passage. Large-amplitude, small-scale internal waves are triggered by tidal forcing, consistent with lee-wave formation at the ridge break. These waves have vertical wavelengths on the order of 400 m. During spring tides, the waves are nonlinear and exhibit convective instabilities on their leading edge. Dissipation rates exceed those predicted by the open-ocean parameterizations by up to a factor of 100, with the disparity increasing as the seafloor is approached. These observations are based on a set of repeated CTD and microconductivity profiles obtained from the research platform (R/P) Floating Instrument Platform (FLIP), which was trimoored over the southern edge of the ridge crest. Ocean velocity and shear were resolved to a 4-m vertical scale by a suspended Doppler sonar. Dissipation was estimated both by measuring overturn displacements and from microconductivity wavenumber spectra. The methods agreed in water deeper than 200 m, where sensor resolution limitations do not limit the turbulence estimates. At intense mixing sites new phenomena await discovery, and existing parameterizations cannot be expected to apply.
  • Article
    Mixing across the Arctic Ocean : microstructure observations during the Beringia 2005 Expedition
    (American Geophysical Union, 2008-04-30) Rainville, Luc ; Winsor, Peter
    Turbulent-scale temperature and conductivity were measured during the pan-arctic Beringia 2005 Expedition. The rates of dissipation of thermal variance and diapycnal diffusivities are calculated along a section from Alaska to the North Pole, across deep flat basins (Canada and Makarov Basins) and steep ridges (Alpha-Mendeleev and Lomonosov Ridges). The mixing rates are observed to be small relative to lower latitudes but also remarkably non-uniform. Relatively elevated turbulence is found over deep topography, confirming the dominant role of bottom-generated internal waves. Measured patterns of mixing in the Arctic are also associated with other mechanisms, such as double-diffusive structures and deep overflows. A better knowledge of the distribution of mixing is essential to understand the dynamics of the changing Arctic environment.