Now showing items 1-15 of 15

  • Deep ocean circulation and transport where the East Pacific Rise at 9–10°N meets the Lamont seamount chain 

    Lavelle, J. William; Thurnherr, Andreas M.; Ledwell, James R.; McGillicuddy, Dennis J.; Mullineaux, Lauren S. (American Geophysical Union, 2010-12-31)
    We report the first 3-D numerical model study of abyssal ocean circulation and transport over the steep topography of the East Pacific Rise (EPR) and adjoining Lamont seamount chain in the eastern tropical Pacific. We begin ...
  • Diapycnal diffusivities from a tracer release experiment in the deep sea, integrated over 13 years 

    Rye, Craig D.; Messias, Marie-Jose; Ledwell, James R.; Watson, Andrew J.; Brousseau, Andrew; King, Brian A. (American Geophysical Union, 2012-02-21)
    A section across the Atlantic at 24°S recorded in March 2009, sampled a tracer plume released in the deep Brazil Basin 13 years earlier. The 1-D diffusion equation was used to model the vertical spread of the tracer, ...
  • Diapycnal mixing in the Antarctic Circumpolar Current 

    Ledwell, James R.; St. Laurent, Louis C.; Girton, James B.; Toole, John M. (American Meteorological Society, 2011-01)
    The vertical dispersion of a tracer released on a density surface near 1500-m depth in the Antarctic Circumpolar Current west of Drake Passage indicates that the diapycnal diffusivity, averaged over 1 yr and over tens of ...
  • Direct estimate of lateral eddy diffusivity upstream of Drake Passage 

    Tulloch, Ross; Ferrari, Raffaele; Jahn, Oliver; Klocker, Andreas; LaCasce, Joseph H.; Ledwell, James R.; Marshall, John C.; Messias, Marie-Jose; Speer, Kevin G.; Watson, Andrew J. (American Meteorological Society, 2014-10)
    The first direct estimate of the rate at which geostrophic turbulence mixes tracers across the Antarctic Circumpolar Current is presented. The estimate is computed from the spreading of a tracer released upstream of Drake ...
  • Hydrography and circulation near the crest of the East Pacific Rise between 9° and 10°N 

    Thurnherr, Andreas M.; Ledwell, James R.; Lavelle, J. William; Mullineaux, Lauren S. (2010-12-12)
    Topography has a strong effect on the physical oceanography over the flanks and crests of the global mid-ocean ridge system. Here, we present an analysis of the hydrography and circulation near the crest of the East ...
  • Mixing in a coastal environment : 1. A view from dye dispersion 

    Ledwell, James R.; Duda, Timothy F.; Sundermeyer, Miles A.; Seim, Harvey E. (American Geophysical Union, 2004-10-26)
    Dye release experiments were performed together with microstructure profiling to compare the two methods of estimating diapycnal diffusivity during summer and fall stratification on the continental shelf south of New ...
  • Modeling turbulent dispersion on the North Flank of Georges Bank using Lagrangian Particle Methods 

    Proehl, Jeffrey A.; Lynch, Daniel R.; McGillicuddy, Dennis J.; Ledwell, James R. (2004-09-29)
    Circulation and transport at the North Flank of Georges Bank are studied using a data-assimilative 3-D model of frontal dynamics under stratified, tidally energetic conditions over steep topography. The circulation model ...
  • Observations and numerical simulations of large-eddy circulation in the ocean surface mixed layer 

    Sundermeyer, Miles A.; Skyllingstad, Eric; Ledwell, James R.; Concannon, Brian; Terray, Eugene A.; Birch, Daniel; Pierce, Stephen D.; Cervantes, Brandy (John Wiley & Sons, 2014-11-06)
    Two near-surface dye releases were mapped on scales of minutes to hours temporally, meters to order 1 km horizontally, and 1–20 m vertically using a scanning, depth-resolving airborne lidar. In both cases, dye evolved into ...
  • The prediction, verification, and significance of flank jets at mid-ocean ridges 

    Lavelle, J. William; Thurnherr, Andreas M.; Mullineaux, Lauren S.; McGillicuddy, Dennis J.; Ledwell, James R. (The Oceanography Society, 2012-03)
    One aspect of ocean flow over mid-ocean ridges that has escaped much attention is the capacity of a ridge to convert oscillatory flows into unidirectional flows. Those unidirectional flows take the form of relatively narrow ...
  • Rates and mechanisms of turbulent dissipation and mixing in the Southern Ocean : results from the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) 

    Sheen, Katy L.; Brearley, J. A.; Naveira Garabato, Alberto C.; Smeed, D. A.; Waterman, Stephanie N.; Ledwell, James R.; Meredith, Michael P.; St. Laurent, Louis C.; Thurnherr, Andreas M.; Toole, John M.; Watson, Andrew J. (John Wiley & Sons, 2013-06-04)
    The spatial distribution of turbulent dissipation rates and internal wavefield characteristics is analyzed across two contrasting regimes of the Antarctic Circumpolar Current (ACC), using microstructure and finestructure ...
  • Stirring by small-scale vortices caused by patchy mixing 

    Sundermeyer, Miles A.; Ledwell, James R.; Oakey, Neil S.; Greenan, Blair J. W. (American Meteorological Society, 2005-07)
    Evidence is presented that lateral dispersion on scales of 1–10 km in the stratified waters of the continental shelf may be significantly enhanced by stirring by small-scale geostrophic motions caused by patches of mixed ...
  • Three-dimensional mapping of fluorescent dye using a scanning, depth-resolving airborne lidar 

    Sundermeyer, Miles A.; Terray, Eugene A.; Ledwell, James R.; Cunningham, A. G.; LaRocque, P. E.; Banic, J.; Lillycrop, W. J. (American Meteorological Society, 2007-06)
    Results are presented from a pilot study using a fluorescent dye tracer imaged by airborne lidar in the ocean surface layer on spatial scales of meters to kilometers and temporal scales of minutes to hours. The lidar used ...
  • Turbulence and diapycnal mixing in Drake Passage 

    St. Laurent, Louis C.; Naveira Garabato, Alberto C.; Ledwell, James R.; Thurnherr, Andreas M.; Toole, John M.; Watson, Andrew J. (American Meteorological Society, 2012-12)
    Direct measurements of turbulence levels in the Drake Passage region of the Southern Ocean show a marked enhancement over the Phoenix Ridge. At this site, the Antarctic Circumpolar Current (ACC) is constricted in its flow ...
  • Use of SF5CF3 for ocean tracer release experiments 

    Ho, David T.; Ledwell, James R.; Smethie, William M. (American Geophysical Union, 2008-02-19)
    SF6 tracer release experiments (TREs) have provided fundamental insights in many areas of Oceanography. Recently, SF6 has emerged as a powerful transient tracer, generating a need for an alternative tracer for large-scale ...
  • Water samplers for open ocean tracer release experiments 

    Donoghue, Terence; Ledwell, James R.; Doherty, Kenneth W. (Woods Hole Oceanographic Institution, 1998-12)
    Conventional "spot" sampling of patchy distributions of oceanic constituents can lead to sampling errors. Interpretation of results based on data of disparate temporal or spatial resolution can be difficult or impossible. ...