Direct estimate of lateral eddy diffusivity upstream of Drake Passage
LaCasce, Joseph H.
Ledwell, James R.
Marshall, John C.
Speer, Kevin G.
Watson, Andrew J.
MetadataShow full item record
As publishedhttps://doi.org/ 10.1175/JPO-D-13-0120.1
KeywordGeographic location/entity; Southern Ocean; Circulation/ Dynamics; Diffusion; Eddies; Ocean circulation; Turbulence; Physical Meteorology and Climatology; Isopycnal mixing
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 Passage as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). The meridional eddy diffusivity, a measure of the rate at which the area of the tracer spreads along an isopycnal across the Antarctic Circumpolar Current, is 710 ± 260 m2 s−1 at 1500-m depth. The estimate is based on an extrapolation of the tracer-based diffusivity using output from numerical tracers released in a one-twentieth of a degree model simulation of the circulation and turbulence in the Drake Passage region. The model is shown to reproduce the observed spreading rate of the DIMES tracer and suggests that the meridional eddy diffusivity is weak in the upper kilometer of the water column with values below 500 m2 s−1 and peaks at the steering level, near 2 km, where the eddy phase speed is equal to the mean flow speed. These vertical variations are not captured by ocean models presently used for climate studies, but they significantly affect the ventilation of different water masses.
Author Posting. © American Meteorological Society, 2014. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 44 (2014): 2593–2616, doi:10.1175/JPO-D-13-0120.1.
Suggested CitationJournal of Physical Oceanography 44 (2014): 2593–2616
Showing items related by title, author, creator and subject.
Rypina, Irina I.; Kirincich, Anthony R.; Lentz, Steven J.; Sundermeyer, Miles A. (American Meteorological Society, 2016-06-29)This paper aims to test the validity, utility, and limitations of the lateral eddy diffusivity concept in a coastal environment through analyzing data from coupled drifter and dye releases within the footprint of a ...
Estimating a submesoscale diffusivity using a roughness measure applied to a tracer release experiment in the Southern Ocean Boland, Emma J. D.; Shuckburgh, Emily; Haynes, Peter H.; Ledwell, James R.; Messias, Marie-Jose; Watson, Andrew J. (American Meteorological Society, 2015-06)The use of a measure to diagnose submesoscale isopycnal diffusivity by determining the best match between observations of a tracer and simulations with varying small-scale diffusivities is tested. Specifically, the robustness ...
Merrifield, Sophia T.; St. Laurent, Louis C.; Owens, W. Brechner; Thurnherr, Andreas M.; Toole, John M. (American Meteorological Society, 2016-04-05)Direct measurements of oceanic turbulent parameters were taken upstream of and across Drake Passage, in the region of the Subantarctic and Polar Fronts. Values of turbulent kinetic energy dissipation rate ε estimated by ...