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Abrupt Transitions in Submesoscale Structure in Southern Drake Passage: Glider Observations and Model Results

Viglione, Giuliana A. and Thompson, Andrew F. and Flexas, M. Mar and Sprintall, Janet and Swart, Sebastiaan (2018) Abrupt Transitions in Submesoscale Structure in Southern Drake Passage: Glider Observations and Model Results. Journal of Physical Oceanography, 48 (9). pp. 2011-2027. ISSN 0022-3670. http://resolver.caltech.edu/CaltechAUTHORS:20180919-144812027

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Abstract

Enhanced vertical velocities associated with submesoscale motions may rapidly modify mixed layer depths and increase exchange between the mixed layer and the ocean interior. These dynamics are of particular importance in the Southern Ocean, where the ventilation of many density classes occurs. Here we present results from an observational field program in southern Drake Passage, a region preconditioned for submesoscale instability owing to its strong mesoscale eddy field, persistent fronts, strong down-front winds, and weak vertical stratification. Two gliders sampled from December 2014 through March 2015 upstream and downstream of the Shackleton Fracture Zone (SFZ). The acquired time series of mixed layer depths and buoyancy gradients enabled calculations of potential vorticity and classifications of submesoscale instabilities. The regions flanking the SFZ displayed remarkably different characteristics despite similar surface forcing. Mixed layer depths were nearly twice as deep, and horizontal buoyancy gradients were larger downstream of the SFZ. Upstream of the SFZ, submesoscale variability was confined to the edges of topographically steered fronts, whereas downstream these motions were more broadly distributed. Comparisons to a one-dimensional (1D) mixing model demonstrate the role of submesoscale instabilities in generating mixed layer variance. Numerical output from a submesoscale-resolving simulation indicates that submesoscale instabilities are crucial for correctly reproducing upper-ocean stratification. These results show that bathymetry can play a key role in generating dynamically distinct submesoscale characteristics over short spatial scales and that submesoscale motions can be locally active during summer months.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1175/JPO-D-17-0192.1DOIArticle
ORCID:
AuthorORCID
Thompson, Andrew F.0000-0003-0322-4811
Flexas, M. Mar0000-0002-0617-3004
Sprintall, Janet0000-0002-7428-7580
Additional Information:© 2018 American Meteorological Society. Manuscript received 19 September 2017, in final form 25 April 2018. GAV and AFT were supported by NSF Award OPP-1246460. JS was supported by NSF Award OPP-1246160. SS thanks the following funding agencies: a Wallenberg Academy Fellowship (WAF 2015.0186) and the South African National Research Foundation (NRF), Grant SNA14071475720. The Group for High Resolution Sea Surface Temperature (GHRSST) Multiscale Ultra-High-Resolution (MUR) SST data were obtained from the NASA EOSDIS Physical Oceanography Distributed Active Archive Center (PO.DAAC) at the Jet Propulsion Laboratory, Pasadena, California (https://doi.org/10.5067/GHGMR-4FJ01). The ERA-Interim data were obtained from ECMWF. The authors thank the Antarctic Support Contract staff as well as the captains and crews of the ARSV Laurence M. Gould and the RRS Ernest Shackleton for their support during the deployment and recovery cruises.
Funders:
Funding AgencyGrant Number
NSFOPP-1246460
NSFOPP-1246160
Wallenberg Academy FellowshipWAF 2015.0186
National Research Foundation (South Africa)SNA14071475720
Subject Keywords:Antarctica; Atmosphere-ocean interaction; Instability; Potential vorticity; Mixed layer; Oceanic mixed layer
Record Number:CaltechAUTHORS:20180919-144812027
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180919-144812027
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89759
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:19 Sep 2018 21:58
Last Modified:19 Sep 2018 21:58

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