Open-ocean submesoscale motions: A full seasonal cycle of mixed layer instabilities from gliders

Thompson, Andrew, Lazar, Ayah, Buckingham, Christian, Naveira Garabato, Alberto C., Damerell, Gillian ORCID: https://orcid.org/0000-0001-5808-0822 and Heywood, Karen ORCID: https://orcid.org/0000-0001-9859-0026 (2016) Open-ocean submesoscale motions: A full seasonal cycle of mixed layer instabilities from gliders. Journal of Physical Oceanography, 46. 1285–1307. ISSN 0022-3670

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Abstract

The importance of submesoscale instabilities, particularly mixed layer baroclinic instability and symmetric instability, on upper-ocean mixing and energetics is well documented in regions of strong, persistent fronts such as the Kuroshio and the Gulf Stream. Less attention has been devoted to studying submesoscale flows in the open ocean, far from long-term, mean geostrophic fronts, characteristic of a large proportion of the global ocean. This study presents a year-long, submesoscale-resolving time series of near-surface buoyancy gradients, potential vorticity, and instability characteristics, collected by ocean gliders, that provides insight into open-ocean submesoscale dynamics over a full annual cycle. The gliders continuously sampled a 225 km2 region in the subtropical northeast Atlantic, measuring temperature, salinity, and pressure along 292 short (~20 km) hydrographic sections. Glider observations show a seasonal cycle in near-surface stratification. Throughout the fall (September–November), the mixed layer deepens, predominantly through gravitational instability, indicating that surface cooling dominates submesoscale restratification processes. During winter (December–March), mixed layer depths are more variable, and estimates of the balanced Richardson number, which measures the relative importance of lateral and vertical buoyancy gradients, depict conditions favorable to symmetric instability. The importance of mixed layer instabilities on the restratification of the mixed layer, as compared with surface heating and cooling, shows that submesoscale processes can reverse the sign of an equivalent heat flux up to 25% of the time during winter. These results demonstrate that the open-ocean mixed layer hosts various forced and unforced instabilities, which become more prevalent during winter, and emphasize that accurate parameterizations of submesoscale processes are needed throughout the ocean.

Item Type:	Article
Additional Information:	© Copyright 2016 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act September 2010 Page 2 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (https://www.ametsoc.org/) or from the AMS at 617-227-2425 or copyrights@ametsoc.org. Citation: Andrew F. Thompson and Ayah Lazar, Christian Buckingham and Alberto C. Naveira Garabato, Gillian M. Damerell and Karen J. Heywood, 2016: Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders. Journal of Physical Oceanography, 46, 1285–1307, doi: 10.1175/JPO-D-15-0170.1.
Faculty \ School:	Faculty of Science > School of Environmental Sciences University of East Anglia Research Groups/Centres > Theme - ClimateUEA
UEA Research Groups:	Faculty of Science > Research Groups > Marine and Atmospheric Sciences (former - to 2017) Faculty of Science > Research Groups > Meteorology, Oceanography and Climate Dynamics (former - to 2017) Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences Faculty of Science > Research Groups > Climate, Ocean and Atmospheric Sciences (former - to 2017)
Depositing User:	Pure Connector
Date Deposited:	22 Mar 2016 09:24
Last Modified:	20 Mar 2023 11:32
URI:	https://ueaeprints.uea.ac.uk/id/eprint/57750
DOI:	10.1175/JPO-D-15-0170.1

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