Smeed
David A.
Smeed
David A.
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ArticleModification of turbulent dissipation rates by a deep Southern Ocean eddy(John Wiley & Sons, 2015-05-07) Sheen, Katy L. ; Brearley, J. Alexander ; Naveira Garabato, Alberto C. ; Smeed, David A. ; St. Laurent, Louis C. ; Meredith, Michael P. ; Thurnherr, Andreas M. ; Waterman, Stephanie N.The impact of a mesoscale eddy on the magnitude and spatial distribution of diapycnal ocean mixing is investigated using a set of hydrographic and microstructure measurements collected in the Southern Ocean. These data sampled a baroclinic, middepth eddy formed during the disintegration of a deep boundary current. Turbulent dissipation is suppressed within the eddy but is elevated by up to an order of magnitude along the upper and lower eddy boundaries. A ray tracing approximation is employed as a heuristic device to elucidate how the internal wave field evolves in the ambient velocity and stratification conditions accompanying the eddy. These calculations are consistent with the observations, suggesting reflection of internal wave energy from the eddy center and enhanced breaking through critical layer processes along the eddy boundaries. These results have important implications for understanding where and how internal wave energy is dissipated in the presence of energetic deep geostrophic flows.
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Book chapterGlobal Oceans [in “State of the Climate in 2020”](American Meteorological Society, 2021-08-01) Johnson, Gregory C. ; Lumpkin, Rick ; Alin, Simone R. ; Amaya, Dillon J. ; Baringer, Molly O. ; Boyer, Tim ; Brandt, Peter ; Carter, Brendan ; Cetinić, Ivona ; Chambers, Don P. ; Cheng, Lijing ; Collins, Andrew U. ; Cosca, Cathy ; Domingues, Ricardo ; Dong, Shenfu ; Feely, Richard A. ; Frajka-Williams, Eleanor E. ; Franz, Bryan A. ; Gilson, John ; Goni, Gustavo J. ; Hamlington, Benjamin D. ; Herrford, Josefine ; Hu, Zeng-Zhen ; Huang, Boyin ; Ishii, Masayoshi ; Jevrejeva, Svetlana ; Kennedy, John J. ; Kersalé, Marion ; Killick, Rachel E. ; Landschützer, Peter ; Lankhorst, Matthias ; Leuliette, Eric ; Locarnini, Ricardo ; Lyman, John ; Marra, John F. ; Meinen, Christopher S. ; Merrifield, Mark ; Mitchum, Gary ; Moat, Bengamin I. ; Nerem, R. Steven ; Perez, Renellys ; Purkey, Sarah G. ; Reagan, James ; Sanchez-Franks, Alejandra ; Scannell, Hillary A. ; Schmid, Claudia ; Scott, Joel P. ; Siegel, David A. ; Smeed, David A. ; Stackhouse, Paul W. ; Sweet, William V. ; Thompson, Philip R. ; Trinanes, Joaquin ; Volkov, Denis L. ; Wanninkhof, Rik ; Weller, Robert A. ; Wen, Caihong ; Westberry, Toby K. ; Widlansky, Matthew J. ; Wilber, Anne C. ; Yu, Lisan ; Zhang, Huai-MinThis chapter details 2020 global patterns in select observed oceanic physical, chemical, and biological variables relative to long-term climatologies, their differences between 2020 and 2019, and puts 2020 observations in the context of the historical record. In this overview we address a few of the highlights, first in haiku, then paragraph form: La Niña arrives, shifts winds, rain, heat, salt, carbon: Pacific—beyond. Global ocean conditions in 2020 reflected a transition from an El Niño in 2018–19 to a La Niña in late 2020. Pacific trade winds strengthened in 2020 relative to 2019, driving anomalously westward Pacific equatorial surface currents. Sea surface temperatures (SSTs), upper ocean heat content, and sea surface height all fell in the eastern tropical Pacific and rose in the western tropical Pacific. Efflux of carbon dioxide from ocean to atmosphere was larger than average across much of the equatorial Pacific, and both chlorophyll-a and phytoplankton carbon concentrations were elevated across the tropical Pacific. Less rain fell and more water evaporated in the western equatorial Pacific, consonant with increased sea surface salinity (SSS) there. SSS may also have increased as a result of anomalously westward surface currents advecting salty water from the east. El Niño–Southern Oscillation conditions have global ramifications that reverberate throughout the report.
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ArticleThe Canary Basin contribution to the seasonal cycle of the Atlantic Meridional Overturning Circulation at 26°N(John Wiley & Sons, 2015-11-07) Perez-Hernandez, M. Dolores ; McCarthy, Gerard D. ; Velez-Belchi, Pedro ; Smeed, David A. ; Fraile-Nuez, Eugenio ; Hernandez-Guerra, AlonsoThis study examines the seasonal cycle of the Atlantic Meridional Overturning Circulation (AMOC) and its eastern boundary contributions. The cycle has a magnitude of 6 Sv, as measured by the RAPID/MOCHA/WBTS project array at 26°N, which is driven largely by the eastern boundary. The eastern boundary variations are explored in the context of the regional circulation around the Canary Islands. There is a 3 month lag between maximum wind forcing and the largest eastern boundary transports, which is explained in terms of a model for Rossby wave generated at the eastern boundary. Two dynamic processes take place through the Lanzarote Passage (LP) in fall: the recirculation of the Canary Current and the northward flow of the Intermediate Poleward Undercurrent. In contrast, during the remaining seasons the transport through the LP is southward due to the Canary Upwelling Current. These processes are linked to the seasonal cycle of the AMOC.
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ArticleRates and mechanisms of turbulent dissipation and mixing in the Southern Ocean : results from the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES)(John Wiley & Sons, 2013-06-04) Sheen, Katy L. ; Brearley, J. Alexander ; Naveira Garabato, Alberto C. ; Smeed, David A. ; Waterman, Stephanie N. ; Ledwell, James R. ; Meredith, Michael P. ; St. Laurent, Louis C. ; Thurnherr, Andreas M. ; Toole, John M. ; Watson, Andrew J.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 data collected as part of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES). Mid-depth turbulent dissipation rates are found to increase from inline image in the Southeast Pacific to inline image in the Scotia Sea, typically reaching inline image within a kilometer of the seabed. Enhanced levels of turbulent mixing are associated with strong near-bottom flows, rough topography, and regions where the internal wavefield is found to have enhanced energy, a less-inertial frequency content and a dominance of upward propagating energy. These results strongly suggest that bottom-generated internal waves play a major role in determining the spatial distribution of turbulent dissipation in the ACC. The energy flux associated with the bottom internal wave generation process is calculated using wave radiation theory, and found to vary between 0.8 mW m−2 in the Southeast Pacific and 14 mW m−2 in the Scotia Sea. Typically, 10%–30% of this energy is found to dissipate within 1 km of the seabed. Comparison between turbulent dissipation rates inferred from finestructure parameterizations and microstructure-derived estimates suggests a significant departure from wave-wave interaction physics in the near-field of wave generation sites.
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ArticleObserved eddy-internal wave interactions in the Southern Ocean(American Meteorological Society, 2020-10-01) Cusack, Jesse M. ; Brearley, J. Alexander ; Naveira Garabato, Alberto C. ; Smeed, David A. ; Polzin, Kurt L. ; Velzeboer, Nick ; Shakespeare, Callum J.The physical mechanisms that remove energy from the Southern Ocean’s vigorous mesoscale eddy field are not well understood. One proposed mechanism is direct energy transfer to the internal wave field in the ocean interior, via eddy-induced straining and shearing of preexisting internal waves. The magnitude, vertical structure, and temporal variability of the rate of energy transfer between eddies and internal waves is quantified from a 14-month deployment of a mooring cluster in the Scotia Sea. Velocity and buoyancy observations are decomposed into wave and eddy components, and the energy transfer is estimated using the Reynolds-averaged energy equation. We find that eddies gain energy from the internal wave field at a rate of −2.2 ± 0.6 mW m−2, integrated from the bottom to 566 m below the surface. This result can be decomposed into a positive (eddy to wave) component, equal to 0.2 ± 0.1 mW m−2, driven by horizontal straining of internal waves, and a negative (wave to eddy) component, equal to −2.5 ± 0.6 mW m−2, driven by vertical shearing of the wave spectrum. Temporal variability of the transfer rate is much greater than the mean value. Close to topography, large energy transfers are associated with low-frequency buoyancy fluxes, the underpinning physics of which do not conform to linear wave dynamics and are thereby in need of further research. Our work suggests that eddy–internal wave interactions may play a significant role in the energy balance of the Southern Ocean mesoscale eddy and internal wave fields.
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ArticleOceanGliders: A component of the integrated GOOS(Frontiers Media, 2019-10-02) Testor, Pierre ; de Young, Brad ; Rudnick, Daniel L. ; Glenn, Scott ; Hayes, Daniel J. ; Lee, Craig M. ; Pattiaratchi, Charitha ; Hill, Katherine Louise ; Heslop, Emma ; Turpin, Victor ; Alenius, Pekka ; Barrera, Carlos ; Barth, John A. ; Beaird, Nicholas ; Bécu, Guislain ; Bosse, Anthony ; Bourrin, François ; Brearley, J. Alexander ; Chao, Yi ; Chen, Sue ; Chiggiato, Jacopo ; Coppola, Laurent ; Crout, Richard ; Cummings, James A. ; Curry, Beth ; Curry, Ruth G. ; Davis, Richard F. ; Desai, Kruti ; DiMarco, Steven F. ; Edwards, Catherine ; Fielding, Sophie ; Fer, Ilker ; Frajka-Williams, Eleanor ; Gildor, Hezi ; Goni, Gustavo J. ; Gutierrez, Dimitri ; Haugan, Peter M. ; Hebert, David ; Heiderich, Joleen ; Henson, Stephanie A. ; Heywood, Karen J. ; Hogan, Patrick ; Houpert, Loïc ; Huh, Sik ; Inall, Mark E. ; Ishii, Masao ; Ito, Shin-ichi ; Itoh, Sachihiko ; Jan, Sen ; Kaiser, Jan ; Karstensen, Johannes ; Kirkpatrick, Barbara ; Klymak, Jody M. ; Kohut, Josh ; Krahmann, Gerd ; Krug, Marjolaine ; McClatchie, Sam ; Marin, Frédéric ; Mauri, Elena ; Mehra, Avichal ; Meredith, Michael P. ; Meunier, Thomas ; Miles, Travis ; Morell, Julio M. ; Mortier, Laurent ; Nicholson, Sarah ; O'Callaghan, Joanne ; O'Conchubhair, Diarmuid ; Oke, Peter ; Pallás-Sanz, Enric ; Palmer, Matthew D. ; Park, Jong Jin ; Perivoliotis, Leonidas ; Poulain, Pierre Marie ; Perry, Ruth ; Queste, Bastien ; Rainville, Luc ; Rehm, Eric ; Roughan, Moninya ; Rome, Nicholas ; Ross, Tetjana ; Ruiz, Simon ; Saba, Grace ; Schaeffer, Amandine ; Schönau, Martha ; Schroeder, Katrin ; Shimizu, Yugo ; Sloyan, Bernadette M. ; Smeed, David A. ; Snowden, Derrick ; Song, Yumi ; Swart, Sebastiaan ; Tenreiro, Miguel ; Thompson, Andrew ; Tintore, Joaquin ; Todd, Robert E. ; Toro, Cesar ; Venables, Hugh J. ; Wagawa, Taku ; Waterman, Stephanie N. ; Watlington, Roy A. ; Wilson, DougThe OceanGliders program started in 2016 to support active coordination and enhancement of global glider activity. OceanGliders contributes to the international efforts of the Global Ocean Observation System (GOOS) for Climate, Ocean Health, and Operational Services. It brings together marine scientists and engineers operating gliders around the world: (1) to observe the long-term physical, biogeochemical, and biological ocean processes and phenomena that are relevant for societal applications; and, (2) to contribute to the GOOS through real-time and delayed mode data dissemination. The OceanGliders program is distributed across national and regional observing systems and significantly contributes to integrated, multi-scale and multi-platform sampling strategies. OceanGliders shares best practices, requirements, and scientific knowledge needed for glider operations, data collection and analysis. It also monitors global glider activity and supports the dissemination of glider data through regional and global databases, in real-time and delayed modes, facilitating data access to the wider community. OceanGliders currently supports national, regional and global initiatives to maintain and expand the capabilities and application of gliders to meet key global challenges such as improved measurement of ocean boundary currents, water transformation and storm forecast.
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ArticleAtlantic meridional overturning circulation: Observed transport and variability(Frontiers Media, 2019-06-07) Frajka-Williams, Eleanor ; Ansorge, Isabelle ; Baehr, Johanna ; Bryden, Harry L. ; Chidichimo, Maria Paz ; Cunningham, Stuart A. ; Danabasoglu, Gokhan ; Dong, Shenfu ; Donohue, Kathleen A. ; Elipot, Shane ; Heimbach, Patrick ; Holliday, Naomi Penny ; Hummels, Rebecca ; Jackson, Laura C. ; Karstensen, Johannes ; Lankhorst, Matthias ; Le Bras, Isabela A. ; Lozier, M. Susan ; McDonagh, Elaine L. ; Meinen, Christopher S. ; Mercier, Herlé ; Moat, Bengamin I. ; Perez, Renellys ; Piecuch, Christopher G. ; Rhein, Monika ; Srokosz, Meric ; Trenberth, Kevin E. ; Bacon, Sheldon ; Forget, Gael ; Goni, Gustavo J. ; Kieke, Dagmar ; Koelling, Jannes ; Lamont, Tarron ; McCarthy, Gerard D. ; Mertens, Christian ; Send, Uwe ; Smeed, David A. ; Speich, Sabrina ; van den Berg, Marcel ; Volkov, Denis L. ; Wilson, Christopher G.The Atlantic Meridional Overturning Circulation (AMOC) extends from the Southern Ocean to the northern North Atlantic, transporting heat northwards throughout the South and North Atlantic, and sinking carbon and nutrients into the deep ocean. Climate models indicate that changes to the AMOC both herald and drive climate shifts. Intensive trans-basin AMOC observational systems have been put in place to continuously monitor meridional volume transport variability, and in some cases, heat, freshwater and carbon transport. These observational programs have been used to diagnose the magnitude and origins of transport variability, and to investigate impacts of variability on essential climate variables such as sea surface temperature, ocean heat content and coastal sea level. AMOC observing approaches vary between the different systems, ranging from trans-basin arrays (OSNAP, RAPID 26°N, 11°S, SAMBA 34.5°S) to arrays concentrating on western boundaries (e.g., RAPID WAVE, MOVE 16°N). In this paper, we outline the different approaches (aims, strengths and limitations) and summarize the key results to date. We also discuss alternate approaches for capturing AMOC variability including direct estimates (e.g., using sea level, bottom pressure, and hydrography from autonomous profiling floats), indirect estimates applying budgetary approaches, state estimates or ocean reanalyses, and proxies. Based on the existing observations and their results, and the potential of new observational and formal synthesis approaches, we make suggestions as to how to evaluate a comprehensive, future-proof observational network of the AMOC to deepen our understanding of the AMOC and its role in global climate.