Gary Stefan F.

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Stefan F.

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  • Article
    The fate of North Atlantic Subtropical Mode Water in the FLAME model
    (American Meteorological Society, 2014-05) Gary, Stefan F. ; Lozier, M. Susan ; Kwon, Young-Oh ; Park, Jong Jin
    North Atlantic Subtropical Mode Water, also known as Eighteen Degree Water (EDW), has the potential to store heat anomalies through its seasonal cycle: the water mass is in contact with the atmosphere in winter, isolated from the surface for the rest of the year, and reexposed the following winter. Though there has been recent progress in understanding EDW formation processes, an understanding of the fate of EDW following formation remains nascent. Here, particles are launched within the EDW of an eddy-resolving model, and their fate is tracked as they move away from the formation region. Particles in EDW have an average residence time of ~10 months, they follow the large-scale circulation around the subtropical gyre, and stratification is the dominant criteria governing the exit of particles from EDW. After sinking into the layers beneath EDW, particles are eventually exported to the subpolar gyre. The spreading of particles is consistent with the large-scale potential vorticity field, and there are signs of a possible eddy-driven mean flow in the southern portion of the EDW domain. The authors also show that property anomalies along particle trajectories have an average integral time scale of ~3 months for particles that are in EDW and ~2 months for particles out of EDW. Finally, it is shown that the EDW turnover time for the model in an Eulerian frame (~3 yr) is consistent with the turnover time computed from the Lagrangian particles provided that the effects of exchange between EDW and the surrounding waters are included.
  • Article
    Overturning in the Subpolar North Atlantic Program : a new international ocean observing system
    (American Meteorological Society, 2017-04-24) Lozier, M. Susan ; Bacon, Sheldon ; Bower, Amy S. ; Cunningham, Stuart A. ; de Jong, Marieke Femke ; de Steur, Laura ; deYoung, Brad ; Fischer, Jürgen ; Gary, Stefan F. ; Greenan, Blair J. W. ; Heimbach, Patrick ; Holliday, Naomi Penny ; Houpert, Loïc ; Inall, Mark E. ; Johns, William E. ; Johnson, Helen L. ; Karstensen, Johannes ; Li, Feili ; Lin, Xiaopei ; Mackay, Neill ; Marshall, David P. ; Mercier, Herlé ; Myers, Paul G. ; Pickart, Robert S. ; Pillar, Helen R. ; Straneo, Fiamma ; Thierry, Virginie ; Weller, Robert A. ; Williams, Richard G. ; Wilson, Christopher G. ; Yang, Jiayan ; Zhao, Jian ; Zika, Jan D.
    For decades oceanographers have understood the Atlantic meridional overturning circulation (AMOC) to be primarily driven by changes in the production of deep-water formation in the subpolar and subarctic North Atlantic. Indeed, current Intergovernmental Panel on Climate Change (IPCC) projections of an AMOC slowdown in the twenty-first century based on climate models are attributed to the inhibition of deep convection in the North Atlantic. However, observational evidence for this linkage has been elusive: there has been no clear demonstration of AMOC variability in response to changes in deep-water formation. The motivation for understanding this linkage is compelling, since the overturning circulation has been shown to sequester heat and anthropogenic carbon in the deep ocean. Furthermore, AMOC variability is expected to impact this sequestration as well as have consequences for regional and global climates through its effect on the poleward transport of warm water. Motivated by the need for a mechanistic understanding of the AMOC, an international community has assembled an observing system, Overturning in the Subpolar North Atlantic Program (OSNAP), to provide a continuous record of the transbasin fluxes of heat, mass, and freshwater, and to link that record to convective activity and water mass transformation at high latitudes. OSNAP, in conjunction with the Rapid Climate Change–Meridional Overturning Circulation and Heatflux Array (RAPID–MOCHA) at 26°N and other observational elements, will provide a comprehensive measure of the three-dimensional AMOC and an understanding of what drives its variability. The OSNAP observing system was fully deployed in the summer of 2014, and the first OSNAP data products are expected in the fall of 2017.
  • Article
    Year-to-year reoutcropping of Eighteen Degree Water in an eddy-resolving ocean simulation
    (American Meteorological Society, 2015-04) Kwon, Young-Oh ; Park, Jong Jin ; Gary, Stefan F. ; Lozier, M. Susan
    Winter outcropping of the Eighteen Degree Water (EDW) and its subsequent dispersion are studied using a ° eddy-resolving simulation of the Family of Linked Atlantic Modeling Experiments (FLAME). Outcropped EDW columns in the model simulations are detected in each winter from 1990 to 1999, and particles are deployed in the center of each outcropped EDW column. Subsequently, the trajectories of these particles are calculated for the following 5 yr. The particles slowly spread away from the outcropping region into the nonoutcropping/subducted EDW region south of ~30°N and eventually to the non-EDW region in the greater subtropical gyre. Approximately 30% of the particles are found in non-EDW waters 1 yr after deployment; after 5 yr, only 25% of the particles are found within EDW. The reoutcropping time is defined as the number of years between when a particle is originally deployed in an outcropping EDW column and when that particle is next found in an outcropping EDW column. Of the particles, 66% are found to reoutcrop as EDW in 1 yr, and less than 5% of the particles outcrop in each of the subsequent 4 yr. While the individual trajectories exhibit significant eddy-like motions, the time scale of reoutcropping is primarily set by the mean circulation. The dominance of reoutcropping in 1 yr suggests that EDW outcropping contributes considerably to the persistence of surface temperature anomalies from one winter to the next, that is, the reemergence of winter sea surface temperature anomalies.
  • Article
    Lagrangian ocean analysis : fundamentals and practices
    (Elsevier, 2017-11-24) van Sebille, Erik ; Griffies, Stephen M. ; Abernathey, Ryan ; Adams, Thomas P. ; Berloff, Pavel S. ; Biastoch, Arne ; Blanke, Bruno ; Chassignet, Eric P. ; Cheng, Yu ; Cotter, Colin J. ; Deleersnijder, Eric ; Döös, Kristofer ; Drake, Henri F. ; Drijfhout, Sybren ; Gary, Stefan F. ; Heemink, Arnold W. ; Kjellsson, Joakim ; Koszalka, Inga M. ; Lange, Michael ; Lique, Camille ; MacGilchrist, Graeme ; Marsh, Robert ; Mayorga-Adame, Claudia G. ; McAdam, Ronan ; Nencioli, Francesco ; Paris, Claire B. ; Piggott, Matthew D. ; Polton, Jeff ; Rühs, Siren ; Shah, Syed H.A.M. ; Thomas, Matthew D. ; Wang, Jinbo ; Wolfram, Phillip J. ; Zanna, Laure ; Zika, Jan D.
    Lagrangian analysis is a powerful way to analyse the output of ocean circulation models and other ocean velocity data such as from altimetry. In the Lagrangian approach, large sets of virtual particles are integrated within the three-dimensional, time-evolving velocity fields. Over several decades, a variety of tools and methods for this purpose have emerged. Here, we review the state of the art in the field of Lagrangian analysis of ocean velocity data, starting from a fundamental kinematic framework and with a focus on large-scale open ocean applications. Beyond the use of explicit velocity fields, we consider the influence of unresolved physics and dynamics on particle trajectories. We comprehensively list and discuss the tools currently available for tracking virtual particles. We then showcase some of the innovative applications of trajectory data, and conclude with some open questions and an outlook. The overall goal of this review paper is to reconcile some of the different techniques and methods in Lagrangian ocean analysis, while recognising the rich diversity of codes that have and continue to emerge, and the challenges of the coming age of petascale computing.
  • Technical Report
    CLIMODE Subsurface Mooring Report : November 2005 - November 2007
    (Woods Hole Oceanographic Institution, 2013-03) Lund, John M. ; Davis, Xujing Jia ; Ramsey, Andree L. ; Straneo, Fiamma ; Torres, Daniel J. ; Palter, Jaime B. ; Gary, Stefan F. ; Fratantoni, David M.
    Two years of temperature, salinity, current, and nutrient data were collected on four subsurface moorings as part of the 2 year field component of the CLIMODE experiment. The moorings were located in North Atlantic’s subtropical gyre, south-east of the Gulf Stream. Two moorings, the most heavily instrumented, were close to the Gulf Stream, in the region where cold air outbreaks force large air-sea fluxes and where Eighteen Degree Water outcrops. Two other moorings were located farther south and carried more limited instrumentation. The moorings were initially deployed in November of 2005, turned around in November of 2006 and finally recovered in November of 2007. During the first year, the moorings close to the Gulf Stream suffered considerable blow down, and some of the instruments failed. During the second year, the blow down was greatly reduced and most instruments collected a full year worth of data.