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José L. L. Azevedo, Doron Nof, and Mauricio M. Mata

1. Introduction Migration of eddies in the ocean can be induced by several mechanisms. The primary mechanism results from latitudinal variation of the Coriolis parameter, which imposes a westward drift on oceanic eddies (e.g., Flierl 1979 ; Nof 1981 ; Killworth 1983 ; Cushman-Roisin et al. 1990 ). Advection by surrounding currents and propulsion related to neighboring eddies or sea bottom topography (i.e., topographic β ) can also induce eddy movement. Chelton et al. (2007 , 2011

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Jacob M. Steinberg, Noel A. Pelland, and Charles C. Eriksen

1. Introduction Eddies play important yet often undetected roles in the transport and distribution of oceanic heat, salt, and nutrients. They occupy a range of spatial scales, are found at various depths in all oceans, and are inherently transient. Submesoscale coherent vortices (SCVs)—gradient-wind balanced, preferentially anticyclonic, subsurface intensified, isolated lenses with horizontal length scales comparable to or smaller than the first baroclinic deformation radius and Rossby numbers

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Carsten Eden, Richard J. Greatbatch, and Dirk Olbers

1. Introduction The Boussinesq form of the conservation equation for a tracer with concentration b in the ocean (or the atmosphere) is given by where u denotes the instantaneous, three-dimensional velocity and Q is a forcing term. Both the ocean and atmosphere are turbulent fluids, full of “rapidly evolving perturbations” (eddies) on a “slowly evolving mean state.” The presence of the eddies means that the instantaneous tracer distribution is often of little interest; instead, it is the

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Hiromichi Ueno, Kanako Sato, Howard J. Freeland, William R. Crawford, Hiroji Onishi, Eitarou Oka, and Toshio Suga

Ohtani 1999 ). The AS and the Alaska Current, a broad northward current flowing in the eastern Gulf of Alaska, are known to involve offshore meanders and anticyclonic eddies (both are referred to as eddies in this paper). In the Gulf of Alaska, three types of eddies have been identified based on their formation region. Haida eddies form in winter off the west coast of the Queen Charlotte Islands (∼53°N) and move mostly westward to the central Gulf of Alaska ( Crawford and Whitney 1999 ; Crawford

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Tzu-Ling Chiang and Tangdong Qu

1. Introduction Subthermocline eddies have been observed in many parts of the global ocean, including those in the Mediterranean outflow (e.g., Richardson et al. 2000 ), in the Red Sea outflow (e.g., Shapiro and Meschanov 1991 ), in the California Undercurrent (e.g., Simpson and Lynn 1990 ), and in the Peru–Chile Undercurrent (e.g., Johnson and McTaggart 2010 ). These subthermocline eddies are largely invisible at the sea surface, but they may significantly affect the heat, freshwater, and

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Mengrong Ding, Pengfei Lin, Hailong Liu, and Fei Chai

1. Introduction As a nonnegligible component of the energy cycle of the global oceans, ubiquitous mesoscale eddies play a vital role in transporting mass, salt, heat, and biogeochemical tracers in the ocean (e.g., Bryden and Brady 1989 ; Stammer 1998 ; Jayne and Marotzke 2002 ; Zhang et al. 2014 ; Griffies et al. 2015 ), as well as in air–sea interactions (e.g., O’Neill et al. 2003 ; Small et al. 2008 ; Frenger et al. 2013 ; Ma et al. 2015 ). Along their westward propagating paths

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Hjálmar Hátún, Charles C. Eriksen, and Peter B. Rhines

this freshwater is likely to be trapped along the Labrador continental shelf ( Myers 2005 ). The West Greenland Current provides an alternate source of low-salinity near-surface water ( Schmidt and Send 2007 ) and warm, saline middepth water as well. The observations discussed herein support this restratification pathway. Recent observational and modeling studies have emphasized the importance of anticyclonic eddies (“Irminger rings”) for the shelf–basin heat exchange in the Labrador Sea, but their

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Ian Grooms, Louis-Philippe Nadeau, and K. Shafer Smith

1. Introduction Mesoscale eddies are a ubiquitous feature of ocean dynamics and have been the subject of myriad investigations. Gill et al. (1974) showed that the potential energy of the large-scale-mean circulation is much greater than its kinetic energy and argued that the conversion of large-scale available potential energy by baroclinic instability is primarily responsible for the ubiquity of mesoscale eddies. Diagnostic studies of eddy energetics in numerical simulations began in the

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Emily Shuckburgh, Guillaume Maze, David Ferreira, John Marshall, Helen Jones, and Chris Hill

1. Introduction Interactions at the ocean surface form an integral part of the variability of the earth system and in particular its climate. These interactions include thermodynamically mediated changes to the ocean heat budget; changes to the ocean salinity budget via evaporation and precipitation; exchanges of gases such as oxygen, carbon dioxide, and nitrous oxide; and processes influencing biological productivity. Ocean mesoscale eddies may modulate such interactions, particularly in eddy

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Stephanie Waterman, Nelson G. Hogg, and Steven R. Jayne

1. Introduction The Kuroshio Extension System Study (KESS) was a large field experiment focused on the Kuroshio Extension (KE) jet at the location of its maximum time-mean eddy kinetic energy (EKE). Among its goals was to better understand the processes governing the intense meandering and eddy variability of the jet and the nature of the interaction of the jet and its eddy variability ( Donohue et al. 2008 ). As such, KESS provides new observations of the KE jet, its eddy variability, and

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