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Audrey Delpech, Claire Ménesguen, Yves Morel, Leif N. Thomas, Frédéric Marin, Sophie Cravatte, and Sylvie Le Gentil

energy sources present in the ocean at low latitude is associated with planetary waves. It has been shown that in the Atlantic and Pacific Oceans, a large source of energy in the deep is associated with annual and semiannual Rossby waves, as well as intra-annual waves: 30-day, 1000-km mixed Rossby–gravity waves, associated with surface tropical instability waves, and short-scale variability, with periods around 70 days and wavelengths around 500 km ( Bunge et al. 2008 ; von Schuckmann et al. 2008

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Audrey Delpech, Claire Ménesguen, Yves Morel, Leif Thomas, Frédéric Marin, Sophie Cravatte, and Sylvie Le Gentil


At low latitudes in the ocean, the deep currents are shaped into narrow jets flowing eastward and westward, reversing periodically with latitude between 15°S and 15°N. These jets are present from the thermocline to the bottom. The energy sources and the physical mechanisms responsible for their formation are still debated and poorly understood. This study explores the role of the destabilization of intra-annual equatorial waves in the jets formation process, as these waves are known to be an important energy source at low latitudes. The study focuses particularly on the role of barotropic Rossby waves as a first step towards understanding the relevant physical mechanisms. It is shown from a set of idealized numerical simulations and analytical solutions that Non-Linear Triad Interactions (NLTI) play a crucial role in the transfer of energy towards jet-like structures (long waves with short meridional wavelengths) that induce a zonal residual mean circulation. The sensitivity of the instability emergence and the scale selection of the jet-like secondary wave to the forced primary wave is analyzed. For realistic amplitudes around 5-20 cm s−1, the primary waves that produce the most realistic jet-like structures are zonally-propagating intra-annual waves with periods between 60 and 130 days and wavelengths between 200 and 300 km. The NLTI mechanism is a first step towards the generation of a permanent jet-structured circulation, and is discussed in the context of turbulent cascade theories.

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W. K. Dewar, J. C. McWilliams, and M. J. Molemaker

speeds of 0.1–0.3 m s −1 . It is also important in eastern ocean basin variability, acting as the apparent source of intense, subsurface, submesoscale anticyclones known as “Cuddies” ( Simpson and Lynn 1990 ; Garfield et al. 1999 ) and contributes to the formation of the eastern Pacific “jets” and “squirts” ( Davis 1985 ; Flament et al. 1985 ; Kosro and Huyer 1986 ). The topography of the California coast consists of a relatively narrow shelf of a few tens of kilometers followed by a steep drop

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François Ascani, Eric Firing, Julian P. McCreary, Peter Brandt, and Richard J. Greatbatch

between solutions 1 and 2. In all solutions, instabilities of the upper-ocean mean equatorial circulation, known as tropical instability waves (TIWs), provide the source for DEIV, and a DEC with some resemblance to Atlantic observations is obtained. Surprisingly, the more realistic DEC is obtained in the more idealized simulation (solution 1). In particular, the EICs are found over a large zonal portion of the basin, and the EDJs form low-frequency, quasi-resonant, baroclinic equatorial basin modes

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Yang Jiao and W. K. Dewar

because of their tendencies toward upscale, inverse energy cascades ( Charney 1971 ). Other possibilities are that the mesoscale is unstable to gravity wave perturbations or loses energy via dissipative interactions with the boundaries. Spontaneous gravity wave generation is possible, but observational and theoretical evidence of it is not strong. Dissipative interactions with the boundaries, which include the ocean surface, are a somewhat more promising pathway. Turbulent, and thus dissipative

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Nils Brüggemann and Carsten Eden

from Lighthill radiation of gravity waves ( Ford et al. 2000 ), gravity wave drag on the balanced flow ( Müller 1976 ), or direct generation of unbalanced ageostrophic instabilities ( Molemaker et al. 2005 ). So far, it is unknown whether these processes of large-scale dissipation are efficient enough to balance the energy input into the ocean by wind and tides ( Ferrari and Wunsch 2009 ). On the other hand, numerical model studies from Capet et al. (2008c) and Molemaker et al. (2010) suggest

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C. Ménesguen, S. Le Gentil, P. Marchesiello, and N. Ducousso

and nearshore dynamics ( Shchepetkin and McWilliams 2005 ; Debreu et al. 2012 ; Soufflet et al. 2016 ). It is a split-explicit, free-surface, and terrain-following vertical coordinate oceanic model discretized on a C grid. The time-stepping algorithm is third-order accurate for the integration of advective terms and second-order accurate for internal gravity waves. It is a leapfrog Adams–Moulton predictor–corrector scheme (LF-AM3) complemented with a forward–backward (FB) feedback to extend the

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Alain Colin de Verdière and Michel Ollitrault

of both topography and oceanic motions (mesoscale eddies, internal waves). Difficulties in such estimations in the atmosphere have been explored by Smith (1978) , who emphasizes the topographic scales that need to be resolved for reliable estimates of the mountain drag. Because the spectrum of topographic slopes in the ocean is typically white at wavenumbers between 10 −2 and 10 cycles km −1 ( Bell 1975 ), the question of the choice of topography and velocity to be used for the evaluation of

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Thomas Meunier, Enric Pallàs Sanz, Miguel Tenreiro, José Ochoa, Angel Ruiz Angulo, and Christian Buckingham

oceanic vortex lenses ( Hua et al. 2013 ; Meunier et al. 2015 , 2018a ; Ménesguen et al. 2018 ). Apart from the lower computational cost when compared with performing simulations using primitive equation models, use of the QG framework offers the distinct advantage of simplifying the basic dynamical mechanisms, facilitating understanding of the physical processes at work. Since neither internal waves nor double diffusion processes exist in this model, a successful simulation of layering in the

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A. M. Treguier, C. Lique, J. Deshayes, and J. M. Molines

1. Introduction At midlatitudes, the atmospheric heat transport is performed by transient disturbances, large-scale cyclones, and anticyclones, as discussed, for example, by Kuo (1956) . At the same latitudes, in the ocean, both the time-mean circulation and the transient eddies contribute to the meridional heat transport ( Smith et al. 2000 ). The importance of the time-mean circulation, in the case of the oceanic heat transport, is due to the existence of large-scale currents such as the

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