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

1. Introduction The deep equatorial and tropical circulation is organized into systems of alternating eastward and westward jets ( Firing 1987 ; Firing et al. 1998 ; Johnson et al. 2002 ; Ollitrault et al. 2006 ; Ascani et al. 2010 ; Cravatte et al. 2012 ; Ollitrault and Colin de Verdière 2014 ; Qiu et al. 2013 ; Cravatte et al. 2017 ). We distinguish in particular (i) meridionally alternating off-equatorial jets with a meridional scale of ~3° within the 15°S–15°N latitude range, which

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

Bryan (1986) . The dynamics of the Gulf Stream and its eddy fluxes are often considered in the framework of a free eastward jet subject to baroclinic instability. In the classical models, such as Phillips or Charney’s (e.g., Pedlosky 1979 ), instability leads to the development of waves and eddies and thus generates a cross-jet eddy heat flux that tends to reduce the temperature gradient across the front. However, the Gulf Stream is a western boundary current, much more complex than a free zonal

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

; Youngs and Johnson 2015, manuscript submitted to J. Phys. Oceanogr. ). This deep equatorial circulation (DEC; see a list of abbreviations in Table 1 ) is composed of two types of flow: equatorial deep jets (EDJs), which are trapped at the equator and alternate with depth with a vertical wavelength of about 400–600 m, and equatorial intermediate currents (EICs), which have a large vertical scale and alternate with latitude every 1°–2° between about 5°S and 5°N. 1 Fig . 1. (a) Mean zonal component of

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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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Yang Jiao and W. K. Dewar

potential energy driven by the mixing. Equivalently, we provide an estimate of the mixing efficiency of CI for comparison with that estimated for K–H instability. We also characterize the evolution more broadly by addressing other energy reservoirs that may be affected by the unstable flow. We examine an idealized setting of a jet meeting the conditions for CI, compute the solution using the MITgcm, and analyze the results. We have examined a couple of profiles but will here focus on one modeled after

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Nils Brüggemann and Carsten Eden

, the setup considered in this study intends to simulate horizontally isotropic turbulence since we assume constant values of vertical and horizontal stratification as well as a constant planetary vorticity. Especially for larger scales, however, a change of the planetary vorticity causes a development of zonal jets and thus a highly anisotropic flow. A characteristic length scale of these zonal jets is the Rhines scale , where β is the change of planetary vorticity and U is a characteristic

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Alain Colin de Verdière and Michel Ollitrault

34°N to about 45°W and has a 72-Sv maximum. The northern cyclonic recirculation has a minimum of −24 Sv. The time-mean Gulf Stream is a jet between these two recirculations. We estimate the maximum eastward Gulf Stream transport from Fig. 3 with an error O (5 ≈ × 3) Sv from Fig. 1 . It reaches 68 Sv at 70°W, increases to about 97.5 Sv at 60°W, and decreases to 83 Sv at 55°W ( Fig. 4 ). This evolution of transport is rather similar to Richardson’s (1985) curve but with somewhat smaller

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