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

Abstract

We perform eddy-resolving and high vertical resolution numerical simulations of the circulation in an idealized equatorial Atlantic Ocean in order to explore the formation of the deep equatorial circulation (DEC) in this basin. Unlike in previous studies, the deep equatorial intraseasonal variability (DEIV) that is believed to be the source of the DEC is generated internally by instabilities of the upper-ocean currents. Two main simulations are discussed: solution 1, configured with a rectangular basin and with wind forcing that is zonally and temporally uniform, and solution 2, with realistic coastlines and an annual cycle of wind forcing varying zonally. Somewhat surprisingly, solution 1 produces the more realistic DEC; the large, vertical-scale currents [equatorial intermediate currents (EICs)] are found over a large zonal portion of the basin, and the small, vertical-scale equatorial currents [equatorial deep jets (EDJs)] form low-frequency, quasi-resonant, baroclinic equatorial basin modes with phase propagating mostly downward, consistent with observations. This study demonstrates that both types of currents arise from the rectification of DEIV, consistent with previous theories. The authors also find that the EDJs contribute to maintaining the EICs, suggesting that the nonlinear energy transfer is more complex than previously thought. In solution 2, the DEC is unrealistically weak and less spatially coherent than in the first simulation probably because of its weaker DEIV. Using intermediate solutions, this study finds that the main reason for this weaker DEIV is the use of realistic coastlines in solution 2. It remains to be determined what needs to be modified or included to obtain a realistic DEC in the more realistic configuration.

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Sandy Grégorio, Thierry Penduff, Guillaume Sérazin, Jean-Marc Molines, Bernard Barnier, and Joël Hirschi

) reduces the interannual AMOC variance but does not suppress it, especially at the basin’s southern end where the intrinsic std dev reaches 0.4 Sv. The contribution R of intrinsic processes to the total variance in the ¼° simulation is shown in Fig. 5c as its envelope defined in section 2f . Roughly 15%–30% of the total variance happens to be due to intrinsic processes over the Atlantic tropics and subtropics, with a marked increase of R from north to south. Three additional features are

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Alain Colin de Verdière and Michel Ollitrault

circulation ECCO model estimate with data constraints including altimetry, CTD and XBT data, and Argo and elephant seals profiles (but no Argo float parking depth velocities) and tested Sverdrup balance by choosing a depth z * where the vertical velocity could be neglected (<10 −8 m s −1 ), usually in the range 1000–1500 m. This test of Sverdrup balance was generally positive in the interior of the subtropical gyres and in the tropics away from the equator. With the Argo float displacements at 1000 and

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