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| Bourles, B; D'Orgeville, Marc; Eldin, G; Gouriou, Y; Chuchla, R; Dupenhoat, Y; Arnault, S. |
| Eastward currents in the thermocline and subthermocline layers of the tropical Atlantic Ocean are described using observations obtained during two boreal summer cruises covering the whole equatorial basin. The analysis focuses on the eastward evolution of zonal currents in the thermocline and sub-thermocline. The Equatorial Undercurrent is not found close to the African coast in boreal summer 2000, maybe because of interannual variability. As observed in the Pacific, the South and North Equatorial Undercurrents are shown to shift poleward from west to east, and the two cruises indicate that the North Equatorial Undercurrent does not enter the Gulf of Guinea. The South and North Intermediate Countercurrents are variable with longitude and, contrarily to the... |
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| Ano: 2002 |
URL: http://archimer.ifremer.fr/doc/00000/10036/9583.pdf |
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| D'Orgeville, Marc; Hua, Bach-lien; Schopp, Richard; Bunge, L. |
| The deep equatorial track of the world ocean is subject to intense zonal flow fields that still remain to be better understood. Inertial instability has been invoked to explain some of its features. Here we present possible in situ imprints of such a mechanism in the equatorial Atlantic Ocean below the thermocline. We analyse the observed pattern of homogeneous density layers of 50 - 100 m vertical scale, which are characterized by a large meridional coherency up to 2degrees of latitude, a concentration in the vicinity of the equator and foremost a vertical localization within regions of well-mixed angular momentum ( westward jets). These distinctive properties suggest inertial instability to be a plausible mechanism for this extended layering. Numerical... |
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| Ano: 2004 |
URL: http://archimer.ifremer.fr/doc/00000/10892/9229.pdf |
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| Hua, Bach-lien; D'Orgeville, Marc; Fruman, Mark; Menesguen, Claire; Schopp, Richard; Klein, Patrice; Sasaki, H. |
| stability of mixed Rossby gravity (MRG) waves has been investigated numerically using three-dimensionally consistent high-resolution Simulations of the continuously stratified primitive equations. For short enough zonal wavelength, the westward phase propagating MRG wave is strongly destabilized by barotropic shear instability leading , to the formation of zonal jets. The large-scale instability of the zonally short wave,generates zonal jets because it consists primarily of sheared meridional motions, as shown recently for the short barotropic Rossby wave problem. Simulations were done in a variety of domain geometries: a periodic re-entrant channel, a basin with a short MRG wave forced in its western part and a very long channel initialized with a... |
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| Ano: 2008 |
URL: http://archimer.ifremer.fr/doc/2008/publication-5913.pdf |
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| D'Orgeville, Marc; Hua, Bach-lien. |
| This study revisits the problem of the zonally symmetric instability on the equatorial beta-plane. Rather than treating the classical problem of a steady basic flow, it treats a sequence of problems of increasing complexity in which the basic flow is oscillatory in time with a frequency omega(0). First, for the case of a homogeneous fluid, a time-oscillating barotropic shear forcing may excite a subharmonic parametric resonance of inertial oscillations. Because of the continuous distribution of inertial oscillation frequencies, this resonance occurs at critical inertial latitudes y(c). such that beta y(c) = +/-omega(0)/2. Next the effects of stratification, characterized by Brunt-Vaisala frequency N, are taken into account. It is shown analytically (in... |
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Palavras-chave: Equatorial wave; Dynamical model; Oscillating shear flows. |
| Ano: 2005 |
URL: http://archimer.ifremer.fr/doc/2005/publication-433.pdf |
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| D'Orgeville, Marc; Hua, Bach-lien; Sasaki, H. |
| The response of the deep equatorial ocean to an oscillatory baroclinic western boundary current is investigated in a continuously stratified primitive equation model. The symmetry of the current about the equator is such that mixed Rossby-gravity (MRG) waves are excited in the western part of the equatorial ocean. Depending on the forcing frequency, short to long scale (when compared to equatorial Rossby radius) monochromatic (MRG) waves are selected. The subsequent MRG wave destabilization generally leads to a much higher vertical mode response than the forced MRG wave mode. In a channel, short MRG waves are destabilized by shear instability (Hua et al., 2007). In a basin, the destabilization occurs in the vicinity of the western boundary and leads to... |
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| Ano: 2007 |
URL: http://archimer.ifremer.fr/doc/2007/publication-2534.pdf |
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