HR: 16:00h
AN: OS52K-07    [PDF]
TI: In situ Evidence of Deep Equatorial Layering due to Inertial Instability
AU: * Marc, d
EM: Marc.d.Orgeville@ifremer.fr
AF: IFREMER "Laboratoire de Physique des Oceans", B.P. 70, Plouzane, 29280 France
AU: Hua, L
EM: Bach.Lien.Hua@ifremer.fr
AF: IFREMER "Laboratoire de Physique des Oceans", B.P. 70, Plouzane, 29280 France
AU: Schopp, R
EM: Richard.Schopp@ifremer.fr
AF: IFREMER "Laboratoire de Physique des Oceans", B.P. 70, Plouzane, 29280 France
AU: Bunge, L
EM: Lucia.Bunge@lodyc.jussieu.fr
AF: IRD "Laboratoire d'Oceanographie Dynamique et de Climatologie", Universite Pierre et Marie Curie 4, Place Jussieu, Paris Cedex 05, 75252 France
AB: In situ latitudinal sections in the equatorial Atlantic provide evidence of thin homogeneous density layers vertically bounded by sharp peaks of Brunt-Vaissala frequency. In depth coordinates, these layers appear spatially disorganized while in isopycnal coordinates, their structure is quite well defined: they can reach two degrees in meridional extension and fifty meters in height. Such observations take place in the entire water column under the thermocline and layers occur in all synoptic sections mostly in the immediate vicinity of the equator. Double diffusion could be a candidate to explain such meridionally extended layering, but a large portion of the deep Atlantic equatorial water column is stable to this instability at the depths where layers are seen. Another mechanism, namely inertial instability, is proposed to explain our observations. The meridionnal distribution of potential vorticity in our data verifies the condition of linear inertial instability and its non-linear evolution is known to trigger extended density layering (Hua et al., JFM 1997). A spatial correlation between Brunt-Vaissala anomalies and gradients of angular momentum is observed for all sections: the same correlation also holds in numerical simulations of non-linear evolution of inertial instability. Thus this supports that layering is produced by inertial instability. The existence of this layering in all equatorial sections and its interpretation in terms of inertial instability highlight the possibility of a deep dynamical mixing process, favoured in the equatorial ocean. To determine the strength of this mixing, we have performed simple numerical simulations of inertial instability. They indicate enhanced levels of both vertical and meridional viscosities.
DE: 4231 Equatorial oceanography
DE: 4568 Turbulence, diffusion, and mixing processes
DE: 9325 Atlantic Ocean
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting