HR: 1300h
AN: OS52D-16    [PDF]
TI: On the Role of Non-Linear Inertial Instability in Vertical Upscale Transfer
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
AB: Diagnostics of potential vorticity in different equatorial in situ observations (see Hua el al. JFM 1997 and d'Orgeville et al., OS39 Oral) show the signature of inertial instability. However it seems to occur at several vertical scales. The simple inviscid linear theory of inertial instability predicts its growth preferentially at the smallest vertical scale, and is therefore not able to explain the observations. Use of a viscous linear theory enables a finite vertical scale, but with realistic oceanic values of dissipation and forcing the selected scale is still smaller than in the observations. Here we explore numerically non-linear inertial instability to address the question of vertical scale selection. We analyse with a primitive equations model the classical zonally symmetric case of a prescribed equatorial barotropic shear flow in stratified conditions, without explicit vertical dissipation to enhance inertial and non-linear effects. In the forced/damped problem, the flow evolution exhibits a vertical upscale transfer as soon as a non-linear regime is reached. This inverse vertical cascade is provided solely through non-linear interactions of several vertical unstable modes, and does not require the parametrisation of a secondary Kelvin-Helmholz instability as in Griffiths (JAS 2003). In this first case, the upscaling approaches the marginal linear unstable vertical mode, while in the free decay problem, the inverse cascade continues beyond. In a longitudinal equatorial channel, we then explore the effect of a zonally varying non-divergent barotropic shear flow. Vertical upscale transfer, still present, depends strongly on the ability of the system to develop absolute instability. Various prescribed flows are presented in this case.
DE: 4231 Equatorial oceanography
DE: 4568 Turbulence, diffusion, and mixing processes
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting