Jet Instability over Smooth, Corrugated, and Realistic Bathymetry - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Journal of Physical Oceanography Année : 2019

Jet Instability over Smooth, Corrugated, and Realistic Bathymetry

J. H Lacasce
  • Fonction : Auteur
Javier Escartin
Eric Chassignet
Xiaobiao Xu

Résumé

The stability of a horizontally and vertically sheared surface jet is examined, with a focus on the vertical structure of the resultant eddies. Over a flat bottom, the instability is mixed baroclinic/barotropic, producing strong eddies at depth that are characteristically shifted downstream relative to the surface eddies. Baroclinic instability is suppressed over a large slope for retrograde jets (with a flow antiparallel to topographic wave propagation) and to a lesser extent for prograde jets (with flow parallel to topographic wave propagation), as seen previously. In such cases, barotropic (lateral) instability dominates if the jet is sufficiently narrow. This yields surface eddies whose size is independent of the slope but proportional to the jet width. Deep eddies still form, forced by interfacial motion associated with the surface eddies, but they are weaker than under bar-oclinic instability and are vertically aligned with the surface eddies. A sinusoidal ridge acts similarly, suppressing baroclinic instability and favoring lateral instability in the upper layer. A ridge with a 1-km wavelength and an amplitude of roughly 10 m is sufficient to suppress baroclinic instability. Surveys of bottom roughness from bathymetry acquired with shipboard multibeam echo sounding reveal that such heights are common beneath the Kuroshio, the Antarctic Circumpolar Current, and, to a lesser extent, the Gulf Stream. Consistent with this, vorticity and velocity cross sections from a 1/508 HYCOM simulation suggest that Gulf Stream eddies are vertically aligned, as in the linear stability calculations with strong topography. Thus, lateral instability may be more common than previously thought, owing to topography hindering vertical energy transfer.
Fichier principal
Vignette du fichier
LaCasce2019.pdf (4.12 Mo) Télécharger le fichier
Origine : Fichiers éditeurs autorisés sur une archive ouverte
Loading...

Dates et versions

hal-02324024 , version 1 (21-10-2019)

Identifiants

Citer

J. H Lacasce, Javier Escartin, Eric Chassignet, Xiaobiao Xu. Jet Instability over Smooth, Corrugated, and Realistic Bathymetry. Journal of Physical Oceanography, 2019, 49 (2), pp.585-605. ⟨10.1175/JPO-D-18-0129.1⟩. ⟨hal-02324024⟩
18 Consultations
47 Téléchargements

Altmetric

Partager

Gmail Facebook X LinkedIn More