Scales, growth rates and spectral fluxes of baroclinic instability in the ocean

• Main Authors: Ross Tulloch, John Marshall, Chris Hill, K. Shafer Smith
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2011
• Subjects: Antarctic; The Antarctic; Antarc*
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.713.5457; http://www.cims.nyu.edu/%7Eshafer/papers/TullochMarshallHillSmith_jpo11.pdf

An observational, modeling, and theoretical study of the scales, growth rates, and spectral fluxes of baro-clinic instability in the ocean is presented, permitting a discussion of the relation between the local instability scale; the first baroclinic deformation scale Rdef; and the equilibrated, observed eddy scale. The geography of the large-scale, meridional quasigeostrophic potential vorticity (QGPV) gradient is mapped out using a cli-matological atlas, and attention is drawn to asymmetries between midlatitude eastward currents and sub-tropical return flows, the latter of which has westward and eastward zonal velocity shears. A linear stability analysis of the climatology, under the ‘‘local approximation,’ ’ yields the growth rates and scales of the fastest-growing modes. Fastest-growing modes on eastward-flowing currents, such as the Kuroshio and the Antarctic Circumpolar Current, have a scale somewhat larger (by a factor of about 2) than Rdef. They are rapidly growing (e folding in 1–3 weeks) and deep reaching, and they can be characterized by an interaction between interior QGPV gradients, with a zero crossing in the QGPV gradient at depth. In contrast, fastest-growing modes in the subtropical return flows (as well as much of the gyre interiors) have a scale smaller thanRdef (by a factor of between 0.5 and 1), growmore slowly (e-folding scale of several weeks), and owe their existence to the interaction of a positive surface QGPV gradient and a negative gradient beneath.