What Can Meandering Front Spectra Tell Us about Jet Stability?

Major ocean fronts, such as the Gulf Stream, Kuroshio Extension, and Antarctic Circumpolar Current (ACC), exhibit a wide spectrum of meander frequencies. These ocean fronts have both lateral and vertical shear pointing to the influence of mixed barotropic and baroclinic instabilities. In particular, the Kuroshio Extension vacillates on interannual time scales between weakly and strongly meandering states following meridional shifts of the mean jet axis. Meridional shifts of ~1 degree have been observed to lag large-scale climate fluctuations in the Pacific Decadal Oscillation, but no dynamical connection has been made to date linking meridional shifts of the jet and the onset of jet instability. Using twenty-three years of the daily AVISO satellite altimetry product and applying a thin-jet analysis with coordinates being longitude and jet latitude anomaly, it is shown that there is a distinct change in the meander spectrum between stable and unstable states. During stable states the jet exhibits weak variance with a red power spectrum. During unstable states there is enhanced variance and a shift in the spectral density that peaks near 40 days at 145E. Simultaneously, the jet stabilization point shifts upstream during unstable states. Band-pass filtering the data shows the presence of wave trains propagating from north to south during unstable states. Barotropic anomalies of a similar nature were observed during the Kuroshio Extension System Study between 2004-2006, showing the presence of these anomalies was not an isolated event. This work suggests that external influences play an important role in the Kuroshio Extension system and that the eddy-mean flow interaction likely disrupts the barotropic governor of the system.