Deep variability in the Kuroshio Extension
In 2004 an array of current and pressure recording inverted echo sounders was deployed within the Kuroshio Extension as part the Kuroshio Extension System Study (KESS). One of the goals of KESS was to investigate the relationship between upper-ocean circulation patterns and the deep-barotropic currents. In order to understand the processes which couple the upper and deep ocean in the Kuroshio Extension it is helpful to first provide a comprehensive investigation of dynamical balances in the deep Kuroshio Extension. ^ In the deep Kuroshio Extension, variability is generated locally and remotely. The strongest deep eddies had cyclonic vorticities greater than 0.2f0, where f0 is the Coriolis parameter, and are caused by topographic stretching when water columns are advected off isolated seamounts in the region. Strong incident currents drive water columns off seamounts to form cyclones with relative vorticity consistent with a layered potential vorticity conservation calculation. ^ Besides locally-generated strong deep eddies, larger-scale and weaker deep cyclones and anticyclones propagated south-southwestward through KESS region. Using complex empirical orthogonal function (CEOF) analysis, the deep-pressure signals were identified as 30-60 day short barotropic topographic Rossby waves (TRWs). As the deep eddies encountered the Kuroshio Extension, upper-ocean meanders steepened and deep eddies intensified. The joint intensification of the upper and deep circulations was also seen by strong energy and vertical coherence in the 30-60 day band near the Kuroshio jet axis. The lateral phase offset between upper and deep ocean anomalies is consistent with joint baroclinic development patterns. ^ Analyses of 30-660 day bottom pressures, from the Ocean General Circulation Model for the Earth Simulator (O1-hS), suggested that the likely origin of the observed TRWs was the Shatsky Rise. Outside the KESS region, 30-60 day band-pass filtered bottom pressures were also consistent with Rossby-wave propagation on a combined planetary and topographic beta plane. The meandering Kuroshio Extension was shown to be the likely generation source of the TRWs. The dominant Kuroshio Extension meander in the 30-60 day band has the correct zonal wavelength to couple to the topographic Rossby wave field on the Shatsky Rise. ^
Andrew Dale Greene,
"Deep variability in the Kuroshio Extension"
Dissertations and Master's Theses (Campus Access).