the same as the barotropic case. The nonlinear behavior is also classified into three regimes referred to as amplitude vacillation, vortex pair and boundary trapped vortex regime, according to the temporal evolution between the potential vorticity centers within the different layer. The amplitude vacillation is characterized by the regular vacillation of the amplitude of the unstable wave, in which the behavior of the phase relationship between the centers is the same as the breaking wave in the barotropic case. The other two regimes are qualitatively same charader as mentioned in the barotropic case. An interesting phenomenon in the presence of the baroclinity is that the dependence of the zero potential vorticity flows on the behavior of the unstable wave. The change of this parameter can lead catastrophic change of the evolutional manner between amplitude vacillation and vortex pair. The theoretical explanation for these phenomena is also explained by the point vortices model.
We emphasized the importance of the temporal evolution of the phase relationship between the vorticity centers in the piecewise uniform (potential) vorticity region with different sign of (potential) vorticity. The idea could be applied to not only the boundary currents but also to various geophysical fluid instabilities. Examples of these will be found in extension of the western boundary currents (free jet), instability of baroclinic vortex and so on.
3. TOPOGRAPHICALLY TRAPPED CURRENT & EDDIES IN THE SOUTHERN CANADA BASIN
Features of the ocean currents in the southern Canada Basin of the Arctic Ocean were investigated using an ADCP data of a Beaufort Gyre Ice-Ocean Environmental Buoy (BG-IOEB) dur1ng 1992-1994. The major results were as follows. The first was the spatial distribution of eddy kinetic energy. On the flat and deep Canada Basin off Alaska, the circulation was governed by mesoscale eddies with their maximum activity in the cold halocline layer (Fig. 11). In contrast, on the Northwind Ridge and Chukchi Plateau the activity of the mesoscale eddies considerably weakened and the circulation was governed by the seafloor topography from the upper cold halocline layer to the Atlantic layer. This implied that the eddy kinetic energy was converted into the energy of topographically trapped currents. The second was a correlation between the seafloor topography and the horizontal velocity in the Atlantic layer below the main pycnocline (Fig. 12). Based on the first result, the eddy-topography interaction (Holloway, 1992) was considered to be a possible driving force for the Atlantic Water intrusion along the shelf breaks or the rims of sea mounts in the Arctic Ocean. We further quantified relationships in current scattering around the small scale submarine canyons and ridges on the Northwind Ridge and Chukchi Plateau using the distribution “topostrophy” indicative of the direction and sense of currents relative to bathymetry. The third was an intensification of both the barotropic and baroclinic current on the eastern slope of the Northwind Ridge (Fig. 13). It could be established through interactions between the Rossby wave and seafloor topography.
