| Summary: | Typescript (photocopy). Recently collected hydrographic data show that each of the four water mass zones previously identified in Drake Passage is characterized by a distinctly different vertical profile of Brunt-Vaisala frequency. Stratification in Drake Passage is rather weak, and the first baroclinic radius of deformation varies from 17.3 km for the Subantarctic Zone in the north to 7.7 km for the Continental Zone in the south. Using current meter records collected in 1979 at nine moorings and in 1977 at five moorings, the vertical structure of the low-frequency currents is described in terms of dynamic normal and empirical modes. Dominance of the barotropic and first baroclinic modes was evident, accounting for typically 83-99% of record variance. The first empirical mode, which explains more than 90% of record variance at most moorings, is surface-intensified, and appears to be a superposition of the barotropic and first baroclinic modes. Time scales are 20-50 days for the first empirical mode and 7-20 days for the bottom-trapped second empirical mode. The coherent spatial scales of the first two dynamic modes and the first empirical mode are similar to those presented by Sciremammano et al. (1980), while the scales of the second empirical mode are somewhat smaller for longitudinal separations. In the northern passage, currents are characterized by smaller time scales (12-15 days). Moreover, the vertical structure is richer probably due to topographic waves trapped near the shelf break or generated by an upstream ridge. Current-topography interaction in the rough bottom area is important in supporting bottom-trapping of currents and creating meanders. The effects of various stratification profiles on oceanic response to atmospheric forcing and on baroclinic instability were considered. The oceanic response to a simple atmospheric forcing function, the length scales of which are of the order of more than 100 km, is dominated by the barotropic mode. For the stratification profiles and mean currents ...
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