Observations of the Dynamics of the Antarctic
Circumpolar Current in the Pacific Sector of the
Southern Océan
E. Zambianchi, G. Budillon, P. Falco and G. Spezie
Istituto di Meteorologia e Oceanografia, Istituto Universitario Navale, Via Acton 38,
80133 Napoli, Italy
Abstract
This paper describes long term measurements of the Antarctic Circumpolar
Current carried out by means of surface and sub-surface drifters deployed as of
the austral summer 1993-94, associated with XBT sections. At the surface, the
velocity présents a gross zonal flow pattern, directed eastwards. The field is characterized by strong méridional shear and by a complex multiple jet structure, suggested in particular by the observations in the vicinity of the Antarctic-Pacific
Ridge. The interaction with the bottom topography is seen to play a major rôle in
shaping both the mean and the eddy fields, with a characteristic space lag which
implies the presence of eddy-generating mechanisms in correspondence of major
topographie features. Our subsurface float observations dénoté a strong vertical
coupling in the velocity field. Velocities around 1000 m depth resemble those at
the surface, with a scale factor of about 1/4 in magnitude. This vertical cohérence
is consistent with previous hydrographie analyses and with preliminary potential
vorticity estimâtes drawn from our surface drifters data.
1 Introduction
The Southern Océan, and its largest circulation feature, the Antarctic Circumpolar
Current (ACC), play a fundamental rôle in the mass and heat budget of the world
océan. For this reason, in the framework of the Italian National Programme for
Antarctic Research (PNRA), a spécifie project has been conceived, entitled CLIMA
(Climatic Long-term Interaction for the Mass balance in Antarctica), whose focus
is the définition of the main aspects of the circulation of the Ross Sea and, at a
larger scale, of the ACC in the western portion of the Pacific sector of the Southern
Océan (PSSO hereafter) of which the Ross Sea constitutes a marginal basin.
In particular, research activities in the project hâve focused, as of 1993, on the
following topics: hydrology and dynamics of the Southern Océan (investigated
both by observations and by numerical simulations); air-sea interactions and rôle
of the meteoclimatic forcing; and fluxes of suspended matter [1].
In the framework of the CLIMA project, a Lagrangian investigation of the surface and subsurface dynamics of the ACC has been undertaken, along with an
attempt to periodically characterize the hydrological structure of the current by the
Circumpolar Current in the Pacific Sector of the
Southern Océan
E. Zambianchi, G. Budillon, P. Falco and G. Spezie
Istituto di Meteorologia e Oceanografia, Istituto Universitario Navale, Via Acton 38,
80133 Napoli, Italy
Abstract
This paper describes long term measurements of the Antarctic Circumpolar
Current carried out by means of surface and sub-surface drifters deployed as of
the austral summer 1993-94, associated with XBT sections. At the surface, the
velocity présents a gross zonal flow pattern, directed eastwards. The field is characterized by strong méridional shear and by a complex multiple jet structure, suggested in particular by the observations in the vicinity of the Antarctic-Pacific
Ridge. The interaction with the bottom topography is seen to play a major rôle in
shaping both the mean and the eddy fields, with a characteristic space lag which
implies the presence of eddy-generating mechanisms in correspondence of major
topographie features. Our subsurface float observations dénoté a strong vertical
coupling in the velocity field. Velocities around 1000 m depth resemble those at
the surface, with a scale factor of about 1/4 in magnitude. This vertical cohérence
is consistent with previous hydrographie analyses and with preliminary potential
vorticity estimâtes drawn from our surface drifters data.
1 Introduction
The Southern Océan, and its largest circulation feature, the Antarctic Circumpolar
Current (ACC), play a fundamental rôle in the mass and heat budget of the world
océan. For this reason, in the framework of the Italian National Programme for
Antarctic Research (PNRA), a spécifie project has been conceived, entitled CLIMA
(Climatic Long-term Interaction for the Mass balance in Antarctica), whose focus
is the définition of the main aspects of the circulation of the Ross Sea and, at a
larger scale, of the ACC in the western portion of the Pacific sector of the Southern
Océan (PSSO hereafter) of which the Ross Sea constitutes a marginal basin.
In particular, research activities in the project hâve focused, as of 1993, on the
following topics: hydrology and dynamics of the Southern Océan (investigated
both by observations and by numerical simulations); air-sea interactions and rôle
of the meteoclimatic forcing; and fluxes of suspended matter [1].
In the framework of the CLIMA project, a Lagrangian investigation of the surface and subsurface dynamics of the ACC has been undertaken, along with an
attempt to periodically characterize the hydrological structure of the current by the