Wave-turbulence-mean flow interaction in the Antarctic Circumpolar Current
Wave-turbulence-mean flow interaction in the Antarctic Circumpolar Current
Abstract:
A high-resolution ocean model and altimetric observations are used to investigate the interaction
of waves, turbulence and mean flow in the Antarctic Circumpolar Current (ACC). Particular
emphasis is placed on the dynamical role of radiation stresses that result from the organisation of
the turbulence by the waves and mean shear and give rise to systematic, long-range momentum
transports, which predominantly accelerate the ACC. The dynamics of the wave-turbulence-mean
flow interaction is investigated by diagnosing the eddy momentum fluxes and their relation to
the downstream evolution of the mean zonal velocity and eddy kinetic energy. The kinematic
suppression of eddy diffusivities by the mean flow, closely related to the radiation stresses via
the Taylor-Bretherton identity, is also diagnosed. It is found that radiation stresses in the ACC,
organised by the baroclinic jets and standing barotropic Rossby waves, are limited in range by major
topographic features. Immediately downstream of topographic features, the standing Rossby waves
become barotropically unstable, leading to regions of enhanced eddy kinetic energy and mixing of
tracers, often referred to as storm tracks; in turn, the lateral redistribution of eddy energy is found
to be important in understanding the downstream evolution of the radiation stresses and their role
in transferring energy back to the mean flow. The implications of these results for the observation
of hydrographic fronts in the ACC are discussed.
of waves, turbulence and mean flow in the Antarctic Circumpolar Current (ACC). Particular
emphasis is placed on the dynamical role of radiation stresses that result from the organisation of
the turbulence by the waves and mean shear and give rise to systematic, long-range momentum
transports, which predominantly accelerate the ACC. The dynamics of the wave-turbulence-mean
flow interaction is investigated by diagnosing the eddy momentum fluxes and their relation to
the downstream evolution of the mean zonal velocity and eddy kinetic energy. The kinematic
suppression of eddy diffusivities by the mean flow, closely related to the radiation stresses via
the Taylor-Bretherton identity, is also diagnosed. It is found that radiation stresses in the ACC,
organised by the baroclinic jets and standing barotropic Rossby waves, are limited in range by major
topographic features. Immediately downstream of topographic features, the standing Rossby waves
become barotropically unstable, leading to regions of enhanced eddy kinetic energy and mixing of
tracers, often referred to as storm tracks; in turn, the lateral redistribution of eddy energy is found
to be important in understanding the downstream evolution of the radiation stresses and their role
in transferring energy back to the mean flow. The implications of these results for the observation
of hydrographic fronts in the ACC are discussed.