Dynamics of the Wind-Driven Sea Level Variation around Antarctica

Coastal sea level variation around Antarctica is characterized by a coherent (circumpolarly in-phase) fluctuation, correlated with the Antarctic Oscillation (AAO). This study addresses the dynamics of the wind-driven sea level variation around Antarctica. A realistic barotropic numerical model reproduced well the observed sea level around Antarctica. From numerical model experiments, the authors demonstrate that the forcing responsible for the coastal sea level is the wind stress at the coastal boundary. Both the dominant coherent signal and westward propagating signals are identified in the model, and these signals are trapped over the shelf and slope around Antarctica. As a mechanism of these trapped signals, the authors consider analytical solutions of the oceanic response to alongshore wind stress over the shelf and slope in the circumpolar domain. In these solutions, besides the shelf wave mode, a wavenumber-zero mode appears and characterizes the coastal dynamics around Antarctica. At periods from 10 to 200 days, the coherent sea level can be explained quantitatively by the solution of this wavenumber-zero mode with a 5-10-day damping time scale. The spectral peaks of the westward propagating signals can be explained by the resonance of the shelf wave mode. The wavenumber-zero mode can respond to the wavenumber-zero forcing at any frequency and the degree of response increases with decreasing frequency. In addition, the wavenumber-zero component of wind stress, corresponding to the AAO variation, is a dominant forcing. Therefore, the coherent sea level variation around Antarctica is preferably generated and becomes a dominant feature in the circumpolar domain, particularly at lower frequencies.