Propagating Bottom Pressure Signals around Antarctica at 1–2-Day Periods and Implications for Ocean Modes

Abstract

Previous studies of barotropic ocean dynamics have shown that several global normal modes are possible at periods between 1 and 2 days. The role of these modes in diurnal tidal dynamics is well documented, but finding evidence for their direct excitation by atmospheric forcing has remained elusive. Analyses of a barotropic ocean model and a limited number of bottom pressure records in the Southern Ocean described here provide evidence for large-scale, coherent signals propagating westward around Antarctica at 1?2-day periods. Phases are roughly consistent with the fundamental Kelvin wave structure underlying a number of normal modes with significant expressions in the Southern Ocean. Model and data results suggest the weak excitation of several of these normal modes by atmospheric pressure fluctuations. Strong dissipation also contributes to their weak amplitudes and makes it difficult to detect a truly global signal in the data.