[A-CG38] Dynamics of Oceanic and Atmospheric Waves, Vortices, and Circulations

[ACG38-09] An interpretation of the "eddy saturation" in the Antarctic Circumpolar Current based on the resonance of baroclinic Rossby waves

*Takuro Matsuta¹, Humio Mitsudera¹ (1.Hokkaido University, The Institute of Low Temperature Science)

Keywords:Antarctic Circumpolar Current, Eddy saturation, Resonance of baroclinic Rossby waves

Although the westerly winds have been intensified and shifted southward in the Southern Ocean since the 20th century, model studies and observations have suggested that the circumpolar transport of the Antarctic Circumpolar Current is relatively insensitive to changes in wind forcing. This is often dubbed as “eddy saturation”. While previous studies have focused on the gyre circulation or the standing meander in the lee of significant topographic features as eddy saturation mechanisms, the stationary wave trapped over the topography has been overlooked. Here, we show that the resonance of the baroclinic Rossby wave contributes to the eddy saturation using numerical experiments. To highlight roles of the resonant baroclinic Rossby wave, we compare the idealized channel under westerly winds with that under easterly winds. The circumpolar transport is saturated for westerly winds above a critical strength, while it responds linearly to changes in the wind forcing below this strength. This eddy saturation regime agrees with the resonant regime of the baroclinic Rossby wave, indicating that the resonant wave is responsible for the eddy saturation. Furthermore, we confirm that the vertical and horizontal structures of the stanidng wave signatures in the eddy saturation regime agrees with those of the analytical solution of the resonant baroclinic Rossby wave qualitatively.