Lee Waves Break Eddy Saturation of the Antarctic Circumpolar Current

Eddy-resolving ocean models suggest that the transport of the Antarctic Circumpolar Current (ACC) may be insensitive to increasing wind. This insensitivity is due to eddies that flatten the isopycnals and compensate for their wind-driven steepening. However, the eddy-resolving models do not accurately represent the eddy dissipation processes that occur at scales smaller than the model resolution, including lee wave generation at rough topography. Using a lee wave parameterization in an idealized model of the Southern Ocean, we show that the ACC transport becomes more sensitive to wind when the lee wave drag is included. The sensitivity arises from the dependence of the lee wave drag on the bottom stratification. When the bottom stratification increases in response to wind, it increases the lee wave generation, and hence the eddy dissipation, at rough topography. As a result, the ACC shear (baroclinic transport) increases to drive stronger eddy generation to compensate.

Automated summary

Using an idealized model of the Southern Ocean and a lee wave parameterization, this study finds that the sensitivity of the Antarctic Circumpolar Current (ACC) to wind increases when lee wave drag is considered. This is due to the dependence of lee wave drag on the bottom stratification, which leads to increased eddy dissipation and stronger eddy generation to compensate for the increased ACC shear (baroclinic transport).