Abstract
Wind is an important driver of large-scale ocean currents, imparting
momentum into the ocean at the sea surface. In particular, strong
westerly winds help to drive the Antarctic Circumpolar Current, which of
key importance for the global climate system. Over the past decades
observations established that the strength of the westerlies over the
Southern Ocean has increased as a result of climate change forcing. This
increase is consistent with global climate model simulations. The future
climate state depends strongly on how will the Antarctic Circumpolar
Current respond to this strengthening. Eddy saturation is a theoretical
regime where the transport of the current remains insensitive to the
strengthening of the westerlies. Instead, the strengthening of the
westerlies energizes transient eddies. Both satellite observations and
numerical simulations suggest that the Antarctic Circumpolar Current is
close to the eddy saturated limit. Traditionally eddy saturation has
been attributed to baroclinic processes, but recent work suggests that
barotropic processes that involve, e.g., standing meanders of the
Antarctic Circumpolar Current, can also be responsible for producing
eddy-saturated states. Here, we discus the different physical entities
of the“usual” baroclinic eddy saturation as well as the recent notion
of barotropic eddy saturation. We assess the relative importance of
barotropic and baroclinic processes in producing eddy-saturated states
using numerical simulations of primitive equations in an idealized
setup. Lastly, we discuss potential implications these processes have on
global ocean modeling.