Circumpolar variations in Southern Ocean eddy energy: An ensemble approach

Abstract:

Eddy energy in the Southern Ocean eddy field influences both the zonal and meridional oceanic transport. It is widely recognised that eddies in the Southern Ocean respond to changes in the wind stress forcing, but there remain uncertainties as to the spatial and temporal nature of the eddy response. This spatio-temporal eddy response is difficult to quantify from observations because the satellite record is short and the signature of the eddy field is noisy (unless eddy statistics are accumulated over a large region).

In this study, we use an ensemble of 50 “eddy-permitting” (0.25° resolution) ocean-sea ice model simulations (OCCIPUT) to investigate Southern Ocean eddy statistics. This large ensemble allows us to resolve eddy statistics over relatively small regions, and to characterise the relative importance of forced and intrinsic variance in the system in each region. This analysis reveals a surprising heterogeneity in the dynamics of Southern Ocean variability: some regions respond strongly and rapidly (< 6 months) to the wind stress and other regions respond to wind stress changes on longer (> annual) timescales, while many regions are dominated purely by intrinsic variability. These different eddy response regimes are categorised in terms of the mean flow dynamics and its interaction with topography in each region to provide an understanding of the dynamical basis of the circumpolar variation in Southern Ocean eddies.