Sack Lunch Seminar (SLS)

Southern Ocean eddies: generation, propagation and decay

The Southern Ocean has high concentrations of eddy kinetic energy, but analysis of altimeter data and an ocean state estimate show that the generation of relatively large amplitude eddies is not a ubiquitous feature of the Southern Ocean but rather a phenomenon that is constrained to isolated, well-defined regions. Five “hotspots” of high probability of eddy generation are identified using altimeter data. These hotspots are located downstream of major topographic features, with their boundaries closely following f/H contours. Eddies generated in these locations do not propagate far but decay within the boundaries of the generation area. The anisotropy of the dispersion of eddy tracks in geographical coordinates versus a rotated coordinates system aligned with f/H contours, shows that eddies tend to follow f/H contours rather than f. Maps of buoyancy and shear production terms computed from a state estimation model show enhanced values of both conversion terms inside the hotspots, with buoyancy production two orders of magnitude larger than shear production. The mean potential density field estimated from Argo floats shows that inside the hotspots isopycnal slopes are steep, indicating availability of potential energy and providing further evidence of the main generation mechanism. The hotspots identified in this paper overlap with previously identified regions of standing meanders. We hypothesize that hotspot locations can be explained by the combined effect of topographic features, standing meanders which enhanced baroclinic instability and availability of potential energy to generate eddies via baroclinic instabilities.