Shear-Induced Submesoscale Eddies along an Eastern Boundary Current

Abstract Generation, occurrence, and properties of submesoscale (10–50-km radius) eddies along the Wadjemup (Rottnest) continental shelf, southwest Australia, are investigated using 9 years (2010–18) of hourly high-frequency (HF) radar surface current observations supplemented by satellite remote sensing and wind data. Majority of anticyclonic (cyclonic) eddies formed in August (September) had lifespans ∼5 h and were 15–20 km in diameter. They were present along the boundaries of the Leeuwin Current (LC) and once formed remained in the vicinity of their generation region. Anticyclonic eddies formed preferentially inshore of the LC, while cyclonic eddies prevailed along offshore boundary of the LC. Seasonally, generation hotspots of anticyclonic eddies migrated latitudinally, while cyclonic eddies were clustered offshore in the Perth Canyon region and had a more complex pattern. For both cyclonic and anticyclonic eddies, the generation mechanism was linked to shear instability in the surface currents, at the interface with mesoscale eddies, and wind-induced shear. The wind-induced shear acted only above a wind speed threshold that enhanced the horizontal shear and contributed to both eddy generation and dissipation. Significance Statement This study aims to explore spatial–temporal variations in the occurrence and properties of submesoscale eddies and their generating conditions along the Wadjemup continental shelf, southwest Australia. This region is a hotspot for the generation of submesoscale (10–50-km radius) eddies in the presence of a highly energetic mesoscale eddy field associated with the Leeuwin Current (LC), an anomalous eastern boundary current. Our results from a unique 9-yr high-frequency radar database of synoptic surface currents highlight the role of ocean surface circulation and wind forcing in promoting shear-induced eddy generation. Although submesoscale eddies are numerous, especially in August–September, and ever present in this region, they are short-lived (<12 h) features formed along shear-induced instabilities in LC interfaces and under southerly wind conditions.