Monitoring Agulhas Current Meanders using Current and Eddy Tracking Algorithms

Abstract

Tracking meanders of the Agulhas Current and their associated cyclonic eddies is essential for understanding episodic upwelling along the southeast coast of South Africa, particularly near Port Alfred where the inshore jet interacts strongly with the shelf. We developed a new temperature-gradient-based current-core tracker, the Port Alfred Current Tracker (PACT) and applied it alongside a sea surface height-derived tracker (an adapted version of Location of the Agulhas Current Core and Edges, LACCE) and the PY-Eddy-Tracker algorithm to detect meander events and associated cyclonic activity using 22 years of high-resolution CROCO output (WOES36). Using these methods, we detected 2.3 large meander events per year from PACT, 1.7 events per year from adapted LACCE, 0.6 events per year from eddy amplitude, 1 event per year from eddy area, and 1.3 events from eddy radius. Upon inspection of the link between Agulhas Current meanders and upwelling in the Port Alfred region, long-term analysis showed that most upwelling events occur in the absence of a meander and it is weakly correlated with meander or cyclonic eddy activity. Nonetheless, individual case studies reveal that long-lived meanders or cyclonic eddies can locally enhance upwelling. These results indicate that Agulhas Current meanders arise from a combination of coherent eddies and shifts in the core jet but upwelling at Port Alfred is primarily driven by strong, smooth current flow rather than meander-induced variability. Combining current-core and eddy-tracking diagnostics provides a more complete understanding of both meandering and upwelling dynamics along the southeast African margin.