Quantifying the Impact of Wind‐Current Feedback on Mesoscale Variability in Forced Simulation Experiments of the Agulhas Current Using an Eddy‐Tracking Algorithm

Abstract

AbstractThe variability in the source regions of the Agulhas Current is influenced by mesoscale eddies. While existing numerical models are successfully able to capture many aspects of the Agulhas Current, many models are unable to accurately represent the observed eddy dissipation and interaction processes, affecting our understanding of mesoscale variability within the current. In this study, we compare two forced simulation experiments in a regional Hybrid Coordinate Ocean Model (HYCOM), where we change the wind forcing, and using an eddy‐tracking algorithm quantify the local effect of the changed wind stress on source region eddies and their interaction with the northern Agulhas Current. There is an overall reduction in eddy kinetic energy (EKE) over the domain, and the representation of Agulhas Current velocities are improved. This study shows that the contribution of meanders and small eddies to the total EKE of the region is greater than the EKE contribution from tracked mesoscale eddies. Changes in eddy properties resulting from the change in forcing from absolute to relative winds (the wind speed relative to the current speed) have resulted in significantly different mesoscale eddy properties. Finally, the evolution of meanders in the Agulhas Current, including the frequency and dissipation of smaller meanders and Natal Pulse type meanders, was assessed using HYCOM experiments and compared to satellite observations. The simulated frequency of smaller meanders compares more favorably to the observations with the change in wind forcing. However, larger Agulhas Current meanders are now too infrequent in the regional HYCOM.