Seasonal variability of Eddy Kinetic Energy in the Brazil current, South Brazil Bight

Abstract

The seasonal variability of Eddy Kinetic Energy (EKE) in the Brazil Current (BC) within the South Brazil Bight (22°S–28°S) remains poorly understood, particularly the role of energy conversion and redistribution terms. Using fourteen years of output from an eddy-resolving numerical simulation, we perform the first seasonal analysis of the EKE budget in this region. We find a pronounced along-stream asymmetry in the EKE seasonal cycle: upstream EKE peaks in summer, while downstream it peaks in winter. The barotropic instability is the primary modulator of EKE within the offshore flank of the mean BC jet. In contrast, baroclinic instability processes dominate beneath the jet core, as indicated by vertical eddy density fluxes. A key finding is that the advection of EKE exhibits the strongest correlation with EKE variability, identifying it as the principal mechanism for redistributing energy from generation sites. While eddy wind work shows no direct influence, pressure work peaks in the region of the Intermediate Western Boundary Current (IWBC), suggesting a potential energy pathway between the BC and the IWBC. Our results establish that the seasonal EKE cycle is not driven by local generation alone but is fundamentally controlled by the advective redistribution of energy from regions of high mesoscale activity.