Spatiotemporal energetics analysis of Deep Western Boundary Current eddies at 11°S, off north-eastern Brazil
André Lopes Brum
A * and José Luiz Lima de Azevedo A
A
Abstract
The three-dimensional energetics of deep mesoscale eddies is investigated in a time-dependent theoretical framework using 36-year output of a 1/10° eddy-resolving ocean general circulation model. Composite analyses are conducted based on 29 anticyclonic eddies in the Deep Western Boundary Current (DWBC) at 11°S. The DWBC constitutes a key component of the lower limb of the Atlantic Meridional Overturning Circulation, crucial for comprehending climate change dynamics. Energetics analyses reveal that within the DWBC isolated eddies, advection is the main source of eddy kinetic energy (EKE) and eddy potential energy (EPE). Near the coast, energy conversion terms show that the anticyclones drain energy from the mean DWBC, enhancing the eddy field. Depth-integrated analysis found direct and inverse energy cascades within the average DWBC eddy with similar magnitude and area coverage size. The eddy–mean flow interaction terms were analysed in an Eulerian frame of reference along the eddy area, depicting their variability while migrating at a fixed point. Overall, direct energy cascade dominates the barotropic energy conversions during eddy migration, with enhanced conversion rates associated with peaks of eddy velocity. By contrast, the baroclinic energy conversions presented alternate direct-inverse energy cascades during eddy migration. At the eddy core depth, the barotropic (baroclinic) energy pathway contributes to the growth (decay) of EKE (EPE) at a rate of ~1.0 J m−3 day−1 (5.4 × 10−6 J m−3 day−1). This study seeks to extend our knowledge of the energy budgets within deep mesoscale eddies, a key factor for understanding ocean dynamics and circulation.
Keywords: baroclinic instability, barotropic instability, deep mesoscale eddies, Deep Western Boundary Current, eddy kinetic energy, eddy potential energy, eddy–mean flow interactions, growth rate, time-dependent framework.
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