On the Frequency-Wavenumber Characteristics of Balanced Motions and Internal Gravity Waves in Eastern Boundary Currents

Internal gravity waves and (sub)mesoscale balanced motions have been shown to interact and exchange kinetic energy. Recent global tide-resolving and submesoscale-permitting global ocean simulations have pointed out the challenge to disentangle the two motions, since both of them share the same spatial and temporal scales. This challenge is emphasized in the Eastern Boundary Currents, due to the low eddy kinetic energy and high kinetic energy from internal gravity waves (IGW). Due to the scales of the phenomena we are interested in examining, data from either intensive measurements or high resolution models are required. Based on frequency-wavenumber spectra computed from a high resolution (1/48°, 25 s) model, we focus our study on the four major eastern boundary currents (California, Peru-Chile, Canarias, and Benguela). Each current is analyzed using around 6 of these spectra, given they are square regions of side 6°. Our analysis focuses on similarities and differences among these current systems, primarily on the ratio of kinetic energy between balanced motions (BM) and (IGW), considering both summer and winter in order to perform a deeper comparison. Our findings have shown that regions within these currents are relatively more energetic than the rest in boreal summer, with kinetic energy differences ranging from 2 to 10 times. More specifically, these energy differences come from either strong IGW or balanced motions. For instance, taking the most energetic region from each current, the California current kinetic energy showed to be dominated by IGW, while in the Benguela current BM are more energetic, highly related to the influence of the Agulhas current.