Dynamical Filtering Highlights the Seasonality of Surface-Balanced Motions at Diurnal Scales in the Eastern Boundary Currents

Balanced motions (BM) and internal gravity waves (IGW) account for most of the kinetic energy budget and capture most of the vertical velocity in the ocean. However, estimating the contribution of BM to both issues at time scales of less than a day is a challenge because BM are obscured by IGW. To study the BM regime, we outlined the implementation of a dynamical filter that separates both classes of motion. This study used a high-resolution global simulation to analyze the Eastern Boundary Currents during the winter and summer months. Our results confirm the feasibility of recovering BM dynamics at short time scales, emphasizing the diurnal cycle in winter and its dampening in summer due to local stratification that prevents large vertical excursion of the surface boundary layer. Our filter opens up new possibilities for more accurate estimation of the vertical exchanges of any tracers at any vertical level in the water column. Moreover, it could be a valuable tool for studies focused on wave-turbulence interactions in ocean simulations.