Current effects on wind generated waves near an Ocean Eddy Dipole

Abstract

Ocean eddy dipoles are among the most common mesoscale features and may be ubiquitous across the global oceans. However, wave–current interactions in their proximity have not been extensively studied. Here we examine the impact of surface currents on the wave field near an ocean eddy dipole. Using the WW3 wave model, we conducted idealized numerical simulations to assess the influence of different configurations on the spatial variability of Significant Wave Height ($H_s$). Additionally, a two-month hindcast of a strong dipole event in the Southwestern Atlantic Ocean was performed using three distinct surface current products: SSalto/Duacs, HYCOM NCODA and GlobCurrent. Among these, HYCOM, which incorporates ageostrophic effects, provided a more detailed representation of oceanic energy compared to GlobCurrent and SSalto/Duacs, which primarily reflect geostrophic components. The hindcast assessment employed denoised altimeter-derived $H_s$ data, with a spatial resolution of approximately 6 km. The greatest increase in wave energy occurs in the region between the peak values of positive and negative vorticity, where the opposing surface currents reach their maximum intensity. Therefore, dipoles act as converging lenses for surface waves, channeling their refraction toward the central jet. Despite its poorer spatial and temporal resolutions, SSalto-Duacs surface current data provides more reliable $H_s$ fields, in the study region where geostrophic dynamics are expected to be significant or even dominant. Both Absolute Dynamic Topography derived surface current inputs produce comparable effects on the wave field, with the inclusion of the Ekman component yielding no substantial enhancement. HYCOM captures a broader range of dynamical processes, essential for accurately representing the total energy, though discrepancies with SSalto/Duacs data may arise from assimilation inaccuracies and model limitations. While gridded altimetry may underestimate total current components during dipole events, it offers precise insights into their positioning and evolution, useful for specific event analysis and near real-time forecasting for marine safety.