Monsoon‐Driven Wave–Current Interactions in the Arabian Sea Great Whirl: Wave Footprints Observed by SWOT/CFOSAT and Simulated by SWAN

Abstract

The Arabian Sea Great Whirl (GW) is a large, quasi‐stationary anticyclonic eddy that develops under the southwest monsoon, combining strong surface‐current shear with an energetic and seasonally organized wavefield. This setting provides a distinctive natural laboratory for examining wave–current interactions beyond the transient mid‐latitude regimes emphasized in previous work. Here we ask whether the GW produces a coherent and observable significant‐wave‐height (SWH) footprint, how the relative orientation of waves and currents controls its asymmetry, and how monsoon wind forcing regulates the relative importance of wind‐driven wave growth and current‐induced modulation. We combine multi‐satellite observations with SWAN (Simulating Waves Nearshore) numerical simulations to address these questions. The GW exhibits an asymmetric SWH pattern, with lower SWH where waves and currents align and higher SWH where they oppose, consistent with current‐induced refraction and wave‐energy redistribution. Wave–current modulation strengthens when eddy‐current gradients dominate the background wavefield, while stronger wind‐wave growth diminishes the current signature. Multiscale spectral analysis reveals scale‐dependent redistribution of SWH variability over the resolvable mesoscale range. Surface Water and Ocean Topography (SWOT) and Surface Waves Investigation and Monitoring onboard the China‐France Oceanography Satellite (CFOSAT‐SWIM) observations reveal a distinct eddy footprint consistent with simulations, and normalized SWH gradients show moderate‐to‐strong correspondence with surface‐current vorticity. These results advance understanding of wave–current interactions in monsoon‐driven eddies and inform regional wave modeling and wave‐based current inference.