How Do Conservative Surface Wave Effects Influence a Coastal Upwelling Front?

The coastal upwelling front plays a crucial role in various marine processes, including coastal material transport, air-sea interaction, fisheries, and the ecological environment. While this front is known to be influenced by factors such as wind and topography, the role of surface waves, particularly in relation to upwelling frontal instability, remains inadequately understood. This study investigated the impact of conservative wave effects (Stokes drift and related forces) on the wind-driven coastal upwelling front over an idealized continental shelf using a coupled wave-circulation model. Our findings indicate that conservative wave effects reduce upwelling in the inshore shallow waters but have minimal impact in the offshore deep waters. Moreover, we find that conservative wave effects accelerate the instability of offshore upwelling fronts in comparison to that without waves. This acceleration is primarily due to the increased vertical shear caused by the enhanced currents in the presence of waves. Further, the time of occurrence of frontal instability depends on wave direction, wave height, and period. Specifically, when waves propagate down-front (in the same direction as the frontal jet), the front becomes more unstable than that with up/cross-front waves. In addition, the presence of tides partially offsets the reduction in inshore upwelling caused by surface waves; however, the upwelling frontal instability remains being accelerated by waves.