Seasonal Variability of Upwelling and Downwelling Surface Current Patterns Near a Small Coastal Embayment

Upwelling in coastal embayments is important to a variety of physical and biological processes. Despite their ubiquity, circulation patterns in small bays (width and length scales ≤ 20 km) in eastern boundary current upwelling systems are relatively understudied compared to their larger counterparts. In this study, we apply a conditional averaging technique to investigate upwelling- and downwelling-driven circulation in a small coastal embayment located in Central California [San Luis Obispo (SLO) Bay]. We also investigate intraseasonal differences in the current patterns in SLO Bay. Conditional averaging reveals distinct intraseasonal differences and features that are obscured by traditional seasonal averages when examining the upwelling jet separation and onshore advection, divergence patterns, and particle trajectories. We show that the upwelling circulation and resulting upwelling jet separation and onshore advection reinforce a convergent upwelling shadow front at this site, with important ecological ramifications. While tuned specifically for SLO Bay, these findings can be used as a baseline for similar small upwelling bays and highlight the importance of conditional averages (versus traditional temporal averages) and coastal upwelling seasonality beyond the bimodal upwelling and non-upwelling description