Estimating Coastal Upwelling from HF Radar Surface Velocity Measurements

Coastal upwelling onset, duration, strength, intermittency and spatial variability define the primary physical drivers of eastern boundary current regimes. Coupling upwelling with nutrient supply defines conditions for the high regional productivity. Present upwelling estimates are derived from atmospheric models. High spatial and temporal resolution of the upwelling cycle has rarely been captured. High Frequency (HF) radar arrays provide such an opportunity. The US West Coast HF array installation was funded by the State of California and operating funds are provided by the NOAA Integrated Ocean Observing System (IOOS) office. San Francisco State University operates the HF radar array in the region from Pt. Reyes south to Pillar Point. This array has been in continuous operation for about 10 years; the hourly data with three to six kilometer spatial resolution provide a study site where these data can be analyzed in different ways to extract the signal of offshore transport along this stretch of coast. The goals are to define the upwelling characteristics, to examine efficient ways to extract the signal from the surface current data and to compare with other upwelling estimates.