PNNL

Abstract

This study characterizes ocean upwelling along the California coast by integrating satellite datasets into the Coastal Upwelling Transport Index (CUTI). Originally designed for ocean reanalysis models, CUTI quantifies upwelling based on the combined Ekman and geostrophic offshore-directed ocean water transport. Our satellite approach provides 30-year daily data with 0.25$^\circ$ spatial resolution along the coast to analyze upwelling patterns, with focus on potential offshore wind energy areas near Morro Bay and Humboldt Bay. Our findings reveal strong upwelling in the summer months, peaking near 38$^\circ$N, with distinct characteristics between the two wind energy areas. Morro Bay exhibits stronger, more consistent upwelling throughout the year, whereas Humboldt Bay shows a pronounced seasonal cycle with occasional winter downwelling. These patterns are primarily driven by synoptic-scale wind variations. Cluster analysis of 1993–2022 satellite maps of CUTI identifies four characteristic upwelling patterns along the coast, corresponding to distinct spatial distributions of sea surface temperature anomalies, Ekman transport, and geostrophic ocean water transport. Upwelling variability is largely driven by wind forcing at seasonal and synoptic scales. This satellite-based CUTI dataset provides an observation-based foundation for natural coastal upwelling off California. With potential offshore wind farms, this natural upwelling might be locally modified surrounding the wind farms. Future research should explore satellite observations of wind-farm-induced sea surface temperature variations, their interactions with wind wakes, and the potential for detecting changes in coastal and curl-driven upwelling in regions with existing wind farms.