Understanding Regional Wind Forcings and Surface Heat Fluxes that cause Sea-Surface Temperature Anomalies during US West Coast Wind Relaxations

Kayla Rosann Flynn, Trinnovim, New York, NY, United States, Melanie R Fewings, University of Connecticut, Department of Marine Sciences, Groton, CT, United States, Chris Gotschalk, University of California Santa Barbara, Marine Science Institute, Santa Barbara, CA, United States and Libe Washburn, University of California Santa Barbara, Marine Science Institute and Department of Geography, Santa Barbara, CA, United States
Abstract:
Weakening and reversals of the prevailing summertime upwelling-favorable winds along the western coast of North America cause a poleward flow of warm waters within ~20 km of the coast, which impacts larval connectivity. Earlier studies of composite anomalies of 500-hPa height, atmospheric pressure, and wind stress linked wind relaxations in central/S. California to preceding Oregon/N. California relaxations or reversals. The synoptic series of events starts with an eastward-moving 500-hPa trough causing the prevailing winds off Oregon to relax. Next, a northeastern extension of the North Pacific High reintensifies the upwelling-favorable winds. Approximately five days after the Oregon relaxation, the central/S. California wind relaxation occurs as low sea-level pressure anomalies follow the North Pacific High. This atmospheric synoptic pattern leads to the question of how the ocean responds to these forcings beyond 20 km from the coast. Composite microwave satellite data during 44 wind relaxation events in summer 2006-2011 indicate sea surface temperature (SST) anomalies up to ~1000 km offshore. The Oregon wind relaxation results in anomalously warm regional SSTs. The North Pacific High stage reintensifies wind stress for 2-3 days, resulting in anomalously cold SSTs. Surprisingly, the cold SST anomaly persists during the central/S. California relaxation. The intensified wind stress during the previous 2-3 days may precondition the surface ocean offshore, preventing a warm SST anomaly during the central/S. California relaxation. To determine the importance of changes in wind-driven vertical mixing vs. changes in surface heat flux in causing the SST anomalies, and whether wind stress-curl-driven upwelling is necessary to explain the observed SST anomalies, we use a 1-D surface layer heat budget and the COARE bulk wind stress and heat flux algorithms together with subsurface temperatures from Argo floats and wind velocities from the QuikSCAT satellite. Understanding ocean and atmospheric responses to wind relaxation events will increase the scientific understanding of coastal upwelling systems worldwide.
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