Dataset: Upwelling index along the north-central California Current from 1988-2010 (California Current upwelling modes project)

Upwelling: Winds and SST
We quantified local upwelling using two variables: 1) an estimate of offshore Ekman transport (Uw) calculated from buoy winds and 2) SST as an integrated estimate of ocean conditions that reflects the shoaling and mixing of deep water in response to upwelling winds, alongshore and cross-shore transport, and air-sea heat fluxes as well as variability in water column characteristics that could impact the upwelling process.  Hourly wind data, from 1988 to 2010, were obtained from 12 NOAA buoys located from 34 to 47°N along the continental shelf of the U.S. west coast, available at http://www.ndbc.noaa.gov.  Missing data ranged from 4% at buoy 46025 to 26% at buoy 46041, with an average of 15% in all buoys.  Gaps were 77 days long on average, with the longest gaps ranging from 4 months at buoy 46025 to 1.8 years at buoy 46011.  Data were highly correlated (r > 0.9 for wind and > 0.75 for SST, except for buoy 46025), so neighboring buoys could be used to fill the gaps via linear regressions.  

Wind stress was calculated from wind speed following Large and Pond (1981), and the alongshore component was calculated using the orientation of the principal axis of the wind, which largely follows the coastal orientation (details in García-Reyes and Largier 2010).  We compared these variables to the upwelling index (UI) provided by NOAA (Schwing and others 1996).  The UI quantifies the offshore Ekman transport caused by alongshore wind stress, but is calculated from cross-shore gradients in sea level pressure.  While UI data is provided at 3° intervals along the Northeast Pacific coast, the scale of the cross-shore sea level pressure used in its calculation is 6°.  Here, we considered data (http://www.pfeg.noaa.gov/products/las.html) from 33 to 48°N across the 1988 to 2010 interval shared by the buoy data.