California's wind energy resource: seasonal cycle, synoptic and diurnal characteristics, and variability

The annual cycle, relevant synoptic climatology, and diurnal patterns of wind in California's major wind generation regions are analyzed using decades' worth of observational data. Wind records near the wind farms at San Gorgonio and Tehachapi passes, Southern California, and Solano County, Northern California near Sacramento are employed. The in situ data are complemented by global reanalysis, 10-km dynamically downscaled regional reanalysis, and other weather station and buoy data. Each site shows preferred wind directions dictated by local orographic forcing as well as different peaks in wind speed and direction distribution in each season, which are explained in terms of climatological circulation patterns. All have greater wind energy in the warmer months, although the northern site peaks later in the summer, more in phase with the temperature cycle but lagging the cycle in zonal SLP gradient that the other sites align with.

The dominant patterns associated with high winds, classified with self-organizing maps, feature a North Pacific SLP high and western North American low. The interplay between synoptic forcing and local circulations is also explored. Local circulations are especially important in the warm months when mesoscale SLP gradients are set up by diurnal heating. The northernmost site displays sharp diurnal wind increases as remnants of a sea breeze propagate inland to the site and amplify the wind induced by the cross-valley SLP gradient.