UC San Diego

The Sierra Barrier Jet (SBJ) is a low-level jet that flows parallel to the west slope of the Sierra Nevada and affects precipitation in California during cool seasons (October to April). This study begins by evaluating the ability of California Reanalysis Downscaling at 10 km (CaRD10) to identify the SBJ by comparison to wind profiler measurements available during cool seasons from 2000 to 2010. After adjusting thresholds for SBJ identification to account for a weak negative bias in CaRD10 Sierra-parallel component (~2m s-1), comparison with observed wind profiler data at Chico demonstrates that CaRD10 performs quite well at detecting strong wind speed and long duration SBJ events that are accompanied with substantial precipitation. And CaRD10 is demonstrated to reproduce seasonal cycle and interannual variability well.

Then CaRD10 is used to study the climatological variability of SBJs from 1950 to 2012 during the cool season. Although large variations among cool season months, the magnitudes of maximum Sierra-parallel component of flow are similar. Total precipitation over an individual cool season in the region north of the Central Valley is greater for those years with a greater number of SBJ events. Although experiencing substantial year-to-year variability, the average duration of SBJ events and the daily precipitation amount associated with SBJ events do exhibit statistically significant increasing trends. With simple investigation on the linkages of SBJs with (El Nino-Southern Oscillation) ENSO and Pacific Decadal Oscillation (PDO), no significant relationships are found.