The Effect of Jet Stream Position on Wind Relaxations off Central and Southern California, U.S.A.
Melanie R Fewings, University of Connecticut, Department of Marine Sciences, Groton, CT, United States, Libe Washburn, University of California Santa Barbara, Marine Science Institute and Department of Geography, Santa Barbara, CA, United States, Clive Dorman, University of California, San Diego, Scripps Institution of Oceanography, San Diego, CA, United States, Chris Gotschalk, University of California Santa Barbara, Santa Barbara, CA, United States, Kevin Sidney Jorden Brown, University of Connecticut, Department of Biomedical Engineering, Groton, CT, United States, Ke Chen, Woods Hole Oceanographic Institution, Woods Hole, MA, United States and John Bane, University of North Carolina at Chapel Hill, Chapel Hill, NC, United States
Abstract:
Near Pt. Conception at the central/southern California border, in summer the prevailing upwelling-favorable winds episodically weaken. These wind relaxations cause oceanic flow reversals within ~20 km of the coast of central California, allowing warm water to flow poleward against the prevailing California Current. These warm flows affect larval transport and the thermal environment of intertidal species. Previously, we showed that these wind relaxations also cause substantial wind stress and sea-surface temperature anomalies up to ~1000 km offshore. We also linked these central/southern California wind relaxations to a sequence of synoptic patterns already known to cause wind reversals off northern California and Oregon. On average, the wind relaxes or reverses off Oregon 5–7 dy before the wind relaxes near Pt. Conception.
Here, we use NDBC buoy data and atmospheric pressure from the North American Regional Reanalysis to study ~250 wind relaxations at Pt. Conception, California and northward to Oregon during summer 1984-2015. We evaluated intraseasonal, interannual, and longer-term changes in the frequency of the wind relaxations at Pt. Conception and found no trend in the number of wind relaxations per summer. However, the timing of wind relaxations is related to the location of the jet stream and to the North Pacific Gyre Oscillation (NPGO). Wind relaxations affecting Pt. Conception tend to occur during positive NPGO and when the jet stream is displaced poleward of its mean summer latitude. This is interesting in light of previous studies showing that intraseasonal oscillations on 20-30 dy time scales in the latitudinal position of the jet stream modulate wind reversals off Oregon, causing cascading effects in coastal marine ecosystems. We discuss how intraseasonal oscillations of the jet stream modulate the timing and occurrence of wind relaxations and reversals off central California, as well as the relation between Oregon and central California wind relaxations.
