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Causes of Poleward Flow

Poleward Flow around Pt. Conception: a response to wind relaxation Christopher Melton Interdepartmental Graduate Program in Marine Science University of California, Santa Barbara seamelton@hotmail.com. Causes of Poleward Flow.

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Causes of Poleward Flow

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  1. Poleward Flow around Pt. Conception: a response to wind relaxationChristopher MeltonInterdepartmental Graduate Program in Marine ScienceUniversity of California, Santa Barbaraseamelton@hotmail.com

  2. Causes of Poleward Flow • Persistent NW winds along the central California coast result in upwelling and cooler coastal water north of Pt. Conception • Weaker flow towards the east Santa Barbara Channel (SBC) results in less upwelling and warmer waters • Water towards the east SBC is typically warmer, less dense, and the undistrubed sea level is higher relative to waters north of Pt. Conception • Strong NW winds ( ~10 – 15 m/s) produce a significant alongshore pressure gradient which opposes the wind direction • When the wind relaxes/reverses due to changes in atmospheric circulation, the pressure gradient force becomes dominant and a strong poleward current develops transporting warm waters north of Pt. Conception

  3. SST Satellite Imagery (ºC)

  4. Temperature time series 15 km 13 hrs 19 km 18 hrs 37km 15 hrs The front propagates at 1.1 km/day or 1.3 cm/s when north of Pt. Conception The warm water front propagates along the inner shelf from ALE to PTS

  5. Alongshore current time series Upwelling favorable NW winds Winds relax… Wind (m/s) Alongshore current (m/s) equatorward flow (+) poleward flow (-) …resulting in strong poleward flow of 0.25 to 0.5 m/s as the warm water front passes

  6. Cross shore current time series Upwelling favorable NW winds Winds relax… Wind (m/s) Cross shore current (m/s) onshore flow offshore flow Strong NW winds force offshore flow at the surface and onshore at depth …causing cross shore flow to reverse and strengthen as the warm water front passes

  7. Vertical velocity structure Alongshore current (m/s) Cross shore current (m/s)

  8. Mean of currents for events at Pt. Purisima Alongshore current (m/s) Vertical shear Cross shore current (m/s) Day = 0 when the rate of change of temperature is a maximum

  9. Mean of currents for events at Pt. Sal equatorward flow Alongshore current (m/s) poleward flow onshore flow Cross shore current (m/s) offshore flow Day = 0 when the rate of change of temperature is a maximum

  10. Summary & Conclusions • Wind relaxation results in alongshore poleward currents which average ~ 15 cm/s, strong events have produced currents upwards of 50 cm/s. • A warm water front develops and propagates poleward along the inner shelf. • Characteristics of the front include: • a rise in temperature at all depths nearly simultaneously • a transiton to onshore flow at the surface and offshore flow at depth with magnitudes of 2 to 4 cm/s • poleward flow increases with the arrival of the front and peaks in magnitude when when the rate of warming reaches a maximum

  11. Acknowledgements Thank you: Libe Washburn Chris Gotschalk Brian Emery PISCO

  12. ARG current summary

  13. ALE current summary

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