Interaction of a Dye Tracer with an Upwelling Front during Variable Winds From a cruise of the June 24-July 1, 2003 Andy Dale, Jack Barth, Murray Levine, Steve Pierce (COAS, Oregon State University) Jay Austin (Old Dominion University) NSF funded
With thanks to …. Murray Stein and crew of New Horizon Dennis Root (dye hardware etc.) Anatoli Erofeev (visualization software) Cambria Colt (Scripps res. tech.) Help at sea …. Said Ahmed Allan Book Renato Castelao Anthony Kirincich Larry O’Neill Bob O’Malley Michael Ott Inspiration …. Houghton, Ledwell etc. Collaborations with …. Tim Cowles’ group (bio-optical profiler/thin layers) Minibat
Offshore Ekman transport What happens to this dye patch during an upwelling-relaxation cycle?? Frontal region
Dye released as an alongshelf streak on a density surface….. Minibat survey ….. Shipboard ADCP Drogued ARGOS/GPS drifter Weighted Minibat 1 knot 6-7 knots Also CTD tow-yos at ~ 1 knot Dye tanks and plumbing Minibat and dye diffuser ~1 km
NOAA buoy Dye release 1 (fluorescein) Dye release 2 (rhodamine) Release 1 Release m 200 m Upwelling Downwelling NOAA buoy R/V New Horizon OREGON
Dye 1 - Fluorescein
1 km ADCP velocity at 16m Dye advects south at ~0.6 m/s START FINISH 0.5 m/s Survey of dye patch hours post-release. Size of dye patch 20 hours after release ~ 1.5km x 3.5 km Dye patch released.
20 hours after release Wind at buoy Release Ekman Transport ~0.20 m/s Plots centered on 120m isobath
23 hours after release Wind at buoy Release
23.5 hours after release Wind at buoy Release
24 hours after release Wind at buoy Release
24.5 hours after release Wind at buoy Release
34 hours after release Wind at buoy Release
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Entrainment to mixed layer Continued entrainment of dye-free water Mean and standard deviation of fluorescein density
Dye 2 - Rhodamine
Release 33 hours after release Orange bar shows an inertial period
43.1 hours after release Release
62.6 hours after release Release
Density Temperature Salinity Rhodamine
Mean and standard deviation of rhodamine density Entrainment Relaxation/ restratification
Conclusions During strongly upwelling-favorable winds, steepening of isopycnals combined with wind-induced mixing generates a surface mixed layer which actively entrains water beneath an upwelling front. When upwelling-favorable winds cease or reverse, restratification is rapid with water from the frontal zone becoming widely distributed across the shelf. Plus … These dye releases have revealed other interesting phenomena not covered here …
Tow-yo section with bifurcated dye patch … 16 hours after release
Density Temperature Salinity Rhodamine
Tow-yo section with internal wave train … 13.9 hours after release