Arctic Boundary Currents over the Chukchi and Beaufort
Arctic Boundary Currents over the Chukchi and Beaufort Slope Seas OSM-2006 Chris Linder, WHOI Andreas Münchow, University of Delaware Robert Pickart, WHOI Thomas Weingartner, University of Alaska Rebecca Woodgate, University of Washington David Kadko, University of Miami 1
The Times are a Changing: ∂ • / ∂t ≠ 0 “Steady State” may not exist Understanding a more dynamic Arctic Ocean circulation requires more modern observational tools OSM-2006 2
Sketch of the Circulation over the Chukchi and Beaufort Seas steady^ OSM-2006 3
ADCP Survey, Sept. -22/24, 2004 55 -m Chukchi shelf 100 -m Chukchi shelf red dots are XBT drops (Pickart and Kadko) OSM-2006 4
Detided velocity components @ 100 -m depth inertial period north velocity (cm/s) east velocity (cm/s) bottom depth (m) Time (hours) OSM-2006 5
XBT ADCP Sept. -22, 2004: Across-shore velocity (onshore) 2. 2 Sv • • Along-shore velocity (westward) 100 -m OSM-2006 6
Volume Flux (Sv=106 m 3/s): 0. 8 Space: 2. 2 1. 7 +0. 5 1. 3 0. 6 +0. 3 +0. 2 2. 2 Sv 0. 4 -0. 5 residual 30 -km Time: mean? diurnal oscillation (vorticity wave)? OSM-2006 7
Eddies in the Arctic Sept. -21/22, 2004 I II III basin IV shelf D I II III L OSM-2006 4 clock-wise rotating (anti-cyclonic) vortices USCGC Healy 75 -k. Hz ADCP 8
• Cold Aagaard (1984) OSM-2006 9
Beaufort Slope Currents 2003 Bottom-intensified • • • cm/s OSM-2006 10
Conclusions: Understanding a more dynamic Arctic Ocean requires more modern observational tools • ADCP velocity data challenges conventional perceptions of Arctic shelf and slope circulations (strong vs. weak local forcing); • Velocity fields express small (baroclinic and topographic) spatial scales of variability (eddies and waves); • Coherent velocity structures in time and space suggest dynamics that are NOT steady and that are NOT captured in hydrographic surveys alone; OSM-2006 11
ADCP Calibration-1: Comparing Velocity Components Transducer misalignment in x-y plane: 44. 1 deg. x-z plane: 1. 17 deg. y-z plane: -1. 10 deg. Scaling by 1. 021158 … looks good, but can’t tell how good … OSM-2006 12
ADCP Calibrations-2: Difference of ADCP-GPS Velocity Components North East Histogram OSM-2006 Integrated Histogram 13
ADCP Processing: Sorting and Screening Single Ping Data ~2 hrs Ensemble average Ensemble water track relative to ship (true North, unsorted) water track relative to bottom (true North, sorted) water track relative to bottom (true East, sorted) water track relative to ship (true East, unsorted) OSM-2006 14
Flows over the Chukchi Plateau @ 102 -m depth DEEP SHALLOW OSM-2006 15
Alaska Arctic Ocean Halocline waters Temperature Salinity OSM-2006 Barrow Canyon Atlantic waters Sept. -2004 (by Bob Pickart) 16
Beaufort Slope Currents 2004 Surface-intensified OSM-2006 17
Barotropic Tidal Currents 5 -km data assimilation 8 constituents, 2 -week rms Siberia ka as Al Canada OSM-2006 from Erofeeva et al. (2004) 18
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