Variation of the Kuroshio in the East China Sea Magdalena Andres Ocean Sciences OS 54B-05 February 24, 2006

North Pacific

East China Sea

Instrumentation: Dec – Nov Inverted echo sounder Hourly measurements of: travel-time pressure bottom currents

700 dbar as the reference Baroclinic Velocity = 0 m/s at 700 dbar Barotropic Velocity = Absolute Velocity at 700 dbar

Hydrocast data from: North Pacific Hydrobase [Macdonald et al., 2001] and Nagasaki Marine Observatory (NMO), Japan Meteorological Agency Travel time as a proxy for T, S,  profiles Historical data: 1720 casts Measured T, S, P  simulated travel time Generate lookup-table relates travel time to vertical T and S profiles

Baroclinic velocity Vertical profiles  horizontal  gradients thermal wind equations  baroclinic velocity

Baroclinic Transport (referenced to 700 dbar)

Bottom Currents C1 C2 C3C4 C6 N V U Mean V U V -2 cm/s -3 cm/s 12 cm/s -1 cm/s -3 cm/s

Absolute Velocity Mean=16.6 Svstd = 3.3 Sv range = 7.3 Sv to 24.9 Sv

 There is a persistent recirculation east of the Kuroshio  Positive velocities reach down to the seafloor  There is often a sub-surface velocity core ~ 200 m deep ~ 75 km east of shelf break What does including the barotropic component tell us?

Conclusions:  Mean Baroclinic Transport: 17.0 Sv (std 2.7 Sv) range: 9.2 to 23.8 Sv  Including the barotropic component doesn’t change the Transport much; does change the picture of horizontal current shear.  Mean Absolute Transport: 16.6 Sv (std 3.3 Sv) range: 7.3 to 24.9 Sv

Comparison to other work 20 month mean into ECS East of Taiwan = 21.5 Sv (Johns et al., 2001) + Preliminary evaluation of ADCPs on the shelf ~ 5 Sv (B.-H. Lim, OS54B-06) 16.6 Sv ~ 22 Sv

Future work Add transports determined with inverted echo sounders line transports to ADCP transport to get complete Kuroshio Transport in ECS Compare Kuroshio Transport to: 1) Flow into the Japan/East Sea 2) Flow through the Tokara Strait 3) Ryukyu Current 4) Approach of mesoscale eddies off of Taiwan

Acknowledgements Jeff Book Gerry Chaplin Kyung-Il Chang Kathy Donohue Andy Greene Hiroshi Ichikawa Byung-Ho Lim Doug Mitchell Jae-Hun Park Karen Tracey Randy Watts Mark Wimbush Crew and students aboard the T/V Kagoshima-maru