Tidal and low-frequency currents along the CK Line (31deg 45min N) over the East China Sea shelf

Abstract The bottom-mounted and ship-mounted ADCP velocities were analyzed to quantify tidal and low-frequency currents between 124.0 deg E and 128.5 deg E over the CK line (31 deg 45 min N) in the East China Sea shelf. The bottom-mounted ADCP, deployed in summer and autumn at station 1 (127 deg 25 min E) or station 2 (125 deg 30 min E), reveals relatively large ( ≃ 0.2 m s − 1 ) mean currents to the north or northwest at station 1 and a small ( ≤ 0.03 m s − 1 ) eastward current at station 2, as well as large tidal currents whose major axis amplitude amounts to 0.25 m s − 1 at station 1 and 0.5 m s − 1 at station 2. The bottom-mounted ADCP velocities were used to correct the tidal harmonic coefficients of the NAO.99Jb model under the assumption of uniform correction coefficients. The corrected coefficients were then used to remove the tidal currents in the ship-mounted ADCP velocity obtained over the whole CK-line. The detided ship-mounted ADCP velocities, which agree well with the bottom-mounted ADCP velocities at stations 1 and 2, show a more detailed spatial structure of the low-frequency current and its seasonal variations. The overall structure is characterized by a large northward/northwestward current in the eastern part and a small eastward current in the western part. The northward/northwestward current is largest ( 0.24 m s − 1 ) and most baroclinic in summer, while it becomes weakest ( 0.11 m s − 1 ) and most barotropic in winter. The zonal position of the boundary between the northward/northwestward current and the eastward current changes seasonally.