UACE2017 Proceedings: Tomographic mapping the tidal current structures in Dalian bay

• Session:
  Ocean Acoustic Tomography - Various application and data
• Paper:
  Tomographic mapping the tidal current structures in Dalian bay
• Author(s):
  Chuanzheng Zhang, Xiao-Hua Zhu, Ze-Nan Zhu, Wenhu Liu, Xiaopeng Fan, Ruixiang Zhao, Menghong Dong, Min Wang
• Abstract:
  During March 7-8 2015, a high-precision experiment for reconstructing the current variation in Dalian Bay (DLB) was successfully conducted by 11 coastal acoustic tomography (CAT) systems. The horizontal distributions of tidal and residual currents were mapped well by the inverse method, which used reciprocal travel time data along 51 successful sound transmission rays. The semi-diurnal tide is dominant, with a maximum speed of 0.69 m/s near the bay mouth that gradually decreases toward the inner bay with an average velocity of 0.31 m/s. The residual current enters DLB from two flanks of the bay mouth and flows out in the inner bay. One anticyclone and one cyclone were noted inside DLB as was one cyclone at the bay mouth. The maximum residual current reached 0.11 m/s, with a mean velocity of 0.03 m/s. The depth-averaged inverse velocities were in excellent agreement with the moored Acoustic Doppler Current Profiler (ADCP) at the center of DLB, with a root–mean–square-difference (RMSD) of 0.04 m/s for the eastward and northward components. The precision of the present tomography measurements was the highest thus far owing to the largest number of transmission rays ever recorded. Sensitivity experiments showed that the RMSD between CAT and moored-ADCP increased from 0.04 m/s to 0.08 m/s for both the eastward and northward velocities when reducing the number of transmission rays from 51 to 11. The observational accuracy was determined by the acoustic ray density of the CAT measurements. The cost-optimal scheme consisted of 29 transmission rays with an acoustic ray density of 2.03 km. Moreover, a dynamic analysis of the residual currents showed that the horizontal pressure gradient of residual sea level and Coriolis force contribute 38.3% and 36.0%, respectively. This indicates that the two terms are the dominant factors of the residual currents in DLB.
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Contact details

• Contact person:
  Dr Chuanzheng Zhang
• e-mail:
  
• Affiliation:
  State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, State Oceanic Administration, Hangzhou, China
• Country:
  China