Characteristics of Microstructure Turbulence Measurements With a Moored Instrument in the South China Sea

A newly designed autonomous instrument was evaluated for long-term ocean turbulence measurements in the South China Sea from October 19, 2013, to February 10, 2014 at 21°09.90′N, 117°42.03′E. A shear velocity time series was collected continuously for 115 days at a single depth of 250 m using two orthogonal shear probes (PNS06). The mechanical design of wings is developed for an observation platform to achieve characteristics of stability and flexibility of current direction tracking. The depth and pitch in comparison with ambient current speed are analyzed, and the results indicate that the platform has satisfied stability requirements for turbulence measurement. The comparison between the instrument heading and current direction shows that the instrument flexibly responds to variations of ambient currents. Throughout the observation period, 62% of the data sets is of significant correlation with correlation coefficients above 0.5, and 4% is of strong correlation. The shear velocity spectra correspond well to the theoretical Nasmyth spectrum, and the magnitude of dissipation rates estimated from shear is approximately Ο(10 −8 ) W kg −1 . The moored instrument is functional as designed and provides a reliable observation platform for extended turbulent measurements.