[A-OS16] Frontiers of Ocean Mixing Research

[AOS16-P04] Moored ADCP measurements of the dissipation rate of turbulent kinetic energy in the Kuroshio

*Yue Fu¹, Takahiro Endoh², Eisuke Tsutsumi³, Ryuichiro Inoue⁴, Takeyoshi Nagai⁵, Hirohiko Nakamura⁶, Ayako Nishina⁶ (1.Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 2.Research Institute for Applied Mechanics, Kyushu University, 3.Atmosphere and Ocean Research Institute, The University of Tokyo, 4.Japan Agency for Marine-Earth Science and Technology, 5.Tokyo University of Marine Science and Technology, 6.Faculty of Fisheries, Kagoshima University)

Keywords:Dissipation rate of turbulent kinetic energy, Time series measurements, Moored ADCP, Structure function method, The Kuroshio, Tokara strait

The dissipation rate of turbulent kinetic energy (ε) is currently used to quantify turbulent mixing in the ocean. Although the value of ε is commonly measured in situ using free-falling microstructure profilers, such measurements are labor intensive and require a dedicated ship. Datasets thus tend to be sparse and rarely exceed one or two days duration.
In this study, we calculate a 3.5-days continuous time series of ε in the Kuroshio by applying the structure function method, previously validated only for coastal areas, to along-beam velocities measured with the ADCP (Acoustic Doppler Current Profiler) moored downstream of the small reef called Hira-se in the Tokara Strait.
The value of ε estimated using the structure function method varies in the range of 10^-6~10^-5 Wkg^-1, being positively correlated with the semidiurnal variation of the mean streamwise velocity. The estimates of ε agree rather well with direct measurements of ε using the EM-APEX (Electromagnetic Autonomous Profiling Explorer) float and the VMP (Vertical Microstructure Profiler), both of which were taken near the mooring when the mean streamwise velocity was small. These results offer the prospect of obtaining continuous estimates of ε even at midwater in the western boundary current over longer time scales, which can be used to examine the intermittency in ε.