[A-OS11] Ocean Mixing Frontiers

[AOS11-11] Observed spectral distortion of temperature microstructure

*Takashi Ijichi¹、Louis St. Laurent² (1.Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo、2.Applied Physics Laboratory, University of Washington)

キーワード：temperature microstructure, finestructure contamination

Measurements of temperature microstructure from fast response thermistors are becoming more prevalent in the ocean-mixing community to estimate dissipation rates of both turbulent kinetic energy and thermal variance. This dissipation estimation method relies on the spectral shape of scalar microstructure prescribed in the high-Reynolds number turbulence theory. Using diverse datasets, we discuss some problematic cases where observed temperature spectra deviate from the corresponding theoretical one, leading to potential bias in dissipation estimates. From a technical viewpoint, the high-frequency thermistor response is suggested to depend on a vehicle flight condition. When temperature microstructure was measured on board autonomous underwater gliders, the thermistor response is found to be better corrected by a single-pole frequency function with a stronger vehicle speed dependence rather than the conventional double-pole function supported from free-falling vertical microstructure profiler data. From a physics viewpoint, the viscous-convective subrange is found to be greatly contaminated by thermohaline finestructure associated with salt finger convection. The Ozmidov wavenumber is suggested to be a threshold parameter that distinguishes turbulent microstructure from such finestructure contamination.