[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)

Keywords: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.