[A-OS11] Ocean Mixing Frontiers

[AOS11-12] 2D Horizontal-Vertical Wavenumber Spectra of Density Finestructure from a towed CTD chain

*Anda Vladoiu¹, Ren-Chieh Lien¹, Eric L Kunze² (1.Applied Physics Laboratory, University of Washington, Seattle, WA, USA, 2.NorthWest Research Associates, Redmond, WA, USA)

Keywords:2D horizontal-vertical wavenumber spectra, isopycnal slope, vertical strain, isopycnal salinity-gradient, anisotropic turbulence, towed CTD chain -measured density finescale

2D horizontal and vertical wavenumber spectra of isopycnal slope, vertical strain and isopycnal salinity-gradient were characterized on horizontal scales between 50 m and 250 km and on vertical scales between 2 and 48 m, using towed CTD chain measurements complemented by shipboard ADCP surveys and concurrent EM-APEX float profiles. 2D wavenumber spectra of isopycnal slope and vertical strain are similar to the Garrett-and-Munk internal-wave model spectrum at vertical wavenumbers below the 0.1-cpm rolloff. At vertical scales smaller than 10 m, the horizontal wavenumber spectrum of isopycnal slope has a +1/3 spectral slope and the vertical wavenumber spectrum of vertical strain has a -1 spectral slope, consistent with previous 1D measurements, numerical simulations and the predictions of anisotropic turbulence theory. Turbulent diapycnal diffusivities were estimated using a vertical strain-based finescale parameterization in the internal-wave subrange at vertical wavelengths of 10-48 m and horizontal wavelengths of 1-5 km, and using horizonal wavenumber spectra of isopycnal slope in the finescale subrange at vertical wavelengths of 2-10 m and horizontal wavelengths of 50-200 m. The two independent estimates from the internal-wave and finescale subranges show good agreement, suggesting that the energy cascade between weakly nonlinear internal waves and isotropic turbulence is connected by a distinct subrange between the rolloff and Ozmidov wavenumbers, consistent with anisotropic turbulence theory. At vertical wavenumbers below 0.1 cpm, horizontal wavenumber spectra for isopycnal salinity-gradient are approximately flat, analogous to most previous studies, while at vertical wavenumbers above 0.1 cpm, the spectra have slopes between +1/3 and +1, similar to passive tracer spectra in the isotropic turbulence subrange. Further investigation of dynamic variables might explain the disagreements between the observed spectra and theoretical predictions.