[A-CG40] 海洋と大気の波動・渦・循環の力学

[ACG40-P03] Temporal variation of energetic turbulence on a seamount flank in Tokara Strait

★Invited Papers

*高橋 杏¹、Lien Ren-Chieh²、Kunze Eric³、Vladoiu Anda²、Ma Barry²、中村 啓彦⁴、仁科 文子⁴、堤 英輔⁴、井上 龍一郎⁵、長井 健容⁷、遠藤 貴洋⁶、伊藤 幸彦¹ (1.東京大学 大気海洋研究所、2.Applied Physics Laboratory, University of Washington、3.NorthWest Research Associates、4.鹿児島大学 水産学部、5.海洋研究開発機構、6.九州大学 応用力学研究所、7.東京海洋大学 )

キーワード：流れ-地形相互作用、乱流、パラメタリゼーション、係留観測

Turbulence is highly intermittent, but temporal variability of turbulence has been less-frequently sampled than spatial variability. In this study, 6-month ADCP and CTD mooring observations were conducted in the wake of Hirase Seamount in Tokara Strait, where Kuroshio and tidal currents impinge on steep topography to excite vigorous turbulence. Horizontal velocities, temperature and salinity sampled every 2.5 mins in 6-m vertical bins over depths of 50–320 m for the ADCP and 240-306 m for the CTDs are used to investigate statistics and temporal variability of strong turbulence. Turbulent kinetic energy dissipation rates ε are estimated from Thorpe-scale (Th; Thorpe 1977) and reduced-shear (RS; Kunze et al. 1990) parameterizations in 1-hour windows. While 1-h estimates ε_Th and ε_RS are scattered with respect to each other, 48-h moving-averages <ε_Th > and <ε_RS > are correlated with R=0.64 (p<0.01). The frequency spectrum of log₁₀(ε_RS ) exhibits a sharp peak at semidiurnal and broad enhancement in subinertial frequencies. Estimated ε_Th and ε_RS range from 10^-8 to 10^-4 W/kg, while <ε_Th > and <ε_RS > from O(10^-7 W/kg) to O(10^-6 W/kg). Temporal variation in <ε> correlates with the current speed u at 200–300 m depths with R=0.62, but less so at 100–200 m with R=0.51 and 50–100 m with R=0.34. The observed relationship ε∝ u³ is consistent with observations in wake eddies generated at the Palau island chain (MacKinnon et al. 2019).