[ACG52-P02] Fine- and micro-scale observations in the Oyashio in winter
Keywords:turbulent mixing, Oyashio
During the R/V Hakuho-maru cruise in Mar. 2015, fine- and microstructure measurements in the Oyashio water were conducted using a CTD/LADCP and vertical microstructure profiler in order to know the spatial variability of wintertime turbulence field, which has not been reported so far at this area. At a station off the shelf break, whose bottom depth is about 530 m, one-day repeated observations were also conducted to know the temporal variability of turbulence intensity.
The energy dissipation rate, ε, was patchily elevated to O(10-8) [W/kg] and was typically O(10-10 - 10-9) [W/kg] in the upper 400 m depth (less dense than 27.0 σθ) across the Oyashio. Off the shelf break, where the one-day observation was conducted, strong turbulence with ε = O(10-7) [W/kg] and Kρ = O(10-3 - 10-2) [m2/s] was observed at around 60 - 70 m depth (26.4 σθ), and ε = O(10-8) [W/kg] and Kρ = O(10-3) [m2/s] at around 350 m depth (26.7 σθ) corresponding to the period of isopycnal heaving of about 50m. This strong mixing around 26.4 σθ (26.7 σθ) was enhanced when the along-isobath (down-sill) flow and its associated shear was strengthened. Harmonic analysis shows that the diurnal tidal flow was large in the upper 50 m, while the mean and semi-diurnal flow were also important at around 26.7 σθ suggesting that the tidal flow may impact on the turbulence field at this place.
The energy dissipation rate, ε, was patchily elevated to O(10-8) [W/kg] and was typically O(10-10 - 10-9) [W/kg] in the upper 400 m depth (less dense than 27.0 σθ) across the Oyashio. Off the shelf break, where the one-day observation was conducted, strong turbulence with ε = O(10-7) [W/kg] and Kρ = O(10-3 - 10-2) [m2/s] was observed at around 60 - 70 m depth (26.4 σθ), and ε = O(10-8) [W/kg] and Kρ = O(10-3) [m2/s] at around 350 m depth (26.7 σθ) corresponding to the period of isopycnal heaving of about 50m. This strong mixing around 26.4 σθ (26.7 σθ) was enhanced when the along-isobath (down-sill) flow and its associated shear was strengthened. Harmonic analysis shows that the diurnal tidal flow was large in the upper 50 m, while the mean and semi-diurnal flow were also important at around 26.7 σθ suggesting that the tidal flow may impact on the turbulence field at this place.