Direct observations of microscale turbulence and thermohaline structure in the Kuroshio Front
Figure S1: Average of normalized shear spectra in the mixed layer is shown in solid curve. Dotted curves show standard deviation in log space. (1.045Mb)
Figure S2: Upper bound of 95% confidence interval for the computed qN−S in 2008 data shown in Figure 9. (1.243Mb)
Figure S3: Along frontal variations in (a) meridional velocity, v, and (b) its vertical gradient, vz, measured with ship-board ADCP at 224 m depth and (c) surface buoyancy, b, from continuous surface temperature records and objectively mapped salinity. (1.009Mb)
Figure S4: (a) Argo float profiling density data obtained in 2009 for (magenta) November 6th; (red) 11th; (blue) 16th; (black) 21st. Each profiling position is marked with corresponding color of (×) on the map of topography shown in color in (b). (1.088Mb)
Figure S5: (a, b, e, f) Vertical gradient of shear rotation, tan−1(vz/uz)z and (c, d, g, h) effective Coriolis parameter normalized by local Coriolis parameter, inline equation averaged over 300 m depth for (a, c) Leg A, (b, d) Leg B, (e, g) Leg E., and (f, h) 2008 data. (1.266Mb)
Doubell, Mark J.
Gallager, Scott M.
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Direct observations of microstructure near the Kuroshio Front were conducted in August 2008 and October 2009. These show negative potential vorticity (PV) in the mixed layer south of the front, where directly measured turbulent kinetic energy dissipation rates are an order magnitude larger than predicted by wind-scaling. These elevated dissipation rates scale better with an empirical scaling, which considers local wind and Ekman buoyancy flux driven by downfront wind. Near-zero PV in the thermocline under the Kuroshio mainstream is observed at 200–300 m depth, with dissipation exceeding open ocean thermocline values by factors of 10–100. Overall, the large turbulent dissipation rates measured in the Kuroshio can be categorized into two groups, one characterized by low Richardson number along the Kuroshio Front thermocline, and the other characterized by high stratification away from the Kuroshio mainstream. The former is attributed to mixing by unbalanced frontal ageostrophic flows, and the latter is attributed to internal wave breaking. On average, both groups appear in regions of large horizontal density gradients. Observed thermohaline structure shows low salinity tongues from the surface to over 300 m depth and deep cold tongues, extending upward from 500 to 100 m depth in a narrow (20 km) zone, suggesting down and upwelling driven by geostrophic straining, which is confirmed by Quasigeostrophic-Omega equation solutions. This implies that adiabatic along isopycnal subduction and diabatic diapycnal turbulent mixing acting in tandem at the Kuroshio Front likely contribute to NPIW formation.
Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C08013, doi:10.1029/2011JC007228.
Suggested CitationArticle: Nagai, Takeyoshi, Tandon, Amit, Yamazaki, Hidekatsu, Doubell, Mark J., Gallager, Scott M., "Direct observations of microscale turbulence and thermohaline structure in the Kuroshio Front", Journal of Geophysical Research 117 (2012): C08013, DOI:10.1029/2011JC007228, https://hdl.handle.net/1912/5378
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