Auxiliary Material for Paper 2011JC007228

Direct observations of microscale turbulence and thermohaline structure in the Kuroshio Front

Takeyoshi Nagai
Department of Ocean Sciences, Tokyo University of Marine Science and Technology, Tokyo, Japan

Amit Tandon
SMAST/Physics Department, University of Massachusetts Dartmouth, North Dartmouth, Massachusetts, USA

Hidekatsu Yamazaki
Department of Ocean Sciences, Tokyo University of Marine Science and Technology, Tokyo, Japan

Mark J. Doubell
South Australian Aquatic Sciences Centre, SARDI Aquatic Sciences, Henley Beach, South Australia, Australia

Scott Gallager
Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA

Nagai, T., A. Tandon, H. Yamazaki, M. J. Doubell, and S. Gallager (2012), Direct observations of microscale turbulence and thermohaline structure in the Kuroshio Front, J. Geophys. Res., 117, C08013, doi:10.1029/2011JC007228.

Introduction

This auxiliary material includes additional figures. The dataset shown as figures in auxiliary material is obtained from an intensive interdisciplinary field campaign that was carried out using R/V Natsushima (JAMSTEC) from October 17 through 24, 2009. We deployed CTD (Advantech Ltd.) with Niskin Bottles, Lowered Acoustic Doppler Current Profiler (LADCP) (300 kHz), and Visual Plankton Recorder (VPR) every 9.26 km (5 miles) at 7-9 stations for each North-South transect to approximately 275 m depth. LADCP was programmed to average velocity data over 10 m with 20 bins and at 1 Hz. Each standard CTD/LADCP profile takes about 40 minutes for deployment and recovery. In addition to the conventional CTD observations, towed, free-fall CTD, Underway CTD (Ocean Science) was also deployed at 11 stations along Leg A. Every 11.1 km (6 miles), XBT (T-7) observations were conducted at 12 stations for each transect to acquire mesoscale temperature field across and along front. XBT observations at each station yielded avertical temperature profile down to 750 m depth. For similar observations in 2008, we deployed XBT every 3.7 km and TurboMAP-II every 28 km across the Kuroshio Front. Details of these observations can be found in Nagai et al. (2009). The observed CTD measurements are used to correct the depth of the LADCP, and velocity profiles are obtained utilizing the shear method (Fischer and Visbeck 1993), Measured temperature and salinity data were averaged every 4 m, and velocity data were interpolated on the same depth grid. These 4 m data were used to construct vertical (y-z) sections of temperature, salinity, velocity, and background Richardson number, making use of optimum interpolation with decorrelation scale of 25 km and 40 m for meridional and vertical direction, respectively.

1. 2011jc007228-fs01.pdf
Figure S1. Average of normalized shear spectra in the mixed layer is shown in solid curve. Dotted curves show standard deviation in log space. The number of the dissipation estimations averaged in the mixed layer is 125 in all the transects in 2008. Broken line shows Nasmyth shear spectrum. Wave number is normalized with Kolmogoroff wave number, $k_s=(\epsilon/\nu^3)^{1/4}$, power density is normalized with $k_s^2 (\epsilon \nu^5)^{1/4} = (\epsilon^3/\nu)^{1/4}$.

2. 2011jc007228-fs02.pdf
Figure S2. Upper bound of 95$\%$ confidence interval for the computed $q_{N-S}$ in 2008 data shown in Figure 9.

3. 2011jc007228-fs03.pdf
Figure S3. Along frontal variations in (a) meridional velocity, $v$, and (b) its vertical gradient, $v_z$, measured with ship-board ADCP at 224 m depth and (c) surface buoyancy, $b$, from continuous surface temperature records and objectively mapped salinity. Solid lines are fitted linear functions to $v$, and $b$. Dashed line indicate average value of $v_z$. These terms are missing in (3) shown in Figure 9.

4. 2011jc007228-fs04.pdf
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 ($\times$) on the map of topography shown in color in (b).

5. 2011jc007228-fs05.pdf
Figure S5. (a, b, e, f) Vertical gradient of shear rotation, $-\tan ^{-1} (v_z/u_z)_z$ and (c, d, g, h) effective Coriolis parameter normalized by local Coriolis parameter, $f^{-1}\sqrt{f^2-fu_y}$ averaged over 300 m depth for (a, c) Leg A, (b, d) Leg B, (e, g) Leg E., and (f, h) 2008 data.

6. 2011jc007228-fs06.pdf
Figure S6. Comparison of observed dissipation rates against Mac{K}innon and Gregg empirical scaling for dissipation rates caused by internal waves. Solid black line indicates 45$^o$, and red line represents linear regression line. Correlation coefficient computed is 0.24, which is found to be significant with 99 $\%$ confidence interval.