Latitudinal variation of vertical eddy diffusivity estimated from the distribution of overturns in the western part of the south Pacific Ocean

Kitade, Y.; Kusaka, T.; Kawamura, Y.; Niwa, Y.; Noda, A.; Hayashi, T.; Hamada, H.; Yamasaki, S.; Koike, Y.; Matsuyama, M.

Latitudinal variation of vertical eddy diffusivity estimated from the distribution of overturns in the western part of the south Pacific Ocean

2003

Abstract: Conductivity, temperature and depth observations were carried out at 13 stations in the western part of the south Pacific Ocean from February 19 to 23 during the T/RV Umitaka-Maru cruise to clarify a latitudinal dependence of vertical eddy diffusivity. Observed potential temperature and salinity show numerous density inversions. The number of density inversions at low latitudes (30 deg-24 deg S) is two times larger than that at high latitudes (35 deg-31 deg S). From the observed density inversion, Thorpe scale, L sub T, and vertical eddy diffusivity, K sub v, are estimated to be L sub T=0.2-0 37m and K sub v =1.1-3.1*l0 E -5 (m square 2 s sup -1) at high latitudes, and L sub T=0.36-0.70m and K sub v=2.8-8.3*10 E -5 (m square 2 s sup -1) at low latitudes. The average value of K sub v at low latitudes is 2.5 times lager than that at high latitudes implies that parametric subharmonic instability associated with semidiurnal internal tide has an important role on the vertical mixing processes in the South Pacific Ocean. Latitudinal distribution of observed K sub v with maximum near 30 deg S suggests importance of vertical mixing due to diurnal internal tide at this latitude.

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