Observations of turbulent energy dissipation rate ε in the Japan Sea

Measurements of turbulent energy dissipation rate ε were obtained in the southern Japan Sea during experimental campaigns in June 2000 and 2001, and November 2001. The data sets show markedly different vertical structures of ε between the two seasons, suggesting that wind stirring is a dominant process in the vertical heat exchange between the upper 200 m and the deeper layers. In June, values of eddy diffusivity Kz computed from ε and buoyancy frequency N2 are generally around 10−6 m2 s−1, reaching 10−4 near the surface and in subsurface mixing patches. In November, Kz is around 10−4 in the surface mixing layer and around 10−5 in the deeper layer below 200 m. During the November observations, fine-scale current velocity shear was obtained with lowered ADCP. Vertical profiles of the Richardson number Ri calculated from the fine-scale velocity shear and N2 show that relatively large values of ε tend to correspond to small values of Ri at the subsurface deeper than 100 m. It is inferred that the energy source of turbulence away from the surface is supplied mainly by near-inertial currents.