Direct measurements of dissipation rate of turbulent kinetic energy of North Pacific subtropical mode water

Measurements of turbulent kinetic energy dissipation rate ɛ were performed in a region of North Pacific subtropical mode water (STMW), and the vertical eddy diffusivity Kz was calculated from the observed ɛ values. In summer, the magnitude of ɛ in the STMW interior was 2–3 × 10−10 Wkg−1, whereas the values at both the upper and lower boundaries of STMW were 4–6 × 10−10 Wkg−1. In winter, on the other hand, ɛ was almost uniform and had a magnitude less than 10−10 Wkg−1 over the whole depth of STMW. The magnitude of Kz was mostly from 10−6 to 10−5 m2s−1 in summer and from 10−7 to 10−5 m2s−1 in winter. These are at least one order of magnitude smaller than the inferred value from a budget analysis of potential vorticity in STMW.