Direct Measurements of Turbulence in the Pacific Equatorial Undercurrent

Abstract

Measurements of small-scale fluctuations of temperature are used to estimate turbulent parameters such as viscous dissipation rate (ε), dissipation rate of temperature variance (χ), and turbulent diffusion coefficients of momentum (νT) and temperature (DT). Results from two locations are reported: one in the center of the undercurrent (ON 150W) and one toward the northern edge (IN 150W); both at depths of about 100 m where high vertical shear and high vertical stability are found. Universal similarity and local isotropy assumptions were used to determine the dissipation rates from measured spectra. While ε(∼0.08 cm2 sec−3) was about the same at both locations, χ at ON [7 × 10−5 (°C)2 sec−1] was larger by a factor of 9. Even greater differences were found in DT: 27 cm2 sec−1 at ON vs 0.52 cm2 sec−1 at 1N indicating large vertical mixing at the equator. From two independent methods νT yielded about the same results within 15%: 12 cm2 sec−1 at 1N and 25 cm2 sec−1 at ON.