Turbulence Measurements from a Towed Body

A towed body suitable for measuring oceanic velocity and temperature microstructure is described. The development was motivated by i) a requirement for long times series to produce statistically reliable estimates of dissipation rates, ii) the desire to observe salt fingers directly, and iii) the need to map the horizontal distribution of turbulence. The major problem with towed measurements is the contamination of the velocity signal by body vibrations which has been reduced by making the body almost neutrally buoyant and by minimizing aerodynamic forces. System noise in terms of ε, the rate of dissipation of kinetic enemy, is 2 × 10−6 W m−3, less than “typical” values of 10−4 W m−3 in wind mixing layers and 10−5 W m−3 in the seasonal thermocline. Observations over the continental slope off Monterey Bay show a 1700 meter long turbulent layer in the seasonal thermocline. Values of log10ε are normally distributed with a standard deviation of 0.3. There is a significant excess of small dissipation values due to intermittency and a small deficit of large values due to a finite Reynolds number. The uniformity of the dissipation values and the responsiveness of dissipation rates to changes in the production of turbulent kinetic energy indicate that the mean vertical shear must be fairly uniform over the 1700 m long turbulent layer.