Microstructure Profiler

A microstructure profiler is an instrument that measures centimeter-scale temperature and velocity-shear fluctuations to estimate the rate of turbulent kinetic energy dissipation and the diapycnal eddy diffusivity. Airfoil shear probes and fast thermistors sample at high frequency on a slowly falling or rising platform isolated from vehicle vibration. Fitting the measured shear spectrum to the Nasmyth universal spectrum yields the dissipation rate epsilon; the Osborn relation then gives the vertical diffusivity Kz as Gamma times epsilon over the buoyancy frequency squared, with a mixing efficiency Gamma near 0.2. These profiles quantify the small-scale mixing that sets the strength of the overturning circulation.