Observations of wind-driven deepening of the surface mixing layer in the Tsushima strait

Abstract

A detailed description of wind-driven deepening of the mixing layer in the Tsushima strait is given by combining current data from the acoustic Doppler current profiler (ADCP) attached to a satellite-tracked surface drifter, with microstructure data from the Turbulence Ocean Microstructure Acquisition Profiler (TurboMAP) deployed from a ship following the surface drifter. By collecting data in a Lagrangian manner we attempted to minimize the effect of horizontal advection. The dissipation rate of turbulent kinetic energy (TKE), ɛ, was measured directly using the TurboMAP, whereas the production rate of TKE, P, was estimated from horizontal velocities obtained using the ADCP based on the one-dimensional linear equation of motion. The TKE budget in the mixing layer is examined by applying the integrated TKE equation to the observed data. The sum of the temporal change of potential energy, shear production, dissipation, TKE flux, and the surface buoyancy flux terms changes dramatically with time, indicating the importance of the temporal change of TKE in the deepening process on a time scale shorter than one day, which is neglected in widely used bulk mixedlayer models.