Experiment of particle dispersion on the sea surface with GPS tracked drifters

Many studies were carried out since 1960s to make direct estimation of the diffusivity in the ocean by various types of releasing experiments of dye or floats. Motions of water on the sea surface were described from a macroscopic point of view by those methods, and diffusion coefficients were estimated from the deformation of the envelope of whole particles. In the present study, we deployed GPS tracked surface drifters, which provide detailed information of the motions of water particles that result in the synoptically estimated diffusivity. Experiments were carried out in Otsuchi Bay, Iwate, Japan. The estimated values of diffusivity in the present study using drifters drogued at 5 m below the sea surface are smaller than the previous estimations using drifting particles on the sea surface. It is suggested that the diffusivity changes vertically in the surface layer. Our experiments have demonstrated the effectiveness of the drifter in observing detailed variability of surface current and applicability to visualization of the coastal current field.