Estimating horizontal diffusivity in the East Sea (Sea of Japan) and the northwest Pacific front satellite-tracked drifter data

We use data of satellite-tracked, mixed-layer drifters collected for the Wo rld Ocean Circulation Experiment/Tropical Ocean-Global Atmosphere (WOCE/TOG A) Surface Velocity Program in the East Sea (Sea of Japan) and the northwes t Pacific Ocean during 1991-1997 to obtain reliable estimates of geographic ally varying horizontal diffusivity, integral timescale and space scale. Fo r the diffusivity we suggest calculation of both the minor principal compon ent of the diffusivity tensor in a definition by Davis [1991] and the half growth rate of the minor principal component of the displacement variance t ensor. Numerical simulation of particle motion is used to prove that the mi nor principal component estimates of diffusivity, in contrast to regular es timates, are insensitive to ensemble averaging over particles taken from a finite area in a shear mean flow. In the East Sea, typical values of the di ffusivity, timescale, and space scale are (1.7-5.2) X 10(7) cm(2) s(-1), 0. 7-1.7 days, and 10-25 km, respectively. In the northwest Pacific Ocean, typ ical estimates of the diffusivity, timescale, and space scale in mean are a factor 2-3 larger, namely, (2.3-15.1) X 10(7) cm(2) s(-1), 1.7-3.7 days, a nd 18-62 km, respectively. It was found that the space scale L and the firs t mode internal Rossby radius Ri are related as L approximate to Ri, which suggests a parameterization of lateral diffusivity k(infinity) of the form k(infinity) = u Ri, where u is the rms current velocity fluctuation.