Lagrangian observations in the Iberian coastal transition zone

Abstract

Satellite-tracked drifters deployed in the Iberian coastal transition zone were gradually carried northward in a poleward flowing continental slope current between September 1986 and March 1987 in convoluted trajectories which revealed the ubiquitous presence of mesoscale eddies. We estimate the rate of dispersion from the Lagrangian statistics of the drifting buoys and present a comparison of the results with those obtained from other oceanic regions. The dispersion of the drifters is well modelled by a simple description of eddy diffusion assuming homogeneous isotropic turbulence (Taylor's theory). The assumption of homogeneity and stationarity facilitated the derivation of stable Lagrangian statistics. After correction for non stationarity, the diffusivities obtained were k 11 = 3.4 × 106 cm2 s−1 in the zonal direction and K 22 = 2.5 × 106 cm2 s−1 in the meridional direction. The Lagrangian integral time scales were respectively T 11 = 1.25 days and T 22 = 1.9 days. Our results and those of other authors, in environments ranging from truly oceanic to eastern boundaries, have all indicated that Taylor's theory fits the observations well. As a first order approximation the assumption of a homogeneous and stationary field would appear quite robust.