Introduction

Lagrangian instruments have been widely used in the last few decades to sample basic ocean properties, even in remote areas of the globe. Since transport properties depend on Lagrangian scales, an integrated analysis of the Lagrangian trajectories observed sparsely in space and time is fundamental for the understanding of the ocean transport properties. This analysis, however, is complex, due to the non-homogeneous character of the mesoscale structures and the existence of different regimes of dispersion.

Nowadays, Lagrangian data, at different depths and in all world ocean basins, are available through the WOCE (2002) archive. The first information that can be extracted from such data is a map of the mean currents and of the eddy kinetic energy, that is typically computed using the binning technique, where the float velocities are averaged over small spatial subregions (bins). This approach, that considers Lagrangian instruments as moving current meters, has often been exploited in the past in order to achieve a better description of the global oceanic circulation (e.g. McNally et al., 1983; Richardson, 1983; Hofmann, 1985; Patterson, 1985; Davis, 1991a; Owens, 1991; Swenson and Niiler, 1996; Bauer et al., 1998; Fratantoni, 2001; Bower et al., 2002).

Lagrangian data have also been employed to study transport properties in the mesoscale range (e.g. Freeland et al., 1975; Riser and Rossby, 1983; Rossby et al., 1983; Colin de Verdière, 1983; Krauss and Böning, 1987; Figueroa and Olson, 1989; Zhang et al., 2001; Bauer et al., 2002).