FRACTAL FRONTS IN THE MEDITERRANEAN-SEA

We analyze three surface temperature fronts in the Mediterranean Sea and show that they display fractal and scaling behavior on space scales of the order of the Rossby deformation radius, i.e. between approximately three and seventy kilometers. The fractal dimension of the front temperature isolines is estimated to be D almost-equal-to 1.2, a value close to the dimension of concentration isolines of passive scalar tracers in turbulent fluids and to the dimension of the trajectories of freely drifting buoys in large and mesoscale ocean flows. The fractal behavior of the temperature isolines and the peculiar properties of frontal regions suggest a fractal nature of the Eulerian surface velocity field. In this context, we discuss a possible purely geometrical origin for the ubiquitous value D almost-equal-to 1.2, 1.3 observed for the isolines of both passive and active tracers in turbulent flows. The problem of linking the possible fractal nature of velocity isolines and the observed fractal behavior of drifter trajectories is considered.