Characterizing chaotic dispersion in a coastal tidal model

Diverse Lagrangian methods are used to study dispersion and mixing in a model in the Norwegian Trondheim fjord. We focus on the tidally driven currents, neglecting wind-forcing, and generate a large number of particle trajectories. We first consider traditional measures (absolute and relative dispersion) involving averages over all particles. We then contour those measures, to gauge the spatial variations. Then we examine a more recently developed measure, the direct Lyapunov exponent (DLE), to further refine the description of the spatial variability. The results suggest regions of strong mixing adjacent to regions with weak mixing, so that particles in nearby regions may experience very distinct evolutions. And M2 dominates the dispersion; adding additional tidal components affects mainly the amplitude of the particle excursions rather than the character of the mixing.