Lagrangian trajectory methods are often applied as deterministic transport models, where transport is due strictly to advection without taking into account stochastic elements of particle dispersion, which raises questions about validity of the model results. The present work investigates the impact of horizontal eddy-diffusivity for a case study of coastal pollution in the Gulf of Finland, where the pollutants are assumed to originate from a major fairway and is transported to the coast by surface currents. Lagrangian trajectories are calculated using the TRACMASS model, with velocity fields calculated by the Rossby Centre circulation model for 1982-2001. Three cases are investigated: (i) trajectory calculation without eddy-diffusivity, (ii) stochastic modelling of eddy-diffusivity with a constant diffusion coefficient, and (iii) stochastic modelling of eddy-diffusivity with a time- and space-variable diffusion coefficient. It is found that the eddy-diffusivity effect increases the number of trajectories that eventually reach the coast, but the impact of horizontal eddy-diffusivity is relatively small for this particular application.
Head: prof. Tarmo Soomere
Laboratory of Wave Engineering
Institute of Cybernetics at Tallinn University of Technology
Fax: +372 620 4151
Phone: +372 620 4176