On the advection of tracer by eddies on the beta-plane: A numerical study

The evolution of tracer "injected" into an equivalent barotropic eddy on th e beta-plane is examined numerically, The eddy is governed by the standard quasigeostrophic equation, and the concentration of tracer is governed by t he advection equation with diffusion, At the initial moment of time, the st reamfunction and distribution of tracer are both radially or elliptically s ymmetric. After the first 10-30 days, a spiral-like strip, where the gradie nt of concentration is large, develops in the tracer field, whereas the edd y remains smooth for a relatively long time. To put this conclusion in quan titative terms, a "tracer variability indicator" is introduced and shown to grow much faster than a similar characteristic of the potential vorticity field (notwithstanding the fact that the tracer concentration and PV satisf y the same governing equation). A simple explanation as to why the tracer i s more affected by filamentation than PV is provided for eddies with small Burger number. It is demonstrated that the high-gradient strip develops, un less stopped by turbulent diffusion, into an inversion (non-monotonicity) o f the tracer concentration field. Finally, the results of simulations are c ompared to the spiral patterns in the real-life eddies observed in the East Australian Current.