DYNAMICS OF ADVECTED TRACERS WITH VARYING BUOYANCY

We study the dynamics of passively advected Lagrangian tracers undergo ing small vertical oscillations around an horizontal reference density surface, in an Eulerian velocity field depending only on the horizont al coordinates. The motion of the advected particles may be chaotic ev en though the fluid (or, equivalently, the non-oscillating) particles undergo regular motion and follow the streamlines of the Eulerian flow . Slowly oscillating particles undergo large-time dispersion, a behavi or which cannot be observed in the motion of non-oscillating particles in the same fluid flow. The system studied here may be considered as an idealized representation of the dynamics of free subsurface buoys o r free balloons in the atmosphere; the results of this study indicate that a proper evaluation of the parameters of the Lagrangian tracers s hould be pursued in order to verify the motion of the Lagrangian trace rs properly represents the behavior of true fluid particles.