The formation and dynamics of vortical structures in two-dimensional f
lows are investigated numerically and theoretically. Localized initial
distributions with random fluctuations are in general found to evolve
into large scale vortical structures. If the initial perturbation con
tains a linear momentum the development into propagating dipolar struc
tures is observed. This development is discussed by employing self-org
anization principles. The detailed structures of the evolving dipoles
depends on the initial condition. It seems that there are no unique di
polar solutions, but a large class of solutions is possible. However,
it is argued that the gross properties of the dipoles do not depend cr
itically on the detailed structure. The vortical structures are found
to trap particles and convect them over distances much larger than the
scale size of the structure. Two examples of trapping/detrapping of p
articles are shown. The trapping of particles by a decaying, expanding
dipolar vortex and the detrapping of particles during the merging of
two Like-signed monopolar vortices.