Ballistic versus diffusive pair dispersion in the Richardson regime

Two-particle dispersion in fully developed turbulence is modeled within an asymmetric Levy-walk framework which yields the Richardson t(3) law and whi ch recovers recently observed results on the probability distribution funct ion of pair separations in two-dimensional turbulence [M.C. Jullien, J. Par et, and P. Tabeling, Phys. Rev. Lett. 82, 2872 (1999)]. The ballistic natur e of the Richardson dispersion is discussed in terms of the persistence par ameter and compared with the Richardson diffusive behavior.