  In this paper, phenomenological developments are used to explore several
aspects of the relative particle dispersion (RPD) in different physical
fully-developed turbulence (FDT) situations. The role played by the FDT cascade
physics underlying this process is investigated. Many of these aspects are
motivated by previous laboratory experiment and numerical simulation results.
These are,
  * spatial intermittency effects exhibiting, * [(a)] reduction of RPD in 3D
FDT, corroborating the numerical simulation results (Boffetta and Sokolov
[11]); *[(b)] prevalence of power-law scaling of RPD in 2D FDT enstrophy
cascade (no matter how weak spatial intermittency effects are), corroborating
the difficulty in observing Lin [12] exponentical scaling law in laboratory
experiments (Jullien [13]);
  * quasi-geostrophic FDT aspects exhibiting an enhanced RPD in the baroclinic
regime of the energy cascade and a negative eddy-viscosity development to shed
some insight into this aspect;
  * quasi-geostrophic FDT aspects exhibiting particle clumping in the
baroclinic regime of the enstrophy cascade;
  * reduction of RPD, development of the ballistic regime and particle
clustering due to compressibility effects in FDT, corroborating the laboratory
experiment and numerical simulation results (Cressman et al. [14]).
  These results are developed from the established scaling relations for the
various physical FDT cases and are further validated via alternative
dimensional/scaling developments for the various physical FDT cases similar to
the one given for 3D FDT by Batchelor and Townsend [15].
