“…In this limit the goal is to derive the expression of the asymptotic diffusion coefficient renormalized by the presence of the small scale velocity field. This can be accomplished exploiting asymptotic methods (see, e.g., [6,8,9,10,11,12,13,14] among the others). However, in many physical circumstances one has that the velocity field may be though as a smallscale advecting velocity field (at scale ℓ) superimposed to a large-scale, slowly varying component (at scale L ≫ ℓ).…”