Spatially correlated and inhomogeneous random advection

We study the equilibrium statistics of an idealized model of random advecti on. Theoretical results for large-scale homogeneous forcing-notably the sha pes of the PDFs-are recovered; they are compared with results for various i nhomogeneous and intermittent forcings. The correlation times of the forcin gs are varied. The PDFs are interpreted in terms of the underlying mixing t ime scales. Conditional statistics of the tracer field-the conditional diff usion in particular-are computed; they are used to elucidate the influence of small-scale tracer-field correlations. We contrast results for spatially smooth and spatially rough velocity fields. (C) 2000 American Institute of Physics. [S1070-6631(00)01104-1].