It is now widely accepted that random-strain theories of turbulent line-stretching are, broadly speaking, applicable to the wintertime stratosphere (cf. Haynes and Anglade 1997). Much theoretical progress has been made in recent years on the extension of these theories to a randomly advected and diffused tracer field; however applicability to the stratosphere is uncertain, largely because of the rather special, spatially homogeneous, tracer forcings used in both analytical and numerical studies. As a step towards understanding random advection-diffusion in geophysical flows we have developed a highly idealized lattice model, to which we have added a number of spatially inhomogeneous forcings, including chemical reaction.
The primary objects of our study are the probability density functions (PDFs) of the tracer concentration and the conditional expectations of the diffusion and dissipation. We show that spatial inhomogeneity in the forcing can have a profound effect on the shape of the tracer probability density functions, specifically through the appearance of non-Gaussian ``shoulders.'' We illustrate these results with several calculations using off-line stratospheric winds, and discuss the implications for common eddy-flux parameterizations of stratospheric mixing and chemistry.
Close window or click on previous window to return to the Conference Program.
12th Conference on Atmospheric and Oceanic Fluid Dynamics