  We develop a simple mean field approach to the transport of a passive scalar
for which the fundamental equation is a second order differential equation in
the transported quantity, not a first order equation. Triple correlations are
included, as they must be for any realistic description of turbulence. No
correlation time enters the theory, only an eddy turnover time. The approach is
simpler than standard approaches which incorporate triple correlations, but
more realistic than Gaussian or short correlation time closures which do not. A
similar approach has proven useful in magnetohydrodynamics.
