A numerical transport scheme which avoids negative mixing ratios.

Abstract

A numerical transport scheme that avoids the problem of spurious generation of negative mixing ratios has been developed. The scheme is computationally simple in any number of spatial dimensions, can be used with nonperiodic boundary conditions, and preserves shapes reasonably well. It is based on the idea of formulating a quadratically conservative finite-difference advection equation and then advecting the square root of the concentration instead of the concentration itself. -from Author