An advective model for two‐dimensional transport of stratospheric trace species

A parameterization of two‐dimensional transport is developed for application to photochemical models of stratospheric trace species. It is shown that in a first approximation tracer transport in the meridional plane may be treated as an advective, rather than a diffusive, process. The mean meridional motion used in this advective model is a modified Eulerian mean which is a good approximation to the Lagrangian mean motion. The potential of the proposed parameterization is demonstrated by a simple numerical experiment in which the equilibrium distribution is computed for a tracer with a uniform tropospheric source and a stratospheric sink proportional to the local mixing ratio. The resulting distribution is qualitatively in accord with the oberved stratospheric distribution of trace species whose sources are in the troposphere, e.g., N 2 O.