Stratospheric ozone in 3-D models: A simple chemistry and the cross-tropopause flux

Two simple and computationally efficient models for simulating stratospheric ozone in three-dimensional global transport models are presented. The first, linearized ozone (or Linoz), is a first-order Taylor expansion of stratospheric chemical rates in which the ozone tendency has been linearized about the local ozone mixing: ratio, temperature, and the overhead column ozone density. The second, synthetic ozone (or Synoz), is a passive, ozone-like tracer released into the stratosphere at a rate equivalent to that of the cross-tropopause ozone flux which, based on measurements and tracer-tracer correlations, we have calculated to be 475 +/- 120 Tg/Sr. Linoz and Synox ha ie been evaluated in the UC Irvine chemical transport model(CTM) with three different archived meteorological fields: the Goddard Institute for Spare Studies (GISS) general circulation model (GCM) version II', the GISS GCM version II, and merged forecast data from the European Centre forecast model (EC/Oslo). Linoz produced realistic annual, cross-tropopause fluxes of 421 Tg/yr for the GISS II' winds and 458 Tg/yr for the EC/Oslo winds; the GISS II winds produced an unrealistic flux of 790 Tg/yr. Linoz and Synoz profiles in the vicinity of the tropopause using the GISS II' and EC/Oslo winds were found to be in good agreement with observations. We conclude that either approach may be adequate for a CTM focusing on tropospheric chemistry but that Linoz can also be used for calculating ozone fields interactively with the stratospheric circulation in a GCM. A future version of Linoz will allow for evolving background concentrations of key source gases? such as CH4 and N2O, and thus be applicable for long-term climate simulations.