A new fast stratospheric ozone chemistry scheme in an intermediate general‐circulation model. I: Description and evaluation

Abstract

AbstractSimulation of future climate‐composition changes requires simulations of coupled dynamical‐radiative‐chemical models of many decades in length. Yet, to assure the generality of the simulation's results against uncertainties in emissions, unforced year‐to‐year variability and dependence on initial conditions, it is necessary to repeat them a significant number of times. The computational cost of such an exercise is still too large when using complex three‐dimensional coupled models.We introduce in this paper a computationally efficient chemical scheme, the FAst STratospheric Ozone Chemistry (FASTOC) scheme, which has advantages over many existing fast methods, as it does not rely on relaxation to assumed conditions, does not rely on tuning parameters, and does not rely on linearization approximations. The scheme is nevertheless three orders of magnitude faster than a stiff kinetic equations solver.Part I of the paper gives a detailed description of the FASTOC model and some performance evaluations when incorporated in a general‐circulation model (GCM). In Part II, the FASTOC model, coupled to a GCM, is specifically applied to study the impact of climate–chemistry interactions on stratospheric ozone in the middle of the twenty‐first century. Copyright © 2005 Royal Meteorological Society