Middle atmosphere chemical transport model evaluation with long-term data sets

Predicting ozone recovery requires an understanding of the sensitivity of stratospheric ozone to the addition of chlorine and bromine to the atmosphere. That sensitivity is determined both by the chemical reactions and by the transport processes that determine the mixture of chlorine and bromine with hydrogen and nitrogen compounds that can interfere with the ozone destruction processes. Models with the same chemical reactions calculate differing results for ozone loss over the past two decades and sometimes widely differing results for ozone recovery. This is most likely a result of their different circulation patterns. We will analyze three chemical transport model simulations of the past 30 years using a variety of long-term data sets to evaluate the model sensitivity to chlorine/bromine, solar cycle, and volcanic aerosols. The three CTM simulations all use winds and temperatures from the finite volume GCM (FVGCM). One uses the Goddard CTM with interannually varying winds and temperatures as generated in the GCM. The other two use the Global Modeling Initiative (GMI) CTM with a single year's winds and temperatures repeated: one uses a year with a typical cold northern hemisphere winter stratosphere and the other uses a year with a typical warm northern hemisphere winter. The GMI simulations explore the extremes of sensitivity of the stratosphere to erturbations, while the Goddard simulation illustrates how dynamic variability can often mask the actual sensitivity to perturbations.