2-DIMENSIONAL MODEL STUDIES OF THE INTERANNUAL VARIABILITY OF TRACE GASES IN THE MIDDLE ATMOSPHERE

A parameterization of the mechanisms believed to be responsible for the quasi-biennial oscillation (QBO) in the zonal winds of the equatorial lower stratosphere has been included in an interactive dynamical-radiative-photochemical model of the atmosphere. As well as a QBO signal in the zonal wind, temperature, and ozone there are QBO signals in a range of other chemical species contained in the model. In the case of long-lived tracers the QBO signal results from the direct effect of the QBO-induced modification to the model circulation. The sign and magnitude of these QBO signals depend on the sign and strength of the vertical gradient of these long-lived tracers in the lower stratosphere. For shorter-lived species a QBO signal can result from the QBO in temperature or in trace gases controlling the species' production and loss. In many cases, much larger interannual variability is predicted for these shorter-lived species. Notably, NO2 and N2O5, whose chemistry is very temperature dependent, show very strong QBO signals. In the case of ozone the transition from dynamical control in the lower stratosphere to photochemical control at higher altitudes can be seen in its QBO signal. These predictions of interannual variability of trace species should be considered when analyzing and interpreting observational data, particularly when calculating year-to-year trends.