GLOBAL QBO IN CIRCULATION AND OZONE .1. REEXAMINATION OF OBSERVATIONAL EVIDENCE

Observational evidence for a global quasi-biennial oscillation (QBO) p attern is reviewed. In particular, the presence of an extratropical, a s well as an equatorial, component of the QBO signal in column ozone i s established. It is found that the ozone interannual variability is s uch that as one moves away from the Tropics, the frequency spectrum of the anomaly changes from one that is dominated by the equatorial QBO frequency of 1/30 mo to a two-peak spectrum around the two frequencies : 1/30 mo and 1/20 mo. Instead of treating the 1/20 mo frequency as a separate phenomenon to be filtered away in extracting the QBO in the e xtratropics, as was previously done, the authors argue that both peaks are integral parts of the extratropical QBO phenomenon. The 1/20 mo f requency happens to be the difference combination of the QBO frequency 1/30 mo and the annual frequency 1/12 mo. Therefore, it can represent the result of the QBO modulating an annual cycle. The authors suggest that previous methods of extracting the extratropical QBO signal seve rely underestimated the contribution of the QBO to the interannual var iability of ozone when data are filtered to pass only the component wi th the period of equatorial QBO. Further, it is argued that the transp ort of equatorial QBO ozone anomaly by a non-QBO circulation can at mo st account for 6-8 Dobson units (DU) of the observed interannual varia bility of column ozone in the extratropics. The remaining variability (up to 20 DU) probably cannot be produced without an anomaly in the tr ansporting circulation in the extratropics.