Isolation of the ozone QBO in SAGE II data by singular-value decomposition

Detailed structure of the global quasi-biennial oscillation (QBO) in ozone is analyzed using Stratospheric Aerosol and Gas Experiment II ozone and nitrogen dioxide data. Emphasis is placed on the midlatitude QBO, in particular its vertical structure and seasonal synchronization. The global QBO signal is isolated using a combination of singular-value decomposition and regression analyses, which combine to act as an accurate QBO digital filter. Results show that the midlatitude ozone QBO has a two-cell structure in the vertical (similar to that at the equator), with in-phase maxima in the lower and middle stratosphere. Both upper- and lower-level anomalies contribute important fractions to the midlatitude column amounts. The lower-level maxima have a broad latitudinal structure (∼15°-60°), and collocation with the strongest background gradients suggests that these anomalies result from mean vertical transport. The middle stratosphere signal maximizes in the subtropics (10°-40°) and is likely due to nitrogen-related chemical effects (which are in turn due to transport variations). The vertically in-phase seasonal synchronization in midlatitudes is evidence of QBO modulation of the winter hemisphere circulation.