Two‐dimensional model simulations of the QBO in ozone and tracers in the tropical stratosphere

Abstract

Meteorological data from the United Kingdom Meteorological Office (UKMO) and constituent data from the Upper Atmospheric Research Satellite (UARS) are used to construct yearly zonal mean dynamical fields for the 1990s for use in the NASA/Goddard Space Flight Center (GSFC) two‐dimensional (2‐D) chemistry and transport model. This allows for interannual dynamical variability to be included in the model constituent simulations. In this study, we focus on the tropical stratosphere. We find that the phase of quasi‐biennial oscillation (QBO) signals in equatorial CH4 and profile and total column O3 data are resolved quite well using this empirically based 2‐D model transport framework. However, the QBO amplitudes in the model constituents are systematically underestimated relative to the observations at most levels. This deficiency is probably due in part to the limited vertical resolutions of the 2‐D model and the UKMO and UARS input data sets. We find that using different heating rate calculations in the model affects the interannual and QBO amplitudes in the constituent fields, but has little impact on the phase. Sensitivity tests reveal that the QBO in transport dominates the ozone interannual variability in the lower stratosphere, with the effect of the temperature QBO being dominant in the upper stratosphere via the strong temperature dependence of the ozone loss reaction rates. We also find that the QBO in odd nitrogen radicals, which is caused by the QBO modulated transport of NOy, plays a significant but not dominant role in determining the ozone QBO variability in the middle stratosphere. The model mean age of air is in good overall agreement with that determined from tropical lower‐middle stratospheric OMS balloon observations of SF6 and CO2. The interannual variability of the equatorial mean age in the model increases with altitude and maximizes near 40 km, with a range of 4–5 years over the 1993–2000 time period.