Abstract
Changes in the stratosphere‐troposphere exchange (STE) of ozone over the last few decades have altered the tropospheric ozone abundance and are likely to continue doing so in the coming century as climate changes. Combining an updated linearized stratospheric ozone chemistry (Linoz v2) with parameterized polar stratospheric clouds (PSCs) chemistry, a 5‐year (2001–2005) sequence of the European Centre for Medium‐Range Weather Forecasts (ECMWF) meteorology data, and the University of California, Irvine (UCI) chemistry transport model (CTM), we examined variations in STE O3 flux and how it perturbs tropospheric O3. Our estimate for the current STE ozone flux is 290 Tg/a in the Northern Hemisphere (NH) and 225 Tg/a in the Southern Hemisphere (SH). The 2001–2005 interannual root‐mean‐square (RMS) variability is 25 Tg/a for the NH and 30 Tg/a for the SH. STE drives a seasonal peak‐to‐peak NH variability in tropospheric ozone of about 7–8 Dobson unit (DU). Of the interannual STE variance, 20% and 45% can be explained by the quasi‐biennial oscillation (QBO) in the NH and SH, respectively. The CTM matches the observed QBO variations in total column ozone, and the STE O3 flux shows negative anomalies over the midlatitudes during the easterly phases of the QBO. When the observed column ozone depletion from 1979 to 2004 is modeled with Linoz v2, we predicted STE reductions of at most 10% in the NH, corresponding to a mean decrease of 1 ppb in tropospheric O3.
Highlights
[4] We find that stratosphere alone produces a peak-topeak seasonal variation in tropospheric column ozone of about 7 – 8 Dobson unit (DU) at northern midlatitudes that parallels the late summer maximum normally attributed to HSU AND PRATHER: STRATOSPHERIC VARIABILITY AND TROPOSPHERIC OZONE
The stratosphere-troposphere exchange (STE) data are fitted to a hemispheric mean, the seasonal harmonics and the three time series of the quasi-biennial oscillation (QBO), the Arctic Oscillation (AO [Thompson and Wallace, 1998]) and the El Nino Southern Oscillation (ENSO) index [Ziemke and Chandra, 2003]
[30] The QBO accounts for about 20% of the Northern Hemisphere (NH) interannual variances in STE
Summary
[2] Scientific efforts to understand the trends and variations in ozone observed over the past few decades have demonstrated the role of both photochemical and meteorological factors in driving stratospheric ozone change [e.g., Randel and Wu, 2007; Stolarski et al, 2006; Salawitch et al, 2005]. [3] The coupling of stratospheric and tropospheric ozone with chemistry models or with chemistry-climate models is occurring across the community [Eyring et al, 2005]. These full models include a nearly complete set of chemical species and reactions that affect ozone, but are costly to. The latitudeseason pattern of STE decrease due to ozone depletion is distinctly different from the pattern of change in total column ozone
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