H. K. Roscoe

Lack of trend in Brewer-Dobson circulation, inferred from measurements of stratospheric NO2 in polar summer

Changes in the speed of the Brewer-Dobson circulation can be deduced from changes in stratospheric NOy, as it is produced by photo-oxidation of N2O from the troposphere. We analyse our NO2 measurements from 1990 to 2007 in Antarctica, and use a chemical model to deduce the NOy from the observed NO2 in midsummer, when the effect of stratospheric aerosol on NO2/NOy is smallest. The midsummer NOy has large inter-annual variability and a broad maximum in 2000-2001, but little overall trend. From our simple model of B-D circulation, the NOy implies similar changes in speed of circulation but of opposite sign - a broad minimum near 2000. Regression shows significant correlation with solar and QBO indices, and there remains a large unexplained cycle of period >17 years. The trend is +1.4 +/-3.5 %/decade.
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