Variability and trends in stratospheric NO 2 in Antarctic summer, and implications for the Brewer-Dobson circulation

Abstract

Published by Copernicus Publications on behalf of the European Geosciences Union. 837 Abstract NO 2 measurements during 1990–2007, obtained from a zenith-sky spectrometer in the Antarctic, are analysed to determine the long-term changes. The changes in midsum-mer should be indicative of any changes in the Brewer-Dobson circulation. An atmo-spheric photochemical box model and a radiative transfer model are used to improve 5 the accuracy of determination of the vertical columns from the slant column measure-ments, and to deduce the amount of NO y from NO 2 . We find that the NO 2 and NO y columns in midsummer have large inter-annual variability superimposed on a broad maximum in 2000, with little overall trend over the full time period. These changes are robust to a variety of alternative settings when determining vertical columns from slant 10 columns or determining NO y from NO 2 . They suggest similar changes in speed of the Brewer-Dobson circulation but with opposite sign, i.e. a broad minimum around 2000.