Analysis of seasonal variation of stratospheric nitric acid

Abstract

Data from the draft COSPAR reference model for stratospheric nitric acid (HNO 3) are analysed. Eight months of LIMS HNO 3 measurements allow the analysis of dynamics of regimes associated with the annual HNO 3 maximum followed by the HNO 3 decrease in the Northern Hemisphere and the annual HNO 3 minimum followed by the HNO 3 increase in the Southern Hemisphere. The HNO 3 minimum is noted earlier (in November) in the Southern Hemisphere subtropical upper stratosphere, from where the regime of minimum HNO 3 values propagates to the southern high-latitude middle stratosphere, and then (in Austral summer) the equatorward propagation of the regime is observed, with a persistent downward component. The regime of the HNO 3 annual maximum in the Northern Hemisphere propagates from the Arctic lower stratosphere (in autumn) and from the tropical middle stratosphere (in late summer), so that in the mid-latitude middle stratosphere the downward propagation of the regime is observed. Evolution of areas with HNO 3 increase and decrease by 1 ppbv against the January HNO 3 distribution quantifies intensity of the HNO 3 decrease in winter-spring in the Northern Hemisphere and the HNO 3 increase in Austral summer-autumn in the Southern Hemisphere.