Abstract
Abstract. Observations from the Ozone Monitoring Instrument (OMI) on the Aura satellite are used to study the effect of energetic particle precipitation (EPP, as proxied by the geomagnetic activity index, Ap) on the Antarctic stratospheric NO2 column in late winter–spring (August–December) during the period from 2005 to 2017. We show that the polar (60–90∘ S) stratospheric NO2 column is significantly correlated with EPP throughout the Antarctic spring, until the breakdown of the polar vortex in November. The strongest correlation takes place during years with the easterly phase of the quasi-biennial oscillation (QBO). The QBO modulation may be a combination of different effects: the QBO is known to influence the amount of the primary NOx source (N2O) via transport from the Equator to the polar region; and the QBO phase also affects polar temperatures, which may provide a link to the amount of denitrification occurring in the polar vortex. We find some support for the latter in an analysis of temperature and HNO3 observations from the Microwave Limb Sounder (MLS, on Aura). Our results suggest that once the background effect of the QBO is accounted for, the NOx produced by EPP significantly contributes to the stratospheric NO2 column at the time and altitudes when the ozone hole is present in the Antarctic stratosphere. Based on our findings, and the known role of NOx as a catalyst for ozone loss, we propose that as chlorine activation continues to decrease in the Antarctic stratosphere, the total EPP-NOx needs be accounted for in predictions of Antarctic ozone recovery.
Highlights
In the polar stratosphere, the dominant source of odd nitrogen, NOx (NO + NO2), is produced via the oxidation of nitrous oxide, N2O (Brasseur and Solomon, 2005): N2O + O(1D) −→ 2NO. (R1)This reaction requires the presence of excited oxygen atoms O(1D), which are produced in the atmosphere by the photolysis of ozone (O3) and, depend on the presence of sunlight
The combined influence of the quasi-biennial oscillation (QBO) and Ap appears to be most significant for high Ap (H-Ap) easterly QBO (eQBO) years and low Ap winters (L-Ap) westerly QBO (wQBO) years (Fig. 3a, d)
Our analysis shows that the influence of the QBO is able to mask the stratospheric Energetic particle precipitation (EPP)-NOx signal in satellite observations in a way that, to our knowledge, has not previously been accounted for: considering the phase of the QBO makes the contribution from EPP more pronounced in the NO2 column, and signals of enhanced EPP-NOx in the polar stratospheric column can be detected until late November
Summary
The dominant source of odd nitrogen, NOx (NO + NO2), is produced via the oxidation of nitrous oxide, N2O (Brasseur and Solomon, 2005): N2O + O(1D) −→ 2NO. (R1)This reaction requires the presence of excited oxygen atoms O(1D), which are produced in the atmosphere by the photolysis of ozone (O3) and, depend on the presence of sunlight. As N2O production in situ in the polar stratosphere is insignificant, the polar stratospheric NOx production is highly dependant on the amount of N2O transported from the tropics (Brasseur and Solomon, 2005). Recent work by Strahan et al (2015) has shown that the phase of the QBO influences the transport of N2O from the “surf zone” to the polar vortex with a lag of 12 months Their results (Fig. 1 of Strahan et al, 2015) indicate that the easterly phase of the QBO during June–July is generally associated with positive N2O anomalies in the polar stratosphere between altitudes of ∼ 24 and 33 km in September, whereas the opposite is true for the westerly phase of the Published by Copernicus Publications on behalf of the European Geosciences Union
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