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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-1048
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
27 Nov 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Spatio-temporal variations of HNO3 total column from 9 years of IASI measurements – A driver study
Gaétane Ronsmans1, Catherine Wespes1, Daniel Hurtmans1, Cathy Clerbaux1,2, and Pierre-François Coheur1 1Université Libre de Bruxelles (ULB), Faculté des Sciences, Chimie Quantique et Photophysique, Brussels, Belgium
2LATMOS/IPSL, UPMC Univ. Paris 06 Sorbonne Universités, UVSQ, CNRS, Paris, France
Abstract. This study aims at understanding the spatial and temporal variability of HNO3 total columns in terms of explanatory variables. To achieve this, multiple linear regressions are used to fit satellite-derived time series of HNO3 daily averaged total columns. First, an analysis of the IASI 9-year time series (2008–2016) is conducted based on various equivalent latitude bands. The strong and systematic denitrification of the southern polar stratosphere is observed very clearly. It is also possible to distinguish, within the polar vortex, three regions wich are differently affected by the denitrification. Three exceptional denitrification episodes in 2011, 2014 and 2016 are also observed in the northern hemisphere, due to unusually low arctic temperatures. The time series are then fitted by multivariate regressions to identify what variables are responsible for HNO3 variability in global distributions and time series, and to quantify their respective influence. Out of an ensemble of proxies (annual cycle, solar flux, quasi-biennial oscillation, multivariate ENSO index, Arctic and Antarctic oscillations and volume of polar stratospheric clouds), only the ones defined as significant (p-value < 0.05) by a selection algorithm are retained for each equivalent latitude band. Overall, the regression gives a good representation of HNO3 variability, with especially good results at high latitudes (60–80 % of the observed variability explained by the model). The regressions show everywhere the dominance of the annual variability, which is related to specific chemistry and dynamic depending on the latitudes. We find that the PSCs also have a major influence in the polar regions, and that their inclusion in the model improves the correlation coefficients and the residuals. However, there is still a relatively large part of the HNO3 variability that remains unexplained by the model, especially in the intertropical regions, where factors not included in the regression model (such as vegetation fires or lightning) may be at play.

Citation: Ronsmans, G., Wespes, C., Hurtmans, D., Clerbaux, C., and Coheur, P.-F.: Spatio-temporal variations of HNO3 total column from 9 years of IASI measurements – A driver study, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-1048, in review, 2017.
Gaétane Ronsmans et al.
Gaétane Ronsmans et al.
Gaétane Ronsmans et al.

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Short summary
The paper aims at understanding the variability of nitric acid (HNO3) in the stratosphere. 9-year timeseries of IASI measurements are analysed and, for the first time for HNO3, fitted with regression models in order to identify the factors at play. It was found that the annual variability is the main driver, and that the polar stratospheric clouds influence greatly the HNO3 concentrations at polar latitudes. The results show the potential of such analyses to better understand the polar processes
The paper aims at understanding the variability of nitric acid (HNO3) in the stratosphere....
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