Using satellite measurements of N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O to remove dynamical variability from HCl measurements

Richard S Stolarski,Anne R Douglass,Susan E Strahan

doi:10.5194/acp-18-5691-2018

Using satellite measurements of N&lt;sub&gt;2&lt;/sub&gt;O to remove dynamical variability from HCl measurements

Richard S Stolarski, Anne R Douglass + Show 1 more

Open Access

https://doi.org/10.5194/acp-18-5691-2018

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Abstract

Abstract. Column HCl measurements show deviations from the expected slow decline following the regulation of chlorine-containing compounds by the Montreal Protocol. We use the simultaneous measurements of N2O and HCl by the Microwave Limb Sounder (MLS) instrument on the Aura satellite to examine this problem. We find that the use of N2O measurements at a specific altitude to represent the impact of dynamical variability on HCl results in a derived linear trend in HCl that is negative (ranging from −2.5 to 5.3 % decade−1) at all altitudes between 68 and 10 hPa. These trends are at or near 2σ statistical significance at all pressure levels between 68 and 10 hPa. This shows that analysis of simultaneous measurements of several constituents is a useful approach to identify small trends from data records that are strongly influenced by dynamical interannual variability.

Highlights

HCl is the primary constituent of inorganic chlorine in the stratosphere, comprising 75–80 % of the inorganic chlorine in the vertical pressure range from 68 to 10 hPa (Zander et al, 1992; Nassar et al, 2006)
Mahieu et al (2014) reported that total column HCl measured at Jungfraujoch showed significant variation from the expected simple linear decrease
N2O measurements since late 2004 made by the Aura Microwave Limb Sounder (MLS) instrument. Since both HCl and N2O have concentration gradients that are acted upon by dynamical processes to create interannual variability, we have used the variability of N2O concentrations determined from MLS observations as a measure of the dynamical variability that should be expected in HCl concentrations

Summary

Introduction

HCl is the primary constituent of inorganic chlorine in the stratosphere, comprising 75–80 % of the inorganic chlorine in the vertical pressure range from 68 to 10 hPa (Zander et al, 1992; Nassar et al, 2006). Rinsland et al (2003), using the Network for the Detection of Atmospheric Composition Change (NDACC) record of ground-based column measurements of HCl and ClONO2 (∼ 1990–2002), showed that their total stratospheric burden had leveled out by approximately 1995 These two gases comprise most of stratospheric inorganic chlorine outside the winter polar vortices. Mahieu et al (2014) use results from model simulations with the SLIMCAT model driven by ERA-Interim meteorological fields from the European Centre for Medium-Range Weather Forecasts (ECMWF) to suggest that variability in the stratospheric circulation causes the accelerated decrease and the unexpected increase in HCl column We will explore this explanation using measurements of N2O from MLS as a measure of this variability in circulation

MLS data

Time series analysis: using N2O measurements as a fitting parameter

Findings

Conclusions