Ozone variability in the troposphere and the stratosphere from the first six years of IASI observations (2008–2013)

Abstract

Abstract. In this paper, we assess how daily ozone (O3) measurements from the Infrared Atmospheric Sounding Interferometer (IASI) on MetOp-A platform can contribute to the analyses of the processes driving O3 variability in the troposphere and the stratosphere and, in the future, to the monitoring of long-term trends. The time development of O3 during the first 6 years of IASI (2008–2013) operation is investigated with multivariate regressions separately in four different layers (ground–300, 300–150, 150–25, 25–3 hPa), by adjusting to the daily time series averaged in 20° zonal bands, seasonal and linear trend terms along with important geophysical drivers of O3 variation (e.g. solar flux, quasi biennial oscillations). The regression model is shown to perform generally very well with a strong dominance of the annual harmonic terms and significant contributions from O3 drivers, in particular in the equatorial region where the QBO and the solar flux contribution dominate. More particularly, despite the short period of IASI dataset available to now, two noticeable statistically significant apparent trends are inferred from the daily IASI measurements: a positive trend in the upper stratosphere (e.g. 1.74 ± 0.77 DU yr−1 between 30–50° S) which is consistent with the turnaround for stratospheric O3 recovery, and a negative trend in the troposphere at the mid-and high northern latitudes (e.g. −0.26 ± 0.11 DU yr−1 between 30–50° N), especially during summer and probably linked to the impact of decreasing ozone precursor emissions. The impact of the high temporal sampling of IASI on the uncertainty in the determination of O3 trend has been further explored by performing multivariate regressions on IASI monthly averages and on ground-based FTIR measurements.