O3 variability in the troposphere and the stratosphere from IASI observations in 2008- 2015

Abstract : In this study, we present geographical patterns of ozone (O3) variability in the troposphere and the stratosphere derived from 8 years of IASI observations (2008-2015). The instrument provides a unique dataset of global vertically-resolved O3 profiles with a high temporal sampling and a fairly good vertical resolution in the troposphere and the stratosphere allowing us to monitor the year-to-year variability in these layers. The retrievals are performed using the FORLI software, a fast radiative transfer model based on the optimal estimation method, set up for near real time and large scale processing of IASI data. Multivariate regressions which include important geophysical drivers of O3 variation (e.g. solar flux - SF, quasi biennial oscillations – QBO, El Niño/Southern Oscillation – ENSO) and a linear trend term have been performed on time series of spatially averaged O3 on spatial grids. The resulting covariates and trend spatial structures are analyzed. In particular, we focus on O3 variation and trends in the troposphere over and downwind anthropogenic polluted areas characterized either by increased (e.g. over Asia) or decreased (e.g. over Europe and the US) O3 precursor emissions. Direct effects of positive (or negatives) ENSO indexes measured during moderate to intense El Niño (or La Niña) episodes in 2009 and 2014 (or 2010) observed in the ozone columns in the tropics will be also discussed.