Evaluation of the Stratospheric O3 Recovery and of its Radiative Effect from the 13-years IASI Record (2008-2020)
Résumé
In this study, we present a global fingerprint of recent changes in mid-upper stratospheric (MUSt;
>25hPa) and in lower stratospheric (LSt, 150-25 hPa) ozone (O3), as well as in the corresponding
longwave radiative effects (LWRE), derived from the first 13 years of the IASI/Metop-A and -B satellite
measurements (January 2008 – December 2020). IASI provides a unique twice daily global dataset of
vertically-resolved O3 profiles and of associated instantaneous radiative kernels (IRKs), which represent
the sensitivity of the outgoing longwave radiation (OLR) flux with respect to the O3 vertical profile,
allowing to monitor changes in both O3 and its corresponding LWRE in these two regions of the
stratosphere. 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.
We describe the O3 response to global atmospheric change and, in particular, to the decline in
stratospheric halogen species, which requires first identifying and quantifying natural cycles that may
produce trend-like segments in the O3 time series. The disentanglement between the O3 response to its
natural drivers and to the anthropogenic influence is performed by applying multivariate regressions,
which account for the main geophysical drivers of O3 variation and a linear trend term, on time series of
spatially gridded daily mean O3. The results of this study confirm the effectiveness of the Montreal
protocol and its amendments. They show the first detection of a significant recovery of O3 concurrently
in the LSt, in the MUSt and in the total column in the southern hemisphere (S.H.) from one single
satellite dataset. The results also show a contrasting significant O3 decline in the LSt in the northern
hemisphere (N.H.). A speeding up in both the O3 healing of the S.H. and in the LSt O3 decline of the
N.H is also demonstrated. Finally, we show how these changes in O3 levels translate to changes in O3
LWRE.