Updated trends of the stratospheric ozone vertical distribution in the 60° S–60° N latitude range based on the LOTUS regression model
Authors: Godin-Beekmann Sophie , Azouz Niramson , Sofieva Viktoria F. , Hubert Daan , Petropavlovskikh Irina , Effertz Peter , Ancellet Gérard , Degenstein Doug A. , Zawada Daniel , Froidevaux Lucien , Frith Stacey , Wild Jeannette , Davis Sean , Steinbrecht Wolfgang , Leblanc Thierry , Querel Richard , Tourpali Kleareti , Damadeo Robert , Maillard Barras Eliane , Stübi René , Vigouroux Corinne , Arosio Carlo , Nedoluha Gerald , Boyd Ian , Van Malderen Roeland , Mahieu Emmanuel , Smale Dan , Sussmann Ralf 
Published: September 2022

Abstract. This study presents an updated evaluation of stratospheric ozone profile
trends in the 60∘ S–60∘ N latitude range over the
2000–2020 period using an updated version of the Long-term Ozone Trends
and Uncertainties in the Stratosphere (LOTUS) regression model that was used
to evaluate such trends up to 2016 for the last WMO Ozone Assessment (2018).
In addition to the derivation of detailed trends as a function of latitude
and vertical coordinates, the regressions are performed with the datasets
averaged over broad latitude bands, i.e. 60–35∘ S,
20∘ S–20∘ N and 35–60∘ N. The
same methodology as in the last assessment is applied to combine trends in
these broad latitude bands in order to compare the results with the previous
studies. Longitudinally resolved merged satellite records are also
considered in order to provide a better comparison with trends retrieved
from ground-based records, e.g. lidar, ozonesondes, Umkehr, microwave and
Fourier transform infrared (FTIR) spectrometers at selected stations where
long-term time series are available. The study includes a comparison with
trends derived from the REF-C2 simulations of the Chemistry Climate Model
Initiative (CCMI-1). This work confirms past results showing an ozone
increase in the upper stratosphere, which is now significant in the three
broad latitude bands. The increase is largest in the Northern and Southern Hemisphere midlatitudes, with ∼2.2 ± 0.7 % per decade at
∼2.1 hPa and ∼2.1 ± 0.6 % per decade at
∼3.2 hPa respectively compared to ∼1.6 ± 0.6 % per decade at ∼2.6 hPa in the tropics. New trend
signals have emerged from the records, such as a significant decrease in
ozone in the tropics around 35 hPa and a non-significant increase in ozone
in the southern midlatitudes at about 20 hPa. Non-significant negative
ozone trends are derived in the lowermost stratosphere, with the most
pronounced trends in the tropics. While a very good agreement is obtained
between trends from merged satellite records and the CCMI-1 REF-C2
simulation in the upper stratosphere, observed negative trends in the lower
stratosphere are not reproduced by models at southern and, in particular, at
northern midlatitudes, where models report an ozone increase. However, the
lower-stratospheric trend uncertainties are quite large, for both measured
and modelled trends. Finally, 2000–2020 stratospheric ozone trends derived
from the ground-based and longitudinally resolved satellite records are in
reasonable agreement over the European Alpine and tropical regions, while at
the Lauder station in the Southern Hemisphere midlatitudes they show some
differences.