Updated trends of the stratospheric ozone vertical distribution in the 60° S–60° N latitude range based on the LOTUS regression model

Abstract

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.

Dynamical linear modeling estimates of long-term ozone trends from homogenized Dobson Umkehr profiles at Arosa/Davos, Switzerland

“…Trend estimates are obtained by fitting a MLR function to the monthly mean ozone time series, presuming a linear dependence of the ozone content towards the explanatory variables and a linear increase or decrease of the ozone content over time. Upper stratospheric post-2000 ozone trends are reported to be significantly positive in the three broad latitude bands, with values of ∼ 2.2 ± 0.7 % per decade at 2.1 hPa in the NH, while nonsignificant negative ozone trends are derived in the lowermost stratosphere, with however large uncertainties (Godin-Beekmann et al, 2022).…”

“…Dobson Umkehr ozone profile data records, which are distributed all around the world Godin-Beekmann et al, 2022;Stone et al, 2015;Miyagawa et al, 2009;Garane et al, 2022), have been extensively used in the pre-1998 stratospheric trend estimates (Reinsel et al, 1989;Randel et al, 1999;Miller et al, 1995). Beginning in 1956 for the oldest, the Umkehr records were unique at that time since satellites records only became available in 1979 (McPeters et al, 1996a;Bhartia et al, 2013), and ozonesondes, starting in 1960 (Smit et al, 2007), do not reach the upper stratosphere.…”

“…Umkehr data also corroborate the satellite findings, showing highly statistically significant evidence of declining ozone concentrations since the mid-1980s in the upper stratosphere and post-2000 positive trends ranging between 2.0 % and 3.1 % per decade in the upper stratosphere of NH midlatitudes. The Umkehr data records are still extensively used for trend estimates along with datasets from other ground-based techniques, satellites and models (Steinbrecht et al, 2017;Harris et al, 2015;Petropavlovskikh et al, 2019;Tarasick et al, 2019;Godin-Beekmann et al, 2022). However, trend estimations on Brewer Umkehr data records are sparse.…”

“…Using microwave radiometer data records, Bernet et al (2019) showed the effect of instrumental artifacts on the long-term ozone profile trends. Recently, trends estimated on updated and reprocessed ozone profiles datasets have resulted in reduced trend uncertainties (Godin-Beekmann et al, 2022).…”

The historical ozone trends simulated with the SOCOLv4 and their comparison with observations and reanalyses

“…There is evidence that the restrictions on halogenated ozonedepleting substances (hODS) introduced by the Montreal Protocol and its amendments and adjustments (MPA) have clearly taken effect over the past 25 years, leading to observable ozone increases at certain latitudes and altitudes (WMO, 2014(WMO, , 2018McKenzie et al, 2019). The positive role of MPA has also been confirmed by model simulations of ozone depletion under the "world-avoided" scenario (Newman et al, 2009;Garcia et al, 2012;Egorova et al, 2013;Goyal et al, 2019). Using the future simulation of multiple chemistry-climate models (CCMs), Dhomse et al (2018) estimated the approximate time of the return of ozone concentrations to pre-1980 levels for different regions, again highlighting the success of MPA in protecting ozone.…”