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 data sets averaged over broad latitude bands, i.e. 60° S–35° S, 20° S–20° N and 35° N–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, ozone sondes, 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 latest REF-C2 simulations of the Chemistry Climate Model Initiative (CCMI). 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 %/decade at ~2.1 hPa, and ~2.1 %/decade at ~3.2 hPa respectively, compared to ~1.6 %/decade at ~2.6 hPa in the tropics. New trend signals have emerged from the records, such as a significant decrease of ozone in the tropics around 35 hPa and a non-significant increase of ozone in the southern mid-latitudes 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 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 close agreement, especially over the European Alpine and tropical regions.

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

“…However, adding three more years between the original version of LOTUS and the update still did not produce statistically significant trends in LSO for the recovery phase. Possibly, the ozone recovery period is not yet long enough to detect statistically significant LSO trends in the LOTUS regression analysis (Godin-Beekmann et al, 2022). The attribution of all necessary regressors is also important to increase the robustness of the trend.…”

“…In the upper stratosphere (above 10 hPa), the ozone abundance declined by about 4-8% between 1980 to the late 1990s due to a continuous increase in stratospheric chlorine loading (e.g., Steinbrecht et al, 2017;WMO, 2018), but since the late 1990s it has been steadily recovering (Ball et al, 2018;WMO, 2018). This recovery is statistically robust according to various analyses of satellite observations and model simulations (Harris et al, 2015;Steinbrecht et al, 2017;Ball et al, 2018;Godin-Beekmann et al, 2022). The main driver of the upper stratospheric ozone recovery is the reduction of halogen loading.…”

Evolution of Ozone above Togo during the 1979-2020 Period

“…According to Ball et al [42], the influence of a consequent increase in tropospheric ozone in the tropics may hide an ever-existing decrease in the lower stratosphere. Indeed, a significant decrease in ozone in the tropics (20 ° S -20 ° N) around 35 hPa has been observed by Godin-Beekmann et al [43] and an increase in tropospheric ozone over the tropics was found by the work of Thompson et al [44] and Leventidou et al [45]. Furthermore, the positive value observed for this trend could be related to the cooling of the upper stratosphere resulting from the increase in greenhouse gas (GHG) emissions, which slows the gas phase ozone loss mechanisms in that region (Chapter 5 of the WMO report, 2018) [40].…”

Total ozone trends at three northern high-latitude stations

“…However, additional predictors may be required when using the regression for local stations, as suggested by Van Malderen et al (2021) and SPARC/IO3C/GAW (2019). A few recent studies used the LOTUS regression to derive local trend profiles at specific stations (Godin-Beekmann et al, 2022;Bernet et al, 2021;Van Malderen et al, 2021), but they did not investigate the use of additional local predictors. Furthermore, all studies using the LOTUS regression concentrate on latitudes between 60 • S and 60 • N and on stratospheric ozone profiles.…”