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The Nimbus 7 limb infrared monitor of the stratosphere (LIMS) instrument operated from October 25, 1978, through May 28, 1979. Its Version 6 (V6) profiles and their Level 3 or zonal Fourier coefficient products have been characterized and archived in 2008 and in 2011, respectively. This paper focuses on the value and use of daily ozone maps from Level 3, based on a gridding of its zonal coefficients. We present maps of V6 ozone on pressure surfaces and compare them with several rocket-borne chemiluminescent ozone measurements that extend into the lower mesosphere. Daily, synoptic maps of V6 ozone and temperature illustrate that they are an important aid in interpreting satellite limb-infrared emission versus local measurements, especially when they occur during dynamically active periods of northern hemisphere winter. We then show a sequence of V6 maps of upper stratospheric ozone, spanning the minor stratospheric warmings of late January and early February 1979. The map sequence of V6 geopotential height reveals how ozone was changing in the vortex and at the centers of adjacent anticyclones. We also report on zonal variations of the tertiary ozone maximum of the upper mesosphere and its associated temperature fields during winter. These several examples provide a guide to researchers for further exploratory analyses of middle atmosphere ozone from LIMS.

For the past 17 years, the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) instrument on the Canadian SCISAT satellite has been measuring profiles of atmospheric ozone. The latest operational versions of the level 2 ozone data are versions 3.6 and 4.1. This study characterizes how both products compare with correlative data from other limb-sounding satellite instruments, namely MAESTRO, MLS, OSIRIS, SABER, and SMR. In general, v3.6, with respect to the other instruments, exhibits a smaller bias (which is on the order of ∼ 3 %) in the middle stratosphere than v4.1 (∼ 2 %–9 %); however, the bias exhibited in the v4.1 data tends to be more stable, i.e. not changing significantly over time in any altitude region. In the lower stratosphere, v3.6 has a positive bias of about 3 %–5 % that is stable to within ±1 % per decade, and v4.1 has a bias on the order of −1 % to +5 % and is also stable to within ±1 % per decade. In the middle stratosphere, v3.6 has a positive bias of ∼ 3 % with a significant negative drift on the order of 0.5 %–2.5 % per decade, and v4.1 has a positive bias of 2 %–9 % that is stable to within ±0.5 % per decade. In the upper stratosphere, v3.6 has a positive bias that increases with altitude up to ∼ 16 % and a significant negative drift on the order of 2 %–3 % per decade, and v4.1 has a positive bias that increases with altitude up to ∼ 15 % and is stable to within ±1 % per decade. Estimates indicate that both versions 3.6 and 4.1 have precision values on the order of 0.1–0.2 ppmv below 20 km and above 45 km (∼ 5 %–10 %, depending on altitude). Between 20 and 45 km, the estimated v3.6 precision of ∼ 4 %–6 % is better than the estimated v4.1 precision of ∼ 6 %–10 %.

Attributable to the Montreal Protocol, the most successful environmental treaty ever, human-made ozone-depleting substances are declining and the stratospheric Antarctic ozone layer is recovering. However, the Antarctic ozone hole continues to occur every year, with the severity of ozone loss strongly modulated by meteorological conditions. In late November and early December 2020, we measured at the northern tip of the Antarctic Peninsula the highest ultraviolet (UV) irradiances recorded in the Antarctic continent in more than two decades. On Dec. 2nd, the noon-time UV index on King George Island peaked at 14.3, very close to the largest UV index ever recorded in the continent. On Dec. 3rd, the erythemal daily dose at the same site was among the highest on Earth, only comparable to those recorded at high altitude sites in the Atacama Desert, near the Tropic of Capricorn. Here we show that, despite the Antarctic ozone recovery observed in early spring, the conditions that favor these extreme surface UV events persist in late spring, when the biologically effective UV radiation is more consequential. These conditions include long-lasting ozone holes (attributable to the polar vortex dynamics) that often bring ozone-depleted air over the Antarctic Peninsula in late spring. The fact that these conditions have been occurring at about the same frequency during the last two decades explains the persistence of extreme surface UV events in Antarctica.

The Kototabang (0.20°S, 100.3°E, 10.36°S dip latitude) Equatorial Atmosphere Radar (EAR) observations of valley region field-aligned irregularities (FAI) reveal maximum percentage of occurrence (PO) of high signal to noise ratio (greater than 3 dB) type-B 150-km echoes during boreal summer (June-August) and winter (December-January) of solar moderate to minimum years 2016–2019. The PO is anomalously high in the solar minimum year 2019 and particularly during the September equinox when a major austral sudden stratospheric warming (SSW) event has occurred. Its possible relation with mesospheric tides and stratospheric ozone is investigated. The space–time spectral analysis of upper mesospheric temperature information obtained from the spaceborne radiometer instrument Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) reveals that migrating semi-diurnal tide (SW2) is dominant during June-August, when the PO of the 150-km echoes maximizes, whereas migrating diurnal tide (DW1) is dominant during equinox months. It also reveals quasi-biennial variability of the DW1 tide probably due to similar variability of the stratospheric ozone. It is suggested that the DW1 tides generated due to solar radiation absorption by stratospheric ozone and tropospheric water vapour can have phases opposite to each other, leading to the suppression of DW1 tide during September 2017 and 2019 resulting in the relative dominance of SW2 tide over DW1 tide. The meridional wind shear associated with the relatively dominant SW2 tide results in an interchange instability developed on the gradient of daytime descending ion layer along with solar minimum conditions leads to plasma irregularities responsible for these echoes. The large eastward propagating diurnal tide with zonal wavenumber 3 (DE3) observed during June-September 2019 is unlikely to cause the instability, due to its weak meridional component.

Simulations of Institute of Numerical Mathematics (INM) coupled climate model 5th version for the period from 2015 to 2100 under moderate (SSP2-4.5) and severe (SSP5-8.5) scenarios of greenhouse gases growth are analyzed to investigate changes of Arctic polar stratospheric vortex, planetary wave propagation, Sudden Stratospheric Warming frequency, Final Warming dates, and meridional circulation. Strengthening of wave activity propagation and a stationary planetary wave number 1 in the middle and upper stratosphere, acceleration of meridional circulation, an increase of winter mean polar stratospheric volume (Vpsc) and strengthening of Arctic stratosphere interannual variability after the middle of 21st century, especially under a severe scenario, were revealed. March monthly values of Vpsc in some winters could be about two times more than observed ones in the Arctic stratosphere in the spring of 2011 and 2020, which in turn could lead to large ozone layer destruction. Composite analysis shows that “warm” winters with the least winter mean Vpsc values are characterized by strengthening of wave activity propagation from the troposphere into the stratosphere in December but weaker propagation in January–February in comparison with winters having the largest Vpsc values.

Total column ozone (TCO) over the Tibetan Plateau (TP) is lower than that over other regions at the same latitude, particularly in summer. This feature is known as the “TP ozone valley”. This study evaluates long-term changes in TCO and the ozone valley over the TP from 1984 to 2100 using Coupled Model Intercomparison Project Phase 6 (CMIP6). The TP ozone valley consists of two low centers, one is located in the upper troposphere and lower stratosphere (UTLS), and the other is in the middle and upper stratosphere. Overall, the CMIP6 models simulate the low ozone center in the UTLS well and capture the spatial characteristics and seasonal cycle of the TP ozone valley, with spatial correlation coefficients between the modeled TCO and the Multi Sensor Reanalysis version 2 (MSR2) TCO observations greater than 0.8 for all CMIP6 models. Further analysis reveals that models which use fully coupled and online stratospheric chemistry schemes simulate the anticorrelation between the 150 hPa geopotential height and zonal anomaly of TCO over the TP better than models without interactive chemistry schemes. This suggests that coupled chemical-radiative-dynamical processes play a key role in the simulation of the TP ozone valley. Most CMIP6 models underestimate the low center in the middle and upper stratosphere when compared with the Microwave Limb Sounder (MLS) observations. However, the bias in the middle and upper stratospheric ozone simulations has a marginal effect on the simulation of the TP ozone valley. Most CMIP6 models predict the TP ozone valley in summer will deepen in the future.

Seasonally dependent quasi-stationary planetary wave activity in the southern hemisphere influences the distribution of ozone within and near the equatorward edge of the stratospheric polar vortex. Accurate representation of this zonal asymmetry in ozone is important in the characterisation of stratospheric circulation and climate and their associated effects at the surface. In this study, we used the Australian Community and Climate Earth System Simulator-Chemistry Climate Model to investigate the influence of greenhouse gases (GHGs) and ozone depleting substances (ODSs) on the zonal asymmetry of total column ozone (TCO) and 10 hPa zonal wind between 50 and 70°S. Sensitivity simulations were used from 1960 to 2100 with fixed ODSs and GHGs at 1960 levels and a regression model that uses equivalent effective stratospheric chlorine and carbon dioxide equivalent radiative forcing as the regressors. The model simulates the spring and summer zonal wave-1 reasonably well, albeit with a slight bias in the phase and amplitude compared to observations. An eastward shift in the TCO and 10 hPa zonal wave-1 is associated with both decreasing ozone and increasing GHGs. Amplitude increases are associated with ozone decline and amplitude decreases with GHG increases. The influence of ODSs typically outweigh those by GHGs, partly due to the GHG influence on TCO phase at 50°S likely being hampered by the Andes. Therefore, over the 21st century, influence from ozone recovery causes a westward shift and a decrease in amplitude. An exception is at 70°S during spring, where the GHG influence is larger than that of ozone recovery, causing a continued eastward trend throughout the 21st century. Also, GHGs have the largest influence on the 10 hPa zonal wave-1 phase, but still only induce a small change in the wave-1 amplitude. Different local longitudes also experience different rates of ozone recovery due to the changes in phase of the zonal wave-1. The results from this study have important implications for understanding future ozone layer distribution in the Southern Hemisphere under changing GHG and ODS concentrations. Important future work would involve conducting a similar study using a large ensemble of models to gain more statistically significant results.

Starting in 1969 and comprising three launches a week, the Uccle (Brussels, Belgium) ozonesonde dataset is one of longest and densest in the world. Moreover, as the only major change was the switch from Brewer-Mast (BM) to electrochemical concentration cell (ECC) ozonesonde types in 1997 (when the emissions of ozone-depleting substances peaked), the Uccle time series is very homogenous. In this paper, we briefly describe the efforts that were undertaken during the first 3 decades of the 50 years of ozonesonde observations to guarantee the homogeneity between ascent and descent profiles, under changing environmental conditions (e.g. SO2), and between the different ozonesonde types. This paper focuses on the 50-year-long Uccle ozonesonde dataset and aims to demonstrate its past, present, and future relevance to ozone research in two application areas: (i) the assessment of the temporal evolution of ozone from the surface to the (middle) stratosphere, and (ii) as the backbone for validation and stability analysis of both stratospheric and tropospheric satellite ozone retrievals. Using the Long-term Ozone Trends and Uncertainties in the Stratosphere (LOTUS) multiple linear regression model (SPARC/IO3C/GAW, 2019), we found that the stratospheric ozone concentrations at Uccle have declined at a significant rate of around 2 % per decade since 1969, which is also rather consistent over the different stratospheric levels. This overall decrease can mainly be assigned to the 1969–1996 period with a rather consistent rate of decrease of around −4 % per decade. Since 2000, a recovery of between +1 % per decade and +3 % per decade of the stratospheric ozone levels above Uccle has been observed, although it is not significant and is not seen for the upper stratospheric levels measured by ozonesondes. Throughout the entire free troposphere, a very consistent increase in the ozone concentrations of 2 % per decade to 3 % per decade has been measured since both 1969 and 1995, with the trend since 1995 being in almost perfect agreement with the trends derived from the In-service Aircraft for a Global Observing System (IAGOS) ascent/descent profiles at Frankfurt. As the number of tropopause folding events in the Uccle time series has increased significantly over time, increased stratosphere-to-troposphere transport of recovering stratospheric ozone might partly explain these increasing tropospheric ozone concentrations, despite the levelling-off of (tropospheric) ozone precursor emissions and notwithstanding the continued increase in mean surface ozone concentrations. Furthermore, we illustrate the crucial role of ozonesonde measurements for the validation of satellite ozone profile retrievals. With the operational validation of the Global Ozone Monitoring Experiment-2 (GOME-2), we show how the Uccle dataset can be used to evaluate the performance of a degradation correction for the MetOp-A/GOME-2 UV (ultraviolet) sensors. In another example, we illustrate that the Microwave Limb Sounder (MLS) overpass ozone profiles in the stratosphere agree within ±5 % with the Uccle ozone profiles between 10 and 70 hPa. Another instrument on the same Aura satellite platform, the Tropospheric Emission Spectrometer (TES), is generally positively biased with respect to the Uccle ozonesondes in the troposphere by up to ∼ 10 ppbv, corresponding to relative differences of up to ∼ 15 %. Using the Uccle ozonesonde time series as a reference, we also demonstrate that the temporal stability of those last two satellite retrievals is excellent.

Overexposure to ultraviolet (UV) radiation is a threat to human health. It can cause skin cancer and cataracts. Human-made ozone-depleting substances (ODSs) reduce the ozone concentration in the Earth’s stratosphere, which acts as a protective shield from UV radiation. To protect and restore the ozone layer, the Montreal Protocol on Substances that Deplete the Ozone Layer was enacted in 1987 to phase out the production and consumption of certain ODSs and was later amended and adjusted to significantly strengthen its requirements. The United States Environmental Protection Agency (EPA) uses its Atmospheric and Health Effects Framework (AHEF) model to assess the adverse human health effects associated with stratospheric ozone depletion and the U.S. health benefits from the global implementation of the Montreal Protocol. Comparing the Montreal Protocol as amended and adjusted with a scenario of no controls on ODSs showed the prevention of an estimated 443 million cases of skin cancer and 63 million cataract cases for people born in the United States between 1890 and 2100. In addition, 2.3 million skin cancer deaths are avoided. Compared with the original 1987 Montreal Protocol, strengthening the Montreal Protocol, through its subsequent amendments and adjustments, resulted in an estimated 230 million fewer skin cancer cases, 1.3 million fewer skin cancer deaths, and 33 million fewer cataract cases.

Monitoring atmospheric anthropogenic halocarbons plays an important role in tracking their atmospheric concentrations in accordance with international agreements on emissions of ozone-depleting substances and, thus, in estimating the ozone layer recovery. Within the Network for the Detection of Atmospheric Composition Change (NDACC), regular Fourier transform infrared (FTIR) measurements can provide information on the abundancies of halocarbons on a global scale. We improved retrieval strategies for deriving the CFC-11 (CCl3F), CFC-12 (CCl2F2), and HCFC-22 (CHClF2) atmospheric columns from IR solar radiation spectra measured by the Bruker IFS125HR spectrometer at the St. Petersburg site (Russia). We used the Tikhonov–Phillips regularization approach for solving the inverse problem with optimized values of regularization parameters. We tested the strategies developed by comparison of the FTIR measurements with independent data. The analysis of the time series of column-averaged dry air mole fractions (Xgas) measured in 2009–2019 gives mean values of 225 pptv (parts per trillion by volume; CFC-11), 493 pptv (CFC-12), and 238 pptv (HCFC-22). Trend values total −0.40 % yr−1 (CFC-11), −0.49 % yr−1 (CFC-12), and 2.12 % yr−1 (HCFC-22). We compared the means, trends, and seasonal variability in XCFC-11, XCFC-12, and XHCFC-22 to that of (1) near-ground volume mixing ratios (VMRs), measured at the observational site Mace Head, Ireland (GVMR), (2) the mean in the 8–12 km layer VMRs, measured by ACE-FTS and averaged over 55–65∘ N latitudes (SVMR), and (3) Xgas values of the Whole Atmosphere Community Climate Model (WACCM) for the St. Petersburg site (WXgas). In general, the comparison of Xgas with the independent data showed a good agreement of their means within the systematic errors of the measurements considered. The trends observed over the St. Petersburg site demonstrate the smaller decrease rates for XCFC-11 and XCFC-12 than that of the independent data and the same increase rate for XHCFC-22. As a whole, Xgas, SVMR, and WXgas showed qualitatively similar seasonal variations, while the GVMR variability is significantly less, and only the WXHCFC-22 variations are essentially smaller than that of XHCFC-22 and SVMRHCFC-22.

ALTIUS (Atmospheric Limb Tracker for the Investigation of the Upcoming Stratosphere) is the upcoming stratospheric ozone monitoring limb sounder from ESA's Earth Watch programme. Measuring in the ultraviolet–visible–near-infrared (UV–VIS–NIR) spectral regions, ALTIUS will retrieve vertical profiles of ozone, aerosol extinction coefficients, nitrogen dioxide and other trace gases from the upper troposphere to the mesosphere. In order to maximize the geographical coverage, the instrument will observe limb-scattered solar light during daytime (i.e. bright limb observations), solar occultations at the terminator and stellar/lunar/planetary occultations during nighttime. This paper evaluates the constraint of ALTIUS ozone profiles on modelled stratospheric ozone by means of an observing system simulation experiment (OSSE). In this effort, a reference atmosphere has been built and used to generate ALTIUS ozone profiles, along with an instrument simulator. These profiles are then assimilated to provide ozone analyses. A good agreement is found between the analyses and the reference atmosphere in the stratosphere and in the extra-tropical upper troposphere. In the tropical upper troposphere, although providing significant information in the analyses, the assimilation of ozone profiles does not completely eliminate the bias with respect to the reference atmosphere. The impacts of the different modes of observations have also been evaluated, showing that all of them are necessary to constrain ozone during polar winters where solar/stellar occultations are the most important during the polar night and bright limb data are the most important during the development of the ozone hole in the polar spring.

A known adverse side effect of stratospheric aerosol modification (SAM) is the alteration of the quasi-biennial oscillation (QBO), which is caused by the stratospheric heating associated with an artificial aerosol layer. Multiple studies found the QBO to slow down or even completely vanish for point-like injections of SO2 at the Equator. The cause for this was found to be a modification of the thermal wind balance and a stronger tropical upwelling. For other injection strategies, different responses of the QBO have been observed. A theory which is able to explain those differences in a comprehensive manner has not yet been presented. This is further complicated by the fact that the simulated QBO response is highly sensitive to the used model even under identical boundary conditions. Therefore, within this study we investigate the response of the QBO to SAM for three different injection strategies (point-like injection at the Equator, point-like injection at 30∘ N and 30∘ S simultaneously, and areal injection into a 60∘ wide belt along the Equator). Our simulations confirm that the QBO response significantly depends on the injection location. Based on the thermal wind balance, we demonstrate that this dependency is explained by differences in the meridional structure of the aerosol-induced stratospheric warming, i.e., the location and meridional extension of the maximum warming. Additionally, we also tested two different injection species (SO2 and H2SO4). The QBO response is qualitatively similar for both investigated injection species. Comparing the results to corresponding results of a second model, we further demonstrate the generality of our theory as well as the importance of an interactive treatment of stratospheric ozone for the simulated QBO response.

We present the results of applying the Lagrangian methods to study the fine dynamic structure of the stratospheric polar vortex in the winter–spring of 2019–2020. Characteristics of the vortex structure for this winter are compared with those of a strong polar vortex and the winter of 2018–2019, when the vortex was weak. Due to the low activity of planetary waves, the polar vortex in 2019–2020 remained stable until the end of April, which created the conditions for record ozone destruction in the Arctic. We present variations of the horizontal dynamic structure obtained using reverse domain filling (RDF) and the vortex strength represented as an M function depending on time and altitude. Variations in ozone and thermodynamic parameters averaged over the ensemble of trajectories inside the vortex using the ERA5 reanalysis data are also presented.

This study quantifies differences among four widely used atmospheric reanalysis datasets (ERA5, JRA-55, MERRA-2, and CFSR) in their representation of the dynamical changes induced by springtime polar stratospheric ozone depletion in the Southern Hemisphere from 1980 to 2001. The intercomparison is undertaken as part of the SPARC (Stratosphere–troposphere Processes and their Role in Climate) Reanalysis Intercomparison Project (S-RIP). The reanalyses are generally in good agreement in their representation of the strengthening of the lower stratospheric polar vortex during the austral spring–summer season, associated with reduced radiative heating due to ozone loss, as well as the descent of anomalously strong westerly winds into the troposphere during summer and the subsequent poleward displacement and intensification of the polar front jet. Differences in the trends in zonal wind between the reanalyses are generally small compared to the mean trends. The exception is CFSR, which exhibits greater disagreement compared to the other three reanalysis datasets, with stronger westerly winds in the lower stratosphere in spring and a larger poleward displacement of the tropospheric westerly jet in summer. The dynamical changes associated with the ozone hole are examined by investigating the momentum budget and then the eddy heat and momentum fluxes in terms of planetary- and synoptic-scale Rossby wave contributions. The dynamical changes are consistently represented across the reanalyses and support our dynamical understanding of the response of the coupled stratosphere–troposphere system to the ozone hole. Although our results suggest a high degree of consistency across the four reanalysis datasets in the representation of these dynamical changes, there are larger differences in the wave forcing, residual circulation, and eddy propagation changes compared to the zonal wind trends. In particular, there is a noticeable disparity in these trends in CFSR compared to the other three reanalyses, while the best agreement is found between ERA5 and JRA-55. Greater uncertainty in the components of the momentum budget, as opposed to mean circulation, suggests that the zonal wind is better constrained by the assimilation of observations compared to the wave forcing, residual circulation, and eddy momentum and heat fluxes, which are more dependent on the model-based forecasts that can differ between reanalyses. Looking forward, however, these findings give us confidence that reanalysis datasets can be used to assess changes associated with the ongoing recovery of stratospheric ozone.

Ozone vertical column densities (VCDs) were retrieved by Zenith Scattered Light-Differential Optical Absorption Spectroscopy (ZSL-DOAS) from January 2017 to February 2020 over Fildes Peninsula, West Antarctica (62.22°S, 58.96°W). Each year, ozone VCDs started to decline around July with a comparable gradient around 1.4 Dobson Units (DU) per day, then dropped to their lowest levels in September and October, when ozone holes appeared (less than 220 DU). Daily mean values of retrieved ozone VCDs were compared with Ozone Monitoring Instrument (OMI) and Global Ozone Monitoring Experiment 2 (GOME-2) satellite observations and the Modern-Era Retrospective analysis for Research and Applications Version 2 (MERRA-2) reanalysis dataset, with correlation coefficients (R2) of 0.86, 0.94, and 0.90, respectively. To better understand the causes of ozone depletion, the retrieved ozone VCDs, temperature, and potential vorticity (PV) at certain altitudes were analyzed. The profiles of ozone and PV were positively correlated during their fluctuations, which indicates that the polar vortex has a strong influence on stratospheric ozone depletion during Antarctic spring. Located at the edge of polar vortex, the observed data will provide a basis for further analysis and prediction of the inter-annual variations of stratospheric ozone in the future.

The Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) instrument operated from 25 October 1978 through 28 May 1979. Its version 6 (V6) profiles were processed and archived in 2002. We present several diagnostic examples of the quality of the V6 stratospheric species distributions based on their level 3 zonal Fourier coefficient products. In particular, we show that there are small differences in the ascending (A) minus descending (D) orbital temperature–pressure or T(p) profiles (their A−D values) that affect (A−D) species values. Systematic A−D biases in T(p) can arise from small radiance biases and/or from viewing anomalies along orbits. There can also be (A−D) differences in T(p) due to not resolving and correcting for all of the atmospheric temperature gradient along LIMS tangent view-paths. An error in T(p) affects species retrievals through (1) the Planck blackbody function in forward calculations of limb radiance that are part of the iterative retrieval algorithm of LIMS, and (2) the registration of the measured LIMS species radiance profiles in pressure altitude, mainly for the lower stratosphere. There are clear A−D differences for ozone, H2O, and HNO3 but not for NO2. Percentage differences are larger in the lower stratosphere for ozone and H2O because those species are optically thick. We evaluate V6 ozone profile biases in the upper stratosphere with the aid of comparisons against a monthly climatology of UV–ozone soundings from rocketsondes. We also provide results of time series analyses of V6 ozone, H2O, and potential vorticity for the middle stratosphere to show that their average (A+D) V6 level 3 products provide a clear picture of the evolution of those tracers during Northern Hemisphere winter. We recommend that researchers use the average V6 level 3 product for their science studies of stratospheric ozone and H2O, while keeping in mind that there are uncorrected nonlocal thermodynamic equilibrium effects in daytime ozone in the lower mesosphere and in daytime H2O in the uppermost stratosphere. We also point out that the present-day Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment provides measurements and retrievals of temperature and ozone that are nearly free of anomalous diurnal variations and of effects from gradients at low and middle latitudes.

Ozone anomalies that occur in the winter–spring period in the Northern Hemisphere have been increasingly observed in recent decades not only in the polar, but also in midlatitudes, including those near populous cities. A decrease in the stratospheric ozone content can lead to dangerous for humans levels of UV radiation; therefore, the study of processes associated with the variability of the content of stratospheric ozone is an urgent task for developing methods to predict the appearance of ozone miniholes and the growth of UV surface illumination. Using the example of measurements of solar IR radiation with a Bruker 125HR Fourier spectrometer in the vicinity of St. Petersburg, we demonstrate the capabilities of the ground-based spectroscopic method for studying and explaining the temporal variability of stratospheric trace gases involved in the cycles of the destruction and formation of the ozone layer. We have shown the importance of the temperature and dynamic state of the stratosphere for the formation of conditions for the chemical destruction of ozone, as well as the efficiency of using measurements of the total HF content as a dynamic tracer that makes it possible to identify periods of potential activation of the chemical mechanism of ozone loss.

The Brewer ozone spectrophotometer (the Brewer) was designed at Environment and Climate Change Canada (ECCC) in the 1970s to make accurate automated total ozone column measurements. Since the 1980s, the Brewer instrument has become a World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) standard ozone monitoring instrument. Now, more than 230 Brewers have been produced. To assure the quality of the Brewer measurements, a calibration chain is maintained, i.e., first, the reference instruments are independently absolutely calibrated, and then the calibration is transferred from the reference instrument to the travelling standard, and subsequently from the travelling standard to field instruments. ECCC has maintained the world Brewer reference instruments since the 1980s to provide transferable calibration to field instruments at monitoring sites. Three single-monochromator (Mark II) type instruments (serial numbers 008, 014, and 015) formed this world Brewer reference triad (BrT) and started their service in Toronto, Canada, in 1984. In the 1990s, the Mark III type Brewer (known as the double Brewer) was developed, which has two monochromators to reduce the internal instrumental stray light. The double-Brewer world reference triad (BrT-D) was formed in 2013 (serial numbers 145, 187 and 191), co-located with the BrT. The first assessment of the BrT's performance was made in 2005, covering the period between 1984 and 2004 (Fioletov et al., 2005). The current work provides an updated assessment of the BrT's performance (from 1999 to 2019) and the first comprehensive assessment of the BrT-D. The random uncertainties of individual reference instruments are within the WMO/GAW requirement of 1 % (WMO, 2001): 0.49 % and 0.42 % for BrT and BrT-D, respectively, as estimated in this study. The long-term stability of the reference instruments is also evaluated in terms of uncertainties of the key instrument characteristics: the extraterrestrial calibration constant (ETC) and effective ozone absorption coefficients (both having an effect of less than 2 % on total column ozone). Measurements from a ground-based instrument (Pandora spectrometer), satellites (11 datasets, including the most recent high-resolution satellite, TROPOspheric Monitoring Instrument), and reanalysis model (the second Modern-Era Retrospective analysis for Research and Applications, MERRA-2) are used to further assess the performance of world Brewer reference instruments and to provide a context for the requirements of stratospheric ozone observations during the last two decades.

We investigate the impact of the so-called energetic particle precipitation (EPP) indirect effect on lower stratospheric ozone, ClO, and ClONO2 in the Antarctic springtime. We use observations from the Microwave Limb Sounder (MLS) and Ozone Monitoring Instrument (OMI) on Aura, the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer (ACE-FTS) on SCISAT, and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat, covering the period from 2005 to 2017. Using the geomagnetic activity index Ap as a proxy for EPP, we find consistent ozone increases with elevated EPP during years with an easterly phase of the quasi-biennial oscillation (QBO) in both OMI and MLS observations. While these increases are the opposite of what has previously been reported at higher altitudes, the pattern in the MLS O3 follows the typical descent patterns of EPP-NOx. The ozone enhancements are also present in the OMI total O3 column observations. Analogous to the descent patterns found in O3, we also found consistent decreases in springtime MLS ClO following winters with elevated EPP. To verify if this is due to a previously proposed mechanism involving the conversion of ClO to the reservoir species ClONO2 in reaction with NO2, we used ClONO2 observations from ACE-FTS and MIPAS. As ClO and NO2 are both catalysts in ozone destruction, the conversion to ClONO2 would result in an ozone increase. We find a positive correlation between EPP and ClONO2 in the upper stratosphere in the early spring and in the lower stratosphere in late spring, providing the first observational evidence supporting the previously proposed mechanism relating to EPP-NOx modulating Clx-driven ozone loss. Our findings suggest that EPP has played an important role in modulating ozone depletion in the last 15 years. As chlorine loading in the polar stratosphere continues to decrease in the future, this buffering mechanism will become less effective, and catalytic ozone destruction by EPP-NOx will likely become a major contributor to Antarctic ozone loss.

This paper quantifies the pre-industrial (1850) to present-day (2014) effective radiative forcing (ERF) of anthropogenic emissions of NOX, volatile organic compounds (VOCs; including CO), SO2, NH3, black carbon, organic carbon, and concentrations of methane, N2O and ozone-depleting halocarbons, using CMIP6 models. Concentration and emission changes of reactive species can cause multiple changes in the composition of radiatively active species: tropospheric ozone, stratospheric ozone, stratospheric water vapour, secondary inorganic and organic aerosol, and methane. Where possible we break down the ERFs from each emitted species into the contributions from the composition changes. The ERFs are calculated for each of the models that participated in the AerChemMIP experiments as part of the CMIP6 project, where the relevant model output was available. The 1850 to 2014 multi-model mean ERFs (± standard deviations) are −1.03 ± 0.37 W m−2 for SO2 emissions, −0.25 ± 0.09 W m−2 for organic carbon (OC), 0.15 ± 0.17 W m−2 for black carbon (BC) and −0.07 ± 0.01 W m−2 for NH3. For the combined aerosols (in the piClim-aer experiment) it is −1.01 ± 0.25 W m−2. The multi-model means for the reactive well-mixed greenhouse gases (including any effects on ozone and aerosol chemistry) are 0.67 ± 0.17 W m−2 for methane (CH4), 0.26 ± 0.07 W m−2 for nitrous oxide (N2O) and 0.12 ± 0.2 W m−2 for ozone-depleting halocarbons (HC). Emissions of the ozone precursors nitrogen oxides (NOx), volatile organic compounds and both together (O3) lead to ERFs of 0.14 ± 0.13, 0.09 ± 0.14 and 0.20 ± 0.07 W m−2 respectively. The differences in ERFs calculated for the different models reflect differences in the complexity of their aerosol and chemistry schemes, especially in the case of methane where tropospheric chemistry captures increased forcing from ozone production.

While the Montreal Protocol is reducing stratospheric ozone loss, recent increases in some ozone depleting substance (ODS) emissions have been identified that may impact southern hemisphere climate systems. In this study, we discuss characteristics of the 2018 and 2019 Antarctic ozone holes using surface in situ, satellite and reanalysis data to gain a better understanding of recent ozone variability. These ozone holes had strongly contrasting characteristics. In 2018, the Antarctic stratospheric vortex was relatively stable and cold in comparison to most years of the prior decade. This resulted in a large and persistent ozone hole that ranked in the upper-tercile of metrics quantifying Antarctic ozone depletion. In contrast, strong stratospheric warming in the spring of 2019 curtailed the development of the ozone hole, causing it to be anomalously small and of similar size to ozone holes in the 1980s. As known from previous studies, the ability of planetary waves to propagate into the stratosphere at high latitudes is an important factor that influences temperatures of the polar vortex and the overall amount of ozone loss in any particular year. Disturbance and warming of the vortex by strong planetary wave activity were the dominant factors in the small 2019 ozone hole. In contrast, planetary wave disturbances to the vortex in the winter–spring of 2018 were much weaker than in 2019. These results increase our understanding of the impact of Montreal Protocol controls on ODS and the effects of Antarctic ozone on the southern hemisphere climate system.

Data on the effect of global warming on the ozone layer and the intensity of near-surface near-noon UVB radiation in 2100 compared to the year 2000 are presented. Changes in the ozone layer are calculated at a latitude of 50° N for January and June of 2100 when compared with 2000 using the one-dimensional photochemical model, as well as the SOCRATES interactive two-dimensional photochemical model, using greenhouse gas concentrations given in the scenarios of the Intergovernmental Panel on Climate Change (IPCC) RCP 4.5 and PCP 6.0. Surface UVB radiation fluxes for the above conditions are calculated using a program developed at the Norwegian Institute for Atmospheric Research in 2005 (by Ola Engelsen).

Intense natural circulation variability associated with stratospheric sudden warmings, vortex intensifications, and final warmings is a typical feature of the winter Arctic stratosphere. The attendant changes in transport, mixing, and temperature create pronounced perturbations in stratospheric ozone. Understanding these perturbations is important because of their potential feedbacks with the circulation and because ozone is a key trace gas of the stratosphere. Here, we use Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2), reanalysis to contrast the typical spatiotemporal structure of ozone during sudden warming and vortex intensification events. We examine the changes of ozone in both the Arctic and the tropics, document the underlying dynamical mechanisms for the observed changes, and analyze the entire life cycle of the stratospheric events – from the event onset in midwinter to the final warming in early spring. Over the Arctic and during sudden warmings, ozone undergoes a rapid and long-lasting increase of up to ∼ 50 DU, which only gradually decays to climatology before the final warming. In contrast, vortex intensifications are passive events, associated with gradual decreases in Arctic ozone that reach ∼ 40 DU during late winter and decay thereafter. The persistent loss in Arctic ozone during vortex intensifications is dramatically compensated by sudden warming-like increases after the final warming. In the tropics, the changes in ozone from Arctic circulation events are obscured by the influences from the quasi-biennial oscillation. After controlling for this effect, small but coherent reductions in tropical ozone can be seen during the onset of sudden warmings (∼ 2.5 DU) and also during the final warmings that follow vortex intensifications (∼ 2 DU). Our results demonstrate that Arctic circulation extremes have significant local and remote influences on the distribution of stratospheric ozone.

The early detection of a global emission increase of CFC-11 after 2012 (Montzka et al., 2018) alerted society to a possible violation of the Montreal Protocol on Substances that Deplete the Ozone Layer (MP). This early alert resulted in parties participating in the MP taking urgent actions (United Nations Environment Programme (UNEP), 2019). As a result, atmospheric measurements made in 2019 suggest a sharp decline in global CFC-11 emissions (Montzka et al., 2021). Despite the success in the early detection and mitigation of some of this problem, regions fully responsible for the recent global emission changes of CFC-11 have not yet been identified. Roughly two thirds (60 ± 40 %) of the emission increase between 2008–2012 and 2014–2017 and two thirds (60 ± 30 %) of emission decline between 2014–2017 and 2019 was explained by regional emission changes in eastern mainland China (Park et al., 2021; Rigby et al., 2019). Here, we used atmospheric CFC-11 measurements made from two global aircraft surveys, the HIAPER Pole-to-Pole Observations (HIPPO) in November 2009–September 2011 and the Atmospheric Tomography Mission (ATom) in August 2016–May 2018, in combination with the global CFC-11 measurements made by the U.S. National Oceanic and Atmospheric Administration during these two periods, to derive global and regional emission changes of CFC-11. Our results suggest Asia accounted for the largest fractions of global CFC-11 emissions in both periods, 43 (37–52) % during November 2009–September 2011 and 57 (49–62) % during August 2016–May 2018. Asia was also primarily responsible for the emission increase between these two periods, accounting for 86 (59–115) % of the global CFC-11 emission rise between the two periods. Besides eastern mainland China, we find that temperate western Asia and tropical Asia also contributed significantly to global CFC-11 emissions during both periods and likely to the global CFC-11 emission increase between these periods. Besides Asia, the atmospheric observations also provide strong constraints on CFC-11 emissions from North America and Europe, suggesting that each of them accounted for 10–15 % of global CFC-11 emissions during the HIPPO period and smaller fractions in the ATom period. For South America, Africa, and Australia, the derived regional emissions had larger dependence on the prior assumptions of emissions and emission changes, due to a lower sensitivity of the observations considered here to emissions from these regions. However, significant increases in CFC-11 emissions from the southern hemispheric lands were not likely due to the observed increase of north-to-south interhemispheric gradients in atmospheric CFC-11 mole fractions from 2012 to 2017.

Stratospheric ozone depletion in the Antarctic is well known to cause changes in Southern Hemisphere tropospheric climate; however, due to its smaller magnitude in the Arctic, the effects of stratospheric ozone depletion on Northern Hemisphere tropospheric climate are not as obvious or well understood. Recent research using both global climate models and observational data has determined that the impact of ozone depletion on ozone extremes can affect interannual variability in tropospheric circulation in the Northern Hemisphere in spring. To further this work, we use a coupled chemistry-climate model to examine the difference in high cloud between years with anomalously low and high Arctic stratospheric ozone concentrations. We find that low ozone extremes during the late twentieth century, when ODS emissions are higher, are related to a decrease in upper tropospheric stability and an increase in high cloud fraction, which may have contributed to Arctic surface warming via a positive longwave cloud radiative effect in the past few decades compared to other regions. A better understanding of how Arctic climate is affected by ODS emissions, ozone depletion and ozone extremes will lead to improved predictions of Arctic climate and its associated feedbacks with atmospheric fields as ozone levels recover.

Middle atmospheric ozone, water vapour and zonal and meridional wind profiles have been measured with the two ground-based microwave radiometers GROMOS-C and MIAWARA-C. The instruments have been located at the Arctic research base AWIPEV at Ny-Ålesund, Svalbard (79∘ N, 12∘ E), since September 2015. GROMOS-C measures ozone spectra in the four cardinal directions with an elevation angle of 22∘. This means that the probed air masses at an altitude of 3 hPa (37 km) have a horizontal distance of 92 km to Ny-Ålesund. We retrieve four separate ozone profiles along the lines of sight and calculate daily mean horizontal ozone gradients which allow us to investigate the small-scale spatial variability of ozone above Ny-Ålesund. We present the evolution of the ozone gradients at Ny-Ålesund during winter 2018/2019, when a major sudden stratospheric warming (SSW) took place with the central date at 2 January, and link it to the planetary wave activity. We further analyse the SSW and discuss our ozone and water vapour measurements in a global context. At 3 hPa we find a distinct seasonal variation of the ozone gradients. The strong polar vortex during October and March results in a decreasing ozone volume mixing ratio towards the pole. In November the amplitudes of the planetary waves grow until they break in the end of December and an SSW takes place. From November until February ozone increases towards higher latitudes and the magnitude of the ozone gradients is smaller than in October and March. We attribute this to the planetary wave activity of wave numbers 1 and 2 which enabled meridional transport. The MERRA-2 reanalysis and the SD-WACCM model are able to capture the small-scale ozone variability and its seasonal changes.

Modeling and observational studies have reported effects of stratospheric ozone extremes on Northern Hemisphere spring climate. Recent work has further suggested that the coupling of ozone chemistry and dynamics amplifies the surface response to midwinter sudden stratospheric warmings (SSWs). Here we study the importance of interactive ozone chemistry in representing the stratospheric polar vortex and Northern Hemisphere winter surface climate variability. We contrast two simulations from the interactive and specified chemistry (and thus ozone) versions of the Whole Atmosphere Community Climate Model, which is designed to isolate the impact of interactive ozone on polar vortex variability. In particular, we analyze the response with and without interactive chemistry to midwinter SSWs, March SSWs, and strong polar vortex events (SPVs). With interactive chemistry, the stratospheric polar vortex is stronger and more SPVs occur, but we find little effect on the frequency of midwinter SSWs. At the surface, interactive chemistry results in a pattern resembling a more negative North Atlantic Oscillation following midwinter SSWs but with little impact on the surface signatures of late winter SSWs and SPVs. These results suggest that including interactive ozone chemistry is important for representing North Atlantic and European winter climate variability., Atmospheric Chemistry and Physics, 20 (17), ISSN:1680-7375, ISSN:1680-7367

Recent studies have found a shift of the Arctic stratospheric polar vortex toward Siberia during late winter since 1980, intensifying the zonally asymmetric ozone (ZAO) depletion in the northern middle and high latitudes with a stronger total column ozone decline over Siberia compared with that above other regions at the same latitudes. Using observations and a climate model, this study shows that zonally asymmetric stratospheric ozone depletion gives a significant feedback on the position of the polar vortex and further favors the stratospheric polar vortex shift toward Siberia in February for the period 1980–99. The polar vortex shift is not significant in the experiment forced by zonal mean ozone fields. The February ZAO trend with a stronger ozone decline over Siberia causes a lower temperature over this region than over the other regions at the same latitudes, due to shortwave radiative cooling and dynamical cooling. The combined cooling effects induce an anomalous cyclonic flow over Siberia, corresponding to the polar vortex shift toward Siberia. In addition, the ZAO depletion also increases the meridional gradient of potential vorticity over Siberia, which is favorable for the upward propagation of planetary wave fluxes from the troposphere over this region. Increased horizontal divergence of planetary waves fluxes over the region 60°–75°N, 60°–90°E associated with ZAO changes accelerates the high-latitude zonal westerlies in the middle stratosphere, further enhancing the shift of the stratospheric polar vortex toward Siberia. After 2000, the ZAO trend in February is weaker and induces a smaller polar vortex shift than that in the period 1980–99.

The major dynamic processes in the Arctic stratosphere in the winter of 2018/2019 and their impact on the troposphere, mesosphere, and ozone layer are analyzed using the NCEP reanalysis and MLS satellite data. Based on the results of simulations with the TRACAO trajectory model, the comparative analysis of stratospheric polar vortex evolution in winters of 2015/2016 and 2018/2019 is performed.

In March 2017, measurements of downward global irradiance of ultraviolet (UV) radiation were started with a multichannel GUV-2511 radiometer in Marambio, Antarctica (64.23∘ S; 56.62∘ W), by the Finnish Meteorological Institute (FMI) in collaboration with the Servicio Meteorológico Nacional (SMN). These measurements were analysed and the results were compared to previous measurements performed at the same site with the radiometer of the Antarctic NILU-UV network during 2000–2008 and to data from five stations across Antarctica. In 2017/2018 the monthly-average erythemal daily doses from October to January were lower than those averaged over 2000–2008 with differences from 2.3 % to 25.5 %. In 2017/2018 the average daily erythemal dose from September to March was 1.88 kJ m−2, while in 2018/2019 it was 23 % larger (2.37 kJ m−2). Also at several other stations in Antarctica the UV radiation levels in 2017/2018 were below average. The maximum UV indices (UVI) in Marambio were 6.2 and 9.5 in 2017/2018 and 2018/2019, respectively, whereas during years 2000–2008 the maximum was 12. Cloud cover, the strength of the polar vortex and the stratospheric ozone depletion are the primary factors that influence the surface UV radiation levels in Marambio. The lower UV irradiance values in 2017/2018 are explained by the high ozone concentrations in November, February and for a large part of October. The role of cloud cover was clearly seen in December, and to a lesser extent in October and November, when cloud cover qualitatively explains changes which could not be ascribed to changes in total ozone column (TOC). In this study, the roles of aerosols and albedo are of minor influence because the variation of these factors in Marambio was small from one year to the other. The largest variations of UV irradiance occur during spring and early summer when noon solar zenith angle (SZA) is low and the stratospheric ozone concentration is at a minimum (the so-called ozone hole). In 2017/2018, coincident low total ozone column and low cloudiness near solar noon did not occur, and no extreme UV indices were measured.

This study presents the continuation of our previous analysis of variations of atmospheric and space weather parameters above Iberian Peninsula along two years near the 24th solar cycle maximum. In the previous paper (Morozova et al., 2017) we mainly discussed the first mode of principal component analysis of tropospheric and lower stratospheric temperature and pressure fields, which was shown to be correlated with lower stratospheric ozone and anti-correlated with cosmic ray flux. Now we extend the investigation to the second mode, which suggests a coupling between the stratosphere and the ionosphere. This second mode, located in the low and middle stratosphere (and explaining ~7% of temperature and ~3% of geopotential height variations), showed to be statistically significantly correlated with variations of the middle stratosphere ozone content and anti-correlated with variations of ionospheric total electron content. Similar co-variability of these stratospheric and ionospheric parameters was also obtained with the wavelet cross-coherence analysis. To investigate the role of atmospheric circulation dynamics and the causal nature of the found correlations, we applied the convergent cross mapping (CCM) analysis to our series. Strong evidence for the stratosphere-ionosphere coupling were obtained for the winter 2012–2013 that is characterized by the easterly QBO phase (quasi-biennial oscillations of the direction of the stratospheric zonal winds) and a strong SSW (sudden stratospheric warming event). Further analysis (for the three-year time interval 2012–2015) hint that SSWs events play main role in emphasizing the stratosphere-ionosphere coupling.

Stratospheric ozone depletion, first observed in the 1980s, has been caused by the increased production and use of substances such as chlorofluorocarbons (CFCs), halons and other chlorine-containing and bromine-containing compounds, collectively termed ozone-depleting substances (ODSs). Following controls on the production of major, long-lived ODSs by the Montreal Protocol, the ozone layer is now showing initial signs of recovery and is anticipated to return to pre-depletion levels in the mid-to-late twenty-first century, likely 2050–2060. These return dates assume widespread compliance with the Montreal Protocol and, thereby, continued reductions in ODS emissions. However, recent observations reveal increasing emissions of some controlled (for example, CFC-11, as in eastern China) and uncontrolled substances (for example, very short-lived substances (VSLSs)). Indeed, the emissions of a number of uncontrolled VSLSs are adding significant amounts of ozone-depleting chlorine to the atmosphere. In this Review, we discuss recent emissions of both long-lived ODSs and halogenated VSLSs, and how these might lead to a delay in ozone recovery. Continued improvements in observational tools and modelling approaches are needed to assess these emerging challenges to a timely recovery of the ozone layer.

The Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) instrument operated from 25 October 1978 through 28 May 1979. This note focuses on its Version 6 (V6) data and indications of ozone loss in the lower stratosphere of the Southern Hemisphere subpolar region during the last week of October 1978. We provide profiles and maps that show V6 ozone values of only 2 to 3 ppmv at 46 hPa within the edge of the polar vortex near 60∘ S from late October through mid-November 1978. There are also low values of V6 nitric acid (∼3 to 6 ppbv) and nitrogen dioxide (

Recent studies demonstrate that the Antarctic Ozone Hole has important influences on Antarctic sea ice. While most of these works have focused on effects associated with atmospheric and oceanic dynamic processes caused by stratospheric ozone changes, here we show that stratospheric ozone-induced cloud radiative effects also play important roles in causing changes in Antarctic sea ice. Our simulations demonstrate that the recovery of the Antarctic Ozone Hole causes decreases in clouds over Southern Hemisphere (SH) high latitudes and increases in clouds over the SH extratropics. The decrease in clouds leads to a reduction in downward infrared radiation, especially in austral autumn. This results in cooling of the Southern Ocean surface and increasing Antarctic sea ice. Surface cooling also involves ice-albedo feedback. Increasing sea ice reflects solar radiation and causes further cooling and more increases in Antarctic sea ice.

This review contains the most important results obtained by Russian scientists in studying atmospheric ozone in 2015–2018 and is a part of the Russian National Report on Meteorology and Atmospheric Sciences that was prepared for the International Association of Meteorology and Atmospheric Sciences (IAMAS). This report was considered and approved at the 27th General Assembly of the International Union of Geodesy and Geophysics (IUGG). A list of main Russian publications on atmospheric ozone and its precursors is appended to it.

The variability of parameters of the Antarctic ozone anomaly is studied using data of the TOMS/OMI satellite monitoring of the ozone layer, MERRA-2 reanalysis, and balloon sounding of the vertical distribution of ozone and temperature at the South Pole. The dynamic processes in the Antarctic stratosphere which define conditions for the significant ozone layer destruction are analyzed. Despite the decrease in the concentration of ozone-depleting substances, the significant ozone loss in the recent 8 years was observed in the Antarctic in 2011 and 2015.

A 3 d episode of anomalously low ozone concentrations in the stratosphere over northern Europe occurred on 3–5 November 2018. A reduction of the total ozone column down to ∼ 200–210 Dobson units was predicted by the global forecasts of the System for Integrated modeLling of Atmospheric coMposition (SILAM) driven by the weather forecast of the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). The reduction down to 210–215 DU was subsequently observed by satellite instruments, such as the Ozone Monitoring Instrument (OMI) and Ozone Mapping Profile Suite (OMPS). The episode was caused by an intrusion of tropospheric air, which was initially uplifted by a storm in the northern Atlantic, south-east of Greenland. Subsequent transport towards the east and further uplift over the Scandinavian ridge of this humid and low-ozone air brought it to ∼25 km altitude, causing ∼30 % reduction of the ozone layer thickness over northern Europe. The low-ozone air was further transported eastwards and diluted over Siberia, so that the ozone concentrations were restored a few days later. Comparison of the model predictions with OMI, OMPS, and MLS (Microwave Limb Sounder) satellites demonstrated the high accuracy of the 5 d forecast of the IFS–SILAM system: the ozone anomaly was predicted within ∼10 DU accuracy and positioned within a couple of hundreds of kilometres. This episode showed the importance of the stratospheric composition dynamics and the possibility of its short-term forecasting, including such rare events.

Using multiple reanalysis datasets and modeling simulations, the trends of Antarctic stratospheric planetary wave activities in early austral spring since the early 2000s are investigated in this study. We find that the stratospheric planetary wave activities in September have weakened significantly since the year 2000, which is mainly related to the weakening of the tropospheric wave sources in the extratropical Southern Hemisphere. As the Antarctic ozone also shows clear shift around the year 2000, the impact of ozone recovery on Antarctic planetary wave activity is also examined through numerical simulations. Significant ozone recovery in the lower stratosphere changes the atmospheric state for wave propagation to some extent, inducing a slight decrease in the vertical wave flux in upper troposphere and lower stratosphere (UTLS). However, the changes in the wave propagation environment in the middle and upper stratosphere over the subpolar region are not significant. The ozone recovery has a minor contribution to the significant weakening of stratospheric planetary wave activity in September. Further analysis indicates that the trend of September sea surface temperature (SST) over 20∘ N–70∘ S is well linked to the weakening of stratospheric planetary wave activities. The model simulations reveal that the SST trend in the extratropical Southern Hemisphere (20–70∘ S) and the tropics (20–20∘ S) induce a weakening of the wave 1 component of tropospheric geopotential height in the extratropical Southern Hemisphere, which subsequently leads to a decrease in stratospheric wave flux. In addition, both reanalysis data and numerical simulations indicate that the Brewer–Dobson circulation (BDC) related to wave activities in the stratosphere has also been weakening in early austral spring since the year 2000 due to the trend of September SST in the tropics and extratropical Southern Hemisphere.

We have implemented a new stratospheric ozone model in the European Centre for Medium-Range Weather Forecasts (ECMWF) system and tested its performance for different timescales to assess the impact of stratospheric ozone on meteorological fields. We have used the new ozone model to provide prognostic ozone in medium-range and long-range (seasonal) experiments, showing the feasibility of this ozone scheme for a seamless numerical weather prediction (NWP) modelling approach. We find that the stratospheric ozone distribution provided by the new scheme in ECMWF forecast experiments is in very good agreement with observations, even for unusual meteorological conditions such as Arctic stratospheric sudden warmings (SSWs) and Antarctic polar vortex events like the vortex split of year 2002. To assess the impact it has on meteorological variables, we have performed experiments in which the prognostic ozone is interactive with radiation. The new scheme provides a realistic ozone field able to improve the description of the stratosphere in the ECMWF system, as we find clear reductions of biases in the stratospheric forecast temperature. The seasonality of the Southern Hemisphere polar vortex is also significantly improved when using the new ozone model. In medium-range simulations we also find improvements in high-latitude tropospheric winds during the SSW event considered in this study. In long-range simulations, the use of the new ozone model leads to an increase in the correlation of the winter North Atlantic Oscillation (NAO) index with respect to ERA-Interim and an increase in the signal-to-noise ratio over the North Atlantic sector. In our study we show that by improving the description of the stratospheric ozone in the ECMWF system, the stratosphere–troposphere coupling improves. This highlights the potential benefits of this new ozone model to exploit stratospheric sources of predictability and improve weather predictions over Europe on a range of timescales.

The California Baseline Ozone Transport Study (CABOTS) was a major air quality study that collected ozone measurements aloft between mid-May and mid-August of 2016. Aircraft measurements, ground-based lidar measurements, and balloon-borne ozonesondes collected precise upper-air ozone measurements across the central and Southern California valley. Utilizing daily ozonesonde data from Bodega Bay, California, and Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), reanalysis data for 25 July to 14 August 2016, three stratospheric intrusion events are identified over Northern California influencing air masses above Bodega Bay and Sacramento simultaneously. Calculated percent daily changes in afternoon ozonesonde observations indicate increasing ozone concentrations from the point of likely stratospheric air injection with the arrival of higher potential vorticity, confirmed by ensemble back trajectories. An analysis of the onsite surface monitoring ozone data indicates ozone increases in the observations for dates of plausible low-level stratospheric air influence. Further, a comparison of Bodega Bay surface ozone observations and 14 Sacramento Valley nonattainment zone surface sites show that the surface ozone observed at the higher-elevation surface sites in the lower Sierra Nevada foothills were positively correlated with elevated ozone captured by the ozonesondes within the lowest 0.5–1 km. The strongest correlations observed (~0.61) were between elevated Bodega Bay ozonesonde data and the Placerville (~612 m) afternoon surface ozone data, an indication that these regions separated by 200 km would be influence by the same ozone source. A comparison of daily changes in afternoon ozone show that the two locales often experience similar daily ozone increases or decreases. While this study leads to a basic quantification of stratospheric influence on surface ozone in the Sacramento nonattainment zone, a future campaign that examines ozone and winds aloft at both locales is suggested to improve the quantification of stratospheric ozone.

Predicting radiative forcing due to Antarctic stratospheric ozone recovery requires detecting changes in the ozone vertical distribution. In this endeavor, the Limb Profiler of the Ozone Mapping and Profiler Suite (OMPS-LP), aboard the Suomi NPP satellite, has played a key role providing ozone profiles over Antarctica since 2011. Here, we compare ozone profiles derived from OMPS-LP data (version 2.5 algorithm) with balloon-borne ozonesondes launched from 8 Antarctic stations over the period 2012–2020. Comparisons focus on the layer from 12.5 to 27.5 km and include ozone profiles retrieved during the Sudden Stratospheric Warming (SSW) event registered in Spring 2019. We found that, over the period December-January–February-March, the root mean square error (RMSE) tends to be larger (about 20%) in the lower stratosphere (12.5–17.5 km) and smaller (about 10%) within higher layers (17.5–27.5 km). During the ozone hole season (September–October–November), RMSE values rise up to 40% within the layer from 12.5 to 22 km. Nevertheless, relative to balloon-borne measurements, the mean bias error of OMPS-derived Antarctic ozone profiles is generally lower than 0.3 ppmv, regardless of the season. We thank the researchers contributing to the World Ozone and UV Data Center (WOUDC) and the Network for the Detection of Atmospheric Composition Change (NDACC) for providing the ozonesonde data. We also thank the OMPS team for the data access and all their hard work in producing such a data set. The support of the Chilean Antarctic Institute (INACH, Preis RT_32-15 and RT_70-18), Consejo Nacional de Ciencia y Tecnología CONICYT (Preis FONDECYT 1191932, REDES180158 and CONICYT-DFG-SouthTrac) and Corporación Fomento de la Producción (Preis CORFO 19BP-117358, 18BPE-93920 and 18BPCR-89100) is gratefully acknowledged. Ozone sounding program at Marambio has been supported by the Finnish Antarctic research program (FINNARP). Peerreview

In 1974, Mario J. Molina and F. Sherwood Rowland warned that chlorofluorocarbons (CFCs) could destroy the stratospheric ozone layer, which protects Earth against the harmful effects of ultraviolet radiation [Molina and Rowland Nature 1974, 249, 810]. In 1975, Ramanathan warned that CFCs are powerful greenhouse gases (GHGs) and would rival carbon dioxide (CO2) in causing climate change if left unabated [Ramanathan Science 1975, 190, 50]. The 1987 Montreal Protocol on Substances that Deplete the Ozone Layer (Protocol), arguably the most successful global environmental treaty in history, was enacted in response to these warnings. This Protocol has phased out almost 99% of the production and consumption of ozone depleting substances (ODSs). Other papers have explored the “world avoided” by actions under the Protocol [Prather et al. Nature 1996, 381, 551; Newman et al. Atmos. Chem. Phys. 2009, 9, 2113; Morgenstern et al. Geophys. Res. Lett. 2008, 35, 1]. They concluded that the ozone layer would have been highly depleted across the globe by the mid-21st century without the Protocol and that the Protocol contributed significantly to reduce climate change. This paper explores what could have been achieved if the world had acted against the continued use of ODSs, which were both ozone-depleting and greenhouse gases, immediately after Molina and Rowland warned of stratospheric ozone depletion and Ramanathan warned of climate forcing using chemicals and technology that were already globally available in the mid-1970s. We show that such “precautionary principle” actions would have reduced global ozone layer depletion, reduced the extent of the ozone hole, brought forward the dates for ozone layer recovery, and helped minimize climate change.

International audience; During the southern spring, a break of the polar vortex over the Antarctic continent frequently occurs. This results in the advection of ozone-poor air mass (O3) to mid-latitudes, characterizing the secondary effect of the Antarctic ozone hole (SEAOH). We present some distinct characteristics the eight greatest reductions of the total O3 column (TOC) over the central region of Rio Grande do Sul (RS, 29.5°S, 54°W), southern Brazil, between August and November from 2012 to 2016 and develop a full scalar diagnostic index of O3 negative anomalies for South America. For developing the index, mean values of the absolute potential vorticity, geopotential height, and wind components were obtained over moving grids with positive and negative O3 anomalies. It was then possible to develop statistical methods to obtain a diagnostic index of the SEAOH (Subantarctic O3 Index), as well as a diagnostic index of incursions of ozone-poor air masses from the tropics (Subtropical O3 Index). The results show that TOC over the central region of RS, for the most intense O3 reduction episodes, is governed by a wide range of contributions from high and low isentropic levels. Significant interaction of air masses of polar and tropical origin via stratosphere–troposphere exchange was found. Finally, the Subantarctic O3 Index combined with the Subtropical O3 Index showed potential use for prediction centres and was skilful in detecting regions with the most negative O3 anomalies, mainly in the mid-latitude region, but also in the subtropical region.

Methyl bromide (CH3Br) is a potent ozone-depleting substance (ODS) that has both natural and anthropogenic sources. CH3Br has been used mainly for preplant soil fumigation, post-harvest grain and timber fumigation, and structural fumigation. Most non-quarantine and pre-shipment (non-QPS) uses were phased out by 2005 for non-Article 5 (developed) countries and by 2015 for Article 5 (developing) countries under the Montreal Protocol on Substances that Deplete the Ozone Layer; some uses have continued under critical-use exemptions (CUEs). Under the protocol, individual nations are required to report annual data on CH3Br production and consumption for quarantine–pre-shipment (QPS) uses, non-QPS uses, and CUEs to the United Nations Environment Programme (UNEP). In this study, we analyzed high-precision, in situ measurements of atmospheric mole fractions of CH3Br obtained at the Gosan station on Jeju Island, South Korea, from 2008 to 2019. The background mole fractions of CH3Br in the atmosphere at Gosan declined from 8.5±0.8 ppt (parts per trillion) in 2008 to 7.4±0.6 ppt in 2019 at a rate of -0.13±0.02 ppt yr−1. At Gosan, we also observed periods of persistent mole fractions (pollution events) elevated above the decreasing background in continental air masses from China. Statistical back-trajectory analyses showed that these pollution events are predominantly traced back to CH3Br emissions from eastern China. Using an interspecies correlation (ISC) method with the reference trace species CFC-11 (CCl3F), we estimate anthropogenic CH3Br emissions from eastern China at an average of 4.1±1.3 Gg yr−1 in 2008–2019, approximately 2.9±1.3 Gg yr−1 higher than the bottom-up emission estimates reported to UNEP. Possible non-fumigation CH3Br sources – rapeseed production and biomass burning – were assessed, and it was found that the discrepancy is most likely due to unreported or incorrectly reported QPS and non-QPS fumigation uses. These unreported anthropogenic emissions of CH3Br are confined to eastern China and account for 30 %–40 % of anthropogenic global CH3Br emissions. They are likely due to delays in the introduction of CH3Br alternatives, such as sulfuryl fluoride (SO2F2), heat, and irradiation, and a possible lack of industry awareness of the need for regulation of CH3Br production and use.

The Arctic stratosphere winter season of 2021–2022 was characterized by a stable, cold stratospheric polar vortex with a volume of polar stratospheric clouds (PSC) close to the maximum values since 1980, before the beginning of minor sudden stratospheric warming (SSW) events in the late February and early March and major SSW on 20 March. Analysis of dynamical processes of the Arctic stratosphere using reanalysis data indicates that the main reasons for the strengthening of the stratospheric polar vortex in January–February are the minimum propagation of planetary wave activity from the troposphere to the stratosphere over the past 40 years and its reflection in the upper stratosphere–lower mesosphere in the second half of January. The first minor SSW was limited to the upper polar stratosphere, whereas the second one propagated to the middle and lower stratosphere and led to the disappearance of the PSC, which prevented significant ozone depletion. Both minor and major SSW events led to a weakening of the residual meridional circulation in the upper Arctic stratosphere and its intensification in the middle and lower stratosphere, which contributed to additional warming of the subpolar region and weakening of the polar vortex.