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Six collocated spectrophotometers based in Arosa/Davos, Switzerland, have been measuring ozone profiles continuously since 1956 for the oldest Dobson instrument and since 2005 for the Brewer instruments. The datasets of these two ground-based triads (three Dobsons and three Brewers) allow for continuous intercomparisons and derivation of long-term trend estimates. Mainly, two periods in the post-2000 Dobson D051 dataset show anomalies when compared to the Brewer triad time series: in 2011–2013, an offset has been attributed to technical interventions during the renewal of the spectrophotometer acquisition system, and in 2018, an offset with respect to the Brewer triad has been detected following an instrumental change on the spectrophotometer wedge. In this study, the worldwide longest Umkehr dataset (1956–2020) is carefully homogenized using collocated and simultaneous Dobson and Brewer measurements. A recently published report (Garane et al., 2022) described results of an independent homogenization of the same dataset performed by comparison to the Modern-Era Retrospective analysis for Research and Applications version 2 (MERRA-2) Global Modeling Initiative (M2GMI) model simulations. In this paper, the two versions of homogenized Dobson D051 records are intercompared to analyze residual differences found during the correction periods. The Aura Microwave Limb Sounder (MLS) station overpass record (2005–2020) is used as an independent reference for the comparisons. The two homogenized data records show common correction periods, except for the 2017–2018 period, and the corrections are similar in magnitude. In addition, the post-2000 ozone profile trends are estimated from the two homogenized Dobson D051 time series by dynamical linear modeling (DLM), and results are compared with the DLM trends derived from the collocated Brewer Umkehr time series. By first investigating the long-term Dobson ozone record for trends using the well-established multilinear regression (MLR) method, we find that the trends obtained by both MLR and DLM techniques are similar within their uncertainty ranges in the upper and middle stratosphere but that the trend's significances differ in the lower stratosphere. Post-2000 DLM trend estimates show a positive trend of 0.2 to 0.5 % yr−1 above 35 km, significant for Dobson D051 but lower and therefore nonsignificantly different from zero at the 95 % level of confidence for Brewer B040. As shown for the Dobson D051 data record, the trend only seems to become significantly positive in 2004. Moreover, a persistent negative trend is estimated in the middle stratosphere between 25 and 30 km. In the lower stratosphere, the trend is negative at 20 km, with different levels of significance depending on the period and on the dataset.

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Water vapour in the upper troposphere and stratosphere has a significant impact both on the radiative and chemical properties of the atmosphere. Reliable water vapour climate data records (CDRs) are essential for use in climate research, to assess vertically resolved trends and associated radiative impacts. Within the ESA Water Vapour Climate Change Initiative (WV_cci), new vertically resolved water vapour CDRs in the stratosphere and UTLS were merged from a range of satellite observations. In this contribution, we provide an overview of these CDRs, highlighting innovations in the merging methodologies and results from a detailed quality assessment. In particular, the long-term trends derived from the new water vapour CDRs are compared to other merged datasets, reanalyses, and simulations from chemistry-climate models, with the ESA WV_cci CDRs deemed to be valuable new datasets for climate studies. We conclude that, mostly driven by dynamical variability, the derived water vapour trends vary significantly depending on the dataset used, chosen time period and location in the atmosphere. Using an off-line radiative transfer model, we estimate the consequence of these differences on the radiative forcing from water vapour changes in the upper troposphere and stratosphere over the past 30+ years.

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 %.

Using Aura Microwave Limb Sounder satellite observations of stratospheric nitrous oxide (N2O), ozone, and temperature from 2005 through 2021, we calculate the atmospheric lifetime of N2O to be decreasing at a rate of −2.1 ± 1.2 %/decade. This decrease is occurring because the N2O abundances in the middle tropical stratosphere, where N2O is photochemically destroyed, are increasing at a faster rate than the bulk N2O in the lower atmosphere. The cause appears to be a more vigorous stratospheric circulation, which models predict to be a result of climate change. If the observed trends in lifetime and implied emissions continue, then the change in N2O over the 21st century will be 27 % less than those projected with a fixed lifetime, and the impact on global warming and ozone depletion will be proportionately lessened. Because global warming is caused in part by N2O, this finding is an example of a negative climate–chemistry feedback.

The Microwave Limb Sounder (MLS), launched on NASA's Aura spacecraft in 2004, measures vertical profiles of the abundances of key atmospheric species from the upper troposphere to the mesosphere with daily near-global coverage. We review the first 15 years of the record of H2O and N2O measurements from the MLS 190 GHz subsystem (along with other 190 GHz information), with a focus on their long-term stability, largely based on comparisons with measurements from other sensors. These comparisons generally show signs of an increasing drift in the MLS “version 4” (v4) H2O record starting around 2010. Specifically, comparisons with v4.1 measurements from the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) indicate a ∼ 2 %–3 % per decade drift over much of the stratosphere, increasing to as much as ∼ 7 % per decade around 46 hPa. Larger drifts, of around 7 %–11 % per decade, are seen in comparisons to balloon-borne frost point hygrometer measurements in the lower stratosphere. Microphysical calculations considering the formation of polar stratospheric clouds in the Antarctic winter stratosphere corroborate a drift in MLS v4 water vapor measurements in that region and season. In contrast, comparisons with the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission, and with ground-based Water Vapor Millimeter-wave Spectrometer (WVMS) instruments, do not show statistically significant drifts. However, the uncertainty in these comparisons is large enough to encompass most of the drifts identified in other comparisons. In parallel, the MLS v4 N2O product is shown to be generally decreasing over the same period (when an increase in stratospheric N2O is expected, reflecting a secular growth in emissions), with a more pronounced drift in the lower stratosphere than that found for H2O. Comparisons to ACE-FTS and to MLS N2O observations in a different spectral region, with the latter available from 2004 to 2013, indicate an altitude-dependent drift, growing from 5 % per decade or less in the mid-stratosphere to as much as 15 % per decade in the lower stratosphere. Detailed investigations of the behavior of the MLS 190 GHz subsystem reveal a drift in its “sideband fraction” (the relative sensitivity of the 190 GHz receiver to the two different parts of the microwave spectrum that it observes). Our studies indicate that sideband fraction drift accounts for much of the observed changes in the MLS H2O product and some portion of the changes seen in N2O. The 190 GHz sideband fraction drift has been corrected in the new “version 5” (v5) MLS algorithms, which have now been used to reprocess the entire MLS record. As a result of this correction, the MLS v5 H2O record shows no statistically significant drifts compared to ACE-FTS. However, statistically significant drifts remain between MLS v5 and frost point measurements, although they are reduced. Drifts in v5 N2O are about half the size of those in v4 but remain statistically significant. Scientists are advised to use MLS v5 data in all future studies. Quantification of interregional and seasonal to annual changes in MLS H2O and N2O will not be affected by the drift. However, caution is advised in studies using the MLS record to examine long-term (multiyear) variability and trends in either of these species, especially N2O; such studies should only be undertaken in consultation with the MLS team. Importantly, this drift does not affect any of the MLS observations made in other spectral regions such as O3, HCl, CO, ClO, or temperature.

Global Climate is one chapter from the State of the Climate in 2019 annual report and is avail- able from https://doi.org/10.1175/BAMS-D-20-0104.1 Compiled by NOAA’s National Centers for Environmental Information, State of the Climate in 2019 is based on contributions from scien- tists from around the world. It provides a detailed update on global climate indicators, notable weather events, and other data collected by environmental monitoring stations and instru- ments located on land, water, ice, and in space. The full report is available from https://doi.org/10.1175/2020BAMSStateoftheClimate.1.

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.

Following the 15 January 2022 Hunga Tonga-Hunga Ha'apai eruption, several trace gases measured by the Aura Microwave Limb Sounder (MLS) displayed anomalous stratospheric values. Trajectories and radiance simulations confirm that the H₂O, SO₂, and HCl enhancements were injected by the eruption. In comparison with those from previous eruptions, the SO₂ and HCl mass injections were unexceptional, although they reached higher altitudes. In contrast, the H₂O injection was unprecedented in both magnitude (far exceeding any previous values in the 17-year MLS record) and altitude (penetrating into the mesosphere). We estimate the mass of H₂O injected into the stratosphere to be 146 ± 5 Tg, or ∼10% of the stratospheric burden. It may take several years for the H₂O plume to dissipate. This eruption could impact climate not through surface cooling due to sulfate aerosols, but rather through surface warming due to the radiative forcing from the excess stratospheric H₂O.

Six collocated spectrophotometers based in Arosa/Davos, Switzerland, have been measuring ozone profiles continuously since 1956 for the oldest Dobson and since 2005 for the most recent Brewer instrument. The datasets of these 2 ground-based triads (3 Dobsons and 3 Brewers) allow continuous intercomparisons and derivation of long-term trend estimates. In this study, the post-2000 ozone profile trends are estimated from the Dobson and the Brewer Umkehr time series, following a careful homogenization of the Dobson D051 dataset. Mainly, two periods in the post-2000 Dobson D051 dataset show anomalies when compared to the Brewer triad time series: in 2011–2013, an offset has been attributed to technical interventions during the renewal of the spectrophotometer acquisition system; in 2018, an offset with respect to the Brewer triad and Aura MLS has been detected following a technical intervention on the spectrophotometer wedge. The Dobson D051 time series was homogenized using its difference to the Brewers triad N values time series and the ozone profiles were retrieved from the modified N values by optimal estimation method (OEM). Simultaneously, the Dobson D051 time series was optimized by NOAA relying on the NASA M2GMI model simulations to identify and correct instrumental artifacts in the record. Comparisons of the two homogenized data records show common correction periods and globally similar intensities of the N values corrections. Long-term trends were estimated by Dynamic Linear Modeling (DLM) from Dobson ozone profile time series and, for the first time, from Brewer ozone profile time series. A positive trend of 0.2 to 0.5 %/year is estimated above 35 km, significant for Dobson D051 but lower and therefore non significantly different from zero at the 95 % level of confidence for Brewer B040. As shown on the Dobson D051 data record, the trend seems to become significantly positive only in 2004. Moreover, a persistent negative trend is estimated in the middle and the lower stratosphere with different levels of significance depending on the dataset.

We have analyzed near-global stratospheric data (and mesospheric data as well for H2O) in terms of absolute abundances, variability, and trends for O3, H2O, HCl, N2O, and HNO3, based on Aura Microwave Limb Sounder (MLS) data, as well as longer-term series from the Global OZone Chemistry And Related trace gas Data records for the Stratosphere (GOZCARDS). While we emphasize the evaluation of stratospheric models via data comparisons through 2014 to free-running (FR-WACCM) and specified dynamics (SD-WACCM) versions of the Community Earth System Model version 1 (CESM1) Whole Atmosphere Community Climate Model (WACCM), we also highlight observed stratospheric changes, using the most recent data from MLS. Regarding highlights from the satellite data, we have used multiple linear regression to derive trends based on zonal mean time series from Aura MLS data alone, between 60∘ S and 60∘ N. In the upper stratosphere, MLS O3 shows increases over 2005–2018 at ∼0.1–0.3 % yr−1 (depending on altitude and latitude) with 2σ errors of ∼0.2 % yr−1. For the lower stratosphere (LS), GOZCARDS O3 data for 1998–2014 point to small decreases between 60∘ S and 60∘ N, but the trends are more positive if the starting year is 2005. Southern midlatitudes (30–60∘ S) exhibit near-zero or slightly positive LS trends for 1998–2018. The LS O3 trends based on 2005–2018 MLS data are most positive (0.1–0.2 % yr−1) at these southern midlatitudes, although marginally statistically significant, in contrast to slightly negative or near-zero trends for 2005–2014. Given the high variability in LS O3, and the high sensitivity of trends to the choice of years used, especially for short periods, further studies are required for a robust longer-term LS trend result. For H2O, upper-stratospheric and mesospheric trends from GOZCARDS 1992–2010 data are near zero (within ∼0.2 % yr−1) and significantly smaller than trends (within ∼0.4–0.7 % yr−1) from MLS for 2005–2014 or 2005–2018. The latter short-term positive H2O trends are larger than expected from changes resulting from long-term increases in methane. We note that the very shallow solar flux maximum of solar cycle 24 has contributed to fairly large short-term mesospheric and upper-stratospheric H2O trends since 2005. However, given known drifts in the MLS H2O time series, MLS H2O trend results, especially after 2010, should be viewed as upper limits. The MLS data also show regions and periods of small HCl increases in the lower stratosphere, within the context of the longer-term stratospheric decrease in HCl, as well as interhemispheric–latitudinal differences in short-term HCl tendencies. We observe similarities in such short-term tendencies, and interhemispheric asymmetries therein, for lower-stratospheric HCl and HNO3, while N2O trend profiles exhibit anti-correlated patterns. In terms of the model evaluation, climatological averages for 2005–2014 from both FR-WACCM and SD-WACCM for O3, H2O, HCl, N2O, and HNO3 compare favorably with Aura MLS data averages over this period. However, the models at mid- to high latitudes overestimate mean MLS LS O3 values and seasonal amplitudes by as much as 50 %–60 %; such differences appear to implicate, in part, a transport-related model issue. At lower-stratospheric high southern latitudes, variations in polar winter and spring composition observed by MLS are well matched by SD-WACCM, with the main exception being for the early winter rate of decrease in HCl, which is too slow in the model. In general, we find that the latitude–pressure distributions of annual and semiannual oscillation amplitudes derived from MLS data are properly captured by the model amplitudes. In terms of closeness of fit diagnostics for model–data anomaly series, not surprisingly, SD-WACCM (driven by realistic dynamics) generally matches the observations better than FR-WACCM does. We also use root mean square variability as a more valuable metric to evaluate model–data differences. We find, most notably, that FR-WACCM underestimates observed interannual variability for H2O; this has implications for the time period needed to detect small trends, based on model predictions. The WACCM O3 trends generally agree (within 2σ uncertainties) with the MLS data trends, although LS trends are typically not statistically different from zero. The MLS O3 trend dependence on latitude and pressure is matched quite well by the SD-WACCM results. For H2O, MLS and SD-WACCM positive trends agree fairly well, but FR-WACCM shows significantly smaller increases; this discrepancy for FR-WACCM is even more pronounced for longer-term GOZCARDS H2O records. The larger discrepancies for FR-WACCM likely arise from its poorer correlations with cold point temperatures and with quasi-biennial oscillation (QBO) variability. For HCl, while some expected decreases in the global LS are seen in the observations, there are interhemispheric differences in the trends, and increasing tendencies are suggested in tropical MLS data at 68 hPa, where there is only a slight positive trend in SD-WACCM. Although the vertical gradients in MLS HCl trends are well duplicated by SD-WACCM, the model trends are always somewhat more negative; this deserves further investigation. The original MLS N2O product time series yield small positive LS tropical trends (2005–2012), consistent with models and with rates of increase in tropospheric N2O. However, longer-term series from the more current MLS N2O standard product are affected by instrument-related drifts that have also impacted MLS H2O. The LS short-term trend profiles from MLS N2O and HNO3 at midlatitudes in the two hemispheres have different signs; these patterns are well matched by SD-WACCM trends for these species. These model–data comparisons provide a reminder that the QBO and other dynamical factors affect decadal variability in a major way, notably in the lower stratosphere, and can thus significantly hinder the goals of robustly extracting (and explaining) small underlying long-term trends. The data sets and tools discussed here for model evaluation could be expanded to comparisons of species or regions not included here, as well as to comparisons between a variety of chemistry–climate models.

Past studies have suggested that ozone in the troposphere has increased globally throughout much of the 20th century due to increases in anthropogenic emissions and transport. We show, by combining satellite measurements with a chemical transport model, that during the last four decades tropospheric ozone does indeed indicate increases that are global in nature, yet still highly regional. Satellite ozone measurements from Nimbus-7 and Earth Probe Total Ozone Mapping Spectrometer (TOMS) are merged with ozone measurements from the Aura Ozone Monitoring Instrument/Microwave Limb Sounder (OMI/MLS) to determine trends in tropospheric ozone for 1979–2016. Both TOMS (1979–2005) and OMI/MLS (2005–2016) depict large increases in tropospheric ozone from the Near East to India and East Asia and further eastward over the Pacific Ocean. The 38-year merged satellite record shows total net change over this region of about +6 to +7 Dobson units (DU) (i.e., ∼15 %–20 % of average background ozone), with the largest increase (∼4 DU) occurring during the 2005–2016 Aura period. The Global Modeling Initiative (GMI) chemical transport model with time-varying emissions is used to aid in the interpretation of tropospheric ozone trends for 1980–2016. The GMI simulation for the combined record also depicts the greatest increases of +6 to +7 DU over India and East Asia, very similar to the satellite measurements. In regions of significant increases in tropospheric column ozone (TCO) the trends are a factor of 2–2.5 larger for the Aura record when compared to the earlier TOMS record; for India and East Asia the trends in TCO for both GMI and satellite measurements are ∼+3 DU decade−1 or greater during 2005–2016 compared to about +1.2 to +1.4 DU decade−1 for 1979–2005. The GMI simulation and satellite data also reveal a tropospheric ozone increases in ∼+4 to +5 DU for the 38-year record over central Africa and the tropical Atlantic Ocean. Both the GMI simulation and satellite-measured tropospheric ozone during the latter Aura time period show increases of ∼+3 DU decade−1 over the N Atlantic and NE Pacific.

The Microwave Limb Sounder (MLS), launched on NASA's Aura spacecraft in 2004, measures vertical profiles of the abundances of key atmospheric species from the upper troposphere to the mesosphere with daily near-global coverage. We review the first 15 years of the record of H2O and N2O measurements from the MLS 190-GHz subsystem (along with other 190-GHz information), with a focus on their long-term stability, largely based on comparisons with measurements from other sensors. These comparisons generally show signs of an increasing drift in the MLS version 4 (v4) H2O record starting around 2010. Specifically, comparisons with v4.1 measurements from the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) indicate a ~2–3 %/decade drift over much of the stratosphere, increasing to as much as ~7 %/decade around 46 hPa. Larger drifts, of around 7–11 %/decade, are seen in comparisons to balloon-borne frost point hygrometer measurements in the lower stratosphere. In contrast, the MLS v4 N2O product is shown to be generally decreasing over the same period (when an increase in stratospheric N2O is expected, reflecting a secular growth in emissions), with a more pronounced drift in the lower stratosphere than that found for H2O. Detailed investigations of the behavior of the MLS 190-GHz subsystem reveal a drift in its sideband fraction (the relative sensitivity of the 190-GHz receiver to the two different parts of the microwave spectrum it observes). Our studies indicate that sideband fraction drift accounts for much of the observed changes in the MLS H2O product and some portion of the changes seen in N2O. The 190-GHz sideband fraction drift has been corrected in the new version 5 MLS algorithms, which have now been used to reprocess the entire MLS record. As a result of this correction, the MLS v5 H2O record shows no statistically significant drifts compared to ACE-FTS. However, statistically significant drifts remain between MLS v5 and frost point measurements, though they are reduced. Drifts in v5 N2O are about half the size of those in v4 but remain statistically significant. Scientists are advised to use MLS v5 data in all future studies. Quantification of inter-regional and seasonal-to-annual changes in MLS H2O and N2O will not be affected by the drift. However, caution is advised in studies using the MLS record to examine long-term (multi-year) variability and trends in either of these species, especially N2O; such studies should only be undertaken in consultation with the MLS team. Importantly, this drift does not affect any of the MLS observations made in other spectral regions such as O3, HCl, CO, ClO, or temperature.

Author(s): Ruiz, DJ; Prather, MJ; Strahan, SE; Thompson, RL; Froidevaux, L; Steenrod, SD | Abstract: Nitrous oxide (N2O) is a long-lived greenhouse gas that affects atmospheric chemistry and climate. In this work, we use satellite measurements of N2O, ozone (O3), and temperature from the Aura Microwave Limb Sounder (MLS) instrument to calculate stratospheric loss of N2O, and thus its atmospheric lifetime. Using three chemistry transport models simulating the Aura period 2005–2017, we verify the stratospheric sink using MLS data and follow that loss signal down to the surface and compare with surface observations. Stratospheric loss has a strong seasonal cycle and is further modulated by the Quasi-Biennial Oscillation (QBO); these cycles are seen equally in both observations and the models. When filtered for interannual variability, the modeled surface signal is QBO-caused, and it reproduces the observed pattern, highlighting the potential role of the QBO in tropospheric chemistry and composition, as well as in model evaluation. The observed annual surface signal in the northern hemisphere matches well with the models run without emissions, indicating the annual cycle is driven mostly by stratosphere-troposphere exchange (STE) flux of N2O-depleted air and not surface N2O emissions. In the southern hemisphere (SH), all three models disagree and thus provide no guidance, except for indicating that modeling annual STE in the SH remains a major model uncertainty. Parallel model simulations of CFCl3, which has greater stratospheric loss that N2O and possibly surreptitious emissions, show that its interannual variations parallel those of N2O, and thus the observed N2O variability can identify the stratospheric component of the observed CFCl3 variability.

In this paper, we present the MErged GRIdded Dataset of Ozone Profiles (MEGRIDOP) in the stratosphere with a resolved longitudinal structure, which is derived from data from six limb and occultation satellite instruments: GOMOS, SCIAMACHY and MIPAS on Envisat, OSIRIS on Odin, OMPS on Suomi-NPP, and MLS on Aura. The merged dataset was generated as a contribution to the European Space Agency Climate Change Initiative Ozone project (Ozone_cci). The period of this merged time series of ozone profiles is from late 2001 until the end of 2018. The monthly mean gridded ozone profile dataset is provided in the altitude range from 10 to 50 km in bins of 10∘ latitude × 20∘ longitude. The merging is performed using deseasonalized anomalies. The created MEGRIDOP dataset can be used for analyses that probe our understanding of stratospheric chemistry and dynamics. To illustrate some possible applications, we created a climatology of ozone profiles with resolved longitudinal structure. We found zonal asymmetry in the climatological ozone profiles at middle and high latitudes associated with the polar vortex. At northern high latitudes, the amplitude of the seasonal cycle also has a longitudinal dependence. The MEGRIDOP dataset has also been used to evaluate regional vertically resolved ozone trends in the stratosphere, including the polar regions. It is found that stratospheric ozone trends exhibit longitudinal structures at Northern Hemisphere middle and high latitudes, with enhanced trends over Scandinavia and the Atlantic region. This agrees well with previous analyses and might be due to changes in dynamical processes related to the Brewer–Dobson circulation.

Hydrogen chloride (HCl) is the most abundant (more than 95 %) among inorganic chlorine compounds Cly in the stratosphere. The HCl molecule has been observed to obtain long-term quantitative estimations of total budget of the stratospheric anthropogenic chlorine compounds. In this study, we provided HCl vertical profiles at altitudes of 16–100 km using the superconducting submillimeter-wave limb-emission sounder (SMILES) from space. We used the SMILES Level-2 research product version 3.0.0. The period of the SMILES HCl observation was from October 12, 2009 to April 21, 2010, and the latitude coverage was 40S–65N. The average HCl vertical profile showed an increase with altitude up to the stratopause (~ 45 km), approximately constant values between the stratopause and the upper mesosphere (~ 80 km), and a decrease from the mesopause to the lower thermosphere (~ 100 km). This behavior was observed in the all latitude regions, and reproduced by the SD-WACCM model. We compared the SMILES HCl vertical profiles in the stratosphere and lower mesosphere with HCl profiles from MLS on the Aura satellite, as well as from ACE-FTS on SCISAT and from TELIS (balloon-borne). The TELIS observations were performed using the superconductive limb emission technique, as used by SMILES. The globally averaged vertical HCl profiles of SMILES well agreed with those of MLS and ACE-FTS within 0.25 and 0.2 ppbv between 20 and 40 km, respectively. The SMILES HCl concentration was smaller than those of MLS and ACE/FTS as the altitude increased from 40 km, and the difference was approximately 0.4–0.5 ppbv at 50–60 km. The difference between SMILES and TELIS HCl observations was about 0.3 ppbv in the polar winter region between 20 and 34 km, except near 26 km. SMILES HCl error sources that may cause discrepancies with the other observations are investigated by a theoretical error analysis. We calculated errors caused by the uncertainties of spectroscopic parameters, instrument functions, and atmospheric temperature profiles. The jacobian for the temperature explains the negative bias of the SMILES HCl concentration at 50–60 km. The HCl vertical profile from the middle troposphere to the lower thermosphere is reported for the first time from SMILES observations; the data quality is quantified by comparisons with other measurements and via theoretical error analysis.

The Limb Profiler (LP) is a part of the Ozone Mapping and Profiler Suite launched on board of the Suomi NPP satellite in October 2011. The LP measures solar radiation scattered from the atmospheric limb in ultraviolet and visible spectral ranges between the surface and 80 km. These measurements of scattered solar radiances allow for the retrieval of ozone profiles from cloud tops up to 55 km. The LP started operational observations in April 2012. In this study we evaluate more than 5.5 years of ozone profile measurements from the OMPS LP processed with the new NASA GSFC version 2.5 retrieval algorithm. We provide a brief description of the key changes that had been implemented in this new algorithm, including a pointing correction, new cloud height detection, explicit aerosol correction and a reduction of the number of wavelengths used in the retrievals. The OMPS LP ozone retrievals have been compared with independent satellite profile measurements obtained from the Aura Microwave Limb Sounder (MLS), Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) and Odin Optical Spectrograph and InfraRed Imaging System (OSIRIS). We document observed biases and seasonal differences and evaluate the stability of the version 2.5 ozone record over 5.5 years. Our analysis indicates that the mean differences between LP and correlative measurements are well within required ±10 % between 18 and 42 km. In the upper stratosphere and lower mesosphere (> 43 km) LP tends to have a negative bias. We find larger biases in the lower stratosphere and upper troposphere, but LP ozone retrievals have significantly improved in version 2.5 compared to version 2 due to the implemented aerosol correction. In the northern high latitudes we observe larger biases between 20 and 32 km due to the remaining thermal sensitivity issue. Our analysis shows that LP ozone retrievals agree well with the correlative satellite observations in characterizing vertical, spatial and temporal ozone distribution associated with natural processes, like the seasonal cycle and quasi-biennial oscillations. We found a small positive drift ∼ 0.5 % yr−1 in the LP ozone record against MLS and OSIRIS that is more pronounced at altitudes above 35 km. This pattern in the relative drift is consistent with a possible 100 m drift in the LP sensor pointing detected by one of our altitude-resolving methods.

The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) was an infrared (IR) limb emission spectrometer on the Envisat platform. Currently, there are four MIPAS ozone data products, including the operational Level-2 ozone product processed at ESA, with the scientific prototype processor being operated at IFAC Florence, and three independent research products developed by the Istituto di Fisica Applicata Nello Carrara (ISAC-CNR)/University of Bologna, Oxford University, and the Karlsruhe Institute of Technology–Institute of Meteorology and Climate Research/Instituto de Astrofísica de Andalucía (KIT–IMK/IAA). Here we present a dataset of ozone vertical profiles obtained by merging ozone retrievals from four independent Level-2 MIPAS processors. We also discuss the advantages and the shortcomings of this merged product. As the four processors retrieve ozone in different parts of the spectra (microwindows), the source measurements can be considered as nearly independent with respect to measurement noise. Hence, the information content of the merged product is greater and the precision is better than those of any parent (source) dataset. The merging is performed on a profile per profile basis. Parent ozone profiles are weighted based on the corresponding error covariance matrices; the error correlations between different profile levels are taken into account. The intercorrelations between the processors' errors are evaluated statistically and are used in the merging. The height range of the merged product is 20–55km, and error covariance matrices are provided as diagnostics. Validation of the merged dataset is performed by comparison with ozone profiles from ACE-FTS (Atmospheric Chemistry Experiment–Fourier Transform Spectrometer) and MLS (Microwave Limb Sounder). Even though the merging is not supposed to remove the biases of the parent datasets, around the ozone volume mixing ratio peak the merged product is found to have a smaller (up to 0.1ppmv) bias with respect to ACE-FTS than any of the parent datasets. The bias with respect to MLS is of the order of 0.15ppmv at 20–30km height and up to 0.45ppmv at larger altitudes. The agreement between the merged data MIPAS dataset with ACE-FTS is better than that with MLS. This is, however, the case for all parent processors as well.

In this work, we analyze the seasonal dependence of ozone trends in the stratosphere using four long-term merged data sets, SAGE-CCI-OMPS, SAGE-OSIRIS-OMPS, GOZCARDS, and SWOOSH, which provide more than 30 years of monthly zonal mean ozone profiles in the stratosphere. We focus here on trends between 2000 and 2018. All data sets show similar results, although some discrepancies are observed. In the upper stratosphere, the trends are positive throughout all seasons and the majority of latitudes. The largest upper-stratospheric ozone trends are observed during local winter (up to 6 % per decade) and equinox (up to 3 % per decade) at mid-latitudes. In the equatorial region, we find a very strong seasonal dependence of ozone trends at all altitudes: the trends vary from positive to negative, with the sign of transition depending on altitude and season. The trends are negative in the upper-stratospheric winter (−1 % per decade to −2 % per decade) and in the lower-stratospheric spring (−2 % per decade to −4 % per decade), but positive (2 % per decade to 3 % per decade) at 30–35 km in spring, while the opposite pattern is observed in summer. The tropical trends below 25 km are negative and maximize during summer (up to −2 % per decade) and spring (up to −3 % per decade). In the lower mid-latitude stratosphere, our analysis points to a hemispheric asymmetry: during local summers and equinoxes, positive trends are observed in the south (+1 % per decade to +2 % per decade), while negative trends are observed in the north (−1 % per decade to −2 % per decade). We compare the seasonal dependence of ozone trends with available analyses of the seasonal dependence of stratospheric temperature trends. We find that ozone and temperature trends show positive correlation in the dynamically controlled lower stratosphere and negative correlation above 30 km, where photochemistry dominates. Seasonal trend analysis gives information beyond that contained in annual mean trends, which can be helpful in order to better understand the role of dynamical variability in short-term trends and future ozone recovery predictions.

International audience; The Stratospheric Aerosol and Gas Experiment III on the International Space Station (SAGE III/ISS) was launched on February 19, 2017 and began routine operation in June 2017. The first two years of SAGE III/ISS (v5.1) solar occultation ozone data were evaluated by using correlative satellite and ground‐based measurements. Among the three (MES, AO3, and MLR) SAGE III/ISS retrieved solar ozone products, AO3 ozone shows the smallest bias and best precision, with mean biases less than 5% for altitudes ~15–55 km in the mid‐latitudes and ~20–55 km in the tropics. In the lower stratosphere and upper troposphere, AO3 ozone shows high biases that increase with decreasing altitudes and reach ~10% near the tropopause. Preliminary studies indicate that those high biases primarily result from the contributions of the oxygen dimer (O4) not being appropriately removed within the ozone channel. The precision of AO3 ozone is estimated to be ~3% for altitudes between 20 and 40 km. It degrades to ~10–15% in the lower mesosphere (~55 km), and ~20–30% near the tropopause. There could be an altitude registration error of ~100 meters in the SAGE III/ISS auxiliary temperature and pressure profiles. This, however, does not affect retrieved ozone profiles in native number density on geometric altitude coordinates. In the upper stratosphere and lower mesosphere (~40–55 km) the SAGE III/ISS (and SAGE II) retrieved ozone values show sunrise/sunset differences of ~5–8%, which are almost twice as large as what was observed by other satellites or model predictions. This feature needs further study.

We assess the interactions between stratospheric water vapor (SWV) and surface temperature during the past two decades using satellite observations and the Community Earth System Model (CESM). From 1992 to 2013, to first order, the observed SWV exhibited three distinct piece-wise trends: a steady increase from 1992 to 2000, an abrupt drop from 2000 to 2004, and a gradual recovery after 2004, while the global-mean surface temperature experienced a strong increase until 2000 and a warming hiatus after 2000. The atmosphere-only CESM shows that the seasonal variation of tropical-mean (30°S–30°N) SWV is anticorrelated with that of the tropical-mean sea surface temperature (SST), while the correlation between the tropical SWV and SST anomalies on the interannual time scale is rather weak. By nudging the modeled SWV to prescribed profiles in coupled atmosphere-slab ocean experiments, we investigate the impact of SWV variations on surface temperature change. We find that a uniform 1 ppmv (0.5 ppmv) SWV increase (decrease) leads to an equilibrium global mean surface warming (cooling) of 0.12 ± 0.05 °C (−0.07 ± 0.05 °C). Sensitivity experiments show that the equilibrium response of global mean surface temperature to SWV perturbations over the extratropics is larger than that over the tropics. The observed sudden drop of SWV from 2000 to 2004 produces a global mean surface cooling of about −0.048 ± 0.041 °C, which suggests that a persistent change in SWV would make an imprint on long-term variations of global-mean surface temperature. A constant linear increase in SWV based on the satellite-observed rate of SWV change yields a global mean surface warming of 0.03 ± 0.01 °C/decade over a 50-year period, which accounts for about 19 % of the observed surface temperature increase prior to the warming hiatus. In the same experiment, trend analyses during different periods reveal a multi-year adjustment of surface temperature before the response to SWV forcing becomes strong relative to the internal variability in the model.

We evaluate the recently delivered Community Earth System Model version 1 (CESM1) Whole Atmosphere Community Climate Model (WACCM) using satellite-derived global composition datasets, focusing on the stratosphere. The simulations include free-running (FR-WACCM) and specified-dynamics (SD-WACCM) versions of the model. Model evaluations are made using global monthly zonal mean time series obtained by the Aura Microwave Limb Sounder (MLS), as well as longer-term global data records compiled by the Global Ozone Chemistry and Related Trace gas Data Records for the Stratosphere (GOZCARDS) project. A recent update (version 2.20) to the original GOZCARDS merged ozone (O3) data set is used. We discuss upper atmospheric climatology and zonal mean variability using O3, hydrogen chloride (HCl), nitrous oxide (N2O), nitric acid (HNO3), and water vapor (H2O) data. There are a few significant model/data mean biases, such as for lower stratospheric O3, for which the models overestimate the mean observed values and seasonal amplitudes. Another clear difference occurs for HNO3 during recurring winter periods of strong HNO3 enhancements at high latitudes; this stems from the known omission of ion chemistry relating to particle precipitation effects, in the global models used here. In the lower stratosphere at high southern latitudes, the variations in polar winter/spring composition observed by MLS are generally well matched by SD-WACCM, the main exception being for the early winter rate of decrease in HCl, which is too slow in the model. In general, the latitude/pressure distributions of annual and semi-annual oscillation amplitudes derived from the MLS data are properly captured by the corresponding model values. Nevertheless, detailed aspects of the interactions between the quasi-biennial, annual, and semi-annual ozone variations in the upper stratosphere are not as well represented by FR-WACCM as by SD-WACCM. One of the evaluation diagnostics we use represents the closeness of fit between the model/data anomaly time series, and we also consider the correlation coefficients. Not surprisingly, SD-WACCM, which is driven by realistic dynamics, generally matches observed deseasonalized anomalies better than FR-WACCM does. Other results indicate that the root mean square variability is sometimes found to be significantly smaller in FR-WACCM than in SD-WACCM and the observations. Most notably, FR-WACCM underestimates the observed interannual variability for H2O by ~ 30 %, typically, and by as much as a factor of two in some regions; this has some implications for the time needed to detect small trends. We have derived trends using a multivariate linear regression (MLR) model, and there is a robust signal in both MLS observations and WACCM of an upper stratospheric O3 increase from 2005 to 2014 by ~ 0.2–0.4 %/yr (±0.2 %/yr, 2σ), depending on which broad latitude bin (tropics or mid-latitudes) is considered. In the lower stratosphere, while some decreases are indicated for 1998–2014 (based on merged GOZCARDS O3), we find near-zero or positive trends when using MLS O3 data alone for 2005–2014, albeit with no robust statistical significance. SD-WACCM results track such positive tendencies (albeit with no statistical significance). For H2O, the most statistically significant trend result for 2005–2014 is an upper stratospheric increase, peaking at slightly more than 0.5 %/yr in the lower mesosphere, in fairly close agreement with SD-WACCM trends, but with smaller values in FR-WACCM. For HCl, while the lower stratospheric vertical gradients of MLS trends are duplicated to some extent by SD-WACCM, the model trends (decreases) are always on the low side of the data trends. There is little model-based indication (in SD-WACCM) of a significantly positive HCl trend derived from the MLS tropical series at 68 hPa; this deserves further study. For N2O, the MLS-derived trends (for 2005–2012) point to negative trends (of up to about −1 %/yr) in the NH mid-latitudes and positive trends (of up to about +3 %/yr) in the SH mid-latitudes, in good agreement with the asymmetry that exists in SD-WACCM trend results. The small observed positive N2O trends of ~ 0.2 %/yr in the 100 to 30 hPa tropical region are also consistent with model results (SD-WACCM in particular), which in turn are very close to the known rate of increase in tropospheric N2O. In the case of HNO3, MLS-derived lower stratospheric trend differences (for 2005–2014) between hemispheres are opposite in sign to those from N2O and in reasonable agreement with both WACCM results, despite large error bars. The data sets and tools discussed here for the evaluation of the models could be expanded to additional comparisons of species not included here, as well as to model intercomparisons using a variety of CCMs, keeping in mind that there are different parameterizations and approaches for both free-running and specified-dynamics simulations.

We present a case study based on balloon-borne ozone measurements during SEACIONS (SouthEast American Consortium for Intensive Ozonesonde Network Study) in August-September 2013. Data from Socorro, NM (34oN, 107oW) show a layer of anomalously low ozone in the upper troposphere (UT) during 8-14 August. Back trajectories, UT jet analyses, and data from the Microwave Limb Sounder (MLS) on the Aura satellite indicate that this feature originated from the marine boundary layer in the eastern/central tropical Pacific, where several disturbances and one hurricane (Henriette) formed within an active region of the Intertropical Convergence Zone in early August 2013. The hurricane and nearby convection pumped boundary layer air with low ozone (20-30 ppbv) into the UT. This outflow was advected to North America 3-5 days later by a strong subtropical jet, forming a tongue of low ozone observed in MLS fields and a corresponding layer of low ozone in Socorro vertical profiles.

We describe the publicly available data from the Global OZone Chemistry And Related trace gas Data records for the Stratosphere (GOZCARDS) project and provide some results, with a focus on hydrogen chloride (HCl), water vapor (H2O), and ozone (O3). This data set is a global long-term stratospheric Earth system data record, consisting of monthly zonal mean time series starting as early as 1979. The data records are based on high-quality measurements from several NASA satellite instruments and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on SCISAT. We examine consistency aspects between the various data sets. To merge ozone records, the time series are debiased relative to SAGE II (Stratospheric Aerosol and Gas Experiments) values by calculating average offsets versus SAGE II during measurement overlap periods, whereas for other species the merging derives from an averaging procedure during overlap periods. The GOZCARDS files contain mixing ratios on a common pressure–latitude grid, as well as standard errors and other diagnostics; we also present estimates of systematic uncertainties in the merged products. Monthly mean temperatures for GOZCARDS were also produced, based directly on data from the Modern-Era Retrospective analysis for Research and Applications. The GOZCARDS HCl merged product comes from the Halogen Occultation Experiment (HALOE), ACE-FTS and lower-stratospheric Aura Microwave Limb Sounder (MLS) data. After a rapid rise in upper-stratospheric HCl in the early 1990s, the rate of decrease in this region for 1997–2010 was between 0.4 and 0.7 % yr−1. On 6–8-year timescales, the rate of decrease peaked in 2004–2005 at about 1 % yr−1, and it has since levelled off, at ~ 0.5 % yr−1. With a delay of 6–7 years, these changes roughly follow total surface chlorine, whose behavior versus time arises from inhomogeneous changes in the source gases. Since the late 1990s, HCl decreases in the lower stratosphere have occurred with pronounced latitudinal variability at rates sometimes exceeding 1–2 % yr−1. Recent short-term tendencies of lower-stratospheric and column HCl vary substantially, with increases from 2005 to 2010 for northern midlatitudes and deep tropics, but decreases (increases) after 2011 at northern (southern) midlatitudes. For H2O, the GOZCARDS product covers both stratosphere and mesosphere, and the same instruments as for HCl are used, along with Upper Atmosphere Research Satellite (UARS) MLS stratospheric H2O data (1991–1993). We display seasonal to decadal-type variability in H2O from 22 years of data. In the upper mesosphere, the anticorrelation between H2O and solar flux is now clearly visible over two full solar cycles. Lower-stratospheric tropical H2O has exhibited two periods of increasing values, followed by fairly sharp drops (the well-documented 2000–2001 decrease and a recent drop in 2011–2013). Tropical decadal variability peaks just above the tropopause. Between 1991 and 2013, both in the tropics and on a near-global basis, H2O has decreased by ~ 5–10 % in the lower stratosphere, but about a 10 % increase is observed in the upper stratosphere and lower mesosphere. However, such tendencies may not represent longer-term trends. For ozone, we used SAGE I, SAGE II, HALOE, UARS and Aura MLS, and ACE-FTS data to produce a merged record from late 1979 onward, using SAGE II as the primary reference. Unlike the 2 to 3 % increase in near-global column ozone after the late 1990s reported by some, GOZCARDS stratospheric column O3 values do not show a recent upturn of more than 0.5 to 1 %; long-term interannual column ozone variations from GOZCARDS are generally in very good agreement with interannual changes in merged total column ozone (Version 8.6) data from SBUV instruments. A brief mention is also made of other currently available, commonly formatted GOZCARDS satellite data records for stratospheric composition, namely those for N2O and HNO3.

Stratospheric transport and polar processing during the 2014/2015 Arctic winter were strongly influenced by a minor sudden stratospheric warming (SSW) in early January. Disturbances to temperatures and trace gases in the middle and upper stratosphere were similar in character to those associated with major SSWs: The stratopause dropped, and vertical temperature gradients weakened, followed by renewed descent of mesospheric air. The lower stratospheric polar vortex was barely disrupted and remained unusually strong throughout the winter. The SSW did, however, cause lower stratospheric temperatures to rise well above chlorine activation thresholds; trace gas abundances from the Aura Microwave Limb Sounder (MLS) were consequently exceptional. The degree of chlorine activation in January was the smallest, and lower stratospheric ozone values in February were the highest, in the 11 year MLS record. The major role played by a minor SSW highlights the Arctic stratosphere's sensitivity to a spectrum of dynamical variability.

Trends in the vertical distribution of ozone are reported and compared for a number of new and recently revised data sets. The amount of ozone-depleting compounds in the stratosphere (as measured by equivalent effective stratospheric chlorine – EESC) was maximised in the second half of the 1990s. We examine the periods before and after the peak to see if any change in trend is discernible in the ozone record that might be attributable to a change in the EESC trend, though no attribution is attempted. Prior to 1998, trends in the upper stratosphere (~ 45 km, 4 hPa) are found to be −5 to −10 % per decade at mid-latitudes and closer to −5 % per decade in the tropics. No trends are found in the mid-stratosphere (28 km, 30 hPa). Negative trends are seen in the lower stratosphere at mid-latitudes in both hemispheres and in the deep tropics. However, it is hard to be categorical about the trends in the lower stratosphere for three reasons: (i) there are fewer measurements, (ii) the data quality is poorer, and (iii) the measurements in the 1990s are perturbed by aerosols from the Mt Pinatubo eruption in 1991. These findings are similar to those reported previously even though the measurements for the main satellite and ground-based records have been revised. There is no sign of a continued negative trend in the upper stratosphere since 1998: instead there is a hint of an average positive trend of ~ 2 % per decade in mid-latitudes and ~ 3 % per decade in the tropics. The significance of these upward trends is investigated using different assumptions of the independence of the trend estimates found from different data sets. The averaged upward trends are significant if the trends derived from various data sets are assumed to be independent (as in Pawson et al., 2014) but are generally not significant if the trends are not independent. This occurs because many of the underlying measurement records are used in more than one merged data set. At this point it is not possible to say which assumption is best. Including an estimate of the drift of the overall ozone observing system decreases the significance of the trends. The significance will become clearer as (i) more years are added to the observational record, (ii) further improvements are made to the historic ozone record (e.g. through algorithm development), and (iii) the data merging techniques are refined, particularly through a more rigorous treatment of uncertainties.

A detailed analysis of the polar ozone loss processes during 10 recent Antarctic winters is presented with high-resolution MIMOSA–CHIM (Modèle Isentrope du transport Méso-échelle de l'Ozone Stratosphérique par Advection avec CHIMie) model simulations and high-frequency polar vortex observations from the Aura microwave limb sounder (MLS) instrument. The high-frequency measurements and simulations help to characterize the winters and assist the interpretation of interannual variability better than either data or simulations alone. Our model results for the Antarctic winters of 2004–2013 show that chemical ozone loss starts in the edge region of the vortex at equivalent latitudes (EqLs) of 65–67° S in mid-June–July. The loss progresses with time at higher EqLs and intensifies during August–September over the range 400–600 K. The loss peaks in late September–early October, when all EqLs (65–83° S) show a similar loss and the maximum loss (> 2 ppmv – parts per million by volume) is found over a broad vertical range of 475–550 K. In the lower stratosphere, most winters show similar ozone loss and production rates. In general, at 500 K, the loss rates are about 2–3 ppbv sh−1 (parts per billion by volume per sunlit hour) in July and 4–5 ppbv sh−1 in August–mid-September, while they drop rapidly to 0 by mid-October. In the middle stratosphere, the loss rates are about 3–5 ppbv sh−1 in July–August and October at 675 K. On average, the MIMOSA–CHIM simulations show that the very cold winters of 2005 and 2006 exhibit a maximum loss of ~ 3.5 ppmv around 550 K or about 149–173 DU over 350–850 K, and the warmer winters of 2004, 2010, and 2012 show a loss of ~ 2.6 ppmv around 475–500 K or 131–154 DU over 350–850 K. The winters of 2007, 2008, and 2011 were moderately cold, and thus both ozone loss and peak loss altitudes are between these two ranges (3 ppmv around 500 K or 150 ± 10 DU). The modeled ozone loss values are in reasonably good agreement with those estimated from Aura MLS measurements, but the model underestimates the observed ClO, largely due to the slower vertical descent in the model during spring.

We present a comprehensive analysis of the trends of stratospheric ozone in the midlatitudes and subtropics. The analysis is performed using ground-based and space-based measurements over the light detection and ranging stations for the period 1985–2012. Also, trends are estimated for the zonal mean data made from a merged satellite data set, Global OZone Chemistry And Related trace gas Data records for the Stratosphere, over 1979–2012. The linear trends in stratospheric ozone are estimated using piecewise linear trend (PWLT) functions. The ozone trends during the increasing phase of halogens (before 1997) range from −0.2 ± 0.08 to −1 ± 0.07% yr−1 in the midlatitudes and −0.2 ± 0.06 to −0.7 ± 0.05 % yr−1 in the subtropics at 15–45 km, depending on altitude. In 1997–2012, the PWLT analyses show a positive trend, significantly different from zero at the 95% confidence intervals, toward ozone recovery in the middle- and low-latitude upper stratosphere (35–45 km), and the trends are about +0.5 ± 0.07% yr−1 at midlatitudes and about +0.3 ± 0.05% yr−1 at subtropical latitudes. However, negative and insignificant trends are estimated in the lower stratosphere (15–20 km) over 1997–2012 in the midlatitudes, mainly due to the dynamics, as demonstrated by the large (50–60%) contributions from the quasi-biennial oscillation, El Nino–Southern Oscillation, and planetary wave activity to recent ozone changes. This suggests that the ozone changes are governed by the interannual variations in meteorology and dynamics of the regions; these factors will influence the recovery detection time and the behavior of the recovery path to pre-1980 levels.

In the framework of the SI2N (SPARC (Stratosphere-troposphere Processes And their Role in Climate)/IO3C (International Ozone Commission)/IGACO-O3 (Integrated Global Atmospheric Chemistry Observations – Ozone)/NDACC (Network for the Detection of Atmospheric Composition Change)) initiative, several long-term vertically resolved merged ozone data sets produced from satellite measurements have been analysed and compared. This paper presents an overview of the methods, assumptions, and challenges involved in constructing such merged data sets, as well as the first thorough intercomparison of seven new long-term satellite data sets. The analysis focuses on the representation of the annual cycle, interannual variability, and long-term trends for the period 1984–2011, which is common to all data sets. Overall, the best agreement amongst data sets is seen in the mid-latitude lower and middle stratosphere, with larger differences in the equatorial lower stratosphere and the upper stratosphere globally. In most cases, differences in the choice of underlying instrument records that were merged produced larger differences between data sets than the use of different merging techniques. Long-term ozone trends were calculated for the period 1984–2011 using a piecewise linear regression with a change in trend prescribed at the end of 1997. For the 1984–1997 period, trends tend to be most similar between data sets (with largest negative trends ranging from −4 to −8% decade−1 in the mid-latitude upper stratosphere), in large part due to the fact that most data sets are predominantly (or only) based on the SAGE-II record. Trends in the middle and lower stratosphere are much smaller, and, particularly for the lower stratosphere, large uncertainties remain. For the later period (1998–2011), trends vary to a greater extent, ranging from approximately −1 to +5% decade−1 in the upper stratosphere. Again, middle and lower stratospheric trends are smaller and for most data sets not significantly different from zero. Overall, however, there is a clear shift from mostly negative to mostly positive trends between the two periods over much of the profile., Atmospheric Chemistry and Physics, 15 (6), ISSN:1680-7375, ISSN:1680-7367

This work is distributed under the Creative Commons Attribution 4.0 License., In this paper we describe the stratospheric and mesospheric ozone (version V5r-O3-m22) distributions retrieved from MIPAS observations in the three middle atmosphere modes (MA, NLC, and UA) taken with an unapodized spectral resolution of 0.0625 cm from 2005 until April 2012. O is retrieved from microwindows in the 14.8 and 10 μm spectral regions and requires non-local thermodynamic equilibrium (non-LTE) modelling of the O and vibrational levels. Ozone is reliably retrieved from 20 km in the MA mode (40 km for UA and NLC) up to ∼105 km during dark conditions and up to ∼95 km during illuminated conditions. Daytime MIPAS O has an average vertical resolution of 3-4 km below 70 km, 6-8 km at 70-80 km, 8-10 km at 80-90, and 5-7 km at the secondary maximum (90-100 km). For nighttime conditions, the vertical resolution is similar below 70 km and better in the upper mesosphere and lower thermosphere: 4-6 km at 70-100 km, 4-5 km at the secondary maximum, and 6-8 km at 100-105 km. The noise error for daytime conditions is typically smaller than 2% below 50 km, 2-10% between 50 and 70 km, 10-20% at 70-90 km, and ∼30% above 95 km. For nighttime, the noise errors are very similar below around 70 km but significantly smaller above, being 10-20% at 75-95 km, 20-30% at 95-100 km, and larger than 30% above 100 km. The additional major O errors are the spectroscopic data uncertainties below 50 km (10-12 %) and the non-LTE and temperature errors above 70 km. The validation performed suggests that the spectroscopic errors below 50 km, mainly caused by the O air-broadened half-widths of the band, are overestimated. The non-LTE error (including the uncertainty of atomic oxygen in nighttime) is relevant only above ∼85 km with values of 15-20 %. The temperature error varies from ∼3% up to 80 km to 15-20% near 100 km. Between 50 and 70 km, the pointing and spectroscopic errors are the dominant uncertainties. The validation performed in comparisons with SABER, GOMOS, MLS, SMILES, and ACE-FTS shows that MIPAS O has an accuracy better than 5% at and below 50 km, with a positive bias of a few percent. In the 50-75 km region, MIPAS O has a positive bias of ∼10 %, which is possibly caused in part by O spectroscopic errors in the 10 μm region. Between 75 and 90 km, MIPAS nighttime O is in agreement with other instruments by 10 %, but for daytime the agreement is slightly larger, ∼10-20 %. Above 90 km, MIPAS daytime O is in agreement with other instruments by 10 %. At night, however, it shows a positive bias increasing from 10% at 90 km to 20% at 95-100 km, the latter of which is attributed to the large atomic oxygen abundance used. We also present MIPAS O distributions as function of altitude, latitude, and time, showing the major O features in the middle and upper mesosphere. In addition to the rapid diurnal variation due to photochemistry, the data also show apparent signatures of the diurnal migrating tide during both day-and nighttime, as well as the effects of the semi-Annual oscillation above ∼70 km in the tropics and mid-latitudes. The tropical. daytime O at 90 km shows a solar signature in phase with the solar cycle. © Author(s) 2018., The IAA team was supported by the Spanish MICINN under the project ESP2014-54362-P and EC FEDER funds. The IAA and IMK teams were partially supported by ESA O3-CCI and MesosphEO projects. Maya Garcia-Comas was financially supported by MINECO through its >Ramon y Cajal> subprogram. Funding for the Atmospheric Chemistry Experiment comes primarily from the Canadian Space Agency. Work at the Jet Propulsion Laboratory was performed under contract with the National Aeronautics and Space Administration.

Stratospheric water vapour is a powerful greenhouse gas. The longest available record from balloon observations over Boulder, Colorado, USA shows increases in stratospheric water vapour concentrations that cannot be fully explained by observed changes in the main drivers, tropical tropopause temperatures and methane. Satellite observations could help resolve the issue, but constructing a reliable long-term data record from individual short satellite records is challenging. Here we present an approach to merge satellite data sets with the help of a chemistry–climate model nudged to observed meteorology. We use the models’ water vapour as a transfer function between data sets that overcomes issues arising from instrument drift and short overlap periods. In the lower stratosphere, our water vapour record extends back to 1988 and water vapour concentrations largely follow tropical tropopause temperatures. Lower and mid-stratospheric long-term trends are negative, and the trends from Boulder are shown not to be globally representative. In the upper stratosphere, our record extends back to 1986 and shows positive long-term trends. The altitudinal differences in the trends are explained by methane oxidation\ud together with a strengthened lower-stratospheric and a weakened upper stratospheric circulation inferred by this analysis. Our results call into question previous estimates of surface radiative forcing based on presumed global long-term increases in water vapour concentrations in the lower stratosphere.

Ozone forms in the Earth's atmosphere from the photodissociation of molecular oxygen, primarily in the tropical stratosphere. It is then transported to the extratropics by the Brewer-Dobson circulation (BDC), forming a protective ozone layer around the globe. Human emissions of halogen-containing ozone-depleting substances (hODSs) led to a decline in stratospheric ozone until they were banned by the Montreal Protocol (MP), and since 1998 ozone in the upper stratosphere shows a likely recovery. Total column ozone (TCO) measurements of ozone between the Earth's surface and the top of the atmosphere, indicate that the ozone layer has stopped declining across the globe, but no clear increase has been observed at latitudes outside the polar regions (60–90). Here we report evidence from multiple satellite measurements that ozone in the lower stratosphere between 60° S and 60° N has declined continuously since 1985. We find that, even though upper stratospheric ozone is recovering in response to the MP, the lower stratospheric changes more than compensate for this, resulting in the conclusion that, globally (60°&tinsp;S–60° N), stratospheric column ozone (StCO) continues to deplete. We find that globally, TCO appears to not have decreased because tropospheric column ozone (TrCO) increases, likely the result of human activity and harmful to respiratory health, are compensating for the stratospheric decreases. The reason for the continued reduction of lower stratospheric ozone is not clear, models do not reproduce these trends, and so the causes now urgently need to be established. Reductions in lower stratospheric ozone trends may partly lead to a small reduction in the warming of the climate, but a reduced ozone layer may also permit an increase in harmful ultra-violet (UV) radiation at the surface and would impact human and ecosystem health.

The Arctic winter 2015/2016 was one of the coldest stratospheric winters in recent years. A stable vortex formed by early December and the early winter was exceptionally cold. Cold pool temperatures dropped below the Nitric Acid Trihydrate (NAT) existence temperature of about 195 K, thus allowing Polar Stratospheric Clouds (PSCs) to form. The low temperatures in the polar stratosphere persisted until early March allowing chlorine activation and catalytic ozone destruction. Satellite observations indicate that sedimentation of PSC particles led to denitrification as well as dehydration of stratospheric layers. Model simulations of the Arctic winter 2015/2016 nudged toward European Center for Medium-Range Weather Forecasts (ECMWF) analyses data were performed with the atmospheric chemistry–climate model ECHAM5/MESSy Atmospheric Chemistry (EMAC) for the Polar Stratosphere in a Changing Climate (POLSTRACC) campaign. POLSTRACC is a High Altitude and LOng Range Research Aircraft (HALO) mission aimed at the investigation of the structure, composition and evolution of the Arctic Upper Troposphere and Lower Stratosphere (UTLS). The chemical and physical processes involved in Arctic stratospheric ozone depletion, transport and mixing processes in the UTLS at high latitudes, polar stratospheric clouds as well as cirrus clouds are investigated. In this study an overview of the chemistry and dynamics of the Arctic winter 2015/2016 as simulated with EMAC is given. Further, chemical-dynamical processes such as denitrification, dehydration and ozone loss during the Arctic winter 2015/2016 are investigated. Comparisons to satellite observations by the Aura Microwave Limb Sounder (Aura/MLS) as well as to airborne measurements with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) performed on board of HALO during the POLSTRACC campaign show that the EMAC simulations are in fairly good agreement with observations. We derive a maximum polar stratospheric O3 loss of ~ 2 ppmv or 100 DU in terms of column in mid March. The stratosphere was denitrified by about 8 ppbv HNO3 and dehydrated by about 1 ppmv H2O in mid to end of February. While ozone loss was quite strong, but not as strong as in 2010/2011, denitrification and dehydration were so far the strongest observed in the Arctic stratosphere in the at least past 10 years.

Satellite measurements sample continuous fields of atmospheric constituents at discrete locations and times. However, insufficient or inhomogeneous sampling, if not taken into account, can result in inaccurate average estimates and even induce spurious features. We propose to characterize the spatiotemporal inhomogeneity of atmospheric measurements by a measure, which is a linear combination of the asymmetry and entropy of a sampling distribution. It is shown that this measure is related to the so-called sampling uncertainty, which occurs due to non-uniform sampling patterns. We have estimated the sampling uncertainty of zonal mean ozone profiles for six limb-viewing satellite instruments participating in the European Space Agency Ozone Climate Change Initiative project using the high-resolution ozone field simulated with the FinROSE chemistry-transport model. It is shown that the sampling uncertainty for the instruments with coarse sampling is not negligible and can be as large as a few percent. It is found that the standard deviation of the sampling uncertainty in the monthly zonal mean data allows for a simple parameterization in terms of the product of the standard deviation of natural variations and the proposed inhomogeneity measure. The sampling uncertainty estimates improve the uncertainty quantification and can be used in comprehensive data analyses. The focus of this work is the vertical ozone distributions measured by limb-viewing satellite instruments, but the developed methods can also be applied to different satellite, ground-based and in situ measurements.

We present the first comprehensive intercomparison of currently available satellite ozone climatologies in the upper troposphere/lower stratosphere (UTLS) (300–70 hPa) as part of the Stratosphere-troposphere Processes and their Role in Climate (SPARC) Data Initiative. The Tropospheric Emission Spectrometer (TES) instrument is the only nadir-viewing instrument in this initiative, as well as the only instrument with a focus on tropospheric composition. We apply the TES observational operator to ozone climatologies from the more highly vertically resolved limb-viewing instruments. This minimizes the impact of differences in vertical resolution among the instruments and allows identification of systematic differences in the large-scale structure and variability of UTLS ozone. We find that the climatologies from most of the limb-viewing instruments show positive differences (ranging from 5 to 75%) with respect to TES in the tropical UTLS, and comparison to a “zonal mean” ozonesonde climatology indicates that these differences likely represent a positive bias for p ≤ 100 hPa. In the extratropics, there is good agreement among the climatologies regarding the timing and magnitude of the ozone seasonal cycle (differences in the peak-to-peak amplitude of