Stratospheric Ozone Variability Research Articles

Ozone Trend Analysis in Natal (5.4°S, 35.4°W, Brazil) Using Multi-Linear Regression and Empirical Decomposition Methods over 22 Years of Observations

Ozone plays an important role in the Earth’s atmosphere. It is mainly formed in the tropical stratosphere and is transported by the Brewer–Dobson Circulation to higher latitudes. In the stratosphere, ozone can filter the incoming solar ultraviolet radiation, thus protecting life at the surface. Although tropospheric ozone accounts for only ~10%, it is a powerful GHG and pollutant, harmful to the health of the environment and living beings. Several studies have highlighted biomass burning as a major contributor to the tropospheric ozone budget. Our study focuses on the Natal site (5.40°S, 35.40°W, Brazil), one of the oldest ozone-observing stations in Brazil, which is expected to be influenced by fire plumes in Africa and Brazil. Many studies that examined ozone trends used the total atmospheric columns of ozone, but it is important to assess ozone separately in the troposphere and the stratosphere. In this study, we have used radiosonde ozone profiles and daily TCO measurements to evaluate the variability and changes of both tropospheric and stratospheric ozone separately. The dataset in this study comprises daily total columns of colocalized ozone and weekly ozone profiles collected between 1998 and 2019. The tropospheric columns were estimated by integrating ozone profiles measured by ozone sondes up to the tropopause height. The amount of ozone in the stratosphere was then deduced by subtracting the tropospheric ozone amount from the total amount of ozone measured by the Dobson spectrometer. It was assumed that the amount of ozone in the mesosphere is negligible. This produced three distinct time series of ozone: tropospheric and stratospheric columns as well as total columns. The present study aims to apply a new decomposition method named Empirical Adaptive Wavelet Decomposition (EAWD) that is used to identify the different modes of variability present in the analyzed signal. This is achieved by summing up the most significant Intrinsic Mode Functions (IMF). The Fourier spectrum of the original signal is broken down into spectral bands that frame each IMF obtained by the Empirical Modal Decomposition (EMD). Then, the Empirical Wavelet Transform (EWT) is applied to each interval. Unlike other methods like EMD and multi-linear regression (MLR), the EAWD technique has an advantage in providing better frequency resolution and thus overcoming the phenomenon of mode-mixing, as well as detecting possible breakpoints in the trend mode. The obtained ozone datasets were analyzed using three methods: MLR, EMD, and EAWD. The EAWD algorithm exhibited the advantage of retrieving ~90% to 95% of ozone variability and detecting possible breakpoints in its trend component. Overall, the MRL and EAWD methods showed almost similar trends, a decrease in the stratosphere ozone (−1.3 ± 0.8%) and an increase in the tropospheric ozone (+4.9 ± 1.3%). This study shows the relevance of combining data to separately analyze tropospheric and stratospheric ozone variability and trends. It highlights the advantage of the EAWD algorithm in detecting modes of variability in a geophysical signal without prior knowledge of the underlying forcings.

Evaluation of total ozone measurements from Geostationary Environmental Monitoring Spectrometer (GEMS)

Abstract. The continued interest in air pollution and stratospheric ozone variability has motivated the development of a Geostationary Environmental Monitoring Spectrometer (GEMS) for hourly ozone monitoring. This paper provides the atmospheric science community with the world's first assessment of GEMS total column ozone (TCO) retrieval performance and diurnal ozone variation. The algorithm used for GEMS is a more advanced version of its predecessor, the Total Ozone Mapping Spectrometer (TOMS) V8, that incorporates several improvements, including a new lookup table, a simple Lambertian-equivalent reflectivity model, and a spectral dependence correction. The GEMS algorithm also uses the optimal estimation method (OEM) to make error analysis more accessible and robust. The estimated retrieval errors range from 1.5 to 2 DU in September and 2 DU in December, with a constant degree of freedom of the signal (DFS) of 1 in September and a variable DFS of 1.25 to 1.4 in December throughout the day, depending on solar zenith angle (SZA). To assess the performance of the GEMS algorithm, the hourly GEMS total ozone was compared with ground-based measurements from Pandora instruments and other satellite platforms from TROPOMI (TROPOspheric Monitoring Instrument) and OMPS (Ozone Mapping and Profiler Suite Nadir Mapper). GEMS has a high correlation of 0.97 and small RMSE values compared to Pandora TCO at Busan and Seoul in South Korea. It is notable that despite exhibiting seasonal dependence in the mean bias of GEMS with Pandora, GEMS is capable of observing daily variations in ozone that are highly consistent with Pandora measurements, with a bias of approximately 1 %. The comparison of GEMS TCO data with TROPOMI and OMPS TCO data shows a high correlation of 0.99 and low RMSE compared to TROPOMI and OMPS TCO data, but the data have a negative bias of −2.38 % and −2.17 %, with standard deviations of 1.33 % and 1.57 %, respectively. Similar to OMPS, the influence of SO2 from volcanic eruptions is not properly removed in some regions, leading to GEMS overestimating TCO in those areas. The mean biases of GEMS TCO data with TROPOMI and OMPS TCO are within ±1 % at low latitudes but become negative at midlatitudes, with an increasingly negative dependence on latitude. Furthermore, this dependence becomes more prominent from summer to winter. The empirical correction applied to the GEMS irradiance data improves the dependence of the mean bias on season and latitude, but a consistent bias still remains, and a marginal positive trend was observed in December. Therefore, further investigation into correction methods is needed. The results are a meaningful scientific advance by providing the first validated, hourly UV ozone retrievals from a satellite in geostationary orbit. This experience can be used to advance research with future geostationary environmental satellite missions, including the incoming TEMPO (Tropospheric Emissions: Monitoring of Pollution) and Sentinel-4.

Stratospheric Ozone Variations Over Obninsk from Data of Lidar and Satellite Measurements

Stratospheric Ozone Variations Over Obninsk from Data of Lidar and Satellite Measurements

ENSO Modoki Impacts on the Interannual Variations of Spring Antarctic Stratospheric Ozone

Abstract Using observation and reanalysis data, we investigated the effect of the sea surface temperature anomalies associated with ENSO Modoki from September to October on interannual variations in Antarctic stratospheric ozone from October to November. It was found that the planetary wave anomalies generated by ENSO Modoki in the tropical troposphere propagate to the southern mid- and then high-latitude stratosphere. The planetary wave anomalies have a profound impact on the polar vortex, subsequently affecting the interannual variations in Antarctic stratospheric ozone. Further analysis revealed that the responses of the polar vortex and ozone to ENSO Modoki are mainly modulated by the wave-1 and wave-3 components, and the effect of wave 2 is opposite and offset by those of wave 1 and wave 3. The contribution of the residual waves (after removing waves 1, 2, 3, and the remaining waves) are relatively small. Furthermore, we evaluated the performance of CMIP6 models in simulating the impacts of ENSO Modoki on the southern stratospheric polar vortex and ozone. We selected seven models that include stratospheric processes and stratospheric chemical ozone. We found that all are capable of distinguishing between eastern Pacific ENSO and ENSO Modoki events. However, only GISS-E2-1-G and MPI-ESM-1-2-HAM can simulate the patterns of ozone, circulation, and temperature in the Southern Hemisphere in a manner that closely resembles the reanalysis results. Further analysis indicated that these two models can better simulate the propagation of planetary wave activities in the troposphere forced by ENSO Modoki, whereas the other models produce significantly different results to those obtained from observations. Significance Statement This study found a significant connection between ENSO Modoki and the interannual variability of Antarctic stratospheric ozone in austral spring and investigated the underlying physical mechanisms in detail. In addition, the performances of CMIP6 models in simulating the impact of ENSO Modoki on the southern stratospheric polar vortex and ozone were evaluated. This study not only helps to further understand the characteristics of past Antarctic ozone changes but also helps developers improve the performance of models in simulating Antarctic stratospheric changes.

The response of aquatic ecosystems to the interactive effects of stratospheric ozone depletion, UV radiation, and climate change

Variations in stratospheric ozone and changes in the aquatic environment by climate change and human activity are modifying the exposure of aquatic ecosystems to UV radiation. These shifts in exposure have consequences for the distributions of species, biogeochemical cycles, and services provided by aquatic ecosystems. This Quadrennial Assessment presents the latest knowledge on the multi-faceted interactions between the effects of UV irradiation and climate change, and other anthropogenic activities, and how these conditions are changing aquatic ecosystems. Climate change results in variations in the depth of mixing, the thickness of ice cover, the duration of ice-free conditions and inputs of dissolved organic matter, all of which can either increase or decrease exposure to UV radiation. Anthropogenic activities release oil, UV filters in sunscreens, and microplastics into the aquatic environment that are then modified by UV radiation, frequently amplifying adverse effects on aquatic organisms and their environments. The impacts of these changes in combination with factors such as warming and ocean acidification are considered for aquatic micro-organisms, macroalgae, plants, and animals (floating, swimming, and attached). Minimising the disruptive consequences of these effects on critical services provided by the world’s rivers, lakes and oceans (freshwater supply, recreation, transport, and food security) will not only require continued adherence to the Montreal Protocol but also a wider inclusion of solar UV radiation and its effects in studies and/or models of aquatic ecosystems under conditions of the future global climate.Graphical abstract

Driving mechanisms for the El Niño–Southern Oscillation impact on stratospheric ozone

Abstract. While the impact of the El Niño–Southern Oscillation (ENSO) on the stratospheric circulation has been long recognized, its effects on stratospheric ozone have been less investigated. In particular, the impact on ozone of different ENSO flavors, eastern Pacific (EP) El Niño and central Pacific (CP) El Niño, and the driving mechanisms for the ozone variations have not been investigated to date. This study aims to explore these open questions by examining the anomalies in advective transport, mixing and chemistry associated with different El Niño flavors (EP and CP) and La Niña in the Northern Hemisphere in boreal winter. For this purpose, we use four 60-year ensemble members of the Whole Atmospheric Community Climate Model version 4. The results show a significant ENSO signal on the total column ozone (TCO) during EP El Niño and La Niña events. During EP El Niño events, TCO is significantly reduced in the tropics and enhanced at middle and high latitudes in boreal winter. The opposite response has been found during La Niña. Interestingly, CP El Niño has no significant impact on extratropical TCO, while its signal in the tropics is weaker than for EP El Niño events. The analysis of mechanisms reveals that advection through changes in tropical upwelling is the main driver for ozone variations in the lower tropical stratosphere, with a contribution of chemical processes above 30 hPa. At middle and high latitudes, stratospheric ozone variations related to ENSO result from combined changes in advection by residual circulation downwelling and changes in horizontal mixing linked to Rossby wave breaking and polar vortex anomalies. The impact of CP El Niño on the shallow branch of the residual circulation is small, and no significant impact is found on the deep branch.

Extreme Change Events of Stratospheric HCl and N2O in the Mid-Latitude Region of the Northern Hemisphere

Hydrogen chloride (HCl) is the main reservoir species of chlorine and chemical decomposition of nitrous oxide (N2O) is the primary source of NOx (=NO + NO2) in the stratosphere. Changes in stratospheric HCl and N2O play a critical role in modulating variations in stratospheric ozone. Thus, long-term trends in stratospheric HCl and N2O have been investigated in many studies, whereas short-term changes have not received enough attention. Here, using satellite observations and a chemical transport model, we found that two extreme change events for HCl and N2O in the Northern Hemisphere mid-latitude middle and lower stratosphere have occurred over past decades, which are characterized by a sharp increase in HCl and a decrease in N2O over several months; for example, HCl increased (and N2O decreased) by 0.135 ppbv (−33.352 ppbv) in 1987/1988 and by 0.196 ppbv (−28.553 ppbv) in 2010/2011. Further analysis shows that the extreme change events of stratospheric HCl and N2O in these two periods are closely related to anomalous residual circulation caused by the joint effects of the strong easterly phase of the semi-annual oscillation and the strong polar vortex.

Influence of Stratospheric Ozone Changes on Stratospheric Temperature Trends in Recent Decades

Associated with the recovery of stratospheric ozone, stratospheric cooling has decelerated since the late 1990s. This study investigates the contribution of ozone changes to the long-term stratospheric temperature trends in recent decades using satellite observations and model simulations. Observational analysis shows that total column ozone experienced little depletion in the Northern Hemisphere (NH) and weak recovery in the Southern Hemisphere (SH) in the period 1998–2020. It is found that the cease of stratospheric ozone depletion has reduced the stratospheric cooling from 1998 onwards, especially in the summer hemisphere. The correlation analysis indicates that the lower-stratospheric temperature is primarily regulated by ozone changes. The ozone recovery in the SH is associated with the weak warming in the lower stratosphere in the period 1998–2020 in summer. The impact of ozone changes is further isolated in the ozone-only experiments from CMIP6. We find that ozone depletion results in significant cooling in the summer hemisphere in the period 1979–1997, especially in the upper and lower stratosphere, while ozone recovery leads to significant warming in the summer hemisphere in the period 1998–2020 in the upper stratosphere. Our results also suggest that the wave-mean flow interactions associated with stratospheric ozone variations may play an important role in regulating the strength of polar vortex in winter.

Zonally asymmetric influences of the quasi-biennial oscillation on stratospheric ozone

Abstract. The quasi-biennial oscillation (QBO), as the dominant mode in the equatorial stratosphere, modulates the dynamical circulation and the distribution of trace gases in the stratosphere. While the zonal mean QBO signals in stratospheric ozone have been relatively well documented, the zonal (longitudinal) differences in the QBO ozone signals have been less studied. Using satellite-based total column ozone (TCO) data from 1979 to 2020, zonal mean ozone data from 1984 to 2020, three-dimensional (3-D) ozone data from 2002 to 2020, and ERA5 reanalysis and model simulations from 1979 to 2020, we demonstrate that the influences of the QBO (using a QBO index at 20 hPa) on stratospheric ozone are zonally asymmetric. The global distribution of stratospheric ozone varies significantly during different QBO phases. During QBO westerly (QBOW) phases, the TCO and stratospheric ozone are anomalously high in the tropics, while in the subtropics they are anomalously low over most of the areas, especially during the winter–spring of the respective hemisphere. This confirms the results from previous studies. In the polar region, the TCO and stratospheric ozone (50–10 hPa) anomalies are seasonally dependent and zonally asymmetric. During boreal winter (December–February, DJF), positive anomalies of the TCO and stratospheric ozone are evident during QBOW over the regions from North America to the North Atlantic (120∘ W–30∘ E), while significant negative anomalies exist over other longitudes in the Arctic. In boreal autumn (September–November, SON), the TCO and stratospheric ozone are anomalously high from Greenland to Eurasia (60∘ W–120∘ E) but anomalously low in other regions over the Arctic. Weak positive TCO and stratospheric ozone anomalies exist over the South America sector (90∘ W–30∘ E) of the Antarctic, while negative anomalies of the TCO and stratospheric ozone are seen in other longitudes. The consistent features of TCO and stratospheric ozone anomalies indicate that the QBO signals in TCO are mainly determined by the stratospheric ozone variations. Analysis of meteorological conditions indicates that the QBO ozone perturbations are mainly caused by dynamical transport and also influenced by chemical reactions associated with the corresponding temperature changes. QBO affects the geopotential height and the polar vortex and subsequently the transport of ozone-rich air from lower latitudes to the polar region, which therefore influences the ozone concentrations over the polar region. The geopotential height anomalies associated with QBO (QBOW–QBOE) are zonally asymmetric with clear wave number 1 features, which indicates that QBO influences the polar vortex and stratospheric ozone mainly by modifying the wave number 1 activities.

Effects of reanalysis forcing fields on ozone trends and age of air from a chemical transport model

Abstract. We use TOMCAT, a 3-dimensional (3D) offline chemical transport model (CTM) forced by two different meteorological reanalysis data sets (ERA-Interim and ERA5) from the European Centre for Medium-Range weather Forecasts (ECMWF) to analyse seasonal behaviour and long-term trends in stratospheric ozone and mean age of air. The model-simulated ozone variations are evaluated against two observation-based data sets. For total column ozone (TCO) comparisons, we use the Copernicus Climate Change Service (C3S) data (1979–2019), while for ozone profiles we use the Stratospheric Water and OzOne Satellite Homogenized (SWOOSH) data set (1984–2019). We find that the CTM simulations forced by ERA-Interim (A_ERAI) and ERA5 (B_ERA5) can both successfully reproduce the spatial and temporal variations in stratospheric ozone. Also, modelled TCO anomalies from B_ERA5 show better agreement with C3S than A_ERAI, especially in Northern Hemisphere (NH) mid latitudes, except that it gives somewhat larger positive biases (> 15 DU, Dobson units) during winter–spring seasons. Ozone profile comparisons against SWOOSH data show larger differences between the two simulations. In the lower stratosphere, ozone differences can be directly attributed to the representation of dynamical processes, whereas in the upper stratosphere they can be directly linked to the differences in temperatures between ERAI and ERA5 data sets. Although TCO anomalies from B_ERA5 show relatively better agreement with C3S compared to A_ERAI, a comparison with SWOOSH data does not confirm that B_ERA5 performs better at simulating the variations in the stratospheric ozone profiles. We employ a multivariate regression model to quantify the TCO and ozone profile trends before and after peak stratospheric halogen loading in 1997. Our results show that, compared to C3S, TCO recovery trends (since 1998) in simulation B_ERA5 are significantly overestimated in the Southern Hemisphere (SH) mid latitudes, while for A_ERAI in the NH mid latitudes, simulated ozone trends remain negative. Similarly, in the lower stratosphere, B_ERA5 shows positive ozone recovery trends for both NH and SH mid latitudes. In contrast, both SWOOSH and A_ERAI show opposite (negative) trends in the NH mid latitudes. Furthermore, we analyse age of air (AoA) trends to diagnose transport differences between the two reanalysis data sets. Simulation B_ERA5 shows a positive AoA trend after 1998 and somewhat older age in the NH lower stratosphere compared to A_ERAI, indicating that a slower Brewer–Dobson circulation does not translate into reduced wintertime ozone buildup in the NH extratropical lower stratosphere. Overall, our results show that models forced by the most recent ERA5 reanalyses may not yet be capable of reproducing observed changes in stratospheric ozone, particularly in the lower stratosphere.

The Simplified Chemistry-Dynamical Model (SCDM V1.0)

Abstract. Recent observational and modeling studies show that variations of stratospheric ozone and the resulting interaction between ozone and the stratospheric circulation play an important role in surface weather and climate. However, in many cases, computationally expensive coupled chemistry models have been used to study these effects. Here, we demonstrate how a much simpler idealized general circulation model (GCM) can be used for studying the impact of interactive stratospheric ozone on the circulation. The model, named Simplified Chemistry-Dynamical Model (SCDM V1.0), is constructed from a preexisting idealized GCM, into which a simplified linear ozone scheme and a parameterization for the shortwave radiative effects of ozone are implemented. The distribution and variability of stratospheric ozone simulated by the new model are in good agreement with the MERRA2 reanalysis, even for extreme circulation events such as Arctic stratospheric sudden warmings. The model thus represents a promising new tool for the study of ozone–circulation interaction in the stratosphere and its associated effects on tropospheric weather and climate.

A global ozone profile climatology for satellite retrieval algorithms based on Aura MLS measurements and the MERRA-2 GMI simulation

Abstract. A new atmospheric ozone profile climatology has been constructed by combining daytime ozone profiles from the Aura Microwave Limb Sounder (MLS) and Modern-Era Retrospective Analysis for Research Applications version 2 (MERRA-2) Global Modeling Initiative (GMI) model simulation (M2GMI). The MLS and M2GMI ozone profiles are merged between 13 and 17 km (∼159 and 88 hPa), with MLS used for stratospheric and GMI for primarily tropospheric levels. The time record for profiles from MLS and GMI is August 2004–December 2016. The derived seasonal climatology consists of monthly zonal-mean ozone profiles in 5∘ latitude bands from 90∘ S to 90∘ N covering altitudes (in Z* log-pressure altitude) from zero to 80 km in 1 km increments. This climatology can be used as a priori information in satellite ozone retrievals, in atmospheric radiative transfer studies, and as a baseline to compare with other measured or model-simulated ozone. The MLS/GMI seasonal climatology shows a number of improvements compared with previous ozone profile climatologies based on MLS and ozonesonde measurements. These improvements are attributed mostly to continuous daily global coverage of GMI tropospheric ozone compared with sparse regional measurements from sondes. In addition to the seasonal climatology, we also derive an additive climatology to account for interannual variability in stratospheric zonal-mean ozone profiles which is based on a rotated empirical orthogonal function (REOF) analysis of Aura MLS ozone profiles. This REOF climatology starts in 1970 and captures most of the interannual variability in global stratospheric ozone including quasi-biennial oscillation (QBO) signatures.

The Diurnal Variation in Stratospheric Ozone from MACC Reanalysis, ERA-Interim, WACCM, and Earth Observation Data: Characteristics and Intercomparison

In this study, we compare the diurnal variation in stratospheric ozone of the MACC (Monitoring Atmospheric Composition and Climate) reanalysis, ECMWF Reanalysis Interim (ERA-Interim), and the free-running WACCM (Whole Atmosphere Community Climate Model). The diurnal variation of stratospheric ozone results from photochemical and dynamical processes depending on altitude, latitude, and season. MACC reanalysis and WACCM use similar chemistry modules and calculate a similar diurnal cycle in ozone when it is caused by a photochemical variation. The results of the two model systems are confirmed by observations of the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) experiment and three selected sites of the Network for Detection of Atmospheric Composition Change (NDACC) at Mauna Loa, Hawaii (tropics), Bern, Switzerland (midlatitudes), and Ny-Ålesund, Svalbard (high latitudes). On the other hand, the ozone product of ERA-Interim shows considerably less diurnal variation due to photochemical variations. The global maxima of diurnal variation occur at high latitudes in summer, e.g., near the Arctic NDACC site at Ny-Ålesund, Svalbard. The local OZORAM radiometer observes this effect in good agreement with MACC reanalysis and WACCM. The sensed diurnal variation at Ny-Ålesund is up to 8% (0.4 ppmv) due to photochemical variations in summer and negligible during the dynamically dominated winter. However, when dynamics play a major role for the diurnal ozone variation as in the lower stratosphere (100–20 hPa), the reanalysis models ERA-Interim and MACC which assimilate data from radiosondes and satellites outperform the free-running WACCM. Such a domain is the Antarctic polar winter where a surprising novel feature of diurnal variation is indicated by MACC reanalysis and ERA-Interim at the edge of the polar vortex. This effect accounts for up to 8% (0.4 ppmv) in both model systems. In summary, MACC reanalysis provides a global description of the diurnal variation of stratospheric ozone caused by dynamics and photochemical variations. This is of high interest for ozone trend analysis and other research which is based on merged satellite data or measurements at different local time.

Three-Year Observations of Ozone Columns over Polar Vortex Edge Area above West Antarctica

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.

Small-scale variability of stratospheric ozone during the sudden stratospheric warming 2018/2019 observed at Ny-Ålesund, Svalbard

Abstract. 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.

Impact of Interannual Ozone Variations on the Downward Coupling of the 2002 Southern Hemisphere Stratospheric Warming

AbstractThe Southern Hemisphere experienced its first recorded major sudden stratospheric warming during September 2002, which subsequently resulted in strong low polarity of the Southern Annular Mode (low SAM) and extreme daily mean maximum temperatures and low rainfall over eastern Australia during October 2002. The warming and weakening of the polar vortex were accompanied by anomalously high values of polar stratospheric ozone, which possibly could have constructively sustained the weakened vortex and subsequent development of low SAM. We explore the impact of this ozone variation by conducting an idealized forecast experiment using the Australian Bureau of Meteorology's operational subseasonal to seasonal prediction system (Australian Community Climate and Earth System Simulator‐Seasonal forecast system version 1, ACCESS‐S1), whose atmospheric model well resolves the stratosphere. The ACCESS‐S1 control forecasts are generated with prescribed climatological monthly mean ozone, whereas the observed monthly mean ozone during 2002 is prescribed during the forecast for the experiment. While the control forecasts initialized on 1 August 2002 demonstrate good skill in predicting the weakening of the polar vortex and the resultant occurrence of low SAM during October, the extremity of the SAM anomaly and associated extreme high temperatures and low rainfall over eastern Australia were significantly underpredicted. Prescribing the observed ozone results in more realistic weakening of the stratospheric vortex and stronger development of low SAM and extreme warm conditions in eastern Australia during October 2002. These results suggest that polar stratospheric ozone variations are a potential source of long lead climate variability, which can be tapped with future ACCESS‐S development.

Model-based climatology of diurnal variability in stratospheric ozone as a data analysis tool

Abstract. Observational studies of stratospheric ozone often involve data from multiple instruments that measure the ozone at different times of day. There has been an increased awareness of the potential impact of the diurnal cycle when interpreting measurements of stratospheric ozone at altitudes in the mid- to upper stratosphere. To address this issue, we present a climatological representation of diurnal variations in ozone with a 30 min temporal resolution as a function of latitude, pressure and month, based on output from the Goddard Earth Observing System (GEOS) general circulation model coupled to the NASA Global Modeling Initiative (GMI) chemistry package (known as the GEOS-GMI chemistry model). This climatology can be applied to a wide range of ozone data analyses, including data intercomparisons, data merging and the analysis of data from a single platform in a non-sun-synchronous orbit. We evaluate the diurnal climatology by comparing mean differences between ozone measurements made at different local solar times to the differences predicted by the diurnal model. The ozone diurnal cycle is a complicated function of latitude, pressure and season, with variations of less than 5 % in the tropics and subtropics, increasing to more than 15 % near the polar day terminator in the upper stratosphere. These results compare well with previous modeling simulations and are supported by similar size variations in satellite observations. We present several example applications of the climatology in currently relevant data studies. We also compare this diurnal climatology to the diurnal signal from a previous iteration of the free-running GEOS Chemistry Climate Model (GEOSCCM) and to the ensemble runs of GEOS-GMI to test the sensitivity of the model diurnal cycle to changes in model formulation and simulated time period.

Numerical Modeling of the Natural and Manmade Factors Influencing Past and Current Changes in Polar, Mid-Latitude and Tropical Ozone

A chemistry–climate model of the lower and middle atmosphere is used to compare the role of natural and anthropogenic factors in the observed variability of stratospheric ozone. Numerical experiments have been carried out on several scenarios of separate and combined effects of solar activity, stratospheric aerosol, sea surface temperature, greenhouse gases, and ozone-depleting substances emissions on ozone for the period from 1979 to 2020. Simulations for the past and present periods are compared to the results of ground-based and satellite observations. Estimates of observed trends in column total ozone for the entire period 1980–2018 and separately for the late twentieth and early twenty-first century are presented.

Interannual Variation of Upper Stratospheric Ozone in the Northern Midlatitudes in Early Winter Caused by Planetary Waves

AbstractOzone mixing ratios in the upper stratosphere, observed with a millimeter‐wave radiometer at Rikubetsu (43.46°N, 143.77°E), Japan, from November 1999 to February 2017 showed both interannual and seasonal variation, which was characterized by a winter maximum and a summer minimum. During the study period, the summer minima were nearly constant whereas the winter maxima varied interannually and also displayed short‐term variability. The observed ozone mixing ratios at 1 hPa were anticorrelated with temperature at 1 hPa from MERRA‐2 data. The slope of the relationship between the logarithm of ozone concentration and the reciprocal of temperature differed between winter data and both summer and annual data. Therefore, we inferred that both chemistry and dynamics affect short‐term variation of ozone mixing ratios in winter. We then examined the contribution of the polar vortex to interannual variations in ozone and temperature at 1 hPa. When the polar vortex was strong, wave number‐1 planetary waves at high latitude propagated toward the midlatitudes instead of vertically. The vertical component of the wave number‐1 Eliassen‐Palm flux along 43°N at 1 hPa was strongly correlated with zonal mean zonal wind along 60°N at 50 hPa. When the zonal mean westerly wind was strong in December, upper stratospheric (~1 hPa) temperatures over Rikubetsu and over a point on the opposite side of the globe (by longitude) were significantly lower and higher, respectively, than the climatological temperature. Thus, planetary wave propagation related to zonal mean westerly wind strength induced early winter interannual variation in upper stratospheric ozone in the midlatitudes.

On the Importance of Interactive Ozone Chemistry in Earth‐System Models for Studying Mesophere‐Lower Thermosphere Tidal Changes during Sudden Stratospheric Warmings

AbstractWe use the CESM2‐Whole Atmosphere Community Climate Model, to study the importance of ozone in the vertical coupling between lower and upper atmosphere during sudden stratospheric warmings (SSWs). During SSWs, the build up of stratospheric ozone concentrations at tropical latitudes and its increased asymmetrical distribution carries the potential to affect the generation of migrating and nonmigrating semidiurnal solar tides. Much of the upper atmospheric variability associated with SSWs is known to be driven by large changes in the vertically propagating semidiurnal migrating (SW2) and nonmigrating (SW1 and SW3) solar tides. In this study, we investigate the effect of stratospheric ozone variability during SSWs on these solar tides. For this purpose, a case study of the 2009 SSW event is carried out using the WACCM with two distinct simulation setups. In the first setup, the ozone concentrations are interactively calculated in the model and resemble the ozone observations during the 2009 SSW event, while in the second setup, the ozone concentrations are specified using zonal mean values. We constrain both of the simulations to the Modern‐Era Retrospective Analysis for Research and Applications‐2 reanalysis so that the background atmosphere through which the solar tides propagate are almost identical in each case. Following the onset of the SSW, we find that in the vicinity of the peak enhancements of SW1, SW2, and SW3 in the mesosphere‐lower thermosphere (MLT), the amplitudes of these semidiurnal solar tides are approximately about 15–50% larger for the simulation with interactive ozone as compared with the one with prescribed ozone, indicating that the stratospheric ozone variability plays an important role in driving semidiurnal solar tidal changes during SSWs.