scholarly journals Nonlinear response of modeled stratospheric ozone to changes in greenhouse gases and ozone depleting substances in the recent past

2015 ◽  
Vol 15 (6) ◽  
pp. 9253-9291 ◽  
Author(s):  
S. Meul ◽  
S. Oberländer-Hayn ◽  
J. Abalichin ◽  
U. Langematz
Keyword(s):  
Greenhouse Gases ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Nonlinear Effects ◽  
Polar Regions ◽  
Recent Past ◽  
Residual Circulation ◽  
Nonlinear Processes ◽  
Ozone Depleting Substances ◽  
The Impact

Abstract. In the recent past, the evolution of stratospheric ozone (O3) was affected by both increasing ozone depleting substances (ODSs) and greenhouse gases (GHGs). The impact of the single forcings on O3 is well known. Interactions between the simultaneously increased GHG and ODS concentrations, however, can occur and lead to nonlinear O3 changes. In this study, we investigate if nonlinear processes have affected O3 changes between 1960 and 2000. This is done with an idealized set of timeslice simulations with the chemistry–climate model (CCM) EMAC. Nonlinearity leads to a net reduction of ozone decrease throughout the stratosphere, with a maximum of 1.2% at 3 hPa. The total ozone column loss between 1960 and 2000 that is mainly attributed to the ODS increase is mitigated in the extra-polar regions by up to 1.1% due to nonlinear processes. A separation of the O3 changes into the contribution from chemistry and transport shows that nonlinear interactions occur in both. In the upper stratosphere a reduced efficiency of the ClOx-catalysed O3 loss chiefly causes the nonlinear O3 increase. An enhanced formation of halogen reservoir species through the reaction with methane (CH4) reduces the abundance of halogen radicals significantly. The temperature induced deceleration of the O3 loss reaction rate in the Chapman cycle is reduced, which leads to a nonlinear O3 decrease and counteracts the increase due to ClOx. Nonlinear effects on the NOx abundance cause hemispheric asymmetric nonlinear changes of the O3 loss. Nonlinear changes in O3 transport occur in particular in the Southern Hemisphere (SH) during the months September to November. Here, the residual circulation is weakened in the lower stratosphere, which goes along with a reduced O3 transport from the tropics to high latitudes. Thus, O3 decreases in the SH polar region, but increases in the SH midlatitudes.

scholarly journals Nonlinear response of modelled stratospheric ozone to changes in greenhouse gases and ozone depleting substances in the recent past

2015 ◽  
Vol 15 (12) ◽  
pp. 6897-6911 ◽  
Author(s):  
S. Meul ◽  
S. Oberländer-Hayn ◽  
J. Abalichin ◽  
U. Langematz
Keyword(s):  
Greenhouse Gases ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Polar Regions ◽  
Recent Past ◽  
Residual Circulation ◽  
Nonlinear Processes ◽  
The Past ◽  
Ozone Depleting Substances ◽  
The Impact

Abstract. In the recent past, the evolution of stratospheric ozone (O3) was affected by both increasing ozone depleting substances (ODSs) and greenhouse gases (GHGs). The impact of the single forcings on O3 is well known. Interactions between the simultaneously increased GHG and ODS concentrations, however, can occur and lead to nonlinear O3 changes. In this study, we investigate if nonlinear processes have affected O3 changes between 1960 and 2000. This is done with an idealised set of time slice simulations with the chemistry-climate model EMAC. Due to nonlinearity the past ozone loss is diminished throughout the stratosphere, with a maximum reduction of 1.2 % at 3 hPa. The total ozone column loss between 1960 and 2000 that is mainly attributed to the ODS increase is mitigated in the extra-polar regions by up to 1.1 % due to nonlinear processes. A separation of the O3 changes into the contribution from chemistry and transport shows that nonlinear interactions occur in both. In the upper stratosphere a reduced efficiency of the ClOx-catalysed O3 loss chiefly causes the nonlinear O3 increase. An enhanced formation of halogen reservoir species through the reaction with methane (CH4) reduces the abundance of halogen radicals significantly. The temperature-induced deceleration of the O3 loss reaction rate in the Chapman cycle is reduced, which leads to a nonlinear O3 decrease and counteracts the increase due to ClOx. Nonlinear effects on the NOx abundance cause hemispheric asymmetric nonlinear changes of the O3 loss. Nonlinear changes in O3 transport occur in particular in the Southern Hemisphere (SH) during the months September to November. Here, the residual circulation is weakened in the lower stratosphere, which goes along with a reduced O3 transport from the tropics to high latitudes. Thus, O3 decreases in the SH polar region but increases in the SH midlatitudes. The existence of nonlinearities implies that future ozone change due to ODS decline slightly depends on the prevailing GHG concentrations. Therefore the future ozone evolution will not simply be a reversal of the past.

Atmospheric impacts of short-lived chlorinated species over the recent past: a chemistry-climate perspective

2021 ◽  
Author(s):  
Ewa Bednarz ◽  
Ryan Hossaini ◽  
Luke Abraham ◽  
Peter Braesicke ◽  
Martyn Chipperfield
Keyword(s):  
Atmospheric Chemistry ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Lower Boundary ◽  
Montreal Protocol ◽  
Recent Past ◽  
Substantial Impact ◽  
Ozone Depleting Substances ◽  
The Impact

<p>The emissions of most long-lived halogenated ozone-depleting substances (ODSs) are now decreasing, owing to controls on their production introduced by Montreal Protocol and its amendments. However, short-lived halogenated compounds can also have substantial impact on atmospheric chemistry, including stratospheric ozone, particularly if emitted near climatological uplift regions. It has recently become evident that emissions of some chlorinated very short-lived species (VSLSs), such as chloroform (CHCl<sub>3</sub>) and dichloromethane (CH<sub>2</sub>Cl<sub>2</sub>), could be larger than previously believed and increasing, particularly in Asia. While these may exert a significant influence on atmospheric chemistry and climate, their impacts remain poorly characterised. </p><p> </p><p>We address this issue using the UM-UKCA chemistry-climate model (CCM). While not only the first, to our knowledge, model study addressing this problem using a CCM, it is also the first such study employing a whole atmosphere model, thereby simulating the tropospheric Cl-VSLSs emissions and the resulting stratospheric impacts in a fully consistent manner. We use a newly developed Double-Extended Stratospheric-Tropospheric (DEST) chemistry scheme, which includes emissions of all major chlorinated and brominated VSLSs alongside an extended treatment of long-lived ODSs.</p><p> </p><p>We examine the impacts of rising Cl-VSLSs emissions on atmospheric chlorine tracers and ozone, including their long-term trends. We pay particular attention to the role of ‘nudging’, as opposed to the free-running model set up, for the simulated Cl-VSLSs impacts, thereby demostrating the role of atmospheric dynamics in modulating the atmospheric responses to Cl-VSLSs. In addition, we employ novel estimates of Cl-VSLS emissions over the recent past and compare the results with the simulations that prescribe Cl-VSLSs using simple lower boundary conditions. This allows us to demonstrate the impact such choice has on the dominant location and seasonality of the Cl-VSLSs transport into the stratosphere.</p>

scholarly journals Contributions to stratospheric ozone changes from ozone depleting substances and greenhouse gases

2010 ◽  
Vol 10 (4) ◽  
pp. 9647-9694 ◽  
Author(s):  
D. A. Plummer ◽  
J. F. Scinocca ◽  
T. G. Shepherd ◽  
M. C. Reader ◽  
A. I. Jonsson
Keyword(s):  
Greenhouse Gases ◽  
21St Century ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Three Dimensional ◽  
Ocean Model ◽  
Residual Circulation ◽  
Chemical Effects ◽  
Ozone Depleting Substances ◽  
Year 2000

Abstract. A state-of-the-art chemistry climate model coupled to a three-dimensional ocean model is used to produce three experiments, all seamlessly covering the period 1950–2100, forced by different combinations of long-lived Greenhouse Gases (GHGs) and Ozone Depleting Substances (ODSs). The experiments are designed to investigate the mechanisms by which GHGs and ODSs affect the evolution of ozone, including changes in the Brewer-Dobson circulation of the stratosphere and cooling of the upper stratosphere by CO2. Separating the effects of GHGs and ODSs on ozone, we find the decrease in upper stratospheric ozone from ODSs up to the year 2000 is approximately 30% larger than the actual decrease in ozone due to the offsetting effects of cooling by increased CO2. Over the 21st century, as ODSs decrease, continued cooling from CO2 is projected to account for more than 50% of the projected increase in upper stratospheric ozone. Changes below 20 hPa show a redistribution of ozone from tropical to extra-tropical latitudes with an increase in the Brewer-Dobson circulation, while globally averaged the amount of ozone below 20 hPa decreases over the 21st century. Further analysis by linear regression shows that changes associated with GHGs do not appreciably alter the recovery of stratospheric ozone from the effects of ODSs; over much of the stratosphere ozone recovery follows the decline of halogen concentrations within statistical uncertainty, though the lower polar stratosphere of the Southern Hemisphere is an exception with ozone concentrations recovering more slowly than indicated by the halogen concentrations. These results also reveal the degree to which climate change, and stratospheric CO2 cooling in particular, mutes the chemical effects of N2O on ozone in the standard future scenario used for the WMO Ozone Assessment. Increases in the residual circulation of the atmosphere and chemical effects from CO2 cooling more than halve the increase in reactive nitrogen in the mid to upper stratosphere that results from the specified increase in N2O between 1950 and 2100.

Improved characterisation of the impact of chlorinated VSLSs on atmospheric chemistry and climate: past, present and future

2020 ◽  
Author(s):  
Ewa Bednarz ◽  
Ryan Hossaini ◽  
Luke Abraham ◽  
Martyn Chipperfield
Keyword(s):  
Atmospheric Chemistry ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Montreal Protocol ◽  
Recent Past ◽  
Substantial Impact ◽  
Emissions Scenarios ◽  
Ozone Depleting Substances ◽  
The Impact ◽  
Future Emissions

<p>The emissions of most long-lived halogenated ozone-depleting substances (ODSs) are now decreasing, owing to controls on their production introduced by Montreal Protocol and its amendments. However, short-lived halogenated compounds can also have substantial impact on atmospheric chemistry, including stratospheric ozone, particularly if emitted near climatological uplift regions. It has recently become evident that emissions of some chlorinated very short-lived species (VSLSs), such as chloroform (CHCl<sub>3</sub>) and dichloromethane (CH<sub>2</sub>Cl<sub>2</sub>), could be larger than previously believed and increasing, particularly in Asia. While these may exert a significant influence on atmospheric chemistry and climate, their impacts remain poorly characterised.</p><p> </p><p>We address this issue using the UM-UKCA chemistry-climate model. We use a newly developed Double-Extended Stratospheric-Tropospheric (DEST) chemistry scheme, which includes emissions of all major chlorinated and brominated VSLSs alongside an extended treatment of long-lived ODSs. Employing novel estimates of Cl-VSLS emissions we show model results regarding the atmospheric impacts of chlorinated VSLSs over the recent past (2000-present), with a focus on stratospheric ozone and HCl trends. Finally, we introduce our plans regarding examining the impacts of chlorinated VSLSs under a range of potential future emissions scenarios; the results of which will be directly relevant for the next WMO/UNEP assessment.</p>

scholarly journals Quantifying the contributions to stratospheric ozone changes from ozone depleting substances and greenhouse gases

2010 ◽  
Vol 10 (18) ◽  
pp. 8803-8820 ◽  
Author(s):  
D. A. Plummer ◽  
J. F. Scinocca ◽  
T. G. Shepherd ◽  
M. C. Reader ◽  
A. I. Jonsson
Keyword(s):  
Greenhouse Gases ◽  
21St Century ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Three Dimensional ◽  
Ocean Model ◽  
Residual Circulation ◽  
Total Column Ozone ◽  
Chemical Effects ◽  
Ozone Depleting Substances

Abstract. A state-of-the-art chemistry climate model coupled to a three-dimensional ocean model is used to produce three experiments, all seamlessly covering the period 1950–2100, forced by different combinations of long-lived Greenhouse Gases (GHGs) and Ozone Depleting Substances (ODSs). The experiments are designed to quantify the separate effects of GHGs and ODSs on the evolution of ozone, as well as the extent to which these effects are independent of each other, by alternately holding one set of these two forcings constant in combination with a third experiment where both ODSs and GHGs vary. We estimate that up to the year 2000 the net decrease in the column amount of ozone above 20 hPa is approximately 75% of the decrease that can be attributed to ODSs due to the offsetting effects of cooling by increased CO2. Over the 21st century, as ODSs decrease, continued cooling from CO2 is projected to account for more than 50% of the projected increase in ozone above 20 hPa. Changes in ozone below 20 hPa show a redistribution of ozone from tropical to extra-tropical latitudes with an increase in the Brewer-Dobson circulation. In addition to a latitudinal redistribution of ozone, we find that the globally averaged column amount of ozone below 20 hPa decreases over the 21st century, which significantly mitigates the effect of upper stratospheric cooling on total column ozone. Analysis by linear regression shows that the recovery of ozone from the effects of ODSs generally follows the decline in reactive chlorine and bromine levels, with the exception of the lower polar stratosphere where recovery of ozone in the second half of the 21st century is slower than would be indicated by the decline in reactive chlorine and bromine concentrations. These results also reveal the degree to which GHG-related effects mute the chemical effects of N2O on ozone in the standard future scenario used for the WMO Ozone Assessment. Increases in the residual circulation of the atmosphere and chemical effects from CO2 cooling more than halve the increase in reactive nitrogen in the mid to upper stratosphere that results from the specified increase in N2O between 1950 and 2100.

Numerical modeling of the natural and anthropogenic factors influence on the past and future changes in polar, mid-latitude and tropical ozone

2020 ◽  
Author(s):  
Sergei Smyshlyaev ◽  
Polina Blakitnaya ◽  
Maxim Motsakov ◽  
Vener Galin
Keyword(s):  
Solar Activity ◽  
Greenhouse Gases ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Stratospheric Ozone ◽  
Stratospheric Aerosol ◽  
Anthropogenic Factors ◽  
The Past ◽  
Ozone Depleting Substances ◽  
Natural And Anthropogenic Factors

<p>The INM RAS – RSHU chemistry-climate model of the lower and middle atmosphere is used to compare the role of natural and anthropogenic factors in the observed and expected 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 2050. Simulations for the past and present periods are compared to the results of ground-based and satellite observations, as well as MERRA and ERA-Interim re-analysis. Estimation of future ozone changes are based on different scenarios of changes in solar activity and emissions of ozone-depleting substances and greenhouse gases, as well as the possibility of large volcanic aerosol emissions at different periods of time.</p>

scholarly journals Detectability of the Impacts of Ozone Depleting Substances and Greenhouse Gases upon Stratospheric Ozone Accounting for Nonlinearities in Historical Forcings

2017 ◽  
Author(s):  
Justin Bandoro ◽  
Susan Solomon ◽  
Benajmin D. Santer ◽  
Douglas E. Kinnison ◽  
Michael J. Mills
Keyword(s):  
Greenhouse Gases ◽  
Climate Model ◽  
Linear Trend ◽  
Stratospheric Ozone ◽  
Global Changes ◽  
Response Patterns ◽  
Pattern Similarity ◽  
Ozone Depleting Substances ◽  
The Individual ◽  
Observational Record

Abstract. We perform a formal attribution study of upper and lower stratospheric ozone changes using observations together with simulations from the Whole Atmosphere Community Climate Model. Historical model simulations were used to estimate the zonal-mean response patterns (fingerprints) to combined forcing by ozone depleting substances (ODS) and well-mixed greenhouse gases (GHG), as well as to the individual forcing by each factor. Trends in the similarity between the searched-for fingerprints and homogenized observations of stratospheric ozone were compared to trends in pattern similarity between the fingerprints and the internally and naturally generated variability inferred from long control runs. This yields estimated signal-to-noise (S/N) ratios for each of the three fingerprints (ODS, GHG, and ODS+GHG). In both the upper stratosphere (defined in this paper as 1 to 10 hPa) and lower stratosphere (40 to 100 hPa), the spatial fingerprints of the ODS+GHG and ODS only patterns were consistently detectable not only during the era of maximum ozone depletion, but also throughout the observational record (1984–2016). Furthermore, we develop a fingerprint attribution method to account for forcings whose time evolutions are markedly nonlinear over the observational record. When the nonlinearity of the time evolution of the ODS and ODS+GHG signals are used in the trend regression, we find that the S/N ratios obtained with the stratospheric ODS and ODS+GHG fingerprints are enhanced relative to standard linear trend analysis. With this method, the complete observational record can be used in the S/N analysis, without applying piece-wise linear regression and introducing arbitrary break points. The GHG-driven fingerprint of ozone changes was not statistically identifiable in the either the upper or lower stratospheric SWOOSH data, irrespective of the method used. Use of the nonlinear signal method, instead of directly operating on ozone trends, also reduces the detection time – the estimate of the date at which ODS and GHG impacts on ozone can be formally identified. In the WACCM future simulations, the GHG signal is statistically identifiable between 2020–2030. Our findings demonstrate the importance of continued stratospheric ozone monitoring to improve estimates of the contributions of ODS and GHG forcing to global changes in stratospheric ozone.

Quantifying the Summertime Response of the Austral Jet Stream and Hadley Cell to Stratospheric Ozone and Greenhouse Gases

2014 ◽  
Vol 27 (14) ◽  
pp. 5538-5559 ◽  
Author(s):  
Edwin P. Gerber ◽  
Seok-Woo Son
Keyword(s):  
Greenhouse Gases ◽  
Climate Sensitivity ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Coupled Model ◽  
Hadley Cell ◽  
Dynamical Response ◽  
Jet Stream ◽  
Temperature Trends ◽  
The Impact

Abstract The impact of anthropogenic forcing on the summertime austral circulation is assessed across three climate model datasets: the Chemistry–Climate Model Validation activity 2 and phases 3 and 5 of the Coupled Model Intercomparison Project. Changes in stratospheric ozone and greenhouse gases impact the Southern Hemisphere in this season, and a simple framework based on temperature trends in the lower polar stratosphere and upper tropical troposphere is developed to separate their effects. It suggests that shifts in the jet stream and Hadley cell are driven by changes in the upper-troposphere–lower-stratosphere temperature gradient. The mean response is comparable in the three datasets; ozone has chiefly caused the poleward shift observed in recent decades, while ozone and greenhouse gases largely offset each other in the future. The multimodel mean perspective, however, masks considerable spread in individual models’ circulation projections. Spread resulting from differences in temperature trends is separated from differences in the circulation response to a given temperature change; both contribute equally to uncertainty in future circulation trends. Spread in temperature trends is most associated with differences in polar stratospheric temperatures, and could be narrowed by reducing uncertainty in future ozone changes. Differences in tropical temperatures are also important, and arise from both uncertainty in future emissions and differences in models’ climate sensitivity. Differences in climate sensitivity, however, only matter significantly in a high emissions future. Even if temperature trends were known, however, differences in the dynamical response to temperature changes must be addressed to substantially narrow spread in circulation projections.

scholarly journals Estimates of Ozone Return Dates from Chemistry-Climate Model Initiative Simulations

2018 ◽  
Author(s):  
Sandip Dhomse ◽  
Douglas Kinnison ◽  
Martyn P. Chipperfield ◽  
Irene Cionni ◽  
Michaela Hegglin ◽  
...  
Keyword(s):  
Climate Model ◽  
Stratospheric Ozone ◽  
Tropospheric Chemistry ◽  
The Arctic ◽  
Polar Regions ◽  
Total Column Ozone ◽  
Column Ozone ◽  
The Tropics ◽  
The Impact ◽  
Total Column

Abstract. We analyse simulations performed for the Chemistry-Climate Model Initiative (CCMI) to estimate the return dates of the stratospheric ozone layer from depletion caused by anthropogenic stratospheric chlorine and bromine. We consider a total of 155 simulations from 20 models, including a range of sensitivity studies which examine the impact of climate change on ozone recovery. For the control simulations (unconstrained by nudging towards analysed meteorology) there is a large spread (±20 DU in the global average) in the predictions of the absolute ozone column. Therefore, the model results need to be adjusted for biases against historical data. Also, the interannual variability in the model results need to be smoothed in order to provide a reasonably narrow estimate of the range of ozone return dates. Consistent with previous studies, but here for a Representative Concentration Pathway (RCP) of 6.0, these new CCMI simulations project that global total column ozone will return to 1980 values in 2047 (with a 1-σ uncertainty of 2042–2052). At Southern Hemisphere mid-latitudes column ozone is projected to return to 1980 values in 2046 (2042–2050), and at Northern Hemisphere mid-latitudes in 2034 (2024–2044). In the polar regions, the return dates are 2062 (2055–2066) in the Antarctic in October and 2035 (2025–2040) in the Arctic in March. The earlier return dates in the NH reflect the larger sensitivity to dynamical changes. Our estimates of return dates are later than those presented in the 2014 Ozone Assessment by approximately 5–15 years, depending on the region. In the tropics only around half the models predict a return to 1980 values, at around 2040, while the other half do not reach this value. All models show a negative trend in tropical total column ozone towards the end of the 21st century. The CCMI models generally agree in their simulation of the time evolution of stratospheric chlorine, which is the main driver of ozone loss and recovery. However, there are a few outliers which show that the multi-model mean results for ozone recovery are not as tightly constrained as possible. Throughout the stratosphere the spread of ozone return dates to 1980 values between models tends to correlate with the spread of the return of inorganic chlorine to 1980 values. In the upper stratosphere, greenhouse gas-induced cooling speeds up the return by about 10–20 years. In the lower stratosphere, and for the column, there is a more direct link in the timing of the return dates, especially for the large Antarctic depletion. Comparisons of total column ozone between the models is affected by different predictions of the evolution of tropospheric ozone within the same scenario, presumably due to differing treatment of tropospheric chemistry. Therefore, for many scenarios, clear conclusions can only be drawn for stratospheric ozone columns rather than the total column. As noted by previous studies, the timing of ozone recovery is affected by the evolution of N2O and CH4. However, the effect in the simulations analysed here is small and at the limit of detectability from the few realisations available for these experiments compared to internal model variability. The large increase in N2O given in RCP 6.0 extends the ozone return globally by ~ 15 years relative to N2O fixed at 1960 abundances, mainly because it allows tropical column ozone to be depleted. The effect in extratropical latitudes is much smaller. The large increase in CH4 given in the RCP 8.5 scenario compared to RCP 6.0 also changes ozone return by ~ 15 years, again mainly through its impact in the tropics. For future assessments of single forcing or combined effects of CO2, CH4, and N2O on the stratospheric column ozone return dates, this work suggests that is more important to have multi-member (at least 3) ensembles for each scenario from each established participating model, rather than a large number of individual models.

scholarly journals The representation of solar cycle signals in stratospheric ozone. Part II: Analysis of global models

2017 ◽  
Author(s):  
Amanda C. Maycock ◽  
Katja Matthes ◽  
Susann Tegtmeier ◽  
Hauke Schmidt ◽  
Rémi Thiéblemont ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Solar Irradiance ◽  
Climate Models ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Temperature Response ◽  
Solar Variability ◽  
High Latitudes ◽  
Stratospheric Temperature ◽  
The Impact

Abstract. The impact of changes in incoming solar irradiance on stratospheric ozone abundances should be included in climate model simulations to fully capture the atmospheric response to solar variability. This study presents the first systematic comparison of the solar-ozone response (SOR) during the 11 year solar cycle amongst different chemistry-climate models (CCMs) and ozone databases specified in climate models that do not include chemistry. We analyse the SOR in eight CCMs from the WCRP/SPARC Chemistry-Climate Model Initiative (CCMI-1) and compare these with three ozone databases: the Bodeker Scientific database, the SPARC/AC&C database for CMIP5, and the SPARC/CCMI database for CMIP6. The results reveal substantial differences in the representation of the SOR between the CMIP5 and CMIP6 ozone databases. The peak amplitude of theSOR in the upper stratosphere (1–5 hPa) decreases from 5 % to 2 % between the CMIP5 and CMIP6 databases. This difference is because the CMIP5 database was constructed from a regression model fit to satellite observations, whereas the CMIP6 database is constructed from CCM simulations, which use a spectral solar irradiance (SSI) dataset with relatively weak UV forcing. The SOR in the CMIP6 ozone database is therefore implicitly more similar to the SOR in the CCMI-1 models than to the CMIP5 ozone database, which shows a greater resemblance in amplitude and structure to the SOR in the Bodeker database. The latitudinal structure of the annual mean SOR in the CMIP6 ozone database and CCMI-1 models is considerably smoother than in the CMIP5 database, which shows strong gradients in the SOR across the midlatitudes owing to the paucity of observations at high latitudes. The SORs in the CMIP6 ozone database and in the CCMI-1 models show a strong seasonal dependence, including large meridional gradients at mid to high latitudes during winter; such seasonal variations in the SOR are not included in the CMIP5 ozone database. Sensitivity experiments with a global atmospheric model without chemistry (ECHAM6.3) are performed to assess the impact of changes in the representation of the SOR and SSI forcing between CMIP5 and CMIP6. The experiments show that the smaller amplitude of the SOR in the CMIP6 ozone database compared to CMIP5 causes a decrease in the modelled tropical stratospheric temperature response over the solar cycle of up to 0.6 K, or around 50 % of the total amplitude. The changes in the SOR explain most of the difference in the amplitude of the tropical stratospheric temperature response in the case with combined changes in SOR and SSI between CMIP5 and CMIP6. The results emphasise the importance of adequately representing the SOR in climate models to capture the impact of solar variability on the atmosphere. Since a number of limitations in the representation of the SOR in the CMIP5 ozone database have been identified, CMIP6 models without chemistry are encouraged to use the CMIP6 ozone database to capture the climate impacts of solar variability.

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