Sensitivity of the southern hemisphere tropospheric jet response to ozone depletion: specified versus interactive chemistry

2020 ◽  
Author(s):  
Sabine Haase ◽  
Jaika Fricke ◽  
Katja Matthes
Keyword(s):  
Southern Hemisphere ◽  
Ozone Depletion ◽  
Climate Models ◽  
Stratospheric Ozone ◽  
Austral Summer ◽  
Atmospheric Model ◽  
Short Wave ◽  
Wave Heating ◽  
Poleward Shift ◽  
The Difference

<p>Southern hemisphere lower stratospheric ozone depletion has been shown to lead to a poleward shift of the tropospheric jet stream during austral summer, influencing surface atmosphere and ocean conditions, such as surface temperatures and sea ice extend. The characteristics of stratospheric and tropospheric responses to ozone depletion, however, differ among climate models largely depending on the representation of ozone in the model.</p><p>The most accurate way to represent ozone in a model is to calculate it interactively. However, due to computational costs, in particular for long-term coupled ocean-atmosphere model integrations, the more common way is to prescribe ozone from observations or calculated model fields.</p><p>Here, we investigate the difference between an interactive chemistry and a specified chemistry version of the same atmospheric model in a fully-coupled setup using a large 9-member model ensemble. In contrast to most earlier studies, we use daily-resolved ozone fields in the specified chemistry simulations to achieve a better comparability between the ozone forcing with and without interactive chemistry. We find that although the short-wave heating rate trend in response to ozone depletion is the same in the different chemistry settings, the interactive chemistry ensemble shows a stronger trend in polar cap stratospheric temperatures and circumpolar stratospheric and tropospheric zonal mean zonal winds as compared to the specified chemistry ensemble. We attribute part of these differences to the missing representation of feedbacks between chemistry and dynamics in the specified chemistry ensemble and part of it to the lack of zonal asymmetries in the prescribed ozone fields.</p><p>This study emphasizes the value of interactive chemistry for the representation of the southern hemisphere tropospheric jet response to ozone depletion.</p>

scholarly journals Sensitivity of the southern hemisphere tropospheric jet response to Antarctic ozone depletion: prescribed versus interactive chemistry

2020 ◽  
Author(s):  
Sabine Haase ◽  
Jaika Fricke ◽  
Tim Kruschke ◽  
Sebastian Wahl ◽  
Katja Matthes
Keyword(s):  
Southern Hemisphere ◽  
Ozone Depletion ◽  
Climate Models ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Austral Summer ◽  
Jet Stream ◽  
Heating Rates ◽  
Sea Ice Extent ◽  
Poleward Shift

Abstract. Southern hemisphere lower stratospheric ozone depletion has been shown to lead to a poleward shift of the tropospheric jet stream during austral summer, influencing surface atmosphere and ocean conditions, such as surface temperatures and sea ice extent. The characteristics of stratospheric and tropospheric responses to ozone depletion, however, differ largely among climate models depending on the representation of ozone in the models. The most accurate way to represent ozone in a model is to calculate it interactively. However, due to computational costs, in particular for long-term coupled ocean-atmosphere model integrations, the more common way is to prescribe ozone from observations or calculated model fields. Here, we investigate the difference between an interactive and a specified chemistry version of the same atmospheric model in a fully-coupled setup using a 9-member chemistry-climate model ensemble. In the specified chemistry version of the model the ozone fields are prescribed using the output from the interactive chemistry model version. In contrast to earlier studies, we use daily-resolved ozone fields in the specified chemistry simulations to achieve a better comparability between the ozone forcing with and without interactive chemistry. We find that although the short-wave heating rate trend in response to ozone depletion is the same in the different chemistry settings, the interactive chemistry ensemble shows a stronger trend in polar cap stratospheric temperatures (by about 0.7 K per decade) and circumpolar stratospheric zonal mean zonal winds (by about 1.6 m/s per decade) as compared to the specified chemistry ensemble. This difference between interactive and specified chemistry in the stratospheric response to ozone depletion also affects the tropospheric response, namely the poleward shift of the tropospheric jet stream. We attribute part of these differences to the missing representation of feedbacks between chemistry and dynamics in the specified chemistry ensemble, which affect the dynamical heating rates, and part of it to the lack of spatial asymmetries in the prescribed ozone fields. This effect is investigated using a sensitivity ensemble that was forced by a three-dimensional instead of a two–dimensional ozone field. This study emphasizes the value of interactive chemistry for the representation of the southern hemisphere tropospheric jet response to ozone depletion and infers that for periods with strong ozone variability (trends) the details of the ozone forcing can be crucial for representing southern hemispheric climate variability.

scholarly journals Sensitivity of the Southern Hemisphere circumpolar jet response to Antarctic ozone depletion: prescribed versus interactive chemistry

2020 ◽  
Vol 20 (22) ◽  
pp. 14043-14061
Author(s):  
Sabine Haase ◽  
Jaika Fricke ◽  
Tim Kruschke ◽  
Sebastian Wahl ◽  
Katja Matthes
Keyword(s):  
Southern Hemisphere ◽  
Ozone Depletion ◽  
Climate Models ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Austral Summer ◽  
Jet Stream ◽  
Heating Rates ◽  
Sea Ice Extent ◽  
Poleward Shift

Abstract. Southern Hemisphere lower-stratospheric ozone depletion has been shown to lead to a poleward shift of the tropospheric jet stream during austral summer, influencing surface atmosphere and ocean conditions, such as surface temperatures and sea ice extent. The characteristics of stratospheric and tropospheric responses to ozone depletion, however, differ among climate models depending on the representation of ozone in the models. The most appropriate way to represent ozone in a model is to calculate it interactively. However, due to computational costs, in particular for long-term coupled ocean–atmosphere model integrations, the more common way is to prescribe ozone from observations or calculated model fields. Here, we investigate the difference between an interactive and a specified chemistry version of the same atmospheric model in a fully coupled setup using a nine-member chemistry–climate model ensemble. In the specified chemistry version of the model the ozone fields are prescribed using the output from the interactive chemistry model version. We use daily resolved ozone fields in the specified chemistry simulations to achieve a very good comparability between the ozone forcing with and without interactive chemistry. We find that although the shortwave heating rate trend in response to ozone depletion is the same in the different chemistry settings, the interactive chemistry ensemble shows a stronger trend in polar cap stratospheric temperatures (by about 0.7 K decade−1) and circumpolar stratospheric zonal mean zonal winds (by about 1.6 m s−1 decade−1 as compared to the specified chemistry ensemble. This difference between interactive and specified chemistry in the stratospheric response to ozone depletion also affects the tropospheric response. However, an impact on the poleward shift of the tropospheric jet stream is not detected. We attribute part of the differences found in the experiments to the missing representation of feedbacks between chemistry and dynamics in the specified chemistry ensemble, which affect the dynamical heating rates, and part of it to the lack of spatial asymmetries in the prescribed ozone fields. This effect is investigated using a sensitivity ensemble that was forced by a three-dimensional instead of a two-dimensional ozone field. This study emphasizes the value of interactive chemistry for the representation of the Southern Hemisphere stratospheric-jet response to ozone depletion and infers that for periods with strong ozone variability (trends) the details of the ozone forcing could also have an influence on the representation of southern-hemispheric climate variability.

scholarly journals Sensitivity of the Amundsen Sea Low to Stratospheric Ozone Depletion

2014 ◽  
Vol 27 (24) ◽  
pp. 9383-9400 ◽  
Author(s):  
Ryan L. Fogt ◽  
Elizabeth A. Zbacnik
Keyword(s):  
Ozone Depletion ◽  
Climate Models ◽  
Stratospheric Ozone ◽  
Austral Summer ◽  
Lower Troposphere ◽  
Southern Annular Mode ◽  
Stratospheric Ozone Depletion ◽  
Austral Spring ◽  
Regional Warming ◽  
Amundsen Sea

Abstract Dramatic sea ice loss in the Amundsen and Bellingshausen Seas and regional warming in West Antarctica and the Antarctica Peninsula have been observed over the last few decades. Both of these changes are strongly influenced by the presence of the Amundsen Sea low (ASL), a climatological region of low pressure in the Amundsen Sea. Studies have demonstrated a deepening of the ASL, particularly in austral spring and to a lesser extent autumn, the former related to decreases in the underlying cyclone central pressures and the latter previously suggested to be due to stratospheric ozone depletion. This study further investigates the sensitivity of the ASL to stratospheric ozone depletion using geopotential height from a suite of chemistry–climate models (CCMs) as well as historical simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5). Overall, both model types capture the mean characteristics of the ASL, although they have notable positive height biases at 850 hPa and a subdued seasonal cycle in its longitudinal position. Comparing across model simulations, it is observed that there is a pronounced influence of stratospheric ozone depletion in the vicinity of the ASL in the stratosphere through the lower troposphere during austral summer, consistent with the positive phase of the southern annular mode. In the autumn, the authors note a weaker, secondary influence of stratospheric ozone depletion on the ASL only in the CMIP5 simulations.

scholarly journals The Antarctic Sea Ice Response to the Ozone Hole in Climate Models

2014 ◽  
Vol 27 (3) ◽  
pp. 1336-1342 ◽  
Author(s):  
Michael Sigmond ◽  
John C. Fyfe
Keyword(s):  
Sea Ice ◽  
Southern Hemisphere ◽  
Ozone Depletion ◽  
Climate Models ◽  
Stratospheric Ozone ◽  
Coupled Model ◽  
Ozone Hole ◽  
Cmip5 Models ◽  
Time Varying ◽  
Sea Ice Extent

Abstract It has been suggested that the increase of Southern Hemisphere sea ice extent since the 1970s can be explained by ozone depletion in the Southern Hemisphere stratosphere. In a previous study, the authors have shown that in a coupled atmosphere–ocean–sea ice model the ozone hole does not lead to an increase but to a decrease in sea ice extent. Here, the robustness of this result is established through the analysis of models from phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5). Comparison of the mean sea ice trends in CMIP3 models with and without time-varying stratospheric ozone suggests that ozone depletion is associated with decreased sea ice extent, and ozone recovery acts to mitigate the future sea ice decrease associated with increasing greenhouse gases. All available historical simulations with CMIP5 models that were designed to isolate the effect of time-varying ozone concentrations show decreased sea ice extent in response to historical ozone trends. In most models, the historical sea ice extent trends are mainly driven by historical greenhouse gas forcing, with ozone forcing playing a secondary role.

scholarly journals Evaluation of the Australian Community Climate and Earth-System Simulator Chemistry-Climate Model

2015 ◽  
Vol 15 (13) ◽  
pp. 19161-19196
Author(s):  
K. A. Stone ◽  
O. Morgenstern ◽  
D. J. Karoly ◽  
A. R. Klekociuk ◽  
W. J. R. French ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Zonal Wind ◽  
Ozone Depletion ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Similar Amount ◽  
Earth System ◽  
Total Column Ozone ◽  
Australian Community ◽  
Community Climate

Abstract. Chemistry climate models are important tools for addressing interactions of composition and climate in the Earth System. In particular, they are used for assessing the combined roles of greenhouse gases and ozone in Southern Hemisphere climate and weather. Here we present an evaluation of the Australian Community Climate and Earth System Simulator-Chemistry Climate Model, focusing on the Southern Hemisphere and the Australian region. This model is used for the Australian contribution to the international Chemistry-Climate Model Initiative, which is soliciting hindcast, future projection and sensitivity simulations. The model simulates global total column ozone (TCO) distributions accurately, with a slight delay in the onset and recovery of springtime Antarctic ozone depletion, and consistently higher ozone values. However, October averaged Antarctic TCO from 1960 to 2010 show a similar amount of depletion compared to observations. A significant innovation is the evaluation of simulated vertical profiles of ozone and temperature with ozonesonde data from Australia, New Zealand and Antarctica from 38 to 90° S. Excess ozone concentrations (up to 26.4 % at Davis during winter) and stratospheric cold biases (up to 10.1 K at the South Pole) outside the period of perturbed springtime ozone depletion are seen during all seasons compared to ozonesondes. A disparity in the vertical location of ozone depletion is seen: centered around 100 hPa in ozonesonde data compared to above 50 hPa in the model. Analysis of vertical chlorine monoxide profiles indicates that colder Antarctic stratospheric temperatures (possibly due to reduced mid-latitude heat flux) are artificially enhancing polar stratospheric cloud formation at high altitudes. The models inability to explicitly simulated supercooled ternary solution may also explain the lack of depletion at lower altitudes. The simulated Southern Annular Mode (SAM) index compares well with ERA-Interim data. Accompanying these modulations of the SAM, 50 hPa zonal wind differences between 2001–2010 and 1979–1998 show increasing zonal wind strength southward of 60° S during December for both the model simulations and ERA-Interim data. These model diagnostics shows that the model reasonably captures the stratospheric ozone driven chemistry-climate interactions important for Australian climate and weather while highlighting areas for future model development.

scholarly journals Tropospheric ozone in CMIP6 Simulations

2020 ◽  
Author(s):  
Paul T. Griffiths ◽  
Lee T. Murray ◽  
Guang Zeng ◽  
Alexander T. Archibald ◽  
Louisa K. Emmons ◽  
...  
Keyword(s):  
Tropospheric Ozone ◽  
Climate Models ◽  
Decadal Variability ◽  
Stratospheric Ozone ◽  
Coupled Model ◽  
Mean Value ◽  
Ozone Production ◽  
Chemical Production ◽  
The Difference ◽  
Using Data

Abstract. The evolution of tropospheric ozone from 1850 to 2100 has been studied using data from Phase 6 of the Coupled Model Intercomparison Project (CMIP6). We evaluate long-term changes using coupled atmosphere-ocean chemistry-climate models, focusing on the CMIP historical and ScenarioMIP ssp370 experiments, for which detailed tropospheric ozone diagnostics were archived. The model ensemble has been evaluated against a suite of surface, sonde, and satellite observations of the past several decades, and found to reproduce well the salient spatial, seasonal and decadal variability and trends. The tropospheric ozone burden increases from 244 ± 30 Tg in 1850 to a mean value of 348 ± 15 Tg for the period 2005–2014, an increase of 40 %. Modelled present day values agree well with previous determinations (ACCENT: 336 ± 27 Tg; ACCMIP: 337 ± 23 Tg and TOAR: 340 ± 34 Tg). In the ssp370 experiments, the ozone burden reaches a maximum of 402 ± 36 Tg in 2090, before declining slightly to 396 ± 32 Tg by 2100. The ozone budget has been examined over the same period using lumped ozone production (PO3) and loss (LO3) diagnostics. There are large differences (30 %) between models in the preindustrial period, with the difference narrowing to 15 % in the present day. Both ozone production and chemical loss terms increase steadily over the period 1850 to 2100, with net chemical production (PO3-LO3) reaching a maximum around the year 2000. The residual term, which contains contributions from stratosphere-troposphere transport reaches a minimum around the same time, while dry deposition increases steadily across the experiment. Differences between the model residual terms are explained in terms of variation in tropopause height and stratospheric ozone burden.

Simulation of Present-Day and Twenty-First-Century Energy Budgets of the Southern Oceans

2010 ◽  
Vol 23 (2) ◽  
pp. 440-454 ◽  
Author(s):  
Kevin E. Trenberth ◽  
John T. Fasullo
Keyword(s):  
Southern Hemisphere ◽  
Cloud Cover ◽  
Climate Models ◽  
Global Climate ◽  
Strong Relationship ◽  
Global Climate Models ◽  
Storm Tracks ◽  
Energy Budgets ◽  
Poleward Shift ◽  
Projected Changes

Abstract The energy budget of the modern-day Southern Hemisphere is poorly simulated in both state-of-the-art reanalyses and coupled global climate models. The ocean-dominated Southern Hemisphere has low surface reflectivity and therefore its albedo is particularly sensitive to cloud cover. In modern-day climates, mainly because of systematic deficiencies in cloud and albedo at mid- and high latitudes, too much solar radiation enters the ocean. Along with too little radiation absorbed at lower latitudes because of clouds that are too bright, unrealistically weak poleward transports of energy by both the ocean and atmosphere are generally simulated in the Southern Hemisphere. This implies too little baroclinic eddy development and deficient activity in storm tracks. However, projections into the future by coupled climate models indicate that the Southern Ocean features a robust and unique increase in albedo, related to clouds, in association with an intensification and poleward shift in storm tracks that is not observed at any other latitude. Such an increase in cloud may be untenable in nature, as it is likely precluded by the present-day ubiquitous cloud cover that models fail to capture. There is also a remarkably strong relationship between the projected changes in clouds and the simulated current-day cloud errors. The model equilibrium climate sensitivity is also significantly negatively correlated with the Southern Hemisphere energy errors, and only the more sensitive models are in the range of observations. As a result, questions loom large about how the Southern Hemisphere will actually change as global warming progresses, and a better simulation of the modern-day climate is an essential first step.

scholarly journals Comparing the Impacts of Tropical SST Variability and Polar Stratospheric Ozone Loss on the Southern Ocean Westerly Winds*

2015 ◽  
Vol 28 (23) ◽  
pp. 9350-9372 ◽  
Author(s):  
David P. Schneider ◽  
Clara Deser ◽  
Tingting Fan
Keyword(s):  
Southern Ocean ◽  
Ozone Depletion ◽  
Stratospheric Ozone ◽  
Austral Summer ◽  
Southern Annular Mode ◽  
Forced Response ◽  
Coupled Models ◽  
Ozone Loss ◽  
The Pacific ◽  
Tropical Ssts

Abstract Westerly wind trends at 850 hPa over the Southern Ocean during 1979–2011 exhibit strong regional and seasonal asymmetries. On an annual basis, trends in the Pacific sector (40°–60°S, 70°–160°W) are 3 times larger than zonal-mean trends related to the increase in the southern annular mode (SAM). Seasonally, the SAM-related trend is largest in austral summer, and many studies have linked this trend with stratospheric ozone depletion. In contrast, the Pacific sector trends are largest in austral autumn. It is proposed that these asymmetries can be explained by a combination of tropical teleconnections and polar ozone depletion. Six ensembles of transient atmospheric model experiments, each forced with different combinations of time-dependent radiative forcings and SSTs, support this idea. In summer, the model simulates a positive SAM-like pattern, to which ozone depletion and tropical SSTs (which contain signatures of internal variability and warming from greenhouse gasses) contribute. In autumn, the ensemble-mean response consists of stronger westerlies over the Pacific sector, explained by a Rossby wave originating from the central equatorial Pacific. While these responses resemble observations, attribution is complicated by intrinsic atmospheric variability. In the experiments forced only with tropical SSTs, individual ensemble members exhibit wind trend patterns that mimic the forced response to ozone. When the analysis presented herein is applied to 1960–2000, the primary period of ozone loss, ozone depletion largely explains the model’s SAM-like zonal wind trend. The time-varying importance of these different drivers has implications for relating the historical experiments of free-running, coupled models to observations.

New Fractional Release Factors, Ozone Depletion Potentials, and Lifetimes for Four Long-Lived CFCs: CFC-13, CFC-114, CFC-114a, and CFC-115

2021 ◽  
Author(s):  
Elinor Tuffnell ◽  
Johannes Laube ◽  
Emma Leedham Elvidge ◽  
Bill Sturges ◽  
Karina Adcock ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Stratospheric Ozone ◽  
Relevant Information ◽  
Atmospheric Model ◽  
World Meteorological Organization ◽  
Air Samples ◽  
Release Factors ◽  
Nasa Goddard Space ◽  
Scientific Assessment ◽  
Fractional Release

<p>Knowing the stratospheric lifetime of an Ozone Depleting Substance (ODS), and its potential depletion of ozone during that time, is vital to reliably monitor and control the use of ODSs. Here, we present improved policy-relevant parameters: Fractional Release Factors (FRFs), Ozone Depletion Potentials (ODPs), and stratospheric lifetimes, for four understudied long-lived CFCs: CFC-13 (CClF<sub>3</sub>), CFC-114 (CClF<sub>2</sub>CCCLF<sub>2</sub>), CFC-114a (CCl<sub>2</sub>FCF<sub>3</sub>), and CFC-115 (C<sub>2</sub>ClF<sub>5</sub>). Previously derived lifetime estimates for CFC-114 and CFC-115 have substantial uncertainties, while lifetime uncertainties for CFC-13 and CFC-114a are absent from the peer-reviewed literature (Carpenter & Danie <em>et al</em>, 2018).</p><p>This study used both observational and model data to investigate these compounds and this work derives, for the first time, observation-based lifetimes utilising measurements of air samples collected in the stratosphere. We also used a version of the NASA Goddard Space Flight Center (GSFC) 2-D atmospheric model driven by temperature and transport fields derived from MERRA/MERRA-2 reanalysis.</p><p>FRFs for these compounds, which had been lacking until now, were derived using stratospheric air samples collected from several research flights with the high-altitude aircraft M55-Geophysica, and the background trend from archived surface air samples from Cape Grim, Tasmania.</p><p> By using a previously-published correlation between lifetime and FRF for seven well-characterised compounds (CF<sub>4</sub>, C<sub>2</sub>F<sub>6</sub>, C<sub>3</sub>F<sub>8</sub>, CHF<sub>3</sub>, HFC-125, HFC-227ea and SF<sub>6</sub>), we were able to derive lifetimes for these four new species. Lifetime estimates for CFC-114a agreed within the uncertainties (agreement to one sigma) with the lifetime estimates compiled in Burkholder <em>et al</em>. (2018), while the one for CFC-114 agreed within 2 sigma (measurement-related uncertainties) with those cited in Burkholder <em>et al</em>. (2018). However, observation-based lifetimes for CFC-13 and CFC-115 only agreed with those in Burkholder <em>et al</em>. (2018) within 3 sigma. The lifetime uncertainties in this study were reduced compared to those in Carpenter & Danie <em>et al</em> (2018).</p><p>As our lifetime estimates for these latter two compounds are notably lower than previous estimates, this suggests that these two compounds may have had greater emissions than previously thought, in order to account for their abundance. It also implies that they will be removed from the atmosphere more quickly than previously thought.</p><p>New ODPs were derived for these compounds from their new lifetimes and FRFs. Since for two of these compounds (CFC-13 and CFC-114a), there is an absence of observation-derived ODPs in the peer-reviewed literature, this is new and relevant information. The ODPs for CFC-114 and CFC-115 are comparable with estimates from the most recent Scientific Assessment of Ozone Depletion (Burkholder <em>et al</em>., 2018). Providing new and updated lifetimes, FRFs and ODPs for these compounds will help improve future estimates of their tropospheric emissions and their resulting damage to the stratospheric ozone layer.</p><p>             </p><p><strong>References</strong></p><p>Burkholder <em>et al</em>. (2018). Appendix A, Table A-1 in <em>Scientific Assessment of Ozone Depletion: 2018, Global Ozone Research and Monitoring Project</em>, Report No. 58, World Meteorological Organization, Geneva, Switzerland,  http://ozone.unep.org/science/assessment/sap.</p><p>Carpenter, L.J., Danie, J.S.<em> et al </em>(2018). Scenarios and Information for Policymakers Chapter 6, Table 6-1 in <em>Scientific Assessment of Ozone Depletion: 2018, Global Ozone Research and Monitoring Project</em>, Report No. 58, World Meteorological Organization, Geneva, Switzerland.</p>

Emergence of Southern Hemisphere circulation changes in response to ozone recovery

2020 ◽  
Author(s):  
Brian Zambri ◽  
Susan Solomon ◽  
David Thompson ◽  
Qiang Fu
Keyword(s):  
Southern Hemisphere ◽  
Ozone Depletion ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Montreal Protocol ◽  
Stratospheric Polar Vortex ◽  
Surface Climate ◽  
Antarctic Ozone ◽  
Ozone Depleting Substances ◽  
Circulation Changes

<p>Ozone depletion in the Southern Hemisphere (SH) stratosphere in the late 20<sup>th</sup> century cooled the air there, strengthening the SH stratospheric westerly winds near 60ºS and altering SH surface climate. Since ~1999, trends in Antarctic ozone have begun to recover, exhibiting a flattening followed by a sign reversal in response to decreases in stratospheric chlorine concentration due to the Montreal Protocol, an international treaty banning the production and consumption of ozone-depleting substances. Here we show that the post–1999 increase in ozone has resulted in thermal and circulation changes of opposite sign to those that resulted from stratospheric ozone losses, including a warming of the SH polar lower stratosphere and a weakening of the SH stratospheric polar vortex.  Further, these altered trends extend to the upper troposphere, albeit of smaller magnitudes.  Observed post–1999 trends of temperature and circulation in the stratosphere are about 20–25% the magnitude of those of the ozone depletion era, and are broadly consistent with expectations based on modeled depletion-era trends and variability of both ozone and reactive chlorine, thereby indicating the emergence of healing of dynamical impacts of the Antarctic ozone hole.</p>

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