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Eric R Nash - One of the best experts on this subject based on the ideXlab platform.
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the unusual Southern Hemisphere stratosphere winter of 2002
Journal of the Atmospheric Sciences, 2005Co-Authors: Paul A Newman, Eric R NashAbstract:The Southern Hemisphere stratospheric winter of 2002 was the most unusual winter yet observed in the Southern Hemisphere climate record. Temperatures near the edge of the Antarctic polar vortex were considerably warmer than normal over the entire course of the winter. The polar night jet was considerably weaker than normal, and was displaced more poleward than has been observed in previous winters. These record high temperatures and weak jet resulted from a series of wave events that took place over the course of the winter. The first large event occurred on 15 May, and the final warming occurred on 25 October. The propagation of these wave events from the troposphere is diagnosed from time series of Eliassen-Palm flux vectors. The wave events tended to occur irregularly over the course of the winter, and pre-conditioned the polar night jet for the extremely large wave event of 22 September. This large wave event resulted in the first ever observed major stratospheric warming in the Southern Hemisphere. This wave event split the Antarctic ozone hole. The combined effect of the wave events of the 2002 winter resulted in the smallest ozone hole observed since 1988.
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The Unusual Southern Hemisphere Stratosphere Winter of 2002
Journal of the Atmospheric Sciences, 2005Co-Authors: Paul Newman, Eric R NashAbstract:AbstractThe Southern Hemisphere (SH) stratospheric winter of 2002 was the most unusual winter yet observed in the SH climate record. Temperatures near the edge of the Antarctic polar vortex were considerably warmer than normal over the entire course of the winter. The polar night jet was considerably weaker than normal and was displaced more poleward than has been observed in previous winters. These record high temperatures and weak jet resulted from a series of wave events that took place over the course of the winter. The propagation of these wave events from the troposphere is diagnosed from time series of Eliassen–Palm flux vectors and autoregression time series. Strong levels of planetary waves were observed in the midlatitude lower troposphere. The combinations of strong tropospheric waves with a low index of refraction at the tropopause resulted in the large stratospheric wave forcing. The wave events tended to occur irregularly over the course of the winter, and the cumulative effect of these wave...
Lorenzo M Polvani - One of the best experts on this subject based on the ideXlab platform.
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a pause in Southern Hemisphere circulation trends due to the montreal protocol
AGU Fall Meeting 2020, 2019Co-Authors: Antara Banerjee, Lorenzo M Polvani, Darryn W Waugh, John C Fyfe, Kailan ChangAbstract:Observations show robust near-surface trends in Southern Hemisphere tropospheric circulation towards the end of the twentieth century, including a poleward shift in the mid-latitude jet1,2, a positive trend in the Southern Annular Mode1,3–6 and an expansion of the Hadley cell7,8. It has been established that these trends were driven by ozone depletion in the Antarctic stratosphere due to emissions of ozone-depleting substances9–11. Here we show that these widely reported circulation trends paused, or slightly reversed, around the year 2000. Using a pattern-based detection and attribution analysis of atmospheric zonal wind, we show that the pause in circulation trends is forced by human activities, and has not occurred owing only to internal or natural variability of the climate system. Furthermore, we demonstrate that stratospheric ozone recovery, resulting from the Montreal Protocol, is the key driver of the pause. Because pre-2000 circulation trends have affected precipitation12–14, and potentially ocean circulation and salinity15–17, we anticipate that a pause in these trends will have wider impacts on the Earth system. Signatures of the effects of the Montreal Protocol and the associated stratospheric ozone recovery might therefore manifest, or have already manifested, in other aspects of the Earth system. The recovery of stratospheric ozone in the Southern Hemisphere in the wake of the Montreal Protocol is driving a pause in atmospheric circulation trends that warrants closer scrutiny across the Earth system.
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large cancellation due to ozone recovery of future Southern Hemisphere atmospheric circulation trends
Geophysical Research Letters, 2011Co-Authors: Michael Previdi, Lorenzo M Polvani, Clara DeserAbstract:Received 7 January 2011; accepted 26 January 2011; published 25 February 2011. [1] The role of stratospheric ozone recovery in the Southern Hemisphere climate system, in the coming decades, is examined by contrasting two 10‐member ensembles of Community Atmospheric Model (CAM3) integrations, over the period 2000–2060. Model integrations in the first ensemble are conducted with a complete set of forcings: greenhouse gas concentrations from the A1B scenario, SSTs from corresponding ocean‐atmosphere coupled model integrations, and ozone starting with severe depletion over the South Pole and recovering by mid‐century. The integrations in the second ensemble are very similar to the first, except that only the transient ozone forcing is specified, and all other forcings are kept at year 2000 levels. Specifying ozone recovery in isolation allows us to determine unambiguously how it impacts the atmospheric circulation. We find that, in DJF, most key indices of atmospheric circulation show significant trends in the second ensemble, due to the closing of the ozone hole. In the first ensemble, however, trends are found to be statistically insignificant for nearly all key circulation indices. This suggests that ozone recovery will result in a nearly complete cancellation (and possible reversal) of the atmospheric circulation effects associated with increasing greenhouse gases, in Southern Hemisphere summer, over the coming half century. Citation: Polvani, L. M., M. Previdi, and C.Deser(2011),Largecancellation,duetoozonerecovery,offuture Southern Hemisphere atmospheric circulation trends, Geophys. Res. Lett., 38, L04707, doi:10.1029/2011GL046712.
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stratospheric ozone depletion the main driver of twentieth century atmospheric circulation changes in the Southern Hemisphere
Journal of Climate, 2011Co-Authors: Lorenzo M Polvani, Gustavo Correa, Darryn W Waugh, Seok-woo SonAbstract:The importance of stratospheric ozone depletion on the atmospheric circulation of the troposphere is studied with an atmospheric general circulation model, the Community Atmospheric Model, version 3 (CAM3), for the second half of the twentieth century. In particular, the relative importance of ozone depletion is contrasted with that of increased greenhouse gases and accompanying sea surface temperature changes. By specifying ozone and greenhouse gas forcings independently, and performing long, time-slice integrations,it is shown thatthe impactsof ozone depletionare roughly2‐3 times larger thanthoseassociated with increased greenhouse gases, for the Southern Hemisphere tropospheric summer circulation. The formation of the ozone hole is shown to affect not only the polar tropopause and the latitudinal position of the midlatitude jet; it extends to the entire Hemisphere, resulting in a broadening of the Hadley cell and a poleward extension of the subtropical dry zones. The CAM3 results are compared to and found to be in excellent agreement with those of the multimodel means of the recent Coupled Model Intercomparison Project (CMIP3) and Chemistry‐Climate Model Validation (CCMVal2) simulations. This study, therefore, strongly suggests that most Southern Hemisphere tropospheric circulation changes, in austral summerover the second half of the twentieth century, have been caused by polar stratospheric ozone depletion.
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ozone hole and Southern Hemisphere climate change
Geophysical Research Letters, 2009Co-Authors: Seok-woo Son, Lorenzo M Polvani, Neil F Tandon, Darryn W WaughAbstract:[1] Climate change in the Southern Hemisphere (SH) has been robustly documented in the last several years. It has altered the atmospheric circulation in a surprising number of ways: a rising global tropopause, a poleward intensification of the westerly jet, a poleward shift in storm tracks, a poleward expansion of the Hadley cell, and many others. While these changes have been extensively related with anthropogenic warming resulting from the increase in greenhouse gases, their potential link to stratospheric cooling resulting from ozone depletion has only recently been examined and a comprehensive picture is still lacking. Examining model output from the coupled climate models participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment (AR4), and grouping them depending on the stratospheric ozone forcing used, we here show that stratospheric ozone affects the entire atmospheric circulation in the SH, from the polar regions to the subtropics, and from the stratosphere to the surface. Furthermore, model projections suggest that the anticipated ozone recovery, resulting from the implementation of the Montreal Protocol, will likely decelerate future climate change resulting from increased greenhouse gases, although it might accelerate surface warming over Antarctica. Citation: Son, S.-W., N. F. Tandon, L. M. Polvani, and D. W. Waugh (2009), Ozone hole and Southern Hemisphere climate change, Geophys. Res. Lett., 36, L15705, doi:10.1029/ 2009GL038671.
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the impact of stratospheric ozone recovery on the Southern Hemisphere westerly jet
Science, 2008Co-Authors: Seok-woo Son, Lorenzo M Polvani, Darryn W Waugh, Hideharu Akiyoshi, Rolando R Garcia, Douglas E Kinnison, Steven Pawson, E Rozanov, Theodore G Shepherd, Kiyotaka ShibataAbstract:In the past several decades, the tropospheric westerly winds in the Southern Hemisphere have been observed to accelerate on the poleward side of the surface wind maximum. This has been attributed to the combined anthropogenic effects of increasing greenhouse gases and decreasing stratospheric ozone and is predicted to continue by the Intergovernmental Panel on Climate Change/Fourth Assessment Report (IPCC/AR4) models. In this paper, the predictions of the Chemistry-Climate Model Validation (CCMVal) models are examined: Unlike the AR4 models, the CCMVal models have a fully interactive stratospheric chemistry. Owing to the expected disappearance of the ozone hole in the first half of the 21st century, the CCMVal models predict that the tropospheric westerlies in Southern Hemisphere summer will be decelerated, on the poleward side, in contrast with the prediction of most IPCC/AR4 models.
Dennis L. Hartmann - One of the best experts on this subject based on the ideXlab platform.
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eddy zonal flow feedback in the Southern Hemisphere
Journal of the Atmospheric Sciences, 2001Co-Authors: David J Lorenz, Dennis L. HartmannAbstract:Abstract The variability of the zonal-mean zonal wind in the Southern Hemisphere is studied using EOF analysis and momentum budget diagnostics of NCEP reanalysis data (1978–97). The leading EOF of the zonal-mean zonal wind is well separated from the remaining EOFs and represents the north–south movement of the midlatitude jet. Analysis of the momentum budget shows that a positive feedback between the zonal-mean wind anomalies and the eddy momentum fluxes accounts for the unusual persistence of EOF1 and plays an important role in the selection of the leading EOF of midlatitude variability. Further analysis also shows a propagating feedback, common to both EOF1 and EOF2, which is responsible for the poleward drift of wind anomalies with time. The observations support the following feedback mechanism. Anomalous baroclinic wave activity is generated at the latitude of anomalous temperature gradient that, by thermal wind, coincides with the latitude of the anomalous zonal jet. The net propagation of baroclinic...
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wave driven zonal flow vacillation in the Southern Hemisphere
Journal of the Atmospheric Sciences, 1998Co-Authors: Dennis L. HartmannAbstract:The variability of the zonal mean flow in the Southern Hemisphere during the period 1985‐94 is studied using European Centre for Medium-Range Forecasts analyses. The dominant mode of variability has approximately equivalent barotropic variations of opposite signs centered at 40 8 and 608S. This structure is dominant in all seasons and has similar variance in all seasons. The temporal variance of the amplitude of this mode is well modeled as Gaussian red noise with a correlation e-folding time of about 10 days. Zonal wind anomalies are maintained against frictional drag by variations in the zonal flow accelerations driven by transient eddies and associated mean meridional circulations. The eddy structures suggest that equatorward propagation is favored when the jet is displaced poleward and zonal propagation is favored when the jet is displaced equatorward.
Seok-woo Son - One of the best experts on this subject based on the ideXlab platform.
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stratospheric ozone depletion the main driver of twentieth century atmospheric circulation changes in the Southern Hemisphere
Journal of Climate, 2011Co-Authors: Lorenzo M Polvani, Gustavo Correa, Darryn W Waugh, Seok-woo SonAbstract:The importance of stratospheric ozone depletion on the atmospheric circulation of the troposphere is studied with an atmospheric general circulation model, the Community Atmospheric Model, version 3 (CAM3), for the second half of the twentieth century. In particular, the relative importance of ozone depletion is contrasted with that of increased greenhouse gases and accompanying sea surface temperature changes. By specifying ozone and greenhouse gas forcings independently, and performing long, time-slice integrations,it is shown thatthe impactsof ozone depletionare roughly2‐3 times larger thanthoseassociated with increased greenhouse gases, for the Southern Hemisphere tropospheric summer circulation. The formation of the ozone hole is shown to affect not only the polar tropopause and the latitudinal position of the midlatitude jet; it extends to the entire Hemisphere, resulting in a broadening of the Hadley cell and a poleward extension of the subtropical dry zones. The CAM3 results are compared to and found to be in excellent agreement with those of the multimodel means of the recent Coupled Model Intercomparison Project (CMIP3) and Chemistry‐Climate Model Validation (CCMVal2) simulations. This study, therefore, strongly suggests that most Southern Hemisphere tropospheric circulation changes, in austral summerover the second half of the twentieth century, have been caused by polar stratospheric ozone depletion.
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ozone hole and Southern Hemisphere climate change
Geophysical Research Letters, 2009Co-Authors: Seok-woo Son, Lorenzo M Polvani, Neil F Tandon, Darryn W WaughAbstract:[1] Climate change in the Southern Hemisphere (SH) has been robustly documented in the last several years. It has altered the atmospheric circulation in a surprising number of ways: a rising global tropopause, a poleward intensification of the westerly jet, a poleward shift in storm tracks, a poleward expansion of the Hadley cell, and many others. While these changes have been extensively related with anthropogenic warming resulting from the increase in greenhouse gases, their potential link to stratospheric cooling resulting from ozone depletion has only recently been examined and a comprehensive picture is still lacking. Examining model output from the coupled climate models participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment (AR4), and grouping them depending on the stratospheric ozone forcing used, we here show that stratospheric ozone affects the entire atmospheric circulation in the SH, from the polar regions to the subtropics, and from the stratosphere to the surface. Furthermore, model projections suggest that the anticipated ozone recovery, resulting from the implementation of the Montreal Protocol, will likely decelerate future climate change resulting from increased greenhouse gases, although it might accelerate surface warming over Antarctica. Citation: Son, S.-W., N. F. Tandon, L. M. Polvani, and D. W. Waugh (2009), Ozone hole and Southern Hemisphere climate change, Geophys. Res. Lett., 36, L15705, doi:10.1029/ 2009GL038671.
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the impact of stratospheric ozone recovery on the Southern Hemisphere westerly jet
Science, 2008Co-Authors: Seok-woo Son, Lorenzo M Polvani, Darryn W Waugh, Hideharu Akiyoshi, Rolando R Garcia, Douglas E Kinnison, Steven Pawson, E Rozanov, Theodore G Shepherd, Kiyotaka ShibataAbstract:In the past several decades, the tropospheric westerly winds in the Southern Hemisphere have been observed to accelerate on the poleward side of the surface wind maximum. This has been attributed to the combined anthropogenic effects of increasing greenhouse gases and decreasing stratospheric ozone and is predicted to continue by the Intergovernmental Panel on Climate Change/Fourth Assessment Report (IPCC/AR4) models. In this paper, the predictions of the Chemistry-Climate Model Validation (CCMVal) models are examined: Unlike the AR4 models, the CCMVal models have a fully interactive stratospheric chemistry. Owing to the expected disappearance of the ozone hole in the first half of the 21st century, the CCMVal models predict that the tropospheric westerlies in Southern Hemisphere summer will be decelerated, on the poleward side, in contrast with the prediction of most IPCC/AR4 models.
Darryn W Waugh - One of the best experts on this subject based on the ideXlab platform.
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a pause in Southern Hemisphere circulation trends due to the montreal protocol
AGU Fall Meeting 2020, 2019Co-Authors: Antara Banerjee, Lorenzo M Polvani, Darryn W Waugh, John C Fyfe, Kailan ChangAbstract:Observations show robust near-surface trends in Southern Hemisphere tropospheric circulation towards the end of the twentieth century, including a poleward shift in the mid-latitude jet1,2, a positive trend in the Southern Annular Mode1,3–6 and an expansion of the Hadley cell7,8. It has been established that these trends were driven by ozone depletion in the Antarctic stratosphere due to emissions of ozone-depleting substances9–11. Here we show that these widely reported circulation trends paused, or slightly reversed, around the year 2000. Using a pattern-based detection and attribution analysis of atmospheric zonal wind, we show that the pause in circulation trends is forced by human activities, and has not occurred owing only to internal or natural variability of the climate system. Furthermore, we demonstrate that stratospheric ozone recovery, resulting from the Montreal Protocol, is the key driver of the pause. Because pre-2000 circulation trends have affected precipitation12–14, and potentially ocean circulation and salinity15–17, we anticipate that a pause in these trends will have wider impacts on the Earth system. Signatures of the effects of the Montreal Protocol and the associated stratospheric ozone recovery might therefore manifest, or have already manifested, in other aspects of the Earth system. The recovery of stratospheric ozone in the Southern Hemisphere in the wake of the Montreal Protocol is driving a pause in atmospheric circulation trends that warrants closer scrutiny across the Earth system.
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Southern Hemisphere extratropical circulation recent trends and natural variability
Geophysical Research Letters, 2015Co-Authors: Jordan L Thomas, Darryn W Waugh, Anand GnanadesikanAbstract:Changes in the Southern Annular Mode (SAM), Southern Hemisphere (SH) westerly jet location, and magnitude are linked with changes in ocean circulation along with ocean heat and carbon uptake. Recent trends have been observed in these fields but not much is known about the natural variability. Here we aim to quantify the natural variability of the SH extratropical circulation by using Coupled Model Intercomparison Project Phase 5 (CMIP5) preindustrial control model runs and compare with the observed trends in SAM, jet magnitude, and jet location. We show that trends in SAM are due partly to external forcing but are not outside the natural variability as described by these models. Trends in jet location and magnitude, however, lie outside the unforced natural variability but can be explained by a combination of natural variability and the ensemble mean forced trend. These results indicate that trends in these three diagnostics cannot be used interchangeably.
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stratospheric ozone depletion the main driver of twentieth century atmospheric circulation changes in the Southern Hemisphere
Journal of Climate, 2011Co-Authors: Lorenzo M Polvani, Gustavo Correa, Darryn W Waugh, Seok-woo SonAbstract:The importance of stratospheric ozone depletion on the atmospheric circulation of the troposphere is studied with an atmospheric general circulation model, the Community Atmospheric Model, version 3 (CAM3), for the second half of the twentieth century. In particular, the relative importance of ozone depletion is contrasted with that of increased greenhouse gases and accompanying sea surface temperature changes. By specifying ozone and greenhouse gas forcings independently, and performing long, time-slice integrations,it is shown thatthe impactsof ozone depletionare roughly2‐3 times larger thanthoseassociated with increased greenhouse gases, for the Southern Hemisphere tropospheric summer circulation. The formation of the ozone hole is shown to affect not only the polar tropopause and the latitudinal position of the midlatitude jet; it extends to the entire Hemisphere, resulting in a broadening of the Hadley cell and a poleward extension of the subtropical dry zones. The CAM3 results are compared to and found to be in excellent agreement with those of the multimodel means of the recent Coupled Model Intercomparison Project (CMIP3) and Chemistry‐Climate Model Validation (CCMVal2) simulations. This study, therefore, strongly suggests that most Southern Hemisphere tropospheric circulation changes, in austral summerover the second half of the twentieth century, have been caused by polar stratospheric ozone depletion.
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ozone hole and Southern Hemisphere climate change
Geophysical Research Letters, 2009Co-Authors: Seok-woo Son, Lorenzo M Polvani, Neil F Tandon, Darryn W WaughAbstract:[1] Climate change in the Southern Hemisphere (SH) has been robustly documented in the last several years. It has altered the atmospheric circulation in a surprising number of ways: a rising global tropopause, a poleward intensification of the westerly jet, a poleward shift in storm tracks, a poleward expansion of the Hadley cell, and many others. While these changes have been extensively related with anthropogenic warming resulting from the increase in greenhouse gases, their potential link to stratospheric cooling resulting from ozone depletion has only recently been examined and a comprehensive picture is still lacking. Examining model output from the coupled climate models participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment (AR4), and grouping them depending on the stratospheric ozone forcing used, we here show that stratospheric ozone affects the entire atmospheric circulation in the SH, from the polar regions to the subtropics, and from the stratosphere to the surface. Furthermore, model projections suggest that the anticipated ozone recovery, resulting from the implementation of the Montreal Protocol, will likely decelerate future climate change resulting from increased greenhouse gases, although it might accelerate surface warming over Antarctica. Citation: Son, S.-W., N. F. Tandon, L. M. Polvani, and D. W. Waugh (2009), Ozone hole and Southern Hemisphere climate change, Geophys. Res. Lett., 36, L15705, doi:10.1029/ 2009GL038671.
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the impact of stratospheric ozone recovery on the Southern Hemisphere westerly jet
Science, 2008Co-Authors: Seok-woo Son, Lorenzo M Polvani, Darryn W Waugh, Hideharu Akiyoshi, Rolando R Garcia, Douglas E Kinnison, Steven Pawson, E Rozanov, Theodore G Shepherd, Kiyotaka ShibataAbstract:In the past several decades, the tropospheric westerly winds in the Southern Hemisphere have been observed to accelerate on the poleward side of the surface wind maximum. This has been attributed to the combined anthropogenic effects of increasing greenhouse gases and decreasing stratospheric ozone and is predicted to continue by the Intergovernmental Panel on Climate Change/Fourth Assessment Report (IPCC/AR4) models. In this paper, the predictions of the Chemistry-Climate Model Validation (CCMVal) models are examined: Unlike the AR4 models, the CCMVal models have a fully interactive stratospheric chemistry. Owing to the expected disappearance of the ozone hole in the first half of the 21st century, the CCMVal models predict that the tropospheric westerlies in Southern Hemisphere summer will be decelerated, on the poleward side, in contrast with the prediction of most IPCC/AR4 models.
