The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Lorenzo M. Polvani - One of the best experts on this subject based on the ideXlab platform.
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Recent Trends in Extreme Precipitation and Temperature over Southeastern South America: The Dominant Role of Stratospheric Ozone Depletion in the CESM Large Ensemble
Journal of Climate, 2017Co-Authors: Lorenzo M. PolvaniAbstract:AbstractObservations show an increase in maximum precipitation extremes and a decrease in maximum temperature extremes over southeastern South America (SESA) in the second half of the 20th century. The Community Earth System Model (CESM) Large Ensemble (LE) experiments are able to successfully reproduce the observed trends of extreme precip- itation and temperature over SESA. Careful analysis of a smaller ensemble of CESM-LE single forcing experiments reveals that the trends of extreme precipitation and temperature over SESA are mostly caused by Stratospheric Ozone Depletion. The underlying dynamical mechanism is investigated, and it is found that, as a consequence of Stratospheric Ozone Depletion and the resulting southward shift of tropospheric jet streams, anomalous easterly ow and more intense cyclones have occurred over SESA, which are favorable for heavier rainfall extremes and milder heat extremes.
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Robust response of the Amundsen Sea Low to Stratospheric Ozone Depletion
Geophysical Research Letters, 2016Co-Authors: Mark R. England, Lorenzo M. Polvani, Karen L. Smith, Laura Landrum, Marika M. HollandAbstract:The effect of Stratospheric Ozone Depletion on the Amundsen Sea Low (ASL), a climatological low-pressure center important for the climate of West Antarctica, remains uncertain. Using state-of-the-art climate models, we here show that Stratospheric Ozone Depletion can cause a statistically significant deepening of the ASL in summer with an amplitude of approximately 1 hPa per decade. We are able to attribute the modeled changes in the ASL to Stratospheric Ozone Depletion by contrasting ensembles of historical integrations with and without a realistic Ozone hole. In the presence of very large natural variability, the robustness of the Ozone impact on the ASL is established by (1) examining ensembles of model runs to isolate the forced response, (2) repeating the analysis with two different climate models, and (3) considering the entire period of Stratospheric Ozone Depletion, the beginning of which predates the satellite era by a couple of decades.
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Drivers of the Recent Tropical Expansion in the Southern Hemisphere: Changing SSTs or Ozone Depletion?
Journal of Climate, 2015Co-Authors: Darryn W Waugh, Chaim I. Garfinkel, Lorenzo M. PolvaniAbstract:AbstractObservational evidence indicates that the southern edge of the Hadley cell (HC) has shifted southward during austral summer in recent decades. However, there is no consensus on the cause of this shift, with several studies reaching opposite conclusions as to the relative role of changes in sea surface temperatures (SSTs) and Stratospheric Ozone Depletion in causing this shift. Here, the authors perform a meta-analysis of the extant literature on this subject and quantitatively compare the results of all published studies that have used single-forcing model integrations to isolate the role of different factors on the HC expansion during austral summer. It is shown that the weight of the evidence clearly points to Stratospheric Ozone Depletion as the dominant driver of the tropical summertime expansion over the period in which an Ozone hole was formed (1979 to late 1990s), although SST trends have contributed to trends since then. Studies that have claimed SSTs as the major driver of tropical expans...
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Climate system response to Stratospheric Ozone Depletion and recovery
Quarterly Journal of the Royal Meteorological Society, 2014Co-Authors: Michael Previdi, Lorenzo M. PolvaniAbstract:We review what is presently known about the climate system response to Stratospheric Ozone Depletion and its projected recovery, focusing on the responses of the atmosphere, ocean and cryosphere. Compared with well-mixed greenhouse gases (GHGs), the radiative forcing of climate due to observed Stratospheric Ozone loss is very small: in spite of this, recent trends in Stratospheric Ozone have caused profound changes in the Southern Hemisphere (SH) climate system, primarily by altering the tropospheric midlatitude jet, which is commonly described as a change in the Southern Annular Mode. Ozone Depletion in the late twentieth century was the primary driver of the observed poleward shift of the jet during summer, which has been linked to changes in tropospheric and surface temperatures, clouds and cloud radiative effects, and precipitation at both middle and low latitudes. It is emphasized, however, that not all aspects of the SH climate response to Stratospheric Ozone forcing can be understood in terms of changes in the midlatitude jet. The response of the Southern Ocean and sea ice to Ozone Depletion is currently a matter of debate. For the former, the debate is centred on the role of ocean eddies in possibly opposing wind-driven changes in the mean circulation. For the latter, the issue is reconciling the observed expansion of Antarctic sea-ice extent during the satellite era with robust modelling evidence that the ice should melt as a result of Stratospheric Ozone Depletion (and increases in GHGs). Despite lingering uncertainties, it has become clear that Ozone Depletion has been instrumental in driving SH climate change in recent decades. Similarly, Ozone recovery will figure prominently in future climate change, with its impacts expected to largely cancel the impacts of increasing GHGs during the next half-century.
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The response of extratropical cyclones in the Southern Hemisphere to Stratospheric Ozone Depletion in the 20th century
Atmospheric Science Letters, 2013Co-Authors: Kevin M. Grise, Seok-woo Son, Gustavo Correa, Lorenzo M. PolvaniAbstract:This study explores the impact of Antarctic Stratospheric Ozone Depletion on extratropical cyclones. Output from the Community Atmosphere Model is combined with a Lagrangian cyclone-tracking algorithm to identify the response of Southern Hemisphere extratropical cyclones to Ozone and greenhouse gas forcings over the period 1960–2000. Stratospheric Ozone Depletion induces a significant poleward shift in cyclone frequency over the Southern Ocean, but has minimal influence on cyclone intensity and lifetime. The response of the cyclones to late 20th century greenhouse gas increases has similar characteristics, but falls within the range of natural variability in the model.
Carlos L. Ballaré - One of the best experts on this subject based on the ideXlab platform.
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solar uv b radiation affects below ground parameters in a fen ecosystem in tierra del fuego argentina implications of Stratospheric Ozone Depletion
Global Change Biology, 2002Co-Authors: Johann G. Zaller, Stephan D. Flint, Martyn M. Caldwell, Ana L. Scopel, Osvaldo E. Salo, Carlos L. BallaréAbstract:Stratospheric Ozone Depletion caused by the release of chlorofluorocarbons is most pronounced at high latitudes, especially in the Southern Hemisphere (including the so-called ‘Ozone hole’). The consequent increase in solar ultraviolet-B radiation (UV-B, 280–315 nm) reaching the earth's surface may cause a variety of alterations in terrestrial ecosystems. Most effects might be expected to occur above-ground since sunlight does not penetrate effectively below-ground. Here, we demonstrate that solar UV-B radiation in a fen in Tierra del Fuego (Argentina), where the Ozone hole passes overhead several times during the Austral spring, is causing large changes of below-ground processes of this ecosystem. During the third and fourth year of a manipulative field experiment, we investigated root systems in these plots and found that when the ambient solar UV-B radiation was substantially reduced, there was a 30% increase in summer root length production and as much as a threefold decrease in already low symbiotic mycorrhizal colonization frequency of the roots compared with plots receiving near-ambient solar UV-B. There was also an apparent shift toward older age classes of roots under reduced solar UV-B. Such large changes in root system behaviour may have decided effects on competition and other ecological interactions in this ecosystem.
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Solar UV‐B radiation affects below‐ground parameters in a fen ecosystem in Tierra del Fuego, Argentina: implications of Stratospheric Ozone Depletion
Global Change Biology, 2002Co-Authors: Johann G. Zaller, Stephan D. Flint, Martyn M. Caldwell, Ana L. Scopel, Osvaldo E. Salo, Carlos L. BallaréAbstract:Stratospheric Ozone Depletion caused by the release of chlorofluorocarbons is most pronounced at high latitudes, especially in the Southern Hemisphere (including the so-called ‘Ozone hole’). The consequent increase in solar ultraviolet-B radiation (UV-B, 280–315 nm) reaching the earth's surface may cause a variety of alterations in terrestrial ecosystems. Most effects might be expected to occur above-ground since sunlight does not penetrate effectively below-ground. Here, we demonstrate that solar UV-B radiation in a fen in Tierra del Fuego (Argentina), where the Ozone hole passes overhead several times during the Austral spring, is causing large changes of below-ground processes of this ecosystem. During the third and fourth year of a manipulative field experiment, we investigated root systems in these plots and found that when the ambient solar UV-B radiation was substantially reduced, there was a 30% increase in summer root length production and as much as a threefold decrease in already low symbiotic mycorrhizal colonization frequency of the roots compared with plots receiving near-ambient solar UV-B. There was also an apparent shift toward older age classes of roots under reduced solar UV-B. Such large changes in root system behaviour may have decided effects on competition and other ecological interactions in this ecosystem.
Martyn M. Caldwell - One of the best experts on this subject based on the ideXlab platform.
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solar uv b radiation affects below ground parameters in a fen ecosystem in tierra del fuego argentina implications of Stratospheric Ozone Depletion
Global Change Biology, 2002Co-Authors: Johann G. Zaller, Stephan D. Flint, Martyn M. Caldwell, Ana L. Scopel, Osvaldo E. Salo, Carlos L. BallaréAbstract:Stratospheric Ozone Depletion caused by the release of chlorofluorocarbons is most pronounced at high latitudes, especially in the Southern Hemisphere (including the so-called ‘Ozone hole’). The consequent increase in solar ultraviolet-B radiation (UV-B, 280–315 nm) reaching the earth's surface may cause a variety of alterations in terrestrial ecosystems. Most effects might be expected to occur above-ground since sunlight does not penetrate effectively below-ground. Here, we demonstrate that solar UV-B radiation in a fen in Tierra del Fuego (Argentina), where the Ozone hole passes overhead several times during the Austral spring, is causing large changes of below-ground processes of this ecosystem. During the third and fourth year of a manipulative field experiment, we investigated root systems in these plots and found that when the ambient solar UV-B radiation was substantially reduced, there was a 30% increase in summer root length production and as much as a threefold decrease in already low symbiotic mycorrhizal colonization frequency of the roots compared with plots receiving near-ambient solar UV-B. There was also an apparent shift toward older age classes of roots under reduced solar UV-B. Such large changes in root system behaviour may have decided effects on competition and other ecological interactions in this ecosystem.
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Solar UV‐B radiation affects below‐ground parameters in a fen ecosystem in Tierra del Fuego, Argentina: implications of Stratospheric Ozone Depletion
Global Change Biology, 2002Co-Authors: Johann G. Zaller, Stephan D. Flint, Martyn M. Caldwell, Ana L. Scopel, Osvaldo E. Salo, Carlos L. BallaréAbstract:Stratospheric Ozone Depletion caused by the release of chlorofluorocarbons is most pronounced at high latitudes, especially in the Southern Hemisphere (including the so-called ‘Ozone hole’). The consequent increase in solar ultraviolet-B radiation (UV-B, 280–315 nm) reaching the earth's surface may cause a variety of alterations in terrestrial ecosystems. Most effects might be expected to occur above-ground since sunlight does not penetrate effectively below-ground. Here, we demonstrate that solar UV-B radiation in a fen in Tierra del Fuego (Argentina), where the Ozone hole passes overhead several times during the Austral spring, is causing large changes of below-ground processes of this ecosystem. During the third and fourth year of a manipulative field experiment, we investigated root systems in these plots and found that when the ambient solar UV-B radiation was substantially reduced, there was a 30% increase in summer root length production and as much as a threefold decrease in already low symbiotic mycorrhizal colonization frequency of the roots compared with plots receiving near-ambient solar UV-B. There was also an apparent shift toward older age classes of roots under reduced solar UV-B. Such large changes in root system behaviour may have decided effects on competition and other ecological interactions in this ecosystem.
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A meta-analysis of plant field studies simulating Stratospheric Ozone Depletion
Oecologia, 2001Co-Authors: Peter S. Searles, Stephan D. Flint, Martyn M. CaldwellAbstract:The potential effects of increased ultraviolet-B radiation (UV-B, 280–320 nm) simulating Stratospheric Ozone Depletion in field studies with vascular plants have previously been summarized only in narrative literature reviews. In this quantitative synthesis, we have assessed the significance of solar UV-B enhancement for ten commonly measured variables involving leaf pigmentation, plant growth and morphology, and photosynthesis using meta-analytic statistical methods. Of 103 papers published between 1976 and mid-1999 from field studies, more than 450 reports from 62 papers were included in the database. Effects of UV-B were most apparent for the case of UV-B-absorbing compounds with an average increase of approximately 10% across all studies when comparing the ambient solar UV-B control to the treatment (involving ambient UV-B plus a UV-B supplement from special UV lamps). Some morphological parameters such as plant height and leaf mass per area showed little or no response to enhanced UV-B. Leaf photosynthetic processes (leaf gas exchange and chlorophyll fluorescence) and the concentration of photosynthetic pigments (total chlorophylls and carotenoids) were also not affected. Shoot biomass and leaf area showed modest decreases under UV-B enhancement. The reduction in shoot biomass occurred only under very high levels of simulated Ozone Depletion and leaf area was affected only when studies inappropriately used the plant (i.e., the subreplicate) rather than the plot as the experimental replicate. To the best of our knowledge, this review provides the first quantitative estimates of UV-B effects in field-based studies using all suitable published studies as a database.
Jess F. Adkins - One of the best experts on this subject based on the ideXlab platform.
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synchronous volcanic eruptions and abrupt climate change 17 7 ka plausibly linked by Stratospheric Ozone Depletion
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Joseph R. Mcconnell, Andrea Burke, Nelia W. Dunbar, Peter Köhler, Jennie L. Thomas, Monica M. Arienzo, Nathan Chellman, Olivia J. Maselli, Michael Sigl, Jess F. AdkinsAbstract:Glacial-state greenhouse gas concentrations and Southern Hemisphere climate conditions persisted until ∼17.7 ka, when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the Southern Hemisphere, with many changes ascribed to a sudden poleward shift in the Southern Hemisphere westerlies and subsequent climate impacts. We used high-resolution chemical measurements in the West Antarctic Ice Sheet Divide, Byrd, and other ice cores to document a unique, ∼192-y series of halogen-rich volcanic eruptions exactly at the start of accelerated deglaciation, with tephra identifying the nearby Mount Takahe volcano as the source. Extensive fallout from these massive eruptions has been found >2,800 km from Mount Takahe. Sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface UV radiation indicate that the eruptions led to Stratospheric Ozone Depletion. Rather than a highly improbable coincidence, circulation and climate changes extending from the Antarctic Peninsula to the subtropics—similar to those associated with modern Stratospheric Ozone Depletion over Antarctica—plausibly link the Mount Takahe eruptions to the onset of accelerated Southern Hemisphere deglaciation ∼17.7 ka.
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Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by Stratospheric Ozone Depletion
Proceedings of the National Academy of Sciences of the United States of America, 2017Co-Authors: Joseph R. Mcconnell, Andrea Burke, Nelia W. Dunbar, Peter Köhler, Jennie L. Thomas, Monica M. Arienzo, Nathan Chellman, Olivia J. Maselli, Michael Sigl, Jess F. AdkinsAbstract:Glacial-state greenhouse gas concentrations and Southern Hemisphere climate conditions persisted until ∼17.7 ka, when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the Southern Hemisphere, with many changes ascribed to a sudden poleward shift in the Southern Hemisphere westerlies and subsequent climate impacts. We used high-resolution chemical measurements in the West Antarctic Ice Sheet Divide, Byrd, and other ice cores to document a unique, ∼192-y series of halogen-rich volcanic eruptions exactly at the start of accelerated deglaciation, with tephra identifying the nearby Mount Takahe volcano as the source. Extensive fallout from these massive eruptions has been found >2,800 km from Mount Takahe. Sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface UV radiation indicate that the eruptions led to Stratospheric Ozone Depletion. Rather than a highly improbable coincidence, circulation and climate changes extending from the Antarctic Peninsula to the subtropics—similar to those associated with modern Stratospheric Ozone Depletion over Antarctica—plausibly link the Mount Takahe eruptions to the onset of accelerated Southern Hemisphere deglaciation ∼17.7 ka.
Stephan D. Flint - One of the best experts on this subject based on the ideXlab platform.
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solar uv b radiation affects below ground parameters in a fen ecosystem in tierra del fuego argentina implications of Stratospheric Ozone Depletion
Global Change Biology, 2002Co-Authors: Johann G. Zaller, Stephan D. Flint, Martyn M. Caldwell, Ana L. Scopel, Osvaldo E. Salo, Carlos L. BallaréAbstract:Stratospheric Ozone Depletion caused by the release of chlorofluorocarbons is most pronounced at high latitudes, especially in the Southern Hemisphere (including the so-called ‘Ozone hole’). The consequent increase in solar ultraviolet-B radiation (UV-B, 280–315 nm) reaching the earth's surface may cause a variety of alterations in terrestrial ecosystems. Most effects might be expected to occur above-ground since sunlight does not penetrate effectively below-ground. Here, we demonstrate that solar UV-B radiation in a fen in Tierra del Fuego (Argentina), where the Ozone hole passes overhead several times during the Austral spring, is causing large changes of below-ground processes of this ecosystem. During the third and fourth year of a manipulative field experiment, we investigated root systems in these plots and found that when the ambient solar UV-B radiation was substantially reduced, there was a 30% increase in summer root length production and as much as a threefold decrease in already low symbiotic mycorrhizal colonization frequency of the roots compared with plots receiving near-ambient solar UV-B. There was also an apparent shift toward older age classes of roots under reduced solar UV-B. Such large changes in root system behaviour may have decided effects on competition and other ecological interactions in this ecosystem.
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Solar UV‐B radiation affects below‐ground parameters in a fen ecosystem in Tierra del Fuego, Argentina: implications of Stratospheric Ozone Depletion
Global Change Biology, 2002Co-Authors: Johann G. Zaller, Stephan D. Flint, Martyn M. Caldwell, Ana L. Scopel, Osvaldo E. Salo, Carlos L. BallaréAbstract:Stratospheric Ozone Depletion caused by the release of chlorofluorocarbons is most pronounced at high latitudes, especially in the Southern Hemisphere (including the so-called ‘Ozone hole’). The consequent increase in solar ultraviolet-B radiation (UV-B, 280–315 nm) reaching the earth's surface may cause a variety of alterations in terrestrial ecosystems. Most effects might be expected to occur above-ground since sunlight does not penetrate effectively below-ground. Here, we demonstrate that solar UV-B radiation in a fen in Tierra del Fuego (Argentina), where the Ozone hole passes overhead several times during the Austral spring, is causing large changes of below-ground processes of this ecosystem. During the third and fourth year of a manipulative field experiment, we investigated root systems in these plots and found that when the ambient solar UV-B radiation was substantially reduced, there was a 30% increase in summer root length production and as much as a threefold decrease in already low symbiotic mycorrhizal colonization frequency of the roots compared with plots receiving near-ambient solar UV-B. There was also an apparent shift toward older age classes of roots under reduced solar UV-B. Such large changes in root system behaviour may have decided effects on competition and other ecological interactions in this ecosystem.
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A meta-analysis of plant field studies simulating Stratospheric Ozone Depletion
Oecologia, 2001Co-Authors: Peter S. Searles, Stephan D. Flint, Martyn M. CaldwellAbstract:The potential effects of increased ultraviolet-B radiation (UV-B, 280–320 nm) simulating Stratospheric Ozone Depletion in field studies with vascular plants have previously been summarized only in narrative literature reviews. In this quantitative synthesis, we have assessed the significance of solar UV-B enhancement for ten commonly measured variables involving leaf pigmentation, plant growth and morphology, and photosynthesis using meta-analytic statistical methods. Of 103 papers published between 1976 and mid-1999 from field studies, more than 450 reports from 62 papers were included in the database. Effects of UV-B were most apparent for the case of UV-B-absorbing compounds with an average increase of approximately 10% across all studies when comparing the ambient solar UV-B control to the treatment (involving ambient UV-B plus a UV-B supplement from special UV lamps). Some morphological parameters such as plant height and leaf mass per area showed little or no response to enhanced UV-B. Leaf photosynthetic processes (leaf gas exchange and chlorophyll fluorescence) and the concentration of photosynthetic pigments (total chlorophylls and carotenoids) were also not affected. Shoot biomass and leaf area showed modest decreases under UV-B enhancement. The reduction in shoot biomass occurred only under very high levels of simulated Ozone Depletion and leaf area was affected only when studies inappropriately used the plant (i.e., the subreplicate) rather than the plot as the experimental replicate. To the best of our knowledge, this review provides the first quantitative estimates of UV-B effects in field-based studies using all suitable published studies as a database.
