Akiyoshi H
National Institute for Environmental Studies, Tsukuba, Ibaraki-ken, Japan

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Publications (7)0 Total impact

  • Source
    Article: Attribution of observed changes in stratospheric ozone and temperature
    N. P. Gillett, Akiyoshi H, Bekki S, Braesicke P, Eyring V, Garcia R, A. Yu. Karpechko, C. A. McLinden, Morgenstern O, D. A. Plummer, J. A. Pyle, Rozanov E, Scinocca J, Shibata K
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    ABSTRACT: Three recently-completed sets of simulations of multiple chemistry-climate models with greenhouse gases only, with all anthropogenic forcings, and with anthropogenic and natural forcings, allow the causes of observed stratospheric changes to be quantitatively assessed using detection and attribution techniques. The total column ozone response to halogenated ozone depleting substances and to natural forcings is detectable in observations, but the total column ozone response to greenhouse gas changes is not separately detectable. In the middle and upper stratosphere, simulated and observed SBUV/SAGE ozone changes are broadly consistent, and separate anthropogenic and natural responses are detectable in observations. The influence of ozone depleting substances and natural forcings can also be detected separately in observed lower stratospheric temperature, and the magnitudes of the simulated and observed responses to these forcings and to greenhouse gas changes are found to be consistent. In the mid and upper stratosphere the simulated natural and combined anthropogenic responses are detectable and consistent with observations, but the influences of greenhouse gases and ozone-depleting substances could not be separately detected in our analysis.
    Atmospheric Chemistry and Physics. 01/2011;
  • Article: Attribution of observed changes in stratospheric ozone and temperature
    N. P. Gillett, Akiyoshi H, Bekki S, Eyring V, Garcia R, C. A. McLinden, A. Yu. Karpechko, D. A. Plummer, Rozanov E, Scinocca J, Shibata K
    [show abstract] [hide abstract]
    ABSTRACT: Three recently-completed sets of simulations of multiple chemistry-climate models with greenhouse gases only, with all anthropogenic forcings, and with anthropogenic and natural forcings, allow the causes of observed stratospheric changes to be quantitatively assessed using detection and attribution techniques. The total column ozone response to halogenated ozone depleting substances and to natural forcings is detectable and consistent in models and observations. However, the total ozone response to greenhouse gases in the models and observations appears to be inconsistent, which may be due to the models' inability to properly simulate tropospheric ozone changes. In the middle and upper stratosphere, simulated and observed SBUV/SAGE ozone changes are broadly consistent, and separate anthropogenic and natural responses are detectable in observations. The influence of ozone depleting substances and natural forcings can also be detected separately in observed lower stratospheric temperature, and the magnitudes of the simulated and observed responses to these forcings and to greenhouse gas changes are found to be consistent. In the mid and upper stratosphere the simulated natural and combined anthropogenic responses are detectable and consistent with observations, but the influences of greenhouse gases and ozone-depleting substances could not be separately detected in our analysis.
    Atmospheric Chemistry and Physics Discussions. 01/2010;
  • Source
    Article: Quantifying uncertainty in projections of stratospheric ozone over the 21st century
    A. J. Charlton-Perez, Hawkins E, Eyring V, Cionni I, G. E. Bodeker, D. E. Kinnison, Akiyoshi H, S. M. Frith, Garcia R, Gettelman A, [......], Morgenstern O, Pitari G, Plummer D, J. A. Pyle, Rozanov E, Scinocca J, Shibata K, T. G. Shepherd, Tian W, D. W. Waugh
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    ABSTRACT: Future stratospheric ozone concentrations will be determined both by changes in the concentration of ozone depleting substances (ODSs) and by changes in stratospheric and tropospheric climate, including those caused by changes in anthropogenic greenhouse gases (GHGs). Since future economic development pathways and resultant emissions of GHGs are uncertain, anthropogenic climate change could be a significant source of uncertainty for future projections of stratospheric ozone. In this pilot study, using an "ensemble of opportunity" of chemistry-climate model (CCM) simulations, the contribution of scenario uncertainty from different plausible emissions pathways for ODSs and GHGs to future ozone projections is quantified relative to the contribution from model uncertainty and internal variability of the chemistry-climate system. For both the global, annual mean ozone concentration and for ozone in specific geographical regions, differences between CCMs are the dominant source of uncertainty for the first two-thirds of the 21st century, up-to and after the time when ozone concentrations return to 1980 values. In the last third of the 21st century, dependent upon the set of greenhouse gas scenarios used, scenario uncertainty can be the dominant contributor. This result suggests that investment in chemistry-climate modelling is likely to continue to refine projections of stratospheric ozone and estimates of the return of stratospheric ozone concentrations to pre-1980 levels.
    Atmospheric Chemistry and Physics Discussions. 01/2010;
  • Source
    Article: Multi-model assessment of stratospheric ozone return dates and ozone recovery in CCMVal-2 models
    Eyring V, Cionni I, G. E. Bodeker, A. J. Charlton-Perez, D. E. Kinnison, J. F. Scinocca, D. W. Waugh, Akiyoshi H, Bekki S, M. P. Chipperfield, [......], T. G. Shepherd, Shibata K, Tian W, Braesicke P, S. C. Hardiman, J. F. Lamarque, Morgenstern O, J. A. Pyle, Smale D, Yamashita Y
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    ABSTRACT: Projections of stratospheric ozone from a suite of chemistry-climate models (CCMs) have been analyzed. In addition to a reference simulation where anthropogenic halogenated ozone depleting substances (ODSs) and greenhouse gases (GHGs) vary with time, sensitivity simulations with either ODS or GHG concentrations fixed at 1960 levels were performed to disaggregate the drivers of projected ozone changes. These simulations were also used to assess the two distinct milestones of ozone returning to historical values (ozone return dates) and ozone no longer being influenced by ODSs (full ozone recovery). The date of ozone returning to historical values does not indicate complete recovery from ODSs in most cases, because GHG-induced changes accelerate or decelerate ozone changes in many regions. In the upper stratosphere where CO2-induced stratospheric cooling increases ozone, full ozone recovery is projected to not likely have occurred by 2100 even though ozone returns to its 1980 or even 1960 levels well before (~2025 and 2040, respectively). In contrast, in the tropical lower stratosphere ozone decreases continuously from 1960 to 2100 due to projected increases in tropical upwelling, while by around 2040 it is already very likely that full recovery from the effects of ODSs has occurred, although ODS concentrations are still elevated by this date. In the midlatitude lower stratosphere the evolution differs from that in the tropics, and rather than a steady decrease in ozone, first a decrease in ozone is simulated from 1960 to 2000, which is then followed by a steady increase through the 21st century. Ozone in the midlatitude lower stratosphere returns to 1980 levels by ~2045 in the Northern Hemisphere (NH) and by ~2055 in the Southern Hemisphere (SH), and full ozone recovery is likely reached by 2100 in both hemispheres. Overall, in all regions except the tropical lower stratosphere, full ozone recovery from ODSs occurs significantly later than the return of total column ozone to its 1980 level. The latest return of total column ozone is projected to occur over Antarctica (~2045–2060) whereas it is not likely that full ozone recovery is reached by the end of the 21st century in this region. Arctic total column ozone is projected to return to 1980 levels well before polar stratospheric halogen loading does so (~2025–2030 for total column ozone, cf. 2050–2070 for Cly+60×Bry) and it is likely that full recovery of total column ozone from the effects of ODSs has occurred by ~2035. In contrast to the Antarctic, by 2100 Arctic total column ozone is projected to be above 1960 levels, but not in the fixed GHG simulation, indicating that climate change plays a significant role.
    Atmospheric Chemistry and Physics. 01/2010;
  • Article: The potential to narrow uncertainty in projections of stratospheric ozone over the 21st century
    A. J. Charlton-Perez, Hawkins E, Eyring V, Cionni I, G. E. Bodeker, D. E. Kinnison, Akiyoshi H, S. M. Frith, Garcia R, Gettelman A, [......], Morgenstern O, Pitari G, Plummer D, J. A. Pyle, Rozanov E, Scinocca J, Shibata K, T. G. Shepherd, Tian W, D. W. Waugh
    [show abstract] [hide abstract]
    ABSTRACT: Future stratospheric ozone concentrations will be determined both by changes in the concentration of ozone depleting substances (ODSs) and by changes in stratospheric and tropospheric climate, including those caused by changes in anthropogenic greenhouse gases (GHGs). Since future economic development pathways and resultant emissions of GHGs are uncertain, anthropogenic climate change could be a significant source of uncertainty for future projections of stratospheric ozone. In this pilot study, using an "ensemble of opportunity" of chemistry-climate model (CCM) simulations, the contribution of scenario uncertainty from different plausible emissions pathways for ODSs and GHGs to future ozone projections is quantified relative to the contribution from model uncertainty and internal variability of the chemistry-climate system. For both the global, annual mean ozone concentration and for ozone in specific geographical regions, differences between CCMs are the dominant source of uncertainty for the first two-thirds of the 21st century, up-to and after the time when ozone concentrations return to 1980 values. In the last third of the 21st century, dependent upon the set of greenhouse gas scenarios used, scenario uncertainty can be the dominant contributor. This result suggests that investment in chemistry-climate modelling is likely to continue to refine projections of stratospheric ozone and estimates of the return of stratospheric ozone concentrations to pre-1980 levels.
    Atmospheric Chemistry and Physics. 01/2010;
  • Source
    Article: Northern winter stratospheric temperature and ozone responses to ENSO inferred from an ensemble of Chemistry Climate Models
    Cagnazzo C, Manzini E, Calvo N, Douglass A, Akiyoshi H, Bekki S, Chipperfield M, Dameris M, Deushi M, Fischer A, Garny H, Gettelman A, M. A. Giorgetta, Plummer D, Rozanov E, T. G. Shepherd, Shibata K, Stenke A, Struthers H, Tian W
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    ABSTRACT: The connection between the El Niño Southern Oscillation (ENSO) and the northern polar stratosphere has been established from observations and atmospheric modeling. Here a systematic inter-comparison of the sensitivity of the modeled stratosphere to ENSO in Chemistry Climate Models (CCMs) is reported. This work uses results from a number of the CCMs included in the 2006 ozone assessment. In the lower stratosphere, the mean of all model simulations reports a warming of the polar vortex during strong ENSO events in February–March, consistent with but smaller than the estimate from satellite observations and ERA40 reanalysis. This anomalous warming is associated with an anomalous dynamical increase of total ozone north of 70° N that is accompanied by coherent total ozone decrease in the Tropics, in agreement with that deduced from the NIWA total ozone database, implying an increased residual circulation in the mean of all model simulations, during ENSO. The spread in the model responses is partly due to the large internal stratospheric variability but it is shown that it crucially depends on the representation of the tropospheric ENSO teleconnection in the models.
    Atmospheric Chemistry and Physics Discussions. 01/2009;
  • Source
    Article: Clear sky UV simulations in the 21st century based on ozone and temperature projections from Chemistry-Climate Models
    Tourpali K, A. F. Bais, Kazantzidis A, C. S. Zerefos, Akiyoshi H, Austin J, Brühl C, Butchart N, M. P. Chipperfield, Dameris M, [......], M. A. Giorgetta, D. E. Kinnison, Mancini E, D. R. Marsh, Nagashima T, Pitari G, D. A. Plummer, Rozanov E, Shibata K, Tian W
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    ABSTRACT: We have used total ozone columns and vertical profiles of ozone and temperature from 11 coupled Chemistry-Climate Models (CCMs) to project future solar ultraviolet radiation levels at the surface in the 21st century. The CCM simulations are used as input to a radiative transfer model for the simulation of the corresponding future UV irradiance levels under cloud free conditions, presented here as time series of monthly erythemal irradiance received at the surface during local noon covering the period 1960 to 2100. Starting from the first decade of the 21st century, the surface erythemal irradiance decreases globally as a result of the projected ozone recovery, at rates which are larger in the first half of the 21st century, compared to the period up to 2100. The magnitude of these decreases varies with latitude and is more pronounced at areas where ozone has been depleted most considerably after 1980. Over midlatitudes surface erythemal irradiance decreases between 5 and 15% by 2100 relative to 2000, while at the southern high latitudes these changes are twice as much. Climate change may affect future cloudiness, surface reflectivity and tropospheric aerosol loading, the effects of which are not included in this study. Therefore, the actual changes in future UV radiation are likely to change accordingly in the areas affected.
    Atmospheric Chemistry and Physics Discussions. 01/2008;

Institutions

  • 2009
    • National Institute for Environmental Studies
      Tsukuba, Ibaraki-ken, Japan
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