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| Titel |
Ozone database in support of CMIP5 simulations: results and corresponding radiative forcing |
| VerfasserIn |
I. Cionni, V. Eyring, J. F. Lamarque, W. J. Randel, D. S. Stevenson, F. Wu, G. E. Bodeker, T. G. Shepherd, D. T. Shindell  , D. W. Waugh |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 21 ; Nr. 11, no. 21 (2011-11-14), S.11267-11292 |
| Datensatznummer |
250010187
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| Publikation (Nr.) |
 copernicus.org/acp-11-11267-2011.pdf |
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| Zusammenfassung |
| A continuous tropospheric and stratospheric
vertically resolved ozone time series, from 1850 to 2099, has been generated
to be used as forcing in global climate models that do not include
interactive chemistry. A multiple linear regression analysis of SAGE I+II
satellite observations and polar ozonesonde measurements is used for the
stratospheric zonal mean dataset during the well-observed period from 1979
to 2009. In addition to terms describing the mean annual cycle, the
regression includes terms representing equivalent effective stratospheric
chlorine (EESC) and the 11-yr solar cycle variability. The EESC regression
fit coefficients, together with pre-1979 EESC values, are used to
extrapolate the stratospheric ozone time series backward to 1850. While a
similar procedure could be used to extrapolate into the future, coupled
chemistry climate model (CCM) simulations indicate that future stratospheric
ozone abundances are likely to be significantly affected by climate change,
and capturing such effects through a regression model approach is not
feasible. Therefore, the stratospheric ozone dataset is extended into the
future (merged in 2009) with multi-model mean projections from 13 CCMs that
performed a simulation until 2099 under the SRES (Special Report on Emission
Scenarios) A1B greenhouse gas scenario and the A1 adjusted halogen scenario
in the second round of the Chemistry-Climate Model Validation (CCMVal-2)
Activity. The stratospheric zonal mean ozone time series is merged with a
three-dimensional tropospheric data set extracted from simulations of the
past by two CCMs (CAM3.5 and GISS-PUCCINI) and of the future by one CCM
(CAM3.5). The future tropospheric ozone time series continues the historical
CAM3.5 simulation until 2099 following the four different Representative
Concentration Pathways (RCPs). Generally good agreement is found between the
historical segment of the ozone database and satellite observations,
although it should be noted that total column ozone is overestimated in the
southern polar latitudes during spring and tropospheric column ozone is
slightly underestimated. Vertical profiles of tropospheric ozone are broadly
consistent with ozonesondes and in-situ measurements, with some deviations
in regions of biomass burning. The tropospheric ozone radiative forcing (RF)
from the 1850s to the 2000s is 0.23 W m−2, lower than previous results.
The lower value is mainly due to (i) a smaller increase in biomass burning
emissions; (ii) a larger influence of stratospheric ozone depletion on upper
tropospheric ozone at high southern latitudes; and possibly (iii) a larger
influence of clouds (which act to reduce the net forcing) compared to
previous radiative forcing calculations. Over the same period, decreases in
stratospheric ozone, mainly at high latitudes, produce a RF of
−0.08 W m−2, which is more negative than the central Intergovernmental Panel on
Climate Change (IPCC) Fourth Assessment Report (AR4) value of −0.05 W m−2,
but which is within the stated range of −0.15 to +0.05 W m−2. The more negative value is explained by the fact that the
regression model simulates significant ozone depletion prior to 1979, in
line with the increase in EESC and as confirmed by CCMs, while the AR4
assumed no change in stratospheric RF prior to 1979. A negative RF of
similar magnitude persists into the future, although its location shifts
from high latitudes to the tropics. This shift is due to increases in polar
stratospheric ozone, but decreases in tropical lower stratospheric ozone,
related to a strengthening of the Brewer-Dobson circulation, particularly
through the latter half of the 21st century. Differences in trends in
tropospheric ozone among the four RCPs are mainly driven by different
methane concentrations, resulting in a range of tropospheric ozone RFs
between 0.4 and 0.1 W m−2 by 2100. The ozone dataset described here has
been released for the Coupled Model Intercomparison Project (CMIP5) model
simulations in netCDF Climate and Forecast (CF) Metadata Convention at the
PCMDI website (http://cmip-pcmdi.llnl.gov/). |
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