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| Titel |
Drivers of hemispheric differences in return dates of mid-latitude stratospheric ozone to historical levels |
| VerfasserIn |
H. Garny, G. E. Bodeker, D. Smale, M. Dameris, V. Grewe |
| 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 ; 13, no. 15 ; Nr. 13, no. 15 (2013-08-01), S.7279-7300 |
| Datensatznummer |
250018792
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| Publikation (Nr.) |
 copernicus.org/acp-13-7279-2013.pdf |
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| Zusammenfassung |
| Chemistry-climate models (CCMs) project an earlier return of northern mid-latitude total column
ozone to 1980 values compared to the southern mid-latitudes. The chemical and dynamical drivers of
this hemispheric difference are investigated in this study. The hemispheric asymmetry in return
dates is a robust result across different CCMs and is qualitatively independent of the method used
to estimate return dates. However, the differences in dates of return to 1980 levels between the
southern and northern mid-latitudes can vary between 0 and 30 yr across the range of CCM
projections analyzed. Positive linear trends in ozone lead to an earlier return of ozone
than expected from the return of Cly to 1980 levels. This forward shift is stronger in
the Northern than in the Southern Hemisphere because (i) trends have a larger effect
on return dates if the sensitivity of ozone to Cly is lower and (ii) the trends in the
Northern Hemisphere are stronger than in the Southern Hemisphere.
An attribution analysis performed with two CCMs shows that chemically-induced changes in ozone
are the major driver of the earlier return of ozone to 1980 levels in northern mid-latitudes;
therefore transport changes are of minor importance. This conclusion is
supported by the fact that the spread in the simulated hemispheric difference in return dates
across an ensemble of twelve models is only weakly related to the spread in the simulated
hemispheric asymmetry of trends in the strength of the Brewer–Dobson circulation. The causes for
chemically-induced asymmetric ozone trends relevant for the total column ozone return date
differences are found to be (i) stronger increases in ozone production due to enhanced NOx
concentrations in the Northern Hemisphere lowermost stratosphere and troposphere, (ii) stronger
decreases in the destruction rates of ozone by the NOx cycle in the Northern Hemisphere
lower stratosphere linked to effects of dynamics and temperature on NOx concentrations, and
(iii) an increasing efficiency of heterogeneous ozone destruction by Cly in the Southern
Hemisphere mid-latitudes as a~result of decreasing lower stratospheric temperatures. |
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