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| Titel |
Reassessment of MIPAS age of air trends and variability |
| VerfasserIn |
F. J. Haenel, G. P. Stiller, T. von Clarmann, B. Funke, E. Eckert, N. Glatthor, U. Grabowski, S. Kellmann, M. Kiefer, A. Linden, T. Reddmann |
| 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 ; 15, no. 22 ; Nr. 15, no. 22 (2015-11-27), S.13161-13176 |
| Datensatznummer |
250120190
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| Publikation (Nr.) |
 copernicus.org/acp-15-13161-2015.pdf |
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| Zusammenfassung |
| A new and improved setup of the SF6 retrieval together with a newly
calibrated version of MIPAS-ENVISAT level 1b spectra (version 5, ESA data
version 5.02/5.06) was used to obtain a new global SF6 data set, covering
the total observational period of MIPAS from July 2002 to April 2012 for the
first time. Monthly and zonally averaged SF6 profiles were converted into
mean age of air using a tropospheric SF6-reference curve. The
obtained data set of age of air was compared to airborne age of air
measurements. The temporal evolution of the mean age of air was then investigated
in 10° latitude and 1–2 km altitude bins. A regression
model consisting of a constant and a linear trend term, two proxies for the
quasi-biennial oscillation variation, sinusoidal terms for the seasonal and
semiannual variation and overtones was fitted to the age of air time series.
The annual cycle for particular regions in the stratosphere was investigated
and compared to other studies. The age of air trend over the total
MIPAS period consisting of the linear term was assessed and compared to
previous findings of Stiller et al. (2012). While the linear increase of
mean age is confirmed to be positive for the northern midlatitudes and
southern polar middle stratosphere, differences are found in the northern
polar upper stratosphere, where the mean age is now found to increase as
well. The magnitude of trends in the northern midlatitude middle
stratosphere is slightly lower compared to the previous version and the
trends fit remarkably well to the trend derived by Engel et al. (2009).
Negative age of air trends found by Stiller et al. (2012) are confirmed
for the lowermost tropical stratosphere and lowermost southern
midlatitudinal stratosphere. Differences to the previous data versions occur
in the middle tropical stratosphere around 25 km, where the trends
are now negative. Overall, the new latitude–altitude distribution of trends
appears to be less patchy and more coherent than the previous one. The new
data provide evidence of an accelerating shallow branch of the Brewer–Dobson
circulation, at least in the Southern Hemisphere. Finally the age of air
decadal trends are compared to trends calculated with simulated SF6
values by the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA)
and good agreement is found. The hemispheric asymmetry in the trends found in
the MIPAS data is also indicated in the trends calculated with simulated
SF6 values by the KASIMA model. |
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