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Titel |
Observed temporal evolution of global mean age of stratospheric air for the 2002 to 2010 period |
VerfasserIn |
G. P. Stiller, T. von Clarmann, F. Haenel, B. Funke, N. Glatthor, U. Grabowski, S. Kellmann, M. Kiefer, A. Linden, S. Lossow, M. López-Puertas |
Konferenz |
EGU General Assembly 2012
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 14 (2012) |
Datensatznummer |
250062302
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Zusammenfassung |
An extensive observational data set from MIPAS measurements, consisting of more than one
million SF6 vertical profiles distributed globally has been condensed into monthly zonal
means of mean age of air for the period September 2002 to January 2010, binned at 10°
latitude and 1-2 km altitude. The data were analysed with respect to their temporal variation
by fitting a regression model consisting of: a constant and a linear increase term, 2 proxies for
the QBO variation, sinusoidal terms for the seasonal and semi-annual variation and
overtones for the correction of the shapes to the observed data set. The impact of
subsidence of mesospheric SF6-depleted air and in-mixing into non-polar latitudes
on mid-latitudinal age of air and its linear increase was assessed and found to be
small.
The linear increase of mean age of stratospheric air was found to be positive and partly
larger than the trend derived by Engel et al. (2009) for most of the Northern mid-latitudes, the
middle stratosphere in the tropics, and parts of the Southern mid-latitudes, as well as for the
Southern polar upper stratosphere. Multi-year decrease of age of air was found for the
lowermost and the upper stratospheric tropics, for parts of Southern mid-latitudes, and for the
Northern polar regions. Analyses of the amplitudes and phases of the seasonal variation shed
light on the coupling between different stratospheric regions. In particular, the Northern
mid-latitude stratosphere is well coupled to the tropics, while the Northern lowermost
mid-latitudinal stratosphere is decoupled, confirming the separation of the shallow
branch of the Brewer-Dobson circulation from the deep branch. We suggest an
overall increased tropical upwelling, together with a weakening of mixing barriers,
especially in the Northern hemisphere, as possible explanations for the observed
patterns.
Reference: Engel, A., Möbius, T., Bönisch, H., Schmidt, U., Heinz, R., Levin, I.,
Atlas, E., Aoki, S., Nakazawa, T., Sugawara, S., Moore, F., Hurst, D., Elkins, J.,
Schauffler, S., Andrews, A., and Boering, K.: Age of stratospheric air unchanged within
uncertainties over the past 30 years, Nature Geosci., 2, 28–31, doi:10.1038/ngeo388, 2009. |
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