Observed temporal evolution of global mean age of stratospheric air for the 2002 to 2010 period 1Karlsruhe Institute of Technology, Institute for Meteorology and Climate Research, Karlsruhe, Germany
05 Apr 2012
2Instituto de Astrofísica des Andalucía, CSIC, Granada, Spain
Received: 28 July 2011 – Published in Atmos. Chem. Phys. Discuss.: 18 October 2011 Abstract. An extensive observational
data set, consisting of more than 106 SF6 vertical profiles from MIPAS
measurements distributed over the whole globe 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 absolute age of air and its linear increase was
assessed and found to be small.
Revised: 28 February 2012 – Accepted: 21 March 2012 – Published: 05 April 2012
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. Analysis of the
amplitudes and phases of the seasonal variation shed light on the coupling of
stratospheric regions to each other. 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 weakening of mixing barriers, especially in the
Northern Hemisphere, as a hypothetical model to explain the observed pattern of
linear multi-year increase/decrease, and amplitudes and phase shifts of the
Citation: Stiller, G. P., von Clarmann, T., Haenel, F., Funke, B., Glatthor, N., Grabowski, U., Kellmann, S., Kiefer, M., Linden, A., Lossow, S., and López-Puertas, M.: Observed temporal evolution of global mean age of stratospheric air for the 2002 to 2010 period, Atmos. Chem. Phys., 12, 3311-3331, doi:10.5194/acp-12-3311-2012, 2012.