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Observed temporal evolution of global mean age of stratospheric air for the 2002 to 2010 period

The seminar talk will provide an overview on the SF6 and mean age of stratospheric air (AoA) data set which has been derived from MIPAS observation over an 8-years period. After a short introduction to the MIPAS mission and the current state of research regarding the Brewer-Dobson circulation, the extensive observational data set, consisting of more than one million of SF6 vertical profiles derived from MIPAS measurements distributed over the whole globe will be presented. The method to condense this data set into monthly zonal means of mean age of stratospheric air for the period September 2002 to January 2010, binned at 10° latitude and 1–2 km altitude, will be explained. The analysis of the data with respect to their temporal variation by multivariate regression will be presented, and the results will be discussed. 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 will also be discussed.

The linear component of the temporal change of AoA will be compared to earlier observations and to model results which are in obvious contrast to our findings. A tentative explanation for the inhomogeneous altitudinal/latitudinal pattern of observed linear increases and decreases will be offered.