First global data set on mean age of stratospheric air and its temporal variations derived from MIPAS
The figure shows the zonal "trends" of mean age of stratospheric air for the period 2002 to 2010 as derived from MIPAS SF6 observations. During this period, age of air increased in the Northern mid-latitudes, the middle stratosphere of the tropics, parts of the Southern mid-latitudes, and in the Southern polar upper stratosphere. In contrast, age of air decreased in the lowermost and upper tropical stratosphere, in parts of the Southern mid-latitudes, and in Northern polar regions. Increasing mixing dur to weakening of mixing barriers may explain this pattern of multi-year linear increase and decrease.
MIPAS SF6 was zonally binned into 10 deg latitude bins and transformed in age of air on basis of in situ ground-based observations by NOAA/ESRL. The age of air time series for all latitude/altitude bins were fitted by a simple parametric approach including a constant, a linear, and various sine and cosine terms for seasonal, semi-annual and further oscillations. A QBO proxy was also fitted to the time series. The linear terms of the fits are presented for their altitude/latitude bins in the figure.
http://www.atmos-chem-phys.net/12/3311/2012/acp-12-3311-2012.html