Variability of stratospheric mean age of air: local effects of residual circulation and eddy mixing
The figure shows the decadal trends derived for age of air over the MIPAS period (2002 - 2012) from observations (bottom) and as modelled with CLaMS. The hemispheric asymmetry and the absolute trends are in nice agreement.
The CLaMS model allows to analyze the trends further with respect to their composition from transport time trends and mixing trends. It is found that in tropical to middle latitudes air becomes older by mixing while in polar regions age of air is decreased by mixing while the residual transport affects age the other way round. Transport times and mixing are antagonists of almost similar strengths. Their individual temporal developments add up to the actual age of air trends, in particular to the hemispheric asymmetry.
For further details see: http://onlinelibrary.wiley.com/doi/10.1002/2014JD022468/full