Determining the age of stratospheric air

Research Project, 2010 – 2013

The speed of the Brewer-Dobson circulation in the stratosphere determines the lifetime of many chemical species in the atmosphere. This is because those species that are long-lived in the troposphere such as CFCs are finally broken down into water soluble species by the intense UV-light available above the ozone layer in the stratosphere. The downward branch of the Brewer-Dobson circulation and cross-tropopause mixing then allow these species to be removed.

Climate models suggest that the Brewer-Dobson circulation will speed up as a result of increased tropospheric large-scale wave activity. This will affect among other things the rate of ozone recovery. The age of stratospheric air (Gamma) is closely related to the strength of this residual circulation and therefore a useful diagnostic for change. Only a very limited data set is available from in-situ whole air sampling experiments that determine the Age of air by comparison of the concentration of long-lived trace gases with their tropospheric historical values. Only one truly global satellite data set is available.

We wish to develop a new method based on the physio-chemical changes in the proportion of water vapour isotopologues to determine Gamma. Preliminary results look very promising. Having established the usefulness and accuracy of the method we will use Odin observations to investigate the inter-annual variability and trends in Gamma.