Stratospheric Transport Variability Diagnosed From Surface Measurements of Long-Lived Trace Gases

We use surface measurements of a number of long-lived trace gases, including CFC-11, CFC-12 and N₂O, and a 3-box model to estimate the interannual variability of bulk stratospheric transport characteristics. The results suggest that in recent years an overall slowdown of the transport of stratospheric air to the troposphere as well as a shift towards a relatively stronger stratospheric circulation in the southern hemisphere compared to the northern hemisphere can explain most of the observed variability at the surface. We compare these results to stratospheric satellite measurements, residual circulation estimates and global model simulations to check for consistency. The implications of fully accounting for stratospheric variability in emission estimates of long-lived trace gases can be significant, including for those gases monitored by the Montreal Protocol and/or of climatic importance.