Abstract

The transport of `very-short lived’ species (i.e., chlorinated and brominated hydrocarbons) from the planetary surface to the stratosphere is known to have a significant impact on stratospheric ozone. Several studies have shown that the amount of chlorine and bromine reaching the stratosphere is strongly dependent upon the geographical location of the source. To investigate this geographical dependence carefully involves simultaneously determining the sensitivity of a single quantity, such as the flux of a species into the stratosphere, upon emissions from many possible source locations. It therefore makes sense to adopt an adjoint approach.

One such approach, intended to maximise the symmetry between forward and adjoint models, is Eulerian backtracking [Hourdin and Talagrand 2006]. The advantages of Eulerian backtracking over other approaches include ease-of-use and stability of model solutions. We describe RETRO -TOM, a new model developed using Eulerian backtracking and intended to serve as a highly-accurate adjoint to the chemistry transport model TOMCAT . We then address the question of how the (time-averaged) stratospheric flux of a finite lifetime species depends upon the location of its surface sources by presenting sensitivity maps obtained using RETRO -TOM.