Interactive comment on “ A climatology of surface ozone in the extra tropics : cluster analysis of observations and model results ” by O . A . Tarasova

General comments "A climatology of surface ozone in extra tropics: cluster analysis of observations and model results" presents a useful new analysis of measured ozone concentrations and applies it to evaluate the performance of a global chemistry transport model. This is potentially a valuable contribution but a few points need further consideration. Introduction Some discussion should be included of previous uses of cluster analysis for the analysis of air pollution; both to cluster back-trajectories, (e.g. Cape et al 2000) and local air