Impact of mixing and chemical change on ozone-tracer relations in the polar vortex

[摘要] Tracer-tracer relations have been used for a long time to separatephysico-chemical change from change caused by transport processes.In particular, for more than a decade, ozone-tracer relations havebeen used to quantify chemical ozone loss in the polar vortex.Theapplication of ozone-tracer relations for quantifying ozone lossrelies on two hypotheses: that a compact ozone-tracer relation isestablished in the 'early' polar vortex and that any change of theozone-tracer relation in the vortex over the course of winter iscaused predominantly by chemical ozone loss.Here, we revisit thisissue by analysing various sets of measurements and the results fromseveral models.We find that mixing across the polar vortex edgeimpacts ozone-tracer relations in a way that may solely lead to an'underestimation' of chemical ozone loss and not to anoverestimation. Further, differential descent in the vortex andinternal mixing has only a negligible impact on ozone lossestimates. Moreover, the representation of mixing inthree-dimensional atmospheric models can have a substantial impacton the development of tracer relations in the model.Rather compactozone-tracer relations develop – in agreement with observations –in the vortex of a Lagrangian model (CLaMS) where mixing isanisotropic and driven by the deformation of the flow.We concludethat, if a reliable 'early vortex' reference can be obtained and ifvortex measurements are separated from mid-latitude measurements,ozone-tracer relations constitute a reliable tool for thequantitative determination of chemical ozone loss in the polarvortex.

[学科分类] 大气科学