Influence of transport and mixing in autumn on stratospheric ozone variability over the Arctic in early winter

摘要

Early winter ozone mixing ratios in the Arctic middle stratosphere show aninterannual variability of about 10%. We show that ozone variability inearly January is caused by dynamical processes during Arctic polar vortexformation in autumn (September to December). Observational data fromsatellites and ozone sondes are used in conjunction with simulations of thechemistry and transport model ATLAS to examine the relationship between themeridional and vertical origin of air enclosed in the polar vortex and itsozone amount. For this, we use a set of artificial model tracers to deducethe origin of the air masses in the vortex in January in latitude andaltitude in September. High vortex mean ozone mixing ratios are correlatedwith a high fraction of air from low latitudes enclosed in the vortex and ahigh fraction of air that experienced small net subsidence (in a Lagrangiansense). As a measure for the strength of the Brewer-Dobson circulation andmeridional mixing in autumn, we use the Eliassen-Palm flux through themid-latitude tropopause averaged from September to November. In the lowerstratosphere, this quantity correlates well with the origin of air enclosedin the vortex and reasonably well with the ozone amount in early winter.