Vertical distribution of ozone annual cycle at Frankfurt from (a) IAGOS (1996–2005) and (b) The mean of 15 ACCMIP models for year 2000 time slice. Vertical lines in the legend of (a) Indicate changes in the regular progression in altitude. Also shown are (c) The relative bias (ACCMIP – IAGOS/IAGOS) by season, and (d) the correlation of the annual cycles, both by level. Neither the IAGOS nor ACCMIP data are filtered to remove stratospheric intrusions. DOI: https://doi.org/10.1525/elementa.265.f5